Patent Publication Number: US-8534247-B2

Title: Valve timing control apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2011-24341 filed on Feb. 7, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a valve timing control apparatus for controlling a valve timing of a valve, which is opened and closed by a camshaft according to a torque transmitted from a crankshaft in an internal combustion engine. 
     2. Description of Related Art 
     Conventionally, a known valve timing control apparatus includes a housing, which is rotatable with rotation of a crankshaft, and a vane rotor, which is rotatable with rotation of a camshaft. JP-A-2010-285918 (US 2010/0313835 A1) describes a valve timing control apparatus in which a rotation phase of a vane rotor is changed toward advance side or retard side relative to a housing by introducing working fluid into an advance chamber or a retard chamber which are separated from each other in a rotation direction by the vane rotor in the housing. The valve timing control apparatus has a control valve and a linear solenoid. The control valve controls the flow of working fluid relative to the advance chamber and the retard chamber based on a reciprocation of a spool in a sleeve. An output shaft of the linear solenoid drives the spool of the control valve. 
     JP-A-2005-45217 (US 2004/0257185) discloses such a linear solenoid having a pair of cylindrical stators that oppose to each other through an air gap in an axis direction and a needle that reciprocates integrally with the output shaft. The pair of cylindrical stators and the needle are accommodated in an internal chamber of a casing. An energized coil generates a magnetic flux that passes through a magnetic circuit, and the pair of stators forms the magnetic circuit together with the needle, so that the needle reciprocates on the inner circumference side. As a result, the control valve controls the flow of working fluid relative to the advance chamber and the retard chamber based on the reciprocation of the spool. Thus, the valve timing is controlled by the change of the rotation phase. 
     In a case where the linear solenoid is applied to the valve timing control apparatus, when the working fluid passes through the sleeve open to the linear solenoid, a part of the working fluid flows into the internal chamber of the casing from a bearing clearance of the output shaft, for example. In this case, if a foreign object such as metal powder having magnetic property (hereinafter referred as magnetic object) is contained in the working fluid, the magnetic object may stay in the air gap between the pair of stators, so that unnecessary short circuit may be generated in the magnetic circuit. 
     As shown in FIG. 14 of JP-A-2005-45217, the linear solenoid has a cylindrical coil bobbin that fits with an outer circumference side of the pair of stators in the internal chamber of the casing, so that the short circuit may be restricted from being generated. However, because the air gap is surrounded by the bobbin from the outer circumference side, the air gap has no outlet for the magnetic object. If the magnetic objects stays in the air gap, the function of restricting the short circuit is lowered. The short circuit causes a lowering in the responsivity of the spool that is driven by the output shaft, so that the responsivity of the valve timing control may be lowered. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a valve timing control apparatus for controlling a valve timing of a valve configured to be opened and closed by a camshaft in accordance with a torque transmitted from a crankshaft of an internal combustion engine includes a housing, a vane rotor, a control valve, and a linear solenoid. The housing is rotatable with the crankshaft. The vane rotor is rotatable with the camshaft, and partitions an interior of the housing into an advance chamber and a retard chamber in a rotative direction. The vane rotor is configured to change a rotation phase relative to the housing to an advance side or a retard side correspondingly when working fluid is supplied into the advance chamber or the retard chamber. The control valve controls a flow of the working fluid relative to the advance chamber and the retard chamber through a spool that is linearly movable in a sleeve through which the working fluid passes, and is arranged in a gang rotating element constructed by the vane rotor and the camshaft. The linear solenoid has an output shaft that linearly reciprocates the spool, a coil, a casing, a needle, a pair of cylindrical stators, and a cylindrical spacer. The coil generates a magnetic flux by being supplied with electricity. The casing defines an internal chamber into which the working fluid flows from the sleeve, and a discharge port from which the working fluid is discharged out of the internal chamber. The needle reciprocates integrally with the output shaft in the internal chamber. The pair of cylindrical stators oppose with each other through an air gap in an axis direction in the internal chamber. The pair of stators and the needle form a magnetic circuit through which the magnetic flux passes so as to drive the needle to reciprocate on an inner circumference side of the pair of stators. The cylindrical spacer fits with an outer circumference side of the pair of stators in the internal chamber so as to restrict a short circuit from being generated in the magnetic circuit between the pair of stators. The air gap is located on an inner circumference side of the spacer. The spacer defines a discharge passage that connects the air gap to the discharge port of the casing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a sectional view illustrating a valve timing control apparatus according to an embodiment; 
         FIG. 2  is a sectional view taken along a line II-II in  FIG. 1 ; 
         FIG. 3  is a sectional view illustrating an operational state of the valve timing control apparatus; 
         FIG. 4  is a sectional view illustrating an operational state of the valve timing control apparatus; 
         FIG. 5  is a sectional view illustrating an operational state of the valve timing control apparatus; 
         FIG. 6  is an enlarged sectional view illustrating a linear solenoid of the valve timing control apparatus; 
         FIG. 7  is an enlarged sectional view of a relevant portion VII in  FIG. 6 ; 
         FIG. 8A  is a side view illustrating a spacer of the linear solenoid, and  FIG. 8B  is a perspective view illustrating the spacer; 
         FIG. 9  is a sectional view illustrating a modification example of  FIG. 6 ; and 
         FIG. 10  is a sectional view illustrating a modification example of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     (Embodiment) 
       FIG. 1  shows an example of a valve timing control apparatus  1  according to an embodiment, which is applied to an internal combustion engine of a vehicle. The valve timing control apparatus  1  controls a valve timing of an intake valve by using a working fluid such as oil. 
     (Basic Construction) 
     The valve timing control apparatus  1  includes an actuator portion  10  and a control portion  40 . The actuator portion  10  is provided to a transmission system, which transmits engine torque from a crankshaft (not shown) to a camshaft  2 , and driven by the working fluid. The control portion  40  controls supply of the working fluid to the actuator portion  10 . 
     (Actuator Portion) 
     In the actuator portion  10 , a metallic housing  11  has a shoe ring  12 , and a rear plate  13  and a front plate  15  are coupled to ends of the ring  12 , respectively, in the axis direction. The shoe ring  12  includes a tubular housing body  120 , multiple shoes  121 ,  122 ,  123  and a sprocket  124 . The shoes  121 ,  122 ,  123  function as partitioning parts. The shoes  121 ,  122 ,  123  are projected to the radially inner side from portions of the housing body  120 . The portions of the shoes  121 ,  122 ,  123  are spaced by a prescribed distance in a rotation direction of the housing body  120 . The shoes  121 ,  122 ,  123 , which are adjacent to each other in the rotation direction, form an accommodation chamber  20  therebetween. The sprocket  124  is connected with the crankshaft via a timing chain (not shown). According to the present structure, engine torque is transmitted from the crankshaft to the sprocket  124  during an operation of the internal combustion engine. Thereby, the housing  11  rotates in the clockwise rotation of  FIG. 2  with rotation of the crankshaft. 
     A metallic vane rotor  14  is accommodated coaxially in the housing  11 , and is slidably in contact with the rear plate  13  and the front plate  15  at both sides in the axial direction. The vane rotor  14  includes a tubular rotation axis  140  and vanes  141 ,  142 ,  143 . The rotation axis  140  is coaxially fixed to the camshaft  2 . In the present structure, the vane rotor  14  is rotatable in the clockwise rotation of  FIG. 2  with rotation of the camshaft  2 . In addition, the vane rotor  14  is rotatable relative to the housing  11 . 
     The vanes  141 ,  142 ,  143  project radially outward from portions of the rotation axis  140 . The portions of the rotation axis  140  are spaced by a prescribed distance in the rotation direction. The vanes  141 ,  142 ,  143  are respectively accommodated in corresponding accommodation chambers  20 . 
     The vanes  141 ,  142 ,  143  respectively partition the accommodation chambers  20  correspondingly to form advance chambers  22 ,  23 ,  24  and retard chambers  26 ,  27 ,  28  in the housing  11 . An advance chamber  22  is formed between the shoe  121  and the vane  141 . An advance chamber  23  is formed between the shoe  122  and the vane  142 . An advance chamber  24  is formed between the shoe  123  and the vane  143 . A retard chamber  26  is formed between the shoe  122  and the vane  141 . A retard chamber  27  is formed between the shoe  123  and the vane  142 . A retard chamber  28  is formed between the shoe  121  and the vane  143 . 
     The vane  141  accommodates a lock member  16  to be fitted with a lock hole  130  of the front plate  13  so as to lock the rotation phase of the vane rotor  14  relative to the housing  11 . Further, the vane  141  has an unlock chamber  17  into which the working oil is introduced to unlock the rotation phase by separating the lock member  16  from the lock hole  130 . 
     In a state that the rotation phase is unlocked by the lock member  16 , if working fluid is introduced into the advance chamber  22 ,  23 ,  24  and is discharged from the retard chamber  26 ,  27 ,  28 , the rotation phase is advanced, so that the valve timing is advanced. In contrast, if working fluid is introduced into the retard chamber  26 ,  27 ,  28 , and is discharged from the advance chamber  22 ,  23 ,  24 , the rotation phase is retarded, so that the valve timing is retarded. 
     (Control Portion) 
     In the control portion  40 , an advance main passage  41  is formed along the inner circumferential periphery of the rotation axis  140 . Advance branch passages  42 ,  43 ,  44  extend through the rotation axis  140 . The advance branch passages  42 ,  43 ,  44  respectively communicate with the corresponding advance chambers  22 ,  23 ,  24  and the common advance main passage  41 . 
     A retard main passage  45  is defined by an annular groove opened in the inner circumferential periphery of the rotation axis  140 . Retard branch passages  46 ,  47 ,  48  extend through the rotation axis  140  and respectively communicate with the corresponding retard chambers  26 ,  27 ,  28  and the common retard main passage  45 . An unlock passage  49  extends through the rotation axis  140  and communicates with the lock chamber  17 . 
     A main supply passage  50  extends through the rotation axis  140 . The main supply passage  50  communicates with a pump  4 , which functions as a supply source, through a conveyance passage  3  of the camshaft  2 . The pump  4  is a mechanical pump driven by the crankshaft with a driving operation of the internal combustion engine. During the engine operation, the pump  4  regularly discharges working fluid drawn from a drain pan  5 . The conveyance passage  3  is always communicating with a discharge port of the pump  4  irrespective to the rotation of the camshaft  2 , thereby working oil is regularly sent from the pump  4  toward the main supply passage  50  during the engine operation. 
     A sub-supply passage  52  extends through the rotation axis  140 , and is branched from the main supply passage  50 . The passage  52  receives working oil supplied from the pump  4  through the main supply passage  50 . 
     A drain collection passage  54  is defined outside of the actuating portion  10  and the camshaft  2 . The passage  54  is exposed to atmospheric air with the drain pan  5  corresponding to a drain collector, and the working oil is dischargeable from the passage  54  to the pan  5 . 
     A control valve  60  is a spool valve to reciprocate a spool  68  in a sleeve  66  in the axis direction using an elastic biasing force generated by a biasing member  80  and a driving force generated by energizing a linear solenoid  70 . The elastic biasing force and the driving force are applied in opposite directions in the axis direction. The control valve  60  and the biasing member  80  are coaxially arranged in a gang rotating element  2 ,  14  constructed by the camshaft  2  and the vane rotor  14 , so that the control valve  60  and the biasing member  80  rotate together with the gang rotating element  2 ,  14 . 
     Specifically, the control valve  60  is defined in a manner that the metallic spool  68  is slidably accommodated in the metallic sleeve  66 . The sleeve  66  has an advance port  661 , a retard port  662 , an unlock port  663 , a main supply port  664 , a sub-supply port  665 , and a drain port  666 . 
     The advance port  661  communicates with the advance main passage  41 . The retard port  662  communicates with the retard main passage  45 . The unlock port  663  communicates with the unlock passage  49 . 
     The main supply port  664  communicates with the main supply passage  50 . The sub-supply port  665  communicates with the sub-supply passage  52 . The pair of the drain port  666  communicates with the drain collection passage  54 . The control valve  60  switches the connection state among the ports  661 ,  662 ,  663 ,  664 ,  665 ,  666  based on a variation in the position of the spool  68 , as shown in  FIGS. 1 ,  3 ,  4  and  5 , thereby controlling the flow of working oil relative to the chamber  17 ,  22 ,  23 ,  24 ,  26 ,  27 ,  28 .  FIG. 1  shows the spool  68  located in a rock region Rl.  FIG. 3  shows the spool  68  located in an advance region Ra.  FIG. 4  shows the spool  68  located in a holding region Rh.  FIG. 5  shows the spool  68  located in a retard region Rr. 
     When the spool  68  is positioned in the lock region Rl, as shown in  FIG. 1 , the advance port  661  is connected to the main supply port  664 . At this time, the working oil supplied from the pump  4  is throttled and introduced into the advance chamber  22 ,  23 ,  24 . Further, the retard port  662  and the unlock port  663  are connected to the drain port  666 . At this time, the working oil of the chamber  26 ,  27 ,  28 ,  17  is discharged into the drain pan  5 . Thus, in the rock region Rl, small amount of the working oil is introduced into the advance chamber  22 ,  23 ,  24  and the working oil is discharged from the retard chamber  26 ,  27 ,  28  and the unlock chamber  17 , so that the rotation phase is locked. 
     When the spool  68  is positioned in the advance region Ra, as shown in  FIG. 3 , the advance port  661  is connected with the main supply port  664 , and the lock activation port  663  is connected to the sub-supply port  665 . At this time, the working oil supplied from the pump  4  is introduced into the advance chamber  22 ,  23 ,  24  and the unlock chamber  17 . Further, the retard port  662  is connected to the drain port  666 . At this time, the working oil of the retard chamber  26 ,  27 ,  28  is discharged into the drain pan  5 . Thus, in the advance region Ra, the working oil is introduced into the advance chamber  22 ,  23 ,  24  and the working oil is discharged from the retard chamber  26 ,  27 ,  28  under the situation that rotation phase is unlocked, so that the rotation phase is advanced and that the valve timing is advanced. 
     When the spool  68  is positioned in the holding region Rh, as shown in  FIG. 4 , the advance port  661  and the retard port  662  are disconnected from any other port. At this time, the working oil can be held in the advance chamber  22 ,  23 ,  24  and the retard chamber  26 ,  27 ,  28 . Further, the lock activation port  663  is connected to the sub-supply port  665 . At this time, the working oil supplied from the pump  4  is introduced into the lock chamber  17 . Thus, in the holding region Rh, the working oil stays in the advance chamber  22 ,  23 ,  24  and the retard chamber  26 ,  27 ,  28  under the situation that rotation phase is unlocked, so that the valve timing is held in a variation range of the rotation phase caused by a fluctuating torque. 
     When the spool  68  is positioned in the retard region Rr, as shown in  FIG. 5 , the retard port  662  is connected to the main supply port  664 , and the unlock port  663  is connected to the sub-supply port  665 . At this time, the working oil supplied from the pump  4  is introduced into the retard chamber  26 ,  27 ,  28  and the unlock chamber  17 . Further, the advance port  661  is connected with the drain port  666 . At this time, the working oil of the advance chamber  22 ,  23 ,  24  is discharged into the drain pan  5 . Thus, in the retard region Rr, the working oil is discharged from the advance chamber  22 ,  23 ,  24  and the working oil is introduced into the retard chamber  26 ,  27 ,  28  under the situation that rotation phase is unlocked, so that the rotation phase is retarded and that the valve timing is retarded. 
     In the control valve  60 , the working oil passes through an internal space  667  of the sleeve  66 . Therefore, especially in the region Rl, Ra, Rr in which the working oil passes through the drain port  666 , the working oil discharged into the drain collection passage  54  located outside is introduced into the drain pan  5  from an opening  668  of the sleeve  66 . The opening  668  forms the drain port  666  located adjacent to the linear solenoid  70 , and communicates with the internal space  667 . 
     A control circuit  90  shown in  FIG. 1  is an electronic control device including, for example, a microcomputer and the like. The control circuit  90  is electrically connected with the solenoid  70  and devices (not shown) of the engine. The control circuit  90  controls energization of the solenoid  70  based on a program memorized in an internal memory. In addition, the control circuit  90  controls a driving operation of the internal combustion engine. 
     (Linear Solenoid) 
     The linear solenoid  70  will be described with reference to  FIGS. 1 ,  6  and  7  in which a left-and-right direction corresponds to a horizontal direction of a vehicle disposed on a horizontal surface, and an up-and-down direction corresponds to a vertical direction of the vehicle. 
     As shown in  FIG. 1 , the flat type linear solenoid  70  has a casing  71 , a mold case  72 , a coil  73 , a terminal  74 , an output shaft  75 , a pair of stators  76 ,  77 , a needle  78 , and a spacer  79 . 
     The casing  71  is constructed by a pair of cups  710 ,  711  made of magnetic material such as steel, and has a hollow shape defining an internal chamber  712 . The casing  71  is fixed to a fix part of the engine such as a chain case, and is always kept in the fixed state relative to the rotation of the control valve  60  integrated with the camshaft  2  and the vane rotor  14 . 
     As shown in  FIG. 1 , the based cylindrical front cup  710  is arranged in a manner that the center of the bottom of the cup  710  coaxially opposes to the opening  668  of the sleeve  66  of the control valve  60 , from which the working oil is discharged from the internal space  667 . The center of the bottom of the front cup  710  has an aspiration hole  713  and a bearing hole  715 . The internal chamber  712  is opened to atmospheric air through the hole  713 . The output shaft  75  is supported by the bearing hole  715  through a bearing bush  714 . The bottom of the front cup  710  has a discharge port  716  from which the working oil of the internal chamber  712  is discharge outside of the casing  71 . The discharge port  716  is distanced from the opening  668 . 
     The mold case  72  is made of nonmagnetic resin, and is arranged to pass between the cups  710 ,  711 , so as to be located astride the inside and outside of the casing  71 . The mold case  72  has a bobbin  720  and a connector  721 . The bobbin  720  is accommodated in the internal chamber  712  of the casing  71 , and includes the coil  73 . The connector  721  protrudes outside of the casing  71 , and covers the terminal  74 . 
     The coil  73  has a cylindrical shape as a whole, and a metal wiring is would around the coil  73 . The coil  73  is coaxially arranged in each of the cups  710 ,  711  of the casing  71 . The metal wiring constructing the coil  73  is electrically connected with the control circuit  90  through the metal terminal  74 . Thereby, the coil  73  generates a flux of magnetic by being magnetized with electricity supplied from the control circuit  90 . 
     As shown in  FIG. 1 , the metallic output shaft  75  is shaped in a pillar stick, and penetrates the front cup  710  of the casing  71  through an inner circumference side of the bearing hole  715 . Outside of the casing  71 , the output shaft  75  coaxially contacts the spool  68  of the control valve  60  in view of the recovering force of the elastic member  80 , so that the spool  68  is reciprocable in both first and second directions Dg, Dr in the axis direction. 
     The front stator  76  is made of magnetic material such as steel, and is formed into a based cylindrical shape integrally with the front cup  710  of the casing  71 . In the internal chamber  712  of the casing  71 , the front stator  76  is coaxially arranged on the outer circumference side of the output shaft  75  and on the inner circumference side of the bobbin  720 . According to this arrangement, the center of the bottom of the front cup  710  opposing to the opening  668  of the sleeve  66  works as a bottom  760  of the front stator  76 . 
     As shown in  FIG. 6 , an inner circumference face  761  of the front stator  76  has an inner circumference tapered part  761   a  which inclines outward as approaching to a tip end  762  of the stator  76  from the bottom  760  in the axis direction. Moreover, an outer circumference face  763  of the front stator  76  has a straight part  763   a  straightly extended from the bottom  760 , and a tapered part  763   b  which inclines inward as approaching to the tip end  762  from the straight part  763   a . Therefore, a thickness of the front stator  76  in the radial direction becomes thin as approaching to the tip end  762  in a portion of the stator  76  forming the tapered part  761   a ,  763   b  on the both sides in the radial direction. 
     As shown in  FIG. 1 , the rear stator  77  has a double cylindrical shape constructed by a pair of pipe components  770 ,  771  made of magnetic material such as steel, and is coaxially arranged in the internal chamber  712  of the casing  71  on the outer circumference side of the output shaft  75  and on the inner circumference side of the bobbin  720 . 
     As shown in  FIG. 6 , the pipe component  770 ,  771  has a cylinder shape with a flange part  772 ,  773  that is in face contact with the bottom of the rear cup  711 . Moreover, the flange part  773  of the external pipe component  771  has a concave  774  on the inner circumference side, and the concave  774  fits to the flange part  772  of the internal pipe component  770 , so that the pipe components  770 ,  771  are magnetically connected with each other. 
     As shown in  FIG. 6 , an inner circumference face  775  of the external pipe component  771  has an inner circumference straight part  775   a  straightly extended from the flange part  773  to a tip end  776  of the external pipe component  771  in the axis direction. Further, an outer circumference face  777  of the external pipe component  771  has a step part  777   a  and a tapered part  777   b . The step part  777   a  is extended from the flange part  773 , and a diameter of the step part  777   a  is reduced compared with that of a flat part. The tapered part  777   b  inclines inward as approaching from the step part  777  to the tip end  776 . Therefore, a thickness of the external pipe component  771  in the radial direction becomes thin as approaching to the tip end  776  in a portion of the external pipe component  771  forming the straight part  775   a  and the tapered part  777   b  on the both sides in the radial direction. 
     As shown in  FIGS. 6 and 7 , the straight part  775   a  has a constant internal diameter, and an inner diameter of the tip end  776  of the external pipe component  771  is coincident with the inner diameter of the straight part  775   a . An inner diameter of the tip end  762  of the front stator  76  is coincident with the minimum inner diameter of the tapered part  761   a . The inner diameter of the tip end  776  is set approximately the same as the inner diameter of the tip end  762 . 
     Moreover, the maximum outer diameter of the tapered part  777   b  of the external pipe component  771  is set approximately the same as the maximum outer diameter of the tapered part  763   b  of the front stator  76 . Thus, the rear stator  77  and the front stator  76  oppose with each other in a state where the air gap AG that continues around the common axis line O is defined between the tip ends  776 ,  762  and between the tapered parts  777   b ,  763   b , in the axis direction. 
     As shown in  FIG. 1 , the cylindrical needle  78  is made of magnetic material such as steel, and is arranged in the internal chamber  712  of the casing  71  in the state that the needle  78  is coaxially fitted and fixed to the outer circumference side of the output shaft  75 . In this embodiment, the output shaft  75  is supported by the internal pipe component  770  of the rear stator  77  through a bearing bush  778 , so that the needle  78  is also supported by the internal pipe component  770 . Therefore, as shown in  FIGS. 1 ,  3 ,  4 , and  5 , the needle  78  is linearly movable together with the output shaft  75  on the inner circumference side of the external pipe component  771  of the rear stator  77 , on the inner circumference side of the air gap AG, and on the inner circumference side of the front stator  76 . 
     As shown in  FIG. 6 , an inner circumference face  782  of the needle  78  has an inner circumference straight part  782   a  straightly extended from a rear end part  781 , and an inner circumference tapered part  782   b  that inclines outward as approaching to a tip end  780  of the needle  78  from the straight part  782   a  in the axis direction. Further, an outer circumference face  783  of the needle  78  has an outer circumference straight part  783   a  straightly extended from the rear end part  781 , and an outer circumference tapered part  783   b  that inclines inward as approaching to the tip end  780  of the needle  78  from the straight part  783   a  in the axis direction. Therefore, a thickness of the needle  78  in the radial direction becomes thin as approaching to the tip end  780  in a portion of the needle  78  forming the tapered part  782   b ,  783   b  on the both sides in the radial direction. 
     The needle  78  forms the magnetic circuit through which the magnetic flux generated by the coil  73  passes together with the pair of stators  76 ,  77 , so that the needle  78  is reciprocated in the both directions Dg, Dr in the axis direction. Especially when the magnetic flux has the maximum density due to the maximum current supplying, the needle  78  makes the spool  68  to contact the sleeve  66  through the output shaft  75 , as shown in  FIG. 5 , so that the needle  78  is restricted from moving in the first direction Dg. In contrast, when the magnetic flux disappears due to the stop of the current supplying for the coil  73 , the rear end portion  781  of the needle  78  contacts the flange part  772  of the rear stator  77  in a state that the tip end  780  is located on the outer circumference side of the air gap AG, as shown in  FIGS. 1 ,  6  and  7 , so that the needle  78  is restricted from moving in the second direction Dr. 
     As shown in  FIG. 1 , the cylindrical spacer  79  made of nonmagnetic material is coaxially arranged in the internal chamber  712  of the casing  71  on the outer circumference side of the pair of stators  76 ,  77  and on the inner circumference side of the bobbin  720 . The center axis line O which is common for the spacer  79 , the stators  76 ,  77 , (the camshaft  2 , the vane rotor  14 , and the control valve  60 ) approximately corresponds to the horizontal direction of the vehicle located on the horizontal surface. 
     As shown in  FIG. 6 , an inner circumference face  790  of the spacer  79  has a tapered part  790   a ,  790   b  which inclines outward as approaching an end portion  793 ,  794  of the spacer  79  in the axis direction. Further, the inner circumference face  790  is coaxially press-fitted with the straight part  763   a  of the outer circumference face  763  of the front stator  76  and the step part  777   a  of the outer circumference face  777  of the external pipe component  771  of the rear stator  77 . Thus, the spacer  79  raises the coaxial accuracy between the stators  76 ,  77 , and restricts the magnetic flux generated by the coil  73  from directly forming a short circuit in the air gap AG between the stators  76 ,  77 . 
     Moreover, the spacer  79  defines a discharge passage  792  that connects the air gap AG to the discharge port  716  of the casing  71 . The discharge passage  792  is constructed by a discharge groove  791  defined on the inner circumference face  790 , and a part of the groove  791  is covered with the stator  76 ,  77 . As shown in  FIG. 8B , the groove  791  has three or more (for example, twelve in  FIG. 8A ) axial grooves  791   a  and one circumferential groove  791   b . The axial grooves  791   a  are located over most area of the spacer  79  except the end portion  793  opposing to the front stator  76 , and are arranged with constant intervals around the center axis line O. The axial groove  791   a  extends in the axis direction along the center axis line O, and communicates with the air gap AG through an aperture not covered with the stator  76 ,  77 . The axial groove  791   a  extends in both sides in the axis direction from the outer circumference side of the air gap AG including the lower part of the air gap AG. Further, in the end portion  793  of the spacer  79  opposing to the discharge port  716 , the circumferential groove  791   b  extends in the circumferential direction around the center axis line O, and connects the axial grooves  791   a  with each other. Therefore, the circumferential groove  791   b  communicates with the axial grooves  791  and the discharge port  716  in the axis direction. 
     When the coil  73  is not energized, as shown in  FIGS. 1 and 6 , the needle  79  receives the biasing force of the elastic member  80  through the spool  68  and the output shaft  75 , so that the rear end portion  781  contacts the flange part  772  of the rear stator  77 . Therefore, the needle  78  and the output shaft  75  are restricted from moving in the second direction Dr, and the spool  68  is positioned in the lock region Rl. At this time, the tip end  780  of the needle  78  is positioned on the outer circumference side of the air gap AG. 
     When energization of the coil  73  is started, the magnetic flux generated by the coil  73  passes from the flange part  772  of the rear stator  77 , and flows from the end portion  781  to the end portion  780  in the needle  78 . Further, the magnetic flux passes through the front stator  76  from the tip end  762  to the bottom  760 , so as to form the magnetic circuit. Therefore, the needle  78  is driven in the first direction Dg against the elastic force of the biasing member  80 , and the output shaft  75  integrated with the needle  78  drives the spool  68  in the first direction Dg. As a result, the rear end portion  781  of the needle  78  is separated from the rear cup  711 . The magnetic flux generated by the coil  73  passes from the tip end  776  of the rear stator  77  toward the tip end  780  of the needle  78 , further, passes through the front stator  76  toward the bottom  760 , so as to form the magnetic circuit. As the current supplied to the coil  73  is increased, as shown in  FIGS. 3 ,  4  and  5 , the needle  78  is moved in the first direction Dg, so that the spool  68  is moved among the regions Ra, Rh, Rr in accordance with the movement of the needle  78 . 
     The working oil easily flows into the internal chamber  712  of the casing  71  from the sleeve  66  through the opening  668  of the sleeve  66  and the aspiration hole  713  of the casing  71 . The spacer  79  fitted to the outer circumference side of the stators  76 ,  77  restricts a direct short circuit from being generated in the air gap AG between the stators  76 ,  77  in the internal chamber  712 . The spacer  79  is located to surround the air gap AG from the outer circumference side. When a magnetic foreign object such as metal powder is generated by a sliding between the housing  11  and the vane rotor  14  or a sliding between the sleeve  66  and the spool  68 , and when the magnetic foreign object is contained in the working oil, the magnetic foreign object may stay or accumulate in the air gap AG so as to form an unnecessary magnetic short circuit. 
     According to the embodiment, the axial groove  791   a  is partially covered with the stators  76 ,  77 , and the circumferential groove  791   b  is entirely covered with the stators  76 ,  77 , in the internal chamber  712 . Therefore, the discharge passage  792  is securely formed by the discharge groove  791 , and connects the air gap AG to the discharge port  716  of the casing  71 . The magnetic foreign object flows into the discharge passage  792  from the air gap AG together with the working oil, so that the magnetic foreign object is discharged out of the casing  71  through the port  716 . 
     At least one of the axial grooves  791   a , for example shown in  FIGS. 6 and 7 , is located under the air gap AG on the outer circumference side, and the magnetic foreign object easily drops into the at least one of the axial grooves  791   a  due to the gravity force. Further, the magnetic foreign object entering the axial groove  791   a  is guided by the working oil in the axis direction in which the groove  791   a  extends in the spacer  79 . Thereby, the object is discharged from the port  716  communicating with the axial groove  791   a  through the circumferential groove  791   b . Thus, the object can be restricted from staying in the air gap AG. 
     The inner circumference tapered part  761   a  of the front stator  76  inclines outward as approaching the tip end  762  adjacent to the air gap AG. Due to the tapered part  761   a , the working oil can smoothly flow toward the air gap AG. Therefore, the object can easily flow into the axial groove  791   a , so that the object can be restricted from staying in the air gap AG. 
     The thickness of the stator  76 ,  77  in the radial direction is made thinner as approaching the tip end  762 ,  776  opposing to the air gap AG, so that the density of the magnetic flux is raised at the tip end  762 ,  776 . Therefore, the magnetic object is easily attracted to the tip end  762 ,  776 . When the magnetic flux disappears, the attracted object is separated from the tip end  762 ,  776  to the air gap AG. As a result, the separated object easily enters the groove  791   a  located on the lower part, so that the object can be restricted from staying in the air gap AG. 
     The thickness of the needle  78 , that forms the magnetic circuit, in the radial direction is made thinner as approaching the tip end  780  opposing to the air gap AG, so that the density of the magnetic flux is raised at the tip end  780 . Therefore, the magnetic object is easily attracted to the tip end  780 . When the magnetic flux disappears, the attracted object is separated from the tip end  780  of the needle  78  located on the inner circumference side of the air gap AG. As a result, the separated object easily enters the groove  791   a , especially located on the lower part, so that the object can be restricted from staying in the air gap AG. 
     Accordingly, the function of the spacer  79  that restricts the magnetic short circuit from being generated can be maintained. Therefore, the responsivity of the spool  68  is raised when the output shaft  75  integrated with the needle  78  drives the spool  68 . Thus, the valve timing can be suitably controlled. In addition, air in the internal chamber  712  that provides a resistance for the movement of the needle  78  is discharged from the aspiration hole  713  in accordance with the movement. Therefore, the spool  68  is smoothly driven by the output shaft  75  integrated with the needle  78 , so that the valve timing can be suitably controlled. 
     The inner circumference face  790  of the spacer  79  has the inclined part  790   a ,  790   b  that inclines outward as approaching the end portion  793 ,  794  of the spacer  79  in the axis direction. Therefore, when the front stator  76  and the external pipe component  771  of the rear stator  77  are coaxially fitted into the spacer  79  from both sides in the axis direction, the stator  76 ,  77  is guided by the inclined part  790   a ,  790   b , so that the fitting can be easily performed. That is, the stator  76 ,  77  can be easily assembled, so that the productivity and the cost performance of the apparatus  1  can be raised. 
     The circumferential position of the spacer  79  is arbitrarily set relative to the stator  76 ,  77 . At least one of the axial grooves  791   a  can be located under the air gap AG between the stators  76 ,  77 . Further, the circumferential position of the spacer  79  is arbitrarily set relative to the discharge port  716 , because the circumferential groove  791   b  can be secured to communicate with the discharge port  716 . Due to such spacer  79 , the assembling can be easily performed, so that the productivity and the cost performance of the apparatus  1  can be raised. 
     (Other Embodiments) 
     The present invention is not limited to the above embodiment. 
     As shown in  FIG. 9 , an inner circumference tapered part  775   b  that inclines outward in the radial direction as approaching the tip end  776  may be formed on the inner circumference face  775  of the rear stator  77 . Further, the inner circumference tapered part  761   a  that inclines outward as approaching the tip end  762  from the bottom  760  may not be formed on the inner circumference face  761  of the front stator  76 . Furthermore, a thickness of at least one of the stator  76  and the stator  77  may be made constant, and a thickness of the needle  78  may be made constant. 
     The casing  71  may not have the aspiration hole  713 , or the hole  713  may be formed to be distanced from the opening  668  of the sleeve  66 . At least one of the inclined parts  790   a ,  790   b  may be omitted. 
     The number of the axial grooves  791   a  may be one. In this case, the axial groove  791   a  is located on the lower side of the air gap AG. Further, as shown in  FIG. 10 , the circumferential groove  791   b  may be omitted, and the axial groove  791   a  is positioned to oppose to the discharge port  716 . Furthermore, a through hole may be defined in the spacer  79 , and is opened in the inner circumference face  790  and the end portion  793  so as to form the discharge passage  792 . 
     The nonmagnetic spacer  79  forming the discharge passage  792  may be integrated with the bobbin  720 . The control valve  60  may have a construction other than the above description, if the spool  68  is driven in the sleeve  66  by the output shaft  75  of the linear solenoid  70 . The valve timing control apparatus  1  may be applied to a device that controls the valve timing of an exhaust valve other than the intake valve, or that controls the both of the exhaust valve and the intake valve. 
     Various modifications and alternations may be diversely made to the above embodiment without departing from the spirit of the present invention.