Most modern cars have a frame as the skeleton of the entire vehicle. Most parts of the car and the overall assembly are fixed by the frame, such as the engine, drive train, suspension, steering system, cab, cargo box and related operating mechanisms. The frame plays the role of supporting and connecting various parts of the car, and bears various loads from inside and outside the car.
The structure of the frame should first meet the requirements of the car's general layout. In the complex driving process of the car, there should be no interference between the various assemblies and parts fixed on the frame. When a car is driving on rough roads, the frame may undergo torsional deformation and bending deformation in the longitudinal plane under load; when one wheel encounters an obstacle, the entire frame may be twisted into a diamond shape. These deformations will change the relative position between the components installed on the frame, thereby affecting its normal operation. Therefore, the frame should also have sufficient strength and appropriate rigidity. In order to improve the lightweight level of the entire vehicle, the frame mass is required to be as small as possible. In addition, the frame should be arranged closer to the ground to lower the center of gravity of the car and improve the driving stability of the car. This is particularly important for passenger cars and cars.