Load plus differential pressure compensator pump control assembly

Abstract

A first device for controlling the position of a displacement control member of a variable displacement pump has an actuator connected to the control member and a valve member which is movable between a first position at which a pump discharge pressure signal is in communication with the actuator and a second position at which said pump discharge pressure signal is blocked from communication with the actuator and the actuator is connected to a drain. The valve member has an end substantially continuously exposed to the pump discharge pressure signal and is responsive thereto for biasing the valve member toward one of the first and second positions. A spring apparatus biases the valve member toward the other of said positions in opposition to the biasing force of said pump discharge pressure signal and establishes a preselected minimum discharge pressure. A second device increases the biasing force of the spring apparatus for increasing the pump discharge pressure in response to a load pressure signal exceeding a preselected pressure level. The spring apparatus has a first spring positioned between the second device and the valve member and a second spring positioned between the housing and the valve member. The second spring biases the valve member toward said other position independently of the first spring for maintaining the pump discharge pressure at a preselected value above the load pressure signal only in response to the pump discharge pressure exceeding the preselected minimum discharge pressure level.