Suspension is a connecting device between the axle and the frame, which is used to transmit force and torque, reduce the impact of road surface on the body, reduce the body vibration caused by road undulation, and ensure the smooth running of the vehicle.

At present, the common suspensions in the commercial vehicle market are mainly leaf spring suspension and air suspension. Although the voice of air suspension is getting higher and higher in recent years, it is still difficult to shake the 80% market application rate of leaf spring suspension. This is mainly because the air suspension has complex structure, high purchase and maintenance costs, poor bearing capacity, and is not suitable for heavy cargo transportation. Therefore, its main application fields are still in light truck or dangerous chemicals transportation, flowers, vegetables, fruits transportation and other working conditions.

Although leaf spring suspension is inferior to air suspension in damping performance and deadweight, it has simple structure, low cost of construction and maintenance, strong rigidity and naturally high bearing capacity.

In addition, the leaf spring has the guiding function and can transmit the force and torque in all directions. The spring can also make the leaf spring show linear or nonlinear elastic characteristics in a certain combination way, so it is still active in a large number of medium or heavy transport vehicles.

·Structural composition of leaf spring suspension:

·Working principle of leaf spring suspension:

When the vehicle is running on the uneven road, the wheel bump drives the axle to jump up, and the leaf spring and the lower end of the shock absorber move up at the same time. The length of the leaf spring will increase during the upward movement, which is coordinated by the extension of the lifting lug; Since the upper end of the shock absorber is fixed, when the lower end moves up, it is equivalent to being in a compression state, and the damping increases to attenuate vibration. When the jump on the axle exceeds the distance between the buffer block and the stop block, the buffer block contacts the stop block and compresses.

·Classification of common leaf spring suspension:

1. Multi leaf spring suspension:

It is commonly used in heavy-duty vehicles, and is composed of multiple reeds with different lengths and consistent widths, generally more than 5. The length of the reed becomes longer from bottom to top, and the reed at the bottom is the shortest, thus forming an inverted triangle, making full use of the force principle of the triangle. In addition, the number of reeds is closely related to the load-bearing capacity. The more reeds are in number and thickness, the stronger the rigidity of the reeds will be, and the load-bearing capacity will also increase. Of course, the weight of the reeds cannot be underestimated.

Although there are many pieces of multi leaf spring suspension, its structure is simple and its maintenance cost is low. Because it is rare for multi leaf spring to be completely destroyed in use, it is often necessary to replace the damaged spring alone. However, when the multi leaf springs are used for a long time, they will make abnormal noises due to mutual friction, and the form balance of the vehicle will be affected after the rigidity is weakened.

2. Few leaf spring suspension:

The few leaf spring is composed of springs with thin ends, middle thickness, equal width, and equal length. Therefore, the sectional area of the steel plate of the few leaf spring changes more, the rolling process is more complex, and the price is more expensive than the ordinary steel plate of the multi leaf spring.

Compared with the multi leaf spring, the bearing capacity of the few leaf spring is weakened to a certain extent, but at the same time, the dead weight will also be reduced. According to relevant data, under the same bearing capacity, the weight of the few leaf spring can be reduced by about 30% - 40% compared with the multi leaf spring.

In addition to reducing the weight of the vehicle, the noise generated by the friction of the few leaf springs is also smaller, and the driving comfort of the vehicle has also been improved to a certain extent. Under the environment of standardized transportation, the few leaf springs have become the most common suspension structure.

However, the maintenance cost of the few leaf spring is relatively high. Once the spring is broken, other springs are easily damaged due to uneven stress. Therefore, the replacement is generally a full set of replacement.

The above two kinds of leaf spring suspensions are the most common in the market. In addition, there are some improved suspensions based on multi spring and few spring:

3. Main and auxiliary composite suspension:

It is composed of main spring and auxiliary spring, and only the main spring plays a role when the vehicle load is small. With the increase of load, the secondary spring and main spring play a role together, and its elastic characteristics show nonlinear changes.

4. Leaf spring with gradual stiffness:

The secondary spring is placed under the main spring, and the main spring and the secondary spring form an integrated structure. Its elastic characteristics show nonlinear changes.

·Precautions in use of leaf spring suspension:

Some car owners believe that the leaf spring suspension is composed of a stack of steel plates, which should not be too fragile, so they do not pay much attention to the protection of the suspension in use. This understanding is actually wrong, and the leaf spring suspension also needs to do a good job of daily maintenance and repair.

1. Develop good driving habits. When heavy vehicles pass rough roads or deceleration strips, slow down the speed and avoid sharp turns as much as possible. Otherwise, it is easy to increase the weight of one side, which will not only damage the reed, but even the steel ring and other parts, affecting the stability of the vehicle.

2. In the process of using leaf spring suspension, the wear coefficient is very large, especially in the case of bad road conditions, it is more likely to occur spring fracture. When replacing the spring, especially the multi leaf spring suspension, its position should be adjusted even if other old springs are not damaged. Otherwise, the rigidity strength of the new reed is inconsistent with that of the old reed, and a gap will be left between them after installation, which will aggravate the wear of the new reed and cause excessive stress on the single reed.

3. Pay more attention to the maintenance of the leaf spring in daily life. The lifting lug must be greased. The upper limit of the auxiliary steel also needs to be greased more to reduce the abnormal noise while lubricating, so that the leaf spring can more calmly cope with the increased friction coefficient, avoid the phenomenon of surface strain, and reduce the possibility of spring fracture.

4. During normal maintenance, attention should also be paid to the tightness of the riding bolt and the central bolt used to fix the leaf spring, so as to avoid the looseness of the riding bolt, resulting in the failure of the whole set of leaf springs, or even threatening the driving. Generally, the higher the vehicle load, the more frequent the inspection.

5. The selection of leaf spring number depends on the vehicle load. When the vehicle is often in a heavy load or biased state, it is necessary to consider improving the leaf spring for the original vehicle to enhance the force bearing performance of the leaf spring and improve its service life.

6. Try to choose the leaf spring produced by a regular brand. After all, the suspension is directly related to the load bearing of vehicles, especially heavy vehicles. It is better to be cautious when selecting products.

I hope all car owners can use leaf spring suspension according to the specifications and conduct regular inspection, maintenance and servicing. After all, the car is "three repairs and seven maintenance". Only when the car is well maintained can we obtain more long-term benefits.