In a suspension system, the elastic element vibrates upon impact. To improve ride comfort, shock absorbers are installed in parallel with the elastic element to dampen vibrations. Most shock absorbers used in automotive suspension systems are hydraulic. Their working principle is as follows: when the vehicle frame (or body) and axle vibrate and relative motion occurs, the piston inside the shock absorber moves up and down, causing the oil in the shock absorber chamber to repeatedly flow from one chamber to another through different orifices. The friction between the orifice walls and the oil, as well as the internal friction between oil molecules, creates a damping force, converting the vehicle's vibration energy into oil heat energy, which is then absorbed by the shock absorber and dissipated into the atmosphere. With constant factors such as the cross-section of the oil passage, the damping force increases or decreases with the relative speed between the vehicle frame and axle (or wheels) and is related to the oil viscosity.
The shock absorber and the elastic element are responsible for buffering impacts and damping vibrations. Excessive damping force will degrade the suspension's elasticity and may even damage the shock absorber's connecting components. Therefore, it is necessary to balance the inherent tension between the elastic element and the shock absorber.
(1) During the compression stroke (when the axle and frame are close together), the shock absorber damping force is relatively small to fully utilize the elasticity of the elastic element and mitigate the impact. At this time, the elastic element plays a major role.
(2) During the suspension extension stroke (when the axle and frame are far apart), the shock absorber damping force should be large to quickly absorb the shock.
(3) When the relative speed between the axle (or wheel) and the suspension is too high, the shock absorber should automatically increase the fluid flow to keep the damping force within a certain limit to avoid excessive impact loads.
The telescopic shock absorber is widely used in automotive suspension systems. A two-way shock absorber that can dampen both the compression and extension strokes is called a two-way shock absorber. Newer types of shock absorbers are also used, including pneumatic shock absorbers and adjustable-drag shock absorbers.
