Air suspension Information

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. Unlike hydropneumatic suspension, which offers many similar features, air suspension does not use pressurized liquid, but pressurized air. The air pressure inflates the bellows, and raises the chassis from the axle.

Air suspension is used in place of conventional steel springs in heavy vehicle applications such as buses and trucks, and in some passenger cars. It is widely used on semi trailers and trains (primarily passenger trains).

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 terms are also used to describe just the rubber bellows element with its end plates).

In 1901 an American, William W. Humphreys, patented an idea - a Pneumatic Spring for Vehicles. The design consisted of a left and right air spring longitudinally channeled nearly the length of the vehicle. The channels were concaved to receive two long pneumatic cushions. Each one was closed at one end and provided with an air valve at the other end.

From 1920, Frenchman George Messier provided aftermarket pneumatic suspension systems. His own 1922-1930 Messier automobiles featured a suspension "to hold the car aloft on four gas bubbles."

During World War II, the U.S. developed the air suspension for heavy aircraft in order to save weight with compact construction. Air systems were also used in heavy trucks and aircraft to attain self-levelling suspension. With adjustable air pressure, the axle height was independent of vehicle load.

In 1946, American William Bushnell Stout built a non-production prototype Stout Scarab that featured numerous innovations, including a four-wheel independent air suspension system.

In 1950, Air Lift Company patented a rubber air spring that is inserted into a cars factory coil spring. The air spring expanded into the spaces in the coil spring, keeping the factory spring from fully compressing, and the vehicle from sagging.

In 1954, Frenchman Paul Magès developed a functioning air/oil hydropneumatic suspension, incorporating the advantages of earlier air suspension concepts, but with hydraulic fluid rather than air under pressure.Citroën replaced the conventional steel springs on the rear axle of their top-of-range model, the Traction Avant 15 Hydraulique. In 1955, the Citroën DS incorporated four wheel hydropneumatic suspension. This combined a very soft, comfortable suspension, with controlled movements, for sharp handling, together with a self-levelling suspension.

In 1956 air suspension was used on EMDs experimental Aerotrain.

In the U.S., General Motors built on its World War II experience with air suspension for trucks and airplanes. It introduced air suspension as standard equipment on the new 1957 Cadillac Eldorado Brougham. An "Air Dome" assembly at each wheel included sensors to compensate for uneven road surfaces and to automatically maintain the cars height. For 1958 and 1959, the system continued on the Eldorado Brougham, and was offered as an extra cost option on other Cadillacs.

In 1958, Buick introduced an optional "Air-Poised Suspension" with four cylinders of air (instead of conventional coil springs) for automatic leveling, as well as a "Bootstrap" control on the dashboard to raise the car 5.5 inches (139.7 millimetres) for use on steep ramps or rutted country roads, as well as for facilitating tire changes or to clean the whitewall tires. For 1959, Buick offered an optional "Air Ride" system on all models that combined "soft-rate" steel coil springs in the front with air springs in the rear.

An optional air suspension system was available on the 1958 and 1959 Rambler Ambassadors, as well as on all American Motors "Cross Country" station wagon models. The "Air-Coil Ride" utilized an engine-driven compressor, reservoir, air bags within the coil springs, and a ride-height control, but the $99 optional system was not popular among buyers and American Motors (AMC) discontinued it for 1960.

Only Cadillac continued to offer air suspension through the 1960 model year, where it was standard equipment on the Eldorado Seville, Biarritz, and Brougham.

In 1960, the Borgward P 100 was the first German car with self-levelling air suspension.

In 1962, the Mercedes-Benz W112 platform featured an air suspension on the 300SE models. The system used a Bosch main valve with two axle valves on the front and one on the rear. These controlled a cone-shaped air spring on each wheel axle. The system maintained a constant ride height utilizing an air reservoir that was filled by a single-cylinder air compressor powered by the engine. In 1964, the Mercedes-Benz 600 used larger air springs and the compressed air system also powered the brake servo.

Rolls-Royce incorporated self-levelling suspension on the 1965 Rolls-Royce Silver Shadow, a system built under license from Citroën.

In 1975, the Mercedes-Benz 450SEL 6.9 incorporated a hydropneumatic suspension when the patents on the technology had expired. This design replaced the expensive, complex, and problematic compressed air system that was still used on the 600 models until 1984.

Air suspension was not included in standard production American-built cars between 1960 and 1983. In 1984, Ford Motor Company incorporated a new design as a feature on the Lincoln Continental Mark VII.

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