Hydraulic shock absorbers are widely used in automobile suspension systems. The principle is that when the frame and the axle reciprocate and the piston reciprocates in the cylinder of the shock absorber, the oil in the shock absorber housing will repeatedly flow from the inner cavity through some narrow pores into the other. An inner cavity. At this time, the friction between the liquid and the inner wall and the internal friction of the liquid molecules form a damping force against vibration.