Flow control apparatus for a power steering device

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. Under low temperature conditions, the second relief valve first operates at the second setting pressure, and then the first relief valve operates in order to reduce the fluid pressure to the first setting pressure. With this operation, the fluid pressure delivered to the power steering device is maintained not to exceed the maximum load pressure even under low temperature condition.