Abstract:
In an internal combustion engine including a valve actuating mechanism, a vibration control member made of vibration control alloy is interposed in a path of vibration transmission between a camshaft and a cylinder head. The vibration control alloy has a vibration isolation capability comparable to that of rubber, but provides a durability and a resistance to degradation comparable to those of metal and alloy that are typically used in internal combustion engines. Therefore, a desired vibration control can be achieved while ensuring a required reliability, durability and resistance to degradation. The present invention is particularly useful when the valve actuating mechanism is provided with a variable lift, variable timing or variable compression mechanism because such a variable mechanism increases the stress to the engine, and tends to cause more vibrations than a more conventional non-variable valve actuating mechanism.

Description:
TECHNICAL FIELD 
   The present invention relates to a vibration control arrangement for internal combustion engines, and in particular to a vibration control arrangement that is effective in reducing the transmission of vibrations from vibration sources in the valve actuation system and/or piston-crank system of an internal combustion engine. 
   BACKGROUND OF THE INVENTION 
   The valve actuation system of an internal combustion engine for opening and closing intake valves and exhaust valves typically uses rocker arms that are each provided with a cam engagement portion for engaging a cam formed on a camshaft and a valve engagement portion for engaging the stem end of a valve. The camshaft is rotatably supported by a cam holder provided on the cylinder head, and a rocker arm shaft that rotatably supports the rocker arm is fixed to the cam holder. In such a valve actuating mechanism, vibrations that are produced as a result of actuation of the valve are transmitted to the outside, and are emitted as noises. In particular, when variable mechanisms such as variable valve lift mechanism, variable valve timing mechanism, a variable compression ratio mechanism, etc. is used, the adjusting mechanism tends to apply an additional stress to various parts of the engine, and the vibration problems often become even more acute. The vibrations are transmitted via at least two paths. Firstly, the vibrations owing to the collision between the valve and the valve engagement portion of the rocker arm are transmitted to the cam holder via the rocker arm. Secondly, the vibrations owing to the collision between the cam and cam engagement portion of the rocker arm are transmitted to the cam holder via the rocker arm or camshaft. In either case, the vibrations transmitted to the cam holder are emitted to the atmosphere via the cylinder head, head cover and so on, and turn into noises. 
   The crankshaft system comprises a connecting rod that transmits the reciprocating movement of the piston, a crankshaft that converts the movement transmitted from the connecting rod into a rotational movement, and a bearing that rotatably supports the journal of the crankshaft. In the case of the crankshaft system, the vibrations transmitted from the connecting rod to the crankshaft and bearing are converted into noises. 
   Conventionally, the transmission of vibrations from vibration sources to various components was controlled by using vibration control material such as rubber and plastic in the path of vibration transmission from the vibrations sources in the valve actuating mechanism and crankshaft system and thereby attenuating the transmission of vibrations from the vibration sources to the various components. Such a prior attempt at reducing vibrations and noises in internal combustion engines is disclosed, for instance, in Japanese patent laid open publication 6-185522. 
   However, the vibration control material such as rubber and plastic has a poor resistance to deformation and prone to degradation as compared with metallic material such as an aluminum alloy which is typically used in various components of the engine. 
   BRIEF SUMMARY OF THE INVENTION 
   In view of such problems of the prior art, a primary object of the present invention is to provide a vibration control arrangement for internal combustion engines that are both effective and durable. 
   A second object of the present invention is to provide a vibration control arrangement for internal combustion engines that are both effective and economical. 
   A third object of the present invention is to provide a vibration control arrangement for internal combustion engines that would not impair the performance of the engine and is reliable is use. 
   According to the present invention, these and other objects can be accomplished by providing a vibration control arrangement for a valve actuating mechanism of an internal combustion engine, the valve actuating mechanism comprising a cam holder fixedly attached to a cylinder head and a camshaft formed with a cam for actuating an engine valve rotatably supported by the cam holder, wherein: a vibration control member made of vibration control alloy is interposed in a path of vibration transmission between the camshaft and the cylinder head. 
   The vibration control alloy has a vibration isolation capability comparable to that of rubber, but provides a durability and a resistance to degradation comparable to those of metal and alloy that are typically used in internal combustion engines. Therefore, a desired vibration control can be achieved while ensuring a required reliability, durability and resistance to degradation. The present invention is particularly useful when the valve actuating mechanism is provided with a variable lift, variable timing or variable compression mechanism because such a variable mechanism increases the stress to the engine, and tends to cause more vibrations than a more conventional non-variable valve actuating mechanism. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Now the present invention is described in the following with reference to the appended drawings, in which: 
       FIG. 1  is a simplified sectional view showing a valve actuating mechanism  100  to which the present invention is applied; 
       FIG. 2  is an enlarge perspective view of an essential part of  FIG. 1 ; 
       FIG. 3  is a view similar to  FIG. 1  showing the cam holder that includes various parts made of vibration control members; 
       FIG. 4  is a view similar to  FIG. 2  showing the lower cam holder that includes various parts made of vibration control member; 
       FIG. 5  is an enlarged sectional view showing the variable valve lift mechanism  120 ; 
       FIG. 6  is a simplified sectional view showing another valve actuating mechanism  100 ′ to which the present invention is applied; 
       FIG. 7  is an exploded perspective view of the valve actuating mechanism  100 ′; 
       FIG. 8  is an exploded perspective view showing a part of  FIG. 6 ; 
       FIG. 9  is a side view showing yet another valve actuating mechanism  100 ″ to which the present invention is applied; 
       FIG. 10  is a side view showing a modification of the valve actuating mechanism  100 ″ shown in  FIG. 9 ; 
       FIG. 11  is an exploded perspective view of a crankshaft system to which the present invention is applied; 
       FIG. 12  is an exploded perspective view of a modified crankshaft system to which the present invention is applied; 
       FIG. 13  is a sectional side view of a variable valve lift mechanism to which the present invention is applied; 
       FIG. 14  is a plan view of the variable valve lift mechanism shown in  FIG. 13 ; 
       FIG. 15  is a sectional side view of a head cover arrangement according to the present invention; 
       FIG. 16  is a view similar to  FIG. 15  showing a modified embodiment of the present invention; 
       FIG. 17  is an exploded perspective view of the fastening mechanism that is used in the embodiment illustrated in  FIG. 16 ; 
       FIG. 18   a  is a perspective view of a part of  FIG. 17 ; 
       FIG. 18   b  is an inverted perspective view of the part shown in  FIG. 18   b;    
       FIG. 19  is a modified fastening mechanism according to the present invention; 
       FIGS. 20 to 22  are sectional side views showing the mode of assembling the fastening mechanism of  FIG. 17 ; and 
       FIG. 23  is a sectional side view showing the mode of deformation of the fastening mechanism of  FIG. 15 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention is characterized by the fact that the parts of an engine valve system or crankshaft system that would transmit vibrations from vibration sources are made of vibration control alloy to effectively attenuate the transmission of vibrations. In the case of a valve actuating mechanism, the vibrations are typically produced as a result of impulsive contacts between each cam and the cam follower part of a corresponding rocker arm and between the valve stem of each valve and the valve stem engaging part of the corresponding rocker arm. In the case of a crankshaft system, as the combustion occurs and the resulting pressure pushes a piston, the plays that may be present in the path of power transmission between the piston and a crankshaft are impulsively closed, and this produces vibrations in various parts of the path of power transmission. 
   The vibration control alloy as used in this application includes, not exclusively, Mn—Cu and Fe—Al vibration control alloys. For instance, the vibration control alloy marketed by Daido Steel, Co., Ltd. of Japan under the tradename of M2052 can be used as such a material. These alloys are provided with mechanical strengths that are comparable to those of aluminum alloys and steels that are commonly used in the valve actuating mechanism and crankshaft system of an engine, but demonstrate a vibration control capability comparable to that of rubber or other elastomeric material. These alloys have thermal expansion coefficients similar to those of common aluminum alloys and steels, and allow clearances between various parts to be maintained within prescribed tolerances. The vibration control alloys that can be used in the present invention are not limited to those mentioned above, but may include other vibration control alloys as long as they have required mechanical strengths and vibration control capabilities. 
   Embodiments of the present invention as applied to the valve actuating mechanism of an internal combustion engine are described in the following with reference to  FIGS. 1 to 7 .  FIGS. 1 and 2  show the outline of the valve actuating mechanism  100  to which the present invention is applied. 
   The valve actuating mechanism  100  comprises a camshaft  110  integrally formed with a cam  111  and a variable valve lift mechanism  120  that opens and closes a valve  130  of the engine in dependence on the rotational angle of the cam  111 . Although the camshaft  110  is typically provided with a plurality of cams  111 , only one of them is referred to in the disclosure to simplify the description. The camshaft  110  is rotatably supported on a cam holder  140  provided on the cylinder head of the engine. 
   The camshaft  110  rotates in synchronism with a crankshaft of the engine not shown in the drawings, and the rotation of the camshaft  110  is transmitted to the rocker arm  121  via the cam  111  integrally formed on the camshaft  110 . The camshaft  110  is provided with a journal  112  rotatably supported by a bearing bore  143  of the cam holder  140 . 
   The variable valve lift mechanism  120  comprises a plurality of members  121  to  129 . The member  121  consists of a rocker arm that angularly reciprocates in dependence on the rotation of the cam  111 . The rocker arm  121  transmits the rotation of the cam  111  to the valve  130 , and is provided with an upper part and lower part that are each bifurcated. The rocker arm  121  is also fitted with an adjust bolt  129  which engages a stem end  131  of the valve  130 . 
   The upper bifurcated part of the rocker arm  121  is provided with a roller follower  122  that engages the cam  111  and is also connected to an end of an upper link  124  via an upper pin  123 . The lower bifurcated part of the rocker arm  121  is connected to an end of a lower link  126  via a lower pin  125 . The other end of the upper link  124  is pivotally connected to a rocker arm shaft  127  fixed to the cam holder  140 , and the other end of the lower link  126  is pivotally connected to a crank pin  128   b  of a crank member  128  that includes a crank web  128   c  that integrally joins the crank pin  128   b  to a crank journal  128   a  of the crank member  128 . The crank pin  128   b  of the crank member  128  can be rotatively actuated around the crank journal  128   a  by an actuator not shown in the drawings. 
   In this variable valve lift mechanism  120 , as the cam  111  of the camshaft  110  rotates and engages the roller follower  122 , the rocker arm  121  is angularly actuated around both the upper pin  123  and lower pin  125 , and opens the valve  130 . At this time, if the crank member  128  is actuated by the actuator into a rotational movement around the crank journal  128   a , the position of the crank pin  128   b  changes as indicated by arrows in  FIG. 1 , and this movement of the center of the rotational movement of the rocker arm  121  causes a change in the lift of the valve  130 . For details of this variable valve lift mechanism  120 , reference should be made to Japanese patent application No. 2002-19687 or 2003-157774 filed by the assignee of this application. 
   The cam holder  140  is attached to the cylinder head not shown in the drawings by using a pair of threaded bolts  141 . For this purpose, the cam holder  140  is formed with holes  142  for receiving these mounting bolts  141 . The cam holder  140  defines the bearing bore  143  for rotatably supporting the journal  112  of the camshaft  110 . The cam holder  140  consists of two halves, or an upper cam holder  140 A and a lower cam holder  140 B, so as to jointly define the bearing bore  143 . The cam holder  140  or, in particular, the lower cam holder  140 B is provided with a support hole  144  ( FIG. 3 ) for supporting the rocker arm shaft  127 , and a receiving hole  145  ( FIG. 3 ) for rotatatively receiving the crank journal  128   a.    
     FIG. 3  shows vibration control alloy members  11 ,  12  and  13  made of vibration control alloy that are used in the parts to which vibrations are transmitted from the vibrations sources of the cam holder  140 .  FIG. 3  shows only an essential part of  FIG. 1 . 
   As shown in  FIG. 3 , the parting plane of the upper cam holder  140 A is defined by a vibration control alloy member  11  having a prescribed thickness. In other words, the part of the upper cam holder  140 A that contacts the lower cam holder  140 B is entirely covered by the vibration control alloy member  11 . Also, the parts that provide seats for the heads of the mounting bolts  141  are each formed with vibration control alloy members  12 . In other words, the parts of the upper cam holder  140 A engaging the heads of the mounting bolts  141  are covered with the vibration control alloy members  12 . 
   Owing to this structure, the vibrations that are transmitted from the rocker arm  121  to the upper cam holder  140 A are attenuated by the vibration control member  11 , and the vibrations that are transmitted from the mounting bolts  141  to the upper cam holder  140 A are attenuated by the vibration control members  12 . 
   Similarly, as shown in  FIG. 3 , the end of the lower cam holder  140 B abutting the cylinder head not shown in the drawing (the lower end in  FIG. 3 ) is formed with a vibration control member  13  having a prescribed thickness. In other words, the part of the lower cam holder  140 B that abuts the cylinder head is covered by the vibration control member  13 . 
   Owing to this structure, the vibrations that are transmitted from the lower cam holder  140 B to the cylinder head are attenuated by the vibration control member  13 , and the transmission of vibrations from the lower cam holder  140 B to the cylinder head can be effectively controlled. The vibrations that are transmitted from the lower cam holder  140 B to the cylinder head means the vibrations that are transmitted from the rocker arm  121  to the lower cam holder  140 B and then to the cylinder head. 
     FIG. 4  shows a case where vibration control alloy members  14  and  15  are formed as cylindrical bushes, each having a prescribed thickness, that define the inner circumferential surfaces of the support hole  144  and receiving hole  145 , respectively.  FIG. 4  shows an essential part of  FIG. 1 , and omits the variable valve lift mechanism  120 . 
   As shown in  FIG. 4 , the inner circumferential surface of the support hole  1445  supporting the rocker arm shaft  127  (see  FIG. 2 ) in the lower cam holder  140 B is defined by the bush or vibration control alloy member  14 . In other words, the part of the lower cam holder  140 B engaging the rocker arm shaft  127  is covered by the vibration control alloy member  14 . 
   Owing to this structure, the vibrations that are transmitted from the rocker arm shaft  127  to the lower cam holder  140 B are attenuated by the vibration control alloy member  14 . Therefore, the transmission of vibrations from the rocker arm shaft  127  to the lower cam holder  140 B can be controlled. The vibrations that are transmitted from the rocker arm shaft  127  to the lower cam holder  140 B are vibrations that are transmitted from the rocker arm  121  (see  FIG. 2 ) to the upper link  124  (see  FIG. 2 ) and then to the rocker arm shaft  127 . 
   As shown in  FIG. 4 , the inner circumferential surface of the receiving hole  145  receiving the crank journal  128   a  (see  FIG. 2 ) in the lower cam holder  140 B is defined by the bush or vibration control alloy member  15 . In other words, the part of the lower cam holder  140 B engaging the crank journal  128   a  is covered by the vibration control alloy member  15 . 
   Owing to this structure, the vibrations that are transmitted from the crank journal  128   a  to the lower cam holder  140 B are attenuated by the vibration control alloy member  15 . Therefore, the transmission of vibrations from the crank journal  128   a  to the lower cam holder  140 B can be controlled. The vibrations that are transmitted from the crank journal  128   a  to the lower cam holder  140 B are vibrations that are transmitted from the rocker arm  121  (see  FIG. 2 ) to the lower link  126  (see  FIG. 2 ). 
     FIG. 5  shows a case where a part of the rocker arm  121  retaining the base end of the adjust bolt  129  is formed with a vibration control alloy member  16 .  FIG. 5  is an enlarged view of a part of the variable valve lift mechanism  120  illustrated in  FIG. 1 . 
   As shown in  FIG. 5 , the part of the rocker arm  121  retaining the base end of the adjust bolt  129  is formed with a vibration control alloy member  16  having a prescribed thickness. In other words, the part that retains the adjust bolt  129  is covered by the vibration control alloy member  16 . 
   Owing to this structure, the vibrations that are transmitted from the adjust bolt  129  to the rocker arm  121  as the adjust bolt  129  collides with the stem end  131  of the valve  30  are attenuated by the vibration control alloy member  16 . Therefore, the transmission of vibrations from the adjust bolt  129  to the rocker arm  121  can be controlled. 
   The variable valve lift mechanism  120  illustrated in  FIGS. 1 and 2  can continually vary the lift of the valve  130  by moving the crank pin  128   b  and changing the position of the rotational center of the rocker arm  121  by using the actuator. Therefore, in this variable valve lift mechanism  120 , as the rotational center of the rocker arm  121  moves, the moment acting upon the rocker arm  121  changes significantly. Therefore, the contact load between the cam  111  and valve  130  also changes significantly, and this causes an increase in vibrations. However, because the part through which the vibrations from the source of vibrations transmit is made of a vibration control alloy, a significant part of the vibrations can be attenuated. 
     FIGS. 6 to 8  show another embodiment of the present invention that is applied to a somewhat different valve actuating mechanism  100 ′. This valve actuating mechanism  100 ′ is similar to that shown in  FIGS. 1 to 5 , but different in the structure of the crank member  128  and the way it is supported. In this valve actuating mechanism  100 ′, the crank member  128  is shared by the variable valve lift mechanisms  120  of different cylinders. In other words, a single crank member  128  actuates a plurality of lower links  126 . Therefore, each crank journal  128   a  connects the adjoining crank webs  128   c  to each other, and a crank pin  128   b  similarly extends between adjoining crank webs  128  in parallel with and adjacent to the corresponding crank journal  128   a . Each crank pin  128   b  is connected to an end of a corresponding lower link  126 . 
   Because of this structure, the crank journal  128   a  cannot be passed through the lower cam holder  140 B from sideways as opposed to the valve actuating mechanism shown in  FIGS. 1 to 5 . Therefore, the lower cam holder  140 B is provided with a recess in a middle part of a bottom end thereof, and the crank journal  128   a  is supported by an upper bearing portion  146  formed in this recess and a bearing cap  148  secured to the recess so as to define a bearing bore  145  for the crank journal  128   a  jointly with the upper bearing portion  146 . The upper bearing portion  146  is made of a vibration control member  17 , and the bearing cap  148  is also made of a vibration control member  18 . 
   Owing to this structure, vibrations that are transmitted from the crank journal  128   a  to the lower cam holder  140 B are attenuated by the vibration control members  17 ,  18 . The vibrations that are transmitted from the crank journal  128   a  to the lower cam holder  140 B are vibrations that are transmitted from the rocker arm  121  (See  FIG. 6 ) to the lower link  126  (See  FIG. 6 ). 
     FIG. 9  shows yet another embodiment of the present invention applied to a valve actuating mechanism  100 ″ somewhat different from that shown in  FIGS. 1 to 5 . This valve actuating mechanism  100 ″ uses an oil tappet  161 . In this embodiment, a part of the cylinder head  160  that retains the oil tappet  161  is made of a vibration control member  19 . Otherwise, the valve actuating mechanism  100 ″ is similar to that shown in  FIGS. 1 to 5 , and the parts corresponding to the previous embodiment are denoted with like numerals without repeating the description of such parts. 
   The valve actuating mechanism  100 ″ illustrated in  FIG. 9  comprises a rocker arm  150  that opens and closes a valve  130  in dependence on the rotation of the cam  111 . One end of the rocker arm  150  is formed with a valve engaging portion  151  that engages a stem end  131  of the valve  130 , and the other end of the rocker arm  150  is provided with an oil tappet socket  152  that receives a semi-spherical head of the oil tappet  161  retained in the cylinder head  160 . The part of the cylinder head  160  retaining the base end of the oil tappet is made of a vibration control member  19 . In other words, the base portion of the oil tappet  161  is covered by the vibration control member  19 . 
   Owing to this structure, when the oil tappet socket  152  has pressed upon the head of the oil tappet  161 , the resulting vibrations are transmitted from the oil tappet socket  152  to the head of the oil tappet  161 , but are attenuated by the vibration control member  19 . Therefore, the transmission of vibrations from the rocker arm  150  to the cylinder  160  can be effectively controlled. 
     FIG. 10  shows yet another embodiment of the present invention applied to a valve actuating mechanism  100 ′″ somewhat different from that shown in  FIG. 9 . This valve actuating mechanism  100 ′″ is similar to that shown in  FIG. 9 , but differs from it in the positioning of the oil tappet  161 . In this embodiment, a tappet socket member  181  defining a socket for receiving a spherical head of an oil tappet  172  is retained by a member that is made of a vibration control member  20 . Otherwise, the valve actuating mechanism  100 ′″ is similar to that shown in  FIG. 9 , and the parts corresponding to the previous embodiment are denoted with like numerals without repeating the description of such parts. 
   The valve actuating mechanism  100 ′″ illustrated in  FIG. 10  comprises a rocker arm  170  that opens and closes the valve  130  in dependence on the rotation of the cam  111 . One end of the rocker arm  170  is formed with a valve engaging portion  171  that engages a stem end  131  of the valve  130 , and the other end of the rocker arm  170  is provided with an end pivot  172  consisting of a semi-spherical member that is received in the socket defined in the tappet socket member  181  retained by the cylinder head  180 . The part of the cylinder head  180  that retains the socket member  181  is made of a vibration control member  20 . In other words, the recess defined in the cylinder head  180  to retain the socket member  181  is covered by the vibration control member  20 . 
   Owing to this structure, when the end pivot  172  hits the tappet socket member  181 , the vibrations that are transmitted from the end pivot  172  to the tappet socket member  181  are attenuated by the vibration control member  20 . Therefore, the transmission of vibrations from the rocker arm  170  to the cylinder head  180  can be effectively controlled. 
     FIG. 11  shows yet another embodiment of the present invention applied to a crankshaft system. The outline of the crankshaft system is now described with reference to  FIG. 11  which is a simplified perspective view of a crankshaft system. 
   As shown in  FIG. 11 , the crankshaft system  200  comprises a crankshaft  210  which converts a reciprocating movement (movement of a piston in an internal combustion engine) transmitted by a connecting rod not shown in the drawing into a rotational movement, and bearings member  221  that each support a journal  211  of the crankshaft  210 . Each bearing member  221  is semi-cylindrical in shape, and may be secured in position by using any conventional means or, alternatively, is integrally cast in the cylinder block  220 . Each bearing member  221  may be provided with a liner that is made of metal or alloy having a lubricating property or steel. A pair of opposing bearings member  221  define a complete bearing for the corresponding journal  211 . 
   In the illustrated embodiment, the bearing member  212  is made of a vibration control member  21 . Because the bearing member  212  is made of the vibration control alloy, the vibrations that are transmitted from the journal  211  to the bearing member  212  are attenuated by the bearing member  212 . Therefore, the transmission of vibrations from the journal  211  to the bearing members  221  can be favorably controlled. The vibrations that are transmitted from the journal  211  to the bearing members  221  are vibrations that are transmitted from a connecting rod not shown in the drawing to the crankshaft  211 . 
     FIG. 12  shows an embodiment in which the bearing member  221  is also integrally cast in the cylinder block  220 , and the bearing member  221  is made of a vibration control alloy. The bearing member  221  in this case consists of a rectangular block defining a semi-cylindrical bearing surface. More specifically, the bearing member  221  is placed in the mold for casting the cylinder block  220 , and is integrally joined to the cylinder block  220  as a result of the casting process. 
   Owing to this structure, the vibrations that are transmitted from the journal  211  to the cylinder block  220  via the bearing member  221  are attenuated by the vibration control member  22 . Therefore, the transmission of vibrations from the journal  221  to the cylinder block  220  can be favorably controlled. The vibrations that are transmitted from the journal  211  to the cylinder block  220  are vibrations that are transmitted from the connecting rod not shown in the drawings to the crankshaft  210 . 
   The vibration control arrangement of the present invention can also be applied to a variable lift valve actuating mechanism that comprises a plurality of rocker arms that provide different valve lifts and a means for selecting one of the rocker arms so that a desired valve lift may be achieved by selecting one of the rocker arms. In such a valve actuating mechanism, when different rocker arms are selected one after the other, large vibrations may be generated owing to the collision between the cam and rocker arm and between the rocker arm and valve. Therefore, by forming a part through which the vibrations from the vibration sources are transmitted with a vibration control member, vibrations that could be produced when changing one rocker arm to another can be attenuated, and the generation of large vibrations at such a time can be avoided. 
   Such a variable lift valve actuating mechanism  190  is illustrated in  FIGS. 13 and 14 . A camshaft  191  is provided with a pair of low speed cams  192   a ,  192   b  and a high speed cam  193 . A rocker shaft  194  pivotally supports three rocker arms  195   a ,  195   b ,  196  one next to the other so as to correspond to the low speed cams  192   a ,  192   b  and high speed cam  193 . A guide hole  197  is formed across the rocker arms  195   a ,  195   b ,  196  in parallel with the axial direction of the rocker shaft  194 , and connecting pins  198  are received in the guide hole  197  to selectively engage and disengage the rocker arms with and from each other by selectively supplying oil pressure into an oil passage  199  that is defined inside the rocker shaft  194  and communicates with the guide hole  197 . For details of this variable lift valve actuating mechanism, reference should be made to Japanese patent application No. 2000-388410. 
   The vibration control arrangement according to the present invention can also be applied to the big end of a connecting rod. In such a case, the bearing metal that is used at the big end of the connecting rod may be made of a vibration control member so as to attenuate the vibration that are transmitted from the piston to the connecting rod. Thereby, the transmission of the vibrations can be favorably controlled. 
   The present invention is also applicable to a variable compression ratio internal combustion engine. In such an engine, when a high compression ratio is selected, the engine is subjected to a relatively high load, and relatively large vibrations tend to be produced in the crankshaft system. Therefore, by using a vibration control member in the path of vibration transmission from a vibration source, the transmission of vibrations can be effectively controlled. For details of such a variable compression engine, reference should be made to Japanese patent laid open publication No. 2001-227367. 
     FIG. 15  is a sectional view of a valve actuating mechanism. A valve chamber  221  defined between a cylinder head  220  and a head cover  260  accommodates a valve actuating mechanism  250  for actuating engine valves. The valve actuating mechanism  250  is mounted on the cylinder head  220  via a cam holder not shown in the drawings. The valve chamber  221  is filled with oil mist when the engine is operating, and a seal member  224  is interposed between the head cover  260  and cylinder head  220  to prevent leakage of such oil mist as well as oil which is normally present in the valve chamber  221  in liquid form. Numeral  222  denote engine valves. 
   The head cover  260  is secured in place by threaded bolts  270  that are passed through openings provided in the head cover  260  and threaded into threaded holes  221  formed in the cylinder head  220 . An annular rubber bushing  280  is interposed between the head of each threaded bolt  270  and the opposing outer surface of the head cover  260 . In this embodiment, each rubber bush  280  is received in a complementary recess defined on the exterior of the head cover  260 . The rubber bushing  280  provides the function of damping and insulting vibrations as well as the function of providing a seal. If desired, the rubber bushing  280  may be replaced with a similar member made of vibration control alloy. 
   During the operation of the valve actuating mechanism  250 , the vibrations produced from the valve actuating mechanism are transmitted to the head cover  260  via the mounting bolts  270 . If there is any gap between the head cover  260  and mounting bolts  270 , the head cover  260  may rattle, and it may cause noises. In particular, when the head cover  260  is not given with an adequate rigidity, there is a greater tendency to produce noises. 
   In the embodiment illustrated in  FIG. 15 , the mounting bolts  270  are made of vibration control alloy. The vibration control alloy that forms the mounting bolts is preferably given with a vibration attenuation ratio of 0.05% or more, and is provided with similar mechanical properties as soft steel. Thus, by forming the mounting bolts with vibration control members, the vibrations transmitted from the cylinder head are attenuated in the head cover, and this significantly contributes to the reduction in noises. 
   In the embodiment illustrated in  FIG. 15 , the annular seal member  224  is made of a vibration control alloy that is preferably given with an attenuation ratio of 0.05% or more. By thus forming the annular seal member  224  with a vibration control member, the transmission of vibrations from the cylinder head  220  to the head cover  260  can be minimized and the generation of noises is minimized as a result. Because the vibration control member is substantially more durable than rubber or other elastomeric material, no gap is created between the seal member and cylinder head even after an extended period of time. This ensures a required sealing capability and prevents rattling of the head cover. As a result, it becomes possible to mount a component such as a rotational angle sensor that requires a high positional precision on the head cover. 
   If desired, the head cover may be made of vibration control alloy while the annular seal member is made of rubber or other elastomer. 
     FIG. 16  shows a modified embodiment of the present invention which is similar to the embodiment illustrated in  FIG. 15 , but differs from the previous embodiment in that the mounting bolts are replaced by fastening members  210  that are essentially made of coil springs. 
   Referring to  FIG. 17 , the fastening member  210  comprises a first threaded bolt  211  provided at one end, a second threaded bolt  212  provided at the other end, and a spring member  213  consisting of a tension coil spring. The first threaded bolt  211  consists of a substantially cylindrical base portion  211   a  and a threaded portion  211   b  which is coaxial with the cylindrical base portion  211   a  and reduced in diameter. The base portion  211   a  is provided with a pair of side faces  211   c  that are flat and parallel to each other. 
   The second threaded bolt  212  consists of a base portion  212   a  having a hexagonal cross section and a threaded portion  212   b  which is coaxial with the base portion  212   a . The base portion  212   a  may be provided with other shapes as long as it may be engaged by a tool to turn it. 
   The spring member  213  joins the base portions  211   a  and  212   a  of the first and second threaded bolts  211  and  212 . The spring member  213  may consist of a member that can provide a resilient reaction when extended, and is preferably made of readily deformable material such that the vibrations may be attenuated as they travel from one end to the other. Therefore, the spring member  13  may not be spiral as illustrated in  FIGS. 17 and 18 , but may also consist of a two-dimensional zig-zag shaped member, for instance, as illustrated in  FIG. 19 . 
   The fastening member  210  is used in combination with a nut  220 , which in this embodiment consists of a cap nut, adapted to be threaded with the threaded portion  211   b  of the first threaded bolt  211 , and a washer assembly  230  defining an inner opening  231   a ,  232   a  complementary in shape to the outer profile of the base portion  211   a  of the first threaded bolt  211 . As illustrated in  FIGS. 18   a  and  18   b , the washer assembly  230  includes a washer main body  231  made of metal, plastic or other relatively hard material and a bush  232  that is made of rubber or other elasomeric material and integrally joined with the washer main body  231  in a coaxial relationship. The washer main body  231  and bush  232  jointly define the inner opening  231   a ,  232   a . The outer periphery of the washer main body  231  is provided with a pair of mutually parallel straight edges  231   b.    
   The mode of mounting the fastending member  210  is described in the following. Referring to  FIG. 20 , the threaded portion  212   b  of the second threaded bolt  212  is threaded into a threaded hole  251  formed in the cylinder head  250 . Preferably, a washer  240  is interposed between the base portion  212   a  of the second threaded bolt  212  and opposing surface of the cylinder head  250 . 
   Referring to  FIG. 21 , the first threaded bolt  211  is passed through an opening  261  provided in the head cover  260 , and the washer assembly  230  is fit on the base portion  211   a  of the first threaded bolt  211  from outside. The cap nut  220  is threaded with the threaded portion  211   b  of the first threaded bolt  211  while the straight edges  231   b  of the washer main body  230  are engaged by a suitable tool. Thus, the cap nut  220  can be fastened while the first threaded bolt  211  is prevented from turning. 
   As a result, the bush  232  having a larger diameter than the opening  261  of the head cover  260  provides both a cushioning function to the pressure of the washer main body  231  and a sealing function when the cap nut  220  is fully threaded with the threaded portion  211   b  of the first threaded bolt  211  and the spring member  213  is extended until a desired tension is produced in the spring member  213 . 
   If the fastening member is made of vibration control alloy, it can attenuate the vibrations even further. The fastening member may be entirely made of vibration control alloy or partially made of vibration control alloy.  FIG. 23  shows how the vibrations are attenuated by the deflection of the spring member  10 . 
   Although the present invention has been described in terms of preferred embodiments thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims. 
   The contents of the original Japanese patent application(s) on which the Paris Convention priority claim is made for the present application are incorporated in this application by reference.