Patent ID: 7374011

Claim:
A power steering apparatus comprising: a housing having a hydraulic chamber; an input shaft adapted to receive a driver's steering input; an output shaft connected with the input shaft by a torsion bar; a piston slidably mounted on the output shaft, and arranged to partition the hydraulic chamber into a first hydraulic chamber and a second hydraulic chamber; a ball screw mechanism disposed between the output shaft and the piston, and configured to convert a rotary motion of the output shaft into an axial motion of the piston; an output member to receive the axial motion of the piston and to deliver an output motion for steering; a control valve configured to supply hydraulic fluid selectively to the first hydraulic chamber and to the second hydraulic chamber, in accordance with an amount of torsion of the torsion bar caused by relative rotation between the input shaft and the output shaft; a first connecting passage connecting the control valve and the first hydraulic chamber; a second connecting passage connecting the control valve and the second hydraulic chamber; a portion defining a first valve receiving hole and provided in the first connecting passage; a portion defining a second valve receiving hole and provided in the second connecting passage; a first damper valve provided in the first valve receiving hole, and configured to open the first connecting passage in response to a hydraulic pressure from the control valve when the hydraulic pressure from the control valve exceeds a first valve opening pressure of the first damper valve, and to open the first connecting passage in response to a hydraulic pressure from the first hydraulic chamber when the hydraulic pressure from the first hydraulic chamber exceeds a second valve opening pressure of the first damper valve which is higher than the first valve opening pressure of the first damper valve; and a second damper valve provided in the second valve receiving hole, and configured to open the second connecting passage in response to a hydraulic pressure from the control valve when the hydraulic pressure from the control valve exceeds a first valve opening pressure of the second damper valve, and to open the second connecting passage in response to a hydraulic pressure from the second hydraulic chamber when the hydraulic pressure from the second hydraulic chamber exceeds a second valve opening pressure of the second damper valve which is higher than the first valve opening pressure of the second damper valve.