Abstract: Apparatus and method is presented for enabling a power steering system comprising an accumulator, a reservoir, and an electronically controlled closed-center control valve assembly for selectively fluidly coupling the accumulator and reservoir to a double-acting power cylinder of a power steering system to function in the manner of a force-based power steering system.

Abstract: A power steering system (10) for a motor vehicle having a power cylinder with the piston mounted in the power cylinder which divides the power cylinder into first (30) and second (32) chambers. The steering system includes a valve assembly having a rotary input member (40) and a valve sleeve 42 and first and second pairs of open center input valves (18), each which has an inlet and an outlet. The inlets of the input valves are fluidly connected to pump output. The valve assembly further includes a pair of closed center input valves (4b) and a normally closed by-pass valve (50). A hydraulic pump (12) is controlled so as to maintain a constant pressure drop between the inlets and outlets of the closed center valve (4b) and normally closed by-pass valves (50) whereby initial fluid flow through the control valve is proportional to the area of a variable orifice comprised within the normally closed by-pass valve (50).