a compendium of tech stuff

Oct 16, 2014

On 11:31 PM by Lalith Varun   3 comments



INTRODUCTION
Leaf springs also referred to as semi-elliptical springs or cart springs are one of the oldest form of suspension used in vehicles, especially heavy vehicles. A leaf spring looks similar to a bow minus the string. It consists of a stack of curved narrow plates of equal width and varied length clamped together with shorter plates at the centre to form a semi-elliptical shape. The center of the arc provides location for the axle, tie holes are provided at either end for attaching to the body.


TYPES
There are different varieties of leaf springs namely mono-leaf springs and multi-leaf springs.
As the name suggests, the mono-leaf suspension consists of a single link. They are thick in the middle and taper out at the end. It doesn't offer much strength and suspension to towed vehicles.

 MONO-LEAF SPRING

Multi-leaf springs are used for heavier vehicles which offer increased strength and suspension.
A more modern design is the parabolic leaf spring. It can have a mono-leaf or multi-leaf configuration. It has fewer leaves in comparison to the semi-elliptical multi-leaf springs whose thickness varies from centre to the end and it follows a parabolic path. This configuration not only saves weight but also gives greater flexibility which improves ride quality. A trade-off of using parabolic leaf spring is reduced load carrying capability.


 MULTI-LEAF SPRING


ADVANTAGES and DISADVANTAGES


ADVANTAGES
1) The construction of the suspension is simple and strong as it acts as a linkage for holding the axle in position and thus a separate linkage isn't necessary.
2) As they locate the rear axle, the need for trailing arms and panhard rod is eliminated, thus saving cost and weight.
3) It supports the weight of the chassis
4) It controls axle dampening
5) It controls chassis roll more efficiently by utilizing a higher rear moment center and a wider spring base. The wider the springs are mounted apart, the lesser the roll tendencies. As the moment center height is high, this shortens the moment arm which in turn produces less roll.


DISADVANTAGES
1) The leaf-spring systems are not easy to install
2) The inter-leaf friction between the leaf springs reduces the ride comfort
3) The leaf springs may tend to lose shape and sag over time. If the sag is uneven, it alters the cross weight of the vehicle which changes the handling. It also changes the axle-to-mount angle
4) Acceleration and braking torque cause wind-up and vibration. Also wind-up causes rear-end squat and nose-diving





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