Power steering valve

Claim 1

A hydraulic control valve for a vehicle power steering system comprising an inlet port and a return port for hydraulic fluid flow supplied by a pump, a hydraulic motor means for effecting a right or left turn force as a function of a pressure differential between right and left sides in said motor means, corresponding outlets formed in said valve for respective fluid flow connection to said right and left sides of said motor means, said motor means being connected to supplement turning forces transmitted from a steering wheel to vehicle wheel steering means, said valve having at least one pair of symmetrical passages connecting the inlet port to the return port, each passage having spaced therein a first variable area orifice adjacent said inlet port and a second variable area orifice adjacent said return port defined by relatively movable parts of the valve with one of said outlets respectively interposed in each said passage between said first and second orifices, said orifices being arranged in each said passage so that, by reason of relative movement between said parts, when the first orifice in the one passage is in the course of opening the second orifice is in the course of closing and when the first orifice in the one passage is in the course of closing the second orifice is in the course of opening according to the magnitude of turning forces applied to produce relative movement of said parts so that hydraulic fluid is directed towards the interposed outlet of the respective passage or away therefrom respectively to cause said motor means to produce a force supplementing said turning forces, the improvement comprising in that, in each of said at least one pair of passages, an additional orifice is added between the outlet in that passage and return port, which additional orifice is closing when the second orifice lying between the outlet in that passage and the return port is opening such that, when the turning forces transmitted from said steering wheel are small, the additional orifice restricts the flow of hydraulic fluid from the outlet to the return port providing a back pressure at the outlet in that passage whereby the turn force effected by said motor means is less than would have been the case in the absence of such additional orifice.