Semi-elliptic leaf spings are almost universally used for suspension in light and heavy commercial vehicles. For cars also, these are widely used for rear suspension, but now replaced completely by coil springs.
CONSTRUCTION
A rear axle leaf spring of semi-elliptic type. The spring consists of a number of leaves called blades. The blades vary in length as shown. The composite spring is passed upon the theory of a beam of uniform strength. The lengthiest blade has eyes on it's ends. This blade is called master leaf. ALL the blades are bound together by means of steel straps as shown.
The spring is supported on the axle, front or rear by means of a U-bolt. One end of the spring is mounted on the frame with as simple pin, while on the other end, connection is made with a shackle. When the vehicle comes across a projection on the road surface, the wheel moves up, deflecting the spring. This changes the length between the spring eyes. If both the ends are fixed, the spring will not be able to accommodate this change of length. This is provided for by means of a shackle at one end Which gives a flexible connection.
Rear Leaf Spring
The spring may be either cambered initially us shown flat. Highly cambered springs provide a soft suspension, but they also increase the tendency to yaw (movement about vertical axis). Flat spring reduce the tendency of the vehicle to dip, i.e. pitching, when braking or accelerating suddenly. Use of longer spring gives a soft suspension. Generally cars springs are kept longer than the front springs. This causes them to vibrate at different frequencies, which prevents excessive bounce.
Whether to have the shackle at the front rear end in case of front axle springs, is made clear by means shows the situation when the shackle is employed at the rear end. In this case the axle movement will be around the front rigid frame-spring connection, while the drag link of the steering system will have it's motion about the drag link-drop arm joint. This results in wheel wobble. If, however, the shackle is mounted on the front end as shown the axle will the have cerebrate of oration at the rear spring-eye. This gives approximately the same are as the radius action of the drag link.
Spring eyes for heavy vehicles are usually bushed with phosphor bronze bushes. However, for cars and light transport vehicles like vans, the use of rubber has also become a common practice. This obviates are necessity of lubrication as in the case of bronze bushes, where it was a necessity. The rubber bushes are quiet in operation and also the wear on pin or the bush is negligible. Moreover, they allow for slight assembly misalignment, Silent
bloc is an example of this type of bushes.
Types:
A few of the leaf springs are shown was used earlier, but these days the most widely used is semi-elliptic type the transverse spring has also been used on some vehicles. This type is the cheapest one, but bas the disadvantage that the vehicle body in this case is attached to the springs at only two places, which imparts the vehicle a tendency to roll easily when it runs fast on sharp corners.
HELPER SPRINGS:
Front Spring
Rear Spring
Spring eyes for heavy vehicles are usually bushed with phosphor bronze bushes. However, for cars and light transport vehicles like vans, the use of rubber has also become a common practice. This obviates are necessity of lubrication as in the case of bronze bushes, where it was a necessity. The rubber bushes are quiet in operation and also the wear on pin or the bush is negligible. Moreover, they allow for slight assembly misalignment, Silent
bloc is an example of this type of bushes.
Types:
A few of the leaf springs are shown was used earlier, but these days the most widely used is semi-elliptic type the transverse spring has also been used on some vehicles. This type is the cheapest one, but bas the disadvantage that the vehicle body in this case is attached to the springs at only two places, which imparts the vehicle a tendency to roll easily when it runs fast on sharp corners.
TYPES OF LEAF SPRING
HELPER SPRINGS:
Helper springs are provided on many commercial vehicles in addition to the main leaf springs. They allow for a wide range of loading. When the vehicle is only lightly loaded, these helper springs do not come into operation. But as the load is increased, they take their share of load. Generally helper springs are used on rear suspension only. the use of a helper Spring. When the load on the road wheel increases so much as to deflect the main spring to such an amount that the ends of the helper spring touch the special brackets fixed to the side member, the helper Spring comes into operation.
Helper Spring
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