Patent Publication Number: US-6220209-B1

Title: Rocking follower mechanism for three-dimensional cam

Description:
The disclosure of Japanese Patent Application No. Hei. 10-234233 filed on Aug. 20, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a rocking follower mechanism for a three-dimensional cam. In particular, the invention relates to a rocking follower mechanism for a three dimensional cam for transmitting a positional variation of a cam surface of a three-dimensional cam to a valve lifter, in response to revolutions of an internal combustion engine. 
     2. Description of Related Art 
     There is a known variable valve timing mechanism capable of varying the on-off timing of an intake valve or an exhaust valve of an internal combustion engine. This is performed in accordance with operation of an internal combustion engine. In one of such variable valve timing mechanisms, there is a known mechanism as shown in FIG. 10. A lift amount of a valve  103  is varied using a three-dimensional cam  102  movable in the rotational axial direction so as to adjust the on-off timing of the valve, as disclosed in Japanese Patent Application Laid-open No. Hei 10-196333, for example. 
     In such a variable valve timing mechanism using a three-dimensional cam, a tilt angle of a cam surface  102   a  varies with the rotation. Also, a guide groove  105 , extending in parallel with the rotational direction of the three-dimensional cam  102 , is formed in the top surface  104   a  of a valve lifter  104 . A semi-columnar follower  106  is capable of rocking in accordance with variation in the tilt angle of the cam surface  102   a . The follower  106  is disposed in the guide groove  105  such that the three-dimensional cam  102  is sufficiently brought into contact with the valve lifter  104 . This results in enhanced durability. 
     Further, in such a structure, the cam surface  102   a  of the three dimensional cam  102  slides on a cam sliding surface of the semi-columnar follower  106  in the axial direction thereof. Therefore, as shown in FIG. 10, the semi-columnar follower  106  has a wide portion  106   b  formed at its center. The guide groove  105  also has a wide groove  105   a  formed therein into which the wide portion  106   b  is inserted. The above described structure may allow a thrust surface  106   c  of the wide portion  106   b  to abut against a thrust surface  105   b  of the expanded- width groove  105   a . As a result, the axial movement of the follower  106  is suppressed against the sliding movement of the cam surface  102   a.    
     However, the wide portion  106   b , formed in the center of the follower  106 , is required to have a cam sliding surface  106   d . The cam sliding surface  106   d  radially extends from the cam sliding surface  106   a  of the follower  106 , on which the three-dimensional cam  102  slides. 
     The cam surface  102   a  of the three-dimensional cam  102  varies its position in contact with the cam sliding surface  106   a , of the follower  106 , by moving along a shaft  107  axially. As a result, the lift amount of the valve  103  is varied. Therefore, a width Cw of the cam surface  102   a , in the axial direction, is greater than a width Fw of the cam sliding surface  106   a  of the follower  106 . 
     Further, the sliding position between the cam surface  102   a , of the three-dimensional cam  102 , and the sliding surface  106   a , of the follower  106 , always varies in the axial direction of the follower  106  (in the direction of the arrow Z in FIG.  10 ). This variance is in response to the rotation of the three-dimensional cam  102 . 
     Therefore, the cam surface  102   a , of the three dimensional cam  102 , slides so as to move along a portion defined by the cam sliding surface  106   a , that is not adjacent to the cam sliding surface  106   d  of the wide portion  106   b , and the cam sliding surface  106   a , which is adjacent to the cam sliding surface  106   d . If the sliding position is moved, the cam surface  102   a  of the three-dimensional cam  102  collides against an angular portion  106   e . The angular portion  106   e  is defined by the thrust surface  106   c  and the cam sliding surface  106   d  of the wide portion  106   b.    
     The aforementioned collision is likely to generate a hit sound. As may be appreciated, this sound is not preferable in view of driving environment of a motor vehicle, for example. Further, the collision may cause abrasion on the cam surface  102   a , of the three-dimensional cam  102 , as well as the cam sliding surface  106   d  of the wide portion  106   b . This abrasion is heavy in comparison with the abrasion caused by the normal sliding movement. Accordingly, such abrasion resulting from the collision is not preferable in view of the durability of the variable valve timing mechanism. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a follower capable of preventing the generation of a hit sound without causing excessive abrasion on the follower itself, as well as a cam surface of a three-dimensional cam, while providing the wide portion in the follower for preventing the axial movement. 
     To achieve the above object, the present invention provides a rocking follower mechanism for a three-dimensional cam. A guide groove is formed on a valve lifter of an internal combustion engine having a wide groove on at least a portion thereof. A rocking follower is supported in the guide groove. The rocking follower has a cam sliding surface that is brought into contact with a cam surface of the three-dimensional cam. The three-dimensional cam has different profiles in the axial direction such that a positional variation of the cam surface, in accordance with the rotation of the internal combustion engine, is transmitted to the valve lifter. The rocking follower includes a wide portion corresponding to the expanded width groove of the guide groove for accommodating the wide portion. As a result, the rocking follower is prevented from moving in a direction of the rocking axis. A wide portion is formed at a position in the rocking follower so as not to be in contact with the cam surface. 
     Accordingly, the wide portion of the rocking follower is positioned so as not to be in contact with and slide on the cam surface of the three-dimensional cam. As a result, the cam surface does not abut against the surface or the angular portion of the wide portion. Therefore, excessive abrasion is not generated on the cam surface of the three-dimensional cam and the rocking follower itself. Further, the hit sound as described above can also be prevented. 
     In accordance with the invention, among surfaces of the wide portion, the surface facing the three-dimensional cam may be formed closer to the valve lifter than the cam sliding surface. 
     With the structure described above, the surface of the expanded edge portion opposing the three-dimensional cam is formed closer to the valve lifter than the cam sliding surface. As a result, the cam surface of the three-dimensional cam is not brought into contact with the surface of the wide portion. Therefore, this arrangement prevents collision of the cam surface of the three-dimensional cam against the surface of the wide portion or the angular portion defined by the thrust surface thereof. 
     In addition, among surfaces of the wide portion, a top of the surface facing the three-dimensional cam may be formed as a tilting surface toward the valve lifter. 
     The top of the surface of the wide portion opposing the three-dimensional cam may be formed as the tilting surface toward the valve lifter. As a result, it is possible to prevent the cam surface of the three-dimensional cam from contacting with the surface of the wide portion. Therefore, collision of the cam surface of the three-dimensional cam against the surface of the wide portion or the angular portion defined by the thrust surface can be avoided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and advantages of the invention will become apparent from the following detailed description of exemplary embodiments when taken in conjunction with the accompanying drawings, in which like reference numerals designate like elements and wherein: 
     FIG. 1 is a schematic diagram illustrating a valve driving mechanism of a first embodiment in accordance with the invention; 
     FIG. 2 is a schematic view of a gasoline engine for a vehicle using the valve driving mechanism shown in FIG. 1 in accordance with the invention; 
     FIG. 3 is a perspective view of a rocking follower mechanism for a three-dimensional cam of the first embodiment in accordance with the invention; 
     FIG. 4 is an exploded perspective view of the rocking follower mechanism for the three-dimensional cam of the first embodiment in accordance with the invention; 
     FIGS. 5A and 5B are plane views illustrating a cam follower of the first embodiment accordance with the invention; 
     FIG. 6 is a perspective view illustrating an arrangement of a cam follower on the cam follower of the first embodiment in accordance with the invention; 
     FIGS. 7 and 8 are perspective views illustrating operation of the rocking follower mechanism of the three-dimensional cam of the first embodiment in accordance with the invention; 
     FIGS. 9A and 9B are perspective views showing a cam follower of a second embodiment in accordance with the invention; and 
     FIG. 10 is an explanatory view illustrating a known rocking follower mechanism of a three-dimensional cam. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     While the invention will hereinafter be described in connection with exemplary embodiments thereof, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents that may be included within the spirit and scope of the invention. 
     For a general understanding of the features of the invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. 
     FIG. 1 shows a valve driving mechanism, which is used with a rocking follower mechanism for a three-dimensional cam in accordance with the invention. FIG. 2 shows a schematic diagram of a gasoline engine (hereinafter referred to as the engine)  1  for a vehicle including the arrangement shown in FIG. 1. A DOHC4 valve type is employed as the valve driving type for the engine  1 . 
     A cylinder block  2 , in the engine  1 , is provided with a plurality of cylinders  3 . Each of the cylinders  3  has a piston  4  disposed therein. Each piston  4  is connected, through a connecting rod  7 , to a crankshaft  6 . The crankshaft  6  is supported by a crankcase  5 . A crankshaft timing pulley  8  is provided at one end of the crankshaft  6 . 
     In a cylinder head  9 , provided above the cylinder block  2 , an intake camshaft  10  is rotatably and axially movable in the lateral direction as shown by the arrow in FIG.  1 . The intake camshaft  10  is supported by a plurality of journal bearings  22 . The intake camshaft  10  is integrally provided with intake cams  11 . That is, two intake cams  11  are associated with each cylinder  3 . Further, in the cylinder head  9 , an exhaust camshaft  12  is rotatively supported by a plurality of journal bearings so as to be immovable in a direction of the rotation axis. The exhaust camshaft  12  is integrally provided with exhaust cams  13 , i.e., two exhaust cams  13  for each cylinder  3 . 
     A camshaft timing pulley  14  and a shaft driving mechanism  15  are integrally provided at one end of the intake cam shaft  10 . A camshaft timing pulley  16  is provided at one end of the exhaust camshaft  12 . The camshaft timing pulleys  14  and  16  are each connected to the crankshaft timing pulley  8  through a timing belt  17 . With such a structure, the intake camshaft  10  and the exhaust camshaft  12  are driven to rotate upon rotation of the crankshaft  6 . 
     In each of the cylinders  3 , two intake valves  18  are disposed therein. Each intake valve  18  is driven through a valve lifter  19  to be operatively connected to the intake cam  11 . Each valve lifter  19  is slidably supported in a lifter bore (not shown) formed in the cylinder head  9  so as not to rotate therein. 
     Further, two exhaust valves  20  are disposed in each of the cylinders  3 . Each exhaust valve  20  is driven through a valve lifter  21  to be operatively connected to the exhaust cam  13 . Each valve lifter  21  is slidably supported in a lifter bore (not shown) formed in the cylinder head  9 . 
     The intake cam  11 , supported with the intake camshaft  10 , is a three-dimensional cam and includes a cam surface  11   a . The cam surface  11   a  is formed such that the height of its cam nose is continuously varied in a direction of the rotation axis in a stepless manner. Further, the exhaust cam  13 , supported by the exhaust camshaft  12 , is a normal cam and the height of its cam nose is not varied in a direction of the rotation axis. 
     As shown in an enlarged perspective view in FIG. 3, the valve lifter  19  has a cylindrical shape. A guide member  19   b  projects from a side surface  19   a  of the valve lifter  19 . The guide member  19   b  is inserted into a guide groove (not shown) formed in an inner peripheral surface of a lifter bore of the cylinder head  9 . In such a manner, the valve lifter  19  is slidably guided in a direction of a center axis so as not to rotate in the lifter bore. 
     A cam follower holder  24  is integrally formed on the upper surface  19   c  of the valve lifter  19 . A cam follower  25  (corresponding to a rocking follower) is supported in the cam follower holder  24  so as to be able to rock widthwise. The valve lifter  19  is urged against the intake cam  11  by a spring  18   a  placed under compression between the valve lifter  19  and the cylinder head  9 . As a result, a cam sliding surface  25   a  of the cam follower  25  is pressed against the cam surface  11   a  of the intake cam  11 . The cam sliding surface  25   a  is allowed to slide in contact with the cam surface  11   a . The cam follower  25  rocks in accordance with the cam surface  11   a.    
     As shown in an exploded perspective view in FIG. 4, the plan view in FIG. 5A and a front view in FIG. 5B, the cam follower  25  is formed of a semicolumnar body  25   b  and a wide portion  25   c  formed in the center of the body  25   b . The wide portion  25   c  has a diameter larger than that of the body  25   b . As shown in FIG. 6, when the body  25   b  is disposed in the cam follower holder  24  of the valve lifter  19  and rocks, an outer peripheral surface of the columnar portion of the body  25  functions as a sliding surface  25   d . The sliding surface  25   d  slides along the guide groove  24   a  having a semicircle cross section formed in the cam follower holder  24 . 
     The wide portion  25   c  of the cam follower  25  is accommodated in a wide groove  24   b , as shown in FIG. 4, formed in the center of the guide groove  24   a . With this structure, a thrust surface  25   e  of the wide portion  25   c  is brought into abutment against a thrust surface  24   c  of the expanded width groove  24   b . As a result, the cam follower  25  is prevented from moving in the axial direction as shown by the arrow B in FIG.  4 . That is, the cam follower  25  disposed in the cam follower holder  24  of the valve lifter  19  can rock around its axis but is not allowed to move along the axial direction. 
     End surfaces  25   f  of the wide portion  25   c  of the cam follower  25  facing the intake cam  11  form tilt surfaces toward the valve lifter  19 . The end surfaces  25   f  are not allowed to reach the cam sliding surface  25   a  as shown in FIG.  5 B. The tilt angle is set to the value ranging from θ=10° to 30°. 
     With the wide portion  25   c  formed in this manner, the intake camshaft  10  rotates from the position shown in FIG. 3 in the direction of the arrow C. The cam surface  11   a  of the intake cam  11  slides along the cam sliding surface  25   a  of the cam follower  25 . As a result, these elements are brought into the positioning shown in FIG.  7 . In the course of operation, in accordance with the invention, as shown in FIG. 3 to FIG. 7, the cam surface  11   a  around the cam nose  11   b  of the intake cam  11  slides to move on the center portion of the cam sliding surface  25   a . The intake cam  11  slides in the axial direction of the cam follower  25 , backwards as viewed in FIG. 3, for example. 
     During this sliding movement, the cam surface  11   a  passes by the center of the cam sliding surface  25   a  adjacent to the wide portion  25   c . Both end surfaces  25   f  of the wide portion  25   c  tilt to recede downward from the cam sliding surface  25   a . Therefore, even if the cam nose  11   b  slides on the center of the cam sliding surface  25   a  as shown in FIG. 8, the cam surface  11   a  of the intake cam  11  is not brought into contact with the opposing end surfaces  25   f  of the wide portion  25   c  in the course of the sliding movement. 
     According to the aforementioned embodiment of the invention, the wide portion  25   c  of the cam follower  25  is formed at a position so as not to contact with the cam surface  11   a  of the intake cam  11 . Therefore, the cam surface  11   a  of the intake cam  11  does not collide against an angular portion  25   g  defined by the thrust surface  25   e  and the end surface  25   f  of the wide portion  25   c , and does not directly abut against the end surfaces  25   f . As a result, excessive abrasion is not generated on the cam surface  11   a  of the intake cam  11  and the cam follower  25  itself, thus preventing generation of the hit sound. As a result, riding comfort of the vehicle can be maintained and noise generation reduced. 
     Next, a second embodiment of the present invention will be described. 
     FIG. 9A is a perspective view of a cam follower  75  of a valve driving mechanism of the second embodiment. FIG. 9B is a front view thereof The structure of the second embodiment is generally the same as that of the first embodiment. However, the second embodiment is different from the first embodiment in that opposing end surfaces  75   f  of a wide portion  75   c  of a cam follower  75  recede downward from a cam sliding surface  75   a  and in parallel therewith. The height of the resultant stepped portion D, defined by the cam sliding surface  75   a  and the end surface  75   f , may be specified to, for example, approximately 0.1 mm. 
     In the first embodiment, since an edge of the end surface  25   f  of the cam follower  25  at the side of the cam sliding surface  25   a  is in contact with the cam sliding surface  25   a , the cam surface  11   a  of the intake cam  11  might come in slight contact with the angular portion  25   g  around the edge portion of the end surface  25   f  depending upon the pressure of the spring  18   a  urging the valve lifter  19  toward the intake cam  11 . However, since the stepped portion D is provided in the second embodiment, there is no such possibility of the contact. Therefore, the riding comfort of the vehicle can be favorably maintained. 
     Further, the first and second embodiments may be combined such that the opposite end surfaces of the cam follower have both the tilt surface and stepped portion, for example. 
     In the first and the second embodiments, the intake cam  11  is formed,as the three-dimensional cam and the corresponding valve lifter  19  is provided with the cam follower  25 . The exhaust cam  13  may be formed as the three-dimensional cam, and the valve lifter  21  may be provided with the same cam follower. In this case, the shaft driving mechanism similar to the shaft driving mechanism  15  can be provided on the exhaust camshaft  12  so as to be movable in the axial direction. 
     While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations may be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.