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Air Suspension System

Yogesh Ambekar Apr 20, 2019
A suspension system in which air is the working fluid as well as the shock absorber is called air suspension system. The detection of causes and solutions for the problems with the linked system are discussed here.
The front and rear suspension system or the suspension units on the two sides of the vehicle are connected with each other in an interconnected suspension system. They are also termed collectively as linked system.
It was very much effective as compared to independent front and rear suspension units and was able to reduce the tendency of a vehicle to bounce, pitch or roll and was able to provide smooth and comfortable drive. Interconnected suspension system is categorized into an air suspension system, hydrolastic suspension and hydro gas suspension system.
  • The automatic control devices installed in the vehicle allows making optimum use of the variable space for deflection of wheel.
  • The height of the automobile remains steady and so the changes in the alignment of headlamp due to varying loads are restricted.
  • It helps to reduce the load while the vehicle in motion i.e., the dynamic loading as the spring rate variation between laden and unladen weight is much less.
  • It gives smooth and comfort ride of the vehicle.
Air springs are classified into two types:
  1. Bellow type and
  2. Piston type

Working of Air Suspension System

The air springs shown are mounted on the front and rear axle. The atmospheric air first passes through the filter where the dirt is removed and passed on to the compressor. Air is compressed here and the pressure of air is raised from atmospheric to about 250 M Pa. This pressure is maintained by the accumulator tank.
The safety relief valve is provided on the accumulator as a safety device and it opens when the pressure rises above 250 M Pa. This air then moves to lift control valve and through leveling valves to the air springs.

Working of Hydrolastic Suspension System

In this case the moving part is assembled and fitted at each of the wheel location. These units are interconnected by pipes carrying the fluid. In this moving unit rubber acts as a spring and the fluid under pressure acts as a damping medium.
The connecting rod of piston is connected to the wheel through suitable linkage in order to receive the movements of the wheel. The movement of the fluid is controlled by a two-way valve assembly. The valves are arranged at right angle to each other.
As the pressure of fluid rises it causes the upper valve to open. In the same way the lower valve opens under pressure and allows the fluid to flow in downward direction. Cars like Morris 1500, BMC 1100, Wolseley 1100 and many more use this type of suspension.

Working of Hydragas Suspension System

It was designed by Moulton Development Limited and British Leyland Motor Corporation and is manufactured by Dunlop suspension Division of Coventry (England). The drawbacks of hydrolastic suspension system were overcome by this design. It is mainly divided into two parts; an internal spring and a damper unit and is assembled at each wheel.
The springing action is taken by inert gas, nitrogen. Weight of the car is supported by some fluid like water under pressure. Insulation of the interconnected front and rear system is done generally with hermetic seals.
As the wheels in motion come across pit or bumps they cause the piston to move and the diaphragm forces the fluid up which causes the damper valve to open and the fluid moves through the opening. Cars like Princess, Austin Ambassador, Rover 100 and many more use this type of suspension.

Problems With Suspension System

Uncomfortable Ride
  • Springs might have got rusted and thereby not able to provide proper springing action. Lubrication should be done to minimize the friction.
  • Shock absorbers might have some problems. Repair or replace it.
  • Pins holding the springs together might have got loose.Tighten them.
  • Pads present at the leaves (curve shaped spring like saucer) might be worn out. Replace them.

Reasons for Suspension Becoming Loose

  1. Due to long period of continuous use, the springs might have become weak. They must therefore be replaced with new ones.
  2. Some springs do not require lubrication yet they might have been lubricated. Clean with some cloth.
  3. Defects in shock absorber. Rectify them.

Reasons for Noise

  1. See the manufacturer's manual if the springs require lubrication.
  2. Pins holding the springs and bushes might have got loose.
  3. Nuts and bolts holding the springs might be loose.
Suspension system is an integral and most vital part in the manufacture of automobiles and therefore proper care needs to be taken while designing and assembling it.