US Patent 7458448 Hydraulic shock absorber

A hydraulic shock absorber in which the flow of hydraulic fluid induced in each of extension and compression hydraulic fluid passages, by sliding movement of a piston, is controlled by a main disk valve to generate damping force. The valve opening pressure of the main disk valve is adjusted by the pressure in a back-pressure chamber. In a low piston speed region, the main disk valve closes a back-pressure chamber inlet passage. Therefore, the pressure in the backpressure chamber will not rise, and sufficiently small damping force is obtained. When the main disk valve opens, the backpressure chamber inlet passage opens simultaneously. Consequently, the pressure in the backpressure chamber rises, and the damping force increases.