In the suspension system, the elastic element vibrates due to impact. In order to improve the driving smoothness of the vehicle, the shock absorber is installed in parallel with the elastic element in the suspension. In order to attenuate the vibration, the shock absorber used in the vehicle suspension system is mostly hydraulic shock absorber. Its working principle is that when there is relative movement due to vibration between the frame (or body) and the axle, the piston in the shock absorber moves up and down, The oil in the shock absorber cavity repeatedly flows from one cavity through different pores into another cavity. At this time, the friction between the hole wall and the oil and the internal friction between the oil molecules form a damping force on the vibration, so that the vehicle vibration energy is transformed into oil heat energy, which is absorbed and emitted into the atmosphere by the shock absorber. When the oil channel section and other factors remain unchanged, the damping force increases or decreases with the relative motion speed between the frame and the axle (or wheel), and is related to the oil viscosity.