TRW Rack & Pinion

The control valve uses rotational motion of the input shaft and sleeve to direct fluid flow. When the steering wheel is turned, resistance of wheels and weight of vehicle cause the torsion bar to deflect. This deflection changes position valve spool and sleeve ports, directing fluid under pressure to appropriate end of power cylinder. The difference in pressure forces on the piston aids in moving the rack to assist turning effort. The piston is attached to the housing rack and the housing tube functions as the power cylinder. The fluid in the opposite power cylinder is forced to the control valve and returned to the pump reservoir. The control valve is forced back to the center position by the torsion bar when steering effort is removed. Pressure is then equalized on each side of the piston and the front wheels return to the straight ahead position.