Some American & British manufacturers use this suspension system. It provides four air bags or air spring assemblies. Air suspension uses air springs instead of conventional steel springs used in other forms of suspensions.
The air spring assembly consists of flexible bags or bellows enclosed in a metal dome. Manufacturers fit them between axles and mount the frame on the air capacity tank. Then, they use a leveling valve to regulate the air supply to maintain a particular distance between the frame and the ground.
A delay device incorporated in the valve provides an instantaneous correction of rebound and roll movements irrespective of load. It uses an engine-driven compressor to maintain a pressure of 5.6 to 7.0 kg/cm2 in the air bellows or reservoir. When a wheel encounters a bump, it applies the load to the frame. Thus, it further compresses the air and absorbs the shock. Therefore, it causes the compression of the spring and opens the leveling valve for supplying air to the spring. The additional air extends the bellows. Finally, it causes the frame to rise to the original position and close the valve.
Advantages Of Air Suspension:
This suspension system is advantageous due to the constant step height provided to the public service vehicles, variable-rate progressive action (spring stiffness increases with deflection), and constant frequency of vibrations compared to metal springs which oscillate more rapidly for unloaded vehicles.
For car suspension systems, springs are not satisfactory alone. However, they are a compromise between flexibility and stiffness. A spring may flex and rebound excessively and repeatedly, providing a rough ride if it is too flexible. On the other hand, more stuff sprung may not flex and rebound properly, resulting in high transmission of shock to the occupants and a stiff ride to the car. A relatively flexible spring with a shock absorber would give an excellent smooth ride.
Manufacturers use Air suspensions instead of conventional steel springs in passenger cars and heavy vehicles such as buses or trucks. In addition, they widely use it in semi-trailers. The primary function of this suspension is to provide for smooth and constant ride quality. However, in some cases, manufacturers use it as sports suspension. Today, vehicles that use air suspension range from Maybach and Rolls-Royce to Audi, Subaru, and Tesla, among others.
Citroën now features Hydractive suspension. It is a computer-controlled version of their Hydro pneumatic system form of air suspension, which includes sport and comfort modes. In addition, some air suspension designs feature height-adjustable suspension controlled by the driver, which is suitable for making it easier to clear bumps or rough terrain.
Tesla Motors offers an optional “Active Air Suspension” on its Model S. It lowers the vehicle for better aerodynamics and increases its range. Common air suspension problems are Airbag or Air–strut failure, Air-line failure, Air-fittings failure, Compressor failure, or Dryer failure.