The frame is usually composed of rails and beams. Its form mainly has the side beam type and the middle beam type two kinds, the beam is used to ensure the
torsional stiffness of the frame and bears the longitudinal load, but also can support the main parts of the car. The structure characteristic of the side beam frame is easy to install the cab,
carriage and some special equipment and arrange other assembly, which is conducive to the modification of the car and the development of a variety of cars