| 摘要 |
An engine valve system is described which comprises two cams 16, 18 mounted coaxially, a summation rocker 40 coupled to followers of both cams and movable in proportion to the instantaneous sum of the lifts of the respective cams and a valve actuating rocker 42 coupled to the summation rocker and operative to open an engine valve in dependence upon the movement of the summation rocker. The first cam 16 is driven by the engine crankshaft and the second cam 18 is coupled to the first cam by way of an actuator 30 that enables the relative phase of the two cams 16 and 18 to be controlled. The actuator 30 driving the second cam 18 is acted upon by an auxiliary load 32, 34, 36 which is such that the reaction torque experienced by the actuator during an engine cycle undergoes periodic reversals of direction. The auxiliary load may be a resilient member such as a spring or it may be a fuel pump, vacuum pump or oil pump or a combination of such loads. The actuator 30 includes mechanisms for selectively preventing relative rotation of the two cams in opposite directions, so that reaction torques acting on the actuator can be utilised to vary the relative phase of the two cams in both directions. |
