Air supply system
The functions of the air supply system are implemented by compressor activation and activation of the solenoid valves. The EHC control unit controls the functions.
F01 shown
| Item | Explanation |
|---|---|
| 1 | 2-pin plug connection for discharge valve |
| 2 | Discharge valve |
| 3 | Air drier |
| 4 | Compressor |
| 5 | 3-pin plug connection for solenoid valve block |
| 6 | Solenoid valve block |
| 7 | 2-pin plug connection for electric motor |
| 8 | Electric motor |
F15 shown
| Item | Explanation |
|---|---|
| 1 | Electric motor |
| 2 | Compressor |
| 3 | Air drier |
| 4 | 2-pin plug connection for discharge valve |
| 5 | 2-pin plug connection for electric motor |
| 6 | 3-pin plug connection for solenoid valve block |
| 7 | Valve block |
The air supply system contains the following components:
- Electric motor for powertrain of the compressor
- Compressor with air drier
- Discharge valve with pressure limitation function
- Solenoid valve block with 2 solenoid valves (2/2-way valves)
Example schematic diagram
| Item | Explanation |
|---|---|
| 1 | Air filter |
| 2 | two-pin plug connection |
| 3 | two-pin plug connection |
| 4 | three-pin plug connection |
| 5 | Solenoid valve for controlling right air spring |
| 6 | Solenoid valve for controlling left air spring |
| 7 | Air spring, rear right |
| 8 | Air spring, rear left |
| 9 | Air drier |
| 10 | Control valve |
| 11 | Discharge valve with pressure limitation function |
| 12 | Compressor |
| 13 | Air intake |
| 14 | Electric motor |
| 15 | Safety valve |
| 16 | Ventilation |
Compressor
The compressor is driven by an electric motor. Voltage is supplied to the electric motor via a relay. The relay is activated by the EHC control unit until the specified nominal height is reached. The compressor temperature is monitored by a time model (stored in the EHC control unit). If the maximum operating time for the compressor is exceeded, further control actions are suppressed. Once the value drops below the threshold value for switching on again, adjustments can be made again.
Air drier
The air taken in by the compressor passes over a water-absorbing filter in the air drier. This withdraws moisture from the air. As long as the air is more moist than the filter, the filter absorbs the moisture. On flowing back, the air is drier than the filter. This returns the moisture to the air and is directed outside.
Solenoid valve block
The solenoid valve block contains the following valves:
- Solenoid valve for controlling the rear left air spring
- Solenoid valve for controlling the rear right air spring
Discharge valve
The discharge valve is activated by the EHC control unit. The air escapes from the solenoid valve block via the discharge valve through the air drier.
The pressure limitation function of the discharge valve limits the pressure in the air supply system as follows: Maximum pressure 13.5 bar (temperature-dependent tolerance +5 to + 6.5 bar = breakaway moment if discharge valve not used for a longer period)
2 air springs
The air springs are integrated in the spring struts. The air springs are surrounded by an aluminum sleeve. The air springs form the airtight and moving connection between the body and the wheel carrier. The air pressure in the air spring supports the vehicle's weight.
Illustration shows F0x air spring.
| Item | Explanation |
|---|---|
| 1 | Shock absorber bearing |
| 2 | Auxiliary spring |
| 3 | Roller piston |
| 4 | Controlled shock absorber |
| 5 | Gaiter |
| 6 | Outer guide |
| 7 | U-type bellows |
| 8 | Residual pressure retention value |
2 ride height sensors
The ride height sensors provide the EHC control unit with information on the heights of the left and right sides of the vehicle. The ride height sensors relevant to EHC are fitted to the rear axle.
| Item | Explanation |
|---|---|
| 1 | Coupling bar |
| 2 | six-pin plug connection |
| 3 | Ride height sensor |
The coupling bar converts the wheel lift into a rotational movement at the ride height sensor. As the spring compresses and rebounds, the output voltage of the ride height sensor changes linearly. On compression at the rear left, the output voltage rises. On rebound, the output voltage falls (rear right exactly vice versa, determined by the installation position).
Check Control
A fault in the single-axle air suspension is shown in the instrument panel by means of a Check Control symbol (yellow). The text for the Check Control message can be called up in the Central Information Display (CID).