Importance

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Abstract

A variable displacement axial piston pump (11) is disclosed of the type including a displaceable cam member (39) to vary the pump displacement in response to operation of a fluid pressure actuated servo assembly (15). The servo assembly includes a servo piston (47), the position of which is controlled in response to control fluid in a pair of servo chambers (53,55). The flow of control fluid pressure from a charge pump (27) to the servo chambers is controlled by a manual controller (17), which includes a main control orifice (105). The nominal gain rate of the pump and servo assembly is determined largely by the main control orifice (105). The servo piston (47) defines a servo orifice (113) communicating between the servo chambers. The servo orifice is sized, relative to the main control orifice whereby, for relatively large control inputs, the gain rate is substantially equal to the nominal gain rate, but for relatively small inputs, the gain rate is substantially less than the nominal gain rate, to provide smoother, more controllable operation of the vehicle.

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First Claim