Suspension Air Supply Unit
| ITEM | DESCRIPTION |
|---|---|
| 1 | Air supply housing outer lid |
| 2 | Air supply housing inner lid |
| 3 | Electric motor |
| 4 | Electrical connector (2 off) |
| 5 | High Pressure (HP) air outlet |
| 6 | Exhaust silencer |
| 7 | Air drier |
| 8 | Intake air filter |
| 9 | Compressor |
| 10 | Air supply housing base |
The suspension air supply unit comprises the following major components:
- The 2-stage piston compressor
- The 12V electric motor
- The solenoid operated exhaust pilot valve
- The pneumatically operated exhaust valve
- The air drier unit
- The compressor temperature sensor.
The air supply housing encloses the suspension air supply unit. The air supply housing is a double layer box which is lined with insulating foam which suppresses the operating noise of the suspension air supply unit. Each layer of the box has a plastic moulded base and a pressed steel lid.
The suspension air supply unit supplies dry, compressed air into the air suspension system. The compressed air is directed into the air springs or the reservoir by solenoid operated valves.
Air is exhausted from the system by opening the exhaust valve. Lowering the suspension is achieved by opening the required air spring valves and the exhaust valve. Opening the reservoir valve is not required to exhaust air unless the reservoir is being vented for a service procedure. For example reservoir replacement or valve block replacement.
The compressor operates to pressurize either the reservoir or to inflate 1 or more of the air springs.
The compressor will not operate when the vehicle is not in power mode 7 (vehicle ready), with the following exceptions:
- During rear height adjust operation when the reservoir pressure is low.
- When under control of the Jaguar Land Rover (JLR) approved diagnostic equipment.
There are a number of conditions that will inhibit operation of the suspension air supply unit. It is vitally important that these system inhibits are not confused with a system malfunction. A full list of suspension air supply unit inhibits are given in the air compressor information below
Electric Motor
The electric motor is a 12V Direct Current (DC) motor with a nominal operating voltage of 13.5V. The motor drives a crank which has an eccentric pin to which the 2 stage piston assembly is attached.
Air Compressor
The compressor comprises a motor driven 2 stage piston assembly which operates in cylinders at opposite ends of the compressor body. The motor rotates a crank which moves the pistons up and down in their cylinder bores. The Low Pressure (LP) cylinder delivers intermediate compressed air to the High Pressure (HP) cylinder on the down stroke. The HP piston delivers fully compressed air with the up stroke. The compressed air is passed, via the delivery valve, through the air drier and into the air suspension system.
The cylinder head is equipped with a temperature sensor. The sensor is connected to the Chassis Control Module (CHCM) which monitors the cylinder temperature and can suspend compressor operation if an overheat condition occurs.
The following table shows the CHCM operating parameters for the differing suspension air supply unit functions and the permitted compressor cylinder head operating temperatures.
| OPERATING CONDITION | RESERVOIR FILLING | LEVELING |
|---|---|---|
| Switch off | 125°C (257°F) | 130°C (266°F) |
| Switch on | 105°C (22TF) | 120°C (247°F) |
Air Drier
The air drier is attached to the compressor which contains a desiccant for removing moisture from the compressed air. The pressurized air is passed through the air drier which removes any moisture in the compressed air before it is passed into the suspension system.
When the air springs are deflated, the exhaust air passes back through the air drier, removing the moisture from the unit and regenerating the desiccant.
The air drier is an essential component which makes sure that only dry air is present in the system. If moist air is present, freezing can occur resulting in poor system operation or component malfunction or failure.
To make sure that the air drier continues to work correctly it is essential during servicing that the affected air springs or the reservoir are deflated. Use the approved diagnostic routine before any connections which hold air in these component are removed.
Pilot Exhaust Valve
The exhaust valve operates when the pilot exhaust valve is opened, allowing air to be exhausted quickly.
The pilot exhaust valve is connected to the air delivery gallery, downstream of the air drier. The pilot valve, when opened, operates the slave exhaust valve, allowing air to exhaust the system.
When the solenoid is energized, pilot air moves the slave exhaust valve plunger. The slave exhaust valve plunger allows the pressurized air from the air suspension system to pass through the air drier to the atmosphere.