Ordinary semi-trailer includes body, axle and suspension system. The axle and suspension system are located at the bottom of the body, of which the axle is barbell-shaped, with wheels at both ends of the axle and the wheels are set transversely at the bottom of the body, and the suspension system is located between the body and the axle, connecting the axle and the body: when the body is dragged by external forces, the body drives the wheels at both ends of the axle through the suspension system. 

Semi-trailer steel plate spring suspension (referred to as steel plate spring suspension) is also divided into less variable section steel plate suspension and equal section multiple steel plate spring suspension. At present, more than 95% of the domestic heavy truck suspension system is a non-independent suspension with steel plate spring as the elastic element and guide device, whose main advantages are simple structure, easy manufacturing, convenient maintenance, mature technology and reliable work. 

Trailer suspension is a device that connects the trailer frame and the wheels of the axle. Its main function is to transfer the various forces and moments acting between the wheels and the frame, reduce and eliminate the impact load and vibration transmitted to the frame by the road through the axle, in order to improve the smoothness of the trailer driving.