Patent Publication Number: US-6701878-B2

Title: Variable valve timing device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. §119 with respect to a Japanese Patent Application 2002-054040, filed on Feb. 28, 2002, the entire content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention generally relates to a variable valve timing device for controlling opening and closing timing of intake and exhaust valves of an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     A known variable valve timing device has been disclosed in a Japanese Patent Laid-Open published as No. 1999(H11)-132014. The disclosed variable valve timing device includes a rotation transmitting member rotatable integrally with one of a rotation shaft of an engine and an intake and exhaust valves controlling member, which is capable of controlling an opening and closing of the intake and exhaust valves of the engine. The disclosed variable valve timing device further includes a rotor member disposed in the rotation transmitting member so as to be rotated relative to the rotation transmitting member and rotatable integrally with the other of the rotation shaft of the engine and the intake and exhaust valves controlling member. A fluid chamber is defined between the rotor member and the rotation transmitting member. A vane is radially equipped to either the rotor member or the rotation transmitting member so as to divide the fluid chamber into an advanced angle chamber and a retarded angle chamber. A covering member is fixed to the rotation transmitting member so as to cover the fluid chamber. A biasing member, for example a torsion coil spring, is disposed between the closing member and the rotor member so as to bias the rotor member in a rotative direction. In this known variable valve timing device with the above-described structure, each of the covering member and the rotor member is provided with a groove which houses an edge portion of the biasing member and possesses a spiral shaped structure. 
     According to the above-disclosed variable valve timing device, each groove of the covering member and the rotor member comes in contact with an entire rolled edge surface of the biasing member. Accordingly, a contact resistance between the biasing member and each groove is relatively large when the rotor member is rotated relative to the rotation transmitting member. In this case, the rotating performance of the rotor member relative to the rotation transmitting member may be deteriorated, thereby affecting on operation of the variable valve timing device. 
     The present invention therefore seeks to provide an improved variable valve timing device in which a relative rotation of a rotor member and a rotation transmitting member may be smoothly performed as being intended, thereby the performance of the variable valve timing device can be improved. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a variable valve timing device includes a rotation transmitting member rotated integrally with one of a rotation shaft of an engine and an intake and exhaust valves controlling member for controlling an opening and closing of intake and exhaust valves of the engine, and a rotor member disposed in the rotation transmitting member to be rotated relative to the rotation transmitting member and rotated integrally with the other of the rotation shaft of the engine and the intake and exhaust valves controlling member, a fluid chamber defined between the rotor member and the rotation transmitting member, a vane radially equipped to one of the rotor member and the rotation transmitting member so as to divide the fluid chamber into an advanced angle chamber and a retarded angle chamber, a covering member fixed to the rotation transmitting member for covering the fluid chamber, and a biasing member disposed between the covering member and the rotor member for biasing the rotor member in a rotative direction thereof. An axial edge surface of the biasing member discontinuously comes in contact with at least one of the rotor member and the covering member. 
     At least the one of the rotor member and the covering member includes a recessed portion for housing an axial edge portion of the biasing member. The recessed portion possesses a discontinuous surface at a bottom thereof. 
     The biasing member is a torsion spring of which one end is engaged to the covering member and other end is engaged to the rotor member. The recessed portion for housing the axial edge portion of the torsion spring is a groove with a substantially helical shaped structure. The discontinuous surface is provided at a bottom of the groove with the substantially helical shaped structure. 
    
    
     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 wherein: 
     FIG. 1 is a front view illustrating a variable valve timing device according to an embodiment of the present invention; 
     FIG. 2 is a cross sectional view of FIG. 1 taken along a line A—A; 
     FIG. 3 is an arrow view of FIG. 2 taken along a line B—B; and 
     FIG. 4 is a schematic explanatory view linearly illustrating a cross section of an annular groove of a rotor member or a plate member so as to explain a structure of a projection provided at the annular groove portion thereof. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As illustrated in FIG. 1, a gear  32  is connected to a rotation shaft of an engine, such as a crank shaft  100 , a member equipped to the crank shaft (not shown), or the like, via a timing chain  90 . More particularly, the gear  32  is integrally provided with a sprocket portion  32   b  on its outer periphery and is connected to the rotation shaft of the engine via the timing chain  90  hooked around the sprocket portion  32   b . The gear  32  is assembled with a housing member  31  (described later). A plate member (a covering member)  33  (described later) covers an end surface of the housing  31  which is opposite to the other end surface thereof at a side of the gear  32 . The plate member  33  possesses an outer periphery which substantially corresponds to an outer periphery of the housing member  31 . The gear  32 , the housing member  31 , and the plate member  33  are fixed at four portions with a constant distance in a peripheral portion between each portion by means of fastening members  64  such as bolts with flanges, whereby the gear  32 , the housing member  31 , and the plate member  33  can be integrated. 
     According to the embodiment of the present invention, an engine power transmitting is described in accordance with a structure of which the rotation of the crank shaft  100  is transmitted to the gear  32  via the timing chain  90 . However, the engine power transmitting is not limited to the aforementioned structure. Alternatively, the engine power transmitting can be performed by use of a belt member, which substitutes for the timing chain  90 , and, a pulley, which substitutes for the gear  32 . The housing  31  and the gear  32  functions as a rotation transmitting member for transmitting an engine revolution to a cam shaft  10  (an intake and exhaust valves controlling member). 
     As illustrated in FIG. 2, the gear  32  possesses an approximately convex cross section in an axial direction thereof. The gear  32  is provided with a bore at a central portion thereof so as to insert the cam shaft  10  which controls the opening and closing time of intake and exhaust valves of the engine (not shown). An inner peripheral surface  32   a  of the gear  32  slidably comes in contact with an outer peripheral surface  10   a  of the cam shaft  10 . According to the embodiment of the present invention, the housing member  31  is a separated assembly from the gear  32 . However, the housing member  31  can be a unit with the gear  32 . 
     The housing member  31  possesses an approximately cylindrical shaped structure opening in an axial direction thereof and has four shoe portions  31   b  projecting in a radially inward direction thereof so as to define four recessed portions  31   a  respectively opened with approximately arc shaped structures. The respective recessed portions  31   a  function as fluid chambers. The housing member  31  further has two pairs of recessed portions  31   c  at an outer peripheral surface. The respective pairs of recessed portions  31   c  are arranged relative to an axis of the housing member  31  and relative to a normal line of the axis thereof. Each shoe portion  31   b  is provided with an inserting bore  31   f  for inserting each fastening member  64 . The inserting bores  31   f  are arranged not to be parallel with the recessed portions  31   c  in a circumferential direction of the housing member  31 . 
     The plate member  33  covering the end surface of the housing  31  is provided with a central bore  33   e , a boss portion  33   a  at a radially outside of the central bore  33   e , and a fixing portion  33   b . The plate member  33  is fixed with the housing member  31  and the gear  32  at the four portions in the circumferential direction by means of the fastening members  64 . 
     The rotor member  20  possesses an outer peripheral surface slidably in contact with an inner peripheral surface of the shoe portions  31   b  of the housing member  31  so that the rotor member  20  can be rotated relative to the housing member  31 . The rotor member  20  is provided with an inner bore  20   c  at a central portion thereof so as to insert a bolt (not shown) fixed to an end of the cam shaft  10 . A recessed portion  20   b  is defined at an end portion at a side of the rotor member  20  fixed to the cam shaft  10 . A positioning pin  23  is disposed in the recessed portion  20   b  so as to position the rotor member  20  and the cam shaft  10 . Therefore, the cam shaft  10  is always positioned at a predetermined position relative to the rotor member  20 , thereby the relative rotation of the cam shaft  10  and the rotor member  20  is not allowed in favor of the positioning pin  23 . The bolt (not shown) disposed in the rotor member  20  is screwed with the cam shaft  10 , whereby the rotor member  20  and the cam shaft  10  can be rotated as a single unit. In this case, as described above, the outer peripheral surface  10   a  of the cam shaft  10  is slidably in contact with the inner peripheral surface  32   a  of the gear  32 , and the outer peripheral surface of the rotor member  20  is slidably in contact with the inner peripheral surfaces of the shoe portions  31   b.    
     The rotor member  20  includes four axially extending passage bores  20   h , three passage bores  20   f , which extend from the passage bores  20   h  in a radially outward direction and communicate with the recessed portions  31   a , a single passage bore  20   f , which communicates with the recessed portion  31   a  via a lock bore  20   g , and four passage bores  20   e , which communicates with the inner bore  20   c  of the rotor member  20 . A clearance between the inner bore  20   c  and the not-shown bolt disposed therein functions as a passage and communicates with a passage (not shown) defined in the cam shaft  10 . These passages function as an oil passage for supplying operation oil to a retarded angle chamber R 2  (described later). The passage bores  20   f , the axial bores  20   h , and a passage (not shown) being different from the passage defined in the cam shaft  10  function as an oil passage for supplying operation oil to an advanced angle chamber R 1 . 
     The outer peripheral surface of the rotor member  20  is provided with four vane grooves  20   d  radially outwardly extending from a center of the rotor member  20  so as to respectively dispose four vanes  21  therein. As illustrated in FIG. 2, each vane  21  possesses a recessed portion  21   a  at an inner diameter side and disposes a leaf spring  22  with an approximately C shaped cross section. Therefore, each vane  21  is biased in a radially outward direction by the leaf spring  22 , thereby an end portion of the vane  21  comes in contact with an inner wall of the recessed portion  31   a . Therefore, each recessed portion  31   a  is divided into two chambers via the vane  21 . The left-hand side of the two chambers is the advanced angle chamber R 1  and the right-hand side thereof is the retarded angle chamber R 2 . 
     One of the four shoe portions  31   b  of the housing member  31  is provided with a bore  31   g  disposing a lock spring  62  therein. A known torsion spring is adopted as the lock spring  62  and one end thereof is engaged to an inner wall of the bore  31   g  and the other end thereof is in contact with an end portion of a lock plate  61 . The lock plate  61  is assembled to be freely slidable between the bore  31   g  and a retracting bore  31   e  in the radial direction of the housing member  31 . When the rotor member  20  is positioned with a predetermined phase relative to the housing member  31 , the retracting bore  31   e  is positioned to oppose the lock bore  20   g  which is defined on the outer peripheral surface of the rotor member  20 . In this case, the lock plate  61  is projected toward the lock bore  20   g  by a biasing force of the lock spring  62  and is then engaged with the lock bore  20   g . Once the lock plate  61  is engaged with the lock bore  20   g , the rotor member  20  can not be rotated relative to the housing member  31 . On the other hand, when the operation oil is supplied to the lock bore  20   g  communicating with the passage bore  20   f , the lock plate  61  is retracted to the retracting bore  31   e  against the biasing force of the lock spring  62  and is then released from the engaged condition to the lock bore  20   g . In this case, the rotor member  20  can be freely rotated relative to the housing member  31 . 
     As especially seen in FIG. 2, a coil shaped torsion spring  24  is disposed between the rotor member  20  and the plate member  33 . The rotor member  20  includes an approximately annular shaped groove portion  20   i  axially opened in the rotor member  20  at a side of an edge surface  20   a . The plate member  33  also includes an approximately annular shaped groove portion  33   c  axially opened in the plate member  33  at a side of a contact surface with the rotor member  20 . One end  24   a  of the torsion spring  24  is engaged with an engaging portion  33   d  (shown in FIG. 1) axially defined in the plate member  33  and the other end  24   b  of the torsion spring  24  is engaged with an engaging portion  20   j  (shown in FIG. 3) axially defined in the rotor member  20 . The torsion spring  24  disposed as described above always biases the rotor  20 , i.e. the cam shaft  10 , in a clockwise direction so as to maintain the advanced angle chamber R 1  with a maximum inner space and the retarded angle chamber R 2  with a minimum inner space. 
     Each bottom portion of the annular groove portions  20   i  and  33   c  is provided with three projections (discontinuous surfaces) P 1 , P 2 , and P 3  which have a constant distance between the adjacent projections in a circumferential direction thereof. The projections P 1 , P 2 , and P 3  of the grooves  20   i  and  33   c  are designed to go up in height in this order corresponding to the axial shape of edge surfaces  24   c  and  24   d  of the torsion spring  24 . More specifically, as illustrated in FIG. 4, each surface of each projection P 1 , P 2 , and P 3  possesses a taper shaped structure with a predetermined angle α relative to a surface vertical to an axis of the plate member  33  or the rotor member  20 . Therefore, a surface connecting the surfaces of the projections P 1 , P 2 , and P 3  possesses a substantially helical shaped structure, wherein the edge surface  24   c  or  24   d  of the torsion spring  24  discontinuously (i.e. without having successive contact portions) comes in contact with the plate member  33  and the rotor member  20  via the three projections P 1 , P 2 , and P 3 . The predetermined angle α is represented by the following formula (inequality). 
     
       
         α≧tan −1 (φ d/ (φ D×π )) 
       
     
     
       
         φ D 2≧φ D≧φD 1 
       
     
     where, 
     φd: diameter of coil of the torsion spring 
     φD: central diameter of the torsion spring 
     φD1: outer diameter of the groove 
     φD2: inner diameter of the groove 
     As the groove portions  20   i  and  33   c  according to the embodiment of the present invention are designed with the foregoing structure, a contact area of the torsion spring  24  with the groove portions  20   i  and  33   c  can be effectively decreased comparing with a known structure in which the entire edge surfaces  24   c  and  24   d  of the torsion spring  24  are in contact with the groove portions  20   i  and  33   c . Therefore, when the rotor  20  is rotated relative to the housing member  31 , the contact resistance of the torsion spring  24  with the rotor member  20  according to the embodiment of the present invention is not affected on the rotation of the rotor member  20  as much as the conventional structure, thereby the performance of the various valve timing system  1  can be effectively improved. 
     According to the embodiment of the present invention, the groove portions  20   i  and  33   c  are respectively provided with the projections P 1 , P 2 , and P 3 . However, the number of the projections P 1 , P 2 , and P 3  are not limited to a certain number. Further, the projections P 1 , P 2 , and P 3  are not always required to be provided with both of the groove portions  20   i  and  33   c  and can be provided with either the groove portion  20   i  or  33   c.    
     Next, the operation of the variable valve timing device  1  according to the embodiment of the present invention is described hereinbelow. 
     The rotation of the crank shaft  100  of the engine is transmitted to the gear  32  via the timing chain  90  so that the gear  32  is rotated in response to the rotation of the crank shaft  100 . The gear  32  and the housing member  31  are fixed to each other by means of the fastening members  64  so as to be rotated as a single unit. For example, when the lock plate  61  is engaged with the lock bore  20   g , the housing member  31  and the rotor  20  is rotated as a single unit. Therefore, the rotation of the crank shaft  100  is transmitted to the cam shaft  10 . The cam shaft  10  is synchronously rotated having the predetermined relative phase to the crank shaft  100 . 
     When the phase of the rotor member  20  relative to the housing member  31  is required to be moved in an advanced direction, i.e. in the clockwise direction, the operation oil is supplied to the lock bore  20   g  and the passage bores  20   f  and the operation oil in the retarded angle chambers R 2  is exhausted via the passage bores  20   e . In this case, the lock plate  61  is retracted from the lock bore  20   g  to the retracting bore  31   e  in response to the operation oil supplied to the lock bore  20   g . The lock plate  61  does not restrain any more the rotor member  20  from being rotated relative to the housing member  31 . The advanced angle changers R 1  are then filled in with the operation oil supplied to the passage bores  20   f , wherein the oil pressure in the advanced angle chambers R 1  is applied to the vanes  21  at a greater pressure level than the oil pressure in the retarded angle chambers R 2 . Therefore, the vanes  21  are moved relative to the housing member  31  in the advanced direction so as to increase the volume of the advanced angle chambers R 1  and to decrease the volume of the retarded angle chambers R 2 . 
     On the other hand, when the phase of the rotor member  20  relative to the housing member  31  is required to be moved in a retarded direction, i.e. in a counterclockwise direction, the operation oil is supplied to the retarded angle chambers R 2  via the passage bores  20   e  and the operation oil in the advanced angle chambers R 1  is exhausted. In this case, the oil pressure in the retarded angle chambers R 2  is applied to the vanes  21  at a greater pressure level than the oil pressure in the advanced angle chambers R 1 . Therefore, the vanes  21  is moved relative to the housing member  31  so as to increase the volume of the retarded angle chambers R 2  and to decrease the volume of the advanced angle chambers R 1 . That is, the phase control of the rotor member  20  relative to the housing member  30  can be performed by operating one of the chambers R 1  and R 2  as an operation oil supplied chamber and the other one thereof as an operation oil exhausted chamber. 
     As described above, when the relative rotation of the rotor member  20  and the housing member  31  is performed in response to the operation oil flaw, the edges surfaces  24   c  and  24   d  of the torsion spring  24  become in contact with the surfaces of the projections P 1 , P 2 , and P 3 , thereby the contact restriction between the torsion spring  24  and the plate member  33  (or the rotor member  20 ) may occur. According to the embodiment of the present invention, the contact area of the torsion spring  24  with the rotor  20  and the plate member  33  can be decreased so that the contact resistance can be naturally decreased. Therefore, the torsion spring  24  according to the embodiment of the present invention can be effectively arranged not to affect on the rotation of the rotor member  20 . 
     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.