Classification from the perspective of materials
From the perspective of damping materials, shock absorbers are mainly divided into hydraulic and pneumatic types, and there is also a variable damping shock absorber.
Hydraulic type
Hydraulic shock absorbers are widely used in automobile suspension systems. The principle is that when the frame and the axle make reciprocating relative motion and the piston moves back and forth in the cylinder of the shock absorber, the oil in the shock absorber housing repeatedly flows from the inner cavity through some narrow pores into another 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 on the vibration.
Pneumatic type
Pneumatic shock absorbers are a new type of shock absorber developed since the 1960s. Its structural feature is that a floating piston is installed at the bottom of the cylinder, and a closed air chamber formed by the floating piston and one end of the cylinder is filled with high-pressure nitrogen. A large-section O-ring is installed on the floating piston, which completely separates the oil and gas. The working piston is equipped with a compression valve and an extension valve that change the cross-sectional area of the channel with the speed of its movement. When the wheel bounces up and down, the working piston of the shock absorber reciprocates in the oil, causing a pressure difference between the upper and lower chambers of the working piston. The pressure oil pushes open the compression valve and the extension valve and flows back and forth. Since the valve exerts a large damping force on the pressure oil, the vibration is attenuated.