Shock absorbers control the oscillation of springs after shock absorption and impacts from the road. Widely used in automobiles, they accelerate the damping of chassis and body vibrations to improve ride comfort. When driving over uneven roads, although shock-absorbing springs can filter road vibrations, the springs themselves will still have reciprocating motion, and shock absorbers are used to control this spring bounce.

In the suspension system, vibrations are generated due to the impact on the elastic components. To improve the ride comfort of the vehicle, shock absorbers are installed in parallel with the elastic components in the suspension to dampen the vibrations. The shock absorbers used in automotive suspension systems are mostly hydraulic shock absorbers. Their working principle is that when the chassis (or body) and the axle vibrate and have relative motion, the piston in the shock absorber moves up and down, and the oil in the shock absorber chamber repeatedly flows from one chamber to another chamber through different orifices. At this time, the friction between the orifice wall and the oil and the internal friction between the oil molecules form a damping force on the vibration, converting the vehicle's vibration energy into oil heat energy, which is then absorbed by the shock absorber and dissipated into the atmosphere. When the oil passage cross-section and other factors remain unchanged, the damping force increases or decreases with the relative speed of movement between the chassis and the axle (or wheel), and is related to the viscosity of the oil.

Shock absorbers and elastic components are responsible for cushioning impacts and damping vibrations. Excessive damping force will impair the elasticity of the suspension and even damage the shock absorber connecting components. Therefore, it is necessary to adjust the contradiction between the elastic components and the shock absorber.
(1) During the compression stroke (the axle and chassis move closer together), the shock absorber damping force is smaller, so that the elasticity of the elastic components can be fully utilized to cushion the impact. At this time, the elastic components play the main role.
(2) During the suspension extension stroke (the axle and chassis move away from each other), the shock absorber damping force should be large to quickly dampen the vibration.
(3) When the relative speed between the axle (or wheel) and the axle is too high, it is required that the shock absorber can automatically increase the oil flow rate, so that the damping force is always maintained within a certain limit to avoid excessive impact load.

The widely used shock absorber in automotive suspension systems is the telescopic shock absorber, which can play a damping role in both compression and extension strokes, called a two-way acting shock absorber. There are also new shock absorbers, including pneumatic shock absorbers and adjustable resistance shock absorbers.

Working principle of the two-way acting telescopic shock absorber: During the compression stroke, the car wheel moves closer to the body, and the shock absorber is compressed. At this time, the piston in the shock absorber moves downward. The volume of the lower chamber of the piston decreases, the oil pressure increases, and the oil flows through the flow valve to the upper chamber (upper chamber) above the piston. The upper chamber is occupied by the piston rod, so the increased volume of the upper chamber is smaller than the decreased volume of the lower chamber, and some oil pushes the compression valve and flows back to the oil reservoir. The throttling of these valves forms the damping force of the suspension compression movement. During the extension stroke of the shock absorber, the wheel is equivalent to moving away from the body, and the shock absorber is stretched. At this time, the piston of the shock absorber moves upward. The oil pressure in the upper chamber of the piston increases, the flow valve closes, and the oil in the upper chamber pushes the extension valve into the lower chamber. Due to the existence of the piston rod, the oil flowing from the upper chamber is not enough to fill the increased volume of the lower chamber, causing a vacuum in the lower chamber. At this time, the oil in the oil reservoir pushes the compensation valve 7 to flow into the lower chamber for replenishment. Due to the throttling effect of these valves, it plays a damping role on the suspension during the extension movement.

Because the stiffness and preload of the extension valve spring are designed to be greater than the compression valve, under the same pressure, the total area of the extension valve and the corresponding normally open gap channels is smaller than the total area of the compression valve and the corresponding normally open gap channels. This makes the damping force generated by the extension stroke of the shock absorber greater than the damping force of the compression stroke, meeting the requirement of rapid damping.