Leaf spring:

A leaf spring is a type of suspension spring commonly used in vehicles, particularly for the rear suspension system in trucks, buses, and older cars. It consists of multiple layers (or “leaves”) of flexible steel, stacked on top of each other, which are bound together to form a single spring unit. The leaves are designed to bend and absorb shocks from the road, providing support and helping the vehicle maintain stability while driving.

 

Key Features and Functions of Leaf Springs:

1. Shock Absorption:

   • Leaf springs help absorb and dissipate the energy generated by bumps, potholes, and other irregularities on the road. This smooths out the ride for the passengers and reduces the impact on the vehicle’s frame.

2. Load Distribution:

   • Leaf springs provide support for the vehicle’s weight and any additional load it may carry. This is why they are commonly found in trucks, trailers, and vehicles designed to carry heavy loads.

3. Durability:

   • Because leaf springs are made from high-strength steel, they are highly durable and can withstand heavy use over long periods. They are also relatively easy to repair or replace when necessary.

4. Simplicity:

   • Leaf springs are a simple design, consisting of multiple layers of metal that are curved to absorb impact. Their simplicity and strength make them easy to manufacture and maintain.

 

Construction and Design:

• Leaves: A leaf spring typically consists of several metal strips of varying lengths stacked together. The longest leaf is at the bottom, while shorter leaves are stacked above it. The stack is secured by a center bolt and often has clips or shackles at the ends to hold the leaves in place.

• Eyebolt or Shackle: The ends of the leaf spring are typically attached to the vehicle’s frame using either an eyebolt or a shackle. These allow the leaf spring to pivot or move with the suspension as it absorbs road shocks.

The leaf spring is the most commonly used “conventional suspension system” (also called as “Independent Suspension System”), typically found in all commercial vehicles like truck, buses, etc. Semi-elliptical leaf springs are used in light as well heavy vehicles. Leaf springs support lateral load, drive thrust, braking torque as well as shocks. Leaf spring consists of leaves which are given initial curvature (also called as camber). Leaves are of different length and are held together by a central bolt. The construction is made such that the unit acts like a beam of uniform strength. ‘U’ bolt is
used to clamp the spring to the axle housing.

The longest leaf (called as master leaf) has an eye shaped end which is used to pass a bolt. The eyes are connected to shackle using brass or bronze or rubber bush.

If the length of leaves is longer, the suspension achieved is softer. For commercial vehicles like trucks, rear leaf springs are kept longer than the front leaf springs, thereby ensuring different natural frequencies of vibration.

Laminated leaf springs:

The laminated leaf springs are self-damping as it is highly cambered, pressurized and are longer with shackle end, thus the friction leaves provide damping.

 

Types of Leaf Springs:

1. Semi-Elliptical Leaf Springs: The most common design, these are shaped like a “U” or arc and are used for vehicle suspensions to provide flexibility and strength.

2. Mono-Leaf Springs: These consist of a single, thick leaf of steel. They are lighter than traditional multi-leaf springs and are used in some modern vehicles, especially those designed for lighter loads.

3. Elliptical Leaf Springs: These are similar to semi-elliptical springs but have a different shape. They are designed for more uniform distribution of stress and are used in certain heavy-duty applications.

Advantages of leaf springs:

1. Higher load carrying capacity (compared to helical coil springs).
2. Easy to manufacture, required.
3. No maintenance required.
4. if one or two leaves are broken/damaged, they can be replaced easily (and entire spring need not be replaced, thereby saving repair costs.

Disadvantages of leaf springs:

1. Leaf spring construction is le /bulky, thereby limiting their use for large size vehicles only.
2. Self-weight of leaf springs is more (compared to helical coil springs).
3. -Moisture can enter into small gaps/spaces present between various leaves, thereby causing fretting corrosion.
4. Fatigue life of leaf springs (especially at very loads) is lesser. Hence, the modern trend for HCV’s is to go for air or hydraulic suspension systems.

Applications of leaf springs:

1. Rear suspension of light motor vehicle (LMV) like passenger cars.
2. Front as well as rear suspension of light/medium/heavy commercial vehicle like trucks, uses, actor-trail er combinations, etc.
3. Railway goods wagons, railway oil tanker wagons.

Conclusion:

In summary, leaf springs are a crucial component in many vehicle suspension systems, providing essential support, shock absorption, and load-bearing capacity. While they may not be as commonly used in modern passenger vehicles due to the rise of more advanced suspension systems, leaf springs remain a popular choice in heavy-duty vehicles and off-road applications. Their durability, simplicity, and strength continue to make them an essential part of many vehicle designs, especially where heavy loads and rugged conditions are involved.