Patent Publication Number: US-7895980-B2

Title: Valve timing adjusting device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2007-297896 filed on Nov. 16, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a valve timing adjusting device which controls timing of opening and closing at least one of an intake valve and an exhaust valve in an internal combustion engine. Hereinafter, the above timing of opening and closing is referred to as valve timing. 
     2. Description of Related Art 
     Conventionally, a valve timing adjusting device that controls timing of opening and closing at least one of an intake valve and an exhaust valve in an internal combustion engine has improved the startability of the engine by a phase control for advancing and retarding valve timing at the start of the engine. As a known technique to assure high startability after a failure such as an engine stall, a return spring is mounted in a valve timing adjusting device for the phase control as described in JP-A-2007-138730. Typically, the phase control is performed for adjusting a phase relation between a crankshaft and a camshaft in the internal combustion engine. 
     However, in a case, where a return spring is mounted over a housing and a vane rotor of the valve timing adjusting device as described in JP-A-2007-138730, a biasing force of the return spring changes between (a) when the vane rotor of the device is positioned at in the most advance position and (b) when the vane rotor is positioned at the most retard position. As a result, the difference of the biasing force influences the phase control caused by working fluid pressure, and thereby making precise phase control difficult. 
     Because an average cam torque is large at the start of the engine at a very low temperature, the return spring biasing force is required to be increased. However, in a case, where the return spring biasing force is increased, the precise phase control by using the working fluid pressure may become difficult in normal operation of the engine disadvantageously. As a result, in the valve timing adjusting device, the return spring biasing force is required to be set to a level, which does not substantially influence the phase control in normal operation of the engine. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the above disadvantages. Thus, it is an objective of the present invention to address at least one of the above disadvantages. 
     To achieve the objective of the present invention, there is provided a valve timing adjusting device for an internal combustion engine, wherein the valve timing adjusting device is provided in a driving force transmission system of the engine, which transmits a driving force from a drive shaft to a driven shaft for opening and closing at least one of an intake valve and an exhaust valve, wherein the valve timing adjusting device adjusts timing of opening and closing the at least one of the intake valve and the exhaust valve. The valve timing adjusting device includes a housing, a first vane rotor, a second vane rotor, a biasing device, and a limiting device. The housing is rotatable together with one of the drive shaft and the driven shaft. The housing defines a plurality of receiving chambers therein, each of which is circumferentially defined within a given angular range. The first vane rotor is rotatable together with the other one of the drive shaft and the driven shaft. The first vane rotor partitions a first one of the plurality of receiving chambers into a first retard chamber and a first advance chamber. The first vane rotor is rotatable relatively to the housing in a retard direction and an advance direction, which is opposite to the retard direction, by pressure of working fluid supplied to the first retard chamber and the first advance chamber. The second vane rotor is positioned coaxially with the first vane rotor. The second vane rotor is rotatable relatively to the drive shaft and the driven shaft. The second vane rotor partitions a second one of the plurality of receiving chambers into a second retard chamber and a second advance chamber. The second vane rotor is rotatable relatively to the housing in the retard direction and the advance direction by pressure of working fluid supplied to the second retard chamber and the second advance chamber. The biasing device has a first end engaged with the first vane rotor and a second end engaged with the second vane rotor. The biasing device biases one of the first vane rotor and the second vane rotor in the advance direction. The biasing device biases the other one of the first vane rotor and the second vane rotor in the retard direction. The limiting device allows the first vane rotor to rotate relative to the second vane rotor when pressure of working fluid supplied from an external fluid supplier is lower than a preset level. The limiting device limits the first vane rotor from rotating relative to the second vane rotor when the pressure of working fluid supplied from the fluid supplier is equal to or higher than the preset level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which: 
         FIG. 1  is a sectional view taken along the line I-I in  FIG. 2  showing a valve timing adjusting device in a first embodiment of the present invention; 
         FIG. 2  is a sectional view taken along the line II-II in  FIG. 1  showing the valve timing adjusting device in the first embodiment; 
         FIG. 3  is a plan view from direction III in  FIG. 2  showing the valve timing adjusting device in the first embodiment; 
         FIG. 4  shows an operational state of the valve timing adjusting device in the first embodiment at a time immediately after engine stop; 
         FIG. 5  shows an operational state of the valve timing adjusting device in the first embodiment at a time immediately after the engine stop; 
         FIG. 6  shows an operational state of the valve timing adjusting device in the first embodiment in the course of or after engine stop or in the course of engine start; 
         FIG. 7  shows an operational state of the valve timing adjusting device in the first embodiment in the course of or after engine stop or in the course of engine start; 
         FIG. 8  shows an operational state of the valve timing adjusting device in the first embodiment after engine start; 
         FIG. 9  shows an operational state of the valve timing adjusting device in the first embodiment after engine start; 
         FIG. 10  shows an operational state of the valve timing adjusting device in a second embodiment of the present invention at a time immediately after engine stop; 
         FIG. 11  shows an operational state of the valve timing adjusting device in the second embodiment at a time immediately after engine stop; 
         FIG. 12  shows an operational state of the valve timing adjusting device in the second embodiment in the course of or after engine stop or in the course of engine start; 
         FIG. 13  shows an operational state of the valve timing adjusting device in the second embodiment in the course of or after engine stop or in the course of engine start; 
         FIG. 14  shows an operational state of the valve timing adjusting device in the second embodiment after engine start; and 
         FIG. 15  shows an operational state of the valve timing adjusting device in the second embodiment after engine start. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Next, the preferred embodiments of the present invention will be described in detail referring to the accompanying drawings. 
     First Embodiment 
       FIGS. 1 to 9  show a valve timing adjusting device  1  according to a first embodiment of the present invention. In the present embodiment, the valve timing adjusting device  1  is a hydraulic control system, which uses hydraulic oil as a working fluid, and which controls valve timing to set the exhaust valve of an internal combustion engine to an advance position at the start of the engine. In other words, the valve timing adjusting device  1  controls the engine phase to advance valve timing at the start of the engine. Typically, the engine phase indicates a phase relation between a crankshaft and a camshaft in the internal combustion engine. 
       FIGS. 1 to 3  show the mechanical structure of the valve timing adjusting device  1 . Each of  FIGS. 4 ,  5  shows an operational state of the valve timing adjusting device  1  at a time immediately after the stop of the internal combustion engine. Each of  FIGS. 6 ,  7  shows an operational state of the device  1  in the course of engine stop. Each of  FIGS. 8 ,  9  shows an operational state of the device  1  in time immediately after the engine start. 
     First, the mechanical structure of the valve timing adjusting device  1  is explained referring to  FIGS. 1 to 3 . The valve timing adjusting device  1  in the present embodiment includes a housing  10 , a first vane rotor  20 , a second vane rotor  25 , a fitting pin  56  (limiting device), and a return spring  60  (biasing device). 
     As shown in  FIG. 2 , the housing  10  as a driving rotator includes a chain sprocket  12 , a shoe housing  13 , and a front plate  11 . As shown in  FIG. 1 , the shoe housing  13  includes shoes  131 ,  132 ,  133 ,  134  (partition members) and a circular peripheral wall  130 , which are all integrally formed. The trapezoidal shoes  131 ,  132 ,  133 ,  134 , which extend radially inwardly from the peripheral wall  130 , are circumferentially disposed at generally regular intervals in the direction of rotation of the peripheral wall  130 . A receiving chamber  111  is provided between the shoes  131  and  132 , a receiving chamber  112  between the shoes  132  and  133 , a receiving chamber  113  between the shoes  133  and  134 , and a receiving chamber  114  between the shoes  134  and  131 . 
     As illustrated in  FIGS. 2 ,  3 , the shoe housing  13  and front plate  11  are fixed coaxially with the chain sprocket  12  through bolts  15 . Coupled with the crankshaft (not shown) serving as the drive shaft of the internal combustion engine, the chain sprocket  12  receives a driving force from the crankshaft and is rotatable together with the crankshaft. The driving force of the crankshaft is transmitted through the valve timing adjusting device  1  to a camshaft  3  (driven shaft) and opens and closes an intake valve (not shown). The camshaft  3  is received in the chain sprocket  12  such that the camshaft  3  is capable of rotating relatively with respect to the chain sprocket  12 . 
     The first vane rotor  20  as a driven rotator is in contact with one axial end face of the camshaft  3 , and the camshaft  3  and the first vane rotor  20  are coupled coaxially by the bolt  5 . The positioning of the first vane rotor  20  and camshaft  3  in the rotational direction is made by fitting a positioning pin (not shown) into the first vane rotor  20  and the camshaft  3  or by a similar method. The camshaft  3 , housing  10 , and first vane rotor  20  rotate clockwise as viewed in  FIG. 1 . Hereinafter this rotational direction is referred to as the advance direction of the camshaft  3  with respect to the crankshaft. The first vane rotor  20  is housed in the housing  10  in a way that the first vane rotor  20  is capable of rotating relatively with respect to the housing  10 . As illustrated in  FIG. 1 , the first vane rotor  20  has a cylindrical boss  26 , which is fixed on the camshaft  3 , and a first vane  41 , which is formed on a radially outer side of the first vane rotor  20 . The first vane  41  is in slidable contact with a radially outer side of a boss  27  of a second vane rotor  25  (described later) and rotatably housed in the receiving chamber  111 . The first vane  41  partitions the receiving chamber  111  into an advance chamber  35  (first advance chamber) and a retard chamber  30  (first retard chamber). 
     The arrows in  FIG. 1 , which indicate the retard and advance directions respectively, represent the retard and advance directions of the first vane rotor  20  with respect to the housing  10 . The first vane  41  has a contact portion  49 , which contacts the shoe  132 , and a contact portion  48 , which contacts the shoe  131 . The contact portions  48 ,  49  limit the range of rotation of the first vane rotor  20  by contacting the shoes  131 ,  132 , respectively. 
     The second vane rotor  25  is located in the housing  10  coaxially with the first vane rotor  20  and is in slidable contact with the camshaft  3  on a side of the first vane rotor  20  toward the chain sprocket  12 . The second vane rotor  25  is provided rotatably relative to the housing  10  and the first vane rotor  20 . As illustrated in  FIG. 1 , the second vane rotor  25  has a cylindrical boss  27 , which is in contact with the camshaft  3 , and second vanes  42 ,  43 , and  44 , which are formed radially outer side of the second vane rotor  25 . The second vanes  42 ,  43 , and  44  slidably contact the radially outer side of the boss  26  of the first vane rotor  20  and are rotatably or movably housed in the receiving chambers  112 ,  113 , and  114 , respectively. 
     The second vane  42  partitions the receiving chamber  112  into an advance chamber  36  and a retard chamber  31 . The second vane  43  partitions the receiving chamber  113  into an advance chamber  37  (second advance chamber) and a retard chamber  32  (second retard chamber). The second vane  44  partitions the receiving chamber  114  into an advance chamber  38  and a retard chamber  33 . The arrows in  FIG. 1 , which indicate the retard and advance directions, represent the retard and advance directions of the second vane rotor  25  with respect to the housing  10 . The second vane  43  has a contact portion  46 , which contacts the shoe  133 , and a contact portion  47 , which contacts the shoe  134 . The contact portions  46 ,  47  limit the range of rotation of the second vane rotor  25  by contacting the shoes  133 ,  134 , respectively. 
     The fitting pin  56  as a limiting device is housed reciprocably in hydraulic chambers  57 ,  58  of the first vane rotor  20 . The boss  26  has a contact portion  50 , which radially outwardly projects from the boss  26 , and the hydraulic chambers  57 ,  58  are provided to the contact portion  50 . The second vane rotor  25  has a hole formation part  54  at a position correspondingly to the contact portion  50 . A fitting hole  53  is formed in the hole formation part  54 . The fitting pin  56  is fittable into the fitting hole  53 . The fitting pin  56 , which as a cylindrical shape with a shoulder or a large diameter portion, is biased by a spring  59  in the direction away from the fitting hole  53  such that the fitting pin  56  is disengaged from the fitting hole  53 . The biasing force of the spring  59  is set to a higher level than the working fluid pressure at the stop of the engine. The hydraulic chamber  57  is communicated with the advance chamber  37  through an advance passage  92 . The hydraulic chamber  58  is communicated with the retard chamber  32  through a retard passage  84 . The pressure of the working fluid supplied to the hydraulic chambers  57 ,  58  is applied in a direction to push the fitting pin  56  into the fitting hole  53 . 
     The hole formation part  54  has a contact portion  55  that extends or stands axially. The fitting hole  53  is provided at a position that axially overlaps the fitting pin  56  when the contact portion  50  and the contact portion  55  contact each other. When the fitting hole  53  and the fitting pin  56  are axially overlapping with each other and the working fluid pressure is equal to or greater than the biasing force of the spring  59 , the fitting pin  56  is fitted into the fitting hole  53 . When the working fluid pressure is below the biasing force of the spring  59 , the fitting pin  56  is taken out of or released from the fitting hole  53 . 
     The return spring  60  is compressedly housed in a cylindrical receiving chamber  21 , which has a bottom, and which is formed on the boss  26  of the first vane rotor  20 . The boss  26  of the first vane rotor  20  has a mounting groove  23 , which is radially inwardly recessed on the boss  26 . A mounting groove  45  is formed in the vane  42  of the second vane rotor  25  as an outward recess in the radial direction. The return spring  60  has one end  61  (first end), which is engaged with the mounting groove  23 , and the other end  62 , which is engaged with the mounting groove  45 . 
     The boss  26  defines a notch  22  that is configured to extend in a range, in which the other end  62  of the return spring  60  is reciprocable in the receiving chamber  112 . Also, the notch  22  is provided to extend in a region that limits leakage of working fluid between the advance chamber  36  and the retard chamber  31 . The return spring  60  biases the first vane rotor  20  clockwise as viewed in  FIG. 1  and biases the second vane rotor  25  counterclockwise. The biasing force of the return spring  60  is set to a lower level than the working fluid pressure in normal operation of the engine, in which the valve timing adjusting device  1  is mounted. Typically, the biasing force of the return spring  60  is set to an average cam torque at the start of the engine at a very low temperature. 
     A stopper piston  70  as a cylindrical fitting member is housed in a through hole in the first vane  41  such that the stopper piston  70  is reciprocable in the rotation axis direction. A fitting ring  71  is press-fitted in a recess in the chain sprocket  12 . The stopper piston  70  is fittable in the fitting ring  71 . A spring  75  biases the stopper piston  70  toward the fitting ring  71 . The stopper piston  70 , the fitting ring  71 , and the spring  75  constitute a restriction mechanism, which limits the first vane  41  and the first vane rotor  20  from rotating relative to the housing  10 . 
     The pressure of the working fluid supplied to a hydraulic chamber  72 , which is formed on the chain sprocket  12  side of the stopper piston  70 , and to a hydraulic chamber  73 , which is formed on the radially outer side of the stopper piston  70 , is applied to the stopper piston  70  in a direction away from the fitting ring  71  such that the stopper piston  70  is taken out of the fitting ring  71 . The hydraulic chamber  72  is communicated with the retard chamber  30  through the retard passage  81 . The tip of the stopper piston  70  is fitted in the fitting ring  71  when the first vane rotor  20  is at the most advance position with respect to the housing  10 . When the stopper piston  70  fits in the fitting ring  71 , relative rotation of the first vane rotor  20  with respect to the housing  10  is limited. A back pressure relief groove  74  is provided on a side the first vane  41 , which side faces in a direction toward the fitting ring  70 . For example, the back pressure relief groove  74  releases the back pressure that varies with sliding motion of the stopper piston. As the first vane rotor  20  rotates with respect to the housing  10  from the most advance position in the retard direction, the stopper piston  70  and fitting ring  71  become displaced from each other, and the stopper piston  70  is disabled to fit into the fitting ring  71 . 
     Seal members  121 ,  122 ,  123 , and  124  are located in sliding gaps between (a) the peripheral wall  130  of the shoe housing  13  and (b) each of the first vane  41  and second vanes  42 ,  43 , and  44  that face the peripheral wall  130  in the radial direction. The seal members  121 ,  122 ,  123 , and  124  are fitted in grooves in the radially outer walls of the first vane  41  and second vanes  42 ,  43 , and  44 , and radially outwardly biased toward the inner side of the peripheral wall  130  by springs or the like. Thus the seal members  121 ,  122 ,  123 , and  124  limit the working fluid from leaking between the respective retard chambers and advance chambers. 
     A fluid supplier  4  shown in  FIG. 2  includes a hydraulic pump and a phase changeover valve. The fluid supplier  4  generates a hydraulic pressure which varies depending on the rotation speed of the engine, and changes the function of an advance passage  90  and a retard passage  80  between a working fluid supply passage and a working fluid discharge passage. The advance passage  90  and the retard passage  80  are always communicated with supply and discharge ports of the fluid supplier  4 . As illustrated in  FIG. 1 , the advance passage  90 , which branches into advance passages  94 ,  95 ,  96 , and  97 , supplies working fluid to the advance chambers  35 ,  36 ,  37 , and  38 , respectively. Also, the advance passage  90  discharges working fluid from the respective advance chambers to an oil pan (not shown). The retard passage  80 , which branches into retard passages  85 ,  86 ,  87 , an  88 , supplies working fluid to the retard chambers  30 ,  31 ,  32 , and  33 , respectively. Also, the retard passage  80  discharges working fluid from the respective retard chambers to the oil pan (not shown). The above means that the advance passages function as both advance supply passages and advance discharge passages, and the retard passages function as both retard supply passages and retard discharge passages. Thus, working fluid can be supplied from the fluid supplier  4  to the advance chambers  35 - 38  and the retard chambers  30 - 33  and discharged from the chambers. 
     Next, an operation of the valve timing adjusting device will be described. 
     (Operation at a Time Immediately After Engine Stop) 
       FIGS. 4 ,  5  show the valve timing adjusting device just after engine stop. The figures show that the engine is stopped in a state, where the valve timing adjusting device  1  is set to a retard position by phase control. More specifically, in the valve timing adjusting device  1 , until just before the engine stops, working fluid is supplied from the fluid supplier  4  to the retard chambers  30 ,  31 ,  32 , and  33  through the retard passage  80  ( 85 ,  86 ,  87 ,  88 ). Thus, the working fluid pressure rotates the first vane rotor  20  and the second vane rotor  25  in the retard direction with respect to the housing  10 , and the working fluid in the advance chambers  35 ,  36 ,  37 , and  38  is discharged to the oil pan through the advance passages  94 ,  95 ,  96 , and  97 ; as a consequence the engine stops. 
     In the valve timing adjusting device, just before engine stop, working fluid is supplied from the retard chamber  32  to the hydraulic chamber  58  through the retard passage  84 , and working fluid is supplied from the advance chamber  37  to the hydraulic chamber  57  through the advance passage  92 . Therefore, in the valve timing adjusting device  1 , at a time immediately after engine stop, the working fluid pressure in the hydraulic chambers  58 ,  57  is applied against a preset biasing force of the spring  59  so that the fitting pin  56  fits in the fitting hole  53 . In addition, the stopper piston  70  is not in alignment with the fitting ring  71  and cannot fit in it. 
     (Operation in the Course of or After Engine Stop or in the Course of Engine Start) 
       FIGS. 6 ,  7  show a state, where the engine stops and no working fluid is supplied from the fluid supplier to the valve timing adjusting device, and thereby the working fluid pressure is below a preset level. Because no working fluid is supplied to the valve timing adjusting device  1  in the course of or after engine stop, the working fluid pressure in the hydraulic chamber  57  and the working fluid pressure in the hydraulic chamber  58  fall below the preset level. In the above, the hydraulic chamber  57  is communicated with the advance chamber  37  through the advance passage  92 , and the hydraulic chamber  58  is communicated with the retard chamber  32  through the retard passage  84 . Consequently, the fitting pin  56  is forcibly taken out of the fitting hole  53  by the preset biasing force of the spring  59  in the course of engine stop or start. 
     As the fitting pin  56  is taken out of the fitting hole  53 , the return spring  60 , which biases the first vane rotor  20  clockwise as viewed in  FIG. 6 , and which biases the second vane rotor  25  counterclockwise, causes the first vane rotor  20  and second vane rotor  25  to rotate in opposite directions. At this time, the contact portion  46  of the second vane  43  contacts the shoe  133 , which limits relative rotation of the second vane rotor  25  in the retard direction with respect to the housing  10 . Therefore, the first vane rotor  20  rotates in the advance direction with respect to the housing  10 . Then, the contact portion  49  of the first vane  41  contacts the shoe  132 , which limits relative rotation of the first vane rotor  20  in the advance direction with respect to the housing  10 . Because the first vane rotor  20  is coupled with the camshaft  3 , the phase of the valve timing adjusting device  1  reaches the advance position. 
     When the first vane  41  is in the most advance position, the stopper piston  70  and fitting ring  71  are axially overlap with each other, and thereby the stopper piston  70  is fitted in the fitting ring  71  by the biasing force of the spring  75 . 
     (Operation After Engine Start) 
       FIGS. 8 ,  9  show a state, where after the engine is started, and thereby working fluid is supplied to the valve timing adjusting device for performing the advance control for advancing valve timing. As the engine is started, working fluid is supplied to the advance chambers  35 ,  36 ,  37 ,  38  through the advance passages  90 ,  94 ,  95 ,  96 ,  97 . The working fluid pressure is applied to the second vanes  42 ,  43 , and  44 , and thereby the second vanes  42 ,  43 , and  44  rotate in the advance direction against the biasing force of the return spring  70 . The working fluid in the retard chambers  31 ,  32 , and  33  is discharged to the oil pan through the retard passages  86 ,  87 ,  88 , and  80 . At this time, the contact portion  49  of the first vane  41  is in contact with the shoe  132 . The stopper piston  70  fits in the fitting ring  71 . Therefore, relative rotation of the first vane rotor  20  in the advance direction with respect to the housing  10  is limited. When the second vane  43  rotates in the advance direction and the contact portions  50 ,  55  contact each other, the fitting pin  56  comes to a position coaxially with the fitting hole  53 . As the working fluid in the advance chamber  37  is supplied to the hydraulic chamber  57  through the advance passage  92 , the working fluid pressure causes the fitting pin  56  to fit in the fitting hole  53  against the biasing force of the spring  59 . Because the fitting pin  56  fits in the fitting hole  53 , the second vane rotor  25  is disabled to rotate relative to the first vane rotor  20 , and thereby the biasing force of the return spring  70  is limited from influencing the phase control by the valve timing adjusting device  1 . 
     In the present embodiment, when no working fluid is supplied to the valve timing adjusting device  1  from the fluid supplier  4  in the course of or after engine stop, the limiting device disengages the first vane rotor  20  from the second vane rotor  25 , and the spring force of the spring  60  causes the first vane rotor  20  and the second vane rotor  25  to rotate in opposite directions in the course of engine stop or engine start. Therefore, the phase of the valve timing adjusting device  1  becomes the advance position at the start of the engine. 
     When working fluid is supplied to the valve timing adjusting device  1  from the fluid supplier  4  to advance or retard the valve timing after the engine is started, the fitting pin  56  is fitted in the fitting hole  53  for engagement. The above means that the return spring  60  is fixed at a shape, and thereby the first vane rotor  20  and the second vane rotor  25  are movable integrally. Consequently, the valve timing adjusting device  1  is capable of performing the phase control only by pressure of working fluid regardless of the influence by the biasing force of the return spring  60 . 
     The limiting device disengages the fitting pin  56  from the fitting hole  53  in the course of engine stop or start, and engages the fitting pin  56  with the fitting hole  53  after engine start. Therefore, the phase control is made by the balance between the biasing force of the return spring  60  and the pressure of working fluid only at the start of the engine. In other words, the biasing force of the return spring  60  is associated with the phase control only at the start of the engine. Due to the above reason, the biasing force of the return spring  60  is set to an average cam torque at the start of the engine at a very low temperature, and thereby the advance control of the valve timing adjusting device  1  for advancing valve timing is efficiently performed at a very low temperature. 
     In the present embodiment, when the engine stops and the pressure of the working fluid supplied from the fluid supplier  4  falls below the preset level, the limiting device removes the limitation on relative rotation of the first vane rotor  20  and the second vane rotor  25 . In other words, when the engine stops, the limiting device disengages the first vane rotor  20  from the second vane rotor  25 . The biasing device  60  biases one of the first vane rotor  20  and the second vane rotor  25  in the advance direction and biases the other one in the retard direction. Therefore, one of the first vane rotor  20  and the second vane rotor  25  moves in the advance direction and the other one moves in the retard direction. The range of the relative rotation of the second vane rotor  25  with respect to the housing  10  is limited. The above configuration causes the first vane rotor  20  to reach a target phase angle or a target position. The range of relative rotation of the first vane rotor  20  with respect to the housing  10  is limited. The above configuration causes the second vane rotor  25  to reach a target phase angle or a target position. 
     On the other hand, when the engine starts and the pressure of the working fluid supplied from the fluid supplier rises up to the preset level or higher, the first vane rotor  20  and the second vane rotor  25  rotate relatively with respect to the housing  10 . The range of relative rotation of the first vane rotor  20  with respect to the housing  10  is limited. The above configuration causes the second vane rotor  25  to rotate relatively with respect to the first vane rotor  20 . The range of relative rotation of the second vane rotor  25  with respect to the housing  10  is limited. The above configuration causes the first vane rotor  20  to rotate relatively with respect to the second vane rotor  25 . When the first vane rotor  20  and the second vane rotor  25  are adjusted to be located at specified positions by the phase control, the limiting device  56  limits the first vane rotor  20  from rotating relative to the second vane rotor  25 . Consequently, the biasing force of the biasing device  60  does not exert an influence on the phase control by working fluid pressure. Thus, a precise phase control by working fluid pressure is achieved. Therefore, the biasing force of the biasing device  60 , which enables the phase of the valve timing adjusting device  1  to reach a target phase position at the start of the engine, can be effectively increased. 
     In the present embodiment, when the limiting device limits relative rotation of the first vane rotor  20  and the second vane rotor  25 , both the vane rotors  20 ,  25  work together integrally to adjust the valve opening/closing timing in the engine. The above configuration enables the precise phase control by working fluid pressure. 
     In the present embodiment, when the working fluid is supplied to one of the advance chamber  37  and the retard chamber  32 , the fitting pin  56  of the limiting device is brought into a fitting engagement with the fitting hole  53 . Consequently, the biasing force of the biasing device  60  does not exert an influence on phase control by working fluid pressure. The above configuration enables the precise phase control by working fluid pressure. 
     In the present embodiment, because the fitting pin  56  is located away from the center of rotation of the first vane rotor  20 , the durability of the fitting pin  56  is increased and precise phase control by working fluid pressure is effectively made. 
     Second Embodiment 
       FIGS. 10 to 15  show a valve timing adjusting device  2  according to a second embodiment of the present invention. 
       FIGS. 10 ,  11  show an operational state of the valve timing adjusting device  2  at a time immediately after the engine stop, and  FIGS. 12 ,  13  show another operational state of the valve timing adjusting device  2  in the course of engine stop, and  FIGS. 14 ,  15  show still another operational state of the device  2  after engine start. 
     First, the mechanical structure of the valve timing adjusting device  2  is explained referring to  FIGS. 10 ,  11 . The components, which are substantially the same as those in the first embodiment, are designated by the same reference numerals and their description is omitted. 
     The valve timing adjusting device  2  in the present embodiment includes a housing  16 , a first vane rotor  220 , a second vane rotor  225 , and a fitting pin  256  as a limiting device, and a return spring  260  as a biasing device. 
     The housing  16  as a driving rotator includes a chain sprocket  18 , a shoe housing  19 , and a front plate  17 . The shoe housing  19  includes shoes  231 ,  232 , and  233  as partition members and a circular peripheral wall  230  which are all integrally formed. The trapezoidal shoes  231 ,  232 , and  233 , which extends radially inwardly from the peripheral wall  230 , are circumferentially disposed at generally regular intervals in the direction of rotation of the peripheral wall  230 . A receiving chamber  211  is provided between the shoes  233  and  231 , a receiving chamber  212  between the shoes  231  and  232 , and a receiving chamber  213  between the shoes  232  and  233 . The shoe housing  19  and front plate  17  are fixed coaxially with the chain sprocket  18  through bolts  15 . Coupled with the crankshaft (not shown) serving as the drive shaft of the internal combustion engine, the chain sprocket  18  receives a driving force from the crankshaft and is rotatable together with the crankshaft. The driving force of the crankshaft is transmitted through the valve timing adjusting device  2  to a camshaft (not shown) serving as a driven shaft and opens and closes an intake valve. The camshaft is received in the chain sprocket  18  such that the camshaft is capable of rotating relatively with respect to the chain sprocket  18 . 
     The first vane rotor  220  as a driven rotator is in contact with one axial end face of the camshaft inserted through an insertion hole  7  of the chain sprocket  18 , and the camshaft and the first vane rotor  220  are coupled coaxially by a bolt (not shown). The positioning of the first vane rotor  220  and the camshaft is made by fitting a positioning pin (not shown) into the first vane rotor  220  and the camshaft or by a similar method. The camshaft, housing  16  and first vane rotor  220  rotate clockwise as viewed in  FIG. 10 . Hereinafter this rotational direction is referred to as the advance direction of the camshaft with respect to the crankshaft. 
     The first vane rotor  220  is housed in the housing  16  such that the first vane rotor  220  is rotatable relatively with respect to the housing  16 . The first vane rotor  220  has a cylindrical boss  271 , a receiving portion  221 , and first vanes  241 ,  242 , and  243 . The boss  271  is fixed on the camshaft, and the receiving portion  221  is provided on an axial side of the boss  271  toward the front plate  17 . The first vanes  241 ,  242 , and  243  are formed on the radially outer side of the boss  271 . The first vanes  241 ,  242 , and  243  are rotatably housed in the receiving chambers  211 ,  212 , and  213 , respectively. The first vane  241  partitions the receiving chamber  211  into an advance chamber  239  and a retard chamber  236 . The first vane  242  partitions the receiving chamber  212  into an advance chamber  237  and a retard chamber  234 . The first vane  243  partitions the receiving chamber  213  into an advance chamber  238  (first advance chamber) and a retard chamber  235  (first retard chamber). The first vane  241  has a slidable contact portion  254  that circumferentially extends toward the advance chamber  239  from a contact portion  250  or an advance-chamber-side edge of the first vane  241  as shown in  FIG. 12 . Thus, the slidable contact portion  254  axially overlaps the second vane  244  of the second vane rotor  220  and slides on an surface of the second vane  244 , which surface faces toward the sprocket  18 . The arrows in  FIG. 10 , which indicate the retard and advance directions, represent the retard and advance directions of the first vane rotor  220  with respect to the housing  16 . The first vane  243  has a contact portion  248 , which contacts the shoe  232 , and a contact portion  246 , which contacts the shoe  233 . The contact portions  248 ,  246  limit the range of rotation of the first vane rotor  220  by contacting the shoes  232 ,  233 , respectively. 
     The second vane rotor  225  is located in the housing  16  coaxially with the first vane rotor  220  and fits with the radially outer side of the receiving portion  221  of the first vane rotor  220  at a position toward the front plate  17  relative to the first vane rotor  220 . The second vane rotor  225  is provided to rotate relatively with respect to the housing  16  and the first vane rotor  220 . The second vane rotor  225  has a boss  270 , which contacts the receiving portion  221 , and a second vane  244 , which is provided on the radially outer side of the boss  270 . The second vane  244  slidably contacts the surface of the slidable contact portion  254  of the first vane  241  in the receiving chamber  211 , which surface faces toward the front plate  17 . The arrows in  FIG. 10 , which indicate the retard and advance directions, represent the retard and advance directions of the second vane rotor  225  with respect to the housing  16 . The second vane  244  partitions the receiving chamber  211  into an advance chamber  239  (second advance chamber) and a retard chamber  236  (second retard chamber). The second vane  244  has a contact portion  247 , which contacts the shoe  233 , and a contact portion  255 , which contacts the contact portion  250  of the first vane  241 . The contact portions  247 ,  255  limit the range of rotation of the second vane rotor by contacting the shoe  233  and the contact portion  250  respectively. 
     The fitting pin  256  as a limiting device is housed reciprocably in the hydraulic chambers  257 ,  258  of the first vane  241 . The hydraulic chambers  257 ,  258  are provided to the slidable contact portion  254  of the first vane  241 . The fitting ring  253  is held pressed in a recess formed at the second vane  244 , which overlaps the slidable contact portion  254 . The fitting pin  256 , which has a cylindrical shape with a shoulder or a large diameter portion, is biased by a spring  259  in the direction away from the fitting ring  253  such that the fitting pin  256  is disengaged from the fitting ring  253 . The biasing force of the spring  259  is set to a higher level than the working fluid pressure at the stop of the engine. The hydraulic chamber  257  is communicated with the advance chamber  239  through an advance passage  294 . The hydraulic chamber  258  is communicated with the retard chamber  236  through a retard passage  284 . The pressure of the working fluid supplied to the hydraulic chambers  257 ,  258  applied in a direction to push the fitting pin  256  into the fitting ring  253 . 
     The fitting ring  253  is formed at a position that becomes coaxial with the fitting pin  256  when the contact portion  250  of the first vane  241  and the contact portion  255  of the second vane  244  contact each other. The fitting ring  253  is fittable with the fitting pin  256 . When the fitting ring  253  and the fitting pin  256  axially overlap with each other and the working fluid pressure is equal to or higher than the biasing force of the spring  259 , the fitting pin  256  is fitted into the fitting ring  253 . When the working fluid pressure is equal to or less than the biasing force of the spring  259 , the fitting pin  256  is taken out of the fitting ring  253 . 
     The return spring  260  is located on the first vane rotor  220  axially on the front plate side and is compressedly housed in the receiving portion  221  that has a cylindrical shape with a bottom. A mounting groove  223  is formed in the receiving portion  221  as an inward recess in the radial direction. A mounting groove  245  is formed in the second vane  244  as an outward recess in the radial direction. The return spring  260  has one end  261  (first end), which is engaged with the mounting groove  223 , and the other end  62  (second end), which is engaged with the mounting groove  245 . 
     A notch  222  is formed in the receiving portion  221  such that the other end  262  of the return spring  260  is capable of reciprocating in the receiving chamber  211 . The return spring  260  biases the first vane rotor  220  clockwise as viewed in  FIG. 10  and biases the second vane rotor  225  counterclockwise. The biasing force of the return spring  260  is set to a lower level than the working fluid pressure in a normal operation of the engine in which the valve timing adjusting device  2  is mounted. Typically, the biasing force of the return spring  260  is set to an average cam torque at the start of the engine at a very low temperature. 
     A stopper piston  70  as a cylindrical fitting member is housed in a through hole in the first vane  243  such that the stopper piston  70  is reciprocable in the rotation axis direction. The stopper piston  70 , the fitting ring, and the spring, which constitute a restriction mechanism to limit the first vanes  241 ,  242 , and  243  and the first vane rotor  220  from rotating relative to the housing  16 , are generally the same as those in the first embodiment, and thereby description thereof is omitted. 
     The advance passages  295 ,  296 , and  297  supply working fluid to the advance chambers  239 ,  237 , and  238 , respectively, and discharge working fluid to an oil pan (not shown) from the respective advance chambers. The retard passages  285 ,  286 , and  287  supply working fluid to the retard chambers  236 ,  234 , and  235 , respectively, and discharge working fluid to the oil pan (not shown) from the respective retard chambers. This means that the advance passages function as both the advance supply passages and the advance discharge passages, and the retard passages function as both the retard supply passages and the retard discharge passages. Thus, the above configuration enables working fluid to be supplied to the advance chambers  239 ,  237 , and  238  and the retard chambers  236 ,  234 , and  235  from the fluid supplier (not shown). Also, the above configuration enables working fluid to be discharged from the above chambers to the fluid supplier. 
     Next, an operation of the valve timing adjusting device will be described. 
     (Operation at a Time Immediately After Engine Stop) 
       FIGS. 10 ,  11  show an example operational state of the valve timing adjusting device  2  at a time immediately after the stop of the engine. In  FIGS. 10 ,  11 , the engine is stopped at a time, when the valve timing adjusting device  2  performs the retard phase control for retarding valve timing. In the valve timing adjusting device  2 , working fluid has been supplied to the retard chambers  236 ,  234 , and  235  from the fluid supplier (not shown) through the retard passages  285 ,  286 , and  287  until immediately before the engine is stopped. Thus, the working fluid pressure has rotated the first vane rotor  220  and second vane rotor  225  in the retard direction relatively to the housing  16 . Accordingly, the working fluid in the advance chambers  239 ,  237 , and  238  has been discharged to the oil pan through the advance passages  295 ,  296 , and  297 . 
     At the above time, in the valve timing adjusting device  2 , the working fluid in the retard chamber  236  is supplied through the retard passage  284  to the hydraulic chamber  258 , and the working fluid in the advance chamber  239  is supplied through the advance passage  294  to the hydraulic chamber  257 . Therefore, the pressure of working fluid in the hydraulic chambers  258 ,  257  is applied against a preset biasing force of the spring  259 , and thereby the fitting pin  256  remains fitted into the fitting ring  253 . However, the stopper piston  70  is not coaxial with the fitting ring and is not fitted into the fitting ring. 
     (Operation in the Course of or After Engine Stop or in the Course of Engine Start) 
       FIGS. 12 ,  13  show an operational state, where the engine stops and no working fluid is supplied to the valve timing adjusting device, and thereby the working fluid pressure is below a preset level. In the course of or after engine stop, because no working fluid is supplied to the valve timing adjusting device  2 , the working fluid pressure in the hydraulic chambers  257 ,  258 , which are communicated with the advance chamber  239  and retard chamber  236  through the advance passage  294  and the retard passage  284  respectively, falls equal to or less than the preset biasing force of the spring  259 . Consequently, the fitting pin  256  is forced out of the fitting ring  253  by the biasing force of the spring  259  in the course of engine stop or start. 
     When the fitting pin  256  is taken out of the fitting ring  253 , the return spring  260  biases the first vane rotor  220  clockwise as viewed in  FIG. 12  and also biases the second vane rotor  225  counterclockwise. At this time, the contact portion  247  of the second vane  244  contacts the shoe  233 , which limits relative rotation of the second vane rotor  225  in the retard direction with respect to the housing  16 . Therefore, the first vane rotor  220  rotates in the advance direction relatively with respect to the housing  16 . Then the contact portion  246  of the first vane  243  contacts the shoe  233 , which limits relative rotation of the first vane rotor  220  in the advance direction with respect to the housing  16 . Because the first vane rotor  220  is coupled with the camshaft (not shown), the phase of the valve timing adjusting device  2  becomes the advance position. 
     When the first vane  243  is in the most advance position, the stopper piston  70  is positioned coaxial with the fitting ring located on the chain sprocket  18 , and thereby the stopper piston  70  is fitted into the fitting ring by the biasing force of the spring. 
     (Operation After Engine Start) 
       FIGS. 14 ,  15  show an operational state, where after the engine is started and working fluid is supplied to the valve timing adjusting device from the fluid supplier (not shown) to advance the valve timing. Working fluid is supplied from the fluid supplier through the advance passage  295  to the advance chamber  239 , and thereby the working fluid pressure is applied to the second vane  244 . At this time, the contact portion  246  of the first vane  243  is in contact with the shoe  233 , so that relative rotation of the first vane rotor  220  in the advance direction with respect to the housing  16  is limited. Therefore, the second vane  244  rotates in the advance direction against the biasing force of the return spring  70 . When the second vane  244  rotates in the advance direction, the slidable contact portion  254  of the first vane rotor  220  slides on the surface of the second vane  244 , on which surface the fitting ring  253  is provided. When the contact portion  250  and contact portion  255  is brought into contact with each other, the fitting pin  256  and the fitting ring  253  become positioned coaxial with each other. The working fluid in the advance chamber  239  is supplied through the advance passage  294  to the hydraulic chamber  257 , and the working fluid in the retard chamber  236  is supplied through the retard passage  284  to the hydraulic chamber  258 . The working fluid pressure causes the fitting pin  256  to fit into the fitting ring  253  against the biasing force of the spring  259 . Because the fitting pin  256  is fitted into or engaged with the fitting ring  253 , the second vane rotor  225  is limited from rotating relative to the first vane rotor  220 , and the biasing force of the return spring  70  does not exert an influence on phase control by the valve timing adjusting device  2 . 
     In the present embodiment, even in the valve timing adjusting device  2 , which has three receiving chambers in the housing  16 , it is possible to limit the biasing force of the return spring  60  from exerting an influence on phase control by working fluid pressure. Furthermore, by increasing the biasing force of the return spring  60 , the valve timing adjusting device  2  at the start of the engine at a very low temperature can be effectively set to a target phase position. 
     In the present embodiment, the fitting pin  256  is provided to the slidable contact portion  254  of the first vane  241 , and the fitting ring  253  is provided to the second vane  244 . Also, the fitting pin  256  and fitting ring  253  are provided to certain positions on the first vane  241  and second vane  244 , which certain positions are located radially outward of the bosses  271 ,  270  of the first vane rotor  220  and the second vane rotor  225 . Thus, durability of the fitting pin  256  and fitting ring  253  is effectively improved. 
     Other Embodiments 
     In the mechanical structure of the valve timing adjusting device  1  in the first embodiment, the first vane rotor  20  includes the first vane  41  having the contact portions  48 ,  49 , which contact the shoes  131 ,  132  to limit the range of rotation of the first vane rotor  20 . However, according to another embodiment of the present invention, instead of the first vane and the contact portions, the first vane rotor may alternatively have projections on the boss of the first vane rotor so that the projections contact the shoes to limit the range of rotation of the first vane rotor. 
     According to still another embodiment of the present invention, instead of the second vane and the contact portions, the second vane rotor may alternatively have projections on the boss of the second vane rotor so that these projections contact shoes to limit the range of rotation of the second vane rotor. 
     In  FIG. 4 , which shows the operational state of the valve timing adjusting device  1  in the first embodiment at the time immediately after engine stop, the contact portion  48  of the first vane  41  contacts the shoe  131  and the contact portion  46  of the second vane  43  contacts the shoe  133 . However, alternatively in a valve timing adjusting device in still another embodiment of the invention, each of the above contact portions may have not contacted the corresponding shoes at the time immediately after engine stop. 
     In  FIG. 10  which shows the operational state of the valve timing adjusting device  2  in the second embodiment at the time immediately after engine stop, the contact portion  248  of the first vane contacts the shoe  232 . However, alternatively in a valve timing adjusting device in another embodiment of the invention, the above contact portion may not have contacted the corresponding shoe at the time immediately after engine stop. 
     In the valve timing adjusting device  1  in the first embodiment, after engine start, the second vane rotor  25  rotates in the advance direction and the fitting pin  56  fits in the fitting hole  53  (advance control). However, in another embodiment of the invention, after engine start, the first vane rotor  20  may alternatively rotate in the retard direction (retard control) such that the fitting pin  56  is fitted into the fitting hole  53 . In the above alternative case, working fluid is supplied from the retard chamber  30  through the retard passage  81  to the hydraulic chamber  72  and the working fluid pressure causes the stopper piston  70  to be disengaged from the fitting ring  71  against the biasing force of the spring  75 . The pressure of the working fluid supplied through the retard passages  80 ,  85  to the retard chamber  30  causes the first vane  41  to rotate in the retard direction against the biasing force of the return spring  70 . The working fluid in the advance chamber  35  is discharged through the advance passages  94 ,  90  to the oil pan. At the above time, the contact portion  46  of the second vane  43  contacts the shoe  133  to limit relative rotation of the second vane rotor  25  in the retard direction with respect to the housing  10 . Therefore, the first vane rotor  20  rotates in the retard direction and the contact portion  50  contacts the contact portion  55 . At this time, the working fluid in the retard chamber  32  is supplied through the retard passage  84  to the hydraulic chamber  587  so that the fitting pin  56  fits in the fitting hole  53 . Consequently, relative rotation of the first vane rotor  20  and second vane rotor  25  becomes impossible and the biasing force of the return spring  70  does not exert an influence on phase control by the valve timing adjusting device  1 . 
     In the valve timing adjusting device  2  in the second embodiment, after engine start, the second vane rotor  225  rotates in the advance direction (advance control), and thereby the fitting pin  256  fits in the fitting ring  253 . However, in still another embodiment of the invention, after engine start, the first vane rotor  220  may alternatively rotate in the retard direction (retard control) such that the fitting pin  256  is fitted into the fitting ring  253 . In the above alternative case, working fluid is supplied from the retard chamber  235  through the retard passage  81 , and the stopper piston  70  is disengaged from the fitting ring. The pressure of the working fluid supplied to the retard chambers  234 ,  235 , and  236  is applied to the first vanes  242 ,  243 , and  241 . Then, the contact portion  247  of the second vane  244  is brought into contact with the shoe  233 , and thereby the shoe  233  limits the second vane rotor  225  from rotating in the retard direction with respect to the housing  16 . Therefore, the first vanes  242 ,  243 , and  241  rotate in the retard direction against the biasing force of the return spring  70 . Because the first vane rotor  220  rotates in the retard direction, and the contact portion  250  and contact portion  255  contact each other, the fitting pin  256  and the fitting ring  253  are brought into the position coaxial with each other. The working fluid in the retard chamber  236  is supplied through the retard passage  284  to the hydraulic chamber  258 , and the working fluid in the advance chamber  239  is supplied through the advance passage  294  to the hydraulic chamber  257 , so that the fitting pin  256  fits in the fitting ring  253 . Consequently, relative rotation of the first vane rotor  220  and second vane rotor  225  becomes impossible, and the biasing force of the return spring  70  does not exert an influence on phase control by the valve timing adjusting device  2 . 
     The valve timing adjusting device in any of the above embodiments controls the phase of the exhaust valve of the engine in the advance direction at the start of the engine. However, the present invention may be applied to a valve timing adjusting device which controls the phase of the exhaust valve of the engine in the retard direction at the start. It is also possible to apply the present invention to a valve timing adjusting device which controls the phase of the intake valve of the engine in the retard or advance direction at the start. 
     The present invention is not limited to the above embodiments and any combination of the above embodiments and various other forms of embodiments of the invention are possible without departing from the spirit thereof.