Working principle of leaf spring

When the leaf spring is installed in the automobile suspension and the vertical load it bears is positive, the spring leaves are deformed by force and tend to bend upward. At this time, the axle and the frame are close to each other. When the axle and the frame are far away from each other, the positive vertical load and deformation of the leaf spring gradually decrease, and sometimes reverse.

The main leaf ear rolling is seriously stressed and is a weak point. In order to improve the stress of it, the end of the second leaf is often bent into an ear and wrapped outside the main leaf ear, which is called a wrap ear. In order to make it possible for each leaf to slide relative to each other during elastic deformation, a large gap is left between the main leaf ear and the second leaf ear. The leaf springs in some suspensions are not made into ears at both ends, but other support connection methods are used, such as rubber support pads.

The flat rectangular steel plate is bent, and the chassis spring is made of several pieces. This end is installed on the hanger with a pin, and the other end is connected to the beam with a hanging ear, so that the spring can be extended and retracted. Currently, it is suitable for medium and large trucks.

As we all know, leaf springs are composed of many elastic steel sheets with the same width and thickness and different lengths. Its function is to connect the frame and the axle in the form of suspension, exposed between the frame and the axle, bear the load impact of the wheel on the frame, reduce the violent vibration of the body, and maintain the stability of the vehicle and adaptability to different road conditions.

When the leaf spring is subjected to load impact, it forms an extension movement, and strong friction is generated between the steel sheets, which produces an extrusion and stretching phenomenon. The two friction surfaces generate two different directions of movement friction, causing the temperature of the leaf spring to rise, surface strain, and fine cracks. As the load impact frequency increases, the frictional movement force generated by the extension movement is also increasing. Fatigue at the stress concentration point will cause single or whole stacks to break.

According to the principle of kinematics, experiments have proved that when the steel parts undergo compression and extension movement, the temperature of the steel parts increases and the strength decreases when the movement frequency increases. Strong lines appear at the stress concentration point and gradually expand and deepen. When fatigue occurs, they will be damaged. The same is true for leaf springs, except that they have high elasticity and are durable. In addition to other reasons, the leaf spring breakage is caused by poor lubrication, which should attract the attention of drivers and technical management personnel, and lubrication of leaf springs should be done in time. In order to reduce friction and disperse stress, avoid scratches on the surface of the steel sheet; reduce the intrusion of dust, soil and water to avoid rust; and dissipate heat and cool down to avoid a decrease in elastic strength.

The lubrication method is: it should be carried out at the end of the running-in period of a new car, and in summer and winter when the car is used. When lubricating, first remove the leaf spring, open the middle through bolt, spread the steel sheet, and then evenly apply lithium-based grease or graphite grease on both sides of the steel sheet. After assembly, an oil film is formed between the two friction surfaces (it only takes the time to replace the fragments to complete the lubrication of the leaf spring assembly).