Air suspension professionals will answer. First explain that air suspension is not the same as active suspension. Air suspension is a suspension system with air springs as elastic elements. Its biggest feature is variable stiffness and easy adjustment. Variable stiffness means that air springs are controlled by a height valve compared to leaf springs, coil springs and other vehicle springs. It has the characteristic that stiffness varies with load. The intuitive experience is that when the large leaf spring truck sits on the road when it is empty, it feels that the car jumps on the road at a very high frequency when it is running. When it is fully loaded, it does not jump so much, and it feels a bit like a car. And if you use an air spring, no matter whether it is empty or fully loaded, the difference in sitting up is very small (there will be a little, but most people can't feel it). Easy to adjust means that its height can be adjusted by charging and discharging air inside (of course, the control system used is more complicated than a single height valve). Its stiffness can be adjusted by changing the cross section of the piston, opening and closing additional air chambers, etc. (this makes it possible to use as the main suspension). At present, the largest user of air suspension is not passenger cars but commercial vehicles (in developed countries, trucks and trailers are equipped with a high rate of equipment, a large amount, and a higher rate of passenger cars, but the amount is not too large because the base is small. We are large and medium-sized The equipment rate of passenger cars is about 30%, the amount is large, the equipment rate of truck trailers is very low, very low, and the amount is basically negligible...), commercial vehicles use basically the simplest control system, and at most there is a height adjustment. Up. Active suspension is a suspension system that can adjust the damping of the damping element (shock absorber) and the stiffness of the elastic element (spring) in real time according to external conditions. If only the damping can be adjusted, it is called a semi-active suspension. "Hydraulic suspension" is not very familiar. It should mean "oil-air spring suspension". It is characterized by the use of high-pressure nitrogen (original erroneously written as high-pressure air, Xie Wang Xiaoxiao pointed out) as the spring and integrated with the shock absorber. Because I don't understand its specific structure, I can't give a detailed explanation. If you compare air suspension and oil-air suspension, there are at least the following differences: 1. The working pressure difference, the working pressure of air suspension is generally around 5-10 bar. The oil-air suspension is generally around 70 bar. In this case, the cylinder diameter of the air spring and the oil-air spring that bear the same load is not small. There are some particularly heavy vehicles (such as 50-ton main station tanks, air springs cannot be used because of the limited diameter space for the springs) 2. Air springs require compressed air sources, and oil-gas springs require hydraulic sources. Generally, passenger cars such as cars and SUVs do not require compressed air, so if you want to equip them with air suspension, you need to introduce a special set. Time is limited and temporarily suspended.