There are three types of shock absorbers used in automobiles: two-way acting cylinder shock absorbers, gas-charged shock absorbers, and damping adjustable shock absorbers.
The bidirectional acting cylinder shock absorber is generally composed of 4 valves, 3 cylinder barrels, 2 lifting lugs and 1 piston and piston rod.

The cylinder barrel 10 is a dust cover. Cylinder barrel 5 is an oil storage cylinder containing part of the oil, and its lower end is connected to the axle by lifting lugs welded together with the base. Cylinder barrel 2 is a working cylinder, which is filled with oil and the upper end is sealed. The upper end of the piston rod 1 is fixed to the frame as one piece with the dust cover 10 and the lifting lug, and the lower end is equipped with a piston 3. The piston divides the working cylinder into two chambers: upper and lower. There are extension valves 4 and flow valves 8 on the piston. The lower part of the working cylinder is equipped with a compression valve 6 and a compensation valve 7 on the support. Flow valves and compensation valves have soft springs and lower oil pressure allows them to close or open. The springs of the compression and extension valves are stiff and require a large oil pressure to open, and the oil pressure is slightly reduced and closed immediately.

Its working principle is that when the frame and the axle reciprocate relative movement, and the piston reciprocates in the cylinder barrel, the oil in the shock absorber reciprocates between the two isolated inner chambers through the narrow pores on the valve, due to the friction between the hole wall and the oil and the internal friction of the liquid molecules to form a damping force, thereby converting the mechanical energy of the body vibration into heat energy to be absorbed by the oil and the shell, and then dispersed into the atmosphere. The damping force is related to the cross-sectional area of the oil channel, the spring rate of the valve and the viscosity of the oil.

When the wheel jumps up, the shock absorber is compressed, and the piston moves down relative to the cylinder barrel, so the volume of the lower cavity of the working cylinder is reduced, the oil pressure rises, and the oil flows into the upper cavity of the working cylinder through the flow valve. Since the upper cavity is occupied by the piston rod, the increased volume of the upper cavity is less than the volume reduced by the lower cavity, so there is still a part of the oil to push open the compression valve and flow back to the oil storage cylinder 5, and the throttling of these valves to the oil forms a damping force on the suspension compression movement. When the wheel falls, the shock absorber is stretched, and the piston moves up relative to the cylinder barrel, so the oil pressure in the upper cavity of the working cylinder rises, the flow valve is closed, and the oil pushes the extension valve into the lower cavity. Similarly, due to the presence of the piston rod, the oil flowing from the upper cavity into the lower cavity is not enough to fill the increased volume of the lower cavity, and a certain vacuum degree is generated in the lower cavity, at which time the oil in the reservoir pushes the compensation valve into the lower cavity to replenish. The throttling action of this process valve creates a damping force on the extension movement of the suspension.

The gas-filled shock absorber consists of a cylinder barrel, two pistons, a sealing ring, and two valves. This is shown in Figure 3.
The working cylinder is equipped with a working piston and a floating piston, the working piston is on the top and the floating piston is on the bottom, dividing the working cylinder into three parts. The closed air chamber formed between the lower part of the floating piston and the cylinder barrel is filled with high-pressure nitrogen, and the large section O-ring at the edge of the floating piston separates the oil above the floating piston from the nitrogen below. The working piston is equipped with a compression valve and an extension valve that can change the channel overflow area with the change of the piston moving speed, and both valves are composed of a set of spring steel sheets of the same thickness and diameter, arranged from large to small.

When the wheels move relative to the frame, the working piston reciprocates in the oil, causing an oil pressure difference between the upper and lower chambers of the working piston, and then the pressure oil pushes the compression valve or extension valve back and forth. Because the valve produces a large damping force on the pressure oil, the vibration is attenuated. Changes in cylinder barrel volume due to the presence of piston rods are compensated by the upward and downward movement of the floating piston.
Adjustable resistance shock absorber The cylinder barrel is equipped with a piston, and a hollow connecting rod is installed in the middle hole of the piston, the upper end of the hollow connecting rod is fixed on the lower shell of the air chamber, and the plunger rod and plunger are also installed in the hollow connecting rod. The upper end of the plunger rod rests against the spring seat and diaphragm. A spring is installed between the spring seat and the plunger rod. The lower end of the hollow connecting rod is made with a orifice near the upper surface of the piston. 

Resistance adjustable shock absorbers are used in suspension where the elastic element is a gas spring. During operation, as the load of the car increases, the air pressure in the air spring increases, and the air pressure in the air chamber connected to it also increases, and the diaphragm is pressed down until it is balanced with the pressure generated by the spring. When the diaphragm is moved down, pressure is applied to the plunger rod and the plunger at its lower end to move down. When the position of the orifice on the plunger relative to the hollow connecting rod reaches the beginning of plugging, the channel cross-sectional area of the orifice begins to decrease, so the amount of liquid passing through the orifice decreases, that is, the flow resistance of the oil increases. When the load of the car decreases, the plunger moves up, and the channel interception area of the orifice increases, reducing the flow resistance of the oil.