Electronic Air Suspension

Electronic Controlled Air Suspension is the name of the air suspension system installed on the Range Rover P38A, the 1995 second-generation Range Rover. It was developed in the early 1990s by the company now known as Dunlop Systems and Components Ltd in Coventry, UK.

Overview

The ECAS provides variable-height suspension for on- and off-road applications. The five suspension heights typically offered by ECAS are (from lowest to highest in terms of height) “Loading,” “Highway,” “Standard,” “Off-Road,” and “Off-Road Extended.” Height is controlled automatically based on speed and undercarriage sensors, but a manual ride height switch allows control over the suspension by the driver. The “Loading” and “Off-Road” heights are available only at speeds typically less than 35 miles per hour (56 km/h). The “Highway” setting is not available manually; it is set when the vehicle moves at over typically 50 miles per hour (80 km/h) for over 30 seconds. Unlike a mechanical spring system (where deflection is proportional to load), height may be varied independently from the load by altering the pressure in the air springs.

The air springs were designed to provide a smooth ride, with the additional ability to raise the body of the vehicle for off-road clearance and lower it for higher-speeds road driving. Mechanical springs, for which deflection is proportional to load, cannot do this; with ECAS height is largely independent of load. The developers of ECAS also designed LoadSafe, a related system to ascertain load and change in load on an LCV type vehicle fitted with air springs.

Components

The system comprises:

  • a vulcanised rubber air spring at each wheel
  • an air compressor, which is typically located in the trunk (boot) or under the bonnet
  • a compressed air storage tank may be included for rapid “kneel”, storing air at ~150psi (1000 kPa)
  • a valve block which routes air from the storage tank to the four air springs via a series of solenoids, valves and many o-rings
  • an ECAS computer which communicates with the car’s main computer the BeCM and decides where to route air pressure
  • a series of 6 mm air pipe which channels air throughout the system (mainly from the storage tank to the air springs via the valve block)
  • an air drier canister containing desiccant
  • height sensors ideally on all 4 vehicle corners based, typically, on resistive contact sensing to give an absolute height reference for each corner of the vehicle.
  • Dunlop Systems and Components Ltd have continued to develop the products to the point where the Electronic Control Unit (ECU) is now able to fit under the vehicle floor. The control valves are much smaller and lighter and they produce their own range of compressors.

Problems

The ECAS computer can, using pre-programmed criteria to detect a fault, disable the system into “Hard Fault Mode” which lowers the vehicle to the suspension bump-stops, leaving it usable with radically reduced performance until repaired.

Many enthusiasts use diagnostic devices such as laptop and hand computers running specially developed software to clear spurious faults and avoid the need for repair. Some manipulate the sensors to set the vehicle to a particular ride height at all times by adjusting the lever ratio on the height-sensing devices, or a supplementary ECU to “fool” the system.

Leaks in the system, often due to main seal wear caused by excessive duty cycle, can cause premature compressor failure. Spares produced by the original supplier are available.

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