Suspension System: Type of Suspension Springs

 Suspension System:

Coil springs

Coil springs are used on the front suspension of most modern light vehicles, and in many cases, they have replaced leaf springs in the rear suspension.
A coil spring is made from a single length of special wire, which is heated and wound on a former, to produce the required shape.
The load-carrying ability of the spring depends on the diameter of the wire, the overall diameter of the spring, its shape, and the spacing of the coils.

And this also decides which vehicle it is suitable for. A light commercial vehicle has springs that are robust and fairly stiff.
On a small passenger car, they are lighter, and more flexible.
The coils may be evenly spaced, or of uniform pitch, or unevenly spaced.
The wire can be the same thickness throughout, or it may taper towards the end of the spring.
The spring itself may be cylindrical, barrel-shaped, or conical.
Generally, a cylindrical spring, with uniform diameter wire, and uniform pitch, has a constant deflection rate. Its length reduces in direct proportion to the load applied.
When the pitch is varied, the deflection rate varies too. The spring is then said to have a progressive rate of deflection.
Similarly for varying wire diameter and the shape.
A spring with a progressive rate deflects readily under a light load, but increases its resistance as the load increases. This gives a softer ride.
As conical and barrel-shaped springs compress, they collapse into themselves. This gives a longer suspension travel for the length of the spring, than for a cylindrical spring. This gives a softer ride for light-load situations, and a harder ride for heavy load situations.
As a cylindrical coil compresses, it can become coil-bound, which limits its travel.
Coil springs can look alike but give very different load ratings, which are often color coded for identification.
They normally use rubber pads to prevent transmission of noise and vibration.

Leaf springs

The leaf spring is one of the oldest forms of springing. It is usually used on rear-wheel-drive vehicles because its simplicity.
They can be mounted longitudinally.
Leaf springs consist of one or more flat springs, made of tempered steel. A number of leaves of different length are used to form a multi-leaf spring.
They are held together by a centre bolt that passes through a hole in the centre of each leaf. It is also used to locate the axle on the spring. The axle is then clamped to the spring by U-bolts that wrap around the axle housing, and through a spring plate underneath the spring.
Rebound clips are formed at intervals around the leaves. They prevent excessive flexing of the main leaf during rebound, and also keep the leaves in alignment.
The longest leaf called the main leaf, is rolled at both ends to form eyes. These eyes are used to mount the spring to the frame of the vehicle.
Some springs have the ends of the second leaf rolled around the eyes of the main leaf, as reinforcement. This leaf is called the wrap leaf.
The front of the spring is attached to a rigid spring hanger on the vehicle frame.
The rear is connected to the frame by a swinging shackle, which provides a link between the spring eye and a bracket on the subframe.
This swinging link is needed, because, as the spring flexes, and flattens out under load, the distance between the spring eyes increases.
Some springs have inserts between the leaves, of plastic, nylon, or rubber. They act as insulators, to reduce noise transfer, and friction as the leaves move under load.
Some older vehicles completely enclose the leaf springs in grease.
The spring eyes are fitted with bushes, usually with a rubber, flexible section, but nylon and urethane bushes are also used, and sometimes bronze for heavy duty applications.
Rubber insulating pads between the spring mounting pad and the spring also act as insulators.
And similarly, between the spring plate and the spring.
The spring forms a flexible suspension unit that locates the axle housing longitudinally and laterally.
It can sustain the torque reaction on acceleration and the braking torque during deceleration, and the driving thrust is transferred through the front half of the spring to the fixed shackle point.

Torsion bars

A torsion bar is a long, alloy-steel bar, fixed rigidly to the chassis or sub-frame, at one end, and to the suspension control arm at the other.
The bar is fitted to the control arm in the unloaded condition, and as the control arm is raised, the bar twists around its centre, which places it under a torsional load.
When the vehicle is placed on the road, with the control arm connected to the suspension assembly, the bar supports the vehicle load, and twists around its centre, to provide the springing action.
Spring rate depends on the length of the bar, and its diameter. The shorter and thicker the bar, the stiffer its spring rate.
Torsion bars can be used across the chassis frame on the same principle, in a trailing arm suspension, or as part of the connecting link between 2 axle assemblies, on a semi-rigid axle beam.
After a lot of use, a torsion bar can sag. On many vehicles, it can be adjusted to allow for this.
It is used in light vehicles as a stabilizer, or anti-roll bar, connected between each side of the suspension on the front, and sometimes the rear.
When the vehicle is turning, centrifugal force acts on the body, and tends to make it lean outwards. The anti-roll bar, or stabilizer, tries to use its connections to each side of the suspension, to resist this roll tendency.

Rubber springs

Rubber is used in most suspension systems as bump and rebound stops.
If the suspension reaches its limit of travel, these stops prevent direct metal-to-metal contact, which reduces jarring of the body of the vehicle. The stops can also be shaped to provide an auxiliary springing function, increasing their resistance progressively with suspension contact.
Some vehicles use rubber as the main springing medium. This rubber cone is this vehicle’s main suspension member.
Increasing the load on the suspension causes the cone to act like a spring being deformed. When the load is removed, the rubber’s elastic properties tend to return it to its original state.
Rubber has a number of advantages. It doesn’t need to be lubricated, it can be made into any shape, as required, and it’s silent during use.