Suspension Control ( Automatic - Electronic ): Description and Operation
Vehicle Dynamic Suspension
The vehicle dynamic suspension is a passive air suspension system providing vehicle levelling independent of load. The system also improves the drag coefficiency by automatically lowering the vehicle for high speed driving.
When driving at high speeds, the air suspension system will lower the vehicle to improve aerodynamics and vehicle stability. The suspension will automatically return the vehicle to the normal ride height when the vehicle slows.
NOTE: Speed lowering is disabled when towing. Only Jaguar approved towing equipment will inhibit this feature.
The air suspension system ensures that the vehicle is always at the correct ride height for varying load conditions.
The air suspension system automatically adjusts the amount of air in the air springs to level the vehicle. Air is supplied either from an air reservoir or a compressor. The compressor will run periodically to fill the air reservoir.
The air suspension module (ASM) controls the operation of the solenoids in the valve block. The front air springs are operated as a pair, the rear air springs are operated independently of each other. The ASM adjusts one axle at a time, for example, when lifting the vehicle the rear axle is controlled first, when lowering the vehicle the front axle is controlled first. This reduces headlamp glare during leveling operations.
The ASM uses two different filter rates. When stationery, a 'fast' filter allows the system to react quickly to payload changes. Whilst driving a 'slow' filter allows for compensation of the fuel level change but does not react to road inputs for example pot holes and speed bumps.
Suspension Height Sensors
Vehicles built before December 2003 have four suspension height sensors which are mounted on the front and rear subframe assemblies, two front and two rear. Vehicles built after December 2003 have only three (the right front sensor being deleted), although the functionality of the system remains the same. The suspension height sensors are linked to the suspension arms by drop link connections and secured by means of a spring clip.
NOTE: There may be some early vehicles which will have four sensors fitted, but which have the three-sensor module, making the right front sensor redundant. To confirm the level of equipment, read the module part number from the special applications menu in configuration on the Jaguar approved diagnostic system. Part numbers before 'BJ' are four sensor, while 'BJ' and after are three sensor. If the Jaguar approved diagnostic system is not available, remove the rear seat and sound deadening and read the part number from the module.
NOTE: Suspension height sensors require calibration if removed/refitted or replaced.
Air Springs
Two derivatives of the air spring are available, comfort and sport, the sport having slightly smaller working volumes for higher spring rates.
The air springs are complemented by two versions of damper assembly, passive and active.
CAUTION: When removing and refitting the air spring and damper assemblies, care must be taken to avoid damage to the internal seal assembly.
CAUTION: When working on the air spring and damper assembly, ensure that no twisting occurs between the air spring top mounting and damper body. Twisting may result in damage to the air spring inner components.
A pressure retaining valve (PRV) is located in each air spring which retains sufficient pressure to protect the air spring membrane during service and handling.
NOTE: De-pressurization and re-pressurization of the air suspension system should be performed using the Jaguar approved diagnostic system prior to, and after, any work being carried out.
Solenoid Valve Block
The solenoid valve block contains five individual solenoid valves (one per air spring and one for the vehicle reservoir). A pressure sensor is incorporated into the solenoid valve block and monitors air spring and reservoir pressure. The solenoid valve block is mounted on isolators to reduce valve operation noise. Pipe connections are provided for the front and rear air spring assemblies and also the reservoir and compressor. The compressor to valve block port and the rear air spring ports are 4 mm in diameter with the front air spring ports being 6 mm in diameter. Each of the solenoid valve block ports and air pipes are color coded (pink, blue, white, yellow, red and brown) for correct connection.
Reservoir
The reservoir has a volume of 4.5 liters with a maximum design pressure of 15 bar (218 psi). Dependent on load conditions, this store of reserve air is sufficient for two full lifts. The system automatically replenishes the reservoir by way of the compressor.
Air Suspension Module
The air suspension module (ASM) is accessed from the right-hand side of the vehicle, behind the back of the rear seat. The ASM can be recognized by the 4 individually colored connectors (gold, grey, yellow and pink) and the 'WABCO' logo on the front of the module. ASM calibration is required when either a replacement module is fitted, or if any height sensors have been removed/refitted or replaced.
NOTE: When installing a new air suspension module it will be necessary to configure the module into the customer mode using the Jaguar approved diagnostic system.
Compressor
The air compressor is located in the left-hand front wheel arch behind the bumper beam assembly. It contains an air filter, an integral regenerative air drier element plus an air exhaust solenoid valve. The compressor is isolated from the main body structure by 3 mounts, each incorporating a rubber bush and metal spring. The maximum pressure developed by the system is 15 bar (218 psi) with a compressor pressure relief valve fitted, set to relieve pressures above 17 Bar (247 psi). The compressor only operates whilst the engine is running. To guard against the compressor overheating the ASM may shut down the compressor to allow cooling to take place. Re-activation of the compressor depends on vehicle activity and is generally no longer than 120 seconds.
Vehicle Dynamic Suspension
Operating modes
Before it will be possible to verify the customer concern, it will be necessary to understand the modes of the system to establish what the system should and should not do in each mode. The table below should help in understanding the operating modes.
TRANSPORTATION MODE
The vehicle will arrive at the dealership in transportation mode, and will need to be reset to customer mode at PIDI (this will be carried out by a Jaguar dealer).
Transportation mode keeps the vehicle in a raised condition to allow adequate clearance for transporter loading and unloading. If the vehicle has lowered, the compressor is used to lift the vehicle. Until a suitable height is reached, the message center will display Vehicle too low. The message, Air Suspension Fault will be displayed on the message center at all times whilst the vehicle is in transportation mode.
CUSTOMER MODE
The modes below are all enabled in this mode.
SLEEP MODE
The system shuts down into sleep mode 30 minutes after the vehicle is left, and "wakes up" to check the ride height every 24 hours. If the vehicle is not level, the system lowers until the vehicle attitude is correct. The system will not lift the vehicle while in sleep mode to conserve reservoir pressure and battery power.
PRELIMINARY MODE
When a door or luggage compartment is opened, or the engine is switched off from a standstill condition, (see below) this mode is enabled.
In Preliminary mode, the reservoir is used to lift the vehicle to level it to within a greater tolerance than in stance or drive modes (see below).
STANCE MODE
When the vehicle is stationary with the engine running, (standstill condition) the vehicle will be levelled to within a closer tolerance than in preliminary mode to ensure that the trim heights are correct before moving off.
Any lifting necessary will be done from the reservoir, unless the vehicle is below a preset minimum height and the reservoir pressure is below a preset minimum, in which case, the compressor be will used to lift the vehicle.
DRIVE MODE
When the vehicle speed is above the preset threshold, the compressor is always used to lift the vehicle. This threshold is also used to initiate recharging of the reservoir. The following functions are enabled in drive mode;
Speed Lowering Function
To reduce aerodynamic drag and enhance vehicle stability, the system lowers the vehicle at high road speeds.
Levelling Inhibit Function
When the system detects significant cornering, braking and acceleration, it inhibits levelling such that it will not attempt to compensate for vehicle attitude changes.
Inclination Function
The system enables this function when parking on an uneven surface, (or with a wheel on a kerb, for example) to ensure the vehicle attitude remains correct when driving off.
Rough Road Detection
When the system detects a rough road surface, the speed lowering function is inhibited, or canceled, bringing the vehicle back up to standard ride height to aid passenger comfort.
Trailer Towing Function
When the system detects that the vehicle is towing, (via the connection of the trailer socket) the speed lowering function is inhibited.
NOTE: This function will only be enabled via the Jaguar approved towing equipment.
Jacking Function
When the system detects that the vehicle is being jacked, or raised on a wheel-free lift, the vehicle enters jacking mode, which inhibits lowering to prevent air loss.
Jacking mode is exited when the vehicle is driven, or the ride height passes below a threshold value.