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.

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, 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 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.

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