Explanation of frame structure and analysis of common faults

The frame is a frame structure, commonly known as a crossbeam, that spans the front and rear axles of a car. It is the base of a car, just like a human skeleton.

Support and connect various car assemblies to maintain their relative correct installation positions and carry various loads inside and outside the car. It must have sufficient strength and stiffness to withstand the load of the car and the impact transmitted from the wheels.

It is generally composed of two longitudinal beams and several crossbeams, supported on the wheels through suspension devices, front and rear axles.

The frame is currently divided into peripheral frame, backbone frame, trapezoidal frame, and truss frame based on different structural forms.

Peripheral frame (commonly used in large sedans)

The middle of the frame is widened without a crossbeam, and its main components are often enclosed in sections.

Features: Low floor height, large passenger compartment area, simple structure, easy to manufacture, etc.

Backbone frame (truck)

The backbone frame has only one longitudinal beam located in the center and running through the front and rear of the car. The cross-sectional shape of the longitudinal beam can be circular or box shaped.

Features: The frame has low mass, high strength and rigidity. At the same time, the manufacturing accuracy requirements of the frame are high, and maintenance and repair are difficult.

Trapezoidal frame (commercial trucks and some passenger cars)

Composed of two longitudinal beams and several crossbeams. The cross-sectional shape of the longitudinal beam is groove shaped, Z-shaped, or box shaped.

Longitudinal beams can be bent in a horizontal or longitudinal plane.

Features: High bending strength, sturdy and convenient installation of parts, etc.

Truss frame (racing)

The truss frame is composed of welded steel pipes.

Features: High stiffness, low mass, but difficult to manufacture.

The frame is composed of welded steel pipes. It has the characteristics of high stiffness and low mass, but it is difficult to manufacture and is mainly used for racing.

Subframe

The subframe is not a complete frame, but a bracket that supports the front and rear axles and suspensions, connecting them to the "front frame" through it, commonly known as the "subframe".

The vertical impact load on the vehicle frame caused by driving on uneven roads exceeds the allowable stress of the frame. In addition, when the car is going up or down slopes, turning, or loading unevenly, it can also cause local overloading of the frame and cause it to break.

2. The frame design or accessory devices cause local torque that causes the frame to break. If the front cross-sectional area of some frame longitudinal beams is small, and due to the influence of the engine and transmission, the distribution of the transverse beams is less, resulting in a decrease in the stiffness of the frame. If under dynamic load, it may cause the front of the longitudinal beam to fracture, which is commonly seen in the lower wing of the longitudinal beam.

In addition, the frame is also subjected to local twisting caused by cantilever loads perpendicular to the longitudinal beam (such as fuel tank, suspension, and spare tire), which is also the cause of frame fracture.

3. When a car is driving, there is significant resistance on one side of the front wheel, which makes the frame prone to diagonal plane deformation.

4. Car collision accidents, severe impacts can cause frame deformation

Frame deformation refers to the change in the original geometric shape of the frame, resulting in changes in the relative positions of various assembly parts installed on the frame, and the deterioration of the technical condition of the vehicle, resulting in the inability of the vehicle to operate normally.

The deformation of the frame is often caused by the force acting on the frame exceeding its elastic limit. After the force used for the frame is eliminated, the frame cannot be restored to its original state, forming a residual