In order to improve vehicle ride comfort, shock absorbers are installed in parallel with elastic elements in suspension system. In order to attenuate vibration, hydraulic shock absorbers are mostly used in suspension system. Their working principle is that there is relative motion between frame (or body) and bridge when vibration occurs. When the piston in the shock absorber moves up and down, the oil in the shock absorber chamber flows repeatedly from one chamber to another through different holes. At this time, the friction between the hole wall and the oil and the internal friction between the oil molecules form a damping force to the vibration, which transforms the vibration energy of the vehicle into the oil thermal energy, and then absorbed and emitted into the atmosphere by the shock absorber. When the cross section and other factors of the oil passage remain unchanged, the damping force increases and decreases with the relative velocity between the frame and the axle (or wheel), and is related to the oil viscosity.