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.

Air suspension Air suspension is a type of vehicle suspension powered by an electric or engine-driven air pump or compressor. This compressor pumps the air into a flexible bellows, usually made from textile-reinforced rubber. The air pressure inflates the bellows, and raises the chassis from the axle. Overview Pneumatic spring on a semitrailer Air suspension is used in place of conventional steel springs in passenger cars, and in heavy vehicle applications such as buses and trucks. It is broadly used on semi trailers and trains (primarily passenger trains). One application was on EMD's experimental Aerotrain. The purpose of air suspension is to provide a smooth, constant ride quality, but in some cases is used for sports suspension. Modern electronically controlled systems in automobiles and light trucks almost always feature self-leveling along with raising and lowering functions. Although traditionally called air bags or air bellows, the correct term is air spring (although these ...
Suspension (vehicle) Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both roadholding/handling and ride quality, which are at odds with each other. The tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different. The front suspension components of a Ford Model T. The rear suspension on a truck: a leaf spring. Part of car front suspension and steeringmechanism: tie rod, steering arm, king pin axis (using ball joints). ...
Strut bar A strut bar, strut brace, or strut tower brace (STB) is an automotive suspension accessory usually used in conjunction with MacPherson struts on monocoque or unibody chassis to provide extra stiffness between the strut towers. With a MacPherson strut suspension system where the spring and shock absorber are combined in the one suspension unit which also replaces the upper control arm, the entire vertical suspension load is transmitted to the top of the vehicle's strut tower, unlike a double wishbone suspension where the spring and shock absorber may share the load separately. In general terms, a strut tower in a monocoque chassis is a reinforced portion of the inner wheel well and is not necessarily directly connected to the main chassis rails. For this reason there is inherent flex within the strut towers relative to the chassis rails. A strut bar is designed to reduce this strut tower flex by tying the two strut towers together. This transmits the load off each strut to...
Dual ball joint suspension A dual ball joint suspension uses a pair of arms, one in tension, one in compression, to replace a wishbone, in a MacPherson or SLA suspension. The outer end of each arm terminates in a ball joint, hence the name. General description The two arms, the spindle, and the body, form a four-bar link. Use of the linkage at the lower suspension connection of either a MacPherson strut or a short long arms suspensionreadily gives an effective virtual ball joint outboard of the spindle, which is very useful for a suspension designer, allowing negative scrub radius whilst allowing the ball joints to move in and thus out of the way of the brakes. Some manufacturers use a double ball joint arm to replace both wishbones on a short long arms suspension. This provides further opportunity for optimising the geometry. Examples It is used on large cars such as the Lexus LS 460, BMW X5, Ford Territory, and General Motors' Zeta-derived models. Disadvantages The extra ball joint adds weight and cost. ...
Anti-roll bar An anti-roll bar (roll bar, anti-sway bar, sway bar, stabilizer bar) is a part of many automobile suspensions that helps reduce the body rollof a vehicle during fast cornering or over road irregularities. It connects opposite (left/right) wheels together through short lever arms linked by a torsion spring. A sway bar increases the suspension's roll stiffness—its resistance to roll in turns, independent of its spring rate in the vertical direction. The first stabilizer bar patent was awarded to Canadian inventor Stephen Coleman of Fredericton, New Brunswick on April 22, 1919. Anti-roll bars were unusual on pre-war cars due to the generally much stiffer suspension and acceptance of body roll. From the 1950s on, however, production cars were more commonly fitted with anti-roll bars, especially those vehicles with softer coil spring suspension.   An anti-roll bar (in black) on the rear of a Porsche, which traverses the underside of the car. Flexible bushings attach it to ...