- Semi-elliptical leaf springs are widely used for suspension in light and heavy commercial vehicle. In car these are used for rear suspension.
- The leaf springs are made of flat semi-elliptical plate.
- The advantage of leaf spring over helical spring is that the ends of the spring may be guided along the definite path as it deflects to acts as a structural member in addition to energy absorbing device.
- Thus, leaf spring carry lateral load, brake torque, driving thrust and shocks.
- It consists of number of semi-elliptical plates called blade or leaves.
- The leaves are given initially curvature or camber so that they tend to straighten under the load.
- The blades vary in length and are held together by a bolt passing through the center acting as a beam of uniform strength.
- The spring is clamped to the axle housing by means of ‘U’ bolts.
- The longest leave is known as master leaves, has its end formed in the shape of an eye through which the bolts are passed to secure the spring to its supports.
- The eyes are attached to shackle provided with bushing of anti-friction material such as bronze or rubber. The other leaves are graduated leaves.
- To prevent digging in the adjacent leaves, the ends of graduated leaves are trimmed in various forms.
- The master leaf has to withstand vertical bending load, side thrust and twisting moment due to presence of stresses caused by these loads so it is usual to provide two full length leaves and rest graduated leaves.
- Rebound clips are located at intermediate position in the length of the spring so that graduated leaves also shear the stresses induced in the full-length leaves when the spring rebound.
- Highly cambered spring provides a 50% suspension but they also increase tendency to jaw (movement about vertical axis). Flat spring reduces tendency of the vehicle to dip (pitching), when brake or accelerate suddenly.
- Use of longer spring gives soft suspension.
- Generally rear spring are kept longer than the front spring. This causes them to vibrate at different frequencies, which prevent excessive bounce.
