L322 Range Rover System Description and Operation
SUSPENSION
60-26
DESCRIPTION AND OPERATION
Operation
General
Under normal operating conditions, the air suspension ECU 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 ECU 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 ECU does not implement any height adjustment changes. When the ECU detects that a corner has
moved outside of the 'dead band', the ECU operates the compressor and/or the valves to raise or lower the
corresponding corner(s) back into the target height.
When the engine is not running, the 'dead band' target height tolerance is increased to +20 mm and -25 mm. During
'wake-up', the tolerance band is
±
20 mm. In all cases, the ECU will bring the corner height as close as possible to the
target height. The ECU monitors the rate of change of height of the corner signals to predict when to close the valve
so that the target height is not overshot.
Reservoir
The reservoir supplies pressurised air to the four air springs, via the valve block, to enable the air suspension system
to carry out ride height changes.
If an upwards height change request is made when the engine is not running, air pressure within the reservoir is used
to lift the vehicle. If the pressure within the reservoir has dropped below 9 bar (130 lbf/in
2
) when an upwards height
change request is made, the lift procedure is performed by the compressor. When the engine is started, the ECU runs
the compressor to increase reservoir pressure to:
l
13.7 bar (199 lbf/in
2
), in systems without an external pressure relief valve
l
12 bar (174 lbf/in
2
), in systems with an external pressure relief valve
