LEAF SPRING


Leaf springs are made up of a number of curved bands of spring steel called leaves sticking together in order from shortest to longest. This stack of leaves is fastened together at the center with a center bolt or U- bolt to prevent the longitudinal movement. Similarly sometimes the leaves are made with pips or projections at the bottom and recess at the top surface. The leaves are arranged in such a way that the projection of the upper spring should mesh in the recess of the lower spring. Also to keep the leaves from slipping out of place, they are held at several places with the clips. Both ends of the longest or main leaves are bent to form spring eyes, used to attach the spring to the frame. 

To adjust the variations in length of the master leaf while the vehicle move across the road irregularities, one end of the spring is connected to the fame through a shackle and the other end is mounted directly on the frame with a pin. For the front suspension, it is a usual practice to provide the shackle in the front side of the spring to reduce the wheel wobble.

Generally, the longer a leaf spring, the softer it will be. Also the more leaves in a leaf spring, the greater the load they will withstand. But on the other hand as the spring will become firmer, the riding comfort will suffer.

The curvature of each leaf is called a nip. As the nip of the leaf is greater, shorter the leaf will be. Each leaf curves sharply than the one above the stack. When the center bolt is tightened, the leaves flatten somewhat and causing the ends of the leaves to press very lightly against one other.

The suitable steels that have been used for the manufacture of leaf springs are chrome-vanadium steel        (C-0.46%, Cr-1.4%, Va-0.18%), silico-manganese steel (C-0.52%, Si-1.95%, Mn-1.05%) and carbon steel (C-0.55%, Mn-0.6%, Si-0.2%).

Types of leaf spring:         

a)  Semi-elliptic type spring  

b)  Quarter elliptic spring   

c)  Transverse type       

d)  Helper springs

The semi-elliptic type leaf spring is the most common type in use where, the spring is attached to the frame at its middle to the axle. One end is connected through a shackle and the other end is connected to the frame through a pin.The quarter elliptic type spring is a cantilever type spring, which is pivoted at its one end and the other end is shackled or pivoted to the axle. The short leaves in this type of springs are arranged in at the top. This type is not in common use now.

Transverse type spring is arranged transversely to the vehicle or parallel to the axle. This spring is rigidly bolted to the frame at its center. Both the ends of the spring are connected to the axle through the shackles. The disadvantage in using this type of spring is that the vehicle tends to roll at the turns since the frame is clamped only to their centers.

The helper springs or auxiliary springs are provided in addition to the main leaf springs when the vehicle is meant to carry heavy loads. This will allow a wide range of loading. Helper springs are an additional set of leaf springs clamped with the same U– bolt on the top of the main spring. Generally the helper springs are used in the rear side only. When the vehicle is lightly loaded, these helper springs will not take any loads and will come in action and share the loads only after certain deflection of the main leaves.