22.2.
Chassis Springs
The main objective of the chassis spring is to absorb the shocks imparted to the wheels by road obstacles. A spring when fitted between the wheel and the frame isolates the body partially from the axle so that the wheel moves up and down without transferring similar movement to the frame. The spring while absorbing road shocks allows the wheel to follow the irregular contour of the road surface. To facilitate this, wheel assembly should be as light as possible. When a vehicle, rides over bump, the wheels rise and deflect the springs. The energy created due to this movement is momentarily stored in the spring. It is then released through expansion, due to the elasticity of the spring material, and during expansion the spring rebounds. The spring then oscillates at its natural frequency, so that the vehicle bounces many times before equilibrium is restored. When the body is rigidly connected to the axle, the kinetic energy developed by the bump is imparted directly to the body, thereby creating high impact stresses, which in turn cause discomfort to passengers.
The type of suspension springs used in automobile are;
(i) Metal springs
(a) Laminated or Leaf (6) Coil (c) Torsion-bar
(ii) Rubber springs
(Hi) Pneumatic springs.
In conventional system of suspension, the springs serve as guide or control members for the front axle. Leaf springs are commonly used in conventional suspension systems while both coil springs and torsion bars are used in independent suspension systems. Coil springs can store about twice as much energy per unit volume as that of leaf springs. Thus for the same job coil springs need weight only about half that of leaf springs. But leaf springs both cushion the shocks and guide or control the cushioned motion. Coil springs can serve the both provided if radius rods or sway bars are used along with. Torsion-bars provide a very compact design but they are inferior to coil springs so far as their action is concerned. Rubber suspension can store more energy per unit mass than any other type of spring material.
