Hydraulic system with flow control means to control pressure distribution between a primary and a secondary hydraulic circuit

Claim 1

Flow control means for use in a hydraulic system of the type comprising pumping means having an outlet port and an inlet port in association with means forming a primary hydraulic circuit and a separate secondary hydraulic circuit comprising: means forming a valve chamber in fluid communication with the pump outlet port; a spool valve linearly movable in said valve chamber and having an orifice through which fluid flow from the pump outlet port is directed, said chamber having axially spaced control lands and openings forming a first flow path which together which said orifice communicates the pump outlet port with the primary circuit and a second flow path for communicating the pump outlet port with the secondary circuit, continuous biasing means loading said valve in one direction; action surfaces on said spool valve subject to the pressures on opposite sides of said orifice to adjust the spool valve linearly against said bias as a function of the pressure drop across said orifice; first and second axially spaced valve lands and a recess on said spool valve controlling the flow of fluid to the secondary circuit as a function of the movement of said valve, said axially spaced valve lands being disposed relative to said contrOl lands and said openings in said valve chamber to supply fluid only to said primary circuit during a first mode of operation whenever the pump flow rate is below a preselected level and to direct the fluid flow to both the primary and secondary circuits whenever the flow rate exceeds the preselected level; a pressure relief valve comprising a cored passage intersecting and connecting to said outlet port, a second spool valve in said passage, biased against a valve seat by a spring, a second passage in said second spool valve connecting said outlet port to an exit port, said second passage being maintained in normally closed position by a spring-biased ball, a stationary chamber at the exit port end of said second spool valve having a restricting orifice in communication with said exit port thereby to create pressure buildup behind said second spool valve upon opening of said ball and move said second spool valve to a position to open a large area which can handle the entire pump output with minimum pressure differential between cracking and full bypass.