| 摘要 |
A mechanism for operating one or more valves of a piston device, in particular an intake or exhaust valve of an internal-combustion engine, which valve can move between an open position and a closed position and is provided with associated restoring means for returning the valve to the closed position. The mechanism comprises a hydraulic valve actuator for operating the valve of the piston device, which valve actuator has a variable chamber which is delimited by a piston which can be coupled to the valve, in such a manner that when hydraulic fluid is supplied to the said chamber the valve opens. Furthermore, there are rotatable first and second cams, each having an associated cam follower, the relative angular position of the first cam and the second cam with respect to one another being adjustable. The mechanism also comprises a pressure actuator in which there is a pressure chamber having a variable volume and having a first and a second plunger, the first cam follower being coupled to the first plunger and the second cam follower being coupled to the second plunger, and retraction of one plunger leading to a reduction in the volume of the pressure chamber. The pressure chamber of the pressure actuator is connected to the variable chamber of the valve actuator to form a common chamber. The common chamber is provided with an opening, which opening has an associated valve assembly for opening and closing the opening. In the open position, the hydraulic pressure is insufficient to open or hold open the valve. The mechanism is designed in such a manner that, at the moment at which the first plunger begins to move out of the extended position into the retracted position, the second plunger is in its retracted position or has almost reached its retracted position, in such a manner that the valve which is operated by the valve actuator opens as a result of the retracting movement of the first plunger.
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