Suspension is a general term for all force transmission connection devices between the frame of the semi-trailer and the axle, which is used to transmit the force and torque acting between the wheel and the frame, buffer the impact force transmitted by the road surface to the frame or body, and reduce the vibration caused by it, so as to ensure that the car can run smoothly.

In general, the suspension of semi-trailers can be divided into four main types: 
1. Rigid suspension. The body chassis of the rigid suspension acts directly on the axles between the wheels, without springs as buffers, and relies entirely on the swing of the balance beam to maintain the relative balance of the front and rear axles in the case of uneven road surfaces.
 This kind of suspension is relatively rare at present, because its shock absorption effect is very poor, and it is mainly used in low-bed semi-trailers that carry goods at low speeds.

 2. Steel plate suspension (leaf spring suspension) is also known as series steel leaf spring balance suspension, which is a common leaf spring suspension, which is mainly composed of leaf springs, suspension bearings, connecting rods, U-bolts, etc. 
The biggest advantage of this trailer suspension is that it has low cost, reliable work and easy maintenance. Because of this, the proportion of steel plate suspension currently applied in domestic semi-trailers is the largest, about 70-80%. 

3. Single-point suspension. That is, the common leaf spring front and rear brackets are reduced into a single bracket and connected to the car body, which can divide the force point equally to different axles, so the bearing capacity is larger, and it is generally used in heavy-duty trailers. 

4. Air suspension. It is also called airbag suspension, its most significant feature is the airbag type air spring, compared with other suspensions, the buffer force of air suspension is better, which can effectively protect the goods and improve the driving comfort, and is mainly used in the transportation of precision instruments and hazardous chemicals.

Most of the semi-trailers exported by Sunsky are customized by customers to use air suspension, so what is the good thing about air suspension?

Advantages of air suspension:
1. Good shock absorption. Compared with traditional leaf springs, the airbag is obviously softer and more comfortable, it forms a soft connection between the frame and the axle, and the bumps and shocks from the road surface can be greatly mitigated, in addition to enhancing driving comfort, it is also a kind of protection for the cargo.  
2. Reduce load stress. The compressibility of the air makes the airbag suspension easily cope with road bumps at the same time, which can reduce the load stress, prolong the service life of the axle and semi-trailer, and reduce the cost of the car to a certain extent.  
3. Its weight is smaller. Lightweight is a development trend in the trailer accessories industry, air suspension compared with traditional suspension, its weight is lighter, for the standard load users can get more free weight space, empty users can save fuel, energy saving and efficiency. 
4. Long service life. The mass of the air spring itself is relatively light, and the friction of the air medium in the airbag is also relatively small, and the service life can reach 2-3 times that of the leaf spring, helping the owner to better save costs.


Air suspension has many advantages, but there are also some disadvantages:
1. Compared with other suspensions, the structure of air suspension is more complex because to use air springs, it is necessary to set up rod systems that can transmit various forces and moments other than vertical force, which also leads to its relatively high price to a certain extent. 
 2. The maintenance cost corresponds to the high price. In addition, compared with traditional leaf springs, airbags are more likely to be damaged in terms of material, and the maintenance cost should not be underestimated.  
3. Once the air suspension fails, it cannot continue to drive, and can only call for trailer service. Unlike traditional suspensions, even if there is an oil leak, you can stick to the service outlet.  
4. The air suspension has good cushioning, but in the case of full load, there will be nodding or tailing when braking or starting, and skilled driving skills are also required.

Although the advantages and disadvantages of air suspension coexist, the advantages are more obvious after comprehensive consideration, otherwise air suspension will not become a mandatory suspension designated by the official. In addition, the commercial vehicle industry is now "lightweight" prevailing, shippers are more and more concerned about cargo damage, and the competition between peers is becoming more and more fierce, so the industry background has also promoted the use of air suspension to a certain extent.

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