Patent Publication Number: US-7909006-B2

Title: Variable valve mechanism

Description:
TECHNICAL FIELD 
     The present invention relates to a variable valve mechanism. 
     BACKGROUND ART 
     A variable valve mechanism disclosed in JP-A-2006-161730 includes: a control shaft, which is capable of varying the rotary angular position continuously or stepwise; a control member, which is mounted on the outer circumferential surface of the control shaft to rotate together with the control shaft; and a change mechanism, which changes the valve operating angle relative to camshaft rotation in accordance with the rotary angular position of the control member. In this variable valve mechanism, the control shaft is shared by a plurality of cylinders while the control member is provided for each cylinder. 
     In the above variable valve mechanism, the valve operating angle may vary from one cylinder to another due to a component part manufacturing error or assembling error. Therefore, the above variable valve mechanism includes an adjustment mechanism, which equalizes the valve operating angles of all cylinders as described below. An insertion hole is made in the control member. Further, a protruding part, which is formed to be smaller than the insertion hole in circumferential width, is positioned to protrude into the insertion hole from the control shaft. There are gaps between the protruding part and the left and right circumferential wall surfaces of the insertion hole. Adjustment members (adjustment shims) are placed in the left and right gaps. The mounting angle of the control member relative to the control shaft can be adjusted by replacing the left and right adjustment members with those having a different shape. When the adjustment is made for all cylinders, the valve operating angles of all cylinders can be equalized. 
     Patent Document 1: JP-A-2006-161730 
     Patent Document 2: JP-A-2005-9446 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     In the prior art variable valve mechanism described above, the gaps into which the adjustment members are inserted are shaped like a wedge. The angle of the wedge varies with the adjustment of the mounting angle of the control member relative to the control shaft. Therefore, uneven contact, point contact, or other improper contact may occur in a region of contact between the control member insertion hole and adjustment members or between the protruding part and adjustment members. If uneven contact or point contact occurs, the surface pressure of the associated contact face increases, thereby accelerating wear. If wear progresses, the adjusted mounting angle becomes incorrect. This causes the valve operating angle to become incorrect as well. 
     The present invention has been made in view of the above circumstances. It is an object of the present invention to provide a variable valve mechanism with simple structure that is capable of accurately adjusting the valve operating angle of an internal combustion engine. 
     Means for Solving the Problem 
     The above object is achieved by a first aspect of the present invention. The first aspect of the present invention is a variable valve mechanism including: 
     a cam which is mounted on a camshaft of an internal combustion engine; 
     an intermediate member which is positioned in the course of a path for transmitting the lift of the cam to a valve; 
     a control shaft which can vary the rotary angular position continuously or stepwise; 
     a control member which is installed to be rotatable around the control shaft; 
     a lock mechanism for preventing the control member from rotating relative to the control shaft; and 
     a coupling member for coupling the control member to the intermediate member; 
     the control shaft being rotated to change the position of the intermediate member and the operating angle of the valve is varied; 
     wherein the lock mechanism includes a control pin, which is inserted into a hole in the control shaft to protrude in the radial direction of the control shaft, a bearing hole, which is formed in the control member in parallel with the control shaft, and an adjustment member, which is rotatably supported by the bearing hole; 
     wherein the adjustment member and the control pin come into surface contact with each other directly or through an interposition member to inhibit the control member from rotating relative to the control shaft; 
     wherein the operating angle of the valve can be adjusted by replacing the adjustment member, the interposition member, or the control pin with another having a different dimension to change the distance between the center line of the bearing hole and the center line of the control pin and change the relative angle between the control shaft and the control member; and 
     wherein the adjustment member rotates within the bearing hole to maintain the surface contact irrespective of the magnitude of the relative angle. 
     A second aspect of the present invention is the variable valve mechanism according to the first aspect, wherein the adjustment member is made of a substantially cylindrical pin. 
     A third aspect of the present invention is the variable valve mechanism according to the first or the second aspect, wherein the surface contact is plane contact. 
     A fourth aspect of the present invention is the variable valve mechanism according to any one of the first to the third aspects, 
     wherein the adjustment member and the control pin are in direct contact with each other; and 
     wherein the operating angle of the valve can be adjusted by replacing the adjustment member with another having a different dimension between the center line thereof and the contact face relative to the control pin or by replacing the control pin with another having a different dimension between the center line thereof and the contact face relative to the adjustment member. 
     A fifth aspect of the present invention is the variable valve mechanism according to any one of the first to the fourth aspects, 
     wherein the adjustment member and the control pin are in direct contact with each other; 
     wherein the adjustment member has cylindrical parts, which are provided on both ends and in contact with the inner circumferential surface of the bearing hole; and 
     wherein the adjustment member&#39;s contact face relative to the control pin is positioned between the cylindrical parts and lower than the cylindrical surfaces thereof. 
     A sixth aspect of the present invention is the variable valve mechanism according to any one of the first to the fifth aspects, 
     wherein the control pin is inserted into the hole in the control shaft in a clearance-fit manner; 
     wherein the adjustment member and the control pin are in direct contact with each other; and 
     wherein the control pin has a protruding part, which is positioned between the contact face relative to the adjustment member and an insert placed in the hole in the control shaft. 
     A seventh aspect of the present invention is the variable valve mechanism according to any one of the first to the sixth aspects, 
     wherein the lock mechanism further includes a screw hole bored through the adjustment member, a bolt insertion hole bored through the control pin, a bolt for fastening the adjustment member to the control pin by running through the bolt insertion hole and screwing into the screw hole, and a nut screwed on a male thread of the bolt protruding through the screw hole; and 
     wherein a gap is provided between the bolt insertion hole and the bolt to allow a bolt position change that occurs when the relative angle between the control shaft and the control member is changed. 
     A eighth aspect of the present invention is the variable valve mechanism according to any one of the first to the seventh aspects, further including: 
     a rocker arm for pushing the valve; 
     a rocker roller which is mounted on the rocker arm; 
     a swing arm which is installed to be swingable around the control shaft and swings when the cam rotates; 
     a swing cam surface which is formed on the swing arm and brought into contact with the rocker roller; and 
     a slider surface which is formed on the swing arm and positioned to face the cam; 
     wherein the intermediate member is positioned between the cam and the slider surface to move toward or away from the center of the control shaft when the control shaft rotates. 
     ADVANTAGES OF THE INVENTION 
     According to the first aspect of the present invention, when, for instance, valve operating angle variations between the cylinders of an internal combustion engine are to be compensated for, the valve operating angle can be adjusted by replacing the adjustment member, interposition member, or control pin with another having a different dimension for the purpose of adjusting the relative angle (mounting angle) between the control shaft and control member. The adjustment member is rotatably supported by the bearing hole, which is made in the control member. Therefore, when the adjustment member rotates, it can absorb changes in the relative angle between the control shaft and control member. Thus, the surface contact between the adjustment member and control pin can be properly maintained. This makes it possible to accurately prescribe the relative angle between the control shaft and control member and adjust the operating angle with high precision. Further, the surface pressure of the contact face between the adjustment member and control pin can be decreased to inhibit the contact face from wearing. This makes it possible to definitely prevent an adjusted operating angle from becoming incorrect. Further, the first aspect of the present invention entails the use of a small number of parts, does not require the parts to be manufactured with high dimensional accuracy, and makes it easy to fabricate the parts. Consequently, the production cost can be reduced. In addition, assembly can be easily achieved to provide increased productivity. 
     According to the second aspect of the present invention, the adjustment member can be made of a substantially cylindrical pin. This makes it possible to fabricate the adjustment member with increased ease and achieve assembly with increased ease. 
     According to the third aspect of the present invention, the direct or indirect surface contact between the adjustment member and control pin can be plane contact. This makes it possible to decrease the surface pressure of the contact face with increased certainty, thereby preventing the contact face from wearing with increased certainty. 
     According to the fourth aspect of the present invention, the adjustment member can be brought into direct contact with the control pin. Further, the valve operating angle can be adjusted by replacing the adjustment member with another having a different dimension or by replacing the control pin with another having a different dimension. Since this eliminates the need for the interposition member, the number of required parts can be further reduced. 
     According to the fifth aspect of the present invention, the adjustment member has a cylindrical part on either side of the contact face that is in contact with the control pin. The surface of the cylindrical part is higher than the contact face. The cylindrical part definitely prevents the adjustment member from backing out of the bearing hole without requiring the use of any additional part. This makes it possible to further reduce the number of required parts. 
     According to the sixth aspect of the present invention, the control pin can be inserted into the hole in the control shaft in a clearance-fit manner. Since this eliminates the need for press in, assembly can be achieved with increased ease. Further, the control pin has a protruding part that retains the control pin. This makes it possible to definitely prevent the control pin from backing out of the hole in the control shaft without requiring the use of any additional part. Consequently, the number of required parts can be further reduced. 
     According to the seventh aspect of the present invention, a bolt can be inserted into a bolt insertion hole made in the control pin and screwed into a screw hole made in the adjustment member for tightening purposes. Therefore, the adjustment member and control pin can be secured together. Further, when a nut is screwed on the male thread of the bolt protruding through the screw hole in the adjustment member, a double-nut effect is produced. This makes it possible to prevent bolt looseness with increased certainty. Further, when the operating angle is adjusted to change the relative angle between the control shaft and control member, the positional relationship between the control pin and bolt changes. According to the seventh aspect of the present invention, a gap exists between the bolt insertion hole and bolt to allow such bolt position changes. Therefore, when the operating angle is adjusted, the surface contact between the control pin and adjustment member can be certainly maintained. 
     According to the eighth aspect of the present invention, the valve operating angle changes when the intermediate member positioned between the cam and the slider surface of the swing arm is moved toward or away from the center of the control shaft. More specifically, moving the intermediate member toward the center of the control shaft increases the swing range of the swing arm, thereby increasing the operating angle. Conversely, moving the intermediate member away from the center of the control shaft decreases the swing range of the swing arm, thereby decreasing the operating angle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view illustrating a variable valve mechanism according to a first embodiment of the present invention. 
         FIG. 2  shows perspective views illustrating a exploded state and assembled state of a control shaft and a control member. 
         FIG. 3  is a cross-sectional view of the assembled control shaft and control member taken in a plane perpendicular to the control shaft. 
         FIG. 4  is a cross-sectional view taken along line X-X of  FIG. 3 . 
         FIG. 5  is a perspective view illustrating control pin according to a second embodiment of the present invention. 
         FIG. 6  is a cross-sectional view of the assembled control shaft and control member according to the second embodiment taken in a plane perpendicular to the control shaft. 
         FIG. 7  shows perspective views illustrating the exploded state and assembled state of the control shaft and control member according to a third embodiment of the present invention. 
         FIG. 8  is a cross-sectional view of the assembled control shaft and control member according to the third embodiment taken in a plane perpendicular to the control shaft. 
         FIG. 9  is a cross-sectional view taken along line Y-Y of  FIG. 8 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will now be described with reference to the accompanying drawings. Like elements in the drawings are designated by the same reference numerals and will not be redundantly described. 
     First Embodiment 
       FIG. 1  is a side view illustrating a variable valve mechanism according to a first embodiment of the present invention. The following description assumes that the variable valve mechanism  10  shown in  FIG. 1  drives an intake valve  12  of an internal combustion engine. However, the present invention can also be applied to a variable valve mechanism that drives an exhaust valve. 
     The variable valve mechanism  10  includes a cam  14 , which is mounted on a camshaft  13 . The camshaft  13  is rotationally driven by a crankshaft of the internal combustion engine. The cam  14  rotates clockwise as viewed in  FIG. 1 . 
     The variable valve mechanism  10  also includes a control shaft  16 , which is positioned in parallel with the camshaft  13 , and a control shaft drive mechanism (not shown), which can rotate the control shaft  16  within a predetermined angular range. The configuration of the control shaft drive mechanism is not specifically defined. However, the control shaft drive mechanism may be composed, for instance, of a worm wheel, which is fastened to one end of the control shaft  16 ; a worm gear, which meshes with the worm wheel; and a servomotor, which rotationally drives the worm gear. When such a configuration is employed, the rotary angular position of the control shaft  16  can be controlled by regulating the rotation direction and rotation amount of the servomotor. 
     The variable valve mechanism  10  also includes a swing arm (swing cam arm)  18 . The swing arm  18  is adapted to swing around the center of the control shaft  16 . The swing arm  18  has a slider surface  20 , which faces the cam  14 . 
     A slider roller  22  is positioned between the swing arm  18  and cam  14 . The slider roller  22  is rotatably supported by the leading end of an intermediate arm  24 . The base end of the intermediate arm  24  is pivotally coupled to a control member  26  by a coupling shaft  27 . The control member  26  rotates together with the control shaft  16 . Therefore, when the control shaft  16  rotates, displacement is transmitted through the control member  26  and intermediate arm  24  to move the slider roller  22 . 
     More specifically, when the control shaft  16  rotates clockwise in a state shown in  FIG. 1 , the slider roller  22  moves away from the swing center of the swing arm  18  (that is, the center of the control shaft  16 ). When the control shaft  16  rotates counterclockwise in a state where the slider roller  22  is positioned apart from the center of the control shaft  16 , the slider roller  22  is pulled by the intermediate arm  24  to approach the center of the control shaft  16 .  FIG. 1  shows a state where the slider roller  22  is positioned close to the center of the control shaft  16 . 
     The slider surface  20  is curved, for instance, to form an arc so that the distance to the center of the camshaft  13  gradually increases with a decrease in the distance to the leading end of the swing arm  18 . The swing arm  18  also has a swing cam surface  28 , which is positioned opposite the slider surface  20 . 
     A lost motion spring  30  pushes the swing arm  18  clockwise as viewed in  FIG. 1 . This pushing force presses the swing arm  18  against the slider roller  22  and presses the slider roller  22  against the cam  14 . 
     The variable valve mechanism  10  further includes a rocker arm  32 , which pushes a valve stem of the intake valve  12  in the lifting direction. The rocker arm  32  is positioned below the swing arm  18  as viewed in  FIG. 1 . A rocker roller  34  is rotatably attached to the middle of the rocker arm  32 . The rocker roller  34  is in contact with the swing cam surface  28 . One end of the rocker arm  32  abuts on an end of the valve stem of the intake valve  12 . The other end of the rocker arm  32  is supported by a hydraulic lash adjuster  36 . A valve spring (not shown) pushes the intake valve  12  in the closing direction, that is, in the direction of pushing the rocker arm  32  upward. This pushing force and the hydraulic lash adjuster  36  press the rocker roller  34  against the swing cam surface  28  of the swing arm  18 . 
     When the cam  14  in the variable valve mechanism  10  described above rotates, the swing arm  18  swings because the lift of the cam  14  is transmitted to the swing arm  18  through the slider roller  22 . 
     As shown in  FIG. 1 , when the slider roller  22  is positioned nearest the center of the control shaft  16 , the lift of the cam  14  is transmitted to the swing arm  18  at a position close to the center of the control shaft  16 . This increases the swing range (oscillation range) of the swing arm  18 . Consequently, the operating angle and maximum lift amount of the intake valve  12  increase. Conversely, when the slider roller  22  is positioned apart from the center of the control shaft  16 , the lift of the cam  14  is transmitted to the swing arm  18  at a position apart from the center of the control shaft  16 . This decreases the swing range (oscillation range) of the swing arm  18 . Consequently, the operating angle and maximum lift amount of the intake valve  12  decrease. 
     As such being the case, the variable valve mechanism  10  can continuously vary the operating angle of the intake valve  12  by rotating the control shaft  16  to move the slider roller  22 . More specifically, changing the rotary angular position of the control shaft  16  clockwise as viewed in  FIG. 1  decreases the operating angle of the intake valve  12 . Conversely, changing the rotary angular position of the control shaft  16  counterclockwise as viewed in  FIG. 1  increases the operating angle of the intake valve  12 . 
     The camshaft  13  and control shaft  16 , which have been described as component parts of the variable valve mechanism  10 , are shared by a plurality of cylinders of the internal combustion engine. However, the other above-described component parts are provided for each cylinder. 
     When an internal combustion engine equipped with the variable valve mechanism  10  is assembled, the operating angle of the intake valve  12  usually varies from one cylinder to another due, for instance, to a component part manufacturing error or assembling error. If the operating angle of the intake valve  12  varies from one cylinder to another, the amount of air also varies from one cylinder to another, thereby adversely affecting the operation of the internal combustion engine. To avoid such a problem, the variable valve mechanism  10  includes an operating angle adjustment mechanism, which is capable of adjusting the operating angle of the intake valve  12  on an individual cylinder basis in order to compensate for intake valve operating angle variations between the cylinders. The configuration of the operating angle adjustment mechanism will now be described. 
       FIG. 2  shows perspective views illustrating the exploded state and assembled state of the control shaft  16  and control member  26 . As indicated in the left view of  FIG. 2 , a pin insertion hole  38  is formed in the control shaft  16  and oriented orthogonally to its axial direction. On the other hand, the control member  26  has a control shaft insertion hole  40  into which the control shaft  16  is to be inserted; a pin receiver hole  42 , which is oriented orthogonally to the axial direction of the control shaft  16 ; a bearing hole  44 , which is oriented in parallel with the control shaft  16 ; and another bearing hole  46  into which the coupling shaft  27  for the intermediate arm  24  is to be inserted. 
     When the control shaft  16  and control member  26  are to be assembled, the control shaft  16  is first inserted into the control shaft insertion hole  40  in the control member  26 . Next, a control pin  48  is inserted into the pin receiver hole  42  in the control member  26  and then into the pin insertion hole  38  in the control shaft  16 . In addition, an adjustment pin  50  is inserted into the bearing hole  44 . The control shaft  16  and control member  26  are now assembled as indicated in the right view of  FIG. 2 . 
     As indicated in the left view of  FIG. 2 , the adjustment pin  50  is substantially cylindrical (shaped like a column). More specifically, the adjustment pin  50  is obtained by trimming the axial center of the column to make it flat. When the adjustment pin  50  is inserted into the bearing hole  44 , the cylindrical portions on both ends are in contact with the inner circumferential surface of the bearing hole  44 . The portion of the control pin  48  that is to be inserted into the pin insertion hole  38  is cylindrical; however, the portion of the control pin  48  that protrudes beyond the control shaft  16  to face the adjustment pin  50  is flat. In the assembled state, the flat portion of the adjustment pin  50  is in contact (surface contact) with the flat portion of the control pin  48 . 
       FIG. 3  is a cross-sectional view of the assembled control shaft  16  and control member  26  taken in a plane perpendicular to the control shaft  16 . In the present embodiment, the control pin  48  and pin insertion hole  38  are tight fit. More specifically, it is assumed that the control pin  48  is press-fit into the pin insertion hole  38  and fastened to the control shaft  16 . On the other hand, the adjustment pin  50  and bearing hole  44  are clearance fit. In other words, the adjustment pin  50  can rotate within the bearing hole  44 . 
     In the state shown in  FIG. 3 , the control pin  48  is in contact with (abuts on) the adjustment pin  50 . This inhibits the control member  26  from rotating clockwise relative to the control shaft  16  as viewed in  FIG. 3 . Therefore, when the control shaft  16  rotates counterclockwise as viewed in  FIG. 3 , the control pin  48  pushes the adjustment pin  50 , thereby causing the control member  26  to rotate together with the control shaft  16 . 
     When the cam  14  rotates clockwise in the variable valve mechanism  10  shown in  FIG. 1 , the slider roller  22  is pulled leftward as viewed in the figure in accordance with the rotation of the cam  14 . The force applied to the slider roller  22  is then transmitted to the control member  26  through the intermediate arm  24 . As a result, force is constantly applied to the control member  26  to rotate it clockwise as viewed in the figure. This force constantly presses the adjustment pin  50  against the control pin  48 . While the cam  14  rotates, that is, the internal combustion engine operates, therefore, clockwise rotation of the control shaft  16  does not separate the control pin  48  from the adjustment pin  50 . 
     As described above, even when the control shaft  16  rotates clockwise or counterclockwise during an internal combustion engine operation, the control member  26  rotates together with the control shaft  16 . A pushing member (lost motion spring) may be added to force the control member  26  to rotate clockwise as viewed in the figure for the purpose of preventing the control pin  48  from leaving the adjustment pin  50  with increased certainty. 
       FIG. 4  is a cross-sectional view taken along line X-X of  FIG. 3 . As shown in  FIG. 4 , the contact face  52  between the control pin  48  and adjustment pin  50  is positioned lower than the cylindrical parts on both ends of the adjustment pin  50 . Since the employed configuration is as described above, the adjustment pin  50  does not back out of the bearing hole  44  as far as the control pin  48  is in contact with the adjustment pin  50 . Therefore, the present embodiment does not need to use any additional part for preventing the adjustment pin  50  from backing out of the bearing hole  44 . This makes it possible to reduce the number of required parts and make assembly easy, thereby contributing toward cost reduction. 
     In  FIG. 3 , the relative angle (mounting angle) between the control member  26  and control shaft  16  can be expressed as the angle θ between a straight line passing through the center of the control shaft  16  and the center of the bearing hole  44  (adjustment pin  50 ) and the center line of the control pin  48 . The angle θ is determined by the distance A between the center line of the bearing hole  44  and the center line of the control pin  48 . The present embodiment can change the angle θ by replacing the adjustment pin  50  with another having a different dimension B that represents the distance between the center line of the adjustment pin  50  and the contact face  52  between the control pin  48  and adjustment pin  50 . The operating angle of the intake valve  12  can be adjusted (fine-tuned) by changing the angle θ. 
     More specifically, when the adjustment pin  50  is replaced with another having a greater dimension B, the distance A increases to increase the angle θ. The angle of the control member  26  then changes slightly clockwise as far as the rotary angular position of the control shaft  16  remains unchanged. This decreases the operating angle of the intake valve  12 . In other words, the operating angle of the intake valve  12  can be fine-tuned in the decreasing direction by replacing the adjustment pin  50  with another having a greater dimension B. Conversely, the operating angle of the intake valve  12  can be fine-tuned in the increasing direction by replacing the adjustment pin  50  with another having a smaller dimension B. 
     After the variable valve mechanism  10  is assembled, the operating angle adjustment mechanism described above is used to equalize the intake valve operating angles of all cylinders. It is assumed that a plurality of (many) adjustment pins  50  differing in dimension B are prepared for the above adjustment. 
     When the variable valve mechanism  10  is to be assembled for the first time, an adjustment pin  50  whose dimension B is equal to a predetermined reference value is used. After completion of assembly, the control shaft  16  is rotated to a predetermined reference rotary angular position. In the resulting state, the operating angle of the intake valve  12  for each cylinder is measured. If the measurement results indicate that the operating angle varies from one cylinder to another, the adjustment pin  50  for each cylinder is replaced with another having a different dimension B in accordance with the difference between the measured value of each cylinder and a predetermined reference value or design value. More specifically, the adjustment pin  50  for a cylinder that is to be fine-tuned to increase the operating angle is replaced with another whose dimension B is smaller than the reference value. Conversely, the adjustment pin  50  for a cylinder that is to be fine-tuned to decrease the operating angle is replaced with another whose dimension B is greater than the reference value. 
     The adjustment pin  50  can be replaced as described below. As shown in  FIGS. 3 and 4 , on the side opposite the adjustment pin  50 , there is a gap  54  between the control pin  48  and the inner wall of the pin receiver hole  42 . Therefore, when the control member  26  is rotated counterclockwise by the amount of gap  54  relative to the control shaft  16  as viewed in  FIG. 3 , the control pin  48  does not interfere with the inside of the circle of the bearing hole  44 . In this state, the adjustment pin  50  can be inserted into or backed out of the bearing hole  44 . 
     When the adjustment pin  50  is replaced to change the angle θ, the angle of the contact face  52  between the control pin  48  and adjustment pin  50  relative to the control member  26  also changes. In this instance, the present embodiment, in which the adjustment pin  50  can rotate within the bearing hole  44 , can absorb the change in the angle of the contact face  52  and properly maintain the surface contact of the contact face  52 . This makes it possible to accurately prescribe the relative angle between the control shaft  16  and control member  26  and adjust the operating angle of the intake valve  12  with high precision. Further, the surface contact of the contact face  52  can be properly maintained. This makes it possible to decrease the surface pressure of the contact face  52  and reduce the wear of the contact face  52  (the wear of the adjustment pin  50  and control pin  48 ) during an internal combustion engine operation. Therefore, it is also possible to definitely prevent an adjusted operating angle from becoming incorrect. 
     In particular, the present embodiment uses a flat contact face  52 . This makes it possible to avoid uneven contact and reduce the surface pressure. In addition, the adjustment pin  50  and control pin  48  can be fabricated with ease. 
     Further, the control member  26  for the variable valve mechanism  10  according to the present embodiment can be manufactured by forming the bearing hole  44  and performing other simple fabrication procedures. The parts required for operating angle adjustment are limited to the control pin  48  and adjustment pin  50 . In addition, the number of required parts is small. Moreover, since the adjustment pin  50  and bearing hole  44  are clearance fit, the adjustment pin  50  can be inserted with ease. 
     Furthermore, the adjustment pin  50  and control pin  48  are merely in contact with each other. While the variable valve mechanism  10  operates, therefore, no strong force is exerted to pull the control pin  48  out of the pin insertion hole  38  in the control shaft  16 . Therefore, the control pin  48  can be easily press-fit into the pin insertion hole  38  with relatively small force. This makes it possible to employ a simplified press-fitting process and avoid applying strong force to the control shaft  16  during press-fitting. Consequently, it is possible to definitely prevent the control shaft  16  from being distorted, deformed, or otherwise damaged. 
     In addition, the above-described operating angle adjustment mechanism, which is included in the variable valve mechanism  10 , can be used after assembly to accurately adjust the operating angle of the intake valve  12 . Therefore, the dimensional accuracy required for various pins and the holes in various component members is not so high. Consequently, dimensional tolerance can be loosened to reduce the fabrication cost. Further, assembly can be achieved with ease to provide improved productivity. 
     As described above, the variable valve mechanism  10  makes it possible to adjust the operating angle of the intake vale  12  with high precision while providing increased ease of assembly and reducing the manufacturing cost. 
     In the first embodiment, which has been described above, the slider roller  22  corresponds to the “intermediate member” according to the first aspect of the present invention; the intermediate arm  24  corresponds to the “coupling member” according to the first aspect of the present invention; and the adjustment pin  50  corresponds to the “adjustment member” according to the first aspect of the present invention. 
     Second Embodiment 
     A second embodiment of the present invention will now be described with reference to  FIGS. 5 and 6 . However, the differences between the second embodiment and the above-described first embodiment will be mainly described while abridging or omitting the description of matters common to these embodiments. 
       FIG. 5  is a perspective view illustrating the control pin  48  according to the second embodiment. This control pin  48  has a protruding part  58 , which is positioned between the contact face  52  between the control pin  48  and adjustment pin  50  and an insert  56  to be inserted into the pin insertion hole  38  in the control shaft  16 . 
       FIG. 6  is a cross-sectional view of the assembled control shaft  16  and control member  26  according to the second embodiment taken in a plane perpendicular to the control shaft  16 . In the present embodiment, the insert  56  of the control pin  48  and the pin insertion hole  38  are clearance fit. More specifically, the control pin  48  is not fastened to the control shaft  16  and can be inserted into and backed out of the pin insertion hole  38 . Therefore, the present embodiment eliminates the necessity of performing a process for press-fitting the control pin  48  into the pin insertion hole  38 . Consequently, assembly can be achieved with increased ease. Meanwhile, after completion of assembly, the protruding part  58  is locked by the adjustment pin  50  as shown in  FIG. 6 . Therefore, the control pin  48  does not back out of the pin insertion hole  38  as far as the control pin  48  is in contact with the adjustment pin  50 . Consequently, it is not necessary to use any additional part for preventing the control pin  48  from backing out of the pin insertion hole  38 . This makes it possible to reduce the number of required parts and facilitate assembly. 
     In the present embodiment, the operating angle of the intake valve  12  can be adjusted either by replacing the adjustment pin  50  as is the case with the first embodiment or by replacing the control pin  48 . More specifically, when many control pins  48  differing in the dimension between the center line of the control pin  48  and the contact face  52  are prepared, the operating angle can be adjusted by selectively using one of the prepared control pins  48 . 
     Third Embodiment 
     A third embodiment of the present invention will now be described with reference to  FIGS. 7 to 9 . However, the differences between the third embodiment and the above-described first embodiment will be mainly described while abridging or omitting the description of matters common to these embodiments. 
       FIG. 7  shows perspective views illustrating the exploded state and assembled state of the control shaft  16  and control member  26  according to the third embodiment. As shown in  FIG. 7 , a shim  60  is sandwiched between the control pin  48  and adjustment pin  50 , and the control pin  48  and adjustment pin  50  are secured (coupled together) with a bolt  62 . In addition, a nut  64  is provided to lock the bolt  62 . 
       FIG. 8  is a cross-sectional view of the assembled control shaft  16  and control member  26  according to the third embodiment taken in a plane perpendicular to the control shaft  16 .  FIG. 9  is a cross-sectional view taken along line Y-Y of  FIG. 8 . As shown in  FIGS. 8 and 9 , the control pin  48  has a bolt insertion hole  66  into which the bolt  62  is to be inserted. The adjustment pin  50  has a screw hole  68 , which has a female thread for screwing onto a male thread of the bolt  62 . The bolt  62  is inserted into the bolt insertion hole  66  and screwed into the screw hole  68  for tightening purposes. This ensures that the control pin  48 , shim  60 , and adjustment pin  50  are coupled together and secured by the bolt  62 . Therefore, the present embodiment can also be applied to a situation where bidirectional turning force is exerted between the control shaft  16  and control member  26 . 
     The leading end of the bolt  62  is passed through the screw hole  68  and protruded toward the opposite side. The nut  64  is threaded onto the protruding part for tightening purposes. In the present embodiment, which includes the nut  64 , the screw hole  68  in the adjustment pin  50  and the nut  64  function as a double nut. This makes it possible to definitely prevent the bolt  62  from loosening even when the angular acceleration of the control shaft  16  drastically changes during an operation of the variable valve mechanism  10 , thereby oscillating the turning force exerted between the control shaft  16  and control member  26 . 
     The shim  60  is shaped like a two-pronged part. The shim  60  is positioned over the bolt  62  so that the bolt  62  is positioned between the two prongs as viewed in  FIG. 8 . Therefore, the shim  60  can be replaced when the bolt  62  is loosened. In the present embodiment, the relative angle θ between the control member  26  and control shaft  16  can be changed by replacing the shim  60  with another having a different thickness C. This makes it possible to adjust the operating angle of the intake valve  12 . 
     When the shim  60  is replaced to change the angle θ, the angle of the contact face between the control pin  48 , shim  60 , and adjustment pin  50  relative to the control member  26  also changes. In this instance, the adjustment pin  50  rotates within the bearing hole  44 , as is the case with the first embodiment, to absorb the above angular change of the contact face, thereby properly maintaining the surface contact of the contact face. Consequently, the third embodiment provides the same advantages as the first embodiment. 
     Further, when the angle θ changes, the positional relationship between the control pin  48  and bolt  62  also changes. More specifically, when the shim  60  is replaced with a thinner one to reduce the angle θ in a situation where the employed configuration is as shown in  FIG. 8 , the position of the bolt  62  relative to the control pin  48  moves upward as viewed in the figure. A gap is provided between the bolt insertion hole  66  and bolt  62  to allow such a bolt position change. More specifically, the bolt insertion hole  66  is elongated in the up-down direction as viewed in  FIG. 8  to form a gap above the bolt  62 . Since such a gap is provided, it is possible to definitely prevent the bolt  62  from interfering with the inner circumferential surface of the bolt insertion hole  66  even when the shim  60  is replaced to change the angle θ. This makes it possible to properly maintain the surface contact between the control pin  48 , shim  60 , and adjustment pin  50 . As a result, the operating angle of the intake valve  12  can always be adjusted with high precision. 
     In the present embodiment, the control pin  48  and the pin insertion hole  38  in the control shaft  16  may be either tight fit (press-fit) or clearance fit. Even when the control pin  48  and pin insertion hole  38  are clearance fit, the control pin  48  does not back out of the pin insertion hole  38  because it is secured with the bolt  62 . When the control pin  48  and pin insertion hole  38  are clearance fit, it is possible to facilitate fabrication and achieve assembly with ease. 
     In the third embodiment, which has been described above, the shim  60  corresponds to the “interposition member” according to the first aspect of the present invention.