Patent ID: 8517154

Claim:
A shock absorber comprising: a cylinder having a hydraulic fluid sealed therein; a piston slidably fitted in the cylinder; a piston rod connected to the piston and extending to an outside of the cylinder; a passage through which a flow of the hydraulic fluid is induced by movement of the piston; a relief valve adapted to restrict the flow of the hydraulic fluid through the passage; a back pressure chamber adapted to apply a pressure therein to the relief valve in a direction for closing the relief valve; and a back pressure introducing passage adapted to introduce the hydraulic fluid into the back pressure chamber; the relief valve being an annular disk valve having an opening at an inner side thereof; the relief valve having a front side and a rear side, the back pressure chamber being disposed at the rear side; the relief valve comprising: an outer peripheral portion provided on the front side, the outer peripheral portion adapted to unseat from and seat on a valve seat to open and close, respectively, the relief valve; an inner peripheral portion supported from the rear side by a support member; and an inner peripheral edge portion adjacent to the opening at the inner side; wherein, when the outer peripheral portion of the relief valve seats on the valve seat to close the relief valve, a gap is provided between the front side of the relief valve and a retaining member adapted to retain the support member, and when the outer peripheral portion of the relief valve unseats from the valve seat to open the relief valve, the inner peripheral edge portion moves within the gap pivotally about the support member as a fulcrum, wherein the inner peripheral edge portion of the relief valve is located at an inner side of the fulcrum, and wherein the back pressure introducing passage comprises a back pressure introducing orifice which is provided in the support member and which has a flow path area, the flow path area of the back pressure introducing orifice being constant regardless of whether the relief valve is open or closed, thereby enabling the hydraulic fluid to be introduced into the back pressure chamber through the inner side opening of the relief valve and the back pressure introducing orifice.