Abstract:
A variable valve timing control device includes a rotation member for opening or closing a valve, a rotation transmission member engaged with the rotation member to be relatively rotatable, a vane provided on either one of the rotation member or the rotation transmission member, a hydraulic chamber formed between the rotation member and the rotation transmission member and including an advance angle chamber and a retarded angle chamber, the advance angle chamber and the retarded angle chamber being formed by dividing the hydraulic chamber by the vane, a first hydraulic passage for supplying and discharging a fluid to the advance angle chamber, and a second hydraulic passage for supplying and discharging the fluid to the retarded angle chamber. The vane includes a surface hardness determined to be higher than a surface hardness of a sliding surface of the rotation member or the rotation transmission member for sliding the vane.

Description:
This application is based on and claims priority under 35 U.S.C. § 119 with respect to Japanese Patent Application No. 2002-063402 filed on Mar. 8, 2002 and Japanese Patent Application No. 2003-051581 filed on Feb. 27, 2003, the entire content of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a variable valve timing control device. More particularly, the present invention pertains to a variable valve timing control device for controlling a valve timing of an intake and exhaust valves of an internal combustion engine. 
   BACKGROUND OF THE INVENTION 
   A known variable valve timing control device is disclosed in Japanese Patent Laid-Open Publication No. H11(1999)-81928. The known variable valve timing control device is provided on a drive force transmission system for transmitting a drive force from a driving shaft of the internal combustion engine to a driven shaft for opening and closing at least one of an intake valve or an exhaust valve of an internal combustion engine. The known variable valve timing control device includes a housing, a vane rotor having vanes rotating relative to the housing within a predetermined angle range, and sealing members supported by the vane rotor to contact the housing for sealing the housing and the vane rotor. With the known variable valve timing control device disclosed in Japanese Patent Laid-Open Publication No. H11(1999)-81928, aluminum or an iron system metal is applied as the housing and the sealing member made of resin with lower hardness than the housing is applied to each tip end of the vane. Because the sealing members always slidingly contact to an internal surface of the housing, the sealing members with low hardness likely to be worn. In case the housing and the vane are applied with the same material such as aluminum, the abrasion may be increased. In this case, for example as shown in  FIG. 2 , when hard foreign materials (e.g., molding sand) included in engine oil are jammed between the vane and the housing during the sliding operation of the vane, the foreign materials are buried in sliding surfaces on the housing side and on the vane side. Thus, the buried foreign materials on the hosing side and on the vane side scrape the opposing sliding surfaces on the housing side and the vane side one another to accelerate the abrasion as aggressive abrasion. Thus, the performance of the variable valve timing control device may be deteriorated. And foreign materials generated by the sliding abrasion influence causing defects such as burning of a camshaft and an operation lock of an OCV (i.e., oil pressure control valve). 
   On the other hand, another known variable valve timing control device is disclosed in Japanese Patent Laid-Open Publication No. H01(1989)-092504. The known variable valve timing control device disclosed in Japanese Patent Laid-Open Publication No. H01(1989)-092504 includes a rotor for opening and closing a valve, a housing engaged with the rotor to be relatively rotatable, a vane provided to be slidably fitted in a vane groove formed on the rotor, a hydraulic chamber formed between the rotor and the housing and divided into an advance angle chamber and a retarded angle chamber by the vane, a first hydraulic passage for supplying or discharging the fluid to or from the advance angle chamber, and a second hydraulic passage for supplying or discharging the fluid to or from the retarded angle chamber. The vane fitted in the vane groove of the rotor is biased towards the housing side by a vane spring so that the rotor and the vane are unitary rotated. With the known variable valve timing control device, the vane groove on the rotor and the vane are repeatedly pushed against one another by the operation chamber hydraulic pressure. In addition, when the vane slides on an internal periphery of the housing in an peripheral direction, the vane slides in a radial direction due to a variation of a clearance between the rotor and the housing and the circularity error of the internal peripheral surface of the housing. When small and hard foreign materials (e.g., molding sand, sand invaded from outside) or carbon soot are invaded from the hydraulic pressure chamber of the variable valve timing control device, the sliding portion is abraded. Particularly, because the molding sand is harder than other foreign materials and has larger particle diameter compared to other foreign materials, the aggressive abrasion at the sliding portions may be caused. Further, in case the vane and the sliding surface of the sliding portion of the vane are ruined, the aggressive abrasion may advance quickly. Due to the influence of the foreign materials generated by the performance deterioration and the sliding abrasion of the variable valve timing control device, drawbacks such as burning of a camshaft and the operation lock of the oil pressure control valve (OCV) may be caused. 
   A need thus exists for a variable valve timing control device which includes high abrasion resistance between a housing and a vane and between a rotor and the vane for preventing a performance deterioration and defects. 
   SUMMARY OF THE INVENTION 
   In light of the foregoing, the present invention provides a variable valve timing control device for controlling a valve timing of an intake valve or an exhaust valve of an internal combustion engine which includes a rotation member for opening or closing a valve, a rotation transmission member engaged with the rotation member to be relatively rotatable, a vane provided on either one of the rotation member or the rotation transmission member, a hydraulic chamber formed between the rotation member and the rotation transmission member and including an advance angle chamber and a retarded angle chamber, the advance angle chamber and the retarded angle chamber being formed by dividing the hydraulic chamber by the vane, a first hydraulic passage for supplying and discharging a fluid to the advance angle chamber, and a second hydraulic passage for supplying and discharging the fluid to the retarded angle chamber. The vane includes a surface hardness determined to be higher than a surface hardness of a sliding surface of the rotation member or the rotation transmission member for sliding the vane. 
   According to another aspect of the present invention, a variable valve timing control device for controlling a valve timing of an intake valve or an exhaust valve of an internal combustion engine includes a rotor for opening or closing a valve, a housing engaged with the rotor to be relatively rotatable, a vane provided on either one of the rotor or the housing, a hydraulic chamber formed between the rotor and the housing and including an advance angle chamber and a retarded angle chamber, the advance angle chamber and the retarded angle chamber being formed by dividing the hydraulic chamber by the vane, a first hydraulic passage for supplying and discharging a fluid to the advance angle chamber, and a second hydraulic passage for supplying and discharging the fluid to the retarded angle chamber. The vane includes a surface hardness determined to be higher than a surface hardness of a sliding surface of the rotor or the housing for sliding the vane. 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures in which like reference numerals designate like elements. 
       FIG. 1  shows a lateral cross-sectional view of a variable valve timing control device according to an embodiment of the present invention. 
       FIG. 2  shows a view showing sliding portions between a housing and a vane according to a known variable valve timing control device. 
       FIG. 3  is a view showing a sliding portion between a housing and a vane according to the embodiment of the present invention. 
       FIG. 4  is a view showing a durability evaluation result of the sliding portion between the housing and the sealing member according to the embodiment of the present invention and the known variable valve timing device. 
       FIG. 5  is a view showing an assembling state of the vane according to the embodiment of the present invention. 
       FIG. 6  is a cross sectional view taken on line VI—VI of FIG.  5 . 
       FIG. 7  is a view showing a comparison of an abrasion index (i.e., abrasion amount) of sliding portions of the vane and a rotor between a known device without surface treatment and the embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   One embodiment of a variable valve timing control device will be explained with reference to the illustrations in the drawing figures. 
   Referring to the illustration in  FIG. 1 , the variable valve timing control device includes a rotor (i.e., serving as a rotation member)  20  unitary assembled to a tip end portion of a camshaft  10  rotatably supported by a cylinder head (not shown) of an internal combustion engine, a housing (i.e., serving as a rotation transmission member)  30  integrally provided with a timing sprocket  31  on an external periphery thereof, and four vanes  70 ,  70 ,  70   a ,  70   b , assembled to the rotor  20 . The timing sprocket  31  is transmitted with the rotational force in the clockwise direction R from a crankshaft (not shown) via a crank sprocket and a timing chain. 
   The rotor  20  is unitary secured to the camshaft  10  with an assembling bolt (not shown). The rotor  20  includes four vane grooves  21 , a receiving groove  22 , four advance angle passages (i.e., serving as a first hydraulic passage)  23  extended in a radial direction and four retarded angle passages (i.e., serving as a second hydraulic passage)  24  extended in a radial direction. Four vanes  70 ,  70 ,  70   a ,  70   b  are provided in respective vane grooves  21  to be movable in the radial direction. A leaf spring  73  (shown in  FIGS. 5-6 ) is provided between a bottom portion of the vane groove  21  and a bottom surface of the vane  70 . Thus, as shown in  FIGS. 5-6 , the vane  70  is always biased outwardly by the leaf spring  73  while sliding on a sliding surface of the housing  30 . The receiving groove  22  is provided with a lock key  80  whose head portion enters the receiving groove  22  by a predetermined amount when relative positions between the camshaft  10  and the rotor  20  and the housing  30  are synchronized at a predetermined phase (i.e., a most retarded angle position). The receiving groove  22  is in communication with one of the advance angle passages  23 . 
   The housing  30  is rotatably assembled relative to an external periphery of the rotor  20  within a predetermined angle range. The timing sprocket  31  is integrally formed on the external periphery of the housing  30 . 
   Four convex portions  33  are formed on an internal periphery of the housing  30  in a peripheral direction. Internal peripheral surfaces of the convex portions  33  contact an external peripheral surface of the rotor  20  to rotatably support the housing  30  by the rotor  20 . One of the convex portions  33  is formed with a retraction groove  34  for accommodating the lock key  80  and an accommodation groove  35  of a spring  60  for biasing the lock key  80  in the radially internal direction. 
   Each vane  70  divides a hydraulic chamber R 0  formed between the housing  30  and the rotor  20  and between two convex portions  33  adjacent to each other in the peripheral direction into an advance angle hydraulic chamber (i.e., serving as an advance angle chamber) R 1  and a retarded angle hydraulic chamber (i.e., serving as a retarded angle chamber) R 2 . The relative rotation amount between the housing  30  and the rotor  20  is defined depending on a peripheral width (i.e., angle) of the hydraulic chamber R 0 . The relative rotation at a most advance angle side is restricted at a position where the vane  70   a  contacts a first side surface  33   a  of the convex portion  33 . The relative rotation between the rotor  20  and the housing  30  at a most retarded angle side is restricted at a position where the vane  70   b  contacts a second side surface  33   b  of the convex portion  33 . The relative rotation between the rotor  20  and the housing  30  is restricted by the insertion of the head portion of the lock key  80  into the receiving groove  22  at the most retarded angle side. 
   The operation of the variable valve timing control device with the foregoing configuration according to the embodiment of the present invention will be explained as follows. 
   The variable valve timing control device obtains desired valve timing by controlling the relative rotation of the rotor  20  relative to the housing  30  by adjusting the hydraulic pressure in each advance angle hydraulic chamber R 1  and each retarded and hydraulic chamber R 2 . Under the condition that the internal combustion engine is stopped, the head portion of the lock key  80  is fitted in the receiving groove  22  of the rotor  20  by the predetermined amount to lock the relative rotation between the rotor  20  and the housing  30  at the most retarded angle position. 
   When the advance angle is required for the valve timing in accordance with the driving condition after the start of the internal combustion engine, the operation fluid (i.e., hydraulic pressure) supplied from an oil pump (not shown) is supplied to the advance angle hydraulic chamber R 1  via the passages  23  by the operation of switching valve (not shown). The operation fluid is supplied to the receiving groove  22  via the passage  23 . On the other hand, the operation fluid (i.e., hydraulic pressure) in the retarded angle hydraulic chamber R 2  is discharged to an oil pan (not shown) from the switching valve via the passages  24 . Under this operation, the lock key  80  moves against the biasing force of the spring  60 . The head portion of the lock key  80  is removed from the receiving groove  22  to release the lock between the rotor  20  and the housing  30 . Accordingly, the rotor  20  unitary rotating with the camshaft  10  and vanes  70  are rotated to the advance angle side (i.e., in the clockwise direction) R relative to the housing  30 . 
   When the retarded angle is required for the valve timing in accordance with the driving condition, the operation fluid (i.e., hydraulic pressure) supplied from the oil pump is supplied to the retarded angle chamber R 2  via the passage  24  by the operation of the switching valve. On the other hand, the operation fluid in the advance angle chamber R 1  is discharged to the oil pan from the switching valve via the passage  23 . Accordingly, the rotor  20  and vanes  70  are rotated to the retarded angle side (i.e., in the counter-clockwise direction) relative to the housing  30 . 
   The detailed explanation of the present invention will be provided referring to  FIGS. 3-7  as follows. When either one of the advance angle or the retarded angle are required in accordance with the foregoing operation conditions and the rotor  20  and the vane  70  are rotated relative to the housing  30 , as shown in  FIG. 5 , the vane  70  is outwardly biased by the leaf spring  73  so that a tip end portion  70 A of the vane  70  slides on a sliding surface  30   a  of the housing  30 . In case the foreign materials (e.g., molding sand) are included in the operation fluid under the foregoing condition, the foreign materials are accumulated on the sliding surface  30   a  of the housing  30  due to the centrifugal force by the rotation of the rotor  20  and the housing  30  and the sliding surface  30   a  of the housing  30  and the tip end portion  70 A of the vane  70  slide against each other to abrade the sliding surface  30   a  and the tip end portion  70 A. However, because the surface hardness of the vane  70  is determined to be greater than the surface hardness of the sliding surface  30   a  of the housing  30 , the foreign materials are buried in the sliding surface  30   a  of the housing  30  before being buried in the tip end portion  70 A of the vane  70  (shown in FIG.  3 ). In addition, because the sliding surface corresponds to a width of the hydraulic chamber R 0  (i.e., of the internal surface of the housing  30 ) in the peripheral direction, the foreign materials buried in the sliding surface of the housing are dispersed in the width of the hydraulic chamber R 0  in the peripheral direction. Thus, as shown in  FIG. 4 , the abrasion of the sliding surface  30   a  of the housing  30  and the tip end portion  70 A of the vane  70  are further reduced compared to the case applying the same material such as aluminum to both the housing  30  and the vane  70 . In addition, by determining the surface roughness of the vane  70  to be equal to or less than 3.2 z, the aggressiveness relative to the sliding surface  30   a  can be mitigated. 
   On the other hand, the vane groove  21  of the rotor  20  and the vane  70  are repeatedly strongly pushed each other by the hydraulic pressure of the advance angle chamber R 1  and the retarded angle chamber R 2 . In addition, when the vane  70  slides on the sliding surface  30   a  of the housing  30  accompanied with a variation of the clearance between the rotor  20  and the housing  30  and the circularity error of the sliding surface  30   a , the vane  70  slides in the radial direction of the rotor  20 . In case the foreign materials included in the operation fluid (e.g., molding sand, sand invaded from outside) or the carbon soot are involved between a fitting portion  21   a  of the vane groove  21  of the rotor  20  and a fitting potion  70 B of the vane  70 , the abrasion of the fitting portion  70 B is generated. However, because the surface hardness of the vane  70  is determined to be greater than the hardness of the molding sand, the molding sand is buried into the fitting portion  21   a  of the vane groove  21  of the rotor  20  made of iron system sintered metal having low hardness so that the abrasion of the fitting portion  70 B of the vane  70  is reduced as shown in FIG.  7 . Further, by determining the surface roughness of the vane  70  to be equal to or less than 3.2 z, the aggressiveness relative to the fitting portion  21   a  is improved to further reduce the abrasion. 
   It is preferable that the vane  70  is made of stainless steal or high speed tool steal treated with the ion plating of chrome nitride or treated with nitrocarburizing. 
   It is preferable to apply the ion plating or the nitrocarburizing treatment only to the sliding portions such as the tip end portion  70 A of the vane  70  and the fitting portion  70 B to reduce the manufacturing cost. 
   It is also preferable that the rotor  20  and the housing  30  are made of aluminum, iron system metal or iron system sintered alloy having lower hardness than the surface hardness of the vane  70 . 
   According to the embodiment of the present invention, the surface hardness of the vane is determined to be greater than the surface hardness of the sliding surface of the either one of the rotation member or the rotation transmission member on which the vane slides. Because the foreign materials are buried in the sliding surface of the rotation member or the rotation transmission member and the surface area of the sliding surface in which the foreign materials are buried is large, the abrasion between the sliding surfaces of the housing and the vane can be reduced. 
   According to the embodiment of the present invention, by forming the vane with the stainless steal treated with nitrocarburizing and forming the rotation member or the rotation transmission member with the aluminum member, the surface hardness of the vane is increased by surface treatment and thus the abrasion between the sliding surfaces of the vane and either one of the rotation member or the rotation transmission member is reduced. 
   According to the embodiment of the present invention, by determining the surface hardness of the vane slidably fitting into the vane groove formed on the rotation member to be greater than the foreign materials included in the operation fluid, the sliding portion of the vane is protected to reduce the abrasion of the sliding portions of the rotation member and the vane. 
   According to the embodiment of the present invention, by forming the vane with the metal treated with nitrocarburizing, the surface hardness of the vane can be increased by the surface treatment. 
   According to the embodiment of the present invention, the vane is made of metal treated with the ion plating. Because the surface treatment temperature is relatively low, the distortion of the vane at the treatment can be prevented to the minimum and thus the precision after the treatment can be ensured. 
   According to the embodiment of the present invention, the surface roughness of the vane after the nitrocarburizing treatment and the ion plating treatment is determined to be equal to or less than 3.2 z. Thus, the aggressive abrasion relative to the sliding mating members can be improved. 
   According to the embodiment of the present invention, the nitrocarburizing treatment or the ion plating is applied to at least one of the fitting portion of the vane relative to the vane groove or the tip end portion of the vane. Thus, the manufacturing cost for the surface treatment can be reduced. 
   The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiment disclosed. Further, the embodiment described herein is 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 present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.