VENTILTIDSSTYRING I FLUIDARBEJDSMASKINE

A fluid-working machine has a working chamber of cyclically varying volume, high and low pressure manifolds, and high and low pressure valves for regulating the flow of fluid between the working chamber and the high and low pressure manifolds respectively. A controller actively controls at least one said valve to determine the net displacement of working fluid of the working chamber on a cycle by cycle basis. At least one said valve is a variable timing valve and the controller causes the valve to open or close at a time determined taking into account one or more properties of the performance of the fluid working machine measured during an earlier cycle of working chamber volume. Properties of the opening or closing of a monitored valve may be taken into account. The variably timed valve may therefore be opened or closed at an optimum time to achieve efficient and reliable operation of the fluid-working machine. The magnitude of the opening or closing force applied to a valve member may also be varied.