Air Suspension System and Shock Absorber Working Principle – Suspension systems

Air suspension system

These types of suspension systems are commonly used in a long-distance vehicle like buses. Due to the benefits of the air suspension system,nowadays this system is widely used in many vehicles.
Schematic representation of this type of air suspension system is shown in the figure . It consists of four air springs which may be a bellow type or piston type. Air compressor is used to pressurize the purified air (through filter) from the atmosphere and stored in the accumulator at a pressure maintained between 5.6 to 7 kg/cm2. To release the excess air and to maintain the pressure inside the accumulator,a safety relief valve is used. The high pressure compressed air enters into the air spring through leveling valve and lift control valve. The lift control valve was operated by a manual lever which is located in the panel board.


1. It reduces noise, vibration, and harshness due to which passenger and driver attain better ride comfort. It reduces the journey tiredness of the
driver and the passenger.
2. Change of spring deflection is quite low when compared with a conventional suspension system for both loading and unloading condition. This helps to reduce the load transfer on the vehicle.
3. Headlamp alignment remains constant though the vehicle is travelling over irregular roads.
4. With the help of automatic controlling tools, this system will provide some space for required wheel movement.

Shock absorber

The spring system prevents the travelers and truckloads that do not
cause any shocks when climbing up the sudden disturbance on the road. However,if the spring are stiffer than expected,it will not absorb the road shock. The spring will keep on oscillate even after crossing the disturbance till the energy is completely die out. Hence, to quickly dissipate the stored energy in springs,dampers are used. According to the working principle shock absorber are classified into three types they are,1. Friction type
2. Hydraulic type
3. Air type

Friction type

When one body is allowed to slide
over the other, the surface of one body offers some resistance to the movement of the other body on it. This resisting force is called friction force. In leaf spring, the interleaf friction is act as a damper. It is
not widely used with other types of springs.

Hydraulic type

This type of damper is most widely
used in the suspension system. It works based on Pascal’slaw. They are further classified into two types.

(i) Pistontype
(ii) Telescopic type

Telescopic type

It works on the basic principle of Pascal’s law. Damping is obtained as high-velocity fluid passing through a tiny hole. This system is also called telescopic shock absorber and because of use of hydraulic, it is also called as hydraulic damper.


Figure shows the construction details of this shock absorber. The head is fixed inside the cylinder. The piston and two way valve located on the top portion of the Cylinder is assembled with piston rod for up and down motion.The other end of the piston rod has eye and it is attached to the chassis frame.On the bottom portion of the cylinder another two way valve named as foot valve is attached. In this two way valve,
one valve is used for fluid inlet and other valve is used for fluid outlet. Cylinder is filled with fluid.Inner portion of the cylinder is called as tube and the gap between the outer portion of the inside tube and that of the inner portion of the outside
tube is used for fluid storage and it is
called as reservoir. A gland is fixed at the top portion of the cylinder. When
damper is in operation, Gland is used to scrap the excess oil in the piston rods to the reservoir. When suspension works,fluid from the glands has been sent it to reservoir through piston rods. The lower portion below the piston of the inner cylinder, is called as compression chamber and the top portion above the piston is called as rebound chamber. Damping fluid is made up of with 60% transform oil blended with 40% turbine oil.

Working principle

When the vehicle passes over the road disturbance, it piston moves down and this movement of piston pressurizes the fluid at the bottom portion. Then this fluid flows into the rebound chamber from compression chamber through a valve located on the top portion of the piston and the remaining portion flows into the reservoir through foot valves.Similarly, when the vehicle comes to normal road condition, the piston moves from downward to the upward direction, so that the fluid at the top portion of the piston is compressed.This pressurized fluid is sent inside the compression chamber through the piston valve and the remaining amount of the fluid which again fed back from the reservoir through the foot valves.Because of this upward and downward motion of the piston, the fluid becomes highly pressurized and hence the energy due to road shock has been absorbed.

Air type

Air suspension is nowadays the most popular on commercial vehicles.
It works on the principle of air so it is called as air type shock absorber.

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