Patent Publication Number: US-9896977-B2

Title: Valve timing control apparatus and manufacturing method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2015-163925 filed on Aug. 21, 2015. 
     TECHNICAL FIELD 
     The present disclosure relates to a valve timing control apparatus, which adjusts valve timing of a subject valve that is opened and closed by a camshaft through transmission of a crank torque from a crankshaft at an internal combustion engine, and a manufacturing method of such a valve timing control apparatus. 
     BACKGROUND 
     In a previously known valve timing control apparatus, an inner rotor, which is rotated in a circumferential direction synchronously with the camshaft, is rotated relative to an outer rotor, which is rotated in the circumferential direction synchronously with the crankshaft, so that the valve timing is adjusted in response to rotational phase between the inner rotor and the outer rotor. 
     For instance, JP2005-155346A (corresponding to US2005/0115528A1) discloses one such a valve timing control apparatus that has the outer rotor, which includes a synchronously rotatable member, a stopper member and a positioning member. Specifically, the synchronously rotatable member is rotated synchronously with the crankshaft when the synchronously rotatable member receives the crank torque. The stopper member is joined to the synchronously rotatable member in the axial direction and is thereby rotated synchronously with the synchronously rotatable member. The stopper member stops rotation of the inner rotor that is rotated relative to the stopper member in the circumferential direction. The positioning member is shaped into a rod form and extends in the axial direction. The positioning member positions the stopper member relative to the synchronously rotatable member in the circumferential direction. 
     In the valve timing control apparatus of JP2005-155346A (corresponding to US2005/0115528A1), the positioning member functions such that the positioning member limits positional deviation of the stopper member relative to the synchronously rotatable member, which receives the crank torque, when the stopper member stops the rotation of the inner rotor. Here, a shaft portion of the positioning member, which extends straight, is press fitted into a press fitting hole portion of the stopper member, which extends straight. Furthermore, a distal end portion of the positioning member projects into a tapered hole portion of the synchronously rotatable member, which has an inner peripheral surface tapered to have an inner diameter that is progressively increased in the axial direction toward the stopper member. The distal end portion of the positioning member, which projects into the tapered hole portion of the synchronously rotatable member, contacts the inner peripheral surface of the tapered hole portion at a specific side in the circumferential direction. The press fitting configuration and the contacting configuration described above can guarantee positioning of the stopper member relative to the synchronously rotatable member in a manner that absorbs positional deviation of the central axis of the press fitting hole portion and the central axis of the tapered hole portion from its normal position (a specified position) and further guarantee the accuracy of the positioning of the inner rotor at the time of stopping the rotation of the inner rotor regardless of manufacturing tolerance. 
     However, in the valve timing control apparatus of JP2005-155346A (corresponding to US2005/0115528A1), the positioning member projects from the press fitting hole portion of the stopper member toward the tapered hole portion side. Therefore, at the time of inserting a distal end part of the shaft portion of the positioning member into the tapered hole portion upon press fitting of the shaft portion of the positioning member into the hole portion to form the positioning structure, the shaft portion tends to be caught by the tapered hole portion side edge of the press fitting hole portion. In such a case, as indicated by a solid line in  FIG. 14A , a stick-slip phenomenon (also referred to as a slip-stick phenomenon) occurs in a period T, which is from the time of projecting the shaft portion from the press fitting hole portion to the time of contacting the distal end part against the inner peripheral surface of the tapered hole portion at the specific side. The stick-slip phenomenon is a phenomenon of self-oscillation of the positioning member that involves repeat of a moving state (slipping state), which is governed by a small kinetic frictional force between the shaft portion and the press fitting hole portion, and a stop state (sticking state), which is governed by a large kinetic frictional force between the shaft portion and the edge. 
     When the stick-slip phenomenon of the positioning member occurs, control of a press-in load (also referred to as a press-fit load) applied to the positioning member to insert the positioning member into the press fitting hole portion becomes difficult at the time of contacting of the distal end part of the positioning member against the tapered hole portion. Therefore, in such a case, the press-in load, which is applied to the positioning member, may become excessively large to cause deformation of the synchronously rotatable member. Here, the deformation of the synchronously rotatable member of the outer rotor, which is rotated by the crank torque transmitted from the crankshaft, has an influence on the adjustment accuracy of the valve timing in accordance with the rotational phase between the outer rotor and the inner rotor. Therefore, it is necessary to limit the deformation of the synchronously rotatable member. 
     SUMMARY 
     The present disclosure is made in view of the above points. 
     According to the present disclosure, there is provided a valve timing control apparatus for adjusting valve timing of a subject valve that is opened and closed by a camshaft through transmission of a crank torque from a crankshaft at an internal combustion engine. The valve timing control apparatus includes an outer rotor and an inner rotor. The outer rotor is rotated synchronously with the crankshaft in a circumferential direction. The inner rotor is rotated synchronously with the camshaft in the circumferential direction and is rotatable relative to the outer rotor at an inside of the outer rotor. The outer rotor includes a synchronously rotatable member, a stopper member and a positioning member. The synchronously rotatable member is rotated synchronously with the crankshaft when the synchronously rotatable member receives the crank torque from the crankshaft. The stopper member is rotated integrally with the synchronously rotatable member that is joined to the stopper member in an axial direction. The stopper member stops rotation of the inner rotor that is rotated relative to the outer rotor in the circumferential direction. The positioning member is shaped into a rod form and extends in the axial direction. The positioning member positions the stopper member relative to the synchronously rotatable member in the circumferential direction. The synchronously rotatable member includes a tapered hole portion that is tapered such that an inner diameter of an inner peripheral surface of the tapered hole portion is progressively increased in the axial direction toward the stopper member. The stopper member includes a press fitting hole portion that extends straight in the axial direction. The positioning member is press fitted into the press fitting hole portion. The positioning member includes a contacting distal end portion, a main shaft portion and a loosely inserting shaft portion. The contacting distal end portion is inserted into the tapered hole portion in the axial direction and contacts the inner peripheral surface of the tapered hole portion on a specific side, which is a circumferential side in the circumferential direction. The main shaft portion extends straight in the axial direction and is press fitted into the press fitting hole portion in the axial direction. The loosely inserting shaft portion is formed between the contacting distal end portion and the main shaft portion and is loosely inserted into the press fitting hole portion in the axial direction. 
     According to the present disclosure, there is also provided a manufacturing method of the valve timing control apparatus according, including a connecting step and a positioning step. In the connecting step, the synchronously rotatable member and the stopper member are connected together in the axial direction. In the positioning step, the positioning member is press fitted into the press fitting hole portion of the stopper member, and the positioning member is further inserted into the tapered hole portion, so that the stopper member is positioned in the circumferential direction relative to the synchronously rotatable member after the synchronously rotatable member and the stopper member are connected together in the connecting step. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a cross sectional view of a valve timing control apparatus according to an embodiment of the present disclosure taken along line I-I in  FIG. 2 ; 
         FIG. 2  is a cross sectional view taken along line II-II in  FIG. 1 ; 
         FIG. 3  is a cross sectional view taken along line III-Ill in  FIG. 1 ; 
         FIG. 4  is an enlarged cross sectional view taken along line IV-IV in  FIG. 2 , showing a positioning member and its surroundings according to the embodiment; 
         FIG. 5  is a flowchart for describing a manufacturing method of the valve timing control apparatus according to the embodiment; 
         FIG. 6  is a characteristic diagram showing comparison of a characteristic of the valve timing control apparatus of the embodiment and a characteristic of a prior art valve timing control apparatus; 
         FIG. 7  is a cross sectional view showing a modification of  FIG. 4 ; 
         FIG. 8  is a cross sectional view showing a modification of  FIG. 1 ; 
         FIG. 9  is a cross sectional view showing a modification of  FIG. 1 ; 
         FIG. 10  is a cross sectional view showing a modification of  FIG. 4 ; 
         FIG. 11  is a cross sectional view showing a modification of  FIG. 4 ; 
         FIG. 12  is a cross sectional view showing a modification of  FIG. 4 ; 
         FIG. 13  is a cross sectional view showing a modification of  FIG. 4 ; 
         FIG. 14A  is a characteristic diagram for describing a characteristic of a prior art valve timing control apparatus; and 
         FIG. 14B  is an enlarged view of an area XIVB in  FIG. 14A . 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present disclosure will be described with reference to the accompanying drawings. 
     As shown in  FIG. 1 , a valve timing control apparatus  1  of the present embodiment is a hydraulic type that uses a pressure of hydraulic oil. The valve timing control apparatus  1  is installed in a transmission system that transmits a crank torque, which is outputted from a crankshaft  3 , to a camshaft  2  through a timing chain  4  at an internal combustion engine. The camshaft  2  opens and closes exhaust valves (serving as subject valves of the present disclosure, which may be simply referred to as valves) when the crank torque is transmitted from the crankshaft  3  to the camshaft  2 . The valve timing control apparatus  1  adjusts valve timing of the exhaust valves. 
     As shown in  FIGS. 1 to 3 , the valve timing control apparatus  1  includes an outer rotor  10 , an inner rotor  20  and a torsion spring  50 . In the valve timing control apparatus  1 , the inner rotor  20  is rotated relative to the outer rotor  10  to adjust the valve timing according to a rotational phase between the outer rotor  10  and the inner rotor  20 . 
     The outer rotor  10  is made of metal and is formed as a sprocket housing in such a manner that a sprocket plate  13  and a cover plate  14  are placed on one axial side and another axial side of a shoe housing  12 , and the sprocket plate  13 , the shoe housing  12  and the cover plate  14  are fixed together by bolts. In the outer rotor  10 , the shoe housing  12  is positioned relative to the sprocket plate  13  in the circumferential direction by a positioning member  18 . The positioning member  18 , which is made of metal and is shaped into an elongated rod form, is installed to the sprocket plate  13 , the shoe housing  12  and the cover plate  14  and is thereby elongated in the axial direction. Thus, the outer rotor  10  includes the above-described components, i.e., the shoe housing  12 , the sprocket plate  13 , the cover plate  14  and the positioning member  18 . 
     As shown in  FIGS. 1 and 2 , the shoe housing  12  includes a receiving tube  120  and a plurality of shoes  122 , which are integrally formed as one-piece component. The shoes  122  are formed at predetermined locations, which are placed one after another at predetermined intervals in a circumferential direction along an inner peripheral surface of the receiving tube  120  configured into a cylindrical tubular form, and each of the shoes  122  is shaped into a generally fan form and radially inwardly projects. A receiving chamber  123  is formed between each circumferentially adjacent two of the shoes  122  in the shoe housing  12 . 
     As shown in  FIGS. 1 and 3 , the sprocket plate  13  has a center hole  130 , which extends through the sprocket plate  13  in the axial direction, and the cover plate  14  has a center hole  140 , which extends through the cover plate  14  in the axial direction. As shown in  FIG. 1 , the sprocket plate  13  includes a plurality of sprocket teeth  133 . The sprocket teeth  133  are formed at predetermined locations, which are placed one after another at equal intervals in a circumferential direction along an outer peripheral surface of the sprocket plate, and each of the sprocket teeth  133  is shaped into a generally fan form and radially outwardly projects. The sprocket plate  13  is coupled to the crankshaft  3  by a timing chain  4 , which is wound around the sprocket teeth  133  and teeth of the crankshaft  3 . With this coupling between the sprocket plate  13  and the crankshaft  3 , the sprocket plate (serving as a synchronously rotatable member)  13  of the outer rotor  10  receives the crank torque of the crankshaft  3  through the timing chain  4  at the time of operating the internal combustion engine. Therefore, the constituent components  12 ,  13 ,  14 ,  18  of the outer rotor  10  are rotated together synchronously with the crankshaft  3  in the circumferential direction (a clockwise direction in  FIG. 2 ). 
     As shown in  FIGS. 1 and 2 , the inner rotor  20 , which is made of metal, is a vane type and is received in an inside of the outer rotor  10 . 
     The inner rotor  20  includes a rotatable shaft  200  and a plurality of vanes  202 , which are integrally formed as one-piece component. The rotatable shaft  200 , which is shaped into a cylindrical tubular form, is coaxially placed in an inside of the outer rotor  10 . As shown in  FIGS. 1 to 3 , the rotatable shaft  200  includes a center recess  201  and an anchoring groove  203 . The center recess  201  is formed as a cylindrical recess and opens in the axial direction toward the cover plate  14 . The anchoring groove  203  is formed as a rectangular groove and opens in an inner peripheral surface of the center recess  201 . 
     With reference to  FIGS. 1 and 2 , the rotatable shaft  200  is coaxially joined to the camshaft  2 , which is inserted into the center hole  130  of the sprocket plate  13 , by a bolt. With this construction, the inner rotor  20  is rotated synchronously with the camshaft  2  in one circumferential direction (the clockwise direction in  FIG. 2 ) and is rotatable relative to the outer rotor  10  in two opposite circumferential directions (the clockwise direction and the counter clockwise direction in  FIG. 2 ). At the time of rotating the inner rotor  20  relative to the outer rotor  10 , one axial end surface and the other axial end surface of the rotatable shaft  200  are slid relative to the sprocket plate  13  and the cover plate  14 , respectively. Also, at the same time, an outer peripheral surface of the rotatable shaft  200  is slid relative to projecting distal end surfaces (radially inner end surfaces) of the shoes  122 . 
     As shown in  FIG. 2 , the vanes  202  are formed at predetermined locations, which are placed one after another at predetermined intervals in the circumferential direction along an outer peripheral surface of the rotatable shaft  200 , and each of the vanes  202  is shaped into a generally fan form and radially outwardly projects. Each of the vanes  202  is inserted into a corresponding one of the receiving chambers  123 . At the time of rotating the inner rotor  20  relative to the outer rotor  10 , one axial end surface and the other axial end surface of each vane  202  are slid relative to the sprocket plate  13  and the cover plate  14 , respectively. Also, at the same time, a projecting distal end surface (radially outer end surface) of each vane  202  is slid relative to an inner peripheral surface of the receiving tube  120 . 
     Each of the vanes  202  partitions the corresponding one of the receiving chambers  123  in the circumferential direction to form an advancing working chamber  34  and a retarding working chamber  35  in the receiving chamber  123 . In this way, in the internal combustion engine, when the hydraulic oil, which is discharged from the pump, is guided into the advancing working chambers  34  through operation of an oil pressure control valve, a rotational torque, which rotates the inner rotor  20  relative to the outer rotor  10  toward an advancing side Da in the circumferential direction, is generated. At this time, in the internal combustion engine, the hydraulic oil is discharged from each retarding working chamber  35  to a drain (e.g., an oil pan) through operation of the oil pressure control valve. Thus, the rotational phase of the inner rotor  20  relative to the outer rotor  10  is advanced, and thereby the valve timing is advanced. In contrast, in the internal combustion engine, when the hydraulic oil, which is discharged from the pump, is guided into the retarding working chambers  35  through operation of the oil pressure control valve, a rotational torque, which rotates the inner rotor  20  relative to the outer rotor  10  toward a retarding side Dr in the circumferential direction, is generated. At this time, in the internal combustion engine, the hydraulic oil is discharged from each advancing working chamber  34  to the drain through operation of the oil pressure control valve. Thus, the rotational phase of the inner rotor  20  relative to the outer rotor  10  is retarded, and thereby the valve timing is retarded. 
     A stopper vane  202   s , which is a specific one of the vanes  202 , is inserted into the receiving chamber  123  formed between an advancing stopper shoe  122   a  and a retarding stopper shoe  122   r , which are specific two of the shoes  122 . As indicated by a solid line in  FIG. 2 , the advancing stopper shoe  122   a  stops further rotation of the inner rotor  20  toward the advancing side Da when the advancing stopper shoe  122   a  abuts against the stopper vane  202   s  of the inner rotor  20 , which is rotated relative to the outer rotor  10  toward the advancing side Da in the circumferential direction. In contrast, as indicated by a dot-dot-dash line in  FIG. 2 , the retarding stopper shoe  122   r  stops further rotation of the inner rotor  20  toward the retarding side Dr when the retarding stopper shoe  122   r  abuts against the stopper vane  202   s  of the inner rotor  20 , which is rotated relative to the outer rotor  10  toward the retarding side Dr in the circumferential direction. Thereby, the shoe housing  12 , which includes the advancing stopper shoe  122   a  and the retarding stopper shoe  122   r , forms a stopper member. 
     With reference to  FIGS. 1 to 3 , the torsion spring  50 , which is made of metal, is a torsion coil spring that is formed by winding a spring wire into a cylindrical coil form about the axis. The torsion spring  50  is coaxially placed in an inside and an outside of the center hole  140  of the cover plate  14 . One end portion  500  of the torsion spring  50  is always engaged with, i.e., is always anchored to the positioning member  18  to apply the restoring force to the outer rotor  10  toward the retarding side Dr. The other end portion  501  of the torsion spring  50 , which is opposite from the one end portion  500 , is always engaged with the anchoring groove  203  to apply the restoring force to the inner rotor  20  toward the advancing side Da. With the above construction, when the inner rotor  20  is rotated relative to the outer rotor  10 , which receives the crank torque, toward the retarding side Dr in the circumferential direction, the restoring force, which is generated by the torsion spring  50 , is increased to urge the inner rotor  20  toward the advancing side Da relative to the outer rotor  10 . Specifically, the torsion spring  50  forms a resilient member. In place of the torsion coil spring, which is in the cylindrical coil form, the torsion spring  50  may be formed by a spiral spring (e.g., a mainspring, a flat coil spring). 
     Next, the positioning structure of the outer rotor  10 , which uses the positioning member  18 , will be described in detail. In the following discussion, the axial direction, the radial direction and the circumferential direction of the outer rotor  10  will be simply referred to as the axial direction, the radial direction and the circumferential direction, respectively. 
     As shown in  FIGS. 1, 2 and 4 , the sprocket plate  13  of the outer rotor  10  includes a blind hole  134  (i.e., a hole that is, for example, reamed, drilled, or milled to a specified depth without breaking through to the other side of the sprocket plate  13 ). The blind hole  134  is formed at a location that is eccentric from, i.e., is displaced from a rotational central axis Cr of the outer rotor  10  in the radial direction in such a manner that a tapered hole portion  136  and a bottom hole portion  137  are coaxially formed in the blind hole  134 . Therefore, a common central axis Cs (see  FIG. 4 ), which is common to the tapered hole portion  136  and the bottom hole portion  137 , is set to be substantially parallel to the rotational central axis Cr. 
     The tapered hole portion  136  opens in a contact surface  13   c  of the sprocket plate  13 , against which the shoe housing  12  contacts in the axial direction. As shown in  FIG. 4 , an inner peripheral surface  136   i  of the tapered hole portion  136  is tapered (is formed in a conical form) such that an inner diameter of the inner peripheral surface  136   i  is progressively increased in the axial direction toward the shoe housing  12 . Here, a taper angle of the inner peripheral surface  136   i  of the tapered hole portion  136  is set to, for example, about 40 degrees. 
     The bottom hole portion  137  is formed on an opposite side of the tapered hole portion  136 , which is opposite from the shoe housing  12  in the axial direction. A bottom side of the bottom hole portion  137 , which is opposite from the tapered hole portion  136  in the axial direction, is closed. An inner peripheral surface  137   i  of the bottom hole portion  137  is tapered (is formed in a conical form) such that an inner diameter of the inner peripheral surface  137   i  is progressively increased in the axial direction toward the tapered hole portion  136 . Here, a taper angle of the inner peripheral surface  137   i  of the bottom hole portion  137  is set to be larger than the taper angle of the tapered hole portion  136 . 
     As shown in  FIGS. 2 and 4 , the sprocket plate  13  of the outer rotor  10  includes a communication groove  138 . The communication groove  138  is formed in a form of a bottomed groove (a groove having a closed bottom) that opens to the contact surface  13   c  and the inner peripheral surface  136   i  of the tapered hole portion  136 . A portion of the contact surface  13   c , at which the communication groove  138  opens, is exposed to a communication working chamber  34   c , which is a specific one of the advancing working chambers  34 . Furthermore, a portion of the inner peripheral surface  136   i  of the tapered hole portion  136 , at which the communication groove  138  opens, forms a communication surface portion  136   ic  on the advancing side Da of the common central axis Cs in the circumferential direction. With the above structure, the blind hole  134  can be opened to the atmosphere through the communication groove  138  and the communication working chamber  34   c  at the time of assembling the valve timing control apparatus  1  described later. 
     As shown in  FIGS. 1, 2 and 4 , the shoe housing  12  of the outer rotor  10  has a through hole  124  that axially extends through a retarding stopper shoe  122   r , which is one of the shoes  122  and partitions, i.e., defines the communication working chamber  34   c . The through hole  124  is formed at the location that is eccentric from, i.e., is displaced from the rotational central axis Cr of the outer rotor  10  in the radial direction in such a manner that a press fitting hole portion  125 , a chamfered hole portion  126  and a guide hole portion  127  are coaxially formed in the through hole  124 . Therefore, a common central axis Ch, which is common to the press fitting hole portion  125 , the chamfered hole portion  126  and the guide hole portion  127 , is set to be substantially parallel to the rotational central axis Cr. Also, the common central axis Ch is substantially parallel to the common central axis Cs of the blind hole  134  and is eccentric to the common central axis Cs of the blind hole  134  in the circumferential direction toward the retarding side Dr. 
     A length of the press fitting hole portion  125 , which is measured in the axial direction, is set such that the press fitting hole portion  125  does not reach to a contact surface  12   cs  of the shoe housing  12 , which contacts the sprocket plate  13 , and a contact surface  12   cc  of the shoe housing  12 , which contacts the cover plate  14 . The press fitting hole portion  125  extends straight in the axial direction as a cylindrical hole portion that has a substantially constant inner diameter along an entire extent of the press fitting hole portion  125 . The inner diameter of the press fitting hole portion  125 , which is measured before or after the press fitting of the main shaft portion  182  into the press fitting hole portion  125 , is set to be smaller than a maximum inner diameter of the tapered hole portion  136  along the entire axial extent of the press fitting hole portion  125 . 
     The chamfered hole portion  126  opens at the contact surface  12   cs  of the shoe housing  12 , which contacts the sprocket plate  13 . The chamfered hole portion  126  is formed continuously between the contact surface  12   cs  and the press fitting hole portion  125  in the axial direction. As shown in  FIG. 4 , an inner diameter of the chamfered hole portion  126  is progressively increased from an edge  125   e , which forms a boundary between the chamfered hole portion  126  and the press fitting hole portion  125 , toward an edge  126   e , which forms a boundary between the chamfered hole portion  126  and the contact surface  12   cs . The chamfered hole portion  126 , which has the progressively increasing inner diameter as discussed above, chamfers an opening edge portion of the through hole  124  at the contact surface  12   cs . Here, the inner diameter of the chamfered hole portion  126  is set to be smaller than the maximum inner diameter of the tapered hole portion  136  along the entire axial extent of the chamfered hole portion  126 . 
     As shown in  FIG. 1 , the guide hole portion  127  opens at the contact surface  12   cc  of the shoe housing  12 , which contacts the cover plate  14 . The guide hole portion  127  is formed on an opposite side of the press fitting hole portion  125 , which is opposite from the chamfered hole portion  126  in the axial direction. The guide hole portion  127  extends straight in the axial direction as a cylindrical hole portion that has a substantially constant inner diameter, which is larger than the inner diameter of the press fitting hole portion  125  measured before or after the press fitting of the main shaft portion  182  into the press fitting hole portion  125 , along an entire axial extent of the guide hole portion  127 . Here, the inner diameter of the guide hole portion  127  is set to be smaller than the maximum inner diameter of the tapered hole portion  136  along the entire axial extent of the guide hole portion  127 . 
     The cover plate  14  of the outer rotor  10  includes a through hole  144 . The through hole  144  of the cover plate  14  is formed at a location that is eccentric from, i.e., is displaced from the rotational central axis Cr of the outer rotor  10  in the radial direction in such a manner that the through hole  144  can be coaxially aligned with the through hole  124  of the shoe housing  12 . Therefore, the common central axis Ch, which is also common to the through hole  144  of the cover plate  14  and the through hole  124  of the shoe housing  12 , is set to be substantially parallel to the rotational central axis Cr and the common central axis Cs. 
     One end of the through hole  144  opens at the contact surface  14   c  of the cover plate  14 , which contacts the shoe housing  12  in the axial direction, and the other end of the through hole  144  opens at an outer surface  14   o  of the cover plate  14 , which is opposite from the shoe housing  12  in the axial direction. The through hole  144  extends straight in the axial direction as a cylindrical hole portion that has a substantially constant inner diameter between the contact surface  14   c  and the outer surface  14   o  of the cover plate  14 . Here, the inner diameter of the through hole  144  is set to be larger than the inner diameter of the press fitting hole portion  125 , which is measured before or after the press fitting of the main shaft portion  182  into the press fitting hole portion  125 , along an entire axial extent of the through hole  144 . 
     As shown in  FIGS. 1 to 4 , the positioning member  18  is inserted into the holes  134 ,  124 ,  144  of the outer rotor  10  at the location, which is eccentric from, i.e., is displaced from the rotational central axis Cr of the outer rotor  10  in the radial direction. The positioning member  18  includes a contacting distal end portion  180 , an anchoring head portion  181 , a main shaft portion  182  and a loosely inserting shaft portion  183 , which are coaxial with each other. Therefore, a common central axis Cp, which is common to the contacting distal end portion  180 , the anchoring head portion  181 , the main shaft portion  182  and the loosely inserting shaft portion  183 , is substantially parallel to the rotational central axis Cr and the common central axis Cs. 
     As shown in  FIGS. 1 and 4 , the contacting distal end portion  180  is formed at one axial end portion of the positioning member  18 , which is located on the sprocket plate  13  side in the axial direction. The contacting distal end portion  180  is axially inserted into the tapered hole portion  136  of the blind hole  134 , which opens toward the shoe housing  12 . As shown in  FIG. 4 , an outer peripheral surface  180   o  of the contacting distal end portion  180  is tapered (is formed in a conical form) such that an outer diameter of the outer peripheral surface  180   o  of the contacting distal end portion  180  is progressively increased in the axial direction toward the shoe housing  12 . 
     The outer diameter of the contacting distal end portion  180  is set to be smaller than the maximum inner diameter of the tapered hole portion  136  along an entire axial extent of the contacting distal end portion  180 . Furthermore, a taper angle of the outer peripheral surface  180   o  of the contacting distal end portion  180  is set be the same as the taper angle of the tapered hole portion  136 . Furthermore, a length of a generatrix of the outer peripheral surface  180   o  of the contacting distal end portion  180  is set be smaller than a length of a generatrix of the inner peripheral surface  136   i  of the tapered hole portion  136 . With the above settings, the contacting distal end portion  180  is eccentric to the tapered hole portion  136  in the circumferential direction toward the retarding side Dr. Furthermore, with the above settings, the outer diameter of the outer peripheral surface  180   o  of the contacting distal end portion  180  is progressively increased along the inner peripheral surface  136   i  of the tapered hole portion  136 . Furthermore, the outer peripheral surface  180   o  of the contacting distal end portion  180  contacts the inner peripheral surface  136   i  of the tapered hole portion  136  along the generatrix of the inner peripheral surface  136   i  on the retarding side Dr of the common central axis Cs in the circumferential direction. That is, with reference to  FIGS. 2 and 4 , a portion of the inner peripheral surface  136   i  of the tapered hole portion  136 , which contacts the outer peripheral surface  180   o  of the contacting distal end portion  180 , forms a positioning surface portion  136   ip  on the retarding side Dr (serving as a specific side, which is a circumferential side in the circumferential direction). 
     As shown in  FIGS. 1 and 3 , the anchoring head portion  181  is formed in the other end portion of the positioning member  18 , which is located on the outer side of the cover plate  14  in the axial direction. The anchoring head portion  181  is shaped into a circular disk form and is formed as a maximum diameter portion in the positioning member  18 . That is, the outer diameter of the anchoring head portion  181  is set to be larger than the outer diameters of the other portions  180 ,  182 ,  183  of the positioning member  18 . 
     As shown in  FIGS. 1 to 4 , the main shaft portion  182  is formed continuously from the anchoring head portion  181  in the positioning member  18 . The main shaft portion  182  extends straight in the axial direction as a cylindrical portion and has a substantially constant outer diameter along an entire extent of the main shaft portion  182  in the positioning member  18 . As shown in  FIG. 4 , a part of the main shaft portion  182 , which is located on the sprocket plate  13  side, is press fitted into the press fitting hole portion  125  except a part  125   s  of the press fitting hole portion  125  located at the sprocket plate  13  side to form an actual press fitting part  182   f  (also see  FIG. 1 ). Specifically, the actual press fitting part  182   f  of the main shaft portion  182  refers to a part of the main shaft portion  182 , which is actually securely press fitted to the press fitting hole portion  125 . The outer diameter of the actual press fitting part  182   f  before the press fitting thereof is set to be slightly larger than the inner diameter of the press fitting hole portion  125  before the press fitting along the entire axial extent of the actual press fitting part  182   f . With the above settings, when the press fit interference of the actual press fitting part  182   f  relative to the press fitting hole portion  125  is ensured to be, for example, 10 to 70 μm, the required anchorage strength of the actual press fitting part  182   f  relative to the press fitting hole portion  125  is ensured. 
     As shown in  FIGS. 1 and 3 , a part of the main shaft portion  182 , which projects outward from the cover plate  14 , cooperates with the anchoring head portion  181  having the large diameter to hold the one end portion  500  of the torsion spring  50  and thereby forms a receiving part  182   r . The receiving part  182   r , which is located on the retarding side Dr of the torsion spring  50  in the circumferential direction, holds the torsion spring  50 , so that the receiving part  182   r  receives the restoring force of the torsion spring  50 , which is applied to the receiving part  182   r  in the circumferential direction toward the retarding side Dr. 
     As shown in  FIGS. 1 and 4 , a part of the main shaft portion  182 , which is located between the actual press fitting part  182   f  and the receiving part  182   r , is loosely inserted into the guide hole portion  127  and the through hole  144  in the axial direction along the entire extent of the guide hole portion  127  and the through hole  144 . Because of this loose insertion, the main shaft portion  182  forms a gap  128 , which is shaped into a continuous annular form and is radially defined between the part of the main shaft portion  182  and inner peripheral surfaces of the guide hole portion  127  and the through hole  144 . 
     The loosely inserting shaft portion  183  is continuously formed between the contacting distal end portion  180  and the main shaft portion  182  in the axial direction in the positioning member  18 . As shown in  FIG. 4 , the loosely inserting shaft portion  183  includes a conical part  184 , which is tapered (i.e., shaped into a conical form), and a cylindrical part  185 , which is shaped into a cylindrical form, and the conical part  184  and the cylindrical part  185  are coaxially formed together. An outer diameter of the conical part  184  is progressively reduced from a boundary between the main shaft portion  182  and the conical part  184  in the axial direction toward the contacting distal end portion  180 . The cylindrical part  185 , which has a constant outer diameter, extends straight in the axial direction from the conical part  184  to the contacting distal end portion  180  in the positioning member  18 . 
     The outer diameter of the loosely inserting shaft portion  183  is set to be smaller than the outer diameter of the main shaft portion  182  and the inner diameter of the press fitting hole portion  125 , which is measured before or after the press fitting of the main shaft portion  182  into the press fitting hole portion  125 , along the entire axial extent of the loosely inserting shaft portion  183 . For example, the outer diameter of the loosely inserting shaft portion  183  is set to be about 3.8 mm relative to the main shaft portion  182 , which has the outer diameter of about 4.0 mm that is measured before the press fitting of the main shaft portion  182  into the press fitting hole portion  125 . With the above settings, the loosely inserting shaft portion  183  is loosely inserted into a part  125   s  of the press fitting hole portion  125 , which is located on the sprocket plate  13  side, an entire extent of the chamfered hole portion  126 , and a part  136   h  of the tapered hole portion  136 , which is located on the shoe housing  12  side. Because of this loose insertion, the loosely inserting shaft portion  183  forms a gap  129 , which is shaped into a continuous annular form and is radially defined between the loosely inserting shaft portion  183  and inner peripheral surfaces of the press fitting hole portion  125 , the chamfered hole portion  126  and the tapered hole portion  136 . 
     Next, a manufacturing method of the valve timing control apparatus  1  of the present embodiment will be described with reference to a flowchart of  FIG. 5 . 
     First of all, at step S 101 , a connecting step is executed. Thereby, the shoe housing  12 , which receives the inner rotor  20  therein, the sprocket plate  13  and the cover plate  14  are connected together, i.e., are joined together in the axial direction by the bolts. At this time, the blind hole  134 , which includes the tapered hole portion  136 , is opened to the surrounding atmosphere through the communication groove  138  and the communication working chamber  34   c . Furthermore, at this time, the through hole  124 , which includes the press fitting hole portion  125 , and the through hole  144  are eccentrically displaced relative to the blind hole  134 , which includes the tapered hole portion  136 , on the retarding side Dr. Here, the amount of eccentricity of the through holes  124 ,  144  relative to the blind hole  134  tends to be influenced by a manufacturing tolerance. Thus, the central axis of the press fitting hole portion  125  and the central axis of the tapered hole portion  136  may possibly be deviated from normal positions (specified positions) thereof, which are set by the design specification. 
     Next, at step S 102 , a positioning step is executed such that the positioning member  18  is installed to the shoe housing  12 , the sprocket plate  13  and the cover plate  14 , which are joined together. Specifically, the positioning member  18 , which is inserted through the through hole  144 , is further inserted into the through hole  124  in the axial direction. Thereby, the contacting distal end portion  180  and the loosely inserting shaft portion  183  are sequentially loosely inserted into the press fitting hole portion  125 , and then the main shaft portion  182  is press fitted into the press fitting hole portion  125 . At this time, a press-in speed of the positioning member  18 , which is the amount of stroke of the positioning member  18  per unit time, is controlled to be a constant speed. Thus, a press-in load, which is a load applied to the positioning member  18  to press the positioning member  18  into the press fitting hole portion  125 , is progressively increased, as indicated by a solid line in a period A in  FIG. 6 . Thereby, a press-in length of the main shaft portion  182  (i.e., a length of the press fitted part of the main shaft portion  182 ) in the press fitting hole portion  125  is progressively increased while the contacting distal end portion  180  and the loosely inserting shaft portion  183  pass through the chamfered hole portion  126  and enter the tapered hole portion  136 . As discussed above, at step S 102 , the main shaft portion  182  is first press fitted into the press fitting hole portion  125  in the axial direction, and the contacting distal end portion  180  is then inserted into the tapered hole portion  136  in the axial direction. 
     At step S 102 , when the press-in length of the main shaft portion  182  in the press fitting hole portion  125  reaches a maximum value of the product, the outer peripheral surface  180   o  of the contacting distal end portion  180 , which is projected into the tapered hole portion  136 , contacts the inner peripheral surface  136   i  of the tapered hole portion  136  on the retarding side Dr in the circumferential direction. That is, the tapered outer peripheral surface  180   o  of the contacting distal end portion  180  contacts the positioning surface portion  136   ip  of the inner peripheral surface  136   i , which is located on the retarding side Dr, along the generatrix in the tapered hole portion  136 . At this time, the press-in load applied to the positioning member  18  is rapidly increased, as indicated by a solid line in a period B in  FIG. 6 . Thus, the press fitting of the main shaft portion  182  into the press fitting hole portion  125  is terminated at a maximum press-in length of each product by sensing the rapid increase in the press-in load. As a result, the main shaft portion  182 , which extends straight, does not reach to the part  125   s  of the press fitting hole portion  125 , which is located on the sprocket plate  13  side. Therefore, the main shaft portion  182  does not project from the edge  125   e  of the press fitting hole portion  125  on the tapered hole portion  136  side (see  FIG. 4 ). In this way, the stick-slip phenomenon of the prior art technique, which is indicated by the dot-dot-dash line in the time period T in  FIG. 6  (the solid line in FIG.  14 A), does not occur in the valve timing control apparatus of the present embodiment, as indicated by a solid line in  FIG. 6 . 
     Thereby, at step S 102 , the outer peripheral surface  180   o  of the contacting distal end portion  180  contacts the inner peripheral surface  136   i  of the tapered hole portion  136  on the retarding side Dr in the circumferential direction, so that the shoe housing  12  is positioned relative to the sprocket plate  13  in the circumferential direction. 
     As shown in  FIG. 5 , according to the manufacturing method of the present embodiment, the operation proceeds from step S 102  to step S 103  where an anchoring step is executed. Thereby, the torsion spring  50  is anchored to the outer rotor  10  and the inner rotor  20 . The manufacturing method of the valve timing control apparatus  1  is now completed, and the thus manufactured valve timing control apparatus  1  is installed in place such that the inner rotor  20  is joined to the camshaft  2 , which is inserted into the center hole  130  of the sprocket plate  13 , by the bolt, and the sprocket plate  13  is coupled to the crankshaft  3  through the timing chain  4 . Thereby, the valve timing control apparatus  1  of the present embodiment is now ready to be used. 
     Now, the operation and the advantages of the present embodiment will be described. 
     In the valve timing control apparatus  1 , the contacting distal end portion  180  of the positioning member  18  is inserted into the tapered hole portion  136  of the sprocket plate  13  in the axial direction, and the main shaft portion  182  of the positioning member  18 , which extends straight in the axial direction, is press fitted into the press fitting hole portion  125 , which extends straight, in the shoe housing  12 . The loosely inserting shaft portion  183 , which is placed between the contacting distal end portion  180  and the main shaft portion  182  in the positioning member  18 , is loosely inserted into the press fitting hole portion  125  in the axial direction. Thereby, the contacting distal end portion  180  of the positioning member  18  contacts the inner peripheral surface  136   i  of the tapered hole portion  136  on the retarding side Dr in the circumferential direction while the main shaft portion  182  of the positioning member  18  does not project from the press fitting hole portion  125  toward the tapered hole portion  136 . Thereby, the main shaft portion  182  is first press fitted into the press fitting hole portion  125 , and the contacting distal end portion  180  is then inserted into the tapered hole portion  136 . Thus, the main shaft portion  182  is not caught by the edge  125   e  on the tapered hole portion  136  side of the press fitting hole portion  125  at the time of positioning the shoe housing  12  relative to the sprocket plate  13  in the circumferential direction. 
     Thus, as shown in  FIG. 6 , through use of the positioning member  18 , which limits generation of the stick-slip phenomenon, the press-in load can be easily controlled at the time of contacting the contacting distal end portion  180  against the inner peripheral surface  136   i  of the tapered hole portion  136  on the retarding side Dr, i.e., the time of contacting the contacting distal end portion  180  against the positioning surface portion  136   ip . As a result, it is possible to limit deformation of the sprocket plate  13  caused by application of excessive press-in load. Therefore, since the deformation of the sprocket plate  13  is limited, it is possible to achieve the required adjustment accuracy of the valve timing, which corresponds to the rotational phase between the outer rotor  10 , which includes the sprocket plate  13 , and the inner rotor  20 , which is placed in the inside of the outer rotor  10 . 
     Furthermore, in the shoe housing  12  of the valve timing control apparatus  1 , the chamfered hole portion  126  is placed between the contact surface  12   cs , which contacts the sprocket plate  13 , and the press fitting hole portion  125 , such that the inner diameter of the chamfered hole portion  126  progressively increases from the press fitting hole portion  125 . Therefore, the edge  125   e , which forms the boundary between the chamfered hole portion  126  and the press fitting hole portion  125 , and the edge  126   e , which forms the boundary between the contact surface  12   cs  and the chamfered hole portion  126 , do not catch the main shaft portion  182 , which is press fitted into the press fitting hole portion  125 . Therefore, the press-in load can be easily controlled, and the deformation of the sprocket plate  13  can be reliably limited. Thus, the reliability with respect to the achievement of the required adjustment accuracy of the valve timing can be improved. 
     Furthermore, the torsion spring  50 , which urges the inner rotor  20  against the outer rotor  10 , is anchored to, i.e., hooked to the positioning member  18  of the valve timing control apparatus  1 , so that the positioning member  18  receives the restoring force of the torsion spring  50  in the circumferential direction toward the retarding side Dr. Therefore, the contacting distal end portion  180  is urged against the positioning surface portion  136   ip  located on the retarding side Dr in the circumferential direction. Therefore, the accuracy of the positioning of the inner rotor  20  at the time of limiting the rotation of the inner rotor  20  with the shoe housing  12  is improved, so that the required adjustment accuracy of the valve timing can be ensured. 
     Furthermore, in the valve timing control apparatus  1 , the outer peripheral surface  180   o  of the contacting distal end portion  180  is tapered such that the outer diameter of the outer peripheral surface  180   o  of the contacting distal end portion  180  is progressively increased in the axial direction toward the shoe housing  12  side along the inner peripheral surface  136   i  of the tapered hole portion  136 . Thus, the tapered outer peripheral surface  180   o  can contact the positioning surface portion  136   ip , which is located on the retarding side Dr in the circumferential direction, along the entire extent of the generatrix of the tapered outer peripheral surface  180   o . Therefore, the accuracy of the positioning of the inner rotor  20  at the time of limiting the rotation of the inner rotor  20  with the shoe housing  12  is improved, so that the required adjustment accuracy of the valve timing can be ensured. 
     In addition, the blind hole  134 , which is formed in the sprocket plate  13  in the valve timing control apparatus  1  and includes the tapered hole portion  136 , can be opened to the atmosphere. Therefore, the air, which is present in the blind hole  134 , may be discharged to the atmosphere side in response to an increase in the amount of projection of the contacting distal end portion  180  into the tapered hole portion  136 . As a result, it is possible to avoid the functioning of the air, which is present between the positioning member  18  and the inner wall surface of the blind hole  134 , as a damper. Thereby, the contacting distal end portion  180  can reliably abut, i.e., contact against the positioning surface portion  136   ip  located on the retarding side Dr in the circumferential direction. Therefore, the accuracy of the positioning of the inner rotor  20  at the time of limiting the rotation of the inner rotor  20  with the shoe housing  12  is improved, so that the required adjustment accuracy of the valve timing can be ensured. 
     Furthermore, according to the manufacturing method of the valve timing control apparatus  1 , the sprocket plate  13  and the shoe housing  12  are joined together in the axial direction. Therefore, there is a possibility of positional deviation of the press fitting hole portion  125  and the tapered hole portion  136  from the normal positions thereof. However, according to the manufacturing method of the present embodiment, the positioning member  18  is first press fitted into the press fitting hole portion  125  and is then inserted into the tapered hole portion  136 . Therefore, when the contacting distal end portion  180  abuts against the inner peripheral surface  136   i  of the tapered hole portion  136  on the retarding side Dr in the circumferential direction, the above-described positional deviation of the press fitting hole portion  125  and the tapered hole portion  136  from the normal positions thereof can be absorbed or alleviated. Furthermore, as discussed above, the main shaft portion  182  does not project from the press fitting hole portion  125  toward the tapered hole portion  136  side. Thus, the control of the press-in load is eased, and thereby the deformation of the sprocket plate  13  can be limited. Accordingly, the accuracy of the positioning of the inner rotor  20  at the time of stopping the rotation of the inner rotor  20  with the shoe housing  12  is ensured, and the deformation of the sprocket plate  13  is limited. As a result, the required adjustment accuracy of the valve timing can be ensured. 
     The embodiment of the present disclosure has been described. However, the present disclosure should not be limited to the described embodiment, and the described embodiment may be modified in various ways within the principle of the present disclosure. 
     Specifically, in a first modification, as shown in  FIG. 7 , the chamfered hole portion  126  of the above embodiment may be eliminated. Furthermore, in a second modification, as shown in  FIG. 8 , the guide hole portion  127  of the above embodiment may be eliminated. Also, in a third modification, as shown in  FIG. 9 , the torsion spring  50  of the above embodiment, which serves as the resilient member, may be eliminated. In the case of the third modification, step S 103  of the manufacturing method of  FIG. 5  is no longer required. 
     In a fourth modification, as shown in  FIG. 10 , the blind hole  134  may be made of only with the tapered hole portion  136  of the above embodiment. In a fifth modification, as shown in  FIG. 11 , a through hole  1134 , which includes the tapered hole portion  136  and opens to the atmosphere, may be formed in place of the blind hole  134  of the above embodiment. In the case of the fifth modification, as shown in  FIG. 11 , the through hole  1134 , which is made of only with the tapered hole portion  136 , may be used. Alternatively, although not depicted, the through hole  1134 , which includes the tapered hole portion  136  and another hole portion, may be used. Furthermore, in a sixth modification, as shown in  FIG. 12 , the communication groove  138  of the above embodiment may be eliminated. 
     In a seventh modification, as shown in  FIG. 13 , the positioning surface portion  136   ip , against which the outer peripheral surface  180   o  of the contacting distal end portion  180  contacts on the advancing angle side Da (serving as a specific side) in the circumferential direction, may be formed in the inner peripheral surface  136   i  of the tapered hole portion  136 . In an eighth modification, the taper angle of the outer peripheral surface  180   o  of the contacting distal end portion  180  may be set to be different from the taper angle of the inner peripheral surface  136   i  of the tapered hole portion  136  as long as the outer peripheral surface  180   o  of the contacting distal end portion  180  can contact the positioning surface portion  136   ip . In a ninth modification, the outer peripheral surface  180   o  of the contacting distal end portion  180  may be formed as a cylindrical surface that extends straight in the axial direction as long as the outer peripheral surface  180   o  of the contacting distal end portion  180  can contact the positioning surface portion  136   ip.    
     In a tenth modification, the receiving part  182   r  of the main shaft portion  182  may be placed on the advancing side Da of the torsion spring  50  in the circumferential direction to hold the torsion spring  50 . In the case of the tenth modification, the receiving part  182   r  of the main shaft portion  182 , which is located on the advancing side Da of the torsion spring  50  in the circumferential direction, receives the restoring force of the torsion spring  50 , which is applied to the receiving part  182   r  in the circumferential direction toward the advancing side Da. Furthermore, in the tenth modification, the positioning surface portion  136   ip  may be formed on the retarding side Dr (serving as the specific side) like in the embodiment described above. Alternatively, in the tenth modification, the positioning surface portion  136   ip  may be formed on the advancing side Da (serving as the specific side) by combining the tenth modification with the seventh modification. 
     In an eleventh modification, the present disclosure may be applied to a valve timing control apparatus that adjusts valve timing of intake valves (serving as subject valves).