초록 ▼

An angular position of a lever with which a rocker arm contacts to define a fulcrum therebetween is varied by rotation of a cam which is installed in a manner to be rotatable relative to its cam shaft and drivingly connected through a spring to the cam shaft or to an output shaft of a driving system

An angular position of a lever with which a rocker arm contacts to define a fulcrum therebetween is varied by rotation of a cam which is installed in a manner to be rotatable relative to its cam shaft and drivingly connected through a spring to the cam shaft or to an output shaft of a driving system.

대표청구항 ▼

1. A variable valve timing mechanism for a valve of an internal combustion engine, comprising: a lever pivotally mounted at one end thereof; a rocker arm engaging said lever to define fulcrum therebetween; a cam shaft located adjacent the other end of said lever; a cam having a hole through wh

1. A variable valve timing mechanism for a valve of an internal combustion engine, comprising: a lever pivotally mounted at one end thereof; a rocker arm engaging said lever to define fulcrum therebetween; a cam shaft located adjacent the other end of said lever; a cam having a hole through which said cam shaft extends in a manner to allow said cam to be rotatable relative thereto, said cam engaging said other end of said lever and rotatable to vary an angular position of said lever relative to said rocker arm for thereby varying the timing of said valve; driving means for driving said cam in accordance with engine operating conditions and including a rotatable output shaft; and resilient means for resiliently transmitting rotational motion of said output shaft to said cam so as to cause rotation of said cam in response to rotation of said output shaft when said rocker arm assures a predetermined position being in non-actuating contact with said valve. 2. A variable valve timing mechanism as set forth in claim 1, in which said cam is loose-fitted on said cam shaft. 3. A variable valve timing mechanism as set forth in claim 1, in which said cam is formed with two cam surfaces which are spaced axially of said cam shaft and which have the same cam profile. 4. A variable valve timing mechanism as set forth in claim 1, said cam is formed with a curved cam surface throughout the outer circumference thereof, said curved cam surface being formed so that it receives from said lever a load toward the center of rotation of said cam when brought into contact at two diametrically opposed cam surface portions, said cam being brought into contact at said two diametrically opposed cam surface portions with said lever under high engine speed conditions and low engine speed conditions, respectively. 5. A variable valve timing mechanism as set forth in claim 1, in which said driving means further comprises a drive shaft drivingly connected to said output shaft, a pair of cog wheels respectively mounted on said drive shaft and said cam shaft for rotation therewith and a cog belt arranged to pass about said cog wheels for transmission of power therebetween, and in which said resilient means comprises a coil spring interposed between said cam and one of said cog wheels mounted on said cam shaft and yieldingly interconnecting while urging same in the opposite directions, and an abutment mounted on said cam shaft for holding said cam axially in place on said cam shaft under the bias of said spring. 6. A variable valve timing mechanism as set forth in claim 1, further comprising guiding means for guidingly connecting said rocker arm at a point intermediate between the ends thereof with said lever, and spring means interposed between said rocker arm and said lever for urging said other end of said lever against said cam. 7. A variable valve timing mechanism as set forth in claim 6, in which said guide means comprises a shaft secured to said rocker arm at a location intermediate between the ends thereof in a manner to project out from either side of the rocker arm, a pair of guide forks provided to either side of said lever and respectively formed with guide slots and a pair of rectangular slides respectively formed with round guide holes and mounted in said guide slots for movement along same but against rotation about the axes of said round guide holes, said shaft being rotatably received at its opposite end portions in said guide slots. 8. A variable valve timing mechanism as set forth in claim 1, in which said cam is formed with at least one nearly flat cam surface portion. 9. A variable valve timing mechanism as set forth in claim 8, in which said cam is formed with said nearly flat cam surface portion at a location where it is brought into contact with said lever under high engine speed conditions. 10. A variable valve timing mechanism as set forth in claim 1, in which said cam has an annular stepped configuration and includes a larger-circumference central portion and a pair of smaller-circumference journal portions which are axially aligned with each other and protrude from said central portion in opposite directions, said cam being formed with a cam surface at said central portion and rotatably mounted at said journal portions on said engine. 11. A variable valve timing mechanism as set forth in claim 10, in which said resilient means comprises a pair of coil springs positioned around said cam shaft and yieldingly interconnecting said journal portions and said cam shaft. 12. A variable valve timing mechanism as set forth in claim 11, in which said cam shaft is directly connected to said output shaft of said driving means. 13. A variable valve timing mechanism as set forth in claim 1, in which said resilient means comprises a spring positioned around said cam shaft and yieldingly interconnecting said cam and said cam shaft. 14. A variable valve timing mechanism as set forth in claim 13, in which said spring is a coil spring. 15. A variable valve timing mechanism as set forth in claim 13, in which said spring is a spiral spring. 16. A variable valve timing mechanism as set forth in claim 13, in which said resilient means further comprises a groove formed in said cam at an end opposite to the end connected to said spring and a pin secured to said cam shaft and movable in said groove, said groove having a predetermined angular extension and said pin being engageable with the ends of said groove to limit a rotatable extent of said cam relative to said cam shaft. 17. A variable valve timing mechanism as set forth in claim 1, in which said driving means further comprises a first gear rotatably mounted on said cam shaft, a second gear meshed with said first gear and a drive shaft drivingly connected to said output shaft and mounting thereon said second gear to rotate therewith, and in which said resilient means comprises a coil spring interposed between said cam and said first gear and yieldingly interconnecting while urging same in opposite directions, and a pair of abutments mounted on said cam shaft for holding said cam and said first gear axially in place on said cam shaft under the bias of said coil spring. 18. A variable valve timing mechanism as set forth in claim 17, in which the number of teeth of said first gear is larger than that of said second gear. 19. A variable valve timing mechanism as set forth in claim 17, in which said abutments comprise a pair of snap rings. 20. A variable valve timing mechanism as set forth in claim 17, in which said cam shaft is stationarily mounted on said engine. 21. A variable valve timing mechanism as set forth in claim 20, in which said cam has a plurality of nearly flat cam surface portions for inducing a stepwise variation of the timing of said valve, said cam also having a waved signal end opposite to the end facing said first gear, and in which said resilient means further comprises a collar secured to said cam shaft and having a waved end, said waved ends of said cam and said collar being so formed that they snugly fit in each other only when some of said cam surface portions is correctly in contact with said lever. 22. A variable valve timing mechanism as set forth in claim 1, in which said driving means further comprises a drive shaft drivingly connected to said output shaft, a main pulley mounted on said drive shaft for rotation therewith, a follower pulley mounted on said cam shaft for rotation therewith and a belt arranged to pass about said pulleys for transmission of power therebetween, and in which said resilient means comprises a coil spring interposed between said cam and said follower pulley and yieldingly interconnecting while urging same in the opposite directions, and an abutment mounted on said cam shaft for holding said cam axially in place on said cam shaft under the bias of said spring. 23. A variable valve timing mechanism as set forth in claim 22, in which said main pulley is smaller in diameter than said follower pulley. 24. A variable valve timing mechanism as set forth in claim 23, in which said belt is of a round section. 25. A variable valve timing mechanism as set forth in claim 23, in which said belt is a flat belt.