Hydraulic system with an open centre valve and a power assisted steering gear incorporating the system.

摘要

An hydraulic system: a power assisted vehicle steering system which includes such an hydraulic system and a method of alleviating noise in an hydraulic system. The hydraulic system as applied to a vehicle steering gear (1) has an open center valve (3) which directs hydraulic fluid under pressure derived from a pump (12) and in response to a steering maneuver through a shaft (4) to a servo motor of the gear (1). Downstream of the open center valve (3) is a restrictor (8) through which hydraulic fluid from the valve (3) passes to a reservoir (11). The restriction effected by the restrictor (8) to fluid flow from the valve (3) to the reservoir is variable to provide a throttling action and a back pressure in the line (6) to alleviate noise in the valve (3).