AutoInfoMe: Automobile Suspension

2.1. Introduction

Automobile suspension is the prime important running system of an automobile, which are directly related to human comfort. Automotive suspension system is especially created for supporting an automobiles body on its undercarriage, including dampers, springs and locating linkages.

The basic function of an automobile suspension system is to enable the wheels of a vehicle to function independently thereby making it more sound, sturdy and suspended.

Suspension refers to the use of front and rear springs to suspend a vehicle’s frame, body, engine & power train above the wheels.

The automobile frame and body are mounted on the front and rear axle not directly but through the springs and shock absorbers. The assembly of parts, which perform the isolation of parts from the road shocks, may be in the forms of bounce, pitch and roll is called ‘Suspension System’.

Fig 2.1: Automobile Suspension

2.2. History:

An early form of suspension in bullock carts and horse carts had the platform swing on iron chains attached to the wheeled frame of the carriage. As the same, automobiles use the 'strap suspension' system. Leather straps are used between chassis frame and wheel axle mounting by the 17th century.

Automobiles were initially developed as self-propelled versions of horse-drawn vehicles. However, horse-drawn vehicles had been designed for relatively slow speeds, and their suspension was not well suited to the higher speeds permitted by the internal combustion engine.

Sixteenth-century wagons and carriages tried to solve the problem of "feeling every bump in the road" by slinging the carriage body from leather straps attached to four posts of a chassis that looked like an upturned table. Because the carriage body was suspended from the chassis, the system came to be known as a "suspension" a term still used today to describe the entire class of solutions.

The slung-body suspension was not a true springing system, but it did enable the body and the wheels of the carriage to move independently.

Semi-elliptical spring designs, also known as cart springs, quickly replaced the leather-strap suspension. Popular on wagons, buggies and carriages, the semi-elliptical springs were often used on both the front and rear axles.

They did, however, tend to allow forward and backward sway and had a high center of gravity. By the time powered vehicles hit the road, other, more efficient springing systems were being developed to smooth out rides for passengers.

The first workable spring-suspension is Leaf springs have been around since the early Egyptians on Horse-drawn carriages and the Ford Model T, mainly mounted in the rear suspension.

In 1901 Mors of Paris first fitted an automobile with shock absorbers. With the advantage of a damped suspension system on his 'Mors Machine'.

Coil springs first appeared on a production vehicle in 1906 in the Brush Runabout made by the Brush Motor Company. Today, coil springs are used in most cars.

In 1920, Leyland Motors used torsion bars in a suspension system.

In 1922, independent front suspension was pioneered on the Lancia Lambda and became more common in mass market cars from 1932. Today most cars have independent suspension on all four wheels.

Why need a suspension? – Ride comfort – Vehicle stability – Durability of components – Suspension makes owning and driving a car more meaningful.

2.3. Functions of automobile suspension system:

1. Suspension system absorbs road shocks and provides comfortable ride as well as safeguards for the passengers and goods.

2. It prevents the vehicle body and frame from road shocks.

3. It gives stability of the vehicle.

4. It gives the good road holding while driving, cornering and braking.

5. It gives cushioning effect and it provides comfort.

6. Resist roll of the chassis, isolating the chassis from roughness in the road.

7. Maintain the wheels in the proper steer and camber attitudes to the road surface.

8. The job of a car suspension is to maximize the friction between the tyres and the road surface, to provide steering stability with good handling and to ensure the comfort of the passengers.

9. React to the control forces produced by the tyres – longitudinal (acceleration and braking) forces, lateral (cornering) forces, and braking and driving torques.

10. Apart from these basic operational aspects, the suspension should also provide a good level of comfort for the passengers, minimizing the movements and accelerations imposed on and perceived by them.

11. System should minimize vertical motion, as well as pitch and roll movements, as the vehicle passes over an irregular road, performs turning manoeuvres, and is accelerated or braked heavily.

2.4. Requirements of automobile suspension system:

1. It is primary need for vehicle ride and human comfort and its privilege.

2. There should be minimum deflection.

3. It should be of low initial cost.

4. It should be of minimum weight.

5. It should have low maintenance and low operating cost.

6. It should have minimum tyre wear.

7. Suspension systems must support both road-holding/handling and ride quality, which are at odds with each other.

8. To keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires.

9. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear.

2.5. Elements of automobile suspension system: