The shock absorber is used to control the shock when the spring rebounds after shock absorption and the impact from the road surface. Widely used in automobiles, in order to accelerate the attenuation of the vibration of the frame and the body to improve the ride comfort of the car. When passing through uneven roads, although the shock-absorbing spring can filter the vibration of the road surface, the spring itself will have a reciprocating motion, and the shock absorber is used to control the spring jump.

In the suspension system, the elastic element vibrates due to the impact. In order to improve the ride comfort of the car, a shock absorber is installed in parallel with the elastic element in the suspension to dampen the vibration. The working principle is that when the frame (or body) and the axle vibrate and there is relative movement, the piston in the shock absorber moves up and down, and the oil in the shock absorber cavity repeatedly passes through a different cavity. The pores flow 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 vibration energy of the car is converted into the heat energy of the oil, which is then absorbed by the shock absorber and released into the atmosphere. When the oil channel section and other factors remain unchanged, the damping force increases or decreases with the relative movement speed between the frame and the axle (or wheel), and is related to the viscosity of the oil.

The shock absorber and the elastic element undertake the task of buffering and shock absorption. If the damping force is too large, the elasticity of the suspension will be deteriorated, and even the shock absorber connection will be damaged. Therefore, it is necessary to adjust the contradiction between the elastic element and the shock absorber.
(1) During the compression stroke (the axle and the frame are close to each other), the damping force of the shock absorber is small, so that the elastic effect of the elastic element can be fully exerted to ease the impact. At this time, the elastic element plays a major role.
(2) During the extension stroke of the suspension (the axle and the frame are far away from each other), the damping force of the shock absorber should be large, and the shock absorber should be quickly damped.
(3) When the relative speed between the axle (or wheel) and the axle is too large, the shock absorber is required to automatically increase the fluid flow, so that the damping force is always kept within a certain limit to avoid excessive impact load.

Cartridge shock absorbers are widely used in automobile suspension systems, and they can act as shock absorbers in both compression and extension strokes. They are called double-acting shock absorbers, and new shock absorbers are used. shock absorbers and adjustable resistance shock absorbers.

Explanation of the working principle of the double-acting cylinder shock absorber: During the compression stroke, the wheel of the car moves closer to the body, the shock absorber is compressed, and 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 chamber above the piston (upper chamber). The upper cavity is occupied by the piston rod, so the increased volume of the upper cavity is smaller than the reduced volume of the lower cavity, and a part of the oil pushes open the compression valve and flows back to the oil storage cylinder. The oil savings of these valves creates a damping force for the suspension's motion in compression. When the shock absorber stretches, 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 upwards. The oil pressure in the upper chamber of the piston rises, the flow valve is closed, and the oil in the upper chamber pushes the expansion valve and flows 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, and a vacuum is generated in the lower chamber. At this time, the oil in the oil storage cylinder pushes the compensation valve 7 and flows into the lower chamber for Replenish. Due to the throttling effect of these valves, the suspension has a damping effect during the extension movement.

Since the stiffness and preload force of the expansion valve spring are designed to be larger than those of the compression valve, under the same pressure, the sum of the channel load areas of the expansion valve and the corresponding normally open slits is smaller than the sum of the cross-sectional areas of the compression valve and the corresponding normally open slits. This makes the damping force generated by the extension stroke of the shock absorber greater than the damping force of the compression stroke, so as to achieve the requirement of rapid shock absorption.