Part 2

Vehicle Dynamic Suspension - Continued

Valve Block Solenoid Specifications

The air supply unit fitted from 2006MY is an improved unit providing quieter operation. Two silencer units are incorporated into the unit assembly to reduce operating noise.

The air supply unit is located in a housing which is mounted in the spare wheel well and secured with four bolts into threaded inserts to the vehicle floorpan. The unit is isolated from the vehicle body via four rubber isolation mounts.

The reservoir valve block is also located within the housing on a separate bracket at the rear of the unit.

The unit is connected to the system via a single air pipe to the reservoir valve block. Three air pipes from the reservoir valve block pass through an aperture in the unit housing and through a grommet in the wheel well. It is important to ensure that this grommet is not disturbed and correctly installed. Incorrect fitment will allow water to enter the wheel well leading to possible damage to and failure of the air supply unit.

The unit comprises a piston compressor, a 12 V electric motor, a solenoid operated exhaust pilot valve, a pressure relief valve, an air dryer unit and two silencers.

The electric motor, compressor, air dryer and pressure limiting and exhaust valve are mounted on a frame which in turn is mounted on flexible rubber mountings to reduce operating noise. The unit is mounted on a pressed base plate which is located on the floor of the wheel well. The unit is protected by a pressed cover which is lined with an insulating foam further limiting the operating noise.

The air supply unit can be serviced in the event of component failure, but is limited to the following components; air dryer, pilot exhaust pipe and the rubber mounts. Removal of the air supply unit does not require the whole air suspension system to be depressurized. The front and rear valve blocks and the reservoir valve block are normally closed when de-energized, preventing air pressure in the air springs and the reservoir escaping when the unit is disconnected.

There are a number of conditions that will inhibit operation of the air supply unit. It is vitally important that these system inhibits are not confused with a system malfunction. A full list of air supply unit inhibits are given in the air suspension control module information.

Electric Motor
The electric motor is a 12V dc motor with a nominal operating voltage of 13.5V. The motor drives a crank which has an eccentric pin to which the compressor connecting rod is attached.

The motor is fitted with a temperature sensor on the brush Printed Circuit Board (PCB) assembly. The sensor is connected to the air suspension control module which monitors the motor temperature and can suspend motor operation if the operating thresholds are exceeded.

The following table shows the control module operating parameters for the differing air supply unit functions and the allowed motor operating temperatures.

Motor Operating Temperatures

The following graph shows motor temperature sensor resistance values against given temperatures.

NOTE: This graph is also applicable for the compressor cylinder head temperature sensor.

The following graph shows air suspension control module output voltages against motor temperature sensor temperatures.

NOTE: This graph is also applicable for the compressor cylinder head temperature sensor.

Compressor
The compressor is used to supply air pressure to the air suspension reservoir. The air suspension control module monitors the pressure within the reservoir and, when the engine is running, maintains a pressure of 14.5 bar gage (210 lbf/in2).

The compressor comprises a motor driven connecting rod and piston which operate in a cylinder with a separate cylinder head. The motor rotates the crank moving the piston up and down in the cylinder bore. The air in the cylinder is compressed with the up stroke and is passed via the delivery valve through the air dryer and into the system.

The cylinder head is fitted with a temperature sensor. The sensor is connected to the air suspension control module which monitors the cylinder temperature and can suspend motor and compressor operation if an overheat condition occurs.

The following table shows the control module operating parameters for the differing air supply unit functions and the allowed compressor cylinder head operating temperatures.

Compressor Cylinder Head Operating Temperatures

Refer to the motor temperature sensor graph for compressor cylinder head temperature sensor resistance values and the air suspension control module output voltage / temperature sensor graph.

Air Dryer

Attached to the compressor is the air dryer which contains a Desiccant for removing moisture from the compressed air. Pressurized air is passed through the air dryer which removes any moisture in the compressed air before it is passed into the reservoir and/or the system.

When the air springs are deflated, the exhaust air also passes through the air dryer, removing the moisture from the unit and regenerating the Desiccant.

The air dryer is an essential component in the system ensuring 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.

Pilot Exhaust Valve

Attached to the cylinder head is a solenoid operated exhaust pilot valve. This valve is opened when the air springs are to be deflated.

The pilot exhaust valve is connected to the air delivery gallery, downstream of the air dryer. The pilot valve, when opened, operates the compressor exhaust valve allowing the air springs to be deflated.

When the solenoid is energized, pilot air moves the exhaust valve plunger, allowing pressurized air from the air springs and/or the reservoir to pass through the air dryer to atmosphere.

Exhaust Valve

The exhaust valve operates when the pilot exhaust valve is opened, allowing air returning from the air springs and/or the reservoir to be exhausted quickly.

The pilot exhaust valve also provides the system pressure relief function which protects the air springs from over inflation. The valve is pneumatically operated, responding to air pressure applied to it to overcome pressure from its internal spring. The valve is connected into the main pressure gallery which is always subject to the system pressure available in either the air springs or the reservoir. The valve is controlled by a spring which restricts the maximum operating pressure to between 22 to 27 bar gage (319 to 391 lbf/in2).

The minimum pressure in the system is also controlled by the exhaust valve to ensure that, even when deflated, the air springs contain a positive pressure with respect to atmosphere. This protects the air spring by ensuring it can still 'roll' over the piston without creasing.

Air Supply Unit Specifications

NOTE: Resistance values will vary with coil temperature. Resistance of test leads must be measured before any readings are taken. Resistance value of the test leads must be subtracted from final solenoid resistance value.

There are a number of conditions that will inhibit operation of the air suspension compressor. It is vitally important that these inhibits are not confused with a system malfunction. A full list of compressor inhibits is contained in the Air Suspension Control information.

Reservoir

The reservoir is an air storage vessel which provides fast air suspension lift times by the immediate availability of pressurized air into the system.

The reservoir is located under the RH (right-hand) sill of the vehicle and is fabricated from steel and secured with four bolts to the underside of the vehicle. The reservoir supplies pressurized air to the four air springs, via the valve blocks, to enable the air suspension system to carry out ride height changes.

The rearward end of the reservoir has a Voss' air fitting which provides for the connection of the air hose between the reservoir and the reservoir valve block. The reservoir has a capacity of 9.5 liters (580 in3). The nominal working pressure of the reservoir is 14.5 bar gage (210 lbf/in2), with a maximum pressure of 22 bar gage (319 lbf/in2).

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.

The front and rear sensors are handed and are colored coded for identification as follows:
^ Right hand front and rear - black colored lever
^ Left hand front and rear - white colored lever

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.

Each sensor comprises a sensor body which contains a single track rotary potentiometer, a lever arm and a drop link. The sensor is supplied with a reference voltage from the air suspension control module which measures the returned voltage to determine the sensor arm position. On the front height sensors the voltage decreases as the vehicle height increases. On the rear sensors the voltage increases as the vehicle height increases.

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 (blue) center line represents the "nominal) condition but depending on tolerances, the actual line may lie anywhere between the (green) upper and (red) lower lines.

Front Height Sensor

The following graph shows the vehicle height displacement from normal against output voltage for the rear height sensors. The (blue) center line represents the "nominal) condition but depending on tolerances, the actual line may lie anywhere between the (green) upper and (red) 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 behind the passenger side of the instrument panel. The control module is housed in a plastic bracket adjacent the 'A' pillar.

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 six 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 information.

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.

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.

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