Hydraulic control apparatus for load independent flow regulation

A flow control apparatus adapted to provide load independent flow regulation in a hydraulic power system or the like, and characterized by the ability to minimize the idling power consumption of the pump when the load is removed from the system, and comprising,

• a housing having a cylindrical bore therein, said bore having closed opposite ends so as to define first and second opposite end portions;
• a pump inlet channel, a sump outlet channel, and a consumer channel, all communicating with said bore in said housing,
• a balance piston slidably disposed in said bore and movable between a bypass or idling postion wherein fluid flows from said pump inlet channel through said bore to said sump outlet channel, and an operating postion wherein such flow is precluded,
• means for conducting fluid from said pump inlet channel into said first end portion of said bore and so as to act against a first end of said piston to urge the piston in a direction toward its bypass position,
• means for urging the piston in the opposite direction and toward its operating postion, and including
• (a) passageway means for conducting fluid from the consumer channel into said second end portion of the bore and so as to act against the second end surface of the piston, and
• (b) a spring disposed in said second end portion of said bore and having one end thereof disposed in contact with said second end of said piston, the improvement therein comprising
• a retaining piston slidably mounted in a cavity disposed in said housing in communication with said first end portion of said bore, said cavity having a transverse dimension substantially greater than that of said bore and said retaining piston having an enlarged head closely received within said cavity and a body portion extending axially toward said first end of said balance piston, with said head defining a forward bore portion between said head and said first end of said balance piston, and a rearward bore portion on the opposite side of said head,
• control means for alternatively
• (a) conducting fluid from said pump inlet channel to said forward bore portion while opening said rearward bore portion to said sump outlet channel, to thereby withdraw said retaining piston from contact with said balance piston, or
• (b) conducting fluid from said pump inlet channel to said rearward bore portion while opening said forward bore portion to said sump outlet channel, to thereby bias said retaining piston into contact with said balance piston,
• whereby the retaining piston is adapted to amplify the force tending to move the balance piston toward the bypass position and against the spring during non-operation of a consumer load, and the amplifying force is removed during operation of the consumer load, to thereby minimize the pressure of the fluid in the pump inlet channel which is required to move the balance piston to the bypass position.