Air Supply Unit
| ITEM | DESCRIPTION |
|---|---|
| 1 | HP (high pressure) exhaust port (to valve block) |
| 2 | Pilot exhaust valve |
| 3 | Electrical connector |
| 4 | Air drier |
| 5 | Air intake/exhaust port |
| 6 | Electric motor |
| 7 | Electrical connector |
| 8 | Main exhaust valve 43 of 119 |
The air supply unit is installed in the luggage compartment, on a bracket in the rear left corner of the spare wheel well. For NVH (noise, vibration and harshness) reasons, the air supply unit is attached to the bracket by three isolator mountings, each incorporating a bush and a metal spring.
The air supply unit incorporates:
- a two stage Air supply unit driven by an electric motor
- an air drier
- a main exhaust valve
- a pilot exhaust valve
- an air intake/exhaust port
- a HP exhaust port.
The Air supply unit motor is operated by power from the air suspension relay in the RJB (rear junction box), which is controlled by the ISCM. To prevent damage caused by overheating, the temperature of the air supply unit and motor is calculated by a software model in the ISCM. The calculated temperature is based on air supply unit operating pressure, voltage, time and ambient air temperature. The ISCM discontinues air supply unit operation if the calculated temperature increases to 100 °C (212 °F). Air supply unit operation resumes when the ISCM calculates the temperature has decreased to 80 °C (176 °F).
The air drier removes moisture from the air delivered by the air supply unit to the HP exhaust port, and consists of a chamber that contains water absorbing desiccant beads. When the air suspension system is depressurized, air is vented back through the air supply unit, to initiate air drier regeneration. The clean dry air vented from the system re-activates the desiccant beads.
The main exhaust valve controls the release of air from the air suspension system through the air intake/exhaust port. It also acts as a PRV (pressure relief valve) and minimum pressure retention valve. The PRV function limits the maximum pressure from the air supply unit to 17.5 bar (254 lbf/in2). The minimum pressure retention function limits the minimum pressure in the system to between 0.25 and 1.00 bar (3.75 and 14.5 lbf/in2).
The pilot exhaust valve is a solenoid operated valve that controls the operation of the main exhaust valve. A PWM (pulse width modulation) signal from the ISCM controls the pilot exhaust valve to apply system pressure to the pilot chamber of the main exhaust valve.