Abstract: There is disclosed a flow control apparatus for a power steering device in which an operating fluid discharged from a pump is delivered to a power steering device through a restricted passage, and the fluid flow is adjusted by a spool valve movable in response to the pressure difference across the restricted passage. The spool valve contains a first relief valve operating at a first setting pressure in response to the fluid pressure transmitted from a passage located at the downstream side of the restricted passage through a connecting passage. The spool valve also contains a second relief valve operating at a second setting pressure higher than the first setting pressure, but lower than a allowable maximum load pressure, in response to the fluid pressure directly transmitted from a chamber located at the upstream side of the restricted passage. During operations under normal temperature conditions, the first relief valve operates when the load pressure reaches the first setting pressure.

Abstract: A flow volume control device for a power assisted steering device having a main control valve device, whose main valve spool is movable to establish the communication of an inlet passage with a bypass passage when the flow rate of pressurized fluid supplied from an engine-driven pump to the steering device through the inlet passage and first and second throttle passages disposed in parallel relation exceeds a predetermined value. For safe driving at a high speed, an auxiliary control valve device is further provided, whose auxiliary valve spool is moved to close the second throttle passage when high-speed driving causes pressurized fluid from the pump to increase in volume, to thereby bring about a predetermined pressure drop across said inlet passage.

Abstract: A valve system in a power steering system is disclosed. It includes a spool valve which is slidably located in a valve bore for by-passing an excess fluid at high vehicular speed in response to the pressure differential across an orifice. A control rod is slidably located in the spool valve and has at the end a metering portion for maintaining a limited flow volume when the spool valve is moved to close a by-pass port with the increase of a working pressure in the power steering system.