Shock absorber with variable damping force

摘要

A shock absorber includes an outer tube filled with hydraulic fluid and an inner tube that extends into the outer tube and that contains an appropriate amount of hydraulic fluid and high pressure air therein. A piston is secured to an open bottom end of the inner tube and is formed with a central through hole and a plurality of fluid passages which communicate the inner and outer tubes. The piston further has a bottom surface which is formed with concentric first and second annular grooves and an annular wall that separates the annular grooves and that is formed with a notch to communicate the annular grooves. The fluid passages extend into the first annular groove. The second annular groove has a depth that increases gradually from one side of the notch to an opposite side thereof. A control rod is disposed inside the inner tube and has a bottom end that extends through the central through hole of the piston. An annular valve piece is connected axially to the bottom end of the control rod, is normally spaced from the bottom surface of the piston, and is formed with a plurality of fluid holes and a fluid slot. The control rod is rotated to rotate therewith the valve piece in order to align respectively the fluid holes in the valve piece with the fluid passages and in order to locate the fluid slot at a desired depth of the second annular groove.