Part 4

Vehicle Dynamic Suspension

Height Sensors









A height sensor is fitted in each corner of the vehicle to monitor the ride height of the vehicle. The sensors are mounted on the front and rear subframes, with a mechanical link to the suspension lower arms. There are four different types of sensor fitted.
If a height sensor is removed from its mounting position for servicing or replacement, the Land Rover approved diagnostic system must be used to recalibrate the system. Calibration will also be required if the suspension arm to which the sensor is connected is removed or replaced or if a replacement drop link is fitted.
A calibration routine is performed using the Land Rover approved diagnostic system to read the position of each corner of the vehicle and record the settings in the control module memory. Once set, the calibration is not required to be performed unless the air suspension control module is removed or replaced, a height sensor is removed or replaced or a suspension arm to which the sensor is connected is removed or replaced. If the removed height sensor is subsequently refitted, the calibration procedure will have to be performed to ensure the integrity of the system.
The height sensors are attached to brackets on the subframes and are connected to the lower arms by links. The links allow articulation of the arm to allow for suspension travel. Each sensor is connected by a six pin multiplug.
The front and rear sensor drop links are serviceable items.
The four suspension height sensors that are used in the air suspension system also supply input to the adaptive dynamics system, two for the front suspension and two for the rear suspension. A front suspension height sensor is attached to each side of the front subframes and connected by a sensor arm and sensor link to the related lower lateral arm of the front suspension. A rear suspension height sensor is attached to each side of the rear subframe and connected by a sensor arm and sensor link to the related upper control arm of the rear suspension. On each suspension height sensor, the sensor arm and sensor link convert linear movement of the suspension into rotary movement of the sensor shaft.
The suspension height sensors measure suspension displacement at each corner of the vehicle and output a corresponding analogue signal to the air suspension module. The algorithms in the air suspension module calculate the position, velocity and frequency content of the signals and use the results for wheel control.
The sensors can be checked by applying 5V across the positive and negative terminals and measuring output signal which should be a nominal 57mV ± 3% per degree of sensor arm movement.
The following graph shows the vehicle height displacement from normal against output voltage for the front height sensors. The center line represents the "nominal" condition but depending on tolerances, the actual line may lie anywhere between the upper and lower lines.

Front Height Sensor





The following graph shows the vehicle height displacement from normal against output voltage for the rear height sensors. The center line represents the "nominal" condition but depending on tolerances, the actual line may lie anywhere between the upper and lower lines.

Rear Height Sensor





Air Springs









The air springs on the front and rear suspension are similar in construction. The air springs are manufactured from a flexible rubber and each air spring forms an air tight cavity which provides the required spring rate for each corner of the vehicle.
As the air spring is compressed, the rubber material compresses and rolls down the side of the vertical housing (piston) below the spring. An air connection port is located on the top of each spring and allows air to be added or removed from each spring. The port is connected via a Voss connector and a plastic tube to the axle valve block.
Replacement of an individual air spring does not require a full depressurization of the air suspension system. Only the corner concerned need be depressurized. This is achieved using a routine in the Land Rover approved diagnostic system.
When servicing of an air spring or a full system depressurization is required, the weight of the vehicle must be supported before the system is depressurized. On reassembly, the air spring must be fully pressurized before the weight of the vehicle is applied to it.

AIR HARNESS









The system is interconnected via 6 mm diameter blue, yellow and black colored nylon pipes. The yellow pipes denote the right hand side and the black pipes denote the left hand side. Blue colored pipes are used to show the pipes which connect the front and rear valve blocks to the reservoir valve.
The air harness comprises a main harness which is located along the full length of the vehicle and connects the reservoir valve block to the front and rear valve blocks and the reservoir and four separate harnesses which are used to connect each valve block to the air springs.
The pipes are attached to the subframes and vehicle body with clips. To ensure that the correct routing is maintained, the pipes have timing marks which align with various clip positions. The timing marks are in the form of a white band around the pipe, indicating the clip position. If the correct routing is not achieved, unnecessary tension at the pipe joints will occur resulting in possible early failure.
If a pipe becomes damaged, an in-line connector is available for repair purposes. The pipes are secured to the body and the chassis with a number of plastic clips.

LEAK DETECTION
Leak detection can be carried out using a Land Rover approved leak detection spray.
If the vehicle appears to be leaking, perform a leak check on all aspects of the system, i.e.; air spring hose fittings and the associated connections on the valve blocks, air springs and reservoir. Failure to correctly diagnose leakage will result in unnecessary exchange of serviceable components and recurrence of original problem.

AIR SUSPENSION CONTROL MODULE
The air suspension system fitted to Range Rover is controlled by the air suspension control module which is located in the RH (right-hand) rear quarter panel.
The control module monitors the height of each corner of the vehicle via four height sensors, which are mounted in-board of each road wheel.
The control module has the following modes of operation:
- Calibration
- Normal
- Periodic Wake-Up.
When a new air suspension control module is fitted, the air suspension system will not function until the air suspension software is loaded and the system calibrated using the Land Rover approved diagnostic system.

Calibration
A calibration routine is performed using the Land Rover approved diagnostic system to access the position of each corner of the vehicle and record the settings in the control module memory. Once set, the calibration is not required to be performed unless the air suspension control module is removed or replaced, a height sensor or bracket is removed, replaced or disturbed or a suspension arm to which the sensor is connected is removed or replaced. If the removed height sensor is subsequently refitted, the calibration procedure will have to be performed to ensure the integrity of the system.
If the air supply unit, the reservoir, a valve block, a damper module or the air harness is removed or replaced, the system will not require recalibration.

Periodic Wake-Up Mode
When the vehicle is parked, the air suspension control module 'wakes up' two hours after the ignition was last switched off and once every twenty four hours thereafter. The vehicle height is checked and if the vehicle is not level within a pre-set tolerance, small downwards height adjustments may be made automatically.

SYSTEM OPERATION
Under normal operating conditions, the air suspension control module keeps the vehicle level at the 'current' ride height. The incoming height signals from the sensors are passed through filters to remove irregular signals produced by road noise or other irregularities. When the vehicle is stationary or a height change is in progress, the signals are passed through a 'fast' filter, which tracks the true rate of change of height. When the vehicle is moving, the signals are passed through a 'slow' filter. The 'slow' filtered signals remove almost all road noise from the signals and output a true long term average for each corner height. The 'slow' filtered signals cannot be used to respond quickly during height changes.
The air suspension control module monitors each corner height signal using the fast filtered signals if the vehicle is stationary or the slow filtered signals if the vehicle is moving. If the height remains in a 'dead band' which is ±10 mm from the target height, the control module does not implement any height adjustment changes. When the control module detects that a corner has moved outside of the 'dead band', the control module operates the compressor and/or the valves to raise or lower the corresponding corner(s) back into the target height.

SYSTEM INHIBITS
A number of conditions exist where a change in ride height is undesirable. To counter this, the air suspension control module is programmed with a number of system inhibits. If any of the conditions detailed below exist, the air suspension control module will suspend height changes and height corrections.

Compressor
Compressor Temperature
Two temperature sensors are located within the compressor to prevent overheating. If the temperature of the motor brush assembly or the compressor cylinder head rise above pre-set limits, the air suspension control module will inhibit the compressor operation. The limits are detailed in tables in the Air Supply Unit section of this product.

Cornering
If the air suspension control module registers a cornering force greater than 0.2g it will inhibit all height changes and corrections. The system will remain inhibited until the cornering force falls to less than 0.15g. The air suspension control module receives a message from the lateral acceleration sensor (which is an integral part of the ABS (anti-lock brake system) yaw rate sensor) on the high speed CAN (controller area network) bus for the cornering force.

Rapid Acceleration
If the air suspension control module registers a rapid acceleration greater than 0.2g it will inhibit all height changes and corrections. The system will remain inhibited until the rapid acceleration falls to less than 0.15g. Acceleration is calculated by the control module from a vehicle speed signal received via the high speed CAN (controller area network) bus.

Rapid Deceleration
If the air suspension control module registers a rapid deceleration smaller than - 0.2g it will inhibit all height changes and corrections. The system will remain inhibited until the rapid deceleration rises above - 0.15g. Deceleration is calculated by the control module from a vehicle speed signal received via the high speed CAN (controller area network) bus.

Vehicle Jack
The air suspension control module will inhibit all height changes and corrections if it detects a corner lowering too slowly for more than 1.2 seconds. This is interpreted as the corner identified as moving too slowly being supported on a jack. In this situation, the corner height will not change when air is released from the air spring because the jack acts as a mechanical prop.
The system will remain inhibited until any of the following conditions exist:
- The air suspension rotary switch is moved to the up or down position
- The vehicle speed rises to more than 2 mph (3 km/h) for more than 45 seconds.

Door Open
The air suspension control module will stop all height change requests while any of the doors are open. Vehicle leveling continues with a door open by keeping the vehicle at the height when the door was opened if the vehicle load changes. Door open status is ignored when the vehicle speed is above 5 km/h.

DIAGNOSTICS
The air suspension control module can store fault codes which can be retrieved using the Land Rover approved diagnostic system. The diagnostics information is obtained via the diagnostic socket which is located below the instrument panel, above the drivers foot pedals. The socket is protected by a hinged cover.
The diagnostic socket allows the exchange of information between the various control modules on the bus systems and the Land Rover approved diagnostic system. This allows the fast retrieval of diagnostic information and programming of certain functions using the Land Rover approved diagnostic system.

Fault Messages
The air suspension has two methods which it can use to inform the driver of a fault in the air suspension system; the air suspension control switch LED (light emitting diode)'s and the instrument cluster message center.
If the air suspension control module suffers a major failure and there is no air suspension control, all the control switch LED (light emitting diode)'s will remain unlit.
If a fault occurs and the control module can determine the ride height and the vehicle is not above on-road height, the driver will be notified via a message in the message center. If the control module cannot determine the height of the vehicle, or the vehicle is above on-road height and cannot be lowered, a message is displayed and accompanied with a maximum speed message.
For additional information, refer to Information and Message Center Description and Operation

RESERVOIR
The reservoir supplies pressurized air to the four air springs, via the reservoir valve block, to enable the air suspension system to raise the vehicle more quickly.
The air suspension control module assumes the reservoir has sufficient pressure, which is measured before a vehicle raise is started. The control module then uses a software model to operate the compressor as required.

SYSTEM PNEUMATIC CIRCUIT
The following schematic diagram shows the connection relationship between the air supply unit, the reservoir, the reservoir valve block, the cross-link valves and the air springs.

System Schematic Circuit Diagram









AIR SUSPENSION CONTROL DIAGRAM

NOTE:
A = Hardwired; D = High speed CAN (controller area network) bus