COIL SPRING SUSPENSION SYSTEM

The coil springs are generally used with independent suspension. Since the energy stored per unit volume of the coil spring is almost double that of the leaf springs, they can be accommodated in restricted space. The coil springs are made from rods of special spring steel formed into the shape of a coil. When a load acts on the spring, the entire spring rod is twisted as the spring contracts to absorb the energy.

Progressive coil spring: If a coil spring is made from a rod of spring steel having uniform diameter, the entire spring will flex uniformly in proportion to changes in load. This restricts the application of this type of spring for the wide range of loading. However, if a spring rod having a constantly changing diameter is used, the ends of the springs will have a smaller spring rate than the center, thus varying the spring index under different loading conditions. Thus the spring ends will contract and absorb light loads and the center part of the spring will allow a wide range of loading. The progressive springs can be made by using unequal pitch spring (low pitch at the ends and high pitch at the middle), conical spring or by providing the helper coil springs with the main spring like in the case of leaf spring.