Power steering system

A power steering system comprising

• an input shaft coupled to a steering wheel,
• a torsion bar for transmitting rotation of said input shaft to an output shaft,
• a power cylinder coupled to said output shaft,
• an oil path switching valve for switching oil paths to said power cylinder in accordance with the difference of turning angle between said input shaft and said output shaft,
• a high pressure oil path for supplying working oil delivered from an oil pump to said power cylinder via said oil path switching valve,
• a low pressure oil path for returning the working oil from said power cylinder to an oil tank via said oil path switching valve,
• a reaction piston for exerting a restraining force between said input shaft and said output shaft to limit the difference of turning angle therebetween,
• a control oil path extending from the midway of said high pressure oil path to said reaction piston,
• a pressure control valve for controlling oil pressure in said control oil path extending to said reaction piston to a level not higher than a predetermined highest pressure, said pressure control vavlv having chambers formed within its valve housing at positions facing its either end, one of said chambers being communicated with said low pressure oil path, said chambers being mutually connected via a drain oil path provided within said pressure control valve, said pressure control valve having an annular control groove and a differential pressure section provided on its outer peripheral surface, and said control groove and said differential pressure section being mutually communicated via an oil path provided within said pressure control valve,
• a return side orifice for communicating said control oil path between said pressure control valve and said reaction piston with said low pressure oil path, and
• a solenoid for actuating said pressure control valve by means of its plunger for generating an axial force which varies in accordance with a car speed and takes substantially a certain strength at every given car speed.

A power steering system comprising

• an input shaft coupled to a steering wheel,
• a torsion bar for transmitting rotation of said input shaft to an output shaft,
• a power cylinder coupled to said output shaft,
• an oil path switching valve for switching oil paths to said power cylinder in accordance with the difference of turning angle between said input shaft and said output shaft,
• a high pressure oil path for supplying working oil delivered from an oil pump to said power cylinder via said oil path switching valve,
• a low pressure oil path for returning the working oil from said power cylinder to an oil tank via said oil path switching valve,
• a reaction piston for exerting a restraining force between said input shaft and said output shaft to limit the difference of turning angle therebetween,
• a control oil path extending from the midway of said high pressure oil path to said reaction piston,
• a pressure control valve for controlling oil pressure in said control oil path extending to said reaction piston to a level not higher than a predetermined highest pressure, said pressure control valve having a chamfer provided on the whole periphery of its control land for causing the working oil to flow smoothly from the in-port side of said control oil path into a control groove provided on the outer peripheral surface of said pressure control valve,
• a return side orifice for communicating said control oil path between said pressure control valve and said reaction piston with said low pressure oil path, and
• a solenoid for actuating said pressure control valve by means of its plunger for generating an axial force which varies in accordance with a car speed and takes substantially a certain strength at every given car speed.