From the perspective of the damping material, shock absorbers are mainly classified into two types: hydraulic and pneumatic, and there is also a type with variable damping.
Hydraulic Type: Hydraulic shock absorbers are widely used in automotive suspension systems. Their principle is that when the vehicle frame and axle reciprocate relative to each other, and the piston moves back and forth within the cylinder of the shock absorber, the oil inside the shock absorber housing repeatedly flows from one inner cavity to another through narrow orifices. At this time, the friction between the liquid and the inner wall, as well as the internal friction of the liquid molecules, creates a damping force against vibration.
Pneumatic Type: Pneumatic shock absorbers are a new type of shock absorber developed since the 1960s. Their structural feature is a floating piston installed at the bottom of the cylinder. High-pressure nitrogen gas fills a sealed chamber formed by the floating piston and one end of the cylinder. A large-section O-ring seal is installed on the floating piston, completely separating the oil and gas. The working piston is equipped with a compression valve and an extension valve whose cross-sectional area changes according to its speed. When the wheels bounce up and down, the working piston of the shock absorber reciprocates in the oil, creating a pressure difference between the upper and lower chambers of the piston. This pressure causes the oil to push open the compression valve and the extension valve, allowing it to flow back and forth. Because the valves exert a significant damping force on the pressure oil, the vibration is attenuated.
