Patent Publication Number: US-2011061616-A1

Title: Valve Timing Control Apparatus for Internal Combustion Engine, and Method of Producing Same

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to valve timing control apparatuses for internal combustion engines, and methods of producing same. 
     Japanese Patent Application Publication No. 5-113112 discloses a valve timing control apparatus for an internal combustion engine, which includes a housing connected to a crankshaft, and a phase change mechanism mounted in the housing, and connected to a camshaft. The housing is formed with a pulley at its outside periphery to which torque is transmitted from the crankshaft through a timing belt that is wound around the pulley, so that the housing rotates in synchronization with the crankshaft. The phase change mechanism operates in response to supply and drainage of working fluid, for changing valve timing, i.e. rotational phase of the camshaft with respect to the crankshaft. 
     SUMMARY OF THE INVENTION 
     The valve timing control apparatus described above is subject to a problem that the timing belt may be degraded by adhesion of working fluid exiting out of the housing. Accordingly, it is desirable to provide a valve timing control apparatus for an internal combustion engine in which such a problem is solved by suitable sealing. 
     According to one aspect of the present invention, a valve timing control apparatus for an internal combustion engine, comprises: a housing body having a hollow cylindrical shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body; a sealing plate fixed to the axial end of the housing body, the sealing plate closing the opening of the housing body; a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane defines a working fluid chamber between the vane and the shoe, and wherein the working fluid chamber is adapted to supply and drainage of working fluid; and a sealing ring disposed between the housing body and the sealing plate, the sealing ring sealing the working fluid chamber, wherein: the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer; the anodic oxide coating film layer is present at the outside periphery; and the sealing ring abuts on the base layer at the axial end. 
     According to another aspect of the present invention, a valve timing control apparatus for an internal combustion engine, comprises: a housing body having a tubular shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; a sealing plate facing an axial end surface of the housing body, and closing the opening of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and a sealing ring disposed between the housing body and the sealing plate, wherein: the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer; and the anodic oxide coating film layer is present at the outside periphery and an inside periphery of the housing body, and absent at the axial end surface of the housing body facing the sealing plate. 
     According to a further aspect of the present invention, a valve timing control apparatus for an internal combustion engine, comprises: a housing body having a tubular shape including an opening at an axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; a sealing plate fixed to the axial end of the housing body, the sealing plate closing the opening of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and a sealing ring disposed between the housing body and the sealing plate, wherein: the housing body is formed of an aluminum-based metal material and anodized, wherein the housing body includes a base layer and an anodic oxide coating film layer; and the anodic oxide coating film layer is present at the outside periphery of the housing body, and absent at a surface of the housing body on which the sealing ring abuts. 
     According to a still further aspect of the present invention, a method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a hollow cylindrical shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body; at least one sealing plate fixed to an axial end surface of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane and the shoe define an advance chamber and a retard chamber between the vane rotor and housing body, and wherein the advance chamber and the retard chamber are adapted to supply and drainage of fluid; and at least one sealing ring disposed between the sealing plate and the axial end surface of the housing body, the method comprises a process of producing the housing body, the process comprising: an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion; a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; and a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length so as to form the third workpiece with a cut surface forming the axial end surface of the housing body on which the sealing ring abuts. 
     According to another aspect of the present invention, a method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a hollow cylindrical shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and formed integrally with a shoe at an inside periphery of the housing body, wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine, and wherein the shoe projects inwardly in a radial direction of the housing body; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a vane rotor adapted to be fixed to a camshaft of the internal combustion engine, and rotatably mounted in the housing body, wherein the vane rotor includes a vane, wherein the vane and the shoe define an advance chamber and a retard chamber between the vane rotor and housing body, and wherein the advance chamber and the retard chamber are adapted to supply and drainage of fluid; and at least one sealing ring disposed between the sealing plate and the housing body, the method comprises a process of producing the housing body, the process comprising: an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion; a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length; and a carving operation of carving a longitudinal end surface of the third workpiece so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts. 
     According to another aspect of the present invention, a method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a tubular shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and at least one sealing ring disposed between the sealing plate and the housing body, the method comprises a process of producing the housing body, the process comprising: an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion; a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; and a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts. 
     According to another aspect of the present invention, a method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body having a tubular shape including an opening at each axial end, wherein the housing body is formed integrally with a pulley at an outside periphery of the housing body, and wherein the pulley is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate fixed to one of the axial ends of the housing body, the sealing plate closing a corresponding one of the openings of the housing body; a phase change mechanism mounted in the housing body, and adapted to change a rotational phase of a camshaft of the internal combustion engine with respect to the housing body in response to supply and drainage of working fluid; and at least one sealing ring disposed between the sealing plate and the housing body, the method comprises a process of producing the housing body, the process comprising: an extruding operation of forming a first workpiece by extruding an aluminum-based metal material, wherein the first workpiece extends in a direction of extrusion; a coating operation of forming a second workpiece by anodizing an entire surface of the first workpiece; a cutting-off operation of forming a third workpiece by cutting out of the second workpiece to a predetermined length; and a carving operation of carving a longitudinal end surface of the third workpiece so as to form the third workpiece with a cut surface forming a surface of the housing body on which the sealing ring abuts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a valve timing control apparatus according to an embodiment of the present invention in which a pair of intake valve timing control apparatuses and a pair of exhaust valve timing control apparatuses are mounted to an internal combustion engine, as viewed in an axial direction of the internal combustion engine. 
         FIG. 2  is an exploded perspective view of the intake valve timing control apparatus. 
         FIG. 3  is a partial side sectional view of the intake valve timing control apparatus, taken along a plane passing through an axis of rotation of the intake valve timing control apparatus. 
         FIG. 4  is a front view of the intake valve timing control apparatus in a most retarded state, as viewed along the axis of rotation. 
         FIG. 5  is a front view of the intake valve timing control apparatus in a most advanced state, as viewed along the axis of rotation. 
         FIGS. 6A ,  6 B and  6 C are views of a housing body of the intake valve timing control apparatus, where  FIG. 6A  is a front view along the axis of rotation,  FIG. 6B  is a side sectional view taken along a plane indicated by F 6 B-F 6 B in  FIG. 6A , and  FIG. 6C  is a rear view along the axis of rotation. 
         FIG. 7  is a perspective view of a first workpiece for the housing body of the intake valve timing control apparatus or a housing body of the exhaust valve timing control apparatus. 
         FIG. 8  is a perspective view of a third workpiece for the housing body of the intake valve timing control apparatus or exhaust valve timing control apparatus. 
         FIGS. 9A and 9B  are views of a vane rotor of the intake valve timing control apparatus, where  FIG. 9A  is a front view along the axis of rotation, and  FIG. 9B  is a side sectional view taken along a plane indicated by F 9 B-F 9 B in  FIG. 9A . 
         FIG. 10  is a perspective view of a first workpiece for the vane rotor of the intake valve timing control apparatus or a vane rotor of the exhaust valve timing control apparatus. 
         FIG. 11  is a perspective view of a second workpiece for the vane rotor of the intake valve timing control apparatus or exhaust valve timing control apparatus. 
         FIG. 12  is a perspective view of a front plate of the intake valve timing control apparatus. 
         FIG. 13  is a partial side sectional view taken along a plane passing through a central longitudinal axis of a positioning pin according to the embodiment that is fixed to an axial end surface of an intake camshaft. 
         FIG. 14  is a partial side sectional view taken along a plane passing through a central longitudinal axis of a lock mechanism according to the embodiment. 
         FIG. 15  is a partial side sectional view of the exhaust valve timing control apparatus, taken along a plane passing through an axis of rotation of the exhaust valve timing control apparatus. 
         FIG. 16  is a front view of the exhaust valve timing control apparatus in a most advanced state, as viewed along the axis of rotation. 
         FIG. 17  is a front view of the exhaust valve timing control apparatus in a most retarded state, as viewed along the axis of rotation. 
         FIGS. 18A ,  18 B and  18 C are views of the housing body of the exhaust valve timing control apparatus, where  FIG. 18A  is a front view along the axis of rotation,  FIG. 18B  is a side sectional view taken along a plane indicated by F 18 B-F 18 B in  FIG. 18A , and  FIG. 18C  is a rear view along the axis of rotation. 
         FIGS. 19A and 19B  are views of the vane rotor of the exhaust valve timing control apparatus, where  FIG. 19A  is a front view along the axis of rotation, and  FIG. 19B  is a side sectional view taken along a plane indicated by F 19 B-F 19 B in  FIG. 19A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     &lt;&lt;Construction of Valve Timing Control Apparatus&gt;&gt;  FIG. 1  is a front view of a valve timing control apparatus according to an embodiment of the present invention in which a pair of intake valve timing control apparatuses  1   a  and a pair of exhaust valve timing control apparatuses  1   b  are mounted to an internal combustion engine, as viewed in an axial direction of the internal combustion engine. The axial direction is an axial direction of a crankshaft of the internal combustion engine, which is identical to an axial direction of intake camshafts or exhaust camshafts. The intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  are individually or collectively referred to as valve timing control apparatus or system  1 . The internal combustion engine is arranged in a vehicle engine room so that the axial directions of the crankshafts and camshafts are perpendicular to a vehicle longitudinal direction. In other words,  FIG. 1  is a view of valve timing control apparatus  1  in a vehicle lateral direction. In a typical motor vehicle, an engine room has a unique three-dimensional curved side wall because of provision of frames (structural members or skeletal members), so that the side wall has a portion projecting inwardly in the engine room.  FIGS. 1 and 15  show an example in which a projection W 1  projects from an engine room side wall W close to one exhaust valve timing control apparatus  1   b,  as schematically shown by a long-dashed short-dashed line.  FIG. 1  shows a section of engine room side wall W (projection W 1 ) taken along the plane indicated by F 1 -F 1  in  FIG. 15 , which is a view in the vehicle lateral direction.  FIG. 15  shows a section of projection W 1  of engine room side wall W taken along the plane indicated by F 15 -F 15  in  FIG. 1  and parallel to the axial direction of the internal combustion engine (X-axis), which is a view in the vehicle lateral direction. The internal combustion engine is a V-type DOHC engine in which a pair of cylinder banks are arranged in a V-shape spreading from the crankshaft as viewed in the axial direction, and each cylinder bank is provided with a camshaft for actuating intake valves, or intake camshaft  3   a,  and a camshaft for actuating exhaust valves, or exhaust camshaft  3   b.  Intake camshafts  3   a  and  3   a  are arranged inside of exhaust camshafts  3   b  and  3   b  in a lateral direction of a cylinder block of the internal combustion engine, as shown in  FIG. 1 . 
     Valve timing control apparatus  1  is mounted to one axial end of the internal combustion engine. Specifically, each intake valve timing control apparatus  1   a  is fixedly mounted to an axial end of respective intake camshaft  3   a,  whereas each exhaust valve timing control apparatus  1   b  is fixedly mounted to an axial end of respective exhaust camshaft  3   b.  Valve timing control apparatus  1  may be provided with only one of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b.  However, provision of both of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  makes it possible to control the valve timing in a more flexible manner. Each intake valve timing control apparatus  1   a  is provided with a pulley  100 . Similarly, each exhaust valve timing control apparatus  1   b  is provided with a pulley  100 . A timing belt  1010  is put over pulleys  100 , as indicated by long dashed double-short dashed lines in  FIG. 1 , so that intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  are connected to one another. Timing belt  1010  is a toothed belt (or cogged belt) made of rubber, but may be alternatively made of a material preferable for weight reduction and cost reduction, such as a synthetic resin. Timing belt  1010  transmits torque from the crankshaft to pulleys  100 . Each of intake valve timing control apparatuses  1   a  and exhaust valve timing control apparatuses  1   b  is rotated by the torque transmitted through the pulley  100 . While rotating, each of intake valve timing control apparatuses  1   a  and exhaust valve timing control apparatuses  1   b  optimally controls variable opening and closing timings of respective intake valves or exhaust valves according to a state of operation of the internal combustion engine. The combination of pulley  100  and timing belt  1010  may be replaced with a combination of a sprocket and a chain as a means for transmitting torque from the crankshaft to a housing “HSG” of intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b.  Alternatively, the torque from the crankshaft may be transmitted indirectly, for example, in such a manner that the torque from the crankshaft is transmitted directly to one of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b,  and transmitted through the one to the other. 
     In the following, an X-axis is assumed to extend in the axial direction of the internal combustion engine, or in the axial direction of camshaft  3   a  or  3   b.  Along the X-axis, a positive direction is defined as a direction from an axial end of camshaft  3   a  or  3   b  where no intake valve timing control apparatus  1   a  or no exhaust valve timing control apparatus  1   b  is provided to an axial end of camshaft  3   a  or  3   b  where intake valve timing control apparatuses  1   a  and exhaust valve timing control apparatuses  1   b  are mounted. 
     &lt;Construction of Intake Valve Timing Control Apparatus&gt; The following describes construction of intake valve timing control apparatus  1   a  with reference to  FIGS. 2 to 14 .  FIG. 2  is an exploded perspective view of intake valve timing control apparatus  1   a,  where parts are arranged in the axial direction.  FIG. 3  is a partial side sectional view of intake valve timing control apparatus  1   a,  taken along a plane passing through an axis of rotation “O” (shown in  FIG. 4 ) of intake valve timing control apparatus  1   a,  i.e. taken along a plane indicated by a long dashed short dashed line F 3 -F 3  in  FIG. 4 .  FIGS. 4 and 5  are front views of intake valve timing control apparatus  1   a  under a condition that a front plate  8 , etc. are removed, as viewed from the X-axis positive side. In  FIGS. 3 and 4 , fluid passages and grooves which are formed in intake camshaft  3   a,  etc. are indicated by broken lines. 
     Intake camshaft  3   a  is made of an iron-based material, and rotatably supported on bearings in a laterally-inside portion of an upper end portion of the cylinder head of the internal combustion engine. Intake camshaft  3   a  is formed with drive cams (intake cams) at the outside peripheral surface, which are located to face or conform to positions of the intake valves. When intake camshaft  3   a  is rotated, the intake cams open and close the intake valves via valve lifters, rocker arms, etc. Intake valve timing control apparatus  1   a  is fixedly attached to an X-axis positive side axial end portion  30  of intake camshaft  3   a  by three camshaft bolts  33 ,  34  and  35 . Each camshaft bolt  33 ,  34  or  35  is a hexagonal-head bolt having a head  331 ,  341  or  351  in the form of a regular hexagonal prism, and a shank formed with a male thread at its outside periphery. Each head  331 ,  341  or  351  is formed integrally with a plane washer  332 ,  342  or  352 , for protection of a bearing surface, etc. The hexagonal-head bolt may be replaced with another fixing means. Each washer  332 ,  342  or  352  is optional. The axial end portion  30  of intake camshaft  3   a  is formed with: three bolt holes  32  through which camshaft bolts  33 ,  34  and  35  are inserted; a portion constituting a retard passage  20 ; and a portion constituting an advance passage  21 . Each bolt hole  32  is formed with a female thread at its inside periphery, and substantially evenly spaced with one another in the circumferential direction around the axis of rotation O, extending from an X-axis positive side axial end surface  300  of axial end portion  30  to a predetermined depth in the X-axis direction. The axial end portion  30  of intake camshaft  3   a  is formed with grooves  200 ,  204 ,  210  and  214 , first fluid passages  202  and  212 , and second fluid passages  201 ,  203 ,  211  and  213 . Each groove  200 ,  204 ,  210  or  214  is an annular circumferential groove formed at the outside periphery of the axial end portion  30  to a predetermined depth, extending all around the outside periphery in the circumferential direction. Grooves  200  and  204  constitute retard passage  20 , whereas grooves  210  and  214  constitute advance passage  21 . Grooves  210  and  200  are arranged in this order as followed from the X-axis negative side to the X-axis positive side, and located in the cylinder head and outside of intake valve timing control apparatus  1   a.  Grooves  214  and  204  are arranged in this order as followed from the X-axis negative side to the X-axis positive side, and located at an X-axis positive side portion of the axial end portion  30  to which a vane rotor  4  is attached. Each first fluid passage  202  or  212  is an axial fluid passage formed in the axial end portion  30 , extending in the X-axis direction. First fluid passage  202  constitutes retard passage  20 , whereas first fluid passage  212  constitutes advance passage  21 . Each second fluid passage  201 ,  203 ,  211  or  213  is a radial fluid passage formed in the axial end portion  30 , extending in a radial direction perpendicular to the X-axis. Second fluid passages  201  and  203  constitute retard passage  20 , whereas second fluid passages  211  and  213  constitute advance passage  21 . Each first fluid passage  202  or  212  has a smaller diameter than bolt hole  32 , extending from the axial end surface  300  in the negative x-axis direction. In other words, each first fluid passage  202  or  212  extends in the axial end portion  30 , and has an opening at the axial end surface  300 . First fluid passage  202  is arranged between bolt hole  32  for camshaft bolt  34  and bolt hole  32  for camshaft bolt  35  in the circumferential direction around the axis of rotation O. Specifically, the distance from the axis of rotation O to the central axis of first fluid passage  202  is substantially equal to the distance from the axis of rotation O to the central axis of each bolt hole  32 , and the central axis of first fluid passage  202  is located on a circular line passing through the central axis of each bolt hole  32 , and in a substantially central position between camshaft bolts  34  and  35 . The size of first fluid passage  202  in the X-axis direction is set so that first fluid passage  202  overlaps with groove  200  in the X-axis direction, and further extends to a position slightly on the X-axis negative side of groove  200 . On the other hand, first fluid passage  212  is arranged between bolt hole  32  for camshaft bolt  33  and bolt hole  32  for camshaft bolt  35  in the circumferential direction, similar to first fluid passage  202 . The size of first fluid passage  212  in the X-axis direction is set so that first fluid passage  212  overlaps with groove  210  in the X-axis direction, and further extends to a position slightly on the X-axis negative side of groove  210 . Second fluid passage  201  extends through between groove  200  and first fluid passage  202 , for fluid communication therebetween. Second fluid passage  203  extends through between groove  204  and first fluid passage  202 , for fluid communication therebetween. Second fluid passage  213  extends through between groove  214  and first fluid passage  212 , for fluid communication therebetween. 
     Intake valve timing control apparatus  1   a  controls variable valve timing of the intake valves by continuously changing a rotational phase of intake camshaft  3   a  with respect to the crankshaft by supplied working fluid. Intake valve timing control apparatus  1   a  includes housing HSG formed with pulley  100 , and a vane rotor  4  as a driven member mounted in housing HSG. Pulley  100  transmits torque from the crankshaft to housing HSG. Vane rotor  4  is mounted inside of housing HSG for relative rotation with respect to housing HSG. The torque is transmitted from housing HSG to vane rotor  4  through working fluid. Vane rotor  4  transmits the torque to intake camshaft  3   a.  Vane rotor  4  constitutes a phase change mechanism for changing the rotational phase of intake camshaft  3   a  with respect to housing HSG or the crankshaft by supply and drainage of working fluid. The phase change mechanism may be of another type, such as a trochoid type. In other words, the driven member of intake valve timing control apparatus  1   a  is not limited to a vane rotor. For example, the relative rotational phase between the housing and the camshaft may be changed according to movement of a member in the axial direction of the valve timing control apparatus, wherein the member has a helical gear (spline). Intake valve timing control apparatus  1   a  is a hydraulic actuator or hydraulically driven type phase actuation mechanism which is operated by receipt of supply of working fluid from a hydraulic fluid supply and drainage mechanism  2  or drainage of working fluid to hydraulic fluid supply and drainage mechanism  2 . Supply and drainage of working fluid by hydraulic fluid supply and drainage mechanism  2  is controlled by a controller “CU” as a control means. 
     Housing HSG includes a housing body  10 , a front plate  8  as a sealing plate, and a rear plate  9  as a sealing plate. Housing body  10  has a hollow cylindrical shape with open longitudinal ends. This is because housing body  10  is formed by extrusion as described in detail below. Front plate  8  has a disc shape, which is fixed to a front longitudinal end (X-axis positive side end) of housing body  10 , for sealing and closing the opening of housing body  10 . Rear plate  9  has a disc shape, which is fixed to a rear longitudinal end (X-axis negative side end) of housing body  10 , for sealing and closing the opening of housing body  10 . Housing body  10  may be alternatively formed with an opening only at one longitudinal end. Namely, housing body  10  may have a hollow cylindrical shape with a closed bottom, or a cup-shape. In other words, one of the sealing plates may be formed integrally with housing body  10 . Housing body  10  is not limited to a cylindrical shape. Housing body  10  is formed integrally with pulley  100  extending over the entire length of the outside periphery of housing body  10  in the X-axis direction. Pulley  100  includes a plurality of projections (teeth) and recesses extending in the X-axis direction, which are arranged in the circumferential direction, and substantially evenly spaced, thus forming a gear or cogged belt wheel over which timing belt  1010  is wound. Pulley  100  is not limited to the integral forming with housing body  10 , but may be formed separately from and coupled to housing body  10 . The torque transmission based on tooth meshing may be replaced with a construction in which torque is transmitted frictionally through surface-to-surface contact between a belt and a pulley. For example, a housing body is formed with a pulley that has a groove at a central position in its width direction, and a belt that has no tooth and has a cross section fitted to the pulley having the groove. The combination of pulley  100  and toothed timing belt  1010  according to the embodiment is advantageous in enhancement in the efficiency of power transmission. When pulley  100  is rotated by the crankshaft, pulley  100  and housing body  10  rotate as a solid unit in a clockwise direction as viewed in  FIG. 4  or in a direction of an arrow shown in  FIG. 1 . 
       FIGS. 6A ,  6 B and  6 C are views of housing body  10 , where  FIG. 6A  is a front view along the axis of rotation from the X-axis positive side,  FIG. 6B  is a side sectional view taken along a plane indicated by F 6 B-F 6 B in  FIG. 6A , and  FIG. 6C  is a rear view along the axis of rotation from the X-axis negative side.  FIGS. 7 and 8  are perspective views of workpieces during a process of manufacturing the housing body  10 . Housing body  10  is manufactured by a process including an extrusion operation, a coating operation, a cutting-off operation, and a carving operation, which are carried out in this order. First, in the extrusion operation, an aluminum-based metal material, such as aluminum, or aluminum alloy such as A6000 or A7000, is heated and extruded from a mold, to form an aluminum extrusion or first workpiece P 1  shown in  FIG. 7 , which extends in the direction of extrusion, and in which continuous shapes of first, second and third shoes  11 ,  12  and  13  are formed at an inside periphery, and a continuous shape of pulley  100  is formed at an outside periphery. Second, in the coating operation, the entire surface, i.e. the inside and outside peripheral surfaces of first workpiece P 1  are applied with anodic oxidation treatment or alumilite treatment, to form a second workpiece P 2  which has anodic oxide coating films at the inside and outside peripheries. Third, in the cutting-off operation, second workpiece P 2  is cut laterally at intervals of a predetermined distance along the axial direction, to form a plurality of identically-shaped third workpieces P 3 , as shown in  FIG. 8 . Finally, in the carving operation, each third workpiece P 3  is applied with carving or cutting, to form a fitting recess  101 , bolt holes  110 ,  120  and  130 , and a positioning recess  114 , as described in detail below, and thereby form a final shape of housing body  10  shown in  FIGS. 6A ,  6 B and  6 C. In this way, each housing body  10  in the final shape is formed with an anodic oxide coating film layer at the inside and outside peripheral surfaces, but the cut surfaces obtained by the cutting-off operation (the axial end surfaces in the X-axis direction) are formed with no anodic oxide coating film layer. Instead, a base layer of the aluminum-based metal material is exposed at the cut surfaces. As shown in  FIGS. 6B and 6C , the open X-axis negative side end of housing body  10  is formed with fitting recess  101  which is a cylindrical recess having a center at the axis of rotation O, and extending to a predetermined depth in the X-axis direction. Specifically, fitting recess  101  is formed by cutting away a part of third workpiece P 3 , into a cylindrical shape having a predetermined radius R about the axis of rotation O, and having a predetermined depth in the X-axis positive direction. Fitting recess  101  includes a bottom surface  102  having a circular shape, and an inside peripheral surface  103  surrounding the bottom surface  102 . Inside peripheral surface  103  has the radius R with respect to the axis of rotation O. Where Ri represents a radius of the inside peripheral surface of housing body  10  about the axis of rotation O, and Ro represents a maximum radius of housing body  10  which is a distance between a tooth tip of pulley  100  and the axis of rotation O, it holds that Ro:Ri≈10:8. It also holds that (Ro+Ri)/2≈R. In other words, fitting recess  101  extends in the radial direction of housing body  10  substantially to a midpoint between the inside and outside peripheral surfaces of housing body  10 . On the other hand, where L represents an axial length L of housing body  10 , and L 2  represents a distance between the bottom surface  102  of fitting recess  101  and the X-axis negative end surface  104  of housing body  10 , it holds that L:L 2 ≈10:2. In other words, fitting recess  101  is formed to extend in the X-axis direction over a range of about 20% or more of the axial length of housing body  10 . The axial length of the inside periphery of housing body  10 , L 1 , is shorter than that of the outside periphery, or that of pulley  100 , L (L 1 &lt;L). In other words, the axial length of pulley  100  in the X-axis direction, L, is set longer than that of the inside periphery of housing body  10 , L 1 . The inside periphery of housing body  10  is formed integrally with first, second and third shoes  11 ,  12  and  13  which extend inwardly in the radial direction. Specifically, first, second and third shoes  11 ,  12  and  13  are arranged in a circumferential direction or direction of rotation about the axis of rotation O, at substantially even intervals, extending from the inside periphery of housing body  10  inwardly toward the axis of rotation O. First, second and third shoes  11 ,  12  and  13  are arranged in this order in the clockwise direction in  FIG. 4 . Each of first, second and third shoes  11 ,  12  and  13  extends in the X-axis direction, and has a cross section having a substantially trapezoidal shape. The width of each of first, second and third shoes  11 ,  12  and  13  in the circumferential direction is set substantially equal to each other. The space between second shoe  12  and third shoe  13 , and the space between third shoe  13  and first shoe  11 , are set substantially equal to each other. The space between first shoe  11  and second shoe  12  is set slightly larger than the other spaces, for accommodating a first vane  41  having a wider width, which is described in detail below. First shoe  11  is formed with a bolt hole  110  substantially at the center of the trapezoidal cross section, where bolt hole  110  extends through the first shoe  11 . Similarly, second shoe  12  and third shoe  13  are formed with a through bolt hole  120  and a through bolt hole  130  respectively. The X-axis positive side end surface of each of first, second and third shoes  11 ,  12  and  13  is fixedly attached to front plate  8 . The X-axis negative side end surface of each of first, second and third shoes  11 ,  12  and  13 , which is a part of the bottom surface  102  of fitting recess  101 , is fixedly attached to rear plate  9 . As viewed from the X-axis positive side, or as shown in  FIG. 6A , second shoe  12  and third shoe  13  are formed with a flat portion  121  and a flat portion  131  in their clockwise sides, respectively. Each of flat portion  121  and flat portion  131  is in a straight line passing through the axis of rotation O of housing body  10 , as viewed in the X-axis direction. On the other hand, the clockwise side of first shoe  11  is formed with a rounded portion  112  at a root portion in an outward position in the radial direction of housing body  10 , and formed with a recess  113  at a tip portion in an inward position in the radial direction of housing body  10 , as viewed in  FIG. 6B . First shoe  11  is formed with a flat portion  111  between rounded portion  112  and recess  113 , similar to second shoe  12  and third shoe  13 . Rounded portion  112  has an inwardly curved and substantially arced edge, as viewed in the X-axis direction. The edge of rounded portion  112  gradually rises from the inside peripheral surface of housing body  10  to merge into the clockwise side edge of first shoe  11 . As shown in  FIG. 6C , on the X-axis negative side of first shoe  11 , rounded portion  112  in bottom surface  102  of fitting recess  101  is formed with a positioning recess  114  adjacent to bolt hole  110 . Positioning recess  114  has a smaller diameter than bolt hole  110 . Rounded portion  112  serves to allow arrangement of positioning recess  114  in first shoe  11 , and enhance rigidity of the root portion of first shoe  11  in the circumferential direction, so as to bear a stress resulting from contact between first vane  41  and first shoe  11 . As viewed from the X-axis positive side, or as viewed in  FIG. 6A , the counterclockwise sides of first, second and third shoes  11 ,  12  and  13  are formed with recesses  115 ,  125  and  135 , respectively. Recesses  115 ,  125  and  135  are relatively wide grooves extending over the entire axial length of housing body  10  in the X-axis direction. As shown in  FIG. 6A , as viewed in the X-axis direction, the tips  116 ,  126  and  136  of first, second and third shoes  11 ,  12  and  13  have radially inside surfaces facing the axis of rotation O, which are inwardly curved like an arc fitted with an outside peripheral surface of a rotor  40  of vane rotor  4 , which is described in detail below. The tip  116  of first shoe  11  is formed with a sealing groove  117  which extends in the X-axis direction. A sealing member  118  and a sealing spring such as a leaf spring  119  not shown are fitted and retained in sealing groove  117 . Sealing member  118  is in liquid-tight sliding contact with the outside peripheral surface of rotor  40 . Leaf spring  119  presses the sealing member  118  onto the outside peripheral surface of rotor  40 . Sealing member  118  is formed of a grass fiber plastic, having a substantially U-shape. Similarly, the tips  126  and  136  of second shoe  12  and third shoe  13  are formed with sealing grooves  127  and  137 , sealing members  128  and  138 , and leaf springs  129  and  139 , respectively, as shown in  FIGS. 3 and 4 . 
     Front plate  8  is formed by forging an iron-based metal material, such as an iron alloy, into a thinner disc shape than rear plate  9 , wherein the iron-based metal material is harder than aluminum-based metal materials. Front plate  8  closes and seals the front axial end of housing body  10 , namely closes and seals the X-axis positive side ends of first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3  defined in housing body  10 . In the present description, “hardness” of an object means a degree of difficulty of changing the outline of the object, and can be measured by a commonly known hardness test. “Wear” of an object means that a surface of the object is worn, and can be categorized in terms of dynamics into sliding wear, collision wear, etc. “Wear resistance” of an object can be measured by a suitable test selected according to the category, or may be determined indirectly based on the hardness test. As shown in  FIG. 3 , the diameter of front plate  8  is set slightly larger than the diameter (specifically, the diameter of tooth top circle) of pulley  100 , so that over the entire circumference of pulley  100 , an outside periphery  80  of front plate  8  projects from pulley  100  outwardly in the radial direction as viewed in the X-axis direction. As shown in  FIG. 2 , front plate  8  is formed with a female thread portion  82  located substantially at the center of the X-axis positive side surface of front plate  8 . Female thread portion  82  projects in the X-axis positive direction. Female thread portion  82  is formed with a large-diameter hole  81  at its center, which extends through front plate  8  in the X-axis direction, and through which camshaft bolts  33 ,  34  and  35  (see  FIG. 4 ) are inserted to pass, when intake valve timing control apparatus  1   a  is assembled. Large-diameter hole  81  of female thread portion  82  is formed with a female thread  820  to which a male thread  700  of a cap  7  is screwed. The annular X-axis positive side surface of female thread portion  82  is formed with an annular sealing ring groove  821 . Front plate  8  is formed with bolt holes  83 ,  84  and  85  located between female thread portion  82  and outside periphery  80 . Bolt holes  83 ,  84  and  85  are arranged and evenly spaced in the circumferential direction as viewed in the X-axis direction, through which bolts b 1 , b 2  and b 3  inserted to pass. In the X-axis direction, bolt holes  83 ,  84  and  85  are located to face or conform to bolt holes  110 ,  120  and  130 , which are formed in first, second and third shoes  11 ,  12  and  13  of housing body  10 , respectively. Front plate  8  is formed with thicker portions  86 ,  87  and  88  around bolt holes  83 ,  84  and  85  respectively. Thicker portions  86 ,  87  and  88  are slightly thicker than the other portion in the X-axis direction, in order to bear the axial force applied by bolts b 1 , b 2  and b 3 . Each of thicker portions  86 ,  87  and  88  has a shape that is spreading inwardly in the radial direction, and continuous with female thread portion  82 . In other words, front plate  8  is formed as thin as possible, except thicker portions  86 ,  87  and  88  for providing a strength enough to bear the axial force applied by bolts b 1 , b 2  and b 3 .  FIG. 12  is a perspective view of front plate  8  as viewed from the X-axis negative side. The X-axis negative side surface of front plate  8  is formed with an annular sealing ring groove  89 . Annular sealing ring groove  89  has a shape including three inwardly curved sections like a three-leaved clover, so that annular sealing ring groove  89  extends circumferentially along the outside periphery  80  with a slight radial clearance r, and passes inside of bolt holes  83 ,  84  and  85 , i.e. passes between the axis of rotation O and each of bolt holes  83 ,  84  and  85 . 
     Cap  7  is formed by forging an iron-based metal material into a hollow cylindrical shape with a bottom, and detachably attached to front plate  8 , thus constituting a front plate (in a broad sense) together with front plate  8 . Cap  7  includes a male thread portion  70 , a division wall portion  71 , and a flange  72 . Male thread portion  70  has a hollow cylindrical shape, extending in the X-axis direction. Division wall portion  71  closes the opening of male thread portion  70 . Flange  72  spreads outwardly in the radial direction from the X-axis positive side end of male thread portion  70 . Male thread portion  70  is formed with a male thread  700  at the outside periphery. Division wall portion  71  is formed integrally with a bolt head portion  710  substantially at the center of the X-axis positive side surface, which has the form of a regular hexagonal prism. Bolt head portion  710  is turned so that cap  7  is screwed into front plate  8 , i.e. male thread  700  of cap  7  is screwed into female thread  820  of front plate  8 , and that large-diameter hole  81  of front plate  8  is closed and sealed. Under this condition, the X-axis negative side surface of flange  72  faces the X-axis positive side axial end surface of female thread portion  82 , and the X-axis negative side axial end surface of male thread portion  70  is located slightly on the X-axis positive side of the X-axis negative side surface of front plate  8 , as shown in  FIG. 3 . Cap  7  is formed with a recess  73  at the X-axis negative side, wherein recess  73  is defined by the X-axis negative side surface of division wall portion  71  as a bottom surface, and the inside periphery of the X-axis negative side portion of male thread portion  70  as a side wall. The depth or size in the X-axis direction, of recess  73 , is half or more of the height or size in the X-axis direction, of head  331 ,  341  or  351  of each camshaft bolt  33 ,  34  or  35 . 
     Rear plate  9  is fixedly inserted in fitting recess  101  of housing body  10 , so as to close and seal the rear axial open end of housing body  10  closer to intake camshaft  3   a,  i.e. the X-axis negative side open end of first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3  which are defined in housing body  10 . Rear plate  9  is formed by forging an iron-based metal material such as S45C or S48 that is harder than the aluminum-based metal material of vane rotor  4 . Rear plate  9  includes a plate body  90  and a cylindrical portion  91 . Cylindrical portion  91  has a cylindrical shape extending in the X-axis negative direction from the X-axis negative side of plate body  90 . As viewed in the X-axis direction, cylindrical portion  91  is located substantially at the center of plate body  90 , coaxially with the axis of rotation O. Cylindrical portion  91  is formed with a through hole  92  inside, through which intake camshaft  3   a  is inserted to pass. Through hole  92  is formed to extend in the X-axis direction, and pass through rear plate  9 , substantially coaxially with the axis of rotation O. The diameter of through hole  92  is set slightly smaller than that of large-diameter hole  81  of front plate  8 . The length of plate body  90  in the X-axis direction is set at most slightly larger than the depth of fitting recess  101  (the length in the X-axis direction, L 2 ). The length of an outside peripheral surface  93  of plate body  90  in the X-axis direction is set substantially equal to the depth of fitting recess  101  (L 2 ). The diameter of plate body  90  is set substantially equal to the diameter of fitting recess  101  (R×2). Plate body  90  is formed with female thread portions  901 ,  902  and  903  around cylindrical portion  91 , which are arranged and evenly spaced in the circumferential direction. Female thread portions  901 ,  902  and  903  are formed with bolt holes extending through plate body  90  in the X-axis direction. The bolt holes are formed with female threads in the inside peripheral surfaces, respectively. Male threads of an X-axis negative side end portions of bolts b 1 , b 2  and b 3  are screwed into the female threads respectively. As viewed in the X-axis direction, female thread portions  901 ,  902  and  903  (bolt holes) are located to face or conform to the bolt holes  110 ,  120  and  130  of first, second and third shoes  11 ,  12  and  13 , and bolt holes  83 ,  84  and  85  of front plate  8 . As shown in  FIG. 2 , plate body  90  is formed with a recess  900  which is located adjacent to and in the clockwise direction from one female thread portion  901  which faces bolt hole  110  of first shoe  11 , as viewed from the X-axis positive side. Recess  900  is formed to extend in the X-axis negative direction to a predetermined depth in plate body  90 . The outside peripheral surface  93  of plate body  90  is formed with a sealing ring groove  906  which extends in the circumferential direction. The X-axis positive side surface of plate body  90  is formed with annular sealing ring grooves  907 ,  908  and  909  which extend circumferentially around female thread portions  901 ,  902  and  903  respectively. Plate body  90  is formed with a pin hole  904  having a bottom, which is located at the outside periphery of the X-axis positive side surface of plate body  90 , and adjacent to and in the counterclockwise direction from recess  900 . Pin hole  904  is located between recess  900  and female thread portion  901 , and in a position in the radial direction of plate body  90  which faces positioning recess  114  of housing body  10  shown in  FIG. 6C . A positioning pin  905  is press-fitted and fixed in pin hole  904 . Positioning pin  905  is a dowel pin whose longitudinal end projects to a predetermined height in the X-axis positive direction from the X-axis positive side surface of plate body  90 . The diameter of the longitudinal end of positioning pin  905  is set slightly smaller than positioning recess  114 , and adapted to be inserted and fitted from the X-axis negative side into positioning recess  114 . The diameter of the longitudinal end of positioning pin  905  and the diameter of positioning recess  114  are set so as to prevent play between housing body  10  and rear plate  9  in the circumferential direction under a condition that positioning pin  905  is inserted and fitted in positioning recess  114 . Pin hole  904  is located in rear plate  9  so that under the condition that positioning pin  905  is inserted and fitted in positioning recess  114 , bolt hole  110  of first shoe  11  of housing body  10  is in substantially the same position as female thread portion  901  of rear plate  9  as viewed in the X-axis direction, and that when flat portion  415  of first vane  41  of vane rotor  4  is in contact with flat portion  111  of first shoe  11  as shown in  FIG. 4 , a slide hole  501  of first vane  41  is in substantially the same position as recess  900  of rear plate  9 , as viewed in the X-axis direction. Pin hole  904  is located closer to first retard chamber R 1  than sealing ring grooves  906  and  907 , and positioning pin  905  is located adjacent to recess  900 . 
     Front plate  8 , housing body  10 , and rear plate  9  are fixed together in the X-axis direction by bolts b 1 , b 2  and b 3 . Bolts b 1 , b 2  and b 3  are inserted from the X-axis positive side to pass through bolt holes  83 ,  84  and  85  of front plate  8 , and bolt holes  110 ,  120  and  130  of housing body  10 , and screwed into female thread portions  901 ,  902  and  903  of rear plate  9 , so as to fix front plate  8  and rear plate  9  to housing body  10 . Sealing rings S 1 , S 2  and S 3  are inserted between housing body  10  and rear plate  9 , and between front plate  8  and housing body  10 . A sealing ring S 4  is inserted between cap  7  and front plate  8 . Sealing rings S 1 , S 2 , S 3  and S 4  are annular sealing members to be mounted, each of which is an O-ring having a circular cross section in this example. Sealing rings S 1 , S 2 , S 3  and S 4  are formed of a rubber such as an acrylic rubber or fluorine rubber, which is superior in durability against working fluid. The rubber may be a nitrile rubber, etc. Each sealing rings S 1 , S 2 , S 3  or S 4  is not limited to O-rings, but may have a different cross section. Sealing rings S 1  and S 2  are disposed between rear plate  9  and housing body  10 . Sealing ring S 1  is arranged between the inside peripheral surface  103  of fitting recess  101  of housing body  10  and outside peripheral surface  93  of plate body  90  of rear plate  9 . Each sealing ring S 2  is arranged between a portion surrounding a respective one of female thread portions  901 ,  902  and  903  in the X-axis positive side end surface of rear plate  9  and the X-axis negative side end surface (bottom surface  102  of fitting recess  101 ) of a respective one of first, second and third shoes  11 ,  12  and  13  of housing body  10 . Sealing ring S 3  is arranged between portions of front plate  8  and housing body  10  which face each other, i.e. between the X-axis negative side end surface of front plate  8  and the X-axis positive side end surface  105  of housing body  10  (first, second and third shoes  11 ,  12  and  13 ). Sealing ring S 3  has the form of a three-leaved clover which is substantially identical to the form of annular sealing ring groove  89  of front plate  8 . Sealing ring S 4  is arranged between the X-axis positive side end surface of female thread portion  82  of front plate  8  and the X-axis negative side end surface of flange  72  of cap  7 . 
     As shown in  FIG. 3 , cylindrical portion  91  of rear plate  9  is provided with an oil seal “OS” at the outside peripheral surface of its X-axis negative side portion, and is rotatably supported through the oil seal OS by the cylinder block of the internal combustion engine. 
       FIGS. 9A and 9B  are views of vane rotor  4 , where  FIG. 9A  is a front view along the axis of rotation from the X-axis positive side, and  FIG. 9B  is a side sectional view taken along a plane indicated by F 9 B-F 9 B in  FIG. 9A . In  FIG. 9A , fluid passages  408  and  409  formed inside the vane rotor  4 , and a recess  44  formed the X-axis negative side of vane rotor  4  are indicated by broken lines. In  FIG. 9B , the opening of one of retard fluid passages  408  and the opening of one of advance fluid passages  409  are shown.  FIGS. 10 and 11  are perspective views of workpieces during a process of manufacturing the vane rotor  4 . Vane rotor  4  is manufactured by a process including an extrusion operation, a cutting-off operation, a carving operation, and a coating operation, which are carried out in this order. First, in the extrusion operation, an aluminum-based metal material as used for housing body  10  is extruded from a mold, to form a first workpiece Q 1  shown in  FIG. 10 , which extends in the direction of extrusion, in which continuous shapes of rotor  40  and first, second and third vanes  41 ,  42  and  43  are formed. Second, in the cutting-off operation, first workpiece Q 1  is cut laterally at intervals of a predetermined distance along the axial direction, to form a plurality of identically-shaped second workpieces Q 2  including a rotor and vanes, as shown in  FIG. 11 . Third, in the carving operation, second workpiece Q 2  is applied with carving or cutting, to form a boss portion  401 , a camshaft insertion hole  402 , a slide hole  501 , etc., and thereby form a final shape of vane rotor  4  shown in  FIGS. 9A and 9B . Finally, in the coating operation, the entire surface of second workpiece Q 2  is applied with anodic oxidation treatment, to form a third workpiece Q 3  which has an anodic oxide coating film layer. When vane rotor  4  is finalized, the anodic oxide coating film layer is formed in the axial end surfaces of vane rotor  4 , and also in the surface of boss portion  401 , camshaft insertion hole  402 , slide hole  501 , etc. Vane rotor  4  is a driven member or driven rotator which can rotate relative to pulley  100  or housing HSG, and serves as a vane member which rotates in the clockwise direction in  FIG. 4  as a solid unit with intake camshaft  3   a.  Vane rotor  4  includes: rotor  40  fixed to intake camshaft  3   a  with three camshaft bolts  33 ,  34  and  35 , substantially coaxially with intake camshaft  3   a;  and first, second and third vanes  41 ,  42  and  43  projecting outwardly in radial directions from rotor  40 , wherein first, second and third vanes  41 ,  42  and  43  are adapted to receive hydraulic pressure. 
     Rotor  40  includes a rotor body  400  and a boss portion  401  which are arranged coaxially. Rotor body  400  is a body of rotor  40 , having a cylindrical shape. In the X-axis direction, the length of rotor body  400  is substantially equal to the length of housing body  10  excluding the length of the fitting recess  101 , L 1 . The outside diameter (i.e. the diameter of the outside periphery) of rotor body  400  is slightly larger than the diameter of large-diameter hole  81  of front plate  8 . Boss portion  401  is cylindrically formed to project from rotor body  400  in the axial direction, or in the X-axis negative direction. The length of boss portion  401  in the X-axis direction, L 3 , is slightly shorter than the length of fitting recess  101  of housing body  10  in the X-axis direction, L 2 . Boss portion  401  has a slightly smaller outer diameter than rotor body  400 , which is slightly smaller than the diameter of through hole  92  of rear plate  9 . The surface of boss portion  401 , including the inside and outside peripheral surfaces of boss portion  401 , is formed with the anodic oxide coating film layer, as described above. Rotor  40  is formed with a camshaft insertion hole  402  having a bottom, which is positioned coaxially with rotor  40 , and extends inside of boss portion  401  and rotor body  400 , where camshaft insertion hole  402  has a diameter that is substantially equal to and slightly larger than the diameter of intake camshaft  3   a.  Camshaft insertion hole  402  extends over the entire axial length of boss portion  401  and a range of two thirds or less of the axial length of rotor body  400 , as shown in  FIG. 9B . Camshaft insertion hole  402  is adapted to intake camshaft  3   a  so that an inserted portion  301  of intake camshaft  3   a  (an X-axis positive side portion of axial end portion  30  of intake camshaft  3   a ) is inserted and mounted in camshaft insertion hole  402 . Rotor body  400  is formed with bolt holes  403 ,  404  and  405  at the bottom of camshaft insertion hole  402 , wherein each bolt hole  403 ,  404  or  405  extends through rotor body  400 . Bolt holes  403 ,  404  and  405  are arranged in the circumferential direction around the axis of rotation O, in this order in the clockwise direction, and substantially evenly spaced from one another. The positions of bolt holes  403 ,  404  and  405  are set to face and conform to bolt holes  32  of axial end portion  30  of intake camshaft  3   a  in the X-axis direction, so that the central axes of bolt holes  403 ,  404  and  405  are substantially identical to the central axes of bolt holes  32  as viewed in the X-axis direction. Namely, the distance between each bolt hole  403 ,  404  or  405  and the axis of rotation O is substantially equal to the distance between the corresponding bolt hole  32  and the axis of rotation O, and the angle defined by the line connecting the axis of rotation O and one of bolt holes  403 ,  404  and  405  and the line connecting the axis of rotation O and another one of bolt holes  403 ,  404  and  405  is substantially equal to the angle defined by the line connecting the axis of rotation O and one of bolt holes  32  and the line connecting the axis of rotation O and another one of bolt holes  32 . Rotor body  400  is formed also with a pin hole having a bottom (recess  44  for positioning) at the bottom of camshaft insertion hole  402 , wherein recess  44  extends to a predetermined depth. As viewed in the X-axis direction, recess  44  has an elliptic shape whose outline includes two straight line sections extending in a radial direction of rotor  40  and facing one another in the circumferential direction, and two curved sections having the form of semicircles and facing one another in the radial direction of rotor  40 . Recess  44  is positioned between bolt hole  404  and bolt hole  405 . Specifically, the distance between the axis of rotation O and the central axis of recess  44  is substantially equal to the distance between the axis of rotation O and each bolt hole  403 ,  404  or  405 , and recess  44  has a central axis at a substantially central position between bolt holes  404  and  405 , on the circle passing through the central axes of bolt holes  403 ,  404  and  405 . On the other hand, in intake camshaft  3   a,  first fluid passage  212  opens at axial end surface  300 , constituting a pin hole or recess.  FIG. 13  is a partial side sectional view taken along a plane passing through a central longitudinal axis of a positioning pin  45 . As shown in  FIG. 13 , positioning pin  45  is press-fitted and fixed to the open end of first fluid passage  212 . Positioning pin  45  is a dowel pin whose longitudinal end portion projects to a predetermined height in the X-axis positive direction from axial end surface  300  of intake camshaft  3   a.  Positioning pin  45  may be of a type other than a dowel pin. The longitudinal end portion of positioning pin  45  has a slightly smaller diameter than the size of recess  44  in the circumferential direction, namely, than the distance between the two straight line sections of recess  44 , and adapted to be inserted and fitted from the X-axis negative side into recess  44 . The diameter of the longitudinal end portion of positioning pin  45  and the size of recess  44  are set so that when positioning pin  45  is inserted and fitted in recess  44 , no backlash occurs between vane rotor  4  and intake camshaft  3   a  in the circumferential direction. Recess  44  is located in vane rotor  4  so that when positioning pin  45  is inserted and fitted in recess  44 , bolt holes  403 ,  404  and  405  of rotor  40  are located coaxially with bolt holes  32  of intake camshaft  3   a.  Camshaft bolts  33 ,  34  and  35  are inserted from the X-axis positive side into corresponding ones of bolt holes  403 ,  404  and  405 , under condition that inserted portion  301  is inserted and fitted in camshaft insertion hole  402 , and positioning pin  45  is inserted and fitted in recess  44 , thereby positioning the vane rotor  4  and intake camshaft  3   a  with respect to one another in the circumferential direction. The head  331 ,  341  or  351  of each camshaft bolt  33 ,  34  or  35  is located at the X-axis positive side of rotor  40 , whereas a portion of the shank of each camshaft bolt  33 ,  34  or  35  projecting from the X-axis negative side of rotor  40  is inserted into the corresponding bolt hole  32 , and the male thread of each camshaft bolt  33 ,  34  or  35  is screwed with the female thread of bolt hole  32 . In this way, rotor  40  is fixed to the axial end surface  300  of intake camshaft  3   a  so that the axial end portion  30  of intake camshaft  3   a  is fixedly mounted to vane rotor  4 . Bolt holes  403 ,  404  and  405  thus constitute a plurality of fixing portions for fixing the rotor  40  to the axial end surface  300  of intake camshaft  3   a.    
     As shown in  FIG. 3 , boss portion  401  of rotor  40  is inserted from the X-axis positive side into the through hole  92  of cylindrical portion  91  of rear plate  9 . Boss portion  401  is mounted with a slight clearance with through hole  92 . The insertion of boss portion  401  in through hole  92  serves to make the axes of rotation of rear plate  9  and vane rotor  4  substantially identical to one another, position the axis of rotation of vane rotor  4  at the axis of rotation O, and make the boss portion  401  to bear the rear plate  9 . Namely, vane rotor  4  is positioned with respect to housing HSG through the boss portion  401  and cylindrical portion  91 , while housing HSG is rotatably supported with respect to vane rotor  4  or intake camshaft  3   a.  Boss portion  401  serves as a bearing (slide bearing) for bearing a load from housing HSG through the cylindrical portion  91 , and supporting the housing HSG for free rotation thereof. The outside peripheral surface of boss portion  401  is in sliding contact with the inside peripheral surface of through hole  92 . The sliding outside peripheral surface of boss portion  401  is provided with an anodic oxide coating film, as described above. 
     Rotor body  400  is formed with first, second and third vanes  41 ,  42  and  43  at the outside periphery, which are arranged and substantially evenly spaced in the circumferential direction, extending outwardly in the radial direction from the axis of rotation O. First, second and third vanes  41 ,  42  and  43  are arranged in this order in the clockwise direction in  FIG. 4 . Specifically, first vane  41  is disposed between bolt holes  403  and  404 , second vane  42  is disposed between bolt holes  404  and  405 , and third vane  43  is disposed between bolt holes  405  and  403 . First, second and third vanes  41 ,  42  and  43  are formed integrally with rotor  40  (rotor body  400 ), and have a cross section having a substantially trapezoidal shape spreading outwardly in the radial direction, as viewed in the X-axis direction. The length of first, second and third vanes  41 ,  42  and  43  in the X-axis direction is set equal to the length of rotor body  400  in the X-axis direction, L 1 . When vane rotor  4  is mounted in housing HSG, the X-axis positive side surfaces (formed with an anodic oxide coating film) of first, second and third vanes  41 ,  42  and  43  face with a quite slight clearance the X-axis negative side surface of front plate  8 . On the other hand, the X-axis negative side surfaces (formed with an anodic oxide coating film) of first, second and third vanes  41 ,  42  and  43  face with a quite slight clearance the X-axis positive side surface of rear plate  9 . The lengths of second vane  42  and third vane  43  in the circumferential direction of vane rotor  4  are substantially equal to each other. The circumferential length of first vane  41  is set larger that those of second vane  42  and third vane  43 , so as to provide a space where a lock mechanism  5  is mounted. The centers of gravity of first, second and third vanes  41 ,  42  and  43  are arranged and substantially evenly spaced in the circumferential direction. However, first vane  41  is slightly heavier than the other vanes, because first vane  41  is large and provided with lock mechanism  5 . Accordingly, the space between first vane  41  and second vane  42 , and the space between third vane  43  and first vane  41 , are set slightly larger than the space between second vane  42  and third vane  43 , so that the center of gravity of the entire vane rotor  4  is conformed to the axis of rotation O. When vane rotor  4  is mounted in housing HSG, first vane  41  is mounted between first shoe  11  and second shoe  12 , second vane  42  is mounted between second shoe  12  and third shoe  13 , and third vane  43  is mounted between third shoe  13  and first shoe  11 . Outside peripheral surfaces  411 ,  421  and  431  of first, second and third vanes  41 ,  42  and  43  are curved to have arced shapes which are fitted with the inside peripheral surface of housing body  10 , as viewed in the X-axis direction, as shown in  FIG. 4 . Outside peripheral surface  411  of first vane  41  is formed with a groove  412  which extends in the X-axis direction. A sealing member  413  and a sealing spring such as a leaf spring  414  not shown are fitted and retained in groove  412 . Sealing member  413  is in liquid-tight sliding contact with the inside peripheral surface of housing body  10 . Leaf spring  414  presses the sealing member  413  onto the inside peripheral surface of housing body  10 . Similarly, outside peripheral surfaces  421  and  431  of second vane  42  and third vane  43  are formed with grooves  422  and  432 , sealing members  423  and  433 , and leaf springs  424  and  434 , respectively. The counterclockwise side of first vane  41  is formed with a flat portion  415  as viewed from the X-axis positive side, as shown in  FIG. 9A . Flat portion  415  is substantially in a straight line passing through the axis of rotation O of rotor  40  as viewed in the X-axis direction. First vane  41  is formed with a recess  416  between flat portion  415  and the root of first vane  41 . Recess  416  has an inwardly curved and substantially arced edge, as viewed in the X-axis direction. Similarly, second vane  42  and third vane  43  are formed with flat portions  425  and  435 , and recesses  426  and  436 , respectively. As viewed from the X-axis positive side, the counterclockwise side of first vane  41  is formed with a rounded portion  417  at a tip portion outside of flat portion  415 . Rounded portion  417  has an outwardly curved and substantially arced edge having a predetermined curvature that is slightly smaller than the curvature of rounded portion  112  of first shoe  11 . Rounded portion  417  serves to allow the flat portion  415  of first vane  41  to be in surface-to-surface contact with the flat portion  111  of first shoe  11  as shown in  FIG. 4 , and serves to reduce the weight of first vane  41 . On the other hand, as viewed from the X-axis positive side, the clockwise sides of first, second and third vanes  41 ,  42  and  43  are formed with recesses  418 ,  428  and  438  respectively, where recesses  418 ,  428  and  438  are relatively wide recesses extending over the entire axial length of vane rotor  4 . As viewed from the X-axis positive side, the clockwise side of first vane  41  is formed integrally with a projection  419  that is located at the root and extends over a predetermined distance, along the outside periphery of rotor  40  (rotor body  400 ) in the clockwise direction. The projection  419  is formed continuous with the root of first vane  41 , and projects from the outside periphery of rotor  40  (rotor body  400 ) outwardly in the radial direction. Similarly, the clockwise side of the root of second vane  42  is formed integrally with a radial projection  429 . 
     Vane rotor  4  defines, in the space between vane rotor  4  and housing HSG, a plurality of working fluid chambers, namely, first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3 , which working fluid is supplied to or drained from. Namely, as viewed in the X-axis direction, three chambers are formed by two adjacent shoes and the outside peripheral surface of rotor  40  (rotor body  400 ), and each of the three chambers is divided by vane  41 ,  42  or  43  into one advance chamber and one retard chamber. First, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3  are separated liquid-tightly from each other by sealing member  413 , etc. Working fluid is supplied from an oil pump  1020  to first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3 , and serves to transmit torque between vane rotor  4  and housing HSG. More specifically, first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3  are defined by the X-axis negative side surface of front plate  8 , the X-axis positive side surface of rear plate  9 , the circumferentially-facing surfaces of first, second and third vanes  41 ,  42  and  43 , and the circumferentially-facing surfaces of first, second and third shoes  11 ,  12  and  13 . For example, first advance chamber A 1  is defined between the clockwise surface of first shoe  11 , the counterclockwise surface of first vane  41 , whereas first retard chamber R 1  is defined between the clockwise surface of first vane  41  and the counterclockwise surface of second shoe  12 , as shown in  FIG. 4 . Similarly, second advance chamber A 2  is defined between second shoe  12  and second vane  42 , second retard chamber R 2  is defined between second vane  42  and third shoe  13 , third advance chamber A 3  is defined between third shoe  13  and third vane  43 , and third retard chamber R 3  is defined between third vane  43  and first shoe  11 . Alternatively, one of the set of first, second and third advance chambers A 1 , A 2  and A 3  and the set of first, second and third retard chambers R 1 , R 2  and R 3  may be omitted. For example, valve timing control apparatus  1  may include a single advance chamber or a single retard chamber. The number of advance chambers and the number of retard chambers are not limited to three, but may be more or less than three. The shoes of the housing body may be omitted, so that the working fluid chambers are defined between the inside peripheral surface of the housing body and the vanes without the shoes. The cylindrical rotor may be omitted so that the vane member is constituted only by the vanes. 
     The range of relative rotation of vane rotor  4  with respect to housing HSG is defined by first and second stopper mechanisms as follows. When vane rotor  4  rotates with respect to housing HSG in the counterclockwise direction by a predetermined angle as viewed from the X-axis positive side, the flat portion  111  of first shoe  11 , which is formed in the clockwise surface of first shoe  11 , is brought into surface-to-surface contact with flat portion  415  of first vane  41 , which is formed in the counterclockwise surface of first vane  41 , as shown in  FIG. 4 . Under this condition, the flat portion  121  of second shoe  12  and the flat portion  425  of second vane  42  face each other with a slight clearance, namely the circumferentially-facing surfaces of second shoe  12  and second vane  42  are kept out of contact with each other. Similarly, flat portion  131  of third shoe  13  and flat portion  435  of third vane  43  face each other with a slight clearance, and are kept out of contact with each other. In this way, rotation of vane rotor  4  with respect to housing HSG in the counterclockwise direction is restricted by contact between flat portion  111  of first shoe  11  and flat portion  415  of first vane  41 . Flat portion  111  of the circumferentially-facing surface of first shoe  11  and flat portion  415  of the circumferentially-facing surface of  41  serve as first stopper portions constituting a first stopper mechanism for restricting relative rotation of vane rotor  4  in the counterclockwise direction (in the retard direction). In FIG.  4  where relative rotation between vane rotor  4  and housing HSG is restricted, an angle α, which is defined about the axis of rotation O by the clockwise side end surface of radial projection  419  and the counterclockwise side end surface of tip  126  of second shoe  12 , is slightly smaller than an angle β, which is defined about the axis of rotation O by the clockwise side end surface of radial projection  429  and the counterclockwise side end surface of tip  136  of third shoe  13 . According to the above relationship, when vane rotor  4  rotates with respect to housing HSG from the position shown in  FIG. 4  by the angle α in the clockwise direction, the tip  126  of second shoe  12  and the radial projection  419  of first vane  41  are brought into surface-to-surface contact with each other as shown in  FIG. 5 . Under this condition, the tip  136  of third shoe  13  and the radial projection  429  of second vane  42  face each other with a predetermined slight clearance in the circumferential direction, so that third shoe  13  and second vane  42  are kept out of contact with each other. Similarly, first shoe  11  and third vane  43  face each other with a predetermined slight clearance, and thus kept out of contact with each other. In this way, rotation of vane rotor  4  with respect to housing HSG in the clockwise direction is restricted by contact between tip  126  of second shoe  12  and radial projection  419  of first shoe  11 . The clockwise surface of radial projection  419  and the counterclockwise surface of tip  126  of second shoe  12  serve as second stopper portions constituting a second stopper mechanism for restricting relative rotation of vane rotor  4  in the clockwise direction (in the advance direction). The contact area between tip  126  of second shoe  12  and radial projection  419  of first shoe  11 , i.e. the contact area of the second stopper mechanism, SS 2 , is set smaller than the contact area between flat portion  111  of first shoe  11  and the flat portion  415  of first vane  41 , i.e. the contact area of the first stopper mechanism, SS 1  (SS 1 &gt;SS 2 ). Incidentally, all over a possible range of the rotational angle of vane rotor  4  with respect to housing HSG, the volumetric capacities of first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3  are prevented from becoming zero. Also, the openings of retard fluid passages  408  and advance fluid passages  409  in first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3  are constantly prevented from being closed. For example, in  FIG. 4 , the volumetric capacity of first advance chamber A 1  and the opening of advance fluid passage  409  are provided by the space defined between recess  113  of first shoe  11  and recess  416  of first vane  41 . Similarly, the volumetric capacity of second advance chamber A 2  and the opening of advance fluid passage  409  are provided by the space, i.e. the clearance described above, which is defined by flat portion  121  of second shoe  12 , and recess  426  and flat portion  425  of second vane  42 . Similarly, the volumetric capacity of third advance chamber A 3  and the opening of advance fluid passage  409  are provided by the space, i.e. the clearance described above, which is defined by flat portion  131  of third shoe  13 , and recess  436  and flat portion  435  of third vane  43 . 
     Hydraulic fluid supply and drainage mechanism  2  supplies working fluid to or drains working fluid from first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3 , so that vane rotor  4  rotates with respect to housing HSG by a predetermined angle in the advance direction or retard direction. Specifically, supply and drainage of working fluid causes changes in the volumetric capacities of first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3 , to generate a torque to rotate vane rotor  4  with respect to housing HSG, so that the torque is transmitted therebetween, and the phase of rotation of intake camshaft  3   a  with respect to rotation of the crankshaft is changed. Hydraulic fluid supply and drainage mechanism  2  includes an oil pump  1020  as a hydraulic pressure source, and a directional control valve  24  as a hydraulic control actuator. The hydraulic circuit includes a retard passage  20  through which working fluid is supplied to or drained from first, second and third retard chambers R 1 , R 2  and R 3 , and an advance passage  21  through which working fluid is supplied to or drained from first, second and third advance chambers A 1 , A 2  and A 3 . Retard passage  20  and advance passage  21  are connected through the directional control valve  24  to a supply passage  22  and a drain passage  23 . Oil pump  1020  is provided in supply passage  22  for pressurizing and supplying working fluid from oil pan  25  to directional control valve  24 . Oil pump  1020  is mounted to the crankshaft, and may be implemented by a unidirectional variable displacement vane pump. The downstream end of drain passage  23  is hydraulically connected to oil pan  25 . Intake camshaft  3   a  and vane rotor  4  (rotor  40 ) include portions constituting the retard passage  20  and advance passage  21 . Rotor body  400  is formed with three retard fluid passages  408  and three advance fluid passages  409 . Each fluid passage  408  or  409  extends through the rotor body  400  in a radial direction of rotor body  400 , and hydraulically connects the inside periphery of camshaft insertion hole  402  and the outside periphery of rotor  40  to one another, so that when vane rotor  4  is fixed to intake camshaft  3   a,  the fluid passage  408  or  409  hydraulically connects the corresponding one of first, second and third advance chambers A 1 , A 2  and A 3  and first, second and third retard chambers R 1 , R 2  and R 3  to corresponding ones of first fluid passages  202  and  212  and second fluid passages  201 ,  203 ,  211  and  213 . As viewed from the X-axis positive side, each retard fluid passage  408  is located at the root of the clockwise side of vane  41 ,  42  or  43 , and each advance fluid passage  409  is located at the root of the counterclockwise side of vane  41 ,  42  or  43 , as shown in  FIGS. 4 and 9A . In the X-axis direction, each retard fluid passage  408  is located at an X-axis positive side portion of camshaft insertion hole  402  or at a substantially central position of rotor body  400  in the axial direction, and each advance fluid passage  409  is located at an X-axis negative side portion of camshaft insertion hole  402  or at an X-axis negative side portion of rotor body  400 , as shown in  FIGS. 3 and 9B . Under condition that the axial end portion  30  of intake camshaft  3   a  is fixedly inserted in camshaft insertion hole  402 , the position of each retard fluid passage  408  is substantially identical to the position of groove  204  in the X-axis direction, so that the retard fluid passage  408  hydraulically communicates at the inside periphery of rotor  40  with groove  204 , and hydraulically communicates at the outside periphery of rotor  40  with retard chamber R 1 , R 2  or R 3 . Similarly, the position of each advance fluid passage  409  is substantially identical to the position of groove  214  in the X-axis direction, so that the advance fluid passage  409  hydraulically communicates at the inside periphery of rotor  40  with groove  214 , and hydraulically communicates at the outside periphery of rotor  40  with advance chamber A 1 , A 2  or A 3 . Extending from directional control valve  24 , retard passage  20  includes groove  200  which is located at the X-axis negative side portion of axial end portion  30  of intake camshaft  3   a,  wherein intake camshaft  3   a  is a rotating member. Groove  200  is hydraulically connected to first fluid passage  202  through the second fluid passage  201 , and first fluid passage  202  is hydraulically connected to groove  204  through the second fluid passage  203 , and groove  204  hydraulically communicates with first, second and third retard chambers R 1 , R 2  and R 3  through retard fluid passages  408 . Incidentally, the opening of first fluid passage  202  at the axial end surface  300  of intake camshaft  3   a  is closed by the bottom surface of camshaft insertion hole  402  when intake camshaft  3   a  is fixed to vane rotor  4  by camshaft bolts  33 ,  34  and  35 . Similar to retard passage  20 , extending from directional control valve  24 , advance passage  21  includes groove  210  which is located at the X-axis negative side portion of axial end portion  30  of intake camshaft  3   a.  Groove  210  is hydraulically connected to first fluid passage  212  through the second fluid passage  211 , and first fluid passage  212  is hydraulically connected to groove  214  through the second fluid passage  213 , and groove  214  hydraulically communicates with first, second and third advance chambers A 1 , A 2  and A 3  through advance fluid passage  409 . Incidentally, the opening of first fluid passage  212  at the axial end surface  300  of intake camshaft  3   a  is closed by positioning pin  45 . The annular shape of each groove  204  or  214  extending in the circumferential direction serves to enhance the flexibility of layout of retard fluid passages  408  and advance fluid passages  409  in vane rotor  4 . Each groove  204  or  214  may be replaced with an annular groove that is formed in the inside periphery of camshaft insertion hole  402  of vane rotor  4  to extend in the circumferential direction. However, the arrangement of each groove  204  or  214  in intake camshaft  3   a  is advantageous in easiness of forming or machining same. Directional control valve  24  is a direct-acting type solenoid valve with four ports and three positions, for controlling the hydraulic pressures of working fluid which is supplied to or drained from first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3 . Directional control valve  24  includes a valve body fixed to the cylinder head, a solenoid “SOL” fixed to the valve body, and a spool valve element slidably mounted inside the valve body. The valve body is formed with a supply port  240  hydraulically connected to supply passage  22 , a first port  241  hydraulically connected to retard passage  20 , a second port  242  hydraulically connected to advance passage  21 , and a drain port  243  hydraulically connected to drain passage  23 . When an electromagnetic coil of solenoid SOL is energized, then solenoid SOL presses the spool valve element to move. The electromagnetic coil is electrically connected to controller CU through a harness. Each of first port  241  and second port  242  opens or closes according to movement of the spool valve element. When solenoid SOL is de-energized, the spool valve element is biased by return spring RS to a position such that the supply port  240  (supply passage  22 ) and second port  242  (advance passage  21 ) are hydraulically connected to each other, and first port  241  (retard passage  20 ) and drain port  243  (drain passage  23 ) are hydraulically connected to each other. On the other hand, when solenoid SOL is energized, the spool valve element is controlled according to a control current from controller CU, to move against the elastic force of return spring RS to a predetermined intermediate position such that the supply port  240  (supply passage  22 ) and first port  241  (retard passage  20 ) are hydraulically connected to each other, and second port  242  (advance passage  21 ) and drain port  243  (drain passage  23 ) are hydraulically connected to each other. Controller CU is an electrical control unit which is configured to measure a current operating state of the internal combustion engine on the basis of signals from sensors such as a crank angle sensor for measuring engine rotational speed, an air flow meter for measuring a quantity of intake air, a throttle valve opening sensor, and a coolant temperature sensor for measuring a coolant temperature of the internal combustion engine. Moreover, controller CU performs a flow direction control of selectively supplying working fluid to or draining working fluid from first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3 , by energizing or de-energizing the solenoid SOL of directional control valve  24  with a pulse control signal, according to the measured operating state of the internal combustion engine. 
     Intake valve timing control apparatus  1   a  is provided with an arrangement that a lock piston  51  locks relative rotation between vane rotor  4  and housing HSG when vane rotor  4  is in a most retarded position which is defined by the first stopper mechanism. Lock piston  51  is an engagement member which is provided in vane rotor  4 , and arranged to move forward or rearward in the X-axis direction according to a state of operation of the internal combustion engine. Lock mechanism  5  is arranged between first vane  41  and rear plate  9 , for locking or releasing relative rotation of vane rotor  4  with respect to rear plate  9  (or housing HSG). Lock mechanism  5  includes slide hole  501 , lock piston  51 , a sleeve  52 , and a coil spring  53 .  FIG. 14  is a partial side sectional view taken along a plane passing through a central longitudinal axis of lock mechanism  5 , showing a state of operation of lock piston  51  when the internal combustion engine is at rest, or the internal combustion engine is being started. 
     First vane  41  is formed with slide hole  501  which extends through first vane  41  in the X-axis direction. Slide hole  501  is a hollow cylindrical portion or cylinder formed to extend in the axial direction of vane rotor  4 . The surface (inside peripheral surface) of slide hole  501  is anodized as described above. A sealing member  502 , which has an annular shape or a hollow cylindrical shape, is formed separately from vane rotor  4 , and pressed-fitted in an X-axis negative side portion of slide hole  501 . Sealing member  502  is a hollow cylindrical member (or ring-shaped member) having a smaller longitudinal size than slide hole  501 , specifically half or less of the longitudinal size of slide hole  501 , wherein sealing member  502  is inserted from the X-axis negative side end of slide hole  501  and press-fitted into the inside of slide hole  501 . Slide hole  501  may be set and fixed in an alternative manner other than press-fitting. Sealing member  502  is formed of a material having a higher wear resistance than anodic oxide coating. Specifically, sealing member  502  is formed of an iron alloy such as a carbon steel such as S45C, into a ring shape, and carburized. 
     Lock piston  51  as a lock member is formed of iron into a pin, having a hollow cylindrical shape with a bottom portion  510  at the X-axis negative side. Lock piston  51  is mounted in slide hole  501  for sliding in the X-axis direction, and projecting from the X-axis negative side of slide hole  501  closer to intake camshaft  3   a  or retreating into the X-axis negative side of slide hole  501 . Lock piston  51  includes a smaller-diameter portion and a larger-diameter portion. The smaller-diameter portion is a distal-side portion of lock piston  51  that is disposed in slide hole  501 , and arranged to move out of and into slide hole  501 . The smaller-diameter portion includes a sliding portion  512 , and an engaging portion  511 . Sliding portion  512  has a hollow cylindrical shape having a closed bottom. Engaging portion  511  is adjacent to and in the X-axis negative direction from bottom portion  510 , where a step is formed between bottom portion  510  and engaging portion  511 . Engaging portion  511  has the form of a substantially truncated cone having a substantially trapezoidal longitudinal section. In this way, engaging portion  511  has an inclined surface or tapered surface with respect to the longitudinal direction, wherein the diameter of the tapered surface decreases as followed toward the tip at the X-axis negative side. The larger-diameter portion is a proximal-side portion of lock piston  51  that is disposed in slide hole  501 . The larger-diameter portion includes an annular flange  513  at the X-axis positive side end, which is adjacent to and on the X-axis positive side of sliding portion  512 . The larger-diameter portion (or flange  513 ) has a larger diameter than the smaller-diameter portion (or sliding portion  512  and engaging portion  511 ). The outside periphery of sliding portion  512  has a slightly smaller diameter than the inside periphery of sealing member  502 . Sliding portion  512  includes an X-axis negative side portion that is accommodated in sealing member  502  so that the outside periphery of sliding portion  512  is in sliding contact with the inside periphery of sealing member  502 . The outside periphery of flange  513  has a slightly smaller diameter than the inside periphery of slide hole  501 . Flange  513  is accommodated in slide hole  501  so that the outside periphery of flange  513  is in sliding contact with the inside periphery of slide hole  501 . The radial clearance between the outside periphery of sliding portion  512  and the inside periphery of sealing member  502  is set smaller than that between the outside periphery of flange  513  and the inside periphery of slide hole  501 . In this way, lock piston  51  has a portion (sliding portion  512 ) in sliding contact with the inside periphery of sealing member  502 , another portion (flange  513 ) in sliding contact with the inside periphery of slide hole  501 , and a tip (engaging portion  511 ) arranged to move forward and rearward in the axial direction (in the X-axis direction) with respect to vane rotor  4  according to the state of operation of the internal combustion engine. 
     On the other hand, rear plate  9  is formed with recess  900  in the X-axis positive side surface. Recess  900  is located in the chamber between first shoe  11  and second shoe  12 , and more adjacent to first shoe  11  on the clockwise side of first shoe  11 . Recess  900  has a bottom in rear plate  9 , without passing through rear plate  9 . Recess  900  is located to face or conform to the tip (engaging portion  511 ) of lock piston  51  as viewed in the X-axis direction, when intake valve timing control apparatus  1   a  is in the most retarded state shown in  FIG. 4 . Sleeve  52 , which is formed in a hollow cylindrical shape separately from rear plate  9 , and referred to as lock recess constituent member, is press-fitted in recess  900  of rear plate  9 . Sleeve  52  may be fixed in an alternative manner other than press-fitting. Sleeve  52  is formed of an iron-based metal material. The inside peripheral surface of sleeve  52  defines engaging recess  521 . Engaging recess  521  is a lock recess in which the smaller-diameter portion (engaging portion  511 ) of lock piston  51  can be inserted. The longitudinal size of engaging recess  521  (sleeve  52 ) is substantially equal to the longitudinal size of engaging portion  511 . Engaging recess  521  has a slightly larger diameter than engaging portion  511 . Engaging recess  521  has a substantially trapezoidal section taken along a plane passing through the central longitudinal axis of sleeve  52 , and gradually spreads toward the X-axis positive side opening. Namely, engaging recess  521  has an inclined surface or tapered surface with respect to the longitudinal direction, wherein the diameter of the tapered surface gradually decreases as followed toward the X-axis negative side bottom. The angle of inclination of the inside peripheral surface (inclined surface) of engaging recess  521  with respect to the X-axis is substantially equal to that of engaging portion  511 . Engaging recess  521  is provided in housing HSG, and on the X-axis positive side surface of rear plate  9 , or on the axial end of housing HSG closer to intake camshaft  3   a,  similar to recess  900 . When vane rotor  4  is relatively rotated toward the most retarded position and the rotation of vane rotor  4  is restricted by the first stopper mechanism, namely, when the volumetric capacity of first advance chamber A 1  is minimized, the position of lock piston  51  (engaging portion  511 ) overlaps or is identical with the position of engaging recess  521  as viewed in the X-axis direction, since recess  900  is located as described above. In other words, the rotational position of vane rotor  4  with respect to housing HSG is set to the most retarded position which is optimal at start of the internal combustion engine, under the condition that lock piston  51  is engaged with engaging recess  521  of sleeve  52 . Under this condition, the central axis of engaging recess  521  is located with a slight offset from the central axis of engaging portion  511  in the counterclockwise direction shown in  FIG. 4  (toward first shoe  11 ) of vane rotor  4 . 
     The inside of slide hole  501  is formed with a back pressure chamber  50  for lock piston  51 . Back pressure chamber  50  is a low pressure chamber that is defined in slide hole  501  by lock piston  51 , and is located opposite to sleeve  52  (or rear plate  9  or intake camshaft  3   a ) with respect to lock piston  51 . Specifically, back pressure chamber  50  is defined by the X-axis negative side surface of front plate  8 , and the inside periphery of lock piston  51  (sliding portion  512 , flange  513 ). 
     Coil spring  53  is a biasing member that constantly biases lock piston  51  in the X-axis negative direction, i.e. toward rear plate  9 , specifically toward engaging recess  521  of sleeve  52 . Coil spring  53  is mounted in a compressed state in back pressure chamber  50 , wherein the X-axis positive side end of coil spring  53  is in contact with the X-axis negative side surface of front plate  8 , and the X-axis negative side end of coil spring  53  is in contact with the bottom portion  510  of lock piston  51 . Namely, in slide hole  501 , coil spring  53  is provided on one side (larger-diameter side or X-axis positive side) of lock piston  51 , and arranged to bias the lock piston  51  toward the other side (smaller-diameter side or X-axis negative side) of lock piston  51 . A spring retainer  54  is mounted in the X-axis positive side of back pressure chamber  50 . Spring retainer  54  has an annular shape, and retains coil spring  53 . The outer diameter of spring retainer  54  is substantially equal to the diameter of the inside peripheral surface of slide hole  501 . The X-axis positive side surface of spring retainer  54  faces the X-axis negative side surface of front plate  8 , whereas the X-axis negative side surface of spring retainer  54  faces the X-axis positive side surface of flange  513  of lock piston  51 . The X-axis positive side end portion of coil spring  53  is fitted with the inside periphery of spring retainer  54 , so as to prevent coil spring  53  from deviating with respect to slide hole  501  in the lateral direction of lock piston  51 . 
     Slide hole  501  is formed with first and second pressure-receiving chambers  55  and  59  for applying hydraulic pressure to lock piston  51 . In slide hole  501 , first pressure-receiving chamber  55  is defined by the X-axis positive side end surface of sealing member  502 , the X-axis negative side surface of flange  513 , the outside peripheral surface of sliding portion  512 , and the inside peripheral surface of slide hole  501 . Second pressure-receiving chamber  59  is defined by the surface (the X-axis negative side tip surface, and inclined surface) of engaging portion  511 , the X-axis positive side surface of rear plate  9  (or the inside peripheral surface of sleeve  52  and the bottom of recess  900 , in the lock state in which engaging portion  511  engages with engaging recess  521 ). First vane  41  is formed with fluid passages for guiding hydraulic pressure from the working fluid chambers to first and second pressure-receiving chambers  55  and  59 . A communication hole  56  is formed to extend in first vane  41  in the circumferential direction of first vane  41 . First retard chamber R 1  is constantly hydraulically connected to first pressure-receiving chamber  55  through the communication hole  56 , so that the hydraulic pressure in first retard chamber R 1  is constantly supplied to first pressure-receiving chamber  55 . The X-axis negative side surface of first vane  41  is formed with a communication groove  57  that extends in the circumferential direction of first vane  41 . First advance chamber A 1  is constantly hydraulically connected to the X-axis negative side end of slide hole  501  through the communication groove  57 , so that the hydraulic pressure in first advance chamber A 1  is constantly supplied to second pressure-receiving chamber  59  (engaging recess  521  in the lock state). 
     Communication hole  56  and communication groove  57  constitute a mechanism for engaging and disengaging the lock piston  51 , together with coil spring  53  as an elastic member for engagement. When vane rotor  4  relatively rotates to the most retard side, and rotation of vane rotor  4  is restricted by the first stopper mechanism, then the position of lock piston  51  is identical to the position of engaging recess  521  as viewed in the X-axis direction, so as to allow lock piston  51  to move in the X-axis negative direction. Under this condition, the biasing force of coil spring  53  serves to assist the lock piston  51  in moving in the X-axis negative direction so that the engaging portion  511  moves out of slide hole  501  of first vane  41 , and engages with engaging recess  521 . The engagement of lock piston  51  with engaging recess  521  restricts or locks relative rotation between rear plate  9  and vane rotor  4 , or relative rotation between housing HSG and intake camshaft  3   a.  On the other hand, lock piston  51  is subject to a hydraulic force at the flange  513  in the X-axis positive direction, wherein the hydraulic force is based on the hydraulic pressure supplied from first retard chamber R 1  to first pressure-receiving chamber  55  through the communication hole  56 . Lock piston  51  is also subject to a hydraulic force at the engaging portion  511  in the X-axis positive direction, wherein the hydraulic force is based on the hydraulic pressure supplied from first advance chamber A 1  to second pressure-receiving chamber  59  through the communication groove  57 . Both of the hydraulic forces serve to assist the lock piston  51  in moving in the X-axis positive direction against the biasing force of coil spring  53 , so that the engaging portion  511  moves out of engaging recess  521 , and into slide hole  501  of rear plate  9 . The engagement of lock piston  51  with engaging recess  521  is thus released. In this way, coil spring  53  serves to maintain the lock state, while communication hole  56  and communication groove  57  serve as a hydraulic circuit for releasing the lock state. 
     Intake valve timing control apparatus  1   a  is provided with a back pressure relief section for relieving pressure in back pressure chamber  50  and keeping same low. The back pressure relief section includes a first back pressure passage  31 , a back pressure hole  407 , and a second back pressure passage. First back pressure passage  31  is formed in intake camshaft  3   a,  whereas back pressure hole  407  and the second back pressure passage are formed in vane rotor  4 . These constituents serve as a passage for relieving the pressure in back pressure chamber  50  to a space in the internal combustion engine. The space in the internal combustion engine is a low pressure space that is defined by a housing (cylinder head, cylinder block, etc.) of the internal combustion engine, and separated liquid-tightly from timing belt  1010 . First back pressure passage  31  is a breathing hole formed in intake camshaft  3   a  to extend in the X-axis direction, from the X-axis positive side axial end surface  300  to a predetermined depth in the X-axis direction. First back pressure passage  31  has an opening at the axial end surface  300 , and hydraulically communicates the axial end surface  300  with an oil-lubricated space in the internal combustion engine. First back pressure passage  31  is located at the axis of rotation of intake camshaft  3   a,  namely, the axis of rotation O, having the same diameter as first fluid passages  202  and  212 . First back pressure passage  31  may be formed to communicate with a low pressure section of hydraulic fluid supply and drainage mechanism  2 , instead of or in addition to the oil-lubricated space in the internal combustion engine. In other words, the space in the internal combustion engine which is related to first back pressure passage  31  includes a hydraulic circuit of hydraulic fluid supply and drainage mechanism  2 . For example, back pressure chamber  50  may be hydraulically connected to directional control valve  24 , so that the working fluid in back pressure chamber  50  is drained to oil pan  25  through the drain passage  23 . If intake valve timing control apparatus  1   a  is constructed so that only first, second and third advance chambers A 1 , A 2  and A 3  are supplied with working fluid, and first, second and third retard chambers R 1 , R 2  and R 3  are supplied with no working fluid, the working fluid in back pressure chamber  50  may be released to a passage that is hydraulically connected to first, second and third retard chambers R 1 , R 2  and R 3 . Back pressure hole  407  is a breathing hole extending through the rotor  40  along the axis of rotation of rotor  40  (axis of rotation O) in the X-axis direction, having a smaller diameter than first back pressure passage  31 , as shown in  FIG. 4 . Back pressure hole  407  faces first back pressure passage  31  in the X-axis direction, wherein the central axis of back pressure hole  407  is identical to the central axis of first back pressure passage  31  as viewed in the X-axis direction. The opening of back pressure hole  407  at the X-axis negative side surface of rotor  40  (at the bottom surface of camshaft insertion hole  402 ) is located to face the opening of first back pressure passage  31  at the axial end surface  300  of intake camshaft  3   a.  As shown in  FIG. 9A , the second back pressure passage is a recess for breathing that is formed in the X-axis positive side end surface of vane rotor  4 , including a circular recess  406  and a radial groove  58 . Circular recess  406  is a shallow cylindrical recess having a central axis that is substantially identical to the central axis of rotor  40 , wherein circular recess  406  extends from the X-axis positive side in the X-axis negative direction to a depth of about 13% of the axial size of rotor body  400 . The bottom of circular recess  406  is formed with bolt holes  403 ,  404  and  405 , and back pressure hole  407 . The depth (size in the X-axis direction) of circular recess  406  is about half or more of the height (size in the X-axis direction) of each head  331 ,  341  or  351 . The diameter of circular recess  406  is slightly smaller than the outside diameter of rotor body  400 , slightly smaller than the diameter of large-diameter hole  81  of front plate  8 , and substantially equal to the diameter of recess  73  of cap  7 . Circular recess  406  is located to face the recess  73  in the X-axis direction. Radial groove  58  is a rectangular groove for hydraulically communicating the circular recess  406  and back pressure chamber  50  with one another, extending from circular recess  406  through the root of first vane  41  outwardly in a radial direction of rotor  40 , and including an end connected to the X-axis positive side end of slide hole  501 . The depth (size in the X-axis direction) of radial groove  58  is substantially equal to that of circular recess  406 . Back pressure chamber  50  is hydraulically connected to back pressure hole  407  and first back pressure passage  31  through the second back pressure passage, and thereby hydraulically connected to the inside of the internal combustion engine. Namely, back pressure chamber  50  is hydraulically connected to circular recess  406  and back pressure hole  407  through the radial groove  58 , and further connected to the low pressure space in the internal combustion engine through the first back pressure passage  31 , as shown in  FIG. 3 . 
     &lt;Construction of Exhaust Valve Timing Control Apparatus&gt; The following describes construction of exhaust valve timing control apparatus  1   b  which is provided for the exhaust valves of the internal combustion engine, with reference to  FIGS. 15 to 19 . In the following, constituent parts of exhaust valve timing control apparatus  1   b,  which are identical or similar to those of intake valve timing control apparatus  1   a,  are provided with identical reference characters, and with no duplicate description, and only different constituent parts are described.  FIG. 15  is a partial side sectional view of exhaust valve timing control apparatus  1   b,  taken along a plane passing through an axis of rotation “O” (shown in  FIG. 16 ) of exhaust valve timing control apparatus  1   b,  i.e. taken along a plane indicated by a long dashed short dashed line F 15 -F 15  in  FIG. 16 .  FIGS. 16 and 17  are front views of exhaust valve timing control apparatus  1   b  under the condition that the front plate  8 , etc. are removed, as viewed from the X-axis positive side. Exhaust valve timing control apparatus  1   b  controls variable valve timing of the exhaust valves by continuously changing a rotational phase of exhaust camshaft  3   b  with respect to the crankshaft by supplied working fluid. Pulley  100 , as well as housing body  10 , is rotated by the crankshaft of the internal combustion engine, in the clockwise direction in  FIG. 16 , according to movement of timing belt  1010  shown by the arrow in  FIG. 1 . As shown in  FIG. 15 , front plate  8  of exhaust valve timing control apparatus  1   b  is provided with no outside periphery  80  which is provided in intake valve timing control apparatus  1   a,  so that the diameter of front plate  8  of exhaust valve timing control apparatus  1   b  is smaller than the diameter (specifically, the diameter of tooth bottom circle) of pulley  100 . The outside periphery of front plate  8  is more adjacent to annular sealing ring groove  89  with a shorter distance than distance r shown in  FIG. 12 . Accordingly, as shown in  FIG. 1 , as viewed in the X-axis direction, the outside periphery (i.e. teeth) of pulley  100  of exhaust valve timing control apparatus  1   b  projects radially outwardly from the outside periphery of front plate  8 . In other words, the diameter of exhaust valve timing control apparatus  1   b  is set smaller than that of intake valve timing control apparatus  1   a  where outside periphery  80  of front plate  8  projects radially outwardly from the outside periphery of pulley  100 . Housing body  10  of exhaust valve timing control apparatus  1   b  is a mirror image of the housing body of intake valve timing control apparatus  1   a  with respect to a plane perpendicular to the X-axis.  FIGS. 18A ,  18 B and  18 C are views of housing body  10  of exhaust valve timing control apparatus  1   b,  where  FIG. 18A  is a front view as viewed from the X-axis positive side,  FIG. 18B  is a side sectional view taken along a plane indicated by F 18 B-F 18 B in  FIG. 18A , and  FIG. 18C  is a rear view as viewed from the X-axis negative side.  FIGS. 7 and 8  are perspective views of workpieces during a process of manufacturing the housing body  10  also for exhaust valve timing control apparatus  1   b.  Housing body  10  of exhaust valve timing control apparatus  1   b  is formed from an aluminum extrusion shown in  FIG. 7 , similar to intake valve timing control apparatus  1   a.  Third workpiece P 3  shown in  FIG. 8  is obtained through the second workpiece P 2  from first workpiece P 1 . Finally, third workpiece P 3  is applied with carving or cutting, to form a fitting recess  101 , bolt hole  110 , etc., and thereby form a final shape of housing body  10  shown in  FIGS. 18A ,  18 B and  18 C. In contrast to intake valve timing control apparatus  1   a  where fitting recess  101  and positioning recess  114  are formed in the side “A” (shown in  FIG. 8 ) of third workpiece P 3  as shown in  FIGS. 6A ,  6 B and  6 C, fitting recess  101  and positioning recess  114  are formed in the side “B” (shown in  FIG. 8 ) of third workpiece P 3  for exhaust valve timing control apparatus  1   b,  as shown in  FIGS. 18A ,  18 B and  18 C. Also, vane rotor  4  of exhaust valve timing control apparatus  1   b  is a mirror image of the vane rotor of intake valve timing control apparatus  1   a  with respect to a plane perpendicular to the X-axis.  FIGS. 19A and 19B  are views of vane rotor  4  of exhaust valve timing control apparatus  1   b,  where  FIG. 19A  is a front view as viewed from the X-axis positive side, and  FIG. 19B  is a side sectional view taken along a plane indicated by F 19 B-F 19 B in  FIG. 19A .  FIGS. 10 and 11  are perspective views of workpieces during a process of manufacturing the vane rotor  4  also for exhaust valve timing control apparatus  1   b.  Vane rotor  4  of exhaust valve timing control apparatus  1   b  is formed from an aluminum extrusion (first workpiece Q 1 ) shown in  FIG. 10 , similar to intake valve timing control apparatus  1   a.  Then, second workpiece Q 2 , which is obtained from first workpiece Q 1 , is applied with carving or cutting, to form a boss portion  401 , a camshaft insertion hole  402 , etc., and thereby form a final shape of vane rotor  4  shown in  FIGS. 19A and 19B . In contrast to intake valve timing control apparatus  1   a  where boss portion  401  and camshaft insertion hole  402  are formed on the side “A” of second workpiece Q 2 , boss portion  401  and camshaft insertion hole  402  are formed on the side “B” of second workpiece Q 2  for exhaust valve timing control apparatus  1   b,  as shown in  FIGS. 19A and 19B . Finally, the entire outside surfaces of second workpiece Q 2  are applied with anodic oxidation treatment, to form a third workpiece Q 3  which has hardened surfaces. In this way, housing bodies  10  and vane rotors  4  of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  are mirror images which are formed from the identical or common workpieces P 3  and Q 2  which are formed before the application of carving. As shown in  FIGS. 16 and 4 , the shapes and relative positions of housing body  10  and vane rotor  4  of exhaust valve timing control apparatus  1   b  are mirror images of those of intake valve timing control apparatus  1   a  as viewed from the X-axis positive side. First, second and third shoes  11 ,  12  and  13  are arranged in this order in the counterclockwise direction in  FIG. 16 . As viewed from the X-axis positive side, the clockwise surfaces of first, second and third shoes  11 ,  12  and  13  are formed with recesses  115 ,  125  and  135  respectively. The counterclockwise surfaces of first, second and third shoes  11 ,  12  and  13  are formed with flat portions  111 ,  121  and  131  respectively. First, second and third vanes  41 ,  42  and  43  are arranged in this order in the counterclockwise direction in  FIG. 16 . As viewed from the X-axis positive side, the clockwise surfaces of first, second and third vanes  41 ,  42  and  43  are formed with flat portions  415 ,  425  and  435  respectively. The counterclockwise surfaces of first, second and third vanes  41 ,  42  and  43  are formed with recesses  418 ,  428  and  438  respectively. The counterclockwise surfaces of the roots of first and second vanes  41  and  42  are formed with radial projections  419  and  429  respectively. Under the condition that the vane rotor  4  is mounted in housing HSG, first vane  41  is mounted in the space between first shoe  11  and second shoe  12 , second vane  42  is mounted in the space between second shoe  12  and third shoe  13 , and third vane  43  is mounted in the space between third shoe  13  and first shoe  11 . Rotor body  400  is formed with three retard fluid passages  408  and three advance fluid passages  409  which are connected between camshaft insertion hole  402  and the outside peripheral surface of rotor  40  (rotor body  400 ). In the case of first vane  41 , retard fluid passage  408  is formed substantially in a midpoint in the X-axis direction as shown in  FIG. 19B , and in the clockwise side of the root of first vane  41  as viewed from the X-axis positive side, as shown in  FIG. 16 , where retard fluid passage  408  is formed to extend through in the radial direction, as shown in  FIG. 16 . On the other hand, advance fluid passage  409  is formed in the X-axis negative side in first vane  41 , and in the counterclockwise side of the root of first vane  41  as viewed from the X-axis positive side, as shown in  FIG. 16 , where advance fluid passage  409  is formed to extend through in the radial direction, as shown in  FIG. 16 . Similarly, retard fluid passages  408  and advance fluid passages  409  are formed in the roots of second vane  42  and third vane  43 , extending through in the radial direction. First, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3  are defined by the X-axis negative side surface of front plate  8 , the X-axis positive side surface of rear plate  9 , the circumferentially-facing surfaces of first, second and third vanes  41 ,  42  and  43 , and the circumferentially-facing surfaces of first, second and third shoes  11 ,  12  and  13 . For example, first advance chamber A 1  is defined between the clockwise surface of second shoe  12 , the counterclockwise surface of first vane  41 , whereas first retard chamber R 1  is defined between the clockwise surface of first vane  41  and the counterclockwise surface of first shoe  11 , as shown in  FIG. 16 . Similarly, second advance chamber A 2  is defined between first shoe  11  and third vane  43 , second retard chamber R 2  is defined between third vane  43  and third shoe  13 , third advance chamber A 3  is defined between third shoe  13  and second vane  42 , and third retard chamber R 3  is defined between second vane  42  and second shoe  12 . Rotation of vane rotor  4  with respect to housing HSG in the clockwise direction is restricted by contact between flat portion  111  of first shoe  11  and flat portion  415  of first vane  41 , where rotation of vane rotor  4  is locked by lock piston  51 , similar to intake valve timing control apparatus  1   a,  as shown in  FIG. 16 . Flat portion  111  of the circumferentially-facing surface of first shoe  11  and flat portion  415  of the circumferentially-facing surface of  41  serve as first stopper portions constituting a first stopper mechanism for restricting relative rotation of vane rotor  4  in the clockwise direction (in the advance direction). On the other hand, rotation of vane rotor  4  with respect to housing HSG in the counterclockwise direction is restricted by contact between tip  126  of second shoe  12  and radial projection  419  of first shoe  11 , where vane rotor  4  is in the end position in the direction away from the position where rotation of vane rotor  4  is locked by lock piston  51 , similar to intake valve timing control apparatus  1   a,  as shown in  FIG. 17 . The counterclockwise surface of radial projection  419  and the clockwise surface of tip  126  of second shoe  12  serve as second stopper portions constituting a second stopper mechanism for restricting relative rotation of vane rotor  4  in the counterclockwise direction (in the retard direction). The first and second stopper mechanisms define a range of relative rotation of vane rotor  4  with respect to housing HSG. As in intake valve timing control apparatus  1   a,  the contact area between tip  126  of second shoe  12  and radial projection  419  of first shoe  11 , i.e. the contact area of the second stopper mechanism, SS 2 , is set smaller than the contact area between flat portion  111  of first shoe  11  and the flat portion  415  of first vane  41 , i.e. the contact area of the first stopper mechanism, SS 1  (SS 1 &gt;SS 2 ). 
     Exhaust camshaft  3   b  is made of iron, and rotatably supported on bearings in a laterally-outside portion of the upper end portion of the cylinder head of the internal combustion engine. Exhaust camshaft  3   b  is formed with drive cams (exhaust cams) at the outside peripheral surface, which are located to face or conform to positions of the exhaust valves. When exhaust camshaft  3   b  is rotated, the exhaust cams open and close the exhaust valves via valve lifters, rocker arms, etc. Exhaust valve timing control apparatus  1   b,  which is fixed to exhaust camshaft  3   b,  is constructed to be locked by lock piston  51  as an engagement member, under the condition that rotation of vane rotor  4  is restricted by the first stopper mechanism at the most advanced position. 
     In contrast to intake valve timing control apparatus  1   a,  exhaust valve timing control apparatus  1   b  is provided with a biasing member for biasing the vane rotor  4  with respect to housing HSG in the advance direction. The biasing member, which is collectively referred to as biasing member  6 , includes three spring units, i.e. first, second and third spring units  61 ,  62  and  63 . First, second and third spring units  61 ,  62  and  63  are mounted in first, second and third advance chambers A 1 , A 2  and A 3  respectively, for biasing the first, second and third vanes  41 ,  42  and  43  of vane rotor  4  with respect to first, second and third shoes  11 ,  12  and  13  of housing body  10  in the clockwise direction. Biasing member  6  may be provided in part of first, second and third advance chambers A 1 , A 2  and A 3 . Biasing member  6  may be provided in first, second and third retard chambers R 1 , R 2  and R 3 . This construction may be used in cases where vane rotor  4  needs to be biased with respect to housing HSG in the retard direction, which cases are possible according to the form of transmitting torque from the crankshaft to the camshaft. Specifically, first spring unit  61  is mounted in first advance chamber A 1  between second shoe  12  and first vane  41 , second spring unit  62  is mounted in second advance chamber A 2  between first shoe  11  and third vane  43 , and third spring unit  63  is mounted in third advance chamber A 3  between third shoe  13  and second vane  42 . The longitudinal ends of first, second and third spring units  61 ,  62  and  63  are mounted in recesses  418 ,  428  and  438 , and recesses  115 ,  125  and  135 , where recesses  418 ,  428  and  438  are formed in the counterclockwise surfaces of first, second and third vanes  41 ,  42  and  43 , respectively, and recesses  115 ,  125  and  135  are formed in the opposite clockwise surfaces of first, second and third shoes  11 ,  12  and  13 , respectively. First spring unit  61  includes a coil spring  610 , and retaining portions  611  and  612  which are spring retainers provided at the longitudinal ends of coil spring  610 . Retaining portion  611  includes a plate portion in which a through hole is formed, and a hollow cylindrical portion which projects from one side surface of the plate portion, and surrounds the through hole. One longitudinal end of coil spring  610  is fitted with the outside periphery of the hollow cylindrical portion of retaining portion  611 . The plate portion of retaining portion  611  has a rectangular shape adapted to be fitted in recess  125  of second shoe  12  without play, and is fitted in recess  125 . Recess  125  restricts movement of retaining portion  611  with respect to second shoe  12  of housing HSG in the radial direction of housing HSG. Front plate  8  and rear plate  9 , which are in contact with the X-axis ends of the plate portion of retaining portion  611 , restrict movement of retaining portion  611  in recess  125  in the X-axis direction within a predetermined range. First advance chamber A 1  is hydraulically connected to first pressure-receiving chamber  55  of lock mechanism  5  shown in  FIG. 14  through the through hole of retaining portion  611  and communication hole  56  of first vane  41 . First retard chamber R 1  is hydraulically connected to engaging recess  521  of lock mechanism  5  through the communication groove  57  of first vane  41 . Retaining portion  612  of first spring unit  61  is constructed similar to retaining portion  611 . Specifically, the hollow cylindrical portion of retaining portion  612  retains the other longitudinal end of coil spring  610 , and the plate portion of retaining portion  612  is supported in recess  418  of first vane  41  so that the recess  418  restricts movement of retaining portion  612  of first spring unit  61  with respect to first vane  41  of vane rotor  4  in the radial direction and in the axial direction of housing HSG. In this way, the positions of the longitudinal ends of coil spring  610  in the radial direction and the axial direction of housing HSG are restricted. During assembling operation, first spring unit  61  is inserted in the X-axis direction into first advance chamber A 1 , so that the retaining portion  611  is fitted in recess  125 , and retaining portion  612  is fitted in recess  418 . Coil spring  610  is mounted in first advance chamber A 1  in a compressed state, so as to constantly bias first vane  41  with respect to second shoe  12  of housing body  10  in the clockwise direction. Second spring unit  62 , and third spring unit  63  are constructed and mounted similar to first spring unit  61 . Second spring unit  62  includes a coil spring  620 , and retaining portions  621  and  622 , and third spring unit  63  includes a coil spring  630 , and retaining portions  631  and  632 . The biasing forces of coil springs  610 ,  620  and  630  are set substantially equal to each other. The diameters of coil springs  610 ,  620  and  630  are equal to about 70% of the maximum widths of first, second and third advance chambers A 1 , A 2  and A 3  in the radial direction, respectively. As compared to cases where another biasing member such as a leaf spring is used, the use of coil springs is effective for easily adjusting the biasing force, and enhancing the mountability to first, second and third advance chambers A 1 , A 2  and A 3 . The construction that a single coil spring is mounted in each of first, second and third advance chambers A 1 , A 2  and A 3 , is effective for making the exhaust valve timing control apparatus  1   b  compact in the axial direction, as compared to cases where two coil springs are arranged in double layers in the X-axis direction in each of first, second and third advance chambers A 1 , A 2  and A 3 . In cases where double coil springs are mounted in each of first, second and third advance chambers A 1 , A 2  and A 3 , it may be difficult to assemble the coil springs to first, second and third advance chambers A 1 , A 2  and A 3 , unless the double coil springs are mounted to retaining portions to form a single spring unit. On the other hand, according to the present embodiment where a single coil spring is mounted in each of first, second and third advance chambers A 1 , A 2  and A 3 , it is easy to mount the coil spring to from a spring unit. Moreover, it is also possible as an alternative to directly mount the coil spring in first, second and third advance chambers A 1 , A 2  and A 3  (recesses  418 ,  125 , etc.), without mounting each of coil springs  610 ,  620  and  630  to retaining portions to form a spring unit. Since recesses  418 ,  428  and  438 , and recesses  115 ,  125  and  135  restrict deviations of first, second and third spring units  61 ,  62  and  63  during operation of exhaust valve timing control apparatus  1   b,  this achieves normal operations of biasing member  6  and exhaust valve timing control apparatus  1   b,  with no special support member. For example, retaining portions  611  and  612  may be omitted. However, the provision of retaining portions  611  and  612  according to the present embodiment is effective for more securely preventing deviations of first, second and third spring units  61 ,  62  and  63 . When vane rotor  4  rotates with respect to housing HSG in the counterclockwise direction, coil springs  610 ,  620  and  630  are compressed. The clockwise side portion of coil spring  610  is located outside of radial projection  419  of first vane  41  in the radial direction of housing HSG. The height of radial projection  419  in the radial direction of vane rotor  4  is set so that the outside periphery of radial projection  419  is close to the outside periphery of coil spring  610  with a slight clearance. Accordingly, when coil spring  610  is compressed and deformed, the periphery of coil spring  610  facing the radial projection  419  is brought into contact with the outside peripheral surface of radial projection  419 , so that coil spring  610  is prevented from deforming over a predetermined distance inwardly in the radial direction of vane rotor  4 . Namely, radial projection  419  serves to guide the coil spring  610 . Radial projection  429  of second vane  42  is constructed similar to radial projection  419 , so as to guide coil spring  630  when vane rotor  4  relatively rotates so as to compress coil spring  630 . As shown in  FIG. 17 , when rotation of vane rotor  4  in the counterclockwise direction is restricted by contact between tip  126  of second shoe  12  and radial projection  419  of first shoe  11 , the opposite shoe-side and vane-side retaining portions  611  and  612  or  621  and  622  or  631  and  632  of each of first, second and third spring units  61 ,  62  and  63  are out of contact with each other, and wounded wires of each of coil springs  610 ,  620  and  630  are out of contact with each other. In other words, when the counterclockwise rotation is restricted by the second stopper mechanism, the circumferential length of each of first, second and third advance chambers A 1 , A 2  and A 3  is set larger than the length of the respective one of coil springs  610 ,  620  and  630  under the condition the wounded wires are completely in contact with each other. 
     Hydraulic fluid supply and drainage mechanism  2  of exhaust valve timing control apparatus  1   b  is constructed similar to intake valve timing control apparatus  1   a.  Exhaust valve timing control apparatus  1   b  includes directional control valve  24  other than directional control valve  24  of intake valve timing control apparatus  1   a,  but shares oil pump  1020  and oil pan  25  with intake valve timing control apparatus  1   a.    
     &lt;&lt;Operations and Produced Effects by Valve Timing Control Apparatus&gt;&gt; The following describes operations of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b.    
     &lt;Operations and Produced Effects Related to Phase Change&gt; The following describes control operations and produced effects related to phase change by intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b.  However, the control operations may be adjusted or modified as appropriate. First, the following describes how intake valve timing control apparatus  1   a  performs a phase change control.  FIG. 4  shows the most retarded state when the internal combustion engine is at rest or at start.  FIG. 5  shows the most advanced state when the internal combustion engine is operating. At start of the internal combustion engine, lock mechanism  5  keeps vane rotor  4  locked in the most retarded position as an initial position which is optimal for cranking the internal combustion engine, as shown in  FIG. 4 . When an ignition switch is turned on, intake valve timing control apparatus  1   a  achieves smooth cranking operation, improving the startability of the internal combustion engine. In a predetermined low speed and low load region after start of the internal combustion engine, the controller CU maintains a condition that no control current is outputted to directional control valve  24 . Accordingly, in directional control valve  24 , the spool valve element is maintained by the elastic force of return spring RS at the position such that the supply port  240  is hydraulically connected to second port  242 , and first port  241  is hydraulically connected to drain port  243 . Accordingly, working fluid, which is discharged by oil pump  1020 , flows in supply passage  22 , enters the valve body through supply port  240 , flows through the second port  242  into advance passage  21 , flows in the first and second fluid passages of intake camshaft  3   a  and the advance fluid passages  409  of vane rotor  4 , and finally flows into first, second and third advance chambers A 1 , A 2  and A 3 . The internal pressures of first, second and third advance chambers A 1 , A 2  and A 3  increase with an increase in the discharge pressure of oil pump  1020 . On the other hand, working fluid is drained from first, second and third retard chambers R 1 , R 2  and R 3  to oil pan  25  through retard passage  20  and drain passage  23 , so that the internal pressures of first, second and third retard chambers R 1 , R 2  and R 3  are held low (at atmospheric pressure). As the internal pressure of first advance chamber A 1  rises, this hydraulic pressure is supplied through the communication groove  57  shown in  FIG. 14  to second pressure-receiving chamber  59 , so that the engaging portion  511  of lock piston  51  is subject to a hydraulic force in the X-axis positive direction. When the hydraulic force is above the elastic force of coil spring  53 , lock piston  51  moves in the X-axis positive direction. When engaging portion  511  has moved completely out of engaging recess  521 , the lock state is canceled. This allows vane rotor  4  to rotate freely, so that the valve timing can be changed arbitrarily. Under the hydraulic pressures supplied to first, second and third advance chambers A 1 , A 2  and A 3 , vane rotor  4  rotates with respect to housing HSG from the position shown in  FIG. 4 , so as to change the rotational phase (relative rotational change angle) of intake camshaft  3   a  with respect to the crankshaft in the advance direction. This advances the opening and closing timing of the intake valves, and thereby increases a valve overlap which is a period when both of the intake valves and exhaust valves are opened. As a result, in the low speed and low load region, the combustion efficiency is improved because of use of inertial charge, thereby stabilizing the rotation of the internal combustion engine, and improving the fuel efficiency. As shown in  FIG. 5 , when vane rotor  4  rotates with respect to housing HSG and reaches the most advanced position such that the volumetric capacities of first, second and third advance chambers A 1 , A 2  and A 3  are maximized, and the volumetric capacities of first, second and third retard chambers R 1 , R 2  and R 3  are minimized, then the valve overlap is maximized. On the other hand, when the internal combustion engine shifts to an operating state in a predetermined high speed and high load region, the controller CU outputs a control current to directional control valve  24 . In directional control valve  24 , the spool valve element moves against the elastic force of return spring RS to the position such that the supply port  240  is hydraulically connected to first port  241 , and second port  242  is hydraulically connected to drain port  243 . Accordingly, working fluid, which is discharged by oil pump  1020 , flows through the first port  241  of directional control valve  24  into retard passage  20 , and flows through the first and second fluid passages of intake camshaft  3   a  and the retard fluid passages  408  of vane rotor  4  to first, second and third retard chambers R 1 , R 2  and R 3 , so that the internal pressures of first, second and third retard chambers R 1 , R 2  and R 3  rise. On the other hand, working fluid is drained from first, second and third advance chambers A 1 , A 2  and A 3  to oil pan  25  through the advance passage  21  and drain passage  23 , so that the internal pressures of first, second and third advance chambers A 1 , A 2  and A 3  fall. Under the condition described above, the hydraulic pressure in second pressure-receiving chamber  59  falls in lock mechanism  5 . On the other hand, as the internal pressure of first retard chamber R 1  increases, this hydraulic pressure is supplied through the communication hole  56  shown in  FIG. 14  to first pressure-receiving chamber  55 , so as to apply a hydraulic force to a pressure-receiving surface of flange  513  of lock piston  51 . Accordingly, lock mechanism  5  is maintained in a released state in which lock piston  51  is brought out of engaging recess  521  against the elastic force of coil spring  53 . When the internal pressures of first, second and third retard chambers R 1 , R 2  and R 3  are above the internal pressures of first, second and third advance chambers A 1 , A 2  and A 3 , then the vane rotor  4  rotates with respect to housing HSG in the counterclockwise direction which is opposite to the direction of rotation of housing HSG indicated by the arrow in  FIG. 4 , so as to change the rotational phase (relative rotational change angle) of intake camshaft  3   a  with respect to the crankshaft in the retard direction. This retards the opening and closing timing of the intake valves, and thereby reduces the valve overlap so as to enhance the output of the internal combustion engine in the high speed and high load region. As shown in  FIG. 4 , when vane rotor  4  rotates with respect to housing HSG and reaches the most retarded position such that the volumetric capacities of first, second and third advance chambers A 1 , A 2  and A 3  are minimized, and the volumetric capacities of first, second and third retard chambers R 1 , R 2  and R 3  are maximized, the valve overlap is minimized. Moreover, for example, when the internal combustion engine shifts into a predetermined middle speed and middle load region, the controller CU controls directional control valve  24  so as to hold the spool valve element in the intermediate operation position such that the supply passage  22  and drain passage  23  are hydraulically disconnected from each other. Accordingly, the internal pressures of first, second and third retard chambers R 1 , R 2  and R 3 , and first, second and third advance chambers A 1 , A 2  and A 3  are held constant, and vane rotor  4  is set in an intermediate rotational position. This serves to achieve a suitable valve timing control in the middle speed and middle load region, and a suitable balance between the fuel efficiency and the output of the internal combustion engine. 
     When the internal combustion engine is operating, and intake camshaft  3   a  is rotating, an alternating torque (or reverse torque) acts on intake camshaft  3   a  due to a reaction torque that is transmitted to the intake cams of intake camshaft  3   a  from the valve springs which bias the intake valves in a closing direction. Namely, depending on the shape of the intake cams, intake camshaft  3   a  is subject to alternately a negative torque which is a counterclockwise torque against clockwise rotation of intake camshaft  3   a,  and a positive torque which is a clockwise torque against counterclockwise rotation of intake camshaft  3   a.  The alternating toque is offset to the negative side as a whole. Namely, if the positive torques and negative torques, which are generated in each period of rotation of intake camshaft  3   a,  are integrated with time, the integral is negative. Accordingly, intake camshaft  3   a  is subject to a negative torque as a whole. When the internal combustion engine is stopped, then operation of oil pump  1020  is stopped, and energization of directional control valve  24  by controller CU is turned off. Accordingly, supply of working fluid to first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3  is stopped. In summary, immediately after the internal combustion engine is stopped, the friction or alternating torque offset to the negative side, which is applied to intake camshaft  3   a,  serves to rotate vane rotor  4  with respect to housing HSG in the direction opposite to the direction of rotation of housing HSG indicated by the arrow in  FIG. 4 , i.e. serves to rotate vane rotor  4  with respect to housing HSG in the retard direction. As a result, after the internal combustion engine is stopped, vane rotor  4  mechanically moves to the predetermined initial position suitable for start or restart of the internal combustion engine, i.e. vane rotor  4  mechanically moves to the most retarded position shown in  FIG. 4 , under the friction or alternating torque applied to intake camshaft  3   a.  In other words, after the internal combustion engine is stopped, the valve timing is mechanically brought to a phase suitable for start or restart of the internal combustion engine. When vane rotor  4  rotates with respect to housing HSG, and reaches the most retarded position, then lock piston  51  overlaps with engaging recess  521  in lock mechanism  5  as viewed in the X-axis direction. When the internal combustion engine is stopped, the engaging portion  511  of lock piston  51  fits and engages with engaging recess  521  by the elastic force of coil spring  53 , so that the lock piston  51  prevents free rotation of vane rotor  4 . As discussed above, in intake valve timing control apparatus  1   a,  vane rotor  4  is mechanically rotated to the most retarded position with respect to housing HSG as an initial position, when the internal combustion engine is stopped. This is effective for setting the intake valve timing control apparatus  1   a  in the initial position when the internal combustion engine is restarted, and achieving a stable start and operation of intake valve timing control apparatus  1   a.    
     The following describes how exhaust valve timing control apparatus  1   b  performs a phase change control. Exhaust valve timing control apparatus  1   b  operates similar to intake valve timing control apparatus  1   a,  except that the advance side and the retard side are reversed.  FIG. 16  shows the most advanced state when the internal combustion engine is at rest or at start.  FIG. 17  shows the most retarded state when the internal combustion engine is operating. At start of the internal combustion engine, lock mechanism  5  holds vane rotor  4  in the most advanced position as an initial position which is optimal for cranking the internal combustion engine, as shown in  FIG. 16 . When the ignition switch is turned on, exhaust valve timing control apparatus  1   b  achieves smooth cranking operation, improving the startability of the internal combustion engine. In the predetermined low speed and low load region after start of the internal combustion engine, first, second and third retard chambers R 1 , R 2  and R 3  are supplied with hydraulic pressures. When the hydraulic force based on the hydraulic pressures exceeds the biasing force of first, second and third spring units  61 ,  62  and  63 , then vane rotor  4  rotates in the retard direction with respect to housing HSG. This retards the rotational phase of exhaust camshaft  3   b,  so as to increase the valve overlap. As shown in  FIG. 17 , when vane rotor  4  rotates with respect to housing HSG and reaches the most retarded position such that the volumetric capacities of first, second and third advance chambers A 1 , A 2  and A 3  are minimized, and the volumetric capacities of first, second and third retard chambers R 1 , R 2  and R 3  are maximized, the valve overlap is maximized. On the other hand, when the internal combustion engine shifts to an operating state in the high speed and high load region, working fluid is supplied to first, second and third advance chambers A 1 , A 2  and A 3 . When the sum of a torque resulting from the hydraulic pressures of first, second and third advance chambers A 1 , A 2  and A 3 , and a torque resulting from the biasing forces of first, second and third spring units  61 ,  62  and  63  is above a torque resulting from the hydraulic pressures of first, second and third retard chambers R 1 , R 2  and R 3 , then the vane rotor  4  relatively rotates in the advance direction. Accordingly, the rotational phase (relative rotational angle) of exhaust camshaft  3   b  is advanced so as to reduce the valve overlap. In other words, first, second and third spring units  61 ,  62  and  63  also serve to assist the phase change in the advance direction. As shown in  FIG. 16 , when vane rotor  4  rotates with respect to housing HSG and reaches the most advanced position such that the volumetric capacities of first, second and third advance chambers A 1 , A 2  and A 3  are maximized, and the volumetric capacities of first, second and third retard chambers R 1 , R 2  and R 3  are minimized, the valve overlap is minimized. When the internal combustion engine is operating, exhaust camshaft  3   b  is subject to an alternating torque which is a negative torque or counterclockwise torque as a whole against clockwise rotation of exhaust camshaft  3   b.  When the internal combustion engine is stopped so as to turn off energization of directional control valve  24 , then the alternating torque acts on the vane rotor  4  in the counterclockwise direction or in the retard direction with respect to housing HSG. On the other hand, biasing member  6  (first, second and third spring units  61 ,  62  and  63 ) constantly biases vane rotor  4  with respect to housing HSG in the clockwise direction or advance direction. Accordingly, after the internal combustion engine is stopped, vane rotor  4  is moved by the biasing force of biasing member  6  under little influence of the alternating torque, to the initial position suitable for start or restart of the internal combustion engine, i.e. to the most advanced position. In other words, the valve timing is mechanically brought to the phase suitable for start or restart of the internal combustion engine. When vane rotor  4  rotates with respect to housing HSG, and reaches the most advanced position, then lock piston  51  overlaps with engaging recess  521  in lock mechanism  5  as viewed in the X-axis direction. When the internal combustion engine is stopped, engaging portion  511  of lock piston  51  fits and engages with engaging recess  521  by the elastic force of coil spring  53 , so that lock piston  51  prevents free rotation of vane rotor  4 . As discussed above, in exhaust valve timing control apparatus  1   b,  vane rotor  4  is rotated by the biasing force of biasing member  6  to the most advanced position as an initial position with respect to housing HSG, when the internal combustion engine is stopped. This is effective for setting the exhaust valve timing control apparatus  1   b  in the initial position when the internal combustion engine is restarted, and achieving a stable start and operation of exhaust valve timing control apparatus  1   b.    
     &lt;Operation and Produced Effects by Lock Mechanism&gt; As discussed above, each lock mechanism  5  operates to allow a corresponding one of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  to start from its initial position shown in  FIG. 4  or  16 , independently of presence or absence of hydraulic pressures. This serves to suppress vibration of vane rotor  4  which may result from the alternating torque applied to camshaft  3   a  or  3   b,  and thereby suppress abnormal noise due to collision between first, second and third shoes  11 ,  12  and  13  of housing HSG and first, second and third vanes  41 ,  42  and  43  of vane rotor  4 , when the internal combustion engine is started. Moreover, it is possible to prevent knocking, etc., and thereby achieve stable operations of the internal combustion engine, intake valve timing control apparatus  1   a,  and exhaust valve timing control apparatus  1   b.  These effects are produced, not only when the internal combustion engine is at start, but also when the internal combustion engine is at idle when no high hydraulic pressure is generated and supplied. The lock position is located at the most retarded position or the most advanced position in the present embodiment, but may be modified to a position between the most retarded position and the most advanced position which is suitable for start, etc., of the internal combustion engine, and used as an initial position of intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b.    
     As described above, lock mechanism  5  includes: slide hole  501  formed in vane rotor  4 ; lock piston  51 ; engaging recess  521  formed in the inside surface of housing HSG; and coil spring  53 . Lock piston  51  moves out of and into vane rotor  4  according to the operating state of the internal combustion engine, and thereby allows or prevents relative rotation between housing HSG and vane rotor  4 . For example, when vane rotor  4  is rotated to the predetermined initial position by the biasing force of biasing member  6  and/or the alternating torque, then lock piston  51  is mechanically engaged with engaging recess  521  by the biasing force of coil spring  53 . This eliminates the necessity of provision of an actuator for actuating the locking operation. This is also effective for simplifying the mechanism, and reducing the manufacturing cost, and enhancing the reliability of the locking operation, as compared to cases where the locking means is implemented by a clutch mechanism or lever mechanism. Instead of or in addition to coil spring  53 , another elastic member, such as a leaf spring, may be used as a biasing member for biasing the lock piston  51 . Although the lock state is released by application of hydraulic pressure to lock piston  51  in the present embodiment, another releasing mechanism may be provided to release the lock piston  51  from engaging recess  521 . Although the lock mechanism (i.e. lock piston  51 ) is provided in first vane  41  of vane rotor  4  in the present embodiment, the lock mechanism may be provided in rotor  40  of vane rotor  4 . However, the provision in first vane  41  is advantageous in reducing the diameter of rotor  40 . Alternatively, the lock mechanism (i.e. lock piston  51 ) may be provided in housing HSG, for locking the vane rotor  4  with respect to housing HSG. However, the provision in vane rotor  4  is advantageous in reducing the size of housing HSG. 
     &lt;Locking Operation Smoothed by Suitable Direction of Movement of Lock Piston&gt; Lock piston  51  may be arranged to move forward and rearward in a direction other than the direction of the axis of rotation O, for example, in a radial direction of housing HSG. In other words, the cylinder accommodating the lock piston  51  may be formed to extend in a direction other than the direction of the axis of rotation O, for example, in a radial direction of housing HSG. However, in the present embodiment, slide hole  501  is formed to extend in the direction of the axis of rotation O (or in the X-axis direction), wherein the tip (engaging portion  511 ) of lock piston  51  moves into or out of slide hole  501  in the direction of the axis of rotation O. This construction is advantageous in reducing the diameter of intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b.  Moreover, the construction is effective for preventing the operation of lock mechanism  5  from being influenced by the centrifugal force resulting form rotation of vane rotor  4 . For example, if lock piston  51  is arranged to move in a radial direction of housing HSG, lock piston  51  is applied with the centrifugal force resulting form rotation of vane rotor  4  which acts in the direction of movement of lock piston  51 . In such cases, when engine speed changes so as to change the magnitude of the centrifugal force, then the force required to actuate the lock piston  51  also changes. The construction according to the present embodiment is however subject to no such problem, and thereby serves to stabilize the locking operation of intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b.    
     &lt;Locking Operation Smoothed by Back Pressure Relief Section&gt; The back pressure relief section serves to smooth the movement of lock piston  51  by eliminating the effect of pressure in back pressure chamber  50 , when intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b  is in operation. Specifically, when engaging portion  511  moves out of engaging recess  521  so that lock piston  51  moves in the X-axis positive direction, and the volumetric capacity of back pressure chamber  50  decreases, then air in back pressure chamber  50  escapes through the back pressure relief section to the low pressure space in the internal combustion engine. This serves to keep the internal pressure of back pressure chamber  50  low. On the other hand, working fluid leaks through the clearance around the back pressure chamber  50 , and flows into back pressure chamber  50 . This working fluid is also drained through the back pressure relief section to the oil-lubricated space in the internal combustion engine. Accordingly, when back pressure chamber  50  is contracting, the movement of lock piston  51  is prevented from being disturbed by such air and oil, and the back pressure of lock piston  51  is relieved. In this way, the back pressure relief section serves to achieve smooth operation of lock piston  51 , i.e. smooth sliding motion of lock piston  51  in slide hole  501 , and allow the lock state to be smoothly released. 
     &lt;Locking Operation Smoothed by Wedging Effect&gt; Since the tip (or engaging portion  511 ) of lock piston  51  has the form of a truncated cone, and has a diameter that gradually decreases as followed in the X-axis negative direction toward engaging recess  521  as described above, lock piston  51  can easily engage with engaging recess  521 . This effect is enhanced by the shape of engaging recess  521  whose diameter gradually increases as followed in the X-axis positive direction toward the opening of engaging recess  521 . The locking operation is thus smoothed. Moreover, each of engaging portion  511  and engaging recess  521  has an inclined surface or tapered surface. Specifically, the outside periphery of engaging portion  511  is formed with the inclined surface whose diameter gradually decreases as followed in the X-axis negative direction toward the tip of engaging portion  511 , whereas the inside periphery of engaging recess  521  is formed with the inclined surface whose diameter gradually decreases as followed in the X-axis negative direction toward the bottom of engaging recess  521 . Under the condition shown in  FIG. 4  that the relative rotation between housing HSG and vane rotor  4  is restricted by the first stopper mechanism, the central axis of engaging recess  521  is located with a slight offset with respect to the central axis of engaging portion  511  in the counterclockwise direction toward first shoe  11 , as shown in  FIG. 14 . Accordingly, when lock piston  51  is inserted in engaging recess  521  to establish the lock state, the inclined surfaces of engaging portion  511  and engaging recess  521  are brought into contact with one another on the clockwise side, thereby causing a component of force for pressing the first vane  41  in the counterclockwise direction toward the first shoe  11 . This is a wedging effect. Namely, when engaging portion  511  is moved in the X-axis negative direction, and engaged with engaging recess  521  under the biasing force of coil spring  53 , the clockwise side inclined surface of engaging portion  511  is brought into sliding and pressing contact with the clockwise side inclined surface of engaging recess  521 , while engaging portion  511  of lock piston  51  is subject to a reaction force in the counterclockwise direction. Accordingly, first vane  41  accommodating the lock piston  51  is also subject to the reaction force in the counterclockwise direction toward the first shoe  11 . As a result, the engagement of lock piston  51  with engaging recess  521  is effective for pressing the first vane  41  onto first shoe  11 , and thereby ensuring that the vane rotor  4  is retained at the bound defined by the first stopper mechanism (i.e. the most retarded position as the initial position). The contact between the inclined surfaces of engaging portion  511  and engaging recess  521  described above is thus achieved by the provision of the offset between the central axes of engaging portion  511  and engaging recess  521 , but may be achieved by suitably modifying the shapes of engaging portion  511  and engaging recess  521 . However, the provision of the offset between the central axes of engaging portion  511  and engaging recess  521  is advantageous in simplifying the structure. Although both of engaging portion  511  and engaging recess  521  are formed with the inclined surfaces in the present embodiment, this construction may be modified so that only one of engaging portion  511  and engaging recess  521  is provided with the inclined surface. This alternative construction can produce a wedging effect as in the present embodiment. However, the construction according to the present embodiment is effective for reducing friction between engaging portion  511  and engaging recess  521 , while effectively producing a wedging effect. 
     &lt;Locking Operation Smoothed by Positioning Means&gt; The positioning between lock piston  51  and engaging recess  521  is accurately implemented by a positioning means including the positioning pin  905 , etc., so as to achieve smooth engaging operation of lock piston  51 . The following describes operation of the positioning means including the positioning pin  905 , etc. First, the following briefly describes a process of assembling the intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b.  First, rear plate  9  is inserted and mounted in fitting recess  101  of housing body  10 . This is implemented by: mounting the sleeve  52  in recess  900  of rear plate  9 ; setting the rear plate  9  so that the X-axis positive side surface of rear plate  9  is directed upwardly in the vertical direction; mounting and holding the sealing ring S 1  in sealing ring groove  906 , and sealing rings S 2  in annular sealing ring grooves  907 ,  908  and  909  in rear plate  9 ; and assembling the housing body  10  from the X-axis positive side (from above in the vertical direction) to rear plate  9  so that the rear plate  9  is fitted in fitting recess  101 . In assembling the housing body  10  to rear plate  9 , the rotational position of housing body  10  with respect to rear plate  9  is adjusted so that the positioning recess  114  of housing body  10  faces or conforms to positioning pin  905  of rear plate  9 . Then, positioning pin  905  is fixedly fitted in positioning recess  114 . In this way, the position of housing body  10  with respect to rear plate  9  in the circumferential direction is set suitably. Under this condition, the bolt holes of female thread portions  901 ,  902  and  903  of rear plate  9  face or conform to bolt holes  110 ,  120  and  130  of housing body  10 , respectively, as viewed in the X-axis direction. Next, vane rotor  4  is inserted and mounted in housing body  10 . Simultaneously, sealing members  118 ,  128  and  138 , and sealing members  413 ,  423  and  433  for sealing between the working fluid chambers A 1 , A 2 , A 3 , R 1 , R 2  and R 3  are also mounted. For exhaust valve timing control apparatus  1   b,  biasing member  6  is also mounted. Moreover, lock mechanism  5  is mounted by: inserting the lock piston  51  in sealing member  502  press-fitted in slide hole  501  of vane rotor  4 ; inserting the coil spring  53  into the inside of lock piston  51 ; and inserting the spring retainer  54  into slide hole  501 . According to the positioning by positioning pin  905 , the sleeve  52 , which is fixed in engaging recess  521  in rear plate  9 , faces and conforms to lock piston  51  in slide hole  501  with a slight offset, under the condition that first vane  41  of vane rotor  4  is in contact with first shoe  11  of housing body  10 . Then, front plate  8  is brought from the X-axis positive side (from above in the vertical direction), and attached to housing body  10 , and bolts b 1 , b 2  and b 3  are used to fix the front plate  8 , housing body  10 , and rear plate  9  together. Front plate  8  is mounted to housing body  10  under the condition that the sealing ring S 3  is mounted in annular sealing ring groove  89  of front plate  8 . The provision of sealing ring grooves  906 ,  907 ,  908 ,  909  and  89  is effective for easily retaining the sealing rings S 1 , S 2  and S 3 , and thereby easily assembling the intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b.  As described above, positioning pin  905  in pin hole  904  and positioning recess  114  serve as a positioning means for adjusting and defining the rotational position of rear plate  9  with respect to housing body  10  by adjusting relative circumferential position between lock piston  51  and engaging recess  521  during assembling operation of intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b.  The radial positions of lock piston  51  and engaging recess  521  are set substantially identical, when rear plate  9  is fitted in fitting recess  101  of housing body  10 . In this way, lock piston  51  and sleeve  52  are correctly positioned, so that the lock piston  51  can smoothly engage with sleeve  52 . The construction that the positioning pin  905  is located adjacent to recess  900  (engaging recess  521 ) is effective for correctly positioning the lock piston  51  and engaging recess  521 . The construction that the pin hole  904  is located on the side of sealing ring grooves  906  and  907  where first retard chamber R 1  is located, is effective for preventing the sealing performance of the sealing rings S 1  and S 2  from being adversely affected. Vane rotor  4  is supported in through hole  92  which is formed in the center of rear plate  9  and through which intake camshaft  3   a  passes, and fixed to the axial end portion  30  of intake camshaft  3   a.  Accordingly, under the influence of a force applied from timing belt  1010  which is wound around pulley  100  of housing HSG, housing HSG may be inclined within a slight angle range with respect to the axis of rotation of vane rotor  4  (i.e. the X-axis), and swing about cylindrical portion  91  of rear plate  9  in which through hole  92  is formed. As a result, engaging recess  521  provided in housing HSG may be deviated with respect to lock piston  51  provided in vane rotor  4 . However, according to the present embodiment where rear plate  9  is formed with engaging recess  521 , the distance (moment arm) between engaging recess  521  and cylindrical portion  91  as a fulcrum, is shorter than in the case where the engaging recess is formed in front plate  8  alternatively. Accordingly, displacement of engaging recess  521  due to swinging motion of housing HSG in a direction perpendicular to the X-axis, is smaller, so that deviation of lock piston  51  from engaging recess  521  is smaller or suppressed. Moreover, the construction that the boss portion  401  of vane rotor  4  is inserted in through hole  92 , is effective for suppressing the inclination and displacement of vane rotor  4  with respect to housing HSG within a predetermined range. 
     &lt;Produced Effects by Timing Belt and Pulley&gt; In the present embodiment, the torque from the crankshaft is transmitted to intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b  by the combination of timing belt  1010  and pulley  100  driven by timing belt  1010 . As compared to an alternative combination of a timing chain and a sprocket driven by the timing chain, the construction according to the present embodiment is advantageous in the quietness, manufacturing cost, and lightness of intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b.    
     &lt;Produced Effects by Weight Reduction&gt; Housing HSG and vane rotor  4  may be formed of a material other than aluminum-based metal materials, for example, an iron-based metal material. However, in a typical valve timing control apparatus using a timing belt and a pulley, the width of the timing belt needs to be wide enough to transmit adequate torque. Accordingly, the width of the pulley needs to be wide enough to engage with the timing belt. This results in an increase in the size of the valve timing control apparatus in the axial direction (the width direction of the pulley), and thereby results in an increase in the weight of the valve timing control apparatus. In contrast, intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b  according to the present embodiment is formed light in weight, because both of housing body  10  and vane rotor  4  are formed of a light metal material, specifically, an aluminum-based metal material. Conversely, the combination of the timing belt and the pulley can be adapted in intake valve timing control apparatus  1   a  or exhaust valve timing control apparatus  1   b,  because the moment of inertia of housing body  10  and vane rotor  4  is small so that the load applied to the torque transmitting section is low. 
     &lt;Durability of Apparatus Enhanced by Features of Form of Fixing Vane Rotor&gt; A typical valve timing control apparatus of so-called a vane type may be subject to a problem that when a vane rotor mounted in a housing is fixed to a camshaft by a single fixing portion, the strength of fixation between the vane rotor and the camshaft is insufficient. For example, in cases where a vane rotor is fixed to a camshaft by a single camshaft bolt that is provided at the axis of rotation, an alternating torque is transmitted from valve springs and applied to the camshaft around the central axis of the camshaft (or camshaft bolt), so that the camshaft bolt tends to be easily loosed. On the other hand, if the camshaft is fixed to the vane rotor by tightly screwing the single camshaft bolt for preventing the looseness, the axial force of the camshaft bolt may cause a large contact pressure to act on the vane rotor. This may result in deforming the vane rotor, when the vane rotor is made of a soft material, such as an aluminum material. In contrast, according to the present embodiment, the fixation is implemented by forming the rotor  40  of vane rotor  4  with a plurality of fixing portions (bolt holes  403 ,  404  and  405 ) for fixing the vane rotor  4  to camshaft  3   a  or  3   b.  In this construction, the applied torque around the central axis of camshaft  3   a  or  3   b  is distributed to the fixing portions (bolt holes  403 ,  404  and  405 ) arranged in the circumferential direction around the central axis of camshaft  3   a  or  3   b,  so that the load to each fixing portion is reduced, and the direction of the force applied to each fixing portion is changed, as compared to cases where the fixation between vane rotor  4  and camshaft  3   a  or  3   b  is implemented by a single fixing portion. Therefore, the strength of fixation between vane rotor  4  and camshaft  3   a  or  3   b  can be enhanced in the present embodiment. The number of the fixing portions is three in the present embodiment, but may be changed to another number greater than or equal to two. However, the fixation based on the three fixing portions is advantageous in enhancing the strength of fixation, while reducing the number of parts, and enhancing the ease of processing and assembling. Each fixing portion is not limited to the form of bolt hole  403 ,  404  or  405 , but may be implemented by swaging, welding, etc. However, the construction according to the present embodiment is advantageous in simplifying the attachment of the valve timing control apparatus to the camshaft, and simplifying the management of fixing force. Specifically, the construction that vane rotor  4  is fixed by three camshaft bolts  33 ,  34  and  35 , is effective for preventing the alternating torque around the axis of rotation O from applying each camshaft bolt  33 ,  34  or  35  with a torque applied around the central axis of camshaft bolt  33 ,  34  or  35 . This prevents camshaft bolt  33 ,  34  or  35  from being loosed. This also serves to provide a sufficient fixing force as a whole, while reducing the axial force of each camshaft bolt  33 ,  34  or  35 . This results in reducing the contact pressure applied to vane rotor  4 , and thereby reducing the deformation of vane rotor  4 . These advantageous effects may be produced by an alternative construction that the fixing portions are spaced from one another, but arranged in the radial direction as different from the present embodiment. However, the construction according to the present embodiment that the fixing portions are arranged in the circumferential direction is advantageous in reliably and evenly distributing the load in the circumferential direction around the axis of rotation O to the plurality of fixing portions, as compared to the alternative construction. In this way, the construction according to the present embodiment is effective for efficiently enhancing the entire strength of fixing, while reducing the load to each fixing portion. The plurality of fixing portions may be unevenly spaced from one another as different from the present embodiment. However, the construction according to the present embodiment that the fixing portions (bolt holes  403 ,  404  and  405 ) are substantially evenly spaced from one another is advantageous in easily keeping the vane rotor  4  in balance around its axis of rotation. This is also advantageous in easily keeping the camshaft  3   a  or  3   b  in balance around its axis of rotation, because the fixing portions (bolt holes  32 ) of camshaft  3   a  or  3   b  are also substantially evenly spaced in conformance with the positions of bolt holes  403 ,  404  and  405 . In addition, according to the present embodiment, each portion between adjacent two of the fixing portions can be formed to have an even and relatively large thickness. This serves to ensure the strength of rotor  40 , even when the fixing portions are formed by removing parts from the base product of rotor  40 , like the bolt hole  403 ,  404  or  405  in the present embodiment, which tends to adversely affect the strength of rotor  40 . The even spacing is also advantageous in effectively preventing the interference among the heads  331 ,  341  and  351  of camshaft bolts  33 ,  34  and  35  that are inserted in bolt holes  403 ,  404  and  405 . 
     &lt;Durability of Apparatus Enhanced by Features of Anodic Oxide Coating Film&gt; Each of housing body  10  and vane rotor  4  is formed of an aluminum-based metal material, and thereby relatively soft. Accordingly, each of housing body  10  and vane rotor  4  is applied with surface treatment, for enhancing the wear resistance and durability. The surface treatment is implemented by anodic oxidation treatment, which is advantageous in rust resistance, wear resistance, evenness of coating thickness, operating facility, etc. Each aluminum-based metal material may be selected from materials that are advantageous in enhancing the wear resistance of the oxide coating film. An anodic oxide coating film is a kind of oxide coating film, which has a relatively high surface roughness, and which is formed with a lot of pores (or projections and recesses). The pores may be sealed or filled by pore-sealing treatment after the anodic oxidation treatment, so that the anodic oxide coating film loses adsorptive activity. In such cases, half pore-sealing treatment is more desirable than full pore-sealing treatment, in order to avoid complicated management, and avoid the occurrence of cracks. In cases of half pore-sealing treatment, each pore still has an opening, and is capable to hold oil therein, thus maintaining a lubricated state, as in cases where no pore-sealing treatment is performed. In order to further enhance the wear resistance, the surface treatment may be implemented by hard alumilite treatment. In such cases, it is desirable that no pore-sealing treatment is performed, because pore-sealing treatment may adversely affect the enhanced wear resistance. The enhancement of wear resistance may be implemented by surface treatment other than anodic oxidation treatment, such as hard chrome plating, or nickel electroless plating. With regard to housing body  10 , the pulley  100  is formed of an aluminum-based metal material, as part of housing body  10 . It is highly desirable to enhance the wear resistance of pulley  100 , because pulley  100  is subject to a driving torque transmitted through the timing belt  1010 . On the other hand, the aluminum-based metal material of housing body  10  is implemented by a relatively soft material, so that it becomes easy to accurately form the teeth of pulley  100 . In the present embodiment, the outside periphery of housing body  10 , i.e. the surface of pulley  100 , is anodized, so that an anodic oxide coating film layer is present at the outside periphery of housing body  10 . This feature is effective for enhancing the hardness and wear resistance of the surface of pulley  100  in meshing contact with timing belt  1010 . On the other hand, the inside periphery of housing body  10  is formed with an anodic oxide coating film layer. This feature serves to enhance the hardness and wear resistance of the inside periphery of housing body  10  that is in sliding contact with first, second and third vanes  41 ,  42  and  43 , and rotor  40 , and in contact with biasing member  6 . Incidentally, at both axial ends of housing body  10 , all of longitudinal end surface  105 , bottom surface  102 , inside peripheral surface  103 , and longitudinal end surface  104  are applied with no anodic oxidation treatment. There is however no problem, because the longitudinal end surface  105 , bottom surface  102 , and inside peripheral surface  103  are in fixed contact with the sealing plates (front plate  8 , and rear plate  9 ), and the longitudinal end surface  104  is in contact with no other member, so that all of longitudinal end surface  105 , bottom surface  102 , inside peripheral surface  103 , and longitudinal end surface  104  are not in sliding contact. With regard to vane rotor  4 , the outside peripheral surface of first, second and third vanes  41 ,  42  and  43 , and rotor  40  (the outside peripheral surface  411 , etc.) is applied with anodic oxidation treatment. This is effective for enhancing the wear resistance of the surface of vane rotor  4  in sliding contact with the inside periphery of housing body  10 . The axial end surfaces of vane rotor  4  are also applied with anodic oxidation treatment. This enhances the wear resistance of the surface of vane rotor  4  in sliding contact with the sealing plates (front plate  8 , and rear plate  9 ) at the axial ends of housing body  10 . Vane rotor  4  may be formed of a slightly harder material than housing body  10 , because the requirement about hardness is lower for vane rotor  4  than for housing body  10  for which it is desirable to use a soft material for accurately forming the teeth of pulley  100 . More specifically, the first stopper mechanism, which is constituted by flat portion  111  of housing body  10  and flat portion  415  of vane rotor  4 , and the second stopper mechanism, which is constituted by tip  126  of housing body  10  and radial projection  419  of vane rotor  4 , are applied with anodic oxidation treatment. This feature is effective for ensuring the hardness of the contact surfaces of each stopper mechanism, and thereby preventing the deformation thereof, enhancing the wear resistance, and enhancing the operation of the stopper mechanisms as described in detail below. Moreover, in valve timing control apparatus  1 , boss portion  401  of vane rotor  4  is subject to a relatively high load in the radial directions, when housing HSG is rotating under condition that torque is transmitted through the timing belt  1010  so that the tension of timing belt  1010  is applied to pulley  100 , because boss portion  401  pivotally supports the housing HSG. This may cause wear in boss portion  401 , if vane rotor  4  including the boss portion  401  is formed of a relatively soft material, such as an aluminum-based metal material. Specifically, it tends to cause adhesion between the inside periphery of through hole  92  of housing HSG and the outside periphery of boss portion  401  in sliding contact with one another, and thereby cause adhesion wear in boss portion  401 . In contrast, in the present embodiment, vane rotor  4  is formed of an aluminum-based material, and the outside periphery of boss portion  401  is formed with an anodic oxide coating film. This serves to suppress such adhesion at the surface of boss portion  401  in sliding contact with housing HSG, and thereby suppress wear of boss portion  401 . The pores of anodic oxide coating film can hold lubricating oil for a long period of time. For example, even in situations where the internal combustion engine is at rest for a period from some days to some months so that the valve timing control apparatus  1  is also at rest, the lubricating oil is held at the sliding contact surface of boss portion  401 , and the held lubricating oil functions well at restart of the internal combustion engine, and serves to suppress wear of boss portion  401 . Namely, the effect of reducing wear of boss portion  401  is further enhanced by the characteristic shape of the anodic oxide coating film. In this way, valve timing control apparatus  1  is maintained in a preferable condition where wear is suppressed by a synergy of the effect of reducing adhesion and the effect of holding lubricating oil. 
     &lt;Durability of Apparatus Enhanced by Features of Materials&gt; Each sealing plate (front plate  8 , rear plate  9 ) are formed of a harder material (iron-based metal material) than housing body  10  (aluminum-based metal material). This feature serves to enhance the strength of front plate  8  that serves as a seat receiving the bolts b 1 , b 2  and b 3 , and enhance the strength of each female thread portion  901 ,  902  or  903  of rear plate  9  in which bolt b 1 , b 2  or b 3  is screwed, thus enhancing the durability of valve timing control apparatus  1 . This feature also serves to suppress wear that may be caused by sliding contact between coil spring  53  of lock mechanism  5  and the X-axis negative side surface of front plate  8 . Moreover, each sealing plate  8 ,  9  is formed of a material (iron-based metal material) having a higher wear resistance than vane rotor  4  (aluminum-based metal material). This feature serves to enhance the durability of the portions of the sealing plates in sliding contact with vane rotor  4  (axial end surfaces, and boss portion  401 ). In other words, the durability of valve timing control apparatus  1  is enhanced, because the sliding surface of vane rotor  4  (axial end surfaces, and boss portion  401 ) is hardened by anodic oxidation treatment, and also the corresponding sliding surface of housing HSG is hardened. Specifically, each sealing plate  8 ,  9  is formed of an iron-based metal material, such as stainless steel, and thereby has a high hardness, high wear resistance, and high durability. This feature is advantageous also in the processing facility, manufacturing cost, etc. More specifically, each sealing plate  8 ,  9  is formed by forging, which is advantageous in strengthening. However, each sealing plate  8 ,  9  may be formed by another processing, such as stamping, casting, etc. Each sealing plate  8 ,  9  may be formed of a material having a higher hardness or higher wear resistance than aluminum-based metal materials, for example, a metal material such as magnesium, or a non-metal material such as ceramics. Sealing plates  8 ,  9  may be formed of an aluminum-based metal material, and anodized at the contact axial end surfaces and the inside periphery of through hole  92  so as to enhance the wear resistance of the portion in sliding contact with vane rotor  4  (axial end surfaces, and boss portion  401 ). 
     &lt;Durability of Apparatus Enhanced by Features of Lock Mechanism&gt; The construction that the vane rotor  4  is formed of an aluminum-based metal material may cause a concern about wear of the cylinder (slide hole  501 ) that is formed in vane rotor  4  and accommodates the lock piston  51 . This is because lock piston  51  moves forward and backward in the cylinder during operation of lock mechanism  5 , and because first, second and third vanes  41 ,  42  and  43  may vibrate due to the alternating torque from camshaft  3   a  or  3   b,  so as to cause fluctuations in hydraulic pressures in the working fluid chambers A 1 , R 1 , and thereby cause fluctuations in hydraulic pressures in first pressure-receiving chamber  55  and second pressure-receiving chamber  59 , even when lock mechanism  5  is not operated. In order to solve this problem, in the present embodiment, sealing member  502  is fixed in slide hole  501 , and lock piston  51  is slidably mounted in sealing member  502 . Sealing member  502  is formed of a material having a higher wear resistance than aluminum-based metal materials, specifically, formed of an iron-based metal material. Namely, sealing member  502  having a higher wear resistance than slide hole  501  is in sliding contact with lock piston  51 . This feature serves to suppress wear of the cylinder (slide hole  501 ) which may be caused by forward and backward movement of lock piston  51  without sealing member  502 . Sealing member  502  is provided separately from vane rotor  4 . This feature is advantageous in enhancing the forming accuracy of the sliding surface of the cylinder, because it is possible to select a material that is highly desirable for sealing member  502  constituting the sliding surface. Sealing member  502  may be formed small, if sealing member  502  remains in contact with lock piston  51 . If lock piston  51  moves in the entire range of slide hole  501 , the size of sealing member  502  in the longitudinal direction may be set equal to that of slide hole  501 . The cross-sectional shape (inside periphery, outside periphery) of sealing member  502  may be other than a circular shape, for example, an elliptic shape or a rectangular shape. In such cases, the cross-sectional shape of slide hole  501  is conformed to the shape of sealing member  502 . 
     On the other hand, the feature that the sealing member  502  is formed of a material having a higher wear resistance and hardness than vane rotor  4  (slide hole  501 ) may cause a concern that during assembling operation, sealing member  502  is fixed in slide hole  501  under condition that the sealing member  502  is inclined with respect to the longitudinal axis of slide hole  501  (which is called galling). In such cases, lock piston  51 , which is slidably mounted in sealing member  502 , is also inclined with respect to the longitudinal axis of slide hole  501 , so that lock piston  51  may be in unbalanced contact with housing HSG (engaging recess  521 ). The unbalanced contact may cause friction, or cause a trouble that lock piston  51  tends to be undesirably easily moved out of engaging recess  521 , thus adversely affecting the operation of lock mechanism  5 . This tends to be more significant in the present embodiment where each of engaging portion  511  and engaging recess  521  is formed with an inclined surface to produce a wedging effect. This may cause a trouble that lock piston  51  tends to be undesirably more easily moved out of engaging recess  521 . In order to solve this problem, in the present embodiment, the surface of slide hole  501  is anodized so as to enhance the hardness. This feature serves to prevent the inclination of sealing member  502  when sealing member  502  is fixed in slide hole  501 , thereby suppressing the occurrence of unbalanced contact, keeping the operation of lock mechanism  5  normal, and keeping the controllability of valve timing control apparatus  1  normal. This advantageous effect is further significant, because each of engaging portion  511  and engaging recess  521  is formed with an inclined surface to produce a wedging effect. Incidentally, the anodic oxidation treatment may be applied only to a portion of the surface of slide hole  501  with which sealing member  502  is in fixed contact. The form of fixing the sealing member  502  to slide hole  501  may be easily implemented by press-fitting. However, the fixation based on press-fitting may cause a relatively high possibility that the sealing member  502  is set with inclination (galling of sealing member  502  is caused against vane rotor  4 ). In contrast, in the present embodiment, sealing member  502  is press-fitted in slide hole  501  that is anodized, namely, sealing member  502  is press-fitted in slide hole  501  whose surface is hardened by anodic oxidation treatment. This feature serves to suppress the inclination of sealing member  502 , while making it easy to mount and fix the sealing member  502  to slide hole  501 . In addition, in the present embodiment, sealing member  502  is formed of a material having a higher hardness or wear resistance than anodic oxidation coating, specifically, formed of an iron-based metal material. This feature serves to enhance the effect of suppressing wear of the cylinder (slide hole  501 ) as compared to cases where the anodized slide hole  501  is directly in sliding contact with lock piston  51 . The feature further serves to suppress the deformation of sealing member  502 , when sealing member  502  is press-fitted in the anodized slide hole  501 . 
     Moreover, the durability of lock mechanism  5  is further enhanced by suppressing the frequency of operation of lock piston  51 . Specifically, lock mechanism  5  is configured so that lock piston  51  operates against the biasing force of coil spring  53  in response to hydraulic pressures in first and second pressure-receiving chambers  55  and  59  which are supplied according to the operating state of the internal combustion engine. Specifically, first pressure-receiving chamber  55  is supplied with the hydraulic pressure in first retard chamber R 1 , whereas second pressure-receiving chamber  59  is supplied with the hydraulic pressure in first advance chamber A 1 . Accordingly, during operation of valve timing control apparatus  1 , lock piston  51  is maintained in its released state, constantly when at least one of the hydraulic pressures in first advance chamber A 1  and first retard chamber R 1  is supplied to lock mechanism  5 . This feature serves to eliminate the necessity of provision of an additional actuator for canceling the lock state, simplify the construction, maintain the reliability of the locking operation, lower the manufacturing cost, and prevent that the locking operation and the releasing operation are frequently repeated in response to movement of vane rotor  4  in the advance direction and the retard direction. This serves to reduce the frequency of operation of lock piston  51 , and thereby enhance the durability of valve timing control apparatus  1 . The construction may be modified so that first pressure-receiving chamber  55  is supplied with the hydraulic pressure from first advance chamber A 1 , and second pressure-receiving chamber  59  is supplied with the hydraulic pressure from first retard chamber R 1 . More specifically, slide hole  501  and sealing member  502  constitute a stepped cylinder having a larger-diameter portion and a smaller-diameter portion, wherein sealing member  502  is inserted and mounted in slide hole  501 , and wherein the size of sealing member  502  in the X-axis direction is smaller than slide hole  501 . In conformance with this shape, lock piston  51  has the form of a stepped pin having a larger-diameter portion (flange  513 ) and a smaller-diameter portion (sliding portion  512 , engaging portion  511 ). The smaller-diameter portion (sliding portion  512 ) of lock piston  51  is disposed in sliding contact with the inside periphery of sealing member  502 , whereas the larger-diameter portion (flange  513 ) of lock piston  51  is disposed in sliding contact with the inside periphery of slide hole  501 . This construction defines the first pressure-receiving chamber  55  in slide hole  501  between sealing member  502  and the larger-diameter portion (flange  513 ) of lock piston  51 . In this way, the provision of sealing member  502  makes it possible to easily define the first pressure-receiving chamber  55  and second pressure-receiving chamber  59  liquid-tightly separated from one another, and apply the lock piston  51  with hydraulic forces which are produced by first advance chamber A 1  and first retard chamber R 1  independently of one another. Alternatively, the shapes of the cylinder (slide hole  501 ) and lock piston  51 , and the arrangement of communication hole  56  and communication groove  57  may be modified so as to modify the shapes and positions of the first and second pressure-receiving chambers  55  and  59  as desired. For example, sealing member  502  may be inserted and mounted from either one of the longitudinal ends of slide hole  501 . The larger-diameter portion (part of flange  513 ) of lock piston  51  may be constructed to move out of vane rotor  4 , and move into engaging recess  521 , whereas the smaller-diameter portion of lock piston  51  constantly remains in slide hole  501 . In such cases, the larger-diameter portion of lock piston  51  serves as the distal end portion of lock piston  51 , whereas the smaller-diameter portion of lock piston  51  serves as the proximal end portion of lock piston  51 . In such cases, the biasing member (coil spring  53 ) may be arranged to bias the lock piston  51  in a direction from the smaller-diameter portion (proximal end) to the larger-diameter portion (distal end). 
     The feature that the slide hole  501  is formed with an anodic oxidation coating film serves to suppress wear of slide hole  501  that may be caused by sliding motion of flange  513  of lock piston  51 . Moreover, the many pores of the anodic oxidation coating film hold lubricating oil for a long period of time. The lubricating oil held at slide hole  501  serves to suppress wear of slide hole  501 , even when the internal combustion engine is restarted so that valve timing control apparatus  1  operates and the rear end corner of flange  513  of lock piston  51  slides on the inside peripheral surface of slide hole  501  after the condition that the internal combustion engine is at rest for a period from some days to some months so that the valve timing control apparatus  1  is also at rest. Namely, the effect of reducing wear of slide hole  501  is further enhanced by the function of holding lubricating oil which is based on the characteristic shape of the anodic oxide coating film. In this way, the anodic oxidation treatment serves to suppress the inclination of sealing member  502  (and the inclination of lock piston  51 ), and enhance the wear resistance and lubrication of the portion of slide hole  501  in sliding contact with flange  513  of lock piston  51 . Moreover, sealing member  502  is formed of a material having a higher wear resistance than anodic oxidation coating, and the clearance between the smaller-diameter portion (sliding portion  512 ) of lock piston  51  and the inside periphery of sealing member  502  is set smaller than the clearance between the larger-diameter portion (flange  513 ) of lock piston  51  and the inside periphery of slide hole  501 . Namely, the frequency or degree of contact between the smaller-diameter portion (sliding portion  512 ) of lock piston  51  and the inside periphery of sealing member  502  is relatively increased, in consideration that the wear resistance of the inside periphery of sealing member  502  is higher than the inside periphery of slide hole  501 . This feature is effective for suppressing wear of the portion of the inside periphery of the cylinder in sliding contact with lock piston  51 . Although sealing member  502  is provided separately from vane rotor  4  in the present embodiment, sealing member  502  may be formed integrally with vane rotor  4  into a stepped shape, and the entire inside peripheral surface of slide hole  501  may be applied with anodic oxidation treatment. This alternative construction also serves to enhance the wear resistance, while defining the first and second pressure-receiving chambers  55  and  59 . However, the construction according to the present embodiment that sealing member  502  is formed separately and mounted in slide hole  501  is advantageous in enhancing the wear resistance of the cylinder against the sliding motion of lock piston  51 , and simply defining the first and second pressure-receiving chambers  55  and  59 . 
     Lock piston  51  is formed of a material having a higher wear resistance than anodic oxidation coating, specifically, formed of an iron-based metal material. This feature serves to enhance the hardness of lock piston  51 , and suppress wear of lock piston  51  effectively. The construction that the slide hole  501  is formed with an anodic oxidation coating film, and sealing member  502  is formed of a material having a higher wear resistance than anodic oxidation coating, is also effective for suppressing wear of lock piston  51  that is in sliding contact with slide hole  501  and sealing member  502 . Sleeve  52  is formed of a material having a high wear resistance, such as an iron-based metal material. This feature is effective for enhancing the hardness of engaging recess  521  that is the inclined surface in sliding contact with engaging portion  511 , and suppressing wear of engaging recess  521 . Although sleeve  52  may be formed integrally with rear plate  9 , the feature according to the present embodiment that the sleeve  52  is provided separately from rear plate  9  makes it possible to adjust the shape, material, etc., of engaging recess  521  so as to allow the lock piston  51  to smoothly engage or disengage with engaging recess  521 , and serves to suppress wear and deformation of rear plate  9  resulting from engagement and disengagement of lock piston  51 . Namely, the feature according to the present embodiment is advantageous in making it possible to use a material particularly suited for high wear resistance, and enhancing the forming accuracy of the inclined surface of engaging recess  521 . 
     &lt;Durability of Apparatus Enhanced by Features of Stopper Mechanism&gt; Contact between the first stopper portions of the first stopper mechanism is frequently repeated, when vane rotor  4  is in the initial position where vane rotor  4 . Moreover, this contact is generally hard, because hydraulic control is at rest when the internal combustion engine is being stopped. Accordingly, the first stopper mechanism may deform due to frequency and hardness of contact in the first stopper mechanism, so that the limit of rotation of vane rotor  4 , i.e. the initial position of vane rotor  4  may change or deviate. In intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b,  the contact area of the first stopper mechanism SS 1  is set larger than the contact area of the second stopper mechanism SS 2  (SS 1 &gt;SS 2 ). This prevents the first stopper mechanism from deforming or deviating the position within which rotation of vane rotor  4  is restricted. The first stopper mechanism is constituted by the circumferentially-facing surface of first vane  41 . Accordingly, the root of first vane  41  has a longer circumferential length, which is advantageous because first vane  41  has a high rigidity, and has a strength enough to restrict and receive relative rotation of vane rotor  4 . On the other hand, radial projection  419  of the second stopper mechanism is formed at the root of first vane  41 , extending outwardly in the radial direction from rotor  40 . As compared to cases where the second stopper mechanism is constituted by the tip of first vane  41 , the bending moment or moment arm about the root of first vane  41  in the circumferential direction when the second stopper mechanism functions to restrict rotation of vane rotor  4 , is smaller so that the root of first vane  41  is generally subject to no excessive force. This is advantageous for enhancing the durability of first vane  41 . In this way, these features according to the present embodiment serve to enhance the rigidity of the first and second stopper mechanisms, suitably restrict the relative rotation, and thereby enhance the durability of valve timing control apparatus  1 . Incidentally, one or more combinations of contact portions of second and third vanes  42  and  43 , and first, second and third shoes  11 ,  12  and  13  may be modified to form first and second stopper mechanisms. In exhaust valve timing control apparatus  1   b,  the second stopper mechanism also serves to limit the amount of displacement (amount of compression) of biasing member  6  (coil springs  610 ,  620  and  630 ) to a predetermined amount. This prevents plastic deformation of biasing member  6  (coil springs  610 ,  620  and  630 ), and prevents the biasing force of biasing member  6  from changing in an irreversible form. Radial projection  429  of second vane  42  and the tip of third shoe  13  serve as a backup stopper mechanism instead of the second stopper mechanism, even when errors occur during manufacturing and assembling operations, or when the stopper portions of the second stopper mechanism are worn. This improves the reliability and accuracy of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b.  Especially in exhaust valve timing control apparatus  1   b,  this is effective for securely preventing the biasing member  6  from plastically deforming. Coil springs  610  and  630  are arranged outside of radial projections  419  and  429  of first and second vanes  41  and  42 , respectively, so that radial projections  419  and  429 , which constitute the second stopper mechanism and backup stopper mechanism respectively, guide the coil springs  610  and  630  of biasing member  6 . This ensures normal operations of biasing member  6  and exhaust valve timing control apparatus  1   b.    
     &lt;Sealing Performance Enhanced by Features of Forming&gt; In general, a device including a housing formed with a pulley to which torque is transmitted through a timing belt that is formed of rubber or synthetic resin and is wound around the pulley, is subject to a problem that the timing belt may be degraded by adhesion of working fluid exiting out of the housing. The housing has to be suitably sealed to solve the problem. This is true for valve timing control apparatus  1 . The feature according to the present embodiment that the housing body  10  is formed by extruding an aluminum-based metal material, serves to prevent working fluid from seeping and leaking through the inside of housing body  10  and arriving at the outside periphery (pulley  100 ) of housing body  10 , as compared to cases where housing body  10  is formed by another processing, for example, by sintering an aluminum-based metal material. The feature that the sealing plates (cap  7 , front plate  8 , and rear plate  9 ) are formed by forging an iron-based metal material, serves to prevent working fluid from seeping and leaking through the inside of the sealing plates (cap  7 , front plate  8 , and rear plate  9 ), as compared to cases where the sealing plates (cap  7 , front plate  8 , and rear plate  9 ) are formed by another processing, for example, by sintering an iron-based metal material. 
     &lt;Sealing Performance Enhanced by Features of Sealing Members&gt; The feature that the sealing rings S 1 , S 2 , S 3  and S 4  are provided in housing HSG serves to prevent working fluid from leaking through clearances, and thus ensure liquid-tightness of housing HSG. Each sealing ring may be replaced with a sealing compound. For example, sealing rings S 2  may be replaced with an adhesive that serves also as a sealing compound, which serves to strengthen the fixing force of each bolt b 1 , b 2  or b 3 . However, the construction according to the present embodiment is advantageous in simply implementing the sealing function. In the present embodiment, with regard to sealing ring S 1  between housing body  10  and rear plate  9 , under the condition that the sealing ring S 1  is mounted in sealing ring groove  906  of rear plate  9 , the inside peripheral surface  103  of fitting recess  101  of housing body  10  is pressed onto sealing ring S 1 , so that sealing ring S 1  is compressed. This construction provides a function of sealing, so as to prevent working fluid from leaking through the boundary between rear plate  9  and housing body  10 , and thus seal the working fluid chambers. With regard to sealing rings S 2 , under the condition that sealing rings S 2  are mounted in annular sealing ring grooves  907 ,  908  and  909  around female thread portions  901 ,  902  and  903 , the X-axis negative side end surface  102  of housing body  10  (first, second and third shoes  11 ,  12  and  13 ) is pressed onto sealing rings S 2 , so that sealing rings S 2  are compressed. This configuration provides a function of sealing, so as to prevent working fluid from leaking through the boundary between rear plate  9  and housing body  10 , and the bolt holes of female thread portions  901 ,  902  and  903 , and thus seal the working fluid chambers. With regard to sealing ring S 3  between housing body  10  and front plate  8 , under the condition that sealing ring S 3  is mounted in annular sealing ring groove  89  of front plate  8 , the X-axis positive side end surface  105  of housing body  10  is pressed onto sealing ring S 3 , so that sealing ring S 3  is compressed. This construction provides a function of sealing, so as to prevent working fluid from leaking through the boundary between front plate  8  and housing body  10 , and thus seal the working fluid chambers. The feature that the sealing ring S 3  and annular sealing ring groove  89  have the form of a three-leaved clover, passing inside of bolt holes  83 ,  84  and  85 , so that the bolt holes  83 ,  84  and  85  are hydraulically separated from the inside of housing HSG, is effective for reducing the number of parts, and improving the facility of assembling, because no individual sealing members are required for bolt holes  83 ,  84  and  85 . Incidentally, sealing ring S 3  may be replaced with a plurality of sealing rings, i.e. a sealing ring that seals the inside portion of front plate  8  and passes outside of bolt holes  83 ,  84  and  85 , and sealing rings each of which surrounds the bolt hole  83 ,  84  or  85  for sealing. With regard to sealing ring S 4 , under the condition that sealing ring S 4  is mounted in annular sealing ring groove  821  of female thread portion  82  of front plate  8 , the X-axis negative side end surface of flange  72  of cap  7  is pressed onto sealing ring S 4 , so that sealing ring S 4  is compressed. This construction provides a function of sealing, so as to prevent working fluid from leaking through the boundary between cap  7  and front plate  8 , and thus sealing the back pressure relief section. Incidentally, sealing ring grooves are optional, and the sealing rings may be mounted for sealing with no annular sealing ring groove formed. Housing body  10 , front plate  8 , and rear plate  9  are fixed together with the plurality of bolts b 1 , b 2  and b 3  which extend in the axial direction of housing HSG. Each bolt b 1 , b 2  or b 3  formed with the male thread is screwed in the female thread formed in the inside periphery of female thread portion  901 ,  902  or  903  of rear plate  9 . The axial force of each bolt b 1 , b 2  or b 3  presses the X-axis negative side end surface (bottom surface  102 ) of housing body  10  (first, second and third shoes  11 ,  12  and  13 ) on sealing rings S 2  around female thread portion  901 ,  902  or  903 , thereby compresses sealing rings S 2  in the X-axis direction. Similarly, the axial force of each bolt b 1 , b 2  or b 3  presses the X-axis positive side end surface  105  of housing body  10  (first, second and third shoes  11 ,  12  and  13 ) on sealing ring S 3  around bolt holes  83 ,  84  and  85 , thereby compresses sealing ring S 3  in the X-axis direction. These features further enhance the sealing of housing HSG. The reaction force of sealing rings S 2  and S 3  serves to strengthen the fixation of bolt b 1 , b 2  and b 3 , and prevent bolts b 1 , b 2  and b 3  from being released. Each female thread portion  901 ,  902  or  903  may be in the form of a recess. Although rear plate  9  is formed with female threads in the present embodiment, this construction may be modified so that each bolt b 1 , b 2  or b 3  extends through and projects from the rear plate  9 , and the projected portion of bolt b 1 , b 2  or b 3  is engaged with a nut. The female threads may be formed in front plate  8  not in rear plate  9 , wherein each bolt b 1 , b 2  or b 3  is inserted from the X-axis negative side to fix the front plate  8 , rear plate  9 , and housing body  10  together. The feature that each sealing ring S 1 , S 2 , S 3  or S 4  is an O-ring having a circular cross-section, makes it easy to mount each sealing ring S 1 , S 2 , S 3  or S 4  in sealing ring groove  906 , etc. When compressed between two contact surfaces, each sealing ring S 1 , S 2 , S 3  or S 4  is brought into intimate contact with the contact surfaces, thereby enhancing the sealing performance. For sealing, it is sufficient that the surfaces of housing body  10  and sealing plate  8  or  9  facing one another abut on the sealing rings, and it is optional that the surfaces of housing body  10  and sealing plate  8  or  9  are in direct contact with one another. Specifically, it is sufficient that the X-axis negative side surface of front plate  8  (i.e. the bottom of sealing ring groove  89 ) abuts on sealing ring S 3 , and the X-axis positive side surface  105  of housing body  10  abuts on sealing ring S 3 , and it is optional that the X-axis negative side surface of front plate  8  and the X-axis positive side surface  105  of housing body  10  abut on one another. Similarly, it is sufficient that the X-axis positive side surface of rear plate  9  (i.e. the bottom of each annular sealing ring groove  907 ,  908  or  909 ) abuts on sealing ring S 2 , and the X-axis negative side surface  102  of housing body  10  abuts on sealing rings S 2 , and it is optional that the X-axis positive side surface of rear plate  9  and the X-axis negative side surface  102  of housing body  10  abut on one another. Further, it is sufficient that the bottom of sealing ring groove  906  abuts on sealing ring S 1 , and the inside peripheral surface  103  of fitting recess  101  of housing body  10  abuts on sealing ring S 1 , and it is optional that the bottom of sealing ring groove  906  and the inside peripheral surface  103  of fitting recess  101  of housing body  10  abut on one another. 
     &lt;Sealing Performance Enhanced by Portion Applied with No Anodic Oxidation Coating&gt; If the surfaces  102 ,  103  and  105  of housing body  10  on which sealing rings S 1 , S 2  and S 3  abut are formed with an anodic oxidation coating film, the valve timing control apparatus  1  may be subject to a problem that the sealing rings S 1 , S 2  and S 3  are not completely in intimate contact with the surfaces  102 ,  103  and  105 , which adversely affects the sealing performance of housing body  10  at the surfaces  102 ,  103  and  105 . This is because an anodic oxidation coating film is an oxidation coating film, having a relatively high surface roughness. Namely, that is because an anodic oxidation coating film is a porous coating film provided with a lot of pores at the surface, unless full pore-sealing treatment is applied after anodic oxidation treatment. In contrast, in the present embodiment, the axial end surfaces of housing body  10  to which the sealing plates  8  and  9  are fixed, namely, the surfaces  102 ,  103  and  105  of housing body  10  to which the sealing rings S 1 , S 2  and S 3  are mounted, are formed with no anodic oxidation coating film. This serves to allow intimate contact between sealing rings S 1 , S 2  and S 3  and surfaces  102 ,  103  and  105  with no clearance therebetween, and thereby enhance the sealing performance of sealing rings S 1 , S 2  and S 3 . The surfaces  102 ,  103  and  105  of housing body  10  are sealed by the sealing plates  8  and  9 , and in sliding contact with no other member. Accordingly, it is unnecessary to enhance the wear resistance of surfaces  102 ,  103  and  105 . The feature that the surface  102 ,  103  or  105  is provided with no anodic oxidation coating film and with the base layer of aluminum-based metal material exposed, is effective for eliminating the necessity of further treatment or processing for surfaces  102 ,  103  and  105 , and thereby reducing the manufacturing cost, while maintaining the sealing performance of housing body  10 . Specifically, the surface of housing body  10  abutting on sealing ring S 3  is a cut surface (X-axis positive side axial end surface  105 ) that is obtained by the cutting-off operation, and the surfaces of housing body  10  abutting on sealing rings S 1  and S 2  are surfaces (bottom surface  102  and inside peripheral surface  103  of fitting recess  101  at the X-axis negative side of housing body  10 ) that are obtained by the carving operation of carving the axial end surface of housing body  10 . Since the cutting-off operation and the carving operation are performed after the coating operation, the surfaces  102 ,  103  and  105  of housing body  10  are formed with no anodic oxidation coating film, so that the base layer is exposed on the surfaces  102 ,  103  and  105 . The surfaces  102 ,  103  and  105  of housing body  10  are thus adapted to be in intimate contact with sealing rings S 1 , S 2  and S 3 . The surfaces  102 ,  103  and  105  of housing body  10 , on which the base layer is exposed, may be formed with a coating film other than anodic oxidation coating films, which coating film does not adversely affect the sealing performance, although such construction increases the manufacturing cost due to additional treatment. Even in cases where the surfaces  102 ,  103  and  105  of housing body  10  to which sealing rings S 1 , S 2  and S 3  are mounted are formed with an anodic oxidation coating film, the sealing may be maintained by applying pore-sealing treatment so as to seal the openings of the pores, and thereby reduce the surface roughness. Such construction is disadvantageous in that the additional treatment causes an increase in the manufacturing cost. Moreover, if the pore-sealing treatment is undesirably applied to other portions, the required characteristics of the other portions may be adversely affected. In contrast, the feature according to the present embodiment that at least the open axial ends of housing body  10  are applied with no pore-sealing treatment, is advantageous in reducing the manufacturing cost, while maintaining the sealing performance. 
     It is sufficient that the open axial ends of housing body  10  abut on the sealing rings, and it is optional that the open axial ends of housing body  10  directly abut on the sealing plates  8  and  9 , as discussed above. However, the optional feature is advantageous as follows. Each surface  102  or  105  of housing body  10  is formed with no anodic oxidation coating film, and thereby not hardened, whereas each sealing plate  8  or  9  is formed of a harder material (iron-based metal material) than housing body  10  (aluminum-based metal material). When the sealing plate  8  or  9  are fixed to housing body  10 , the intimateness of contact between housing body  10  and sealing plate  8  or  9  can be enhanced by screwing the bolts b 1 , b 2  and b 3  tightly so as to bring the housing body  10  and sealing plate  8  or  9  into direct contact with one another. Specifically, the axial end surfaces of the sealing plates (the X-axis negative side surface of front plate  8 , and the X-axis positive side surface of rear plate  9 ) may be formed with slight roughness (with fine projections and depressions) by the manufacturing process, but the projections and depressions at the relatively hard surface are pressed on the relatively soft surface  102  or  105  of housing body  10 , so that the relatively soft surface  102  or  105  deforms slightly in conformance with the shape of the projections and recesses. This enhances the intimateness of contact between housing body  10  and sealing plate  8  or  9 , and thereby further enhances the sealing performance. 
     &lt;Sealing Performance Enhanced by Sealing at Journal Portion of Housing&gt; The oil seal OS provided at the outside periphery of cylindrical portion  91  of rear plate  9  of housing HSG serves to seal the clearance between the cylinder head and the outside periphery of the cylindrical portion  91 . This serves to prevent that working fluid leaking out to the cylinder head side through the clearance CL shown in  FIG. 3  between the inside periphery of cylindrical portion  91  and the outside periphery of camshaft  3   a  or  3   b,  or working fluid in the internal combustion engine, leaks through the clearance at the outside periphery of cylindrical portion  91  into contact with timing belt  1010  or other equipment. The feature that the cylindrical portion  91  of rear plate  9  is formed of an iron-based metal material and thereby has a higher wear resistance, is effective for suppressing wear of the outside peripheral surface of cylindrical portion  91  resulting from sliding contact with oil seal OS, and thereby reliably sealing the outside periphery of cylindrical portion  91 . 
     &lt;Sealing Performance Enhanced by Arrangement of Back Pressure Relief Section&gt; In general, in a valve timing control apparatus in which an engaging member in a housing functions to lock the valve timing at engine start, the engaging member can be smoothly released from its engaged state by suitably lowering the back pressure of the engaging member. If the back pressure is lowered by relieving the back pressure directly to the outside of the housing, then working fluid may get in touch with a timing belt that drives the valve timing control apparatus. In order to solve this problem, the back pressure relief section is provided, which relieves the pressure in back pressure chamber  50  into the internal space of the internal combustion engine, and keeps the pressure in back pressure chamber  50  low, while maintaining the sealing performance of housing HSG. The fluid passage for reliving the back pressure of back pressure chamber  50  communicates with the inside of the internal combustion engine, but has no intermediate point that communicates directly with the outside of housing HSG. The back pressure relief section serves to discharge working fluid of back pressure chamber  50  to the internal space of the internal combustion engine, so as to prevent the timing belt  1010  from being degraded by oil, and thereby enhance the durability of timing belt  1010 . 
     &lt;Apparatus Made Compact in Radial Direction by Features of Pulley&gt; The outside periphery of housing body  10  is formed integrally with pulley  100 . This feature makes it possible to reduce the diameter of valve timing control apparatus  1 , as compared to cases in which a pulley is provided separately from a housing body. The construction that the pulley  100  is formed over the entire axial length of the outside periphery of housing body  10 , makes it possible to provide the teeth of pulley  100  with a width enough to engage with timing belt  1010 , even if the width of timing belt  1010  is required to be above a predetermined lower limit. Namely, even when the axial length of housing HSG is set as small as the width of timing belt  1010  where rear plate  9  is fixedly inserted in fitting recess  101  of housing body  10 , it is possible to provide the teeth of pulley  100  with a width enough to engage with timing belt  1010  and transmit a torque to timing belt  1010   
     &lt;Apparatus Made Compact in Axial Direction by Formation of Fitting Recess in Housing Body&gt; In valve timing control apparatus  1 , the axial ends of housing body  10  are closed and sealed by front plate  8  and rear plate  9  respectively. The construction that the rear plate  9  is fixedly inserted in fitting recess  101  of housing body  10  which is formed at one axial end of housing body  10 , makes it possible to reduce the axial size of valve timing control apparatus  1 , as compared to cases where front plate  8  and rear plate  9  are simply fixed to the axial end surfaces  104  and  105  of housing body  10  respectively. The construction that the entire axial length of the outside periphery of rear plate  9  in the X-axis direction, i.e. the entire axial length of plate body  90  in the X-axis direction, is fixedly inserted in fitting recess  101 , is further advantageous in minimizing the axial size of valve timing control apparatus  1 . Rear plate  9  is formed with engaging recess  521  (or recess  900  for fixing the sleeve  52 ) which extends in the X-axis direction, where engaging recess  521  engages with lock piston  51  which is mounted to move in and out from vane rotor  4  in the X-axis direction. Accordingly, the axial length of rear plate  9  is set larger than that of front plate  8 . If the thicker rear plate  9  is simply fixed to the axial end surface of housing body  10 , the axial length of the entire valve timing control apparatus  1 . According to the present embodiment, the construction that the fitting recess  101  is formed in one axial end of housing body  10 , and rear plate  9  (not front plate  8 ) is fixedly inserted in fitting recess  101 , makes it possible to efficiently reduce the axial size of valve timing control apparatus  1 . This enhances the flexibility of layout of an engine room to which valve timing control apparatus  1  is mounted. Front plate  8 , rear plate  9  and housing body  10  are fixed by the plurality of bolts b 1 , b 2  and b 3 . The female thread hole into which the male thread of each of bolts b 1 , b 2  and b 3  is screwed is required to have a some length. The construction according to the present embodiment that all of engaging recess  521  and the female thread holes are formed in rear plate  9 , is further advantageous in minimizing the axial size of valve timing control apparatus  1 . Front plate  8  may be formed thinner than rear plate  9 , because front plate  8  is formed with no female thread hole, etc. Accordingly, even when front plate  8  is simply fixed to the axial end surface  105  of housing body  10 , the axial length of valve timing control apparatus  1  is little increased. On the other hand, the construction that the female thread holes are formed in rear plate  9  which is formed thicker because rear plate  9  is formed with engaging recess  521 , and the thicker rear plate  9  is fixedly inserted in fitting recess  101 , is advantageous in minimizing the axial size of valve timing control apparatus  1 . Engaging recess  521  may be formed in front plate  8 , not in rear plate  9 . Moreover, housing body  10  may be formed with another fitting recess to which front plate  8  is fixedly inserted. However, in the present embodiment, front plate  8  is simply fixed to the axial side surface  105  of housing body  10 , in order to provide lock piston  51  with a required range of movement in the axial direction or provide slide hole  501  of vane rotor  4  with a required length in the X-axis direction. 
     &lt;Apparatus Made Compact in Radial Direction by Features of Sealing Structure&gt; It is generally difficult to provide a space for a sealing member, in cases where the boundary between the axial end surfaces of housing body  10  and rear plate  9  is sealed, i.e. the boundary between the bottom surface  102  of fitting recess  101  and the X-axis negative side surface of rear plate  9  is sealed. Specifically, as shown in  FIG. 6C , the radial length of bottom surface  102  of fitting recess  101  except the portions where first, second and third shoes  11 ,  12  and  13  are formed, (R−Ri), is short to form a sealing groove where a sealing member is mounted. Accordingly, when the boundary (bottom surface  102  of fitting recess  101 ) where the axial end surfaces are in contact with each other is provided with an adequate space where a sealing member is mounted or a sealing groove is formed, the diameter of housing body  10  in the radial direction is increased. On the other hand, the length of fitting recess  101  in the X-axis direction and the length of rear plate  9  in the X-axis direction are relatively large so that a sealing member can be mounted or a sealing groove can be formed. Accordingly, the problem described above can be solved by providing a sealing member between the inside periphery of fitting recess  101  and the outside periphery of rear plate  9 . However, the radial length (Ro−R) of housing body  10  is small to form a sealing groove in the inside peripheral surface of housing body  10  (inside peripheral surface  103  of fitting recess  101 ). Accordingly, if the sealing groove is formed in the inside peripheral surface of housing body  10  (inside peripheral surface  103  of fitting recess  101 ), the radial size of housing body  10  must be increased so as to increase the radial length (Ro−R). In order to solve this problem, the outside periphery of rear plate  9  is formed with sealing ring groove  906  to which sealing ring S 1  is mounted, so as to seal the boundary between fitting recess  101  and rear plate  9 . This sealing structure makes it possible to reduce the radial length (Ro−R), i.e. the radial thickness of housing body  10 , and thereby minimize increase in the radial size of valve timing control apparatus  1 , while minimizing the axial size of valve timing control apparatus  1  by the provision of fitting recess  101 . On the other hand, the X-axis negative side surfaces of first, second and third shoes  11 ,  12  and  13  have adequate spaces where sealing members are mounted around bolt holes  110 ,  120  and  130 . Accordingly, rear plate  9  is formed with annular sealing ring grooves  907 ,  908  and  909  around female thread portions  901 ,  902  and  903 , where annular sealing ring grooves  907 ,  908  and  909  faces bolt holes  110 ,  120  and  130 , and sealing rings S 2  are mounted in annular sealing ring grooves  907 ,  908  and  909 . It is possible as an alternative to prevent working fluid from leaking through the bolt holes of female thread portions  901 ,  902  and  903  by a construction that the bolt holes of female thread portions  901 ,  902  and  903  are formed with bottoms, without passing through the rear plate  9 . In this case, however, the provision of the bottoms may cause an increase in the axial length of rear plate  9 , because the lengths of female thread portions  901 ,  902  and  903  are increased to maintain the axial lengths of the female threads for bolts b 1 , b 2  and b 3 . In contrast, according to the present embodiment, the construction that the bolt holes of female thread portions  901 ,  902  and  903  are formed to extend through the rear plate  9  with no bottoms, is effective for reducing the axial length of rear plate  9 . Incidentally, the construction that the recess  900  of rear plate  9  and pin hole  904  have bottoms, causes no increase in the axial length of rear plate  9 , because the length of recess  900  in the X-axis direction is only required to allow engagement of lock piston  51 , and the length of pin hole  904  in the X-axis direction is only required to allow fixation of the positioning pin  905 . This feature is effective for preventing working fluid from leaking from housing HSG to outside without sealing for recess  900  and pin hole  904 . On the other hand, the boundary between front plate  8  and housing body  10  includes a space having an adequate radial size where a sealing member can be mounted, because the X-axis positive side surface of housing body  10  is formed with no fitting recess. Specifically, as shown in  FIG. 6A , the radial length Ro−Ri of housing body  10  is large enough to mount a sealing member or form a sealing groove. Accordingly, sealing ring S 3  is arranged between the contact axial end surfaces of housing body  10  and front plate  8 , i.e. between the X-axis negative side surface  105  of housing body  10  and the X-axis positive side surface of front plate  8 . For mounting the sealing ring S 3 , front plate  8  is formed with annular sealing ring groove  89 . The sealing groove may be formed in housing body  10 , not in front plate  8 . However, housing body  10  has an inside space for accommodating the phase change mechanism, and thereby has only a small space (area or thickness) at the axial end which can be formed with a sealing groove, without adversely affecting the strength of housing body  10 . On the other hand, sealing plate  8  or  9  is subject to no such requirement, so that it is easy to form the sealing plate  8  or  9  with a sealing groove. The feature according to the present embodiment that the annular sealing ring grooves  907 ,  908 ,  909  and  89  are formed in sealing plates  8  and  9 , serves to reduce the manufacturing cost of valve timing control apparatus  1 . If sealing plates  8  and  9  are formed integrally with sealing grooves by casting, the manufacturing cost is further lowered. 
     &lt;Apparatus Made Compact by Arrangement of Back Pressure Relief Section&gt; Back pressure chamber  50  is formed at the X-axis positive side of slide hole  501  of vane rotor  4 , wherein the tip (or engaging portion  511 ) of lock piston  51  is arranged to move and project in the X-axis negative direction from vane rotor  4 . On the other hand, the internal combustion engine is located on the X-axis negative side of vane rotor  4  and rear plate  9 . Accordingly, in order to relieve the internal pressure (oil or air) of back pressure chamber  50  while ensuring the sealing performance of housing HSG, the back pressure relief section needs to include a fluid passage (back pressure hole  407 ) that passes through the vane rotor  4  in housing HSG from the X-axis positive side axial end to the X-axis negative side axial end. In valve timing control apparatus  1 , the fixing portions (bolt holes  403 ,  404  and  405 ) are formed in rotor  40  and arranged and spaced from one another in the circumferential direction, which fixing portions serve to fix the vane rotor  4  to camshaft  3   a  or  3   b.  Accordingly, the fluid passage (back pressure hole  407 ) of the back pressure relief section needs to be arranged with no interference with the fixing portions (bolt holes  403 ,  404  and  405 ). Moreover, camshaft bolts  33 ,  34  and  35 , which are inserted in bolt holes  403 ,  404  and  405 , respectively, have heads  331 ,  341  and  351  (including the washers  332 ,  342  and  352 ) located at the X-axis positive side surface of vane rotor  4 . Accordingly, in cases where the fluid passage (back pressure hole  407 ) is formed to have an opening at the X-axis positive side surface of vane rotor  4 , the fluid passage of the back pressure relief section needs to be arranged with no interference with the heads  331 ,  341  and  351 . In order to satisfy these requirements, it may be conceived that the back pressure hole  407  is located in an annular outside space surrounding the fixing portions (i.e. in a space farther from the axis of rotation O than the farthest point of the inside periphery of each bolt hole  403 ,  404  or  405 , or in a space outside a circle containing and circumscribing the bolt holes  403 ,  404  and  405  as viewed in the X-axis direction), specifically, in an annular outside space surrounding the heads  331 ,  341  and  351  of camshaft bolts  33 ,  34  and  35  (i.e. in a space outside a circle circumscribing the heads  331 ,  341  and  351 ). This construction tends to result in an increase in the radial size of rotor  40 . In contrast, in the present embodiment, back pressure hole  407  is located radially inside of or closer to the axis of rotation O than the fixing portions (bolt holes  403 ,  404  and  405 ), or in the space inside the circle circumscribing the bolt holes  403 ,  404  and  405 , and specifically at the axis of rotation of rotor  40  (at the axis of rotation O). Specifically, since the fixing portions are implemented by bolt holes  403 ,  404  and  405 , camshaft bolts  33 ,  34  and  35  have heads  331 ,  341  and  351 , and back pressure hole  407  has an opening at the X-axis positive side of rotor  40  in the present embodiment, back pressure hole  407  needs to be located with no interference with heads  331 ,  341  and  351 . The construction according to the present embodiment makes it possible to make the valve timing control apparatus  1  compact, because no space for back pressure hole  407  is needed at the outside space of rotor  40 . In other words, the construction according to the present embodiment that the plurality of bolt holes  403 ,  404  and  405  are formed for insertion of camshaft bolts  33 ,  34  and  35 , provides rotor  40  and camshaft  3   a  or  3   b  with a space for back pressure hole  407  at the inside space (including the axis of rotation O) surrounded by the bolt holes  403 ,  404  and  405 , in contrast to cases where a single bolt hole is formed at the axis of rotation. Although back pressure hole  407  is formed in rotor  40  so as to extend through the rotor  40  in the X-axis direction, and located to face the first back pressure passage  31  of camshaft  3   a  or  3   b  in the X-axis direction in the present embodiment, this construction may be modified so that the back pressure hole  407  is inclined with respect to the X-axis, and the opening of back pressure hole  407  at the X-axis negative side of rotor  40  faces the first back pressure passage  31  of camshaft  3   a  or  3   b  in the X-axis direction. Although the second back pressure passage communicating the back pressure chamber  50  and back pressure hole  407  with one another is composed of radial groove  58  and circular recess  406  in the present embodiment, this construction may be modified so that the second back pressure passage is constituted by a hole extending in vane rotor  4  with inclination. In the modification, back pressure hole  407  may be constructed to have no opening facing the circular recess  406  at the X-axis positive side of rotor  40 . The construction according to the present embodiment may be modified so that the X-axis negative side opening of back pressure hole  407  is located distant from the first back pressure passage  31 , and one of the X-axis negative side end surface of rotor  40  and the X-axis positive side end surface of camshaft  3   a  or  3   b  is formed with a portion such as a groove or recess for communicating the X-axis negative side opening of back pressure hole  407  and the first back pressure passage  31  with one another. This modification makes it possible to locate the back pressure hole  407  independently of the position of first back pressure passage  31 , and thereby enhances the flexibility of design. The construction according to the present embodiment that the back pressure hole  407  is formed to extend in the X-axis direction, is advantageous because it is unnecessary to intricately form an inclined hole constituting the back pressure hole  407 . The construction that the X-axis negative side opening of back pressure hole  407  is located to face the first back pressure passage  31 , is advantageous in the facility of forming and the manufacturing cost, because it is unnecessary to form a groove or recess connecting the back pressure hole  407  and first back pressure passage  31  to one another. However, the construction that the X-axis negative side opening of back pressure hole  407  is located to face the first back pressure passage  31 , is subject to a requirement that back pressure hole  407  must be located in consideration of a positional relationship with the fluid passages formed in camshaft  3   a  or  3   b  other than first back pressure passage  31 . Namely, the first back pressure passage  31 , which is formed in camshaft  3   a  or  3   b  to extend in the X-axis direction, is required not to overlap with first fluid passages  202  and  212 , and second fluid passages  201 ,  203 ,  211  and  213  (see  FIG. 3 ) as viewed in the X-axis direction. Accordingly, the X-axis negative side opening of back pressure hole  407  facing the first back pressure passage  31  in the X-axis direction is also required to be located to satisfy the same requirement. For example, if the arrangement that the X-axis negative side opening of back pressure hole  407  is located in the inside space surrounded by bolt holes  403 ,  404  and  405 , is implemented by a construction that that the X-axis negative side opening of back pressure hole  407  is located between bolt holes  404  and  405 , or between bolt holes  405  and  403 , then it is possible that the first back pressure passage  31  facing the X-axis negative side opening of back pressure hole  407  interferes with first fluid passages  202  and  212 , and second fluid passages  201 ,  203 ,  211  and  213  in camshaft  3   a  or  3   b.  In this viewpoint, the construction that the back pressure hole  407  is located between bolt holes  403  and  404  where first fluid passages  202  and  212 , and second fluid passages  201 ,  203 ,  211  and  213  are not located, is advantageous. In the present embodiment, first fluid passages  202  and  212  are the closest to the axis of rotation O among all the fluid passages formed in camshaft  3   a  or  3   b,  wherein the central axes of first fluid passages  202  and  212 , and the central axes of bolt holes  403 ,  404  and  405  are arranged substantially on the same circle having a center at the axis of rotation O. Accordingly, the construction that the back pressure hole  407  is located in the space that is inside the above circle, and excludes the space of first fluid passages  202  and  212 , and bolt holes  403 ,  404  and  405 , makes it possible to avoid interference between back pressure hole  407  and the fluid passages of camshaft  3   a  or  3   b.  Specifically, if the X-axis negative side opening of back pressure hole  407  is located radially inside of or closer to the axis of rotation O than first fluid passages  202  and  212 , or in the space inside the circle containing and circumscribing the first fluid passages  202  and  212  about the axis of rotation O as viewed in the X-axis direction, then it is unnecessary to adjust the arrangement of fluid passages  202 , etc. of camshaft  3   a  or  3   b,  wherein the strength of fixation is ensured by the plurality of fixing portions, while expansion of the radial size of rotor  40  is suppressed. In other words, in cases where three or more fixing portions (bolt holes) are arranged and spaced from one another in the circumferential direction so that three or more intermediate spaces are defined between the fixing portions as in the present embodiment, a pair of advance-side and retard-side fluid passages formed in camshaft  3   a  or  3   b  are located in two of the intermediate spaces so that one intermediate space remains in which no fluid passage is formed. The remaining intermediate space is available for provision of back pressure hole  407  (and first back pressure passage  31 ). For example, back pressure hole  407  (and first back pressure passage  31 ) may be located between bolt holes  403  and  404  in the circumferential direction, which is advantageous in reducing the distance between back pressure hole  407  and back pressure chamber  50 . For example, circular recess  406  may be omitted, wherein radial groove  58  is extended inwardly in the radial direction and connected to both of back pressure hole  407  and back pressure chamber  50 . More specifically, in the present embodiment, back pressure hole  407  is located at the axis of rotation of rotor  40 . This feature serves to enhance the balance of vane rotor  4  around the axis of rotation O. This feature further makes it possible to ensure the radial thickness of rotor  40 , and thereby enhance the strength of rotor  40  formed with bolt holes  403 ,  404  and  405 , because the distance between back pressure hole  407  and the outside periphery of rotor  40  is constant as followed along the outside periphery of rotor  40 . The feature still further makes it possible to easily arrange the bolt holes  403 ,  404  and  405  evenly spaced in the circumferential direction around the axis of rotation, and thereby further enhance the balance of vane rotor  4  around the axis of rotation. 
     It is advantageous that the diameter of back pressure hole  407  is set as small as possible, because the small diameter of back pressure hole  407  makes it possible to enhance the flexibility of layout of back pressure hole  407 , and make rotor  40  compact. However, if the size of back pressure hole  407  in the X-axis direction in rotor  40  is large, the facility of forming is lowed because it is generally difficult to form a narrow long hole. In the present embodiment, rotor  40  is formed with circular recess  406  and camshaft insertion hole  402  having a bottom, wherein back pressure hole  407  extends through the rotor  40 , and has an opening at the bottom of each of circular recess  406  and camshaft insertion hole  402 . Namely, the length of back pressure hole  407  in the X-axis direction is reduced by the depth of camshaft insertion hole  402  and the depth of circular recess  406 , which makes it easy to form the rotor  40  with back pressure hole  407 . In this way, the construction according to the present embodiment is advantageous in enhancing the facility of forming of back pressure hole  407 , and makes rotor  40  compact by forming the back pressure hole  407  with a relatively small diameter (smaller than the diameter of first back pressure passage  31  of camshaft  3   a  or  3   b ). 
     The feature that the first back pressure passage  31  communicating with the oil-lubricated space of the internal combustion engine is formed in camshaft  3   a  or  3   b,  makes it possible to make valve timing control apparatus  1  compact, as compared to cases where a back pressure passage is provided separately and arranged outside (for example, at the outside periphery) of camshaft  3   a  or  3   b.  This feature serves to eliminate the necessity of increasing the diameter of the portion of valve timing control apparatus  1  that is connected to the internal combustion engine, i.e. the diameter of the cylindrical portion  91  provided with oil seal OS that is disposed between cylindrical portion  91  and the cylinder head. Moreover, it is possible to avoid interference between first back pressure passage  31  and groove  204  or  214 . Specifically, first back pressure passage  31  is formed at the axis of rotation (axis of rotation O) of camshaft  3   a  or  3   b  so to face the X-axis negative side opening of back pressure hole  407 . This feature serves to maintain the balance of camshaft  3   a  or  3   b  about the axis of rotation, and makes it possible to easily connect the first back pressure passage  31  and the fluid passages that are formed in camshaft  3   a  or  3   b  for lubrication, because the fluid passages are located at the axis of rotation O in many cases. Moreover, the location of first back pressure passage  31  according to the present embodiment is advantageous in the strength of camshaft  3   a  or  3   b,  and makes it easy to form the first back pressure passage  31 , even if the length of first back pressure passage  31  is relatively large. This feature enhances the flexibility of layout of first fluid passages  202 , etc. in camshaft  3   a  or  3   b.  Namely, since there are remaining a lot of even spaces around first back pressure passage  31  in camshaft  3   a  or  3   b,  the first fluid passage  202 , etc. can be located in any space of the remaining spaces. Incidentally, in contrast to rotor  40  that is subject to demand for compactness, camshaft  3   a  or  3   b  is subject to no such demand, so that the diameter of first back pressure passage  31  may be larger than that of back pressure hole  407 , which is advantageous in that first back pressure passage  31  can be more easily formed than back pressure hole  407 . 
     With regard to the back pressure relief section, the second back pressure relief passage is formed in vane rotor  4 , so that valve timing control apparatus  1  can be made compact. Specifically, radial groove  58  and circular recess  406  constituting the second back pressure relief passage are formed at the X-axis positive side axial end surface of vane rotor  4 . On the other hand, front plate  8  is formed with no recess nor groove constituting the second back pressure relief passage. Accordingly, the axial size of valve timing control apparatus  1  can be reduced, because it is unnecessary to increase the thickness of housing HSG for formation of such a recess or groove. On the other hand, the size of vane  41 ,  42  or  43  in the X-axis direction is unchanged through formation of the second back pressure relief passage. This serves to maintain the pressure-receiving area of vane rotor  4  against working fluid, and thereby maintain the ability of operation of vane rotor  4 . Circular recess  406  is formed with bolt holes  403 ,  404  and  405  in addition to back pressure hole  407 . In other words, circular recess  406  serves to provide a space accommodating the heads  331 ,  341  and  351 , and constitute the back pressure relief section. The construction that the heads  331 ,  341  and  351  are accommodated in circular recess  406  is advantageous because the heads  331 ,  341  and  351  do not project excessively from the axial end surface of vane rotor  4  in the X-axis positive direction toward the front plate  8 . Cap  7  is formed with recess  73  at the surface facing the circular recess  406 , wherein the recess  73  accommodates the heads  331 ,  341  and  351  that project from the axial end surface of vane rotor  4 . Namely, as shown in  FIG. 3 , part of each head  331 ,  341  or  351  extends into recess  73 . This feature makes it possible to reduce the axial size of valve timing control apparatus  1 . Circular recess  406  may be replaced by forming the rotor  40  with a plurality of recesses each of which accommodates a corresponding one of heads  331 ,  341  and  351 . In other words, circular recess  406  may be modified to have a non-circular shape. However, circular recess  406  is advantageous in the facility of forming, and in reducing the inertial mass of vane rotor  4 , because a relatively large portion is removed to form the circular recess  406 . Circular recess  406  may be omitted, wherein the back pressure relief section is implemented, for example, by a construction that the radial groove  58  is extended toward the axis of rotation O, and connected to back pressure hole  407 . 
     &lt;Guiding for Timing Belt&gt; A pulley that includes projections and depressions extending in the axial direction can be subject to a problem that a timing belt tends to move in the axial direction with respect to the pulley. In intake valve timing control apparatus  1   a,  the front plate  8 , which is provided at the X-axis positive side of housing HSG, serves as a belt guide to restrict movement of timing belt  1010  in the X-axis direction. Specifically, the construction that the outside periphery  80  of front plate  8  projects outwardly in radial directions with respect to the bottom of each depression of pulley  100 , and has an outside edge that is located outside of the roots of teeth of pulley  100 , serves to prevent the timing belt  1010  from moving in the X-axis positive direction, wherein the movement of timing belt  1010  is obstructed by the outside periphery  80  of front plate  8 . The outside edge of the outside periphery  80  of front plate  8  is located radially outside of the outside edge of timing belt  1010  putted on pulley  100 , so that front plate  8  serves more effectively as a belt guide to restrict the movement or deviation of timing belt  1010 . This feature is optional, because it is sufficient that the construction that the outside periphery  80  of front plate  8  projects outwardly in radial directions with respect to the bottom of each depression of pulley  100 . It is sufficient that the outside periphery  80  of front plate  8  includes at least a portion projecting outwardly in radial directions with respect to the bottom of a depression of pulley  100 , where the portion is within a range where timing belt  1010  and pulley  100  are in contact with one another (in an angular range of about 90 degrees in intake valve timing control apparatus  1   a  in  FIG. 1 ). It is optional that the entire outside periphery  80  of front plate  8  projects outwardly in radial directions with respect to the bottom of each depression of pulley  100 . The restriction of movement of timing belt  1010  in the X-axis positive direction results also in restricting the movement of timing belt  1010  in the X-axis negative direction, and preventing the timing belt  1010  from dropping from pulley  100 . Namely, it is sufficient that the belt guide is provided at at least one axial end of pulley  100 , and it is optional that the belt guide is provided at another axial end of pulley  100 . Although exhaust valve timing control apparatus  1   b  is provided with no belt guide, the movement of timing belt  1010  can be restricted by the belt guide of intake valve timing control apparatus  1   a,  wherein timing belt  1010  is putted on both of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b.    
     &lt;Mountability Enhanced&gt; In recent years, motor vehicles are subject to increasing demand for compactness in size, while internal combustion engines are provided with an increasing number of auxiliary devices. For compactness, an engine and auxiliary devices are arranged efficiently in an engine room, wherein the remaining space is minimized. Accordingly, it is desirable to make a valve timing control apparatus compact by designing dimensions in millimeter so that the valve timing control apparatus can be mounted efficiently in an engine room. For example, if a valve timing control apparatus is arranged close to a side wall of an engine, and is provided with a belt guide that can interfere with the side wall, it is desirable to enhance the mountability of the valve timing control apparatus. In order to solve this problem, in the present embodiment, the belt guide is provided in intake valve timing control apparatus  1   a  which is farther from the engine room side wall W than exhaust valve timing control apparatus  1   b,  and is attached to intake camshaft  3   a  which is farther from the engine room side wall W than exhaust camshaft  3   b.  In other words, no belt guide is provided in exhaust valve timing control apparatus  1   b  which is closer to the engine room side wall W than intake valve timing control apparatus  1   a,  and is attached to exhaust camshaft  3   b  which is closer to the engine room side wall W than intake camshaft  3   a.  This feature serves to avoid interference with the engine room side wall W, and thereby enhance the mountability of valve timing control apparatus  1 . In the present embodiment, where the engine room side wall W includes the projection W 1 , the exhaust valve timing control apparatus  1   b,  which is disposed outside in the width direction of the cylinder block, tends to be close to the projection W 1  in the X-axis direction as shown in  FIG. 15 , or in the direction perpendicular to the X-axis direction as shown in  FIG. 1 . Particularly, the ends of exhaust valve timing control apparatus  1   b  in the X-axis direction tend to interfere with the projection W 1 . This problem is solved by the construction according to the present embodiment that each depression of pulley  100  of exhaust valve timing control apparatus  1   b  is opened at both ends in the X-axis direction. This construction serves to reduce the possibility of interference between the outside portion (specifically, the ends in the X-axis direction) of exhaust valve timing control apparatus  1   b  and the projection W 1  of engine room side wall W, however the projection W 1  is shaped. In contrast to the case of intake valve timing control apparatus  1   a,  the construction that the front plate  8  of exhaust valve timing control apparatus  1   b  has no portion or no belt guide that projects outwardly in a radial direction with respect to the bottom of a depression of pulley  100 , and each depression of pulley  100  is fully opened at the X-axis positive side end, serves to avoid interference with the projection W 1 . Each depression of pulley  100  of exhaust valve timing control apparatus  1   b  is fully opened also at the X-axis negative side end, which serves to avoid interference with the projection W 1 . These features serve to enhance the flexibility of layout of the engine room in which valve timing control apparatus  1  is mounted. According to the present embodiment, the mountability of exhaust valve timing control apparatus  1   b  is enhanced, especially for vehicles in which severe dimensional requirements are present about the X-axis positive side of exhaust valve timing control apparatus  1   b  (the side farther from the cylinder block, or the camshaft tip side). This is because the movement of timing belt  1010  in the X-axis positive direction is restricted more effectively than in the X-axis negative direction, where intake valve timing control apparatus  1   a  is provided with the belt guide closer to front plate  8  at the X-axis positive side. If intake valve timing control apparatus  1   a  is provided with the belt guide closer to rear plate  9  at the X-axis negative side, then the mountability of exhaust valve timing control apparatus  1   b  is enhanced especially for vehicles in which severe dimensional requirements are present about the X-axis negative side of exhaust valve timing control apparatus  1   b  (the side closer to the cylinder block, or the camshaft root side). Incidentally, even if each depression of pulley  100  is not fully but partly opened at the X-axis positive side end, the advantageous effect described above can be achieved to some extent, although it is smaller. Specifically, even in cases where the diameter of front plate  8  of exhaust valve timing control apparatus  1   b  is larger than in the present embodiment, so as to form a belt guide, the interference between the projection W 1  and the belt guide can be avoided to some extent, if the maximum diameter of the belt guide is smaller than the diameter of tooth top circle of pulley  100 . Moreover, even in cases where the diameter of front plate  8  of exhaust valve timing control apparatus  1   b  is larger than in the present embodiment, so as to form a belt guide for completely closing the X-axis positive side of each depression of pulley  100 , the interference between the projection W 1  and the belt guide can be avoided to some extent, if the belt guide does not project outwardly with respect to the outside surface of timing belt  1010  putted on pulley  100 , although the effect is smaller. This is because the diameter of this exhaust valve timing control apparatus  1   b  is still smaller than that of intake valve timing control apparatus  1   a,  so as to make it possible to reduce the width of the unit of the internal combustion engine, intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  are mounted, and thereby enhance the flexibility of layout in the engine room, as compared to cases where exhaust valve timing control apparatus  1   b  is provided with a belt guide that is identical to that of intake valve timing control apparatus  1   a,  i.e. a belt guide projecting outwardly with respect to timing belt  1010 . 
     The construction according to the present embodiment that the intake valve timing control apparatus  1   a  farther from the engine room side wall is provided with the belt guide is adapted to a V-type DOHC engine in which a pair of cylinder banks are arranged in a V-shape spreading from the crankshaft, and each cylinder bank is provided with an intake camshaft and an exhaust camshaft, wherein intake valve timing control apparatus  1   a  is attached to the intake camshaft, and exhaust valve timing control apparatus  1   b  is attached to the exhaust camshaft. However, this construction may be adapted to another type engine, such as a straight-type engine, thus producing similar advantageous effects. As in the present embodiment, a general V-type engine is subject to more severe requirements than other type engines, because auxiliary devices mounted to the sides of the V-type engine project toward an engine room side wall, and the size of the V-type engine itself tends to increase in recent years. The present embodiment is adapted to such a V-type engine, in which intake valve timing control apparatus  1   a  farther from the engine room side wall W is provided with a belt guide. This feature is effective for enhancing the mountability of the valve timing control apparatus, especially for V-type engines that are subject to more severe requirements. Specifically, in each cylinder bank, only intake valve timing control apparatus  1   a,  which is attached to one of intake camshaft  3   a  and exhaust camshaft  3   b  closer to the other cylinder bank, i.e. attached to intake camshaft  3   a,  is provided with a belt guide, wherein intake camshaft  3   a  closer to the other cylinder bank is inside of exhaust camshaft  3   b  in the width direction of the cylinder block, and farther from the engine room side wall W. In other words, exhaust valve timing control apparatus  1   b,  which is attached to exhaust camshaft  3   b  that is outside of intake camshaft  3   a  in the width direction of the cylinder block, is provided with no belt guide, so that each depression of pulley  100  is opened at both longitudinal ends. This construction is applied to each cylinder bank in the present embodiment, but may be applied only one cylinder bank. Although the single timing belt  1010  is wound around intake valve timing control apparatuses  1   a  and exhaust valve timing control apparatuses  1   b  at both cylinder banks so that the timing belt  1010  drives both of intake camshaft  3   a  and exhaust camshaft  3   b  in the present embodiment, this construction may be modified so that two timing belts are provided each of which is driven by the crankshaft and wound around intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  of a corresponding one of the cylinder banks, and each of which drives intake camshaft  3   a  and exhaust camshaft  3   b  of the corresponding cylinder bank. In cases where a V-type engine is mounted in an engine room so that camshafts extend in a direction that crosses a vehicle longitudinal direction, for example, the camshafts extend in a direction perpendicular to the vehicle longitudinal direction as in the present embodiment, exhaust valve timing control apparatus  1   b,  which is provided outside in the width direction of the cylinder block, projects toward a front or rear side wall of the engine room. This construction is subject to severe requirements for dimensional management. In the present embodiment, of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  attached to the V-type engine, only intake valve timing control apparatus  1   a  is provided with a belt guide, which serves to solve the disadvantage in the mountability. Incidentally, the construction according to the present embodiment may be adapted to an engine of an arbitrary type in which a camshaft extends in a vehicle longitudinal direction, or extends in a diagonal direction with respect to the vehicle longitudinal direction. 
     &lt;Manufacturing Cost Reduced by Mirror Image Arrangement&gt; Intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  are constituted by the common third workpiece P 3  for housing body  10 , and the common second workpiece Q 2  for vane rotor  4 . Housing body  10  and vane rotor  4  of intake valve timing control apparatus  1   a,  and housing body  10  and vane rotor  4  of exhaust valve timing control apparatus  1   b,  are formed as mirror images of each other, by application of carving to respective ones of the opposite surfaces (side A, or side B) of the common extrusions (P 3 , Q 2 ). This feature serves to simplify the process of manufacturing, and thereby reduce the manufacturing cost. Moreover, vane rotor  4  and housing body  10  of exhaust valve timing control apparatus  1   b  are transformed into mirror images, and the stoppers are arranged in mirror positions, to constitute the intake valve timing control apparatus  1   a.  This feature allows the first stopper mechanism of each of intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b  functions at the initial position, where the first stopper mechanism has a larger contact area, as shown in  FIGS. 4 and 16 , and thereby prevents the stopper mechanisms from deforming and changing the rotation limit position. 
     &lt;Manufacturing Cost Reduced by Extrusion Forming&gt; The components (housing HSG, vane rotor  4 ) of valve timing control apparatus  1  may be formed by an operation other than extrusion, such as die-casting. The formation by extrusion according to the present embodiment makes mass production easy. In the case of housing body  10 , a plurality of base workpieces (third workpieces P 3 ) are formed simultaneously by obtaining a long continuous member (first workpiece P 1 , second workpiece P 2 ), and dividing it. In this way, many base workpieces (third workpieces P 3 ) are obtained by a few steps, and commonly used to construct the intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b.  This is effective for further simplifying the process of manufacturing, and thereby reducing the manufacturing cost. The feature according to the present embodiment that the pulley  100  of housing body  10  is constituted by a plurality of projections which are arranged in the circumferential direction, and extend in the axial direction, makes it possible to form the pulleys  100  of a plurality of housing bodies  10  simultaneously by the extrusion operation in the form of first workpiece P 1 , where it is unnecessary to form the pulley  100  of each housing body  10  one by one. This feature makes it possible to reduce the workload, and make the forming easy, and reduce the cost of forming. For example, if die-casting such as high-pressure die-casting is used for forming the housing body  10 , it is impossible to eliminate a tapered shape which is provided so that a formed material can be drawn from a mold. If the outside periphery of housing body  10  has a tapered shape, when housing body  10  is formed integrally with pulley  100 , it is difficult to form the projections or teeth of pulley  100  with high accuracy. On the other hand, according to the present embodiment, housing body  10  is formed by extrusion, and formed with no tapered shape, so that it is possible to form the pulley  100 , etc. with high accuracy. In the case of vane rotor  4 , a plurality of base workpieces (second workpieces Q 2 ) are formed simultaneously by obtaining a long continuous member (first workpiece Q 1 ), and dividing it. In this way, many base workpieces (second workpieces Q 2 ) are obtained by a few steps, and commonly used to construct the intake valve timing control apparatus  1   a  and exhaust valve timing control apparatus  1   b.  This is effective for further simplifying the process of manufacturing, and thereby reducing the manufacturing cost. 
     &lt;Manufacturing Cost Reduced by Features of Manufacturing Process&gt; The manufacturing process for manufacturing the components of valve timing control apparatus  1  according to the present embodiment is characterized at least in the order of operations constituting the manufacturing process, and serves to reduce the manufacturing cost as follows. According to the present embodiment, housing body  10  is manufactured by the process including the extrusion operation, the coating operation, and the cutting-off operation (and the carving operation) which are performed in this order. Accordingly, first workpiece P 1  is applied with surface treatment, before first workpiece P 1  is cut and divided into a plurality of second workpieces P 2 . If the extrusion operation, the cutting-off operation (and the carving operation), and the coating operation are performed in this order, it is necessary to apply each second workpiece P 2  with anodic oxidation treatment one by one, which increases the workload and time, and thereby increases the manufacturing cost. This supposed process is subject to a further problem that for maintaining the sealing performance by ensuring the intimate contact between housing body  10  and sealing rings S 1 , S 2  and S 3 , the open end surfaces  105 ,  102  and  103  of housing body  10  need to be applied with full pore-sealing treatment at the anodic oxidation coating film or treatment of removing the anodic oxidation coating film. Namely, it is necessary to apply surface treatment to the surfaces of each second workpiece P 2  one by one, which surfaces face the sealing plates  8  and  9 , and abut on the sealing rings S 1 , S 2  and S 3 . This increases the cost of forming (workload, and time). In contrast, the forming process according to the present embodiment that the entire first workpiece P 1  which is obtained by extrusion is applied with anodic oxidation treatment at one time, is advantageous in reducing the cost of forming. Moreover, the feature according to the present embodiment that the cut surfaces obtained by the cutting-off operation are used without further treatment, to constitute surfaces abutting on the sealing rings S 1 , S 2  and S 3 . Specifically, housing body  10  is formed in a shape having openings at axial ends by the extrusion operation and the cutting-off operation. For sealing the openings of housing body  10 , sealing rings S 1 , S 2  and S 3  are provided between housing body  10  and respective ones of sealing plates  8  and  9 . One axial end surface (the X-axis positive side cut surface  105 ) of housing body  10  obtained by the cutting-off operation is used as a surface abutting on the sealing ring S 3 . The feature that the cut surface  105  is formed with no anodic oxidation coating film, serves to ensure the intimate contact with sealing ring S 3 , and thereby maintain the sealing performance. This feature serves to eliminate the necessity of full pore-sealing treatment or the like for the anodic oxidation coating film at the X-axis positive side end of housing body  10 , and further reduce the cost of forming. The feature that the cut surface  105  where the base layer of aluminum-based metal material is exposed is applied with no further surface treatment, and used to abut on the sealing ring S 3 , is advantageous in eliminating the necessity of treatment for forming a coating film for maintaining the sealing performance, and thereby further reducing the cost of forming. The forming process according to the present embodiment includes the carving operation of carving the other axial end surface (the X-axis negative side open end surface) of housing body  10 . Similar to the cut surfaces obtained by the cutting-off operation, the cut surfaces obtained by the carving operation are formed with no anodic oxidation coating film, so that the sealing rings can be arranged to abut on any place in the cut surfaces. This serves to reduce the cost of forming, while maintaining the sealing performance. In other words, this feature serves to maintain the sealing performance however the axial end surface of housing body  10  is shaped, and thereby enhance the flexibility of design. In the present embodiment, the X-axis negative side longitudinal end surface  104  of housing body  10  is applied with carving to form the fitting recess  101  in which rear plate  9  is fixedly inserted. This is advantageous in making the valve timing control apparatus  1  compact in the axial direction. Since the fitting recess  101  obtained by carving is formed with no anodic oxidation coating film, the intimate contact with sealing ring S 1  is well maintained. Of second workpieces P 2  of housing bodies  10  obtained through the cutting-off operation, the second workpiece P 2  of housing body  10  that is obtained from one longitudinal end of first workpiece P 1  is formed with an anodic oxidation coating film at one axial end through the coating operation. For this housing body  10 , at least part of this anodic oxidation coating film is removed during the carving operation at the axial end surface, and adapted to abut on the sealing rings S 1  and S 2 , thus maintaining the sealing performance. Incidentally, both of the axial end surfaces of housing body  10  may be applied with carving for forming a recess in which a sealing plate is inserted. The carving operation may be omitted, where the cut surfaces obtained by the cutting-off operation can be used as surfaces abutting on the sealing rings. On the other hand, vane rotor  4  is manufactured by the process including the extrusion operation, the cutting-off operation, the carving operation, and the coating operation, which are performed in this order. This feature is advantageous in that the sliding portions of the surface of vane rotor  4  can be formed with an anodic oxidation coating film simultaneously, and the vane rotor  4  can be thus easily formed to have enhanced hardness and wear resistance. Specifically, during the forming process, first, second and third vanes  41 ,  42  and  43 , and boss portion  401  of rotor  40  are formed, and thereafter the entire surface of vane rotor  4  is applied with anodic oxidation treatment. Accordingly, the single coating operation is sufficient for applying anodic oxidation treatment to the surface of each vane  41 ,  42  or  43  in sliding contact with housing HSG, the surface of each axial end surface of vane rotor  4  in sliding contact with sealing plate  8  or  9 , and the surface of boss portion  401  in sliding contact with housing HSG. This makes it possible to easily manufacture the valve timing control apparatus  1  in which the sealing member  502  is prevented from being mounted in slide hole  501  with inclination, or wear of vane rotor  4  resulting from sliding motion of flange  513  of lock piston  51  is suppressed. Incidentally, it is conceivable that the sealing performance at the boundary between advance chamber A 1 , A 2  or A 3  and retard chamber R 1 , R 2  or R 3  may be lowered due to the feature that the outside periphery of vane rotor  4  and the inside periphery of housing body  10 , including the portions in sliding contact with sealing member  118  and sealing member  413 , are formed with anodic oxidation coating. However, this feature is relatively insignificant, because this sealing place is not subject to severe requirements as the boundary between the inside and outside of housing HSG (at the axial ends of housing body  10 ). 
     &lt;Manufacturing Cost Reduced by Facility of Attachment&gt; The initial phase of camshaft  3   a  or  3   b  with respect to the crankshaft is set by the positioning means (positioning pin  45 , etc.) during attachment of valve timing control apparatus  1 . First, the following describes a process of attaching the valve timing control apparatus  1  to the internal combustion engine, before describing advantageous effects. The attaching process is implemented by attaching an assembly unit without cap  7  to camshaft  3   a  or  3   b,  and then fixing the cap  7  to the assembly unit. The attaching process is started by an operation of inserting the axial end portion  30  of camshaft  3   a  or  3   b  from the X-axis negative side into the through hole  92  of housing HSG, and inserting and setting same into camshaft insertion hole  402  of vane rotor  4  mounted in housing HSG of the assembly unit. The attaching process proceeds to an operation of inserting and setting the camshaft bolts  33 ,  34  and  35  from the X-axis positive side through the large-diameter hole  81  of housing HSG into bolt holes  403 ,  404  and  405  of vane rotor  4 , and into bolt holes  32  of camshaft  3   a  or  3   b.  Then, the attaching process proceeds to an operation of setting the sealing ring S 4  in annular sealing ring groove  821 , and fixing the cap  7  to the female thread portion  82  of housing HSG so as to close the large-diameter hole  81 . The provision of annular sealing ring groove  821  serves to easily retain the sealing ring S 4  in position, and enhance the facility of assembling. The bottom of camshaft insertion hole  402  is formed with recess  44 . The axial end surface  300  includes the opening of first fluid passage  212  in which positioning pin  45  is fixedly inserted, thus forming a projection. When the axial end portion  30  of camshaft  3   a  or  3   b  is set in camshaft insertion hole  402 , the projection (positioning pin  45 ) is fitted in recess  44 , and the axial end portion  30  is inserted toward the bottom of camshaft insertion hole  402 , so as to make the axial end surface  300  abut on the bottom of camshaft insertion hole  402 . The fitting between positioning pin  45  and recess  44  serves to restrict the relative rotation between vane rotor  4  and camshaft  3   a  or  3   b,  and thus position the vane rotor  4  and camshaft  3   a  or  3   b  with one another in the rotational direction, and thereby set the rotational phase of camshaft  3   a  or  3   b  (vane rotor  4 ) with respect to the crankshaft (housing HSG). In this way, positioning pin  45  serves as a blind plug closing the first fluid passage  212 , and also serves as a positioning means in combination with recess  44 . Positioning pin  45  (in first fluid passage  212 ) and recess  44  constitute a positioning means for the rotational position of vane rotor  4  with respect to camshaft  3   a  or  3   b,  i.e. the rotational phase of camshaft  3   a  or  3   b  with respect to the crankshaft, when valve timing control apparatus  1  is attached to camshaft  3   a  or  3   b.  Incidentally, the cross-section of recess  44  is not limited to an elliptic shape, but may have a different shape, such as a circular shape, if recess  44  is adapted to be fitted to positioning pin  45  for restricting the relative rotation. However, the construction according to the present embodiment that recess  44  has an elliptic cross-section, makes it easy to fit the positioning pin  45  with recess  44 , because recess  44  is provided with a margin in the radial direction of rotor  40  so that errors in manufacturing and the like can be absorbed. First fluid passage  212  serves as a passage of working fluid, and also serves as a hole for fixing the positioning pin  45 . This feature is advantageous in eliminating the necessity of an additional operation of forming the axial end portion  30  with a projection for positioning, and thereby reducing the manufacturing cost. Since the opening of first fluid passage  202  of camshaft  3   a  or  3   b  at the axial end surface  300  is in intimate contact with and closed by the bottom of camshaft insertion hole  402 , it is unnecessary to provide a blind plug for closing the opening. This serves to reduce the number of parts, and the manufacturing cost. Incidentally, the positioning means may be implemented by a construction that the bottom of camshaft insertion hole  402  is formed with a projection which is adapted to be fitted in a recess of the axial end surface  300  (for example, the opening of first fluid passage  212 ). However, the construction according to the present embodiment that the axial end surface  300  is formed with the projection for positioning is advantageous in ease of assembling operation, as compared to the case of the construction that the bottom of camshaft insertion hole  402  is formed with a projection. The projection for positioning is implemented by a combination of a pin hole and a pin in the present embodiment, but may be implemented by machining or the like. However, the form according to the present embodiment is advantageous in making it possible to arbitrarily select a pin that is suitable for positioning, as compared to the case of direct formation based on machining or the like. The recess for positioning is constituted by the opening of the fluid passage in the present embodiment, but may be implemented by a recess that is formed by machining or the like. 
     The provision of boss portion  401  makes it easy to attach the valve timing control apparatus  1  to an existing engine. In cases where a housing is directly rotatably supported by a camshaft, attachment of a valve timing control apparatus to an engine needs to be implemented by attaching a vane rotor to the camshaft while checking a clearance between the housing and the camshaft, which may be disadvantageous in ease of assembling operation. Moreover, it is further necessary to change the design in conformance with the attachment, for example, by extending the end portion of the camshaft, so that the housing is suitably rotatably supported by the end portion of the camshaft, and thereby it is difficult to attach the valve timing control apparatus  1  to an existing engine. In contrast, the feature according to the present embodiment that the attachment of the valve timing control apparatus  1  to the engine is implemented by inserting the boss portion  401  into the through hole  92 , and then inserting the axial end portion  30  of camshaft  3   a  or  3   b,  is advantageous in ease of inserting operation, because the axis of rotation of vane rotor  4  is suitably positioned to be identical to the axis of rotation of housing HSG. Namely, it is unnecessary to care about whether camshaft  3   a  or  3   b  is accurately positioned with a predetermined clearance with housing HSG, because the insertion of axial end portion  30  into camshaft insertion hole  402  serves to mechanically position the axis of rotation of vane rotor  4  to be identical to the axis of rotation of housing HSG, and thereby it is easy to attach the vane rotor  4  to camshaft  3   a  or  3   b.  Moreover, the feature that the housing HSG is rotatably supported by boss portion  401  in a predetermined angular range beforehand, makes it unnecessary to change the design in conformance with the attachment, for example, by extending the end portion of the camshaft, so that the housing is suitably rotatably supported by the end portion of the camshaft. In this way, valve timing control apparatus  1  can be easily attached to an existing engine. 
     The feature that the front plate  8  is provided with the detachable cap  7 , makes it easy to turn and engage the camshaft bolts  33 ,  34  and  35 . Specifically, while valve timing control apparatus  1  is being attached, the assembly unit without cap  7  is attached to camshaft  3   a  or  3   b  so that housing HSG has an opening (large-diameter hole  81 ) at one axial end, through which the camshaft bolts  33 ,  34  and  35  can be inserted, and turned to fix the assembly unit (vane rotor  4 ) to camshaft  3   a  or  3   b.  Thereafter, the opening of housing HSG is closed by cap  7 . Incidentally, when attached to housing HSG, the cap  7  faces the circular recess  406  of vane rotor  4 , and faces the heads  331 ,  341  and  351  of camshaft bolts  33 ,  34  and  35 , and thereby serves to prevent working fluid from leaking from the back pressure relief section, and serves with the recess  73  to accommodate the heads  331 ,  341  and  351  of camshaft bolts  33 ,  34  and  35 . 
     The following describes a first group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 5-113112 discloses a valve timing control apparatus for an internal combustion engine, which includes a housing connected to a crankshaft, and a phase change mechanism mounted in the housing, and connected to a camshaft. The housing is formed with a pulley at its outside periphery to which torque is transmitted from the crankshaft through a timing belt that is wound around the pulley, so that the housing rotates in synchronization with the crankshaft. The phase change mechanism operates in response to supply and drainage of working fluid, for changing valve timing, i.e. rotational phase of the camshaft with respect to the crankshaft. The valve timing control apparatus described above is subject to a problem that the timing belt may be degraded by adhesion of working fluid exiting out of the housing. Accordingly, it is desirable to provide a valve timing control apparatus for an internal combustion engine in which such a problem is solved by suitable sealing. The problem is solved by a valve timing control apparatus comprising: a housing body having a tubular shape including an opening at an axial end; a sealing plate closing the opening of the housing body; and a sealing ring disposed between the housing body and the sealing plate; wherein an anodic oxide coating film layer is absent at a surface of the housing body in contact with the sealing ring. This feature serves to suitably maintain the sealing performance. The following describes each technical feature, and advantageous effects produced by the feature in detail. 
     &lt;1-1&gt; A valve timing control apparatus for an internal combustion engine, comprises: a housing body ( 10 ) having a tubular shape including an opening at an axial end ( 105 ), wherein the housing body ( 10 ) is formed integrally with a pulley ( 100 ) at an outside periphery of the housing body ( 10 ), and wherein the pulley ( 100 ) is adapted to receive torque from a crankshaft of the internal combustion engine; a sealing plate ( 8 ,  9 ) fixed to the axial end ( 104 ,  105 ) of the housing body ( 10 ), the sealing plate ( 8 ,  9 ) closing the opening of the housing body ( 10 ); a phase change mechanism (vane rotor  4 ) mounted in the housing body ( 10 ), and adapted to change a rotational phase of a camshaft ( 3   a,    3   b ) of the internal combustion engine with respect to the housing body ( 10 ) in response to supply and drainage of working fluid; and a sealing ring (S 1 , S 2 , S 3 ) disposed between the housing body ( 10 ) and the sealing plate ( 8 ,  9 ), wherein: the housing body ( 10 ) is formed of an aluminum-based metal material and anodized, wherein the housing body ( 10 ) includes a base layer and an anodic oxide coating film layer; and the anodic oxide coating film layer is present at the outside periphery of the housing body ( 10 ), and absent at a surface (axial end surface  105 , bottom surface  102 , inside peripheral surface  103 ) of the housing body ( 10 ) on which the sealing ring (S 1 , S 2 , S 3 ) abuts. The feature that the housing body ( 10 ) is formed integrally with the pulley ( 100 ), serves to reduce the radial size of the valve timing control apparatus ( 1 ). The feature that the housing body ( 10 ) is formed of the aluminum-based metal material, serves to reduce the weight of the valve timing control apparatus ( 1 ). The feature that the housing body ( 10 ) is anodized and the anodic oxide coating film layer is present at the outside periphery of the housing body ( 10 ), serves to enhance the wear resistance of the pulley ( 100 ). The feature that the anodic oxide coating film layer is absent at the surface (axial end surface  105 , bottom surface  102 , inside peripheral surface  103 ) of the housing body ( 10 ) on which the sealing ring (S 1 , S 2 , S 3 ) abuts, serves to maintain the sealing performance, and suppress degradation of a timing belt ( 1010 ) put over the pulley ( 100 ). 
     &lt;1-2&gt; In addition to the feature &lt;1-1&gt;: the housing body ( 10 ) has a hollow cylindrical shape, wherein the housing body ( 10 ) is formed integrally with a shoe ( 11 ,  12 ,  13 ) at an inside periphery of the housing body ( 10 ), and wherein the shoe ( 11 ,  12 ,  13 ) projects inwardly in a radial direction of the housing body ( 10 ); the phase change mechanism ( 4 ) includes a vane rotor ( 4 ) adapted to be fixed to a camshaft ( 3   a,    3   b ) of the internal combustion engine, and rotatably mounted in the housing body ( 10 ), wherein the vane rotor ( 4 ) includes a vane ( 41 ,  42 ,  43 ), wherein the vane ( 41 ,  42 ,  43 ) defines a working fluid chamber (advance chamber A 1 , A 2  or A 3 , retard chamber R 1 , R 2  or R 3 ) between the vane ( 41 ,  42 ,  43 ) and the shoe ( 11 ,  12 ,  13 ), and wherein the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) is adapted to supply and drainage of working fluid; and the sealing ring (S 1 , S 2 ) seals the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) at the axial end ( 104 ,  105 ) of the housing body ( 10 ). The feature &lt;1-1&gt; can be thus adapted to the valve timing control apparatus provided with the vane-type phase change mechanism ( 4 ). 
     &lt;1-3&gt; In addition to the feature &lt;1-1&gt;, the sealing ring (S 1 , S 2 , S 3 ) abuts on the base layer at the axial end ( 104 ,  105 ). This feature serves to reduce the workload of manufacturing the housing body ( 10 ), and thereby reduce the manufacturing cost. 
     &lt;1-4&gt; In addition to the feature &lt;1-1&gt;, the anodic oxide coating film layer is present also at an inside periphery of the housing body ( 10 ). This feature serves to enhance the wear resistance of the inside periphery of the housing body ( 10 ) in sliding contact with the phase change mechanism (vane rotor  4 ). 
     &lt;1-5&gt; In addition to the feature &lt;1-1&gt;, the valve timing control apparatus further comprises a plurality of bolts (b 1 , b 2 , b 3 ) extending in an axial direction of the housing body ( 10 ), and fixing the sealing plate ( 8 ,  9 ) to the housing body ( 10 ). This feature serves to compress the sealing ring (S 1 , S 2 , S 3 ) by the axial force of the bolts (b 1 , b 2 , b 3 ), and thereby further enhance the sealing performance. 
     &lt;1-6&gt; In addition to the feature &lt;1-5&gt;, the sealing plate ( 8 ,  9 ) is formed of a harder material than the housing body ( 10 , aluminum-based metal material). This feature serves to enhance the durability of the sealing plate ( 8 ,  9 ), and enhance the intimateness of contact between the housing body ( 10 ) and the sealing plate ( 8 ,  9 ), thereby further enhancing the sealing performance. Specifically, the feature that the sealing plate ( 8 ,  9 ) is formed of an iron-based metal material, serves to further enhance this advantageous effect. 
     &lt;1-7&gt; In addition to the feature &lt;1-1&gt;: the housing body ( 10 ) includes an opening at another axial end ( 104 ,  105 ); and the valve timing control apparatus further comprises another sealing plate ( 8 ,  9 ) fixed to the other axial end ( 104 ,  105 ). This feature serves to maintain the sealing performance of the housing body ( 10 ) at its both axial ends. 
     &lt;1-8&gt; In addition to the feature &lt;1-1&gt;, the sealing plate ( 8 ,  9 ) includes a sealing ring groove ( 906 ,  907 ,  908 ,  909 ,  89 ) that retains the sealing ring (S 1 , S 2 , S 3 ). This feature serves to easily retain the sealing ring (S 1 , S 2 , S 3 ), and thereby enhance the facility of assembling the valve timing control apparatus. The feature that the sealing plate ( 8 ,  9 ) includes the sealing ring groove ( 906 ,  907 ,  908 ,  909 ,  89 ), serves to make the valve timing control apparatus compact, and reduce the manufacturing cost. 
     &lt;1-9&gt; A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body ( 10 ) having a tubular shape including an opening at each axial end ( 104 ,  105 ), wherein the housing body ( 10 ) is formed integrally with a pulley ( 100 ) at an outside periphery of the housing body ( 10 ), and wherein the pulley ( 100 ) is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate ( 8 ) fixed to one of the axial ends ( 105 ) of the housing body ( 10 ), the sealing plate ( 8 ) closing a corresponding one of the openings of the housing body ( 10 ); a phase change mechanism (vane rotor  4 ) mounted in the housing body ( 10 ), and adapted to change a rotational phase of a camshaft ( 3   a,    3   b ) of the internal combustion engine with respect to the housing body ( 10 ) in response to supply and drainage of working fluid; and at least one sealing ring (S 3 ) disposed between the sealing plate ( 8 ) and the housing body ( 10 ), the method comprises a process of producing the housing body ( 10 ), the process comprising: an extruding operation of forming a first workpiece (P 1 ) by extruding an aluminum-based metal material, wherein the first workpiece (P 1 ) extends in a direction of extrusion; a coating operation of forming a second workpiece (P 2 ) by anodizing an entire surface of the first workpiece (P 1 ); and a cutting-off operation of forming a third workpiece (P 3 ) by cutting out of the second workpiece (P 2 ) to a predetermined length so as to form the third workpiece (P 3 ) with a cut surface (axial end surface  105 ) forming a surface ( 105 ) of the housing body ( 10 ) on which the sealing ring (S 3 ) abuts. This feature allows to form a plurality of the third workpieces (P 3 ) of the housing body ( 10 ) by dividing the first workpiece (P 1 ) that is obtained by extrusion, and thereby serves to enhance the production efficiency. The feature that the process comprises the coating operation of forming the second workpiece (P 2 ) by anodizing the entire surface of the first workpiece (P 1 ), serves to reduce the cost of anodic oxidation treatment. The feature that the process comprises the cutting-off operation of forming the third workpiece (P 3 ) with the cut surface ( 105 ) forming the surface ( 105 ) of the housing body ( 10 ) on which the sealing ring (S 3 ) abuts, serves to further reduce the cost of anodic oxidation treatment. 
     &lt;1-10&gt; In addition to the feature &lt;1-9&gt;: the housing body ( 10 ) has a hollow cylindrical shape, wherein the housing body ( 10 ) is formed integrally with a shoe ( 11 ,  12 ,  13 ) at an inside periphery of the housing body ( 10 ), and wherein the shoe ( 11 ,  12 ,  13 ) projects inwardly in a radial direction of the housing body ( 10 ); the phase change mechanism ( 4 ) includes a vane rotor ( 4 ) adapted to be fixed to a camshaft ( 3   a,    3   b ) of the internal combustion engine, and rotatably mounted in the housing body ( 10 ), wherein the vane rotor ( 4 ) includes a vane ( 41 ,  42 ,  43 ), wherein the vane ( 41 ,  42 ,  43 ) defines a working fluid chamber (advance chamber A 1 , A 2  or A 3 , retard chamber R 1 , R 2  or R 3 ) between the vane ( 41 ,  42 ,  43 ) and the shoe ( 11 ,  12 ,  13 ), and wherein the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) is adapted to supply and drainage of working fluid; and the sealing ring (S 1 , S 2 ) seals the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) at the corresponding axial end ( 104 ,  105 ) of the housing body ( 10 ). The feature &lt;1-9&gt; can be thus adapted to the valve timing control apparatus provided with the vane-type phase change mechanism ( 4 ). 
     &lt;1-11&gt; In addition to the feature &lt;1-9&gt;, the pulley ( 100 ) includes a plurality of projections arranged in a circumferential direction of the housing body ( 10 ), and wherein each projection extends in an axial direction of the housing body ( 10 ). This feature makes it possible to form a plurality of the housing bodies ( 10 ) with the pulleys ( 100 ) simultaneously with high accuracy, and thereby reduce the manufacturing cost. 
     &lt;1-12&gt; A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a housing body ( 10 ) having a tubular shape including an opening at each axial end ( 104 ,  105 ), wherein the housing body ( 10 ) is formed integrally with a pulley ( 100 ) at an outside periphery of the housing body ( 10 ), and wherein the pulley ( 100 ) is adapted to receive torque from a crankshaft of the internal combustion engine; at least one sealing plate ( 9 ) fixed to one of the axial ends ( 104 ) of the housing body ( 10 ), the sealing plate ( 9 ) closing a corresponding one of the openings of the housing body ( 10 ); a phase change mechanism (vane rotor  4 ) mounted in the housing body ( 10 ), and adapted to change a rotational phase of a camshaft ( 3   a,    3   b ) of the internal combustion engine with respect to the housing body ( 10 ) in response to supply and drainage of working fluid; and at least one sealing ring (S 1 , S 2 ) disposed between the sealing plate ( 9 ) and the housing body ( 10 ), the method comprises a process of producing the housing body ( 10 ), the process comprising: an extruding operation of forming a first workpiece (P 1 ) by extruding an aluminum-based metal material, wherein the first workpiece (P 1 ) extends in a direction of extrusion; a coating operation of forming a second workpiece (P 2 ) by anodizing an entire surface of the first workpiece (P 1 ); a cutting-off operation of forming a third workpiece (P 3 ) by cutting out of the second workpiece (P 2 ) to a predetermined length; and a carving operation of carving a longitudinal end surface of the third workpiece (P 3 ) so as to form the third workpiece (P 3 ) with a cut surface (inside peripheral surface  103 , bottom surface  102 ) forming a surface of the housing body ( 10 ) on which the sealing ring (S 1 , S 2 ) abuts. This feature serves to maintain the sealing performance while allowing the open axial end of the housing body ( 10 ) to be carved into an arbitrary shape, and thereby serves to enhance the flexibility of design of the valve timing control apparatus while reducing the cost of anodic oxidation treatment. 
     &lt;1-13&gt; In addition to the feature &lt;1-12&gt;, the carving operation is implemented by carving the longitudinal end surface of the third workpiece (P 3 ) so as to form the third workpiece (P 3 ) with a fitting recess ( 101 ), wherein the fitting recess ( 101 ) includes the cut surface ( 103 ,  102 ), and wherein the sealing plate ( 9 ) is fixed in the fitting recess ( 101 ). The feature that the sealing ring (S 1 , S 2 ) is mounted in the fitting recess ( 101 ) including the cut surface ( 103 ,  102 ), serves to maintain the sealing performance, while reducing the axial size of the valve timing control apparatus, and thereby enhancing the mountability of the valve timing control apparatus. 
     &lt;1-14&gt; In addition to the feature &lt;1-13&gt;, the method further comprises providing the sealing ring (S 1 ) between an inside periphery of the fitting recess ( 101 ) and an outside periphery of the sealing plate ( 9 ). This feature serves to reduce the radial size of the valve timing control apparatus in addition to the axial size. 
     &lt;Second Group of Technical Features&gt; The following describes a second group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 2001-115807 discloses a valve timing control apparatus for an internal combustion engine, which includes a housing connected to a crankshaft, and includes a vane rotor including a boss portion, wherein the boss portion serves as a bearing for the housing. In this valve timing control apparatus, the housing is rotating, while being subject to a torque transmitted from the crankshaft, so that the boss portion is subject to a high load from the housing. If the vane rotor including the boss portion is formed of a relatively soft material, such as an aluminum-based metal material, the boss portion may be worn heavily. In view of the foregoing, it is desirable to provide a valve timing control apparatus for an internal combustion engine, in which wear of a boss portion can be reduced. The problem is solved by a valve timing control apparatus in which a portion of a boss portion in sliding contact with a housing is applied with anodic oxidation treatment. This feature serves to reduce the wear of the boss portion. The following describes each technical feature, and advantageous effects produced by the feature in detail. 
     &lt;2-1&gt; A valve timing control apparatus for an internal combustion engine, comprises: a housing (HSG) adapted to receive torque from a crankshaft of the internal combustion engine, and formed with a through hole ( 92 ) extending along an axis of rotation (O); and a vane rotor ( 4 ) rotatably mounted in the housing (HSG), wherein the vane rotor ( 4 ) includes a boss portion ( 401 ) adapted to be fixed to a camshaft ( 3   a,    3   b ) of the internal combustion engine, and wherein the boss portion ( 401 ) extends along the axis of rotation (O), and includes a portion in sliding contact with the through hole ( 92 ), wherein the vane rotor ( 4 ) is formed of an aluminum-based metal material, and the portion of the boss portion ( 401 ) is anodized. The feature that the boss portion ( 401 ) bears the housing (HSG) through the through hole  92 , serves to enhance the facility of attaching the valve timing control apparatus to the camshaft ( 3   a,    3   b ) of an existing internal combustion engine. The feature that the vane rotor ( 4 ) is formed of the aluminum-based metal material, serves to reduce the weight of the valve timing control apparatus. The feature that the boss portion ( 401 ) includes a portion in sliding contact with the through hole ( 92 ), wherein the portion of the boss portion ( 401 ) is anodized, serves to suppress wear of the boss portion ( 401 ). 
     &lt;2-2&gt; In addition to the feature &lt;2-1&gt;: the housing (HSG) includes: a housing body ( 10 ) having a hollow cylindrical shape including an opening at an axial end ( 104 ), wherein the housing body ( 10 ) is adapted to receive torque from the crankshaft, and formed integrally with a shoe ( 11 ,  12 ,  13 ) at an inside periphery of the housing body ( 10 ), and wherein the shoe ( 11 ,  12 ,  13 ) projects inwardly in a radial direction of the housing body ( 10 ); and a sealing plate (rear plate  9 ) fixed to the axial end ( 104 ) of the housing body ( 10 ), the sealing plate ( 9 ) closing the opening of the housing body ( 10 ), wherein the sealing plate ( 9 ) is formed with the through hole ( 92 ) at a central portion ( 91 ); and the vane rotor ( 4 ) includes: a rotor ( 40 ) from which the boss portion ( 401 ) projects along the axis of rotation (O); and a vane ( 41 ,  42 ,  43 ) projecting outwardly in the radial direction of the housing body ( 10 ) with respect to the rotor ( 40 ), and defining a working fluid chamber (advance chamber A 1 , A 2  or A 3 , or retard chamber R 1 , R 2  or R 3 ) between the vane ( 41 ,  42 ,  43 ) and the shoe ( 11 ,  12 ,  13 ), wherein the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) is adapted to supply and drainage of working fluid. 
     &lt;2-3&gt; In addition to the feature &lt;2-1&gt;, the vane rotor ( 4 ) has an anodized axial end surface in sliding contact with the housing (HSG). This feature serves to enhance the wear resistance of the portion of the vane rotor ( 4 ) in sliding contact with the housing (HSG: sealing plate  8 ,  9 ). 
     &lt;2-4&gt; In addition to the feature &lt;2-2&gt;, the sealing plate ( 9 ) is formed of a harder material than the vane rotor ( 4 ). This serves to enhance the durability of the valve timing control apparatus. Specifically, the sealing plate ( 9 ) is formed of an iron-based metal material. This feature is advantageous in the facility of processing, the manufacturing cost, etc. 
     &lt;2-5&gt; In addition to the feature &lt;2-1&gt;, an entire surface of the vane rotor ( 4 ) is anodized. This feature serves to enhance the facility of manufacturing the valve timing control apparatus which produces the advantageous effects according to the features &lt;2-1&gt; and &lt;2-3&gt;, because it is sufficient to apply surface treatment once to the entire surface of the vane rotor ( 4 ) that includes portions in sliding contact with the housing (HSG). 
     &lt;2-6&gt; A method of producing the valve timing control apparatus according to the feature &lt;2-1&gt;, the method comprises a process of producing the vane rotor ( 4 ), the process comprising anodizing an entire surface of the vane rotor ( 4 ). This feature serves similar to the feature &lt;2-5&gt;. Specifically, the method is a method of producing the valve timing control apparatus according to the feature &lt;2-2&gt; that is provided with the housing (HSG) and the vane rotor ( 4 ), the method comprising a process of producing the vane rotor ( 4 ), the process comprising: forming the vane ( 41 ,  42 ,  43 ) and the rotor ( 40 ); and then anodizing an entire surface of the vane rotor ( 4 ). 
     &lt;2-7&gt; In addition to the feature &lt;2-6&gt;, the process comprises: an extruding operation of forming a first workpiece (Q 1 ) by extruding an aluminum-based metal material, wherein the first workpiece (Q 1 ) extends in a direction of extrusion; a cutting-off operation of forming a second workpiece (Q 2 ) by cutting out of the first workpiece (Q 1 ) to a predetermined length; and a carving operation of forming the second workpiece (Q 2 ) with the boss portion ( 401 ) by carving. This feature makes it possible to produce many vane rotors ( 4 ) at one time, and thereby serves to reduce the manufacturing cost. 
     &lt;Third Group of Technical Features&gt; The following describes a third group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 2005-520084 discloses a valve timing control apparatus for an internal combustion engine, which is adapted to be fixed to a camshaft, and to which torque is transmitted through a belt, and which includes a belt guide for restricting movement of the belt in an axial direction of the camshaft. This valve timing control apparatus is subject to a problem that in an engine room of a motor vehicle to which the internal combustion engine is mounted, the belt guide is close to a side wall of the engine room so that the mountability of the valve timing control apparatus is low. In view of the foregoing, it is desirable to provide a valve timing control apparatus for an internal combustion engine, whose mountability is maintained in spite of provision of a belt guide. This problem is solved by a valve timing control system which includes an intake valve timing control apparatus fixed to an intake camshaft and an exhaust valve timing control apparatus fixed to an exhaust camshaft, and includes a belt wound over the intake camshaft and the exhaust camshaft for transmitting torque therebetween, wherein one of the intake valve timing control apparatus and the exhaust valve timing control apparatus farther from an engine room side wall is provided with a belt guide. This feature serves to maintain the mountability of the valve timing control apparatus. The following describes each technical feature, and advantageous effects produced by the feature in detail. 
     &lt;3-1&gt; A valve timing control system for an internal combustion engine, wherein the internal combustion engine includes an intake camshaft ( 3   a ) adapted to drive an intake valve, an exhaust camshaft ( 3   b ) adapted to drive an exhaust valve, and a belt ( 1010 ) wound over the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ) for transmitting torque therebetween, the valve timing control system comprising: a first valve timing control apparatus ( 1   a ) adapted to be fixed to one of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ); and a second valve timing control apparatus ( 1   b ) adapted to be fixed to another one of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ), and adapted to be located closer to a side wall (W) of an engine room in which the internal combustion engine is mounted than the first valve timing control apparatus ( 1   a ), wherein: the first valve timing control apparatus ( 1   a ) includes a belt guide ( 80 ) adapted to restrict movement of the belt ( 1010 ) in at least one axial direction (in the X-axis positive direction); and the movement of the belt ( 1010 ) is free with respect to the second valve timing control apparatus ( 1   b ). Namely, only the first valve timing control apparatus ( 1   a ) farther from the side wall (W) is provided with a belt guide ( 80 ). This feature serves to maintain the mountability of the valve timing control system. 
     &lt;3-2&gt; In addition to the feature &lt;3-1&gt;: each of the first and second valve timing control apparatuses ( 1   a,    1   b ) includes a pulley ( 100 ) including a projection and a recess, wherein the projection and recess extend in the axial direction; and the belt ( 1010 ) is wound around each pulley ( 100 ) for transmitting torque. This feature serves to effectively restrict the movement of the belt ( 1010 ) by the belt guide ( 80 ), although the belt guide ( 80 ) tends to move in the axial direction with respect to the pulley ( 100 ) because the projection and recess of pulley ( 100 ) extend in the axial direction. 
     &lt;3-3&gt; In addition to the feature &lt;3-2&gt;: the belt guide ( 80 ) is disposed at an axial end of the pulley ( 100 ) of the first valve timing control apparatus ( 1   a ), wherein the belt guide ( 80 ) projects outwardly with respect to a bottom of the recess in a radial direction of the pulley ( 100 ); and the recess of the pulley ( 100 ) of the second valve timing control apparatus ( 1   b ) is open at both axial ends. This feature serves to prevent each axial end of the second valve timing control apparatus ( 1   b ) from interfering with the side wall (W: projection W 1 ), and thereby maintain the mountability of the valve timing control apparatus further effectively. 
     &lt;3-4&gt; In addition to the feature &lt;3-3&gt;, the belt guide ( 80 ) extends outside of the belt ( 1010 ) in the radial direction of the pulley ( 100 ) in the first valve timing control apparatus ( 1   a ). This feature serves to enhance the function of the belt guide ( 80 ). 
     &lt;3-5&gt; In addition to the feature &lt;3-3&gt;: each of the first and second valve timing control apparatuses ( 1   a,    1   b ) includes: a housing body ( 10 ) adapted to be attached to an axial end of the corresponding one of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ), and formed integrally with the pulley ( 100 ) at an outside periphery of the housing body ( 10 ); a front plate ( 8 ) sealing a first axial end (X-axis positive side axial end) of the housing body ( 10 ); and a rear plate ( 9 ) sealing a second axial end (X-axis negative side axial end) of the housing body ( 10 ) closer to the corresponding one of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ); and the front plate ( 8 ) of the first valve timing control apparatus ( 1   a ) forms the belt guide ( 80 ). The feature that the housing body ( 10 ) is formed integrally with the pulley ( 100 ), serves to reduce the radial size of each of the first and second valve timing control apparatuses ( 1   a,    1   b ), and thereby enhance the mountability of the valve timing control system. The feature that the front plate ( 8 ) of the first valve timing control apparatus ( 1   a ) forms the belt guide ( 80 ), serves to maintain the mountability of the valve timing control system, especially for a motor vehicle where the axial end (the X-axis positive side axial end) of the camshaft farther from the camshaft is subject to severe dimensional requirements in an engine room. 
     &lt;3-6&gt; In addition to the feature &lt;3-1&gt;, axial directions of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ) cross a vehicle longitudinal direction. Specifically, the axial directions of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ) are substantially perpendicular to the vehicle longitudinal direction. 
     &lt;3-7&gt; In addition to any one of the features &lt;3-1&gt; to &lt;3-6&gt;: the internal combustion engine is a V-type engine; and the first and second valve timing control apparatuses ( 1   a,    1   b ) are adapted to the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ) that are provided at least one bank of the internal combustion engine. The produced effects &lt;3-1&gt; to &lt;3-6&gt; are more significant for V-type engines which are subject to severe dimensional requirements. Especially, the features &lt;3-1&gt; to &lt;3-5&gt; serve to maintain the mountability of the valve timing control system more significantly for V-type engines applied with the feature &lt;3-6&gt; where the axial directions of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ) cross (specifically, substantially perpendicular to) the vehicle longitudinal direction. Specifically, of the first and second valve timing control apparatuses ( 1   a,    1   b ) of one cylinder bank, only the first valve timing control apparatus ( 1   a ) is provided with the belt guide ( 80 ) according to the feature &lt;3-1&gt;, wherein the first valve timing control apparatus ( 1   a ) is attached to one of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ) closer to the other cylinder bank. More specifically, each of the first and second valve timing control apparatuses ( 1   a,    1   b ) includes a pulley ( 100 ) including a projection and a recess, wherein the projection and recess extend in the axial direction; and the belt ( 1010 ) is wound around each pulley ( 100 ) for transmitting torque. The belt guide ( 80 ) is disposed at an axial end of the pulley ( 100 ) of the first valve timing control apparatus ( 1   a ), wherein the first valve timing control apparatus ( 1   a ) is attached to the intake camshaft ( 3   a ) closer to the other cylinder bank, wherein the belt guide ( 80 ) projects outwardly from a bottom of the recess in a radial direction of the pulley ( 100 ); and the recess of the pulley ( 100 ) of the second valve timing control apparatus ( 1   b ) is open at both axial ends, wherein the second valve timing control apparatus ( 1   b ) is attached to one of the intake camshaft ( 3   a ) and the exhaust camshaft ( 3   b ) that is located outside of the cylinder bank (farther from the other cylinder bank). 
     &lt;Fourth Group of Technical Features&gt; The following describes a fourth group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 11-218008 discloses a valve timing control apparatus of a vane type for an internal combustion engine, which includes a housing to which torque is transmitted form outside, and a vane rotor rotatably mounted in the housing, wherein the vane rotor is fixed to a camshaft by a single bolt at the axis of rotation of the vane rotor. This valve timing control apparatus is subject to a problem that the bolt tends to be released, for example, by an alternating torque from valve springs. In view of the foregoing, it is desirable to provide a valve timing control apparatus in which fixation of a vane rotor to a camshaft is strengthened. This problem is solved by a valve timing control apparatus in which a rotor of a vane rotor includes a plurality of fixing portions which are arranged and spaced from one another in a circumferential direction. This feature serves to strengthen the fixation of the vane rotor. The following describes each technical feature, and advantageous effects produced by the feature in detail. 
     &lt;4-1&gt; A valve timing control apparatus for an internal combustion engine, comprises: a hollow housing (HSG) adapted to receive torque; and a vane rotor ( 4 ) rotatably mounted in the housing (HSG), including a rotor ( 40 ) adapted to be fixed to a camshaft ( 3   a,    3   b ) of the internal combustion engine, wherein the rotor ( 40 ) includes a plurality of fixing portions (bolt holes  403 ,  404  and  405 ) adapted to be fixed to the camshaft ( 3   a,    3   b ), and wherein the fixing portions ( 403 ,  404 ,  405 ) are arranged in a circumferential direction of the rotor ( 40 ), and separated from one another. The feature that the rotor ( 40 ) includes the plurality of fixing portions ( 403 ,  404 ,  405 ), serves to strengthen the fixation of the vane rotor ( 4 ) to the camshaft ( 3   a,    3   b ). The feature that the fixing portions ( 403 ,  404 ,  405 ) are arranged in the circumferential direction of the rotor ( 40 ), and separated from one another, serves to strengthen the fixation of the vane rotor ( 4 ) effectively. 
     &lt;4-2&gt; In addition to the feature &lt;4-1&gt;: the torque is transmitted to the housing (HSG) through a belt ( 1010 ); the vane rotor ( 4 ) includes: a plurality of vanes ( 41 ,  42 ,  43 ) projecting outwardly in radial directions of the rotor ( 40 ) with respect to the rotor ( 40 ), and defining at least one working fluid chamber (first, second and third advance chambers A 1 , A 2  and A 3 , and first, second and third retard chambers R 1 , R 2  and R 3 ) in the housing (HSG), wherein the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) is adapted to supply and drainage of working fluid; and a cylinder (slide hole  501 ) formed in the vane rotor ( 4 ), extending in a direction of an axis of rotation (O) of the vane rotor ( 4 ); and the valve timing control apparatus further comprises: an engaging member (lock piston  51 ) slidably mounted in the cylinder ( 501 ), and arranged to move forward and rearward in the cylinder ( 501 ) according to an operating state of the internal combustion engine; an engaging recess ( 521 ) provided in an axial end portion of the housing (HSG) closer to the camshaft ( 3   a,    3   b ); a biasing member (coil spring  53 ) mounted in a back pressure chamber ( 50 ) formed in the cylinder ( 501 ), and arranged to bias the engaging member ( 51 ) toward the engaging recess ( 521 ); and a back pressure relief section (back pressure hole  407 ) formed in a central portion of the rotor ( 40 ) surrounded by and closer to the axis of rotation (O) than the fixing portions (bolt holes  403 ,  404  and  405 ), for relieving pressure from the back pressure chamber ( 50 ) to a space within the internal combustion engine. The feature that the torque is transmitted through the belt ( 1010 ), serves to reduce the manufacturing cost, and reduce the weight of the valve timing control apparatus. The feature that the cylinder ( 501 ), engaging member ( 51 ), engaging recess ( 521 ), and biasing member (coil spring  53 ) constitute a lock mechanism, serves to suppress, by the simply-constructed lock mechanism, noise that may be caused by the valve timing control apparatus at start of the internal combustion engine. The feature that the cylinder (slide hole  501 ) extends in the direction of the axis of rotation (O) of the vane rotor ( 4 ), serves to stabilize the locking operation. The feature that the back pressure relief section ( 407 ) is formed for relieving pressure from the back pressure chamber ( 50 ), serves to smooth the lock release operation of the lock mechanism, namely, smooth the disengaging motion of the engaging member ( 51 ) from the engaging recess ( 521 ). The feature that the back pressure relief section ( 407 ) is formed for relieving pressure from the back pressure chamber ( 50 ) to the space within the internal combustion engine, where the back pressure chamber ( 50 ) is formed in the cylinder ( 501 ) and located at a side (the X-axis positive side) farther from the camshaft ( 3   a,    3   b ) or the internal combustion engine, serves to enhance the durability of the belt ( 1010 ). The feature that the back pressure relief section ( 407 ) is formed in the central portion of the rotor ( 40 ) surrounded by and closer to the axis of rotation (O) than the fixing portions ( 403 ,  404 ,  405 ), serves to reduce the radial size of the rotor ( 40 ) or the vane rotor ( 4 ), and thereby make the valve timing control apparatus compact in size. The plurality of vanes ( 41 ,  42 ,  43 ) define at least one advance chamber (A 1 , A 2  or A 3 ) and at least one retard chamber (R 1 , R 2  or R 3 ) between the vanes ( 41 ,  42 ,  43 ) and shoes ( 11 ,  12  and  13 ), wherein the advance chamber and the retard chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) are adapted to supply and drainage of working fluid. 
     &lt;4-3&gt; In addition to the feature &lt;4-2&gt;: the rotor ( 40 ) is formed with a communication hole (retard fluid passage  408 , advance fluid passage  409 ) hydraulically connected between the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) and a fluid passage (first fluid passages  202  and  212 ; second fluid passages  201 ,  203 ,  211  and  213 ) formed in the camshaft ( 3   a,    3   b ), wherein the fluid passage ( 202 ,  212 ;  201 ,  203 ,  211 ,  213 ) is located between adjacent two of the fixing portions ( 403 ,  404 ,  405 ) in a circumferential direction of the rotor ( 40 ); and the back pressure relief section (back pressure hole  407 ) is located closer to the axis of rotation (O) than the fluid passage ( 202 ,  212 ;  201 ,  203 ,  211 ,  213 ). This feature serves to make the valve timing control apparatus compact in size, wherein it is unnecessary to rearrange the passages (first fluid passage  202 , etc.) for supply and drainage of working fluid. 
     &lt;4-4&gt; In addition to the feature &lt;4-1&gt;, each of the fixing portions (bolt holes  403 ,  404  and  405 ) is a bolt insertion hole extending through the rotor ( 40 ), wherein a camshaft bolt ( 33 ,  34 ,  35 ) extends through the bolt insertion hole, and fixes the rotor ( 40 ) to an axial end surface ( 300 ) of the camshaft ( 3   a,    3   b ). This feature makes it possible to easily assemble the valve timing control apparatus, and easily manage the strength of fixation, as compared to another manner such as swaging or welding. 
     &lt;4-5&gt; In addition to the feature &lt;4-2&gt;: the camshaft ( 3   a,    3   b ) is formed with a first back pressure passage ( 31 ) inside, wherein the first back pressure passage ( 31 ) is hydraulically connected between the axial end surface ( 300 ) of the camshaft ( 3   a,    3   b ) and the space within the internal combustion engine; and the back pressure relief section ( 407 ) is a back pressure hole that is hydraulically connected to the back pressure chamber ( 50 ), and arranged in such a position at a surface closer to the camshaft ( 3   a,    3   b ) as to face the first back pressure passage ( 31 ). The feature that the camshaft ( 3   a,    3   b ) is formed with a first back pressure passage ( 31 ) inside, serves to make the valve timing control apparatus compact in size. The feature that the opening of the back pressure relief section ( 407 ) faces the first back pressure passage ( 31 ), is advantageous in the facility of processing, and the manufacturing cost. 
     &lt;4-6&gt; In addition to the feature &lt;4-5&gt;, the back pressure hole ( 407 ) is located at the axis of rotation (O) of the rotor ( 40 ). This feature serves to enhance the balance of the vane rotor ( 4 ) around the axis of rotation, and serves to ensure the radial thickness of the rotor ( 40 ), and thereby ensure the strength of the vane rotor ( 4 ). 
     &lt;4-7&gt; In addition to the feature &lt;4-5&gt;: the first back pressure passage ( 31 ) is located at an axis of rotation (O) of the camshaft ( 3   a,    3   b ); and the back pressure hole ( 407 ) extends through the rotor ( 40 ), and faces the first back pressure passage ( 31 ). This feature serves to enhance the balance of the camshaft ( 3   a,    3   b ) around the axis of rotation, and also produces the same effect according to the feature &lt;4-6&gt;. 
     &lt;4-8&gt; In addition to the feature &lt;4-1&gt;, the fixing portions (bolt holes  403 ,  404  and  405 ) are substantially evenly spaced in the circumferential direction. This feature makes it easy to maintain the balance of each of the vane rotor ( 4 ) and the camshaft ( 3   a,    3   b ) around the axis of rotation. The further feature that each fixing portion is a bolt insertion hole (bolt hole  403 ,  404  or  405 ), serves to maintain the strength of the rotor ( 40 ). 
     &lt;4-9&gt; In addition to the feature &lt;4-2&gt;: the rotor ( 40 ) is formed with a communication hole (retard fluid passage  408 , advance fluid passage  409 ) hydraulically connected between the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) and a fluid passage ( 202 ,  212 ;  201 ,  203 ,  211 ,  213 ) formed in the camshaft ( 3   a,    3   b ), wherein the fluid passage ( 202 ,  212 ;  201 ,  203 ,  211 ,  213 ) is located between adjacent two of the fixing portions ( 403 ,  404 ,  405 ) in a circumferential direction of the rotor ( 40 ); the rotor ( 40 ) is formed with a camshaft insertion hole ( 402 ) having a bottom, wherein the camshaft ( 3   a,    3   b ) is inserted in the camshaft insertion hole ( 402 ); and the communication hole (retard fluid passage  408 , advance fluid passage  409 ) extends through the rotor ( 40 ) in a radial direction of the rotor ( 40 ). This feature serves to enhance the facility of processing and the flexibility of layout of the back pressure relief section (back pressure hole  407 ), and makes it easy to make the rotor ( 40 ) compact in size. 
     &lt;4-10&gt; In addition to the feature &lt;4-9&gt;: the fluid passage ( 202 ,  212 ;  201 ,  203 ,  211 ,  213 ) includes: a first fluid passage ( 202 ,  212 ) extending in an axial direction of the camshaft ( 3   a,    3   b ); and a second fluid passage ( 201 ,  203 ,  211 ,  213 ) extending from the first fluid passage ( 202 ,  212 ) in a radial direction of the camshaft ( 3   a,    3   b ) and communicating with the communication hole (retard fluid passage  408 , advance fluid passage  409 ); and the first fluid passage ( 202 ) has an opening at an axial end surface ( 300 ) of the camshaft ( 3   a,    3   b ), wherein the opening of the first fluid passage ( 202 ) is closed by the bottom of the camshaft insertion hole ( 402 ). This feature serves to eliminate the necessity of providing the first fluid passage ( 202 ) with a blind plug, and thereby reduce the number of parts and the manufacturing cost. 
     &lt;4-11&gt; In addition to the feature &lt;4-10&gt;, the valve timing control apparatus further comprises a positioning pin ( 45 ) fixedly inserted in the opening of the first fluid passage ( 202 ), and inserted in a recess ( 44 ) formed in the bottom of the camshaft insertion hole ( 402 ), so as to position the rotor ( 40 ) and the camshaft ( 3   a,    3   b ) with respect to one another in a rotational direction. The feature that the opening of the first fluid passage ( 202 ) is used to fix the positioning pin ( 45 ), and thereby constitutes a positioning means, serves to reduce the manufacturing cost. 
     &lt;4-12&gt; In addition to the feature &lt;4-2&gt;: the vane rotor ( 4 ) is formed with a second back pressure passage ( 58 ,  406 ) that includes a recess formed in an axial end surface (X-axis positive side axial end surface) of the vane rotor ( 4 ) farther from the camshaft ( 3   a,    3   b ); and the back pressure relief section ( 407 ) is a back pressure hole that is hydraulically connected to the back pressure chamber ( 50 ) through the second back pressure passage (radial groove  58 , circular recess  406 ). This feature serves to reduce the axial size of the housing (HSG), while maintaining the working ability of the vane rotor ( 4 ). 
     &lt;4-13&gt; In addition to the feature &lt;4-12&gt;: each of the fixing portions (bolt holes  403 ,  404  and  405 ) is a bolt insertion hole extending through the rotor ( 40 ), wherein a camshaft bolt ( 33 ,  34 ,  35 ) extends through the bolt insertion hole, and fixes the rotor ( 40 ) to an axial end surface ( 300 ) of the camshaft ( 3   a,    3   b ); the second back pressure passage ( 58 ,  406 ) includes: a circular recess ( 406 ) formed in the axial end surface of the vane rotor ( 4 ); and a radial groove ( 58 ) extending from the circular recess ( 406 ) outwardly in a radial direction of the rotor ( 40 ), and hydraulically communicating with the back pressure chamber ( 50 ); and the circular recess ( 406 ) is formed with the bolt insertion holes ( 403 ,  404 ,  405 ) and the back pressure hole ( 407 ). This feature serves to suppress projection of the head ( 331 ,  341  or  351 ) of the camshaft bolt ( 33 ,  34  or  35 ), and thereby reduce the axial size of the valve timing control apparatus. This feature also serves to enhance the facility of processing and the flexibility of layout of the back pressure hole ( 407 ), and thereby makes it easy to make the rotor ( 40 ) compact in size. 
     &lt;4-14&gt; In addition to the feature &lt;4-13&gt;, the housing (HSG) includes: a housing body ( 10 ) having a hollow cylindrical shape; a front plate ( 8 ) sealing a first axial end of the housing body ( 10 ), and including a detachable cap ( 7 ) in a position to face the circular recess ( 406 ) of the vane rotor ( 4 ); and a rear plate ( 9 ) sealing a second axial end of the housing body ( 10 ) closer to the camshaft ( 3   a,    3   b ), wherein the camshaft ( 3   a,    3   b ) is inserted in the rear plate ( 9 ). This feature serves to suppress degradation of the belt ( 1010 ), while enhancing the mountability of the valve timing control apparatus. 
     &lt;4-15&gt; In addition to the feature &lt;4-14&gt;, the cap ( 7 ) is formed with a recess ( 73 ) at a surface facing the circular recess ( 406 ), wherein the recess ( 73 ) accommodates at least a part of a head ( 331 ,  341 ,  351 ) of the camshaft bolt ( 33 ,  34 ,  35 ). This feature serves to absorb the projection of the head ( 331 ,  341 ,  351 ) of the camshaft bolt ( 33 ,  34 ,  35 ), and thereby serves to make the valve timing control apparatus compact in size. 
     &lt;Fifth Group of Technical Features&gt; The following describes a fifth group of technical features, and advantageous effects produced by the features. Japanese Patent Application Publication No. 2000-002104 discloses a valve timing control apparatus of a vane type for an internal combustion engine, which includes an engaging member for restricting relative rotation between a vane rotor and a housing, wherein: the vane rotor is formed with a cylinder in which a hollow cylindrical member is fixed; and the engaging member is mounted in the cylinder, in sliding contact with an inside periphery of the hollow cylindrical member. This valve timing control apparatus is subject to a problem that the hollow cylindrical member may be fixed with inclination with respect to the cylinder, and thereby the engaging member may be mounted with inclination with respect to the cylinder. In view of the foregoing, it is desirable to provide a valve timing control apparatus for an internal combustion engine, in which inclination of an engaging member is suppressed. This problem is solved by a valve timing control apparatus in which a cylinder to which a cylindrical member is fixed is applied with anodic oxidation treatment. This feature serves to suppress inclination of the engaging member. The following describes each technical feature, and advantageous effects produced by the feature in detail. 
     &lt;5-1&gt; A valve timing control apparatus for an internal combustion engine, comprises: a hollow housing (HSG) adapted to receive torque; a vane rotor ( 4 ) formed of an aluminum-based metal material, and rotatably mounted in the housing (HSG), the vane rotor ( 4 ) including: a plurality of vanes ( 41 ,  42 ,  43 ) defining at least one working fluid chamber (first, second and third advance chambers A 1 , A 2  and A 3 , first, second and third retard chambers R 1 , R 2  and R 3 ) in the housing (HSG), wherein the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) is adapted to supply and drainage of working fluid; and a cylinder (slide hole  501 ) formed in the vane rotor ( 4 ), and anodized; a hollow cylindrical member (sealing member  502 ) fixed in the cylinder ( 501 ); a lock member (lock piston  51 ) slidably mounted in the hollow cylindrical member ( 502 ), the lock member ( 51 ) including a tip arranged to move forward and rearward with respect to the vane rotor ( 4 ) according to an operating state of the internal combustion engine; a lock recess (engaging recess  521 ) provided in an axial end portion of the housing (HSG) facing the tip of the lock member ( 51 ), wherein the tip of the lock member ( 51 ) is adapted to be inserted in the lock recess ( 521 ); and a biasing member (coil spring  53 ) mounted in the cylinder ( 501 ), and arranged to bias the lock member ( 51 ) toward the lock recess ( 521 ). The feature that the cylinder ( 501 ), lock member ( 51 ), lock recess ( 521 ), and biasing member (coil spring  53 ) constitute a lock mechanism, serves to suppress, by the simply-constructed lock mechanism, noise that may be caused by the valve timing control apparatus at start of the internal combustion engine. The feature that the vane rotor ( 4 ) is formed of the aluminum-based metal material, serves to reduce the weight of the valve timing control apparatus ( 1 ). The feature that the hollow cylindrical member is fixed in the cylinder whose surface is hardened by anodic oxidation treatment, serves to suppress inclination of the hollow cylindrical member, and thereby maintain the working ability of the lock member, and maintain the controllability of the valve timing control apparatus. The feature &lt;5-1&gt; is implemented so that: the torque is transmitted from a crankshaft to the housing (HSG); the housing (HSG) is formed integrally with a shoe ( 11 ,  12 ,  13 ) at an inside periphery of the housing (HSG), and wherein the shoe ( 11 ,  12 ,  13 ) projects inwardly in a radial direction of the housing (HSG); the plurality of vanes ( 41 ,  42 ,  43 ) define an advance chamber (A 1 , A 2  or A 3 ) and a retard chamber (R 1 , R 2  or R 3 ) in cooperation with the shoe ( 11 ,  12 ,  13 ); a rotor ( 40 ) is disposed in a position surrounded by and closer to an axis of rotation than the vanes ( 41 ,  42 ,  43 ); the lock member is a lock pin ( 51 ); and the hollow cylindrical member (sealing member  502 ) is a ring-shaped member. 
     &lt;5-2&gt; In addition to the feature &lt;5-1&gt;, the cylinder (slide hole  501 ) extends in an axial direction of the vane rotor ( 4 ) so that the tip of the lock member (lock piston  51 ) moves forward and rearward in the cylinder ( 501 ) in the axial direction of the vane rotor ( 4 ). This feature serves to stabilize the locking operation. 
     &lt;5-3&gt; In addition to the feature &lt;5-1&gt;, the hollow cylindrical member (sealing member  502 ) is formed of a material having a higher wear resistance than anodic oxide coating. This feature serves to suppress wear of the cylinder (slide hole  501 ) effectively. 
     &lt;5-4&gt; In addition to the feature &lt;5-1&gt;, the hollow cylindrical member (sealing member  502 ) is press-fitted in the cylinder (slide hole  501 ). This feature makes it easy to set and fix the hollow cylindrical member, and prevent the hollow cylindrical member from being fixed with inclination. 
     &lt;5-5&gt; In addition to the feature &lt;5-1&gt;, a surface of the vane rotor ( 4 ) including an inside peripheral surface of the cylinder (slide hole  501 ) is anodized. This feature makes it possible to easily manufacture the valve timing control apparatus according to the feature &lt;5-1&gt;, while enhancing the wear resistance of a portion of the vane rotor ( 4 ) in sliding contact with the housing (HSG). 
     &lt;5-6&gt; In addition to the feature &lt;5-1&gt;: the hollow cylindrical member (sealing member  502 ) has a shorter longitudinal size than the cylinder (slide hole  501 ), and extends from a longitudinal end of the cylinder ( 501 ); the lock member (lock piston  51 ) includes a small-diameter portion (sliding portion  512 , engaging portion  511 ) and a large-diameter portion (flange  513 ); the small-diameter portion ( 512 ,  511 ) is slidably fitted to an inside periphery of the hollow cylindrical member ( 502 ); and the large-diameter portion ( 513 ) is slidably fitted to an inside periphery of the cylinder ( 501 ). This feature serves to simply define a plurality of chambers for applying individual forces to the lock member. The feature &lt;5-6&gt; is implemented so that: the small-diameter portion (engaging portion  511 ) of the lock member (lock piston  51 ) is adapted to move forward and backward with respect to the vane rotor ( 4 ), and move into the lock recess (engaging recess  521 ). The small-diameter portion ( 512 ,  511 ) is a distal end portion of the lock member, whereas the large-diameter portion ( 513 ) is a proximal end portion of the lock member, wherein the biasing member is arranged to bias the lock member from the large-diameter portion (proximal end portion) to the small-diameter portion (distal end portion). 
     &lt;5-7&gt; In addition to the feature &lt;5-6&gt;: the vanes ( 41 ,  42 ,  43 ) define at least two of the working fluid chambers as an advance chamber (first advance chamber A 1 ) and a retard chamber (first retard chamber R 1 ) in the housing (HSG); one of the advance chamber and the retard chamber (A 1 ) is hydraulically connected for hydraulic pressure supply to a space (second pressure-receiving chamber  59 ) between the tip of the lock member (lock piston  51 ) and the axial end portion (the X-axis positive side surface of rear plate  9 ) of the housing (HSG) facing the tip of the lock member ( 51 ); and another one of the advance chamber and the retard chamber (R 1 ) is hydraulically connected for hydraulic pressure supply to a space (first pressure-receiving chamber  55 ) between the large-diameter portion (flange  513 ) of the lock member ( 51 ) and the hollow cylindrical member (sealing member  502 ). This feature serves to reduce the frequency of operation of the lock member, and thereby enhance the durability of the valve timing control apparatus. 
     &lt;5-8&gt; In addition to the feature &lt;5-6&gt;: the hollow cylindrical member (sealing member  502 ) is formed of a material having a higher wear resistance than anodic oxide coating; and a smaller clearance is provided between the small-diameter portion (sliding portion  512 ) of the lock member (lock piston  51 ) and the inside periphery of the hollow cylindrical member ( 502 ) than between the large-diameter portion (flange  513 ) of the lock member ( 51 ) and the inside periphery of the cylinder (slide hole  501 ). This feature serves to further suppress wear of the sliding portion in sliding contact with the lock member. 
     &lt;5-9&gt; In addition to the feature &lt;5-1&gt;: the housing (HSG) is formed with a shoe ( 11 ) at an inside periphery of the housing (HSG); and one of the tip (engaging portion  511 ) of the lock member (lock piston  51 ) and the lock recess (engaging recess  521 ) has an inclined surface through which the biasing member (coil spring  53 ) applies a biasing force so as to press one of the vanes ( 41 ) to the shoe ( 11 ). This feature serves to produce a wedging effect by which the vane rotor ( 4 ) can be reliably fixed in a lock position, while maintaining the working ability of the lock member according to the feature &lt;5-1&gt;. The feature &lt;5-9&gt; is implemented so that the tip (engaging portion  511 ) of the lock member is formed with a tapered surface whose diameter gradually decreases as followed toward the tip end, whereas the lock recess (engaging recess  521 ) is formed with a tapered surface whose diameter gradually decreases as followed toward the bottom end. This feature serves to reduce wear of the surfaces of the lock member and the lock recess, while enhancing the wedging effect, because both of the lock member and the lock recess are formed with inclined surfaces. 
     &lt;5-10&gt; A method of producing a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus comprising: a hollow housing (HSG) adapted to receive torque, and is formed with a shoe ( 11 ,  12 ,  13 ) at an inside periphery of the housing (HSG), wherein the shoe ( 11 ,  12 ,  13 ) projects inwardly in a radial direction of the housing (HSG); a vane rotor ( 4 ) formed of an aluminum-based metal material, and rotatably mounted in the housing (HSG), the vane rotor ( 4 ) including: a rotor ( 40 ); a plurality of vanes ( 41 ,  42 ,  43 ) projecting outwardly with respect to the rotor ( 40 ), and defining at least one working fluid chamber (advance chamber A 1 , A 2  or A 3 , or retard chamber R 1 , R 2  or R 3 ) together with the shoe ( 11 ,  12 ,  13 ), wherein the working fluid chamber (A 1 , A 2 , A 3 , R 1 , R 2 , R 3 ) is adapted to supply and drainage of working fluid; and a cylinder (slide hole  501 ) extending in an axial direction of the vane rotor ( 4 ); a ring-shaped member (sealing member  502 ) formed of a material having a higher wear resistance than anodic oxide coating, and fixed in the cylinder ( 501 ); a lock pin (lock piston  51 ) including a tip (sliding portion  512 ) slidably mounted in the ring-shaped member ( 502 ), wherein the tip (engaging portion  511 ) is arranged to move forward and rearward in the axial direction with respect to the vane rotor ( 4 ) according to an operating state of the internal combustion engine; a lock recess (engaging recess  521 ) provided in an axial end portion of the housing (HSG) facing the tip of the lock pin ( 51 ), wherein the tip of the lock pin ( 51 ) is adapted to be inserted in the lock recess ( 521 ); and a biasing member (coil spring  53 ) mounted in the cylinder ( 501 ), and arranged to bias the lock pin ( 51 ) toward the lock recess ( 521 ), the method comprises: a first operation of forming the cylinder ( 501 ) in the vane rotor ( 4 ); a second operation of anodizing an entire surface of the vane rotor ( 4 ) after the first operation; and a third operation of press-fitting the ring-shaped member ( 502 ) into the cylinder ( 501 ) so as to fix the ring-shaped member ( 502 ) to the cylinder ( 501 ), after the second operation. This feature makes it possible to easily manufacture the valve timing control apparatus according to the features &lt;5-1&gt; to &lt;5-5&gt;. 
     The entire contents of Japanese Patent Application No. 2009-214723 filed Sep. 16, 2009 are incorporated herein by reference. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.