Air Suspension - Overview

Overview

Whilst not using high pressure mineral oil (as does the Citroën system), the system aims to achieve a result similar to the hydropneumatic suspension arrangement introduced in 1954 by Citroën.

In 1901 William W. Humphreys patented (#673682) 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 con-caved to receive two long pneumatic cushions. Each one was closed at one end and provided with an air-valve at the other end.

An early attempted implementation of air suspension was by Messier in the 1920s.

Immediately following World War II, William Bushnell Stout built one last prototype Stout Scarab, called the Stout Scarab Experimental. It was shown in 1946 and was more conventional in appearance than the prewar Scarabs, although still equipped with a rear engine. It was 2-door and featured a wraparound windshield. It featured the world's first fiberglass body, and like its metal counterparts, it was monocoque, built up out of only eight separate pieces. More importantly, it featured the world's first fully functioning air suspension system, previously developed by Firestone. It never went into production.

With a "leg up" on other companies, GM used its experience with commercial bus air suspension to introduce systems for its automobile lines, introducing it as standard equipment on the Cadillac Eldorado Brougham in the 1957 model year. The following year it was offered as optional equipment on all Cadillacs, and in 1959 it was made standard equipment on all Eldorados. Air bags at each wheel replaced standard coil springs, and had sensors to keep the car level under load and in turns. It was too slow to react in sudden maneuvers. Period reviews rated the air suspension somewhat superior in ride quality, but not dramatically. Some reliability issues plagued these systems as well.

Cadillac discontinued air suspension after the 1960 model year. Air suspension would not return to standard production until Lincoln introduced it as standard equipment on the Lincoln Continental Mark VII in the 1984 model year.

Vehicles that use air suspension today include models from Maybach, Rolls-Royce, Lexus, Jeep Grand Cherokee, Cadillac (GM), Mercedes-Benz, Land Rover/Range Rover, SsangYong, Audi, Subaru, Volkswagen, and Lincoln and Ford, among others. Citroën now feature Hydractive suspension, a computer controlled version of their Hydropneumatic system, which features sport and comfort modes, lowers the height of the car at high speeds and continues to maintain ride height when the engine is not running.

The air suspension designs from Land Rover, SsangYong, Subaru and some Audi, VW, and Lexus models, feature height adjustable suspension controlled by the driver, suitable for clearing rough terrain. The Lincoln Continental and Mark VIII also featured an air suspension system in which the driver could choose how sporty or comfortable they wanted the suspension to feel. These suspension settings were also linked to the memory seat system, meaning that the car would automatically adjust the suspension to individual drivers. The control system in the Mark VIII lowered the suspension by about 25 mm (1 inch) at speeds exceeding about 100 km/h (60 mph) for improved aerodynamic performance. Due to the many advantages air suspensions provide, and with the advancement of new materials and technologies, these systems are being designed on many future platforms. This is especially important as car manufacturers strive to improve gas mileage by reducing weight and utilizing active suspension technology to maximize performance. The electric car maker Tesla Motors plans to offer "Active Air Suspension" as an option on the Tesla Model S as a means to automatically lower the vehicle for optimized aerodynamics and increased range while allowing the user to change the setting as desired.

In addition to passenger cars, air suspension is broadly used on semi trailers, trains (primarily passenger trains) and buses, which are all transportation sectors that helped pioneer the use and design of air suspension. One application was on EMD's experimental Aerotrain.