Patent ID: 6595170
Filing Date: 2003-07-22
Classification: F01L,F02B,Y02T

Abstract:
A mechanism for operating a valve of a piston device, 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,which 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, a rotatable first cam with a first cam profile, a rotatable second cam with a second cam profile, the first cam profile and the second cam profile each comprising a rising flank, a stationary flank and a falling flank, a first cam follower which can be operated by the first cam, a second cam follower which can be operated by the second cam, the relative angular position of the first cam and the second cam with respect to one another being adjustable, 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, in such a manner that a plunger is stationary if the associated cam follower is operated by the stationary flank, the first and second plungers each being displaceable between a retracted position and an extended position, in such a manner that the position of the first and second plungers defines the volume of the pressure chamber, the retraction of a plunger leading to a reduction in the volume of the pressure chamber, the pressure chamber of the pressure actuator being connected to the variable chamber of the valve actuator to form a common chamber, the common chamber being provided with a common chamber opening which common chamber opening has an associated valve assembly for opening and closing the common chamber opening, wherein that the valve assembly associated with the common chamber opening is adapted to open said common chamber opening if the first plunger moves to the extended position or if the second plunger moves to the retracted position, so that hydraulic fluid can flow out of the common chamber, and wherein if the common chamber opening is open the hydraulic pressure in the common chamber is insufficient to open or hold open the valve operated by the hydraulic valve actuator, and in that 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; in which the valve assembly has a housing in which there is a first rotatable valve body and a second rotatable valve body which each rotate in an associated bore in the housing, in which the first valve body rotates at the same speed as the first cam and has a fixed angular position with respect to the said first cam and in which the second valve body rotates at the same speed as the second cam and has a fixed angular position with respect to the said second cam, in which each body is provided with a recess extending through an arc in the circumference of the valve bodies, and in which the housing is provided at each bore with a connection to the common chamber and with ports which are connectable to a hydraulic system, the recesses each having such an extension that said common chamber opening is open during the movement of the first plunger from the retracted position to the extended position and also during the movement of the second plunger from the extended position to the retracted position, so that hydraulic fluid can flow out of the common chamber.