Patent ID: 7155906

Claim:
A hydraulic power steering system comprising: a steering mechanism adapted to be connected to steered road wheels; a hydraulic power cylinder accommodating therein a piston connected to the steering mechanism for steering assistance, and having first and second hydraulic chambers defined on both sides of the piston; a reversible pump having a pair of discharge ports; a first fluid line intercommunicating the first hydraulic chamber and a first one of the discharge ports of the pump; a second fluid line intercommunicating the second hydraulic chamber and the second discharge port; a torque sensor that detects a steering torque applied to the steering mechanism; a motor that drives the pump; a motor control circuit that controls the motor responsively to a command signal determined based on the steering torque detected; a communicating circuit through which the first and second fluid lines are communicated with each other; a directional control valve disposed in the communicating circuit and having a poppet valve mechanism, said mechanism comprising two axially arranged poppet valves; and a valve control circuit that opens the directional control valve in presence of a hydraulic power steering system failure including at least one of a motor failure, a reversible pump failure, an ECU failure, and a torque sensor failure, to intercommunicate the first and second fluid lines with the directional control valve opened.