The greater the damping force of the shock absorber, the faster the vibration is reduced, but the effect of the parallel elastic elements can not be fully exerted. At the same time, the excessive damping force may also lead to damage to the connecting parts and frame of the shock absorber. In order to solve this contradiction between elastic elements and shock absorbers, the following requirements are put forward for shock absorbers.
(1) In the compression stroke of the suspension, the damping force of the shock absorber should be small so as to make full use of the elasticity of the elastic elements to mitigate the impact.
(2) In the suspension stretching stroke (the distance between the bridge and the frame) the damping force of the shock absorber should be large in order to reduce the vibration rapidly.
(3) When the relative speed between the axle (or wheel) and the frame is too high, the shock absorber should be able to automatically increase the area of the liquid flow passage, so that the damping force is always within a certain limit to avoid excessive impact load.
Cylinder shock absorber is widely used in automobile suspension system, and it can reduce vibration in compression and stretching stroke. It is called bidirectional action shock absorber, and a new type of shock absorber is adopted, which includes air-filled shock absorber and resistance adjustable shock absorber.