Have you ever looked under a heavy vehicle like a bus or a truck? You probably must have noticed a layered semi-elliptical structure near the wheel.
Yes! It’s none other than the Leaf spring. What is a leaf spring? its advantages, applications, types, and much more coming up…
Get your FREE copy of the PDF on Leaf springs at the end of this article.
What is a leaf spring?
A leaf spring is a type of spring made by a number of plates (leaves) stacked upon each other in increasing order of sizes. It is used to absorb shocks and vibrations in heavy commercial vehicles like trucks, vans, buses, etc.
Today we would be looking at a semi-elliptic type leaf spring.
Construction of Leaf spring
Following are the parts of the leaf spring
- Metal plates or leaves
- Central clamp
- Rebound clips
Flat metal plates or leaves
The leaf spring consists of a number of metal plates also known as leaves layered upon each other in the decreasing order of their size. The leaves are given a curvature called the camber which gives the leaf spring its semi-elliptic look.
The master leaf has its ends rolled as shown in the figure. These rolled ends of the master leaf are known as the eye.
Just below the master leaf, another almost full-length leaf called the second master leaf is placed to support the master leaf. (refer to figure) The remaining leaves are known as “graduated leaves“.
The central clamp’s function is to hold all the leaves together. It consists of U bolts and a central bolt so that the leaves don’t fall apart.
The rebound clips are made up of steel bands placed at a certain position on either side of the central clamp and their main function is to prevent the leaf spring from failing during a rebound.
A leaf spring usually does not break when it is compressed i.e. when the axle of the automobile undergoes a bump. However, when the force is suddenly removed the leaf spring might fail.
This is because when the spring is being compressed from below, each leaf is supported by the leaf below it, but, when the load is suddenly released it would not find support if not for the rebound clips which hold them together and provide support. (I recommend watching this minute-long clip) https://www.youtube.com/embed/Qcr8QglqC5M
Before starting off with the working of the leaf spring, let us understand how the leaf spring is assembled to the axle of the automobile.
Assembly of leaf spring
The leaf spring is placed below the axle and U bolts are passed over the axle and the plate for U bolts is placed below the leaf spring such that the leaf spring is sandwiched between the axle at the top and the plate at its bottom when tightened. Refer to the figure given below.
Out of the two eyes of the leaf spring, one eye is fixed whereas the other eye is connected to the shackle. Both eyes are provided with bushings of an anti-friction material like rubber, brass, nylon, etc.
What is a leaf spring shackle?
The leaf spring shackle is a free-swinging part where one end of it is fixed to the frame and the other part is connected to the eye of the leaf spring.
The function of the shackle is to provide flexibility to the leaf spring and prevents it from breaking under load.
What is the purpose of a leaf spring shackle?
When the vehicle goes through bumps on the road, it exerts a force on the leaf spring from below.
Now assume that if both the eyes of the leaf spring are fixed, under such circumstances the leaf spring would compress, but, as it undergoes compression, naturally its ends try to move outwards.
Since the ends are fixed it would not have any flexibility and thus it cannot compress properly. If the load or shock is greater, then the leaf spring might break.
To prevent this, a shackle is provided for the leaf spring as shown in the image above.
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Working of leaf spring
When the vehicle goes over a bump, the axle tends to move up and down. However, as the leaf spring is provided, it supports the axle and helps absorb the vibrations and shocks.
Let us understand the working with an example!
Assume that a truck goes over a speed bump, this causes the wheel and the axle to be forced upwards.
So as the axle moves upwards, the leaf spring moves along with it but due to its semi-elliptical shape and it absorbs as well as transfers the upward force to the chassis frame. (as shown in the above image).
The shackle of the leaf spring helps it to expand when force is applied.
Types of leaf spring
The following are the different types of leaf springs:
- Elliptic leaf spring
- Semi elliptic leaf spring
- Three quarter elliptic leaf spring
- Quarter leaf spring
- Transverse leaf spring
Advantages of leaf spring
The following are the advantages of leaf spring:
- Leaf springs are light in weight and strong.
- It provides good damping action.
- It provides good support to the axle and the chassis.
- Leaf springs are simple in design.
- Leaf springs can withstand a large amount of load when compared to helical springs.
Applications of Leaf spring
The application of the leaf spring is to absorb shocks and vibrations in mostly heavy commercial vehicles like trucks, vans, buses, railway carriages, etc.
So That’s a brief on Leaf springs, we’ll soon be back with another exciting article!
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