Vehicle power steering control system

Claim 1

A power-assisted steering control system for a motor vehicle having a source of pressurized fluid and a fluid reservoir and comprising: a steering gear defining therein a chamber and being operatively disposed between said source of pressurized fluid and said fluid reservoir; at least one fluid operated steering assistance actuator operatingly disposed in said chamber; a valve to selectively connect said chamber with said source of pressurized fluid; a fluid pressure control valve being operatively disposed between said source of pressurized fluid and said fluid reservoir, and being operative to modulate the pressure of fluid supplied to said chamber, said fluid pressure control valve forming therein a bore which is stepped to provide axially adjacent bore portions of difference cross-sectional area with shoulders between the bore portions and which receives axially movably a flow control member having at least one axially extending slot such as to allow said fluid to pass therethrough, an effective cross-sectional area of said at least one axially extending slot being varied in dependence upon axial movement of said flow control member such as to control the amount of said fluid flowing therethrough, thereby to modulate the pressure of said fluid supplied to said chamber; and an electrical actuator responsive to at least one of the vehicle speed and the gradient of the road surface on which the vehicle is driven and having a mechanical actuating member operatively connected with said flow control member, said mechanical actuating member being moved substantially proportionally to the degree of at least one of the vehiCle speed and the gradient.