The principle and failure cause of Mercedes-Benz air suspension
1. Working principle of air suspension
The air suspension is mainly composed of a control computer, an air compressor(air pump), a pressure storage tank, a front pneumatic and rear shock absorber and an air control valve block. There are three main functions, namely, the level control of the body, the level adjustment of the body, and the ADS function is to use an air compressor to form compressed air, and send the compressed air to the air chamber of the spring and shock absorber. There are vehicle height sensors nearby, according to the output signal of the vehicle height sensor, the on-board computer judges the change of the vehicle height, and then controls the compressor and the exhaust valve to compress or extend the spring, so as to reduce the vibration. This changes the height of the vehicle.
1. Level control and level adjustment function
The first two functions of the air suspension system are mutually controlled and are divided into the following three states.
(1) Close and hold state: When the vehicle is lifted, the system will close the relevant solenoid valve, and the computer will memorize the vehicle height, so that the vehicle can maintain the original height after falling.
(2) Normal state, that is, the engine running state: when the vehicle is parked, after a door or luggage compartment lid is opened, if the vehicle height changes by more than 10mm, the system will readjust the vehicle height; during driving, if the vehicle height changes by more than 20mm, the system will readjust the body height every 15mIn.
(3) Wake-up state (working time is about 1 min): When the system control unit is woken up by the remote control key, door switch and trunk lid switch, the system will check the vehicle height through the vehicle level sensor. If the height of the body is more than 30mm lower than the normal height, the air storage tank will provide pressure to raise the body to the normal height, and the pressure of the pressure storage tank must be greater than 1.1MPa at this time; if the height of the body is more than 65mm lower than the normal height, the pressure of the pressure storage tank When it is less than 1.1MPa, the system will command the air pump to work to provide pressure to make the body height reach -63mm, and the battery voltage at this time must be greater than 12.4V; if the body height rises by more than 10mm due to unloading, the system will give up to lower the body. to normal height.
2. ADS function
The ADS function can adjust the softness and hardness of the shock absorber. The shock absorber has three gears: normal, Microsoft and hard. This function can be controlled by the control button in the cab.
The leveling function of the body can also be operated via the body controls in the cab. When the button is pressed, the body will be automatically raised by 25mm, and the body will return to normal state by pressing it again. The normal state refers to the height of the vehicle stored in the system control computer when it leaves the factory.
3. The phenomenon of air suspension failure
1. Air suspension stay;
2. The vehicle is high on one side and low on the other;
3. Air suspension fault light alarm;
Third, the reasons for the failure of the air suspension
1. There is leakage in the air suspension system or each connecting part;
2. Various sensor failures, such as body height sensor, acceleration sensor;
3. The pneumatic shock absorber is damaged;
4. Air compressor failure;
5. Air suspension control unit/system power circuit failure;