| 摘要 |
An apparatus for varying the motion characteristics of a valve typically in an engine includes a rotating member such as a valve crank shaft having a conrod with a sliding pin. The sliding pin is constrained to move along a path in a guide member. The guide member is adjustably attached to the engine, and by adjusting the position of the guide member, the trajectory taken by the pin can be varied. The pin also moves along a path of a pivotally attached rocker arm, the path of the rocker arm being different to the path of the guide member. The difference in the paths causes the rocker arm to pivot, and this in turn causes motion in a valve in contact with the end of the rocker arm. By moving the guide member, the differences in the path of the guide member and rocker arm can be accentuated or minimised, thereby altering the motion characteristics of the rocker arm and in turn the valve. This enables the valve opening duration and/or valve lift to be varied. The valve may be fixed to the end of the valve to allow for desmodromic valve actuation, or the valve may include a spring to keep the valve stem in contact with the rocker arm. In one embodiment the rocker arm has an actuator having contact surfaces on the valve which are of substantially constant diameter, in order for the valve clearance to be kept constant as the rocker arm pivots to open and close the valve. An apparatus for adjusting the valve clearance on the above device, including a valve stem having a thread is also disclosed.
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