| 摘要 |
The intake and exhaust poppet valves are opened/ closed by respective camshafts via hydraulic elements transmitting the actuating force from the cams to the associated valves. Each camshaft is driven at engine speed and each cam has an actuating profile of duration at least the same in numerical value as the intended valve opening duration for the engine in four-stroke mode. The lost-motion system comprises a hydraulic tappet 22 in a cylinder 24 and a fast-acting solenoid valve 30 for opening and closing an oil release path from the cylinder 24 to a reservoir 26. In four-stroke mode the lost-motion is controlled to deactivate one cam event in every two revolutions of the camshaft while in two-stroke mode the lost-motion is controlled to permit activation of every cam event on the camshaft and at the same time modify the duration of each cam event to produce a shorter valve opening duration. An electromagnetic percussion hammer unit 50, having coils 48, armature 46 and hammer 44 with resilient striking pad 42, is provided to impart a shock pulse of pressure to the tappet 22 to arrest the closing velocity of the valve 12 as it approaches its seat. |
