Abstract:
In a valve timing control device, a control means is configured to carry out feeding one of retarding and advancing chambers with a hydraulic pressure upon starting of the engine; actuating one of first and second disengaging mechanisms to cancel the engagement of one of first and second projectable members with the corresponding one of first and second engaging portions; feeding the other of the retarding and advancing chambers with a hydraulic pressure to turn a vane member in a housing within a range determined by each of the first and second engaging portions; and actuating, while the vane member is under the rotational movement within the range, the other of the first and second disengaging mechanisms to cancel the engagement of the other of the first and second projectable members with the corresponding one of the first and second engaging portions.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a valve timing control device of an internal combustion engine, that variably controls an open/close timing of engine valves (viz., intake and/or exhaust valves) in accordance with an operation condition of the engine. 
   2. Description of the Related Art 
   Hitherto, various valve timing control devices have been proposed and put into practical use particularly in the field of automotive internal combustion engines. 
   One of them is shown in Japanese Laid-open Patent Application (Tokkai) 2002-357105. 
   The valve timing control device of the publication generally comprises a vane member that is rotatable about its axis relative to a housing between the most retarded position and the most advanced position. For rotating the vane member in retarding or advancing direction, there are defined between the vane member and the housing retarding and advancing chambers. That is, when the retarding chambers are fed with a hydraulic pressure, the vane member is turned in a retarding direction thereby to retard the open/close operation of engine valves (viz., intake and/or exhaust valves), while when the advancing chambers are fed with the hydraulic pressure, the vane member is turned in an advancing direction thereby to advance the open/close operation of the engine valves. 
   The valve timing control device further comprises a rotation restricting means that restricts rotation of the vane member from a center position to the most retarded position or the most advanced position in a given condition. 
   The rotation restricting means comprises retarding and advancing pins that are retractably installed in respective holding bores formed in the vane member, retarding and advancing recesses that are formed in the housing and sized to receive leading ends of the retarding and advancing pins respectively, biasing springs that are respectively installed in the retarding and advancing recesses to bias the pins in a direction to project outward that is toward the retarding and advancing recesses, push back chambers that are respectively defined by the retarding and advancing recesses to push back the pins toward the holding bores against the biasing springs when fed with a hydraulic fluid and a hydraulic pressure control means that controls the pressure of the hydraulic fluid in accordance with an operation condition of the engine. 
   When the engine is stopped, the push back chambers are suppressed from being fed with the hydraulic fluid and thus, the retarding and advancing pins are projected into the corresponding retarding and advancing recesses due to the force of the biasing springs. With this, the vane member is held or locked at the center position. 
   While, when, after staring of the engine, the same is brought a predetermined operation condition, both the push back chambers are fed with a hydraulic fluid thereby to disengage the retarding and advancing pins from the corresponding recesses, and the vane member is turned in the retarding or advancing direction in the above-mentioned manner in accordance with the operation condition of the engine. 
   SUMMARY OF THE INVENTION 
   However, in the above-mentioned valve timing control device, the following phenomenon tends to occur when the engine is intended to start after long halt thereof. As is known, when the engine is at a standstill for a long time, the retarding and advancing chambers are almost empty of the hydraulic fluid. 
   When under such condition the engine is started, it tends to occur that the push back chambers become filled with the hydraulic pressure before the retarding and advancing chambers. That is, before the retarding and advancing chambers are sufficiently filled with the hydraulic fluid, the locked state of the vane member at the center position becomes cancelled. If, upon canceling of the locked state of the vane member, an alternating torque produced by a camshaft of the engine is transmitted to the vane member, vibration of the vane member occurs, which tends to produce an uncomfortable noise. 
   Of course, such undesirable phenomenon can be solved by waiting the canceling of the locked state of the vane member until the retarding and advancing chambers are sufficiently filled with the hydraulic fluid. However, in this case, another undesirable phenomenon tends to occur wherein due to the force of the hydraulic fluid in the retarding and advancing chambers and the alternating torque from the camshaft, the vane member becomes to have a certain torque and thus the retarding and advancing pins are forced to press against edges of the corresponding recesses inducing a so-called locked condition of the pins. Under such condition, canceling of the locked state of the vane member is not smoothly carried out. 
   It is therefore an object of the present invention to provide a valve timing control device of an internal combustion engine, which is free of the above-mentioned drawbacks. 
   In accordance with a first aspect of the present invention, there is provided a valve timing control device of an internal combustion engine, which comprises a rotational member that is to be driven by a crankshaft of the engine; a camshaft having thereon cam lobes for operating engine valves; a housing provided by one of the rotational member and the camshaft, the housing having hydraulic chambers defined therein; a vane member provided by the other of the rotational member and the camshaft and rotatably received in the housing, the vane member having vanes each being received in one of the hydraulic chambers to divide the same into a retarding chamber and an advancing chamber, the vane member being rotatable between the most retarded position and the most advanced position over a center position therebetween; a hydraulic circuit constructed to selectively feed a hydraulic pressure to the retarding and advancing chambers to turn the vane member in a retarding or advancing direction relative to the housing; an oil pump driven by the engine for producing the hydraulic pressure; first and second projectable members each being held by one of the housing and the vane member and biased to project toward the other of the housing and the vane member; a first engaging portion that, when engaged with the first projectable member, restricts a rotational movement of the vane member from the center position in the advancing direction and permits a rotational movement of the same by a given degree from the center position in the retarding direction; a second engaging portion that, when engaged with the second projectable member, restricts a rotation movement of the vane member from the center position in the retarding direction and permits a rotational movement of the same by a given degree from the center position in the advancing direction; a first disengaging mechanism that cancels the engagement of the first projectable member with the first engaging portion when hydraulically actuated; a second disengaging mechanism that cancels the engagement of the second projectable member with the second engaging portion when hydraulically actuated; and a control means that is configured to carry out feeding one of the retarding and advancing chambers with a hydraulic pressure upon starting of the engine; actuating one of the first and second disengaging mechanisms to cancel the engagement of one of the first and second projectable members with the corresponding one of the first and second engaging portions; feeding the other of the retarding and advancing chambers with a hydraulic pressure thereby to turn the vane member in the housing within a range determined by each of the first and second engaging portions; and actuating, while the vane member is under the rotational movement within the range, the other of the first and second disengaging mechanisms to cancel the engagement of the other of the first and second projectable members with the corresponding one of the first and second engaging portions. 
   In accordance with a second aspect of the present invention, there is provided a valve timing control device of an internal combustion engine, which comprises a rotational member that is to be driven by a crankshaft of the engine; a camshaft having thereon cam lobes for operating engine valves; a housing provided by one of the rotational member and the camshaft, the housing having hydraulic chambers defined therein; a vane member provided by the other of the rotational member and the camshaft and rotatably received in the housing, the vane member having vanes each being received in one of the hydraulic chambers to divide the same into a retarding chamber and an advancing chamber, the vane member being rotatable between the most retarded position and the most advanced position over a center position therebetween; a hydraulic circuit constructed to selectively feed a hydraulic pressure to the retarding and advancing chambers to turn the vane member in a retarding or advancing direction relative to the housing; an oil pump driven by the engine for producing the hydraulic pressure; first and second projectable members each being held by one of the housing and the vane member and biased by a biasing member to project toward the other of the housing and the vane member; a first engaging recess that, when engaged with the first projectable member, restricts a rotational movement of the vane member from the center position in the advancing direction and permits a rotational movement of the same by a given degree from the center position in the retarding direction; a second engaging recess that, when engaged with the second projectable member, restricts a rotational member of the vane member from the center position in the retarding direction and permits a rotational movement of the same by a given degree from the center position in the advancing direction; a biasing mechanism that is provided by at least one of the second projectable member and the second engaging recess, the biasing mechanism pressing the first projectable member against one wall of the first engaging recess when the second projectable member is brought into engagement with the second engaging recess with the aid of the biasing member; a first disengaging mechanism that cancels the engagement of the first projectable member with the first engaging recess by using the hydraulic pressure fed to the retarding chambers; a second engaging mechanism that cancels the engagement of the second projectable member with the second engaging recess by using a hydraulic pressure applied thereto; and a control means that is configured to carry out feeding the advancing chambers with a hydraulic pressure upon starting of the engine; actuating the second disengaging mechanism to cancel the engagement of the second projectable member with the second engaging recess; feeding the retarding chambers with a hydraulic pressure; and actuating the first disengaging mechanism to cancel the engagement of the first projectable member with the first engaging recess. 
   In accordance with a third aspect of the present invention, there is provided a valve timing control device of an internal combustion engine, which comprises a rotational member that is to be driven by a crankshaft of the engine; a camshaft having thereon cam lobes for operating engine valves; a housing provided by one of the rotational member and the camshaft, the housing having hydraulic chambers defined therein; a vane member provided by the other of the rotational member and the camshaft and rotatably received in the housing, the vane member having vanes each being received in one of the hydraulic chambers to divide the same into a retarding chamber and an advancing chamber, the vane member being rotatable between the most retarded position and the most advanced position over a center position therebetween; a hydraulic circuit constructed to selectively feed a hydraulic pressure to the retarding and advancing chambers to turn the vane member in a retarding or advancing direction relative to the housing; an oil pump driven by the engine for producing the hydraulic pressure; first and second projectable members each being held by one of the housing and the vane member and biased to project toward the other of the housing and the vane member; a first engaging means for, when engaged with the first projectable member, restricting a rotational movement of the vane member from the center position in the advancing direction and permitting a rotational movement of the same by a given degree from the center position in the retarding direction; a second engaging means for, when engaged with the second projectable member, restricting a rotation movement of the vane member from the center position in the retarding direction and permitting a rotational movement of the same by a given degree from the center position in the advancing direction; a first disengaging means for canceling the engagement of the first projectable member with the first engaging means when hydraulically actuated; a second disengaging means for canceling the engagement of the second projectable member with the second engaging means when hydraulically actuated; and a control means that is configured to carry out feeding one of the retarding and advancing chambers with a hydraulic pressure upon starting of the engine; actuating one of the first and second disengaging means to cancel the engagement of one of the first and second projectable members with the corresponding one of the first and second engaging means; feeding the other of the retarding and advancing chambers with a hydraulic pressure thereby to turn the vane member in the housing within a range determined by each of the first and second engaging means; and actuating, while the vane member is under the rotational movement within the range, the other of the first and second disengaging means to cancel the engagement of the other of the first and second projectable members with the corresponding one of the first and second engaging means. 
   Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of an essential portion of a valve timing control device of the present invention; 
       FIG. 2  is a perspective view of the valve timing control device of the present invention; 
       FIG. 3  is a sectional view of the valve timing control device of the present invention, showing a condition wherein a vane member is held in a center position; 
       FIG. 4  is a view similar to  FIG. 3 , but showing a condition wherein the vane member is held in a retarded position; 
       FIG. 5  is a view also similar to  FIG. 3 , but showing a condition wherein the vane member is held in an advanced position; 
       FIG. 6  is a schematically illustrated rotation restricting means employed in the present invention, showing a condition of the means when an associated engine is at a standstill; 
       FIG. 7  is a view similar to  FIG. 6 , but showing a condition taken when an oil pump becomes powered by a cranking operation of the engine; 
       FIG. 8  is a view similar to  FIG. 6 , but showing a condition taken just after the cranking operation of the engine; 
       FIG. 9  is a view similar to  FIG. 6 , but showing a condition taken when the engine is under idling; 
       FIG. 10  is a view similar to  FIG. 6 , but showing a condition taken when the engine is under a phase retarded control; 
       FIG. 11  is a view similar to  FIG. 6 , but showing a condition taken when the engine is under a phase advanced control; 
       FIG. 12  is a view similar to  FIG. 6 , but showing a condition taken when the engine assumes a stand-by condition for stopping; 
       FIG. 13  is a view similar to  FIG. 6 , but showing a condition taken when the engine stops after the stand-by condition; 
       FIG. 14  is a flowchart showing programmed operation steps of a first example executed by a control unit, by which the timing of disengaging a second engaging pin from a second engaging recess is determined; 
       FIG. 15  is a flowchart similar to  FIG. 14 , but showing a second example; 
       FIG. 16  is a flowchart similar to  FIG. 14 , but showing a third example; and 
       FIG. 17  is a flowchart showing programmed operation steps that are executed by the control unit when the engine takes a stand-by condition for stopping. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following, a valve timing control device  100  of the present invention will be described in detail with reference to the accompanying drawings. 
   As will become apparent from the following, valve timing control device  100  is a device that controls the open/close timing of intake valves of an associated internal combustion engine. 
   For ease of understanding, various directional terms, such as, right, left, upper, lower, rightward, etc., are used in the following description. However, such terms are to be understood with respect to only a drawing or drawings on which the corresponding part or portion is shown. 
   Referring to  FIG. 1  of the drawings, there is shown in a sectional manner a valve timing control device  100  of the present invention. 
   Valve timing control device  100  generally comprises a sprocket  1  that is driven by a crankshaft of an associated internal combustion engine through a timing chain, an intake camshaft  2  that extends along an axis of the engine and is concentrically disposed in sprocket  1  in a manner to permit a relative rotation therebetween, a phase change mechanism  3  that is arranged between sprocket  1  and intake camshaft  2  to change a relative angular positioning therebetween and a hydraulic circuit  4  that actuates the phase change mechanism  3 . 
   As is seen from  FIGS. 1 and 2 , sprocket  1  comprises a cylindrical body portion  5  that has a thicker wall and a gear portion  6  that is integrally formed on one axial edge of cylindrical body portion  5 . Although not shown in the drawings, the timing chain is put on and engaged with gear portion  6  to drive sprocket  1 . Cylindrical body portion  5  constitutes a rear cover that closes a rear open end of an after-mentioned housing. 
   As is seen from  FIG. 1 , cylindrical body portion  5  is formed at a radially outer part with an axially extending through bore  5   a.    
   Intake camshaft  2  is rotatably supported on a cylinder head (not shown) through bearings and has thereon a plurality of axially spaced cams for actuating intake valves (viz., engine valves) of the associated internal combustion engine. As shown in  FIG. 1 , intake camshaft  2  is formed at its left end with an internally threaded center bore  2   a.    
   As is seen from  FIGS. 1 and 3 , phase change mechanism  3  comprises a cylindrical housing  7  integrally and coaxially connected to sprocket  1 , a vane member  9  that is coaxially fixed to the left end of intake camshaft  2  through a cam bolt  8  engaged with threaded center bore  2   a  and rotatably installed in the above-mentioned cylindrical housing  7 , three retarding chambers  11  (see  FIG. 3 ) that are defined at clockwise sides between three inwardly projected partition portions  10  of housing  7  and three outwardly projected vanes  16  of vane member  9  and three advancing chambers  12  that are defined at counterclockwise sides between three inwardly projected partition portions  10  of housing  7  and three outwardly projected vanes  16  of vane member  9 . 
   Referring back to  FIG. 1 , cylindrical housing  7  comprises a cylindrical body, a generally annular front cover  13  that covers a front (or left) open end of the cylindrical body, and the above-mentioned sprocket  1  that covers the rear open end of the cylindrical body. 
   As is seen from  FIGS. 1 ,  2  and  3 , the housing body, annular front cover  13  and body portion  5  of sprocket  1  are united tightly by means of three bolts  14  that pass through the three inwardly projected partition portions  10  of housing  7 . 
   As is seen from  FIG. 2 , annular front cover  13  is integrally formed at its left center part with a smaller diameter cylindrical portion  13   a.    
   As is seen from  FIGS. 1 and 3 , vane member  9  is constructed of a metal and comprises a rotor portion  15  that is fixed to the end of intake camshaft  2  by cam bolt  8  and three vanes  16  that project radially outward from rotor portion  15  at equally spaced intervals (viz., 120 degrees). 
   As is seen from  FIG. 1 , rotor portion  15  of vane member  9  is cylindrical in shape and integrally formed at a left end with a smaller diameter cylindrical supporting portion  15   a . Between this supporting portion  15   a  and rotor portion  15 , there is defined a stepped surface  15   b . As shown, the above-mentioned front cover  13  is rotatably disposed on cylindrical supporting portion  15   a  while being in contact with stepped surface  15   b.    
   As shown in  FIG. 3 , each vane  16  of vane member  9  is placed between two adjacent partition portions  10  of housing  7  and provided at a top portion thereof with a sealing member  17  for sealing between the top portion and an inner surface of the cylindrical body of housing  7 . 
   As shown in the drawing, each partition portions  10  of housing  7  has at one side one retarding chamber  11  and at the other side one advancing chamber  12 . 
   As is seen from  FIG. 1 , the three retarding chambers  11  are connected through first connecting passages  11   a  formed in rotor portion  15  of vane member  9 , and the three advancing chambers  12  are connected through second connecting passages  12   a  formed also in rotor portion  15  of vane member  9 . 
   As is seen from  FIG. 1 , hydraulic circuit  4  is constructed to selectively feed the hydraulic fluid (or pressure) to retarding and advancing chambers  11  and  12 . That is, hydraulic circuit  4  comprises a retarding fluid passage  18  that connects to retarding chambers  11  through first connecting passages  11   a , an advancing fluid passage  19  that connects to advancing chambers  12  through second connecting passages  12   a , an oil pump  20  that selectively feeds the retarding and advancing fluid passages  18  and  19  with a hydraulic fluid (or hydraulic pressure) and a first electromagnetic switch  21  that switches the flow directions of the retarding and advancing fluid passages  18  and  19  in accordance with an operation condition of the associated engine. Oil pump  20  may be a common pump such as a trochoide pump or the like that is powered by the engine. 
   As shown in  FIG. 1 , retarding and advancing fluid passages  18  and  19  have one ends that are connected to inlet/outlet openings of first electromagnetic switch  21  and the other ends  18   a  and  19   a  that are connected to the above-mentioned first and second connecting passages  11   a  and  12   a  through respective passages (no numerals) formed in intake camshaft  2 . 
   As is seen from  FIG. 1 , first electromagnetic switch  21  is of a three position proportional type and comprises a valve body, a spool axially movably installed in the valve body and an electromagnet. The axial movement of the spool is controlled by a control unit (not shown) in such a manner as to connect an outlet passage  20   a  of oil pump  20  to either one of retarding and advancing fluid passages  18  and  19  and at the same time connect a drain passage  22  to the other of the fluid passages  18  and  19 . As shown, an inlet part of oil pump  20  and terminal part of drain passage  22  are led to an interior of an oil pan  23 . 
   Information signals from a crank angle sensor (CRAS), an air flow meter (AFM), a water temperature sensor (WTS), a throttle valve open degree sensor (TVODS), a cam angle sensor (CAAS), etc., are fed to the control unit to detect a current operation condition of the engine. Based on the current operation condition of the engine, the control unit outputs instruction signals to first electromagnetic switch  21  and an after-mentioned second electromagnetic switch  36 . The crank angle sensor senses a crank angle of the engine (viz., engine speed), the air flow meter senses an air flow rate in an air induction part of the engine, the water temperature sensor senses the temperature of the engine cooling water, the throttle valve open degree sensor senses an open degree of a throttle valve arranged in the air induction part of the engine, and the cam angle sensor senses an angle shown by intake camshaft  2 . 
   As is seen from  FIGS. 1 and 3 , valve timing control device further comprises a rotation restricting means that is able to hold vane member  9  at a center position relative to cylindrical housing  7 , that is, a center position between the most retarded position and the most advanced position. 
   As is seen from  FIGS. 1 and 3 , rotation restricting means generally comprises first and second engaging recesses  24  and  25  that are formed in mutually spaced parts of cylindrical body portion  5  of sprocket  1 , and first and second engaging pins  26  and  27  that are axially movably received in respective bores formed in the two vanes  16  of the vane member  9  and arranged to be engageable with first and second engaging recesses  24  and  25 , and a hydraulic control mechanism  28  that operates to selectively establish and cancel the engagement between first and second engaging pins  26  and  27  and first and second engaging recesses  24  and  25 . 
   As is seen from  FIG. 4 , first engaging recess  24  of body portion  5  of sprocket  1  is provided at a somewhat advancing position with respect to the most retarded position of vane member  9 . 
   As is seen from  FIG. 6 , the diameter of first engaging recess  24  is larger than that of the leading portion  26   b  of first engaging pin  26 , and thus, the pin  26  is permitted to move slightly in a circumferential direction in engaging recess  24  even when engaged with recess  24 . 
   As is understood from  FIGS. 4 and 6 , also second engaging recess  25  is provided at a somewhat advancing position with respect to the most retarded position of vane member  9 . That is, when first engaging pin  26  is in engagement with first engaging recess  24 , second engaging pin  27  takes a position engageable with second engaging recess  25 . 
   As is seen from  FIG. 6 , the recess  25  is a tapered recess with a conical inner surface  25   c . As shown, the recess  25  is communicated with the outside through an air vent passage  25   b  formed in a bottom of the recess  25 . Due to provision of this passage  25   b , engagement and disengagement of second engaging pin  27  with or from the recess  25  are facilitated. 
   As is seen from  FIG. 1 , first engaging pin  26  is axially movably received in a first pin bore  16   a  formed in one of the three vanes  16  of vane member  9 , and has at its left part a larger diameter land portion  26   a  that serves as a pressure receiving part and at its right part a cylindrical portion  26   b  that has a flat right end. As shown, a first coil spring  29  is compressed between first engaging pin  26  and an inner surface of front cover  13  to bias the pin  26  rightward, that is, in a direction to establish the engagement between the pin  26  and first engaging recess  24 . The pin  26  has an axially extending blind bore for receiving a right part of the spring  29 . 
   As is seen from  FIG. 1 , second engaging pin  27  is axially movably received in a second pin bore  16   b  formed in the other one of the three vanes  16  of vane member  9 , and has at its left part a larger land portion  27   a  that serves as a pressure receiving part and at its right part a cylindrical portion that has a conical right end  27   b.    
   As is seen from  FIG. 6 , the size of conical right end  27   b  of second engaging pin  27  is smaller than that of conical second engaging recess  25 , and thus, the pin  27  is permitted to move slightly in a circumferential direction in the recess  25  even when engaged with the recess  25 . 
   It is to be noted that, due to the conical shape that both end  27   b  of pin  27  and recess  25  have, ingress and egress of end  27   b  into and from recess  25  induce a slight rotation of vane member  9  about its axis relative to cylindrical housing  7 . 
   Referring back to  FIG. 1 , a second coil spring  30  is compressed between second engaging pin  27  and the inner surface of front cover  13  to bias the pin  27  rightward, that is, in a direction to establish the engagement between the pin  27  and second engaging recess  25 . Like the above-mentioned first engaging pin  26 , the second pin  27  has an axially extending blind bore for receiving a right part of the spring  30 . 
   As is seen from  FIG. 1 , hydraulic control mechanism  28  comprises a pin engaging chamber  31  that is merged with the left part of first pin bore  16   a  in which first coil spring  29  is installed, a first pin disengaging chamber  32  that is defined between a stepped part of first pin bore  16   a  and larger diameter land portion  26   a  of first engaging pin  26 , a second pin disengaging chamber  33  that is defined between a stepped part of second pin bore  16   b  and larger diameter land portion  27   a  of second engaging pin  27 , a first fluid passage  34  that extends between pin engaging chamber  31  and either one of outlet passage  20   a  of oil pump  20  and drain passage  22 , a second fluid passage  35  that extends between second pin disengaging chamber  33  and either one of outlet passage  20   a  and drain passage  22 , and a second electromagnetic switch  36  that switches first and second fluid passages  34  and  35  for connection with oil outlet passage  20   a  or drain passage  22  in accordance with an instruction signal applied thereto from the control unit, that is, in accordance with an operation condition of the engine. 
   As is easily understood from  FIG. 6 , pin engaging chamber  31  is constructed to bias first engaging pin  26  toward first engaging recess  24  with both a force that is possessed by the hydraulic pressure fed thereto from oil pump  20  through first fluid passage  34  and a force that is produced by first coil spring  29 . 
   While, first and second pin disengaging chambers  32  and  33  are each constructed to bias first or second engaging pin  26  or  27  against the biasing force of first or second coil spring  29  or  30  in a direction away from first or second engaging recess  24  or  25  with a force that is possessed by the hydraulic pressure fed thereto from oil pump  20 . As will be described in detail hereinafter, application of the hydraulic pressure to first and second pin disengaging chambers  32  and  33  is made together with application of the same to retarding or advancing chamber  11  or  12 . 
   As is seen from  FIG. 1 , first fluid passage  34  has one end that is connected to an inlet/outlet opening of second electromagnetic switch  36  and the other end that is connected to pin engaging chamber  31  through a first axial passage  34   a  formed in a cylindrical supporting rod  37  and a first radial passage  38  formed in vane member  9 , while second fluid passage  35  has one end that is connected to the other inlet/outlet opening of second electromagnetic switch  36  and the other end that is connected to second pin disengaging chamber  33  through a second axial passage  35   a  formed in cylindrical supporting rod  37  and a second radial passage  39  formed in vane member  9 . 
   It is to be noted that, as will be seen from  FIG. 6 , the hydraulic pressure fed to one retarding chamber  11  is also fed to first pin disengaging chamber  32  through a connecting passage  40  formed in vane member  9 . 
   Second electromagnetic switch  36  is of a two-position ON/OFF type and comprises a valve body, a spool axially movably installed in the valve body and an electromagnet. The axial movement of the spool is controlled by the above-mentioned control unit in such a manner as to connect outlet passage  20   a  of oil pump  20  to either one of first and second fluid passages  34  and  35  and at the same time connect drain passage  22  to the other of passages  34  and  35 . 
   As is seen from  FIG. 1 , between a cylindrical clearance between an outer surface of cylindrical supporting rod  37  and an inner surface of cylindrical supporting portion  15   a  of rotor portion  15  of vane member  9 , there are operatively arranged two seal rings  41   a  and  41   b.    
   As is seen from  FIG. 6 , first engaging recess  24  of rotation restricting means is communicated with one of advancing chambers  12  through a connecting passage  42  formed in vane member  9 . As is seen from the drawing, connecting passage  42  extends radially outward from first engaging recess  24 , and thus, when, with first engaging pin  26  kept in engagement with recess  24 , a hydraulic pressure is applied to connecting passage  42 , there is produced a force by which leading end  26   b  of pin  26  is pressed against a side wall of recess  24 . This will be much well understood from  FIG. 7 . 
   Referring back to  FIG. 1 , around cylindrical supporting portion  15   a  of rotor portion  15  of vane member  9 , there is disposed a coil spring  43  that functions to bias vane member  9  in a direction from the most retarded position to the center position relative to cylindrical housing  7 . For this biasing action, coil spring  43  has one end  43   a  (see  FIG. 2 ) hooked to a recess formed in cylindrical portion  13   a  of annular front cover  13  and the other end  43   b  engaged with an elongate slot  15   c  (see  FIG. 3 ) formed in rotor portion  15  of vane member  9 . 
   As shown in  FIG. 1 , within cylindrical portion  13   a  of annular front cover  13 , there is tightly installed a stopper ring  44  by which a left end of coil spring  43  is held. 
   In the following, operation of valve timing control device  100  of the present invention will be described with reference to the drawings, particularly  FIGS. 3 to 5  and  6  to  13 . 
   For ease of understanding, the description will be commenced with respect to a standstill condition of the associated engine. 
   Under such condition, vane member  9  assumes the center position as shown in  FIG. 3 . In this case, oil pump  20  does not work, and thus, as is seen from  FIG. 6 , all of the three retarding chambers  11 , three advancing chambers  12 , first and second engaging recesses  24  and  25 , pin engaging chamber  31  and first and second pin disengaging chambers  32  and  33  are not supplied with a sufficient hydraulic pressure. Thus, first and second engaging pins  26  and  27  are engaged at their leading ends  26   b  and  27   b  with first and second engaging recesses  24  and  25  respectively with the biasing force of first and second coil springs  29  and  30 . That is, the center position of vane member  9  is substantially locked. 
   Under this condition, first electromagnetic switch  21  assumes a condition wherein due to the force of a spring (no numeral), the spool is forced to take one position to connect outlet passage  20   a  of oil pump  20  to advancing fluid passage  19  and connect drain passage  22  to retarding fluid passage  18 , and at the same time, second electromagnetic switch  36  assumes a condition wherein due to the force of a spring (no numeral), the spool is forced to take one position to connect outlet passage  20   a  of oil pump  20  to first fluid passage  34  and connect drain passage  22  to second fluid passage  35 . 
   When now an ignition switch (not shown) of the engine is turned ON, oil pump  20  becomes powered by the cranking of the engine. Upon this, as is seen from  FIG. 7 , a certain amount of hydraulic fluid is led to pin engaging chamber  31  through first fluid passage  34 , and also to first engaging recess  24  through one advancing chamber  12  and connecting passage  42 . With this fluid supply, the engagement between first engaging pin  26  and first engaging recess  24  becomes much tightly made, while the engagement between second engaging pin  27  and second engaging recess  25  is kept without change in engaging force. 
   When, after completion of the cranking, the engine takes a transit condition just before starting its idling operation, hydraulic control mechanism  28  takes such a condition as depicted by  FIG. 8 . That is, upon such condition, an instruction signal is fed from the control unit to second electromagnetic switch  36  causing the same to take another condition wherein the spool takes the other position to connect drain passage  22  to first fluid passage  34  and connect outlet passage  20   a  of oil pump  20  to second fluid passage  35 . With this, pin engaging chamber  31  is subjected to a pressure decrease and second pin disengaging chamber  33  is subjected to a pressure increase, so that second engaging pin  27  is smoothly disengaged from second engaging recess  25  canceling the engagement therebetween. 
   While, under this condition, first engaging pin  26  keeps the engagement with first engaging recess  24  because leading end  26   b  of pin  26  is pressed against a side wall of recess  24  by the force produced by the hydraulic fluid in connecting passage  42 . 
   It is to be noted that, as is seen from  FIG. 8 , since leading end  26   b  of first engaging pin  26  has the flat end intimately pressed against a flat bottom of first engaging recess  24 , the hydraulic fluid in connecting passage  42  does not produce a force to bias pin  26  in a direction away from recess  24 . 
   As is described hereinabove, until the time depicted by  FIG. 8 , at least first engaging pin  26  keeps the engagement with first engaging recess  24 , and thus, vane member  9  keeps the center position relative to cylindrical housing  7 . This means improvement in engine starting performance. 
   When now the engine is started and brought to an idling operation, hydraulic control mechanism  28  takes such a condition is as depicted by  FIG. 9 . Second electromagnetic switch  36  is kept unchanged. However, in this case, an instruction signal is fed from the control unit to first electromagnetic switch  21  causing the same to take a condition wherein the spool takes a position to close advancing fluid passage  19  to keep the pressure in three advancing chambers  12  and connect outlet passage  20   a  of oil pump  20  to retarding fluid passage  18 . 
   With this, retarding chambers  11  are subjected to a pressure increase causing vane member  9  to turn slightly in a phase retarding direction, and thus, first engaging pin  26  is moved slightly in first engaging recess  24  in a direction to cancel the intimate contact of leading end  26   b  thereof with the inner wall of recess  24 . 
   At the same time, the hydraulic pressure is fed to first pin disengaging chamber  32  through connecting passage  40 . With this, first engaging pin  26  that has been released from the side wall of first engaging recess  24  is smoothly and fully disengaged from the recess  24  canceling the engagement therebetween. 
   Thus, now, vane member  9  is unlocked and thus permitted to rotate in both, that is, retarding and advancing directions relative to cylindrical housing  7 . 
   When thereafter the engine is brought to for example a lower speed lower load operation mode, hydraulic control mechanism  28  takes such a condition as depicted by  FIG. 10 . That is, upon this operation change, an instruction signal is fed from the control unit to first electromagnetic switch  21  causing the same to take a condition wherein the spool takes a position to connect drain passage  22  to advancing fluid passage  19  and connect outlet passage  20   a  of oil pump  20  to retarding fluid passage  18 . Actually, the connection between outlet passage  20   a  and retarding fluid passage  18  is kept from the previous condition. 
   With this, as is seen from  FIG. 4 , the hydraulic pressure in three advancing chambers  12  is reduced and at the same time the hydraulic pressure in three retarding chambers  11  is increased, and thus, vane member  9  is turned to the most retarded position relative to cylindrical housing  7 . This means that intake camshaft  2  is turned to the most retarded position relative to sprocket  1  thereby reducing the overlap between intake and exhaust valves. Thus, a residual gas in each cylinder is reduced inducing improvement in combustion efficiency, stability in rotation and improvement in fuel consumption. 
   When thereafter the engine is brought to for example a higher speed higher load operation mode, hydraulic control mechanism  28  takes such a condition as depicted by  FIG. 11 . That is, upon this operation change, an instruction signal is fed from the control unit to first electromagnetic switch  21  causing the same to take a condition wherein the spool takes a position to outlet passage  20   a  of oil pump  20  to advancing fluid passage  19  and connect drain passage  22  to retarding fluid passage  18 . 
   With this, as is seen from  FIG. 5 , the hydraulic pressure in three advancing chambers  12  is increased and at the same time the hydraulic pressure in three retarding chambers  11  is reduced, and thus, vane member  9  is turned to the most advanced position relative to cylindrical housing  7 . This means that intake camshaft  2  is turned to the most advanced position relative to sprocket  1  thereby increasing the overlap between intake and exhaust valves. Thus, the air charging efficiency of each cylinder is increased and the output torque of the engine is increased. 
   When it is intended to stop engine, the associated motor vehicle is brought into its standstill causing the engine to take an idling condition. Thus, under this condition, vane member  9  is returned to the center position (see  FIG. 3 ) for the reason as has been explained in the section of  FIG. 9 . 
   When now an ignition switch is turned OFF, hydraulic control mechanism  28  takes such a condition as depicted by  FIG. 12 . That is, in a short period for which the engine still rotates slowly before its complete stopping, an instruction signal is fed from the control unit to first electromagnetic switch  21  causing the same to take a condition wherein the spool takes a position to block advancing fluid passage  19  and connect outlet passage  20   a  of oil pump  20  to retarding fluid passage  18 . Because, under such slow rotation of the engine, the hydraulic pressure from outlet passage  20   a  is very small and thus vane member  9  is slightly moved from the center position to a slightly retarded position. 
   In the above-mentioned short period, an instruction signal is fed from the control unit to second electromagnetic switch  36  causing the same to take a condition wherein the spool takes a position to connect outlet passage  20   a  of oil pump  20  to first fluid passage  34  and connect drain passage  22  to second fluid passage  35 . 
   Accordingly, first engaging pin  26  is forced to move into first engaging recess  24  to establish a locked engagement therebetween. For the reason as is mentioned hereinabove, that is, because vane member  9  assumes the slightly retarded position, first engaging pin  26  engaged with recess  24  takes a retarded position relative to recess  24 . Thus, as is seen from the drawing, second engaging pin  27  fails to engage with second engaging recess  25  while being biased toward recess  25  due to the force of second coil spring  30 . 
   Just before the complete stopping of the engine, hydraulic control mechanism  28  takes such a condition as depicted by  FIG. 13 . That is, due to the work of the control unit, first electromagnetic switch  21  is forced to assume a condition wherein the spool takes a position to connect outlet passage  20   a  of oil pump  20  to advancing fluid passage  19  and connect drain passage  22  to retarding fluid passage  18 . 
   With this, three advancing chambers  12  become higher in pressure causing vane member  9  to turn back slightly in the advancing direction to the center position having leading end  26   b  of first engaging pin  26  slide on the flat bottom of first engaging recess  24 . With this slight rotation of vane member  9 , second engaging pin  27  is permitted to engage with second engaging recess  25 , as shown. Thus, vane member  9  is fully locked at the center position by the two engaging pins  26  and  27 , as shown in  FIGS. 3 and 13 . 
   As is described hereinabove, in accordance with the present invention, at the time of staring the engine, disengagement of first and second engaging pins  26  and  27  from their corresponding first and second engaging recesses  24  and  25  is not simultaneously carried out. During a time from the engine cranking to the time just before the engine idling operation, only the disengagement of second engaging pin  27  from second engaging recess  25  is carried out. That is, during the time, first engaging pin  26  is forced to keep the engagement with first engaging recess  24  having leading end  26   b  pressed against the side wall of first engaging recess  24 . At the time when retarding or advancing chambers  11  or  12  are filled with the hydraulic pressure, the disengagement of first engaging pin  26  from first engaging recess  24  is carried out. Accordingly, undesired vibration of vane member  9 , which would be caused by an alternating torque applied thereto at the engine starting, is sufficiently suppressed. 
   For keeping the engagement of first engaging pin  26  with first engaging recess  24 , leading end  26   b  of pin  26  is tightly pressed against the side wall of recess  24 . That is, a frictional force produced between leading end  26   b  and the side wall suppresses the disengagement of pin  26  from recess  24 . 
   In the period from the OFF turning of the ignition switch to the complete stop of the engine, first engaging pin  26  is brought into engagement with first engaging recess  24  at first and then second engaging pin  27  is brought into engagment with second engaging recess  25 . This two step action brings about an assured locking of vane member  9  to sprocket  1  at the center position, and thus, undesired vibration of vane member  9  is assuredly suppressed. 
   Because of usage of two engaging pins  26  and  27 , positioning of vane member  9  relative to sprocket  1  is assured at the time of starting the engine, and thus, the engine starting performance is improved. 
   Because of the conical shape that both leading end  27   b  of second engaging pin  27  and second engaging recess  25  have, the engagement and disengagement between leading end  27   b  and recess  25  are easily and assuredly made. 
   In the following, three, viz., first, second and third methods for determining the timing of disengaging second engaging pin  27  from second engaging recess  25  at the engine starting will be described with reference to  FIGS. 14 to 16 . 
   In  FIG. 14 , there is shown a flowchart for the first method. 
   In this method, at step S- 1 , judgment is carried out as to whether or not a predetermined time has passed after starting of the engine. If YES, that is, if the predetermined time has passed, the operation flow goes to step S- 2  to cause second electromagnetic switch  36  to take a condition to feed second pin disengaging chamber  33  with a certain hydraulic pressure for the disengagement of pin  27  from recess  25 . In this method, it is possible to estimate the time needed until, upon starting of the engine, three advancing chambers  12  are sufficiently filled with the hydraulic pressure. 
   In  FIG. 15 , there is shown a flowchart of the second method. 
   In this method, at step S- 11 , judgment is carried out as to whether a current engine speed has become higher than a predetermined speed or not. If YES, that is, if the current engine speed has become higher than the predetermined speed, the operation flow goes to step S- 12  to cause switch  36  to take the condition to feed chamber  33  with a certain hydraulic pressure for the disengagement of pin  27  from recess  25 . Under operation of the engine, oil pump  20  is sufficiently driven. Thus, in this second method, three advancing chambers  12  can be filled quickly with the hydraulic pressure upon starting of the engine. 
   In  FIG. 16 , there is shown a flowchart of the third method. 
   In this method, at step S- 21 , judgment is carried out as to whether the hydraulic pressure supplied to three advancing chambers  12  has become higher than a predetermined pressure or not. If YES, that is, if the pressure in chambers  12  has become higher than the predetermined pressure, the operation flow goes to step S- 22  to cause switch  36  to take the condition to feed chamber  33  with a certain hydraulic pressure for the disengagement of pin  27  from recess  25 . According to this third method, the hydraulic pressure led to first engaging recess  24  from one advancing chamber  12  through connecting passage  42  becomes high, and thus, the force by which leading end  26   b  of first engaging pin  26  is pressed against side wall of first engaging recess  24  is increased. Thus, unexpected disengagement of first pin  26  from recess  24  is suppressed. 
     FIG. 17  shows programmed operation steps executed by the control unit for carrying out the control for stand-by condition for engine stopping that is depicted by  FIG. 12 . 
   That is, at step S- 31 , judgment is carried out as to whether the current engine speed is lower than a predetermined speed or not. If YES, that is, if the current engine speed is lower than the predetermined speed, the operation flow goes to step S- 32 . At this step S- 32 , judgment is carried out as to whether a rotation angle (or cam phase) of intake camshaft  2  is within a predetermined range or not. If YES, the operation flow goes to step S- 33  to cause switch  36  to take a condition to feed pin engaging chamber  31  with a certain hydraulic pressure from output passage  20   a  of oil pump  20 . With this, first engaging pin  26  is brought into engagement with first engaging recess  24  to achieve a locked engagement therebetween. 
   The entire contents of Japanese Patent Application 2004-187186 filed Jun. 25, 2004 are incorporated herein by reference. 
   Although the invention has been described above with reference to the embodiment of the invention, the invention is not limited to such embodiment as described above. Various modifications and variations of such embodiment may be carried out by those skilled in the art, in light of the above description.