The general name of all force transmission connecting devices between automobile frame (or bearing body) and axle (or wheel). Its function is to transfer force and torque between the wheel and the frame, buffer the impact force transmitted from the rough road to the frame or body, and reduce the resulting vibration to ensure that the car can drive smoothly.

When the vehicle is driving on uneven roads, the suspension system must enable the tire and wheel assembly to move vertically while keeping the tire horizontal with the road surface. This requires the steering knuckle to be suspended between the lower control arm and the strut assembly. The lower control arm is connected to the steering knuckle at the outermost point of the control arm. This connection is achieved through a ball joint. The innermost end of the control arm is connected with the frame at two points through a semi-rigid bushing. The upper part of the steering knuckle is connected with the sliding column assembly. The strut assembly is connected to the vehicle body through an upper bearing. The steering knuckle can move up and down independently of the body structure and frame.

When the vehicle drives over the bumpy road, most of the up and down movement of the steering knuckle is absorbed by the coil spring. The spring remains tensioned on the strut assembly. The sliding column is used with this system to buffer the vibration of the coil spring. The sliding column is essentially a hydraulic cylinder. The sliding column is filled with oil, and a movable shaft is connected with the piston in the sliding column. The valve in the shock absorber generates resistance to the flow of oil, which prevents the rapid movement of piston and shaft. Each end of the shock absorber is connected in this way to take advantage of the reaction force of a single spring. Each end of the sliding column is the connection point between the suspension system and the vehicle and serves as a coil spring seat. This allows the strut to use the damping operation to reduce the reaction force of the spring alone. The lower control arm can rotate vertically on the frame. The ball joint keeps the steering knuckle perpendicular to the road surface.