Hydraulic supply circuit for vehicle steering system

Claim 1

In an hydraulic supply circuit for a vehicle power steering system of the type having a steering actuator and control valve therefor with hydraulic input, sump and overflow connections and in which any pressurized fluid not consumed by the actuator is diverted to the overflow connection, the combination comprising a positive displacement pump having a sump connection and an output line, a drive therefor, the output line being connected to the input connection of the steering system, a gas/oil accumulator having a charging line and a discharging line, an unloading valve in the charging line for diverting fluid from the charging line to the sump when the accumulator has been charged to maximum rated pressure, a charge-discharge valve having charge and discharge passages alternatively open in respective charge and discharge modes but otherwise closed, the charge passage being interposed between the overflow connection and the accumulator charging line so that in the charge mode the accumulator is charged by the overflow, the discharge passage being interposed between the accumulator discharge line and the input connection of the steering system so that in the discharge mode pressurized fluid is supplied from the accumulator to the input connection for maintaining the steering system in operation while the overflow connection is blocked, and means including a flow sensing device in the output line of the pump for maintaining the charge-discharge valve in its charge mode as long as fluid is pumped at normal rate by the pump but for causing the charge-discharge valve to switch to its discharge mode for emergency steering upon interruption of the flow.