Patent ID: 7694785

Claim:
A controllable damping force hydraulic shock absorber comprising: a sealed cylinder in which a hydraulic fluid is contained; a piston slidably fitted into the cylinder; a piston rod connected to the piston and extending to an outside of the cylinder; an extension-side hydraulic fluid passage and a compression-side hydraulic fluid passage provided in the piston; an extension-side main valve provided in the extension-side hydraulic fluid passage; an extension-side back-pressure chamber for controlling a valve-opening pressure of the extension-side main valve; an extension-side orifice passage for introducing the hydraulic fluid from the extension-side hydraulic fluid passage to the extension-side back-pressure chamber; a compression-side main valve provided in the compression-side hydraulic fluid passage; a compression-side back-pressure chamber for controlling a valve-opening pressure of the compression-side main valve; a compression-side orifice passage for introducing the hydraulic fluid from the compression-side hydraulic fluid passage to the compression-side back-pressure chamber; a common passage for allowing communication between the extension-side back-pressure chamber and the compression-side back-pressure chamber; and a damping force controlling valve disposed in the common passage to be commonly used for an extension side stroke and a compression side stroke of the shock absorber, the damping force controlling valve being adapted to be seated on and separated from a seat portion formed in a valve chamber communicating with the common passage, thereby opening and closing a hydraulic fluid flow passage between the common passage and the valve chamber, wherein, in one of the extension side stroke and the compression side stroke, the hydraulic fluid in the same side one of the extension-side back-pressure chamber and the compression-side back-pressure chamber flows through the common passage and the hydraulic fluid passage of the other side.