What is an independent Suspension?

In this brief article, we will discuss the Independent Suspension, its design features, advantages, and applications.

What is an independent Suspension?

An independent suspension is one in which the left/right wheel’s vertical motion does not affect the vertical motion of the opposite side wheel. Unlike in the case of the dependent suspension, there is no solid structure that directly connects the left and right wheels.

What is the difference between an Independent and a dependent Suspension?

To understand the concept of an independent suspension it is essential to know what a dependent suspension is. In the earliest forms of 4 -wheeled vehicles, the front wheels, and the rear wheels were connected by the front axle and the rear axle respectively. The axle was a solid beam that had the knuckle attached at each end, in the case of the front suspension. In the case of the rear, the axle consisted of 2 tubes connected at the center to a differential. The earliest form of suspension for the front and rear axles was the leaf spring type. Because the left and right wheels were connected rigidly, the vertical motion of the left and right wheels was always coupled. In other words, when the left wheel went upwards over a bump, it pushed the right wheel to go downwards.

Most modern cars have an anti-roll bar in the front suspension and in the rear suspension too. Though the anti-roll bar connects the left and right side wheels, it doesn’t make one wheel dependent on the other. Rather, the Anti-roll bar causes one wheel’s motion to affect only the wheel rate (stiffness) of the other side suspension.

The History of the Independent Suspension

The origins of the Independent suspension can be traced back to the Lancia Lambda of 1922

Advantages of the Independent Suspension

  • The Independent suspension is typically used where the vehicle’s ride quality and handling characteristics are a high priority
  • Owing to its lower unsprung mass and the ability of each wheel to follow the unevenness of the road without being affected by the other wheel on the vehicle, ride and handling are greatly improved in an independent suspension.
  • In Off Roading conditions, where wheel articulations are important, an independent suspension would be beneficial to ensure that all 4 tires contact with any given uneven patch

Drawbacks of the Independent Suspension

  • Developing a new Independent suspension would require comparatively higher engineering effort and expense, as compared to an axle beam or a solid driven axle type of setup. 
  • Due to the number of parts and complexity, an independent suspension solution could also result in higher manufacturing costs.
  • The number of parts and different types of joints involved in the independent suspension system increases the number of maintenance issues and associated costs.

What are the Different Types of Independent Suspension?

The different types of independent suspension are:

  • Double wishbone suspension
  • Multi-link suspension
  • MacPherson strut
  • Transverse leaf-spring
  • Torsion Bar Suspension

Double Wishbone Suspension

Double Wishbone Suspension is probably a more commonly found type of independent suspension. It consists of two wishbone arms and a knuckle or wheel carrier. The Wishbones are mounted to the chassis/body at two mounts each, which are usually flexible cylindrical rubber bushings on the one end. At the other end, the wishbones are attached to the knuckle through one ball-joint each.

Multi Link suspension

The multi-link suspension can be found in basically 2 different forms. For the front suspension, a multi-link suspension appears similar to a double wishbone, except that there are two upper control arms and 2 lower control arms instead of one upper wishbone and one lower wishbone.

In the rear suspension a multi-link suspension could be either 3-link or 4-link depending on the layout. In a 5-link layout, the control arms would be Upper Control Arm, Lower control arm, Toe Control Link, Trailing Arm. The control arms would usually be attached through rubber bushings at the ends.

Macpherson Strut Suspension

Since economy cars are the most in number, and almost every economy car has at least a front MacPherson Strut suspension, the MacPherson Strut suspension could be considered as the world’s most common type of car suspension. 

The MacPherson strut became more popular with cars that have a front-wheel drive configuration, mostly in the economy segment because of the convenience and space the MacPhsersone strut offered. This did not prevent Rear wheel drive performance cars from adopting the MacPherson front suspension. Some of the notable examples are the Porsche 911, BMW 1, 2 and 3 Series M models and the Mustang GT350.

Transverse leaf-spring

A transverse leaf suspension has the 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 transverse leaf suspension is quite rarely seen on cars nowadays. It was more prevalent in Triumphs, Heralds and Fiats from back in the 1960’s. It can be found on the front suspension of the Utility Van Iveco Daily, sold in Europe.

Torsion Bar Suspension

Torsion Bar suspension uses the twist resistance of a rod and translates that into the vertical motion of the suspension. One end of the Torsion bar is anchored to the chassis, while the other end is fixed to the lower wishbone pivot. 

Some well-known and high selling cars that had a Torsion Bar type of front suspension are the Volkswagen Beetle (upto 1966), early (1940’s) Porsche Racing prototype cars and GM Light-duty 4-wheel drive trucks like GMC Sierra, Chevy Silverado

Conclusion

In this brief article, we have discussed the Independent suspension, its design features, advantages, and applications.

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