Suspension System

1. Purpose of Suspension System

1.1. Support the weight of the vehicle1.2. Cushion bumps and holes in the road1.3. Maintain traction between the tires and the road1.4. Hold the vehicle in alignment

2. Components of suspension systemMain two parts are springs and shock absorber. Springs support the weight of the vehicle and its load, and absorb road shocks. Shock absorbers help control or dampen spring action. The vehicle bouncing caused by spring oscillation due to a hole or a bumper in the road is quickly (within few spring movement cycles) finished over by shock absorbers. Springs and shock absorbers may be either mechanically or electronically controlled.

3. Types o springs Coil type Leaf type Torsion bar Air suspension

3.1. Coil TypeIt is a steel rod wound in to a coil.

3.2. Leaf SpringIt is a flexible steel plate, that keeps the motion perpendicular to the axis of the plate. Two types are available. i) single leaf and, ii) multi leaf springs. Several flexible steel plates with graduated lengths stacked and held together by makes multi leaf spring. When tire passes a bump or a hole, spring bends to absorb shock and slides on each other.

3.3. Torsion BarThe torsion bar is a straight steel rod. It is rigidly fastened at one end to the vehicle frame or body and the other end attaches to the upper or lower control arm. As the control arm moves up and down in response to wheel movement, the torsion bar twists to provide the spring action.

3.4. Air springThe air spring is a rubber cylinder or air bag filled with compressed air. A plastic piston on the lower control valve moves up and down with the lower control arm causing compressed air to provide spring action. Change in load in vehicle cause the valve at the top, to open to release or add air. An air compressor is connected to the valve to add required air.

4. Sprung and unsprung weightSprung weight is the weight supported by springs whereas the unsprung weight is the weight not supported by springs. This includes the axels, axel shafts, wheels and tires. In order to reduce the roughness of ride , unsprung weight should be kept as low as possible.

5. Spring RateThe spring rate is the load required to extend or reduce the spring by a unit length. If the spring rate remains constant for varying loads, it is called linear rate spring. If it does not remain constant it is variable rate spring. Winding a coil from a tapered rod is an example for variable rate spring.