How do Leaf Springs Work?

In this brief article, we will discuss how the leaf spring suspension works, the advantages and disadvantages of leaf springs.

Basic Working principle of a leaf spring

The Basic working principle of the Leaf Spring Suspension is the Cantilever beam bending mechanism. The leaf spring is constructed as a stack of leafs or slender spring-steel plates that are arranged in a semi-elliptic shape. The stack is tightened at the center using 2 U-Bolts and fastened to the axle at the axle-seat.

In principle, you could consider the leaf spring assembly as 2 Cantilever beams that are subject to ‘Bending’ at either end. At the 2 ends of the leaspring the topmost leaf is rolled into a circular shape. The circular ends are pressfitted with a ‘Pin’ or hinge at each end that are usually serviceable joints that enable the leaspring ends to freely move in the vertical direction. So the bending stiffness of the leaf spring is converted into a vertical directional stiffness of the axle movement.

What are the Different Types of Leaf Spring?

The 2 main types of leaf spring are:

  • Semi-Elliptic leaf spring
  • Parabolic leaf spring

2 Variations of Parabolic Leaf Springs

  • Transverse leaf spring
  • Air-Leaf single

The main differences between the Semi-Elliptic and Parabolic leaf spring are:

  • In the semi-elliptic leaf spring, each leaf is of constant thickness or, in other words, the cross-section of each leaf is constant throughout its length
  • In a Parabolic leaf spring, the individual leafs of the pack are each of varying cross-section, except for the center clamping portion, where the leaf spring is flat. The cross-section varies in a parabolic shape from the center to the ends.
  • In a Semi-elliptic leaf spring there is relative sliding motion between the leafs as the leaf spring travels between rebound and bump. For a Parabolic leaf spring, there is almost no contact area between one leaf and the other, except for the center clamping area and the 2 ends, where there is no sliding.
  • The Sliding motion leads to a Damping effect in semi-elliptic, but there is almost no damping in the case of Parabolic suspension.

A transverse leaf suspension has the parabolic leaf spring transversely mounted and clamped at the middle, leaving the two free ends that can bend along with the wheel movement. In the Corvette rear suspension, the transverse arrangement had a lateral control arm as well. The shock absorber has mounting provisions on the knuckle, quite similar to the double wishbone arrangement.

The Air-Leaf type of leaf spring is a Single-Leaf with an eye at only one end. It is almost always of the Parabolic type. The air-leaf is hinged to the chassis at the eye-end and bolted to the bottom mount of an air bag at the other end. The air-leaf type of suspension is mainly used in commercial trailer trucks, for better ride comfort.

Advantages of Leaf Springs

  • Leaf Springs are simple in construction and do not require any other control arms, as the leaf itself is capable of constraining lateral and longitudinal degrees of freedom.
  • The development of leaf spring suspension is less complicated due to the less number of parts involved
  • Leaf Springs are suited to heavy duty axles in articulation conditions

Disadvantages of Leaf springs

  • The damping in Semi-elliptic leaf spring suspensions is inherent in the leaf spring itself. This makes it difficult to tune the ride quality using telescopic dampers. So there will always be a compromise in ride quality for semi-elliptic leaf springs.
  • Commercial vehicle Leaf Springs are suited to only dependent solid axles. Only in the case of transverse leaf spring, can it be applied to an independent suspension.
  • Leaf Springs occupy large amounts of space and are therefore not suited for compact monocoque vehicle applications. Conventional leaf springs are rather suited to body-over-chassis type of construction like trucks and SUVs.

Conclusion

In this brief article, we have discussed how the leaf spring suspension works, the advantages and disadvantages of leaf springs.

In case of any queries or comments, please feel free to ask.

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