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Leaf spring


1. Definition of Leaf Springs

Leaf Spring is the most widely used elastic component in automotive suspension. It is an approximately equal strength elastic beam composed of several alloy spring plates of equal width but not equal length (thickness can be equal or not).

2. Classification of leaf springs

Leaf springs come in two forms:

(1) Multi leaf spring: composed of multiple steel plates of different lengths and widths stacked together. The steel plates of multiple leaf springs are stacked into an inverted triangle shape, with the longest steel plate at the top and the shortest steel plate at the bottom. The number of steel plates is related to the weight of the supporting bus. The thicker and shorter the steel plates, the greater the spring stiffness. However, when the steel plate spring is used for a long time, the pieces will slide and rub against each other, producing noise. The relative friction between steel plates can also cause spring deformation, resulting in uneven driving.

(2) Small leaf spring: composed of steel plates with thin ends and equal width and length in the middle, stacked together. The steel plate cross-section of a few leaf spring varies greatly, and the cross-section from the middle to the two ends gradually varies. Therefore, the rolling process is more complex and the price is also more expensive than that of a multi leaf spring. Compared with multi leaf springs, under the same stiffness (i.e., the same load-bearing capacity), a few leaf spring is about 50% lighter than a multi leaf spring, reducing fuel consumption and increasing driving smoothness. Moreover, there is point contact between the few leaf springs, reducing relative friction and vibration, and increasing ride comfort.

3. Principle of Steel Plate Spring

When a steel plate spring is installed in a car suspension and the vertical load it bears is in the positive direction, each spring plate undergoes force deformation and tends to arch upwards. At this point, the axle and frame approach each other. When the axle and frame are far away from each other, the positive vertical load and deformation on the steel plate spring gradually decrease, and sometimes even reverse.

The main film ear is severely stressed and is a weak point. To improve the stress situation of the main film ear, the end of the second film is often bent into a ear and wrapped outside the main film ear, known as the ear wrap. In order to allow for relative sliding of each piece during elastic deformation, a large gap is left between the main piece rolling ear and the second piece wrapping ear. In some suspensions, the two ends of the steel plate spring are not made into rolling ears, and other support connection methods are used, such as rubber support pads.

The flat rectangular steel plate is curved in shape, and a chassis composed of several stacked plates is equipped with springs. One end is installed on the hanger with pins, and the other end is connected to the main beam with lifting eyes, allowing the springs to expand and contract. Currently suitable for medium to large cargo trucks.

4. Advantages and disadvantages of steel plate springs

Automotive springs are widely used suspension elastic components in traditional automobiles. Its advantages are simple structure, reliable operation, low cost, and convenient maintenance. It is not only the elastic component of the suspension, but also the guiding device of the suspension. One end of it is hinged to the frame, which can transmit various forces and moments, and determine the trajectory of the wheels. At the same time, it also has a certain frictional damping effect. Kill three with one stone, so it is widely used on non independent suspensions.

Its disadvantages are that it can only be used for non independent suspensions, with heavy weight, high stiffness, poor comfort, long longitudinal dimensions, which are not conducive to shortening the front and rear suspensions of the car, and the steel plate spring pins at the connection with the frame are prone to wear and tear.

Despite its many drawbacks, leaf springs are still widely used in various automobiles today. In order to improve the performance of steel plate springs, reduce weight, and increase service life, variable cross-section steel plate springs, single leaf springs, etc. have emerged.

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