Flow control apparatus for power steering

Abstract

In order to prevent sudden fluctuations in the supply of hydraulic fluid fed to a power steering or like servo mechanism and to enable the downshifting of a transmission used to drive the pump and an ancillary device such as an alternator, at speeds suited to the specifications of the alternator, a 'flow-down' valve induces first and second flow reductions which are separated by an engine speed range which enables the higher downshift speed to be selected at an engine speed suited to the specifications of the alternator. The first flow reduction or flow-down occurs within a relatively narrow engine speed range. This facilitates the above mentioned selection and additionally enables a change from a high power steering assist at low speed to an intermediate one. The second 'flow-down' enables a more gradual change from the intermediate assist to a low level one suitable for high speed driving. In the embodiment of the invention, the engine speeds at which the transmission is downshifted are selected to correspond to the pump speed just before and just after the first flow reduction occurs in the upshift and downshift conditions of the transmission, respectively. Shifting of the transmission due to sharp changes in load is inhibited when the engine is operating between the first and second speeds.