Patent Publication Number: US-2011067658-A1

Title: Valve timing control apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2009-219057, filed on Sep. 24, 2009, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure generally relates to a valve timing control apparatus for controlling opening and closing timing of an air intake valve and an exhaust valve of an internal combustion engine. 
     BACKGROUND 
     Generally, a valve timing control apparatus is used for an internal combustion engine such as an engine for a vehicle and the like. Furthermore, the valve timing control apparatus adjusts opening and closing timing of a valve in a manner where the valve timing control apparatus changes a relative rotational phase formed between a driving-side rotating member, which synchronously rotates with a crankshaft, and a driven-side rotating member, which synchronously rotates with a camshaft, in order to achieve an appropriate driving state of the internal combustion engine. 
     An improvement in shift speed of the relative rotational phase of the driven-side rotating member relative to the driving-side rotating member is required for the valve timing control apparatus in order to improve fuel efficiency of the internal combustion engine, to reduce gas emission and the like. Furthermore, reduction in an operation hydraulic pressure necessary for shifting the relative rotational phase of the driven-side rotating member relative to the driving-side rotating member is required in order to reduce work load of an oil pump, which supplies oil to the valve timing control apparatus, each sliding member provided at an inside of the internal combustion engine and the like. 
     A valve timing control apparatus disclosed in JP4351065B (corresponding U.S. Pat. No. 6,941,912) (i.e. an apparatus for adjusting a relative rotational angle of an internal combustion engine relative to a driving wheel) includes a driving-side rotating member (which corresponds to a cell wheel in JP4351065B) rotating together with a crankshaft of the internal combustion engine as a unit, a driven-side rotating member (which corresponds to a rotor in JP4351065B), which is arranged in a coaxial manner relative to the driving-side rotating member and rotates together with a camshaft for opening and closing a valve of the internal combustion engine as a unit, a retarded angle chamber (which corresponds to a pressure space in JP4351065B) used for shifting a relative rotational phase of the driven-side rotating member relative to the driving-side rotating member in a retarded angle direction, and an advanced angle chamber (which corresponds to the pressure space in JP4351065B) used for shifting the relative rotational phase in an advanced angle direction. 
     Furthermore, the valve timing control apparatus disclosed in JP4351065B includes plural controlling valves and is configured so as to return the operation oil discharged from one of the retarded angle chamber and the advanced angle chamber to the other one of the retarded angle chamber and the advanced angle chamber by controlling plural controlling valves in order to improve a shift speed of the relative rotational phase, thereby reducing a necessary supply of an operation oil to be supplied from the oil pump to the valve timing control apparatus. 
     Generally, the relative rotational phase repeatedly shifts (jiggles) in the advanced angle direction and the retarded angle direction little by little because of a torque fluctuation of the cam. Accordingly, the operation hydraulic pressure within the advanced angle chamber and the retarded angle chamber changes little by little because of the repeated and slight shifts (jiggles) of the relative rotational phase in the advanced angle direction and the retarded angle direction, thereby generating hydraulic pressure pulsation. According to the valve timing control apparatus disclosed in JP4351065B, the control valves need to be opened and closed at a high speed so as to synchronize with the hydraulic pressure pulsation. Specifically, in a case where a temperature of the operation oil is low, viscosity of the operation oil is high. Therefore, the control valves may not be stably opened and closed at the high speed. Furthermore, the valve timing control apparatus disclosed in JP4351065B needs to include plural control valves, which may result in an increase in a number of components used for the valve timing control apparatus. Therefore, the valve timing control apparatus disclosed in JP451065B may not be appropriately adapted to a vehicle engine, whose size is restricted to a size mountable to the vehicle, and may not fit into a limited mounting space in the vehicle. Furthermore, because the number of components used for the valve timing control apparatus disclosed in JP451065B is relatively high because of plural control valves, a weight of the valve timing control apparatus increases, which may interfere with improvement in the fuel consumption of the internal combustion engine. 
     A need thus exists to provide a valve timing control apparatus which is not susceptible to the drawback mentioned above. 
     SUMMARY 
     According to an aspect of this disclosure, a valve timing control apparatus includes a driving-side rotating member being synchronously rotatable with a crankshaft of an internal combustion engine, the driving-side rotating member including a housing member formed in a cylindrical shape so that the housing member has an opening portion at one of end portions thereof in an axial direction of the camshaft and a plate member configured so as to close the opening of the housing member, a driven-side rotating member arranged in a coaxial manner relative to the driving-side rotational member and being synchronously rotatable with a camshaft that controls opening and closing operations of a valve of the internal combustion engine, a retarded angle chamber defined by the driving-side rotating member and the driven-side rotating member and used for changing a relative rotational phase of the driven-side rotating member relative to the driving-side rotating member in a retarded angle direction in response to an operation oil supplied to the retarded angle chamber, an advanced angle chamber defined by the driving-side rotating member and the driven-side rotating member and used for changing the relative rotational phase of the driven-side rotating member relative to the driving-side rotating member in an advanced angle direction in response to the operation oil supplied to the advanced angle chamber, and a through hole formed at one of the housing member and the plate member so as to extend in the axial direction of the camshaft so that the driven-side rotating member is connected to the camshaft via the through hole, wherein a bearing portion between the driving-side rotating member and the driven-side rotating member is configured by an inner circumferential surface of the through hole and one of an outer circumferential surface of the driven-side rotating member and an outer circumferential surface of the camshaft, and a first slidably contact portion, which serves as the bearing portion, out of a plurality of slidably contact portions between the driving-side rotating member and the driven-side rotating member is configured so as to have a lower sliding resistance than other slidably contact portions. 
     According to another aspect of this disclosure, a valve timing control apparatus includes a driving-side rotating member being synchronously rotatable with a crankshaft of an internal combustion engine, a driven-side rotating member arranged in a coaxial manner relative to the driving-side rotational member and being synchronously rotatable with a camshaft that controls opening and closing operations of a valve of the internal combustion engine, a power transmission member transmitting a rotational force generated by the crankshaft to the driving-side rotating member, a retarded angle chamber defined by the driving-side rotating member and the driven-side rotating member and used for changing a relative rotational phase of the driven-side rotating member relative to the driving-side rotating member in a retarded angle direction in response to an operation oil supplied to the retarded angle chamber, an advanced angle chamber defined by the driving-side rotating member and the driven-side rotating member and used for changing the relative rotational phase of the driven-side rotating member relative to the driving-side rotating member in an advanced angle direction in response to the operation oil supplied to the advanced angle chamber, and a first slidably contact portion between the driving-side rotating member and the driven-side rotating member receiving a tightening force generated by the power transmission member in a radial direction of the driving-side rotating member, the first slidably contact portion configured so as to have a smaller sliding resistance than other slidably contact portions between the driving-side rotating member and the driven-side rotating member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional diagram illustrating a valve timing control apparatus according to a first embodiment; 
         FIG. 2  is a diagram illustrating the valve timing control apparatus being viewed in a direction indicated by arrows II-II in  FIG. 1 ; 
         FIG. 3  is a diagram schematically illustrating a mounting position of the valve timing control apparatus; 
         FIG. 4  is a graph showing a comparison between a response speed of a known valve timing control apparatus and a response speed of the valve timing control apparatus according to the first embodiment; and 
         FIG. 5  is a diagram illustrating a valve timing control apparatus according to a second embodiment being viewed in a direction indicated by arrows V-V in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments, in which a valve timing control apparatus is adapted to a vehicle engine as a valve timing control apparatus at an air intake valve of the vehicle engine or as a valve timing control apparatus at an exhaust valve of the vehicle engine, will be described below in accordance with the attached drawings. 
     First Embodiment  
     A valve timing control apparatus  1  according to a first embodiment includes a driving-side rotating member  3 , a driven-side rotating member  5 , a retarded angle chamber  6  (in this embodiment, plural retarded angle chambers  6  are formed) and an advanced angle chamber  7  (in this embodiment, plural advanced angle chambers  7  are formed). The driven-side rotating member  3  is configured so as to rotate synchronously with a crankshaft  2  of an engine  100  (an example of an internal combustion engine). The driven-side rotating member  5  is configured so as to be arranged in a coaxial manner relative to the driving-side rotating member  3  and so as to rotate synchronously with a camshaft  4  for opening and closing a vale of the engine  100 . Each of the retarded angle chambers  6  is defined by the driving-side rotating member  3  and the driven-side rotating member  5 . Similarly, each of the advanced angle chambers  7  is defined by the driving-side rotating member  3  and the driven-side rotating member  5 . More specifically, the retarded angle chambers  6  are used for shifting a relative rotational phase of the driven-side rotating member  5  relative to the driving-side rotating member  3  in a retarded angle direction by supplying an oil (an operation oil) thereto. On the other hand, the advanced angle chambers  7  are used for shifting the relative rotational phase in an advanced angle direction by supplying the operation oil thereto. The driven-side rotating member  5  includes a protrusion  5 A, which protrudes towards the camshaft  4 . 
     The driving-side rotating member  3  includes a housing  3 B (a housing member), a front plate  3 A (a plate member) and a rear plate  3 C (the plate member). The housing  3 B is arranged at an outer circumferential portion of the driven-side rotating member  3  in a radial direction thereof. The front plate  3 A is arranged at a portion of the driving-side rotating member  3  opposite from the camshaft  4  relative to the housing  3 B. The rear plate  3 C is arranged at a portion of the driving-side rotating member  3  closer to the camshaft  4  relative to the housing  3 B. 
     A timing sprocket  3 D is formed at an outer circumferential surface of the rear plate  3 C. A power transmission member  8 , such as a timing chain, a timing belt or the like, is provided between the timing sprocket  3 D and a gear  101  attached at the crankshaft  2  of the engine  100 . 
     The rear plate  3 C includes a through hole  3 E, which extends in an axial direction of the camshaft  4  and through which the protrusion  5 A of the driven-side rotating member  5  is connected with the camshaft  4 . Accordingly, the protrusion  5 A penetrates the rear plate  3 C so as to protrude towards the camshaft  4  to a greater extent than the rear plate  3 C when the driving-side rotating member  3  and the driven-side rotating member  5  are assembled. 
     Plural protruding portions  3 F are formed at an inner circumferential portion of the housing  3 B so as to inwardly protrude in a radial direction thereof while keeping a distance between the neighboring protruding portions  3 F in a rotational direction of the housing  3 B. Furthermore, a withdrawal groove  9 B and an accommodation bore  9 D are formed at the inner circumferential portion of the housing  3 B. The withdrawal groove  9 B is configured so as to accommodate therewithin a lock member  9 A. The accommodation bore  9 D is configured so as to be in communication with the withdrawal groove  9 B and so as to accommodate therewithin a spring  9 C for inwardly biasing the lock member  9 A in the radial direction. 
     The driven-side rotating member  5  is integrally assembled at an edge portion of the camshaft  4 , which configures a rotating shaft of the cam that controls the opening and closing timing of the air intake value or the exhaust vale of the engine  100 . Furthermore, the driven-side rotating member  5  is provided within the driving-side rotating member  3  while allowing the driven-side rotating member  5  to be rotatable relative to the driving-side rotating member  3  in a predetermined relative rotational range. A lock groove  9 E is formed at the driven-side rotating member  5 . More specifically, the lock groove  9 E is configured so as to accommodate therewithin the lock member  9 A when the lock member  9 A is inwardly displaced in the radial direction. Additionally, the driven-side rotating member  5  includes the protrusion  5 A, which protrude towards the camshaft  4 . In this embodiment, the protrusion  5 A is configured so as to protrude towards the camshaft  4  to the greater extent than the rear plate  3 C. 
     A lock mechanism  9  includes the lock member  9 A, the withdrawal groove  9 B, the spring  9 C, the accommodation bore  9 D and the lock groove  9 E. 
     A space defined by the driving-side rotating member  3  and the driven-side rotating member  5  between the neighboring protruding portions  3 F is divided into two chambers (i.e. the retarded angle chamber  6  and the advanced angle chamber  7 ) by means of a vane  10 . In this embodiment, the valve timing control apparatus  1  includes four retarded angle chambers  6  and four advanced angle chambers  7 . 
     The relative rotatable range of the driven-side rotating member  5  relative to the driving-side rotating member  3  corresponds to a moving range of the vane  10  in an advanced angle direction S 1  or in a retarded angle direction S 1  until the vane  10  contacts the protruding portion  3 F, in other words, a range between a most advanced angle phase and a most retarded angle phase (including the most advanced angle phase and the most retarded angle phase). 
     Slidably contact portions between the driving-side rotating member  3  and the driven-side rotating member  5  according to the first embodiment include slidably contact portion between the protruding portions  3 F of the driving-side rotating member  3  and an outer circumferential surface of the driven-side rotating member  5 , a slidably contact portion between the front plate  3 A and a surface of the driven-side rotating member  3  facing the front plate  3 A and a slidably contact portion between the rear plate  3 C and a surface of the driven-side rotating member  3  facing the rear plate  3 C. The slidably contact portion between the rear plate  3 C and the surface of the driven-side rotating member  3  facing the rear plate  3 C includes a first slidably contact portion  5 B and a second slidably contact portion  5 C. More specifically, the first slidably contact portion  5 B includes an outer circumferential surface of the protrusion  5 A of the driven-side rotating member  5  and an inner circumferential surface of the through hole  3 E, which is formed in a circular shape at the rear plate  3 C. The outer circumferential surface of the protrusion  5 A of the driven-side rotating member  5  and an inner circumferential surface of the through hole  3 E slidably contact each other. The second slidably contact portion  5 C includes a side surface of the rear plate  3 C and a side surface of the driven-side rotating member  5 , except for the protrusion  4 A, which slidably contact each other. 
     The slidably contact portion  5 B serves as a bearing portion between at least one of the camshaft  4  and the driven-side rotating member  5  on the one hand and the driving-side rotating member  3  on the other hand. A relatively great force is likely to act on the first slidably contact portion  5 B in a predetermined radial direction of the camshaft  4 , in other words, the force generated in the radial direction of the camshaft  4  is not likely to act equally on entire first slidably contact portion  5 B. More specifically, as illustrated in  FIG. 3 , a rotational force generated by the crankshaft  2  is transmitted to the valve timing control apparatus  1  via the power transmission member  8 . In  FIG. 3 , the power transmission member  8  connects two valve timing control apparatuses  1  and the gear  101  of the crankshaft  2 . More specifically, the power transmission member  8  is provided around the valve timing control apparatuses  1  and the gear  101  of the crankshaft  2  so as to tighten up the valve timing control apparatuses  1  and the gear  101  towards a rotational center of the power transmission member  8  in order to avoid unintentional disengagement of the power transmission member  8  from the valve timing control apparatuses  1 . Therefore, a tightening force F acts in the radial direction of each of the valve timing control apparatuses  1 . Hence, the force F in the predetermined radial direction acts on the first slidably contact portion  5 B. Accordingly, a sliding resistance at the valve timing control apparatus  1  becomes great because of the force F acting on the first slidably contact portion  5 B. 
     Therefore, a resin member  11 , which is expected to reduce the sliding resistance, may be used to form the first slidably contact portion  5 B. More specifically, a polytetrafluoroethylene resin having oil resistance and heat resistance may be used to form the first slidably contact portion  5 B. 
     Accordingly, by forming the first slidably contact portion  5 B by using the resin member  11 , the sliding resistance generated between the inner circumferential surface of the rear plate  3 C and the outer circumferential surface of the protrusion  5 A may be reduced. As a result, a shifting speed of the relative rotational phase of the driven-side rotating member  5  relative to the driving-side rotating member  3  may be improved. Furthermore, an operation hydraulic pressure necessary for shifting the relative rotational phase formed between the driving-side rotating member  3  and the driven-side rotating member  5  may be reduced. 
     The resin member  11 , which is expected to reduce the sliding resistance, may be adapted to the valve timing control apparatus to form the first slidably contact portion  5 B in a manner where a surface treatment is applied to the outer circumferential surface of the protrusion  5 A and the inner circumferential surface of the through hole  3 E formed in the circular shape at the rear plate  3 C, or a cylindrical shaped bush may be press-fitted onto the outer circumferential surface of the protrusion  5 A or into the inner circumferential surface of the through hole  3 E formed in the circular shape at the rear plate  3 C. 
     A graph illustrated in  FIG. 4  is a measurement data obtained by comparing a response speed of a known valve timing control apparatus (which is indicated as “Type 1” in the graph) and a response speed of the valve timing control apparatus  1  according to the embodiment (which is indicated as “Type 2” in the graph). The response speeds in a case where a valve lift amount of the air intake valve is small (which is indicated as “Low Lift” in the graph) and where the valve lift amount is great (which is indicated as “High Lift” in the graph) are measured. Furthermore, the response speeds are measured under a condition where an engine rotational number (i.e. an engine rotational speed) is 600 rotations per minute (which is indicated as 600 rpm in the graph), under a condition where the engine rotational number is 800 rotations per minute (which is indicated as 800 rpm in the graph), and under a condition where the engine rotational number is 1000 rotations per minute (which is indicated as 1000 prm in the graph). A vertical axis indicates an average value of the response speed in a case where the relative rotational phase of the driven-side rotating member  5  relative to the driving-side rotating member  3  is shifted in the advanced angle direction S 1  and an average value of the response speed in a case where the relative rotational phase is shifted in the retarded angle direction S 2  (refer to “Response speed” in the graph). Additionally, the response speeds are measured in the same condition (for example, the same type of an operation oil is used, an oil temperature is maintained at the same, the valve timing control apparatuses are shaped in the same, volumes of the advanced angle chambers are set to be the same, volumes of the retarded angle chambers are set to be the same, and the like) for the known valve timing control apparatus and the valve timing control apparatus  1  according to the embodiment. 
     As is evident from the graph illustrated in  FIG. 4 , the response speed of the valve timing control apparatus  1  according to the embodiment is improved at any engine rotational number (i.e. the engine rotational speed) when comparing to the know valve timing control apparatus. Specifically, the lower the engine rotational number is, the more the response speed of the valve timing control apparatus  1  is improved. The measurement results show that a difference in the sliding resistances between the first slidably contact portion  5 B of the valve timing control apparatus according to the first embodiment and the corresponding slidably contact portion of the known valve timing control apparatus is prominently reflected to the difference in response speeds between the valve timing control apparatus  1  according to the first embodiment and the known valve timing control apparatus. More specifically, in the case where the engine rotational number becomes lower, a rotational number (i.e. a rotational speed) of an oil pump, which is actuated in response to the rotational force of the crankshaft  2 , becomes also lower, therefore, the hydraulic pressure acting on the advanced chambers  6  and the retarded chambers  7  becomes low. Hence, in the case where the hydraulic pressure acting on the advanced chambers  6  and the retarded chambers  7  is low, the relative rotational phase established between the driving-side rotating member  3  and the driven-side rotating member  5  of the valve timing control apparatus  1  according to the embodiment is quickly shifted when comparing to the known valve timing control apparatus, because the sliding resistance of the first slidably contact portion  5 B is low and therefore, the necessary hydraulic pressure to shift the relative rotational phase is low. Furthermore, when comparing to the response speeds in the case where the valve lift amount is great and the response speeds in the case where the valve lift amount is small, the response speed of the valve timing control apparatus  1  according to the embodiment is further improved as the valve lift amount becomes lower when comparing to the known valve timing control apparatus. The measurement results show that the difference in the sliding resistances between the first slidably contact portion  5 B of the valve timing control apparatus  1  according to the first embodiment and the corresponding sliding surface of the known valve timing control apparatus is prominently reflected to the difference in the response speeds between the valve timing control apparatus  1  according to the first embodiment and the known valve timing control apparatus according. More specifically, the response speed of the valve timing control apparatus  1  according to the embodiment is considered to be improved in a case where a torque fluctuation becomes lower as the valve lift amount becomes lower because of the relatively low sliding resistance of the first slidably contact portion  5 B. Accordingly, as is verified by the measurement results indicated in  FIG. 4 , the valve timing control apparatus  1  according to the first embodiment achieves improvement in response speed. 
     Second Embodiment  
     A second embodiment of the valve timing control apparatus  1  will be described below. The valve timing control apparatus  1  according to the second embodiment differs from the valve timing control apparatus  1  according to the first embodiment in that the valve timing control apparatus  1  according to the second embodiment includes a ball bearing  12  (a bearing member) having the first slidably contact portion  5 B in stead of the resin member  11  having the first slidably contact portion  5 B. In the case where the ball bearing  12  is provided at the valve timing control apparatus  1 , an oil providing groove  13  may be formed at the surface of the driven-side rotating member  5  facing the rear plate  3 C, so that an oil is provided between the outer circumferential surface of the protrusion  5 A and an inner circumferential surface of the ball bearing  12 . According to the second embodiment, as is the case with the first embodiment, the shifting speed of the relative rotational phase of the driven-side rotating member  5  relative to the driving-side rotating member  3  may be improved. Furthermore, the operation hydraulic pressure necessary for shifting the relative rotational phase may be reduced. 
     Other Embodiments  
     In the first and second embodiments, the driven-side rotating member  5  includes the protrusion  5 A protruding to the camshaft  4 . However, the driven-side rotating member  5  may be modified so as not to include the protrusion  5 A. Instead, in this case, the camshaft  4  may be modified so as to extend until the camshaft  4  penetrates the through hole  3 E of the rear plate  3 C in order to connect the camshaft  4  with the rear plate  3 C. In this case, the first slidably contact portion  5 B, which serves as the bearing portion, configures the bearing portion (the bearing member) together with the through hole  3 E of the rear plate  3 C and the outer circumferential surface of the camshaft  4  facing the rear plate  3 C. 
     In the first and second embodiments, the driving-side rotating member  3  includes the housing  3 B, the front plate  3 A and the rear plate  3 C. However, the driving-side rotating member  3  does not necessarily need to include the housing  3 B, the front plate  4 A and the rear plate  3 C individually and separately from each other. For example, the driving-side rotating member  3  may be modified so that the front plate  3 A and the housing  3 B are integrally formed, or the housing  3 B and the rear plate  3 C are integrally formed. 
     Accordingly, the first slidably contact portion  5 B having the bearing portion is configured so as to have a lower sliding resistance when comparing to other slidably contact portions, which are also included in a known valve timing control apparatus. Therefore, other slidably contact portions (i.e. the slidably contact portions except for the first slidably contact portion  5 B) do not need to be specifically changed or modified from the known valve timing control apparatus, and materials used for the known driving-side rotating member and the known driven-side rotating member may be used for the driving-side rotating member  3  and the driven-side rotating member  5  of the valve timing control apparatus  1 . Hence, only the sliding resistance of the first slidably contact portion  5 B needs to be considered in order to obtain appropriate response speed of the valve timing control apparatus  1 . Accordingly, an increase of material costs and processing cost may be minimized. Furthermore, the shifting speed of the relative rotational phase of the driven-side rotating member  5  relative to the driving-side rotating member  3  may be improved, and the operation hydraulic pressure necessary for shifting the relative rotational phase may be decreased. Furthermore, according to the embodiments, only the first slidably contact portion  5 B needs to be considered in order to obtain appropriate response speed of the valve timing control apparatus  1 . Therefore, the valve timing control apparatus  1  of the embodiments may be configured so as to have approximately the same weight as the known valve timing control apparatus. 
     According to the embodiments, the driven-side rotating member  5  includes the protrusion  5 A, which is formed so as to penetrate the through hole  3 E to protrude towards the camshaft  4 . The slidably contact portion between the inner circumferential surface of the through hole  3 E and the outer circumferential surface of the protrusion  5 A serves as the first slidably contact portion  5 B. 
     According to the first embodiment, the first slidably contact portion  5 B is formed of the resin member  11 . 
     Accordingly, only the first slidably contact portion  5 B, which needs to have the low sliding resistance, is made of the resin member  11 . Therefore, an increase of the manufacturing costs of the valve timing control apparatus  1  may be avoided. Furthermore, the sliding resistance of the first slidably contact portion  5 B may be reduced by applying a simple processing to the valve timing control apparatus  1 . 
     According to the second embodiment, the first slidably contact portion  5 B includes the ball bearing  12  between the inner circumferential surface of the driving-side rotating member  5  on the one hand and one of the outer circumferential surface of driven-side rotating member  3  and the outer circumferential surface of the camshaft  4  on the other hand. 
     Accordingly, the ball bearing  12  is provided at the first slidably contact portion  5 B, which needs to have the low sliding resistance. Therefore, the increase of the manufacturing costs of the valve timing control apparatus  1  may be avoided. Furthermore, the sliding resistance of the first slidably contact portion  5 B may be reduced only by adding a simple component thereto. 
     The principles, preferred embodiment and mode of operation of this disclosure have been described in the foregoing specification. However, the disclosure which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the disclosure. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the disclosure as defined in the claims, be embraced thereby.