Independent Suspension

Independent Suspension

Systems Coil springs are generally used with independent suspension

systems; the springs are Coil spring lower fitting usually fitted on each

Coil spring upper fitting

side of the vehicle, between the stub axle assembly and the body. The spring remains in the correct position because recesses are made in both the stub axle assembly and body. The spring is always under compression due to the weight of the vehicle and hence holds itself in place.

Coil Spring Features The coil spring is a torsion bar wound into a spiral. It can be progressive if the diameter of the spring is tapered conically. A coil spring cannot

Details of a coil spring

transmit lateral or longitudinal forces, hence the need for links or arms. It produces little internal damping. No maintenance is required and high travel is possible.

Leaf Springs The leaf spring can provide all the control for the wheels during acceleration, braking, cornering, and general movement caused by the road surface. They are used with fixed axles. Leaf

Laminated springs

springs can be described as: Laminated or multi-leaf springs Single leaf or mono-leaf springs.

Multi-Leaf Spring The multi-leaf spring was widely used at the rear of cars and light vehicles, and is still used in commercial vehicle suspension systems. It consists of a number of steel strips or leaves

Commercial vehicle leaf spring

placed on top of each other and then clamped together. The length, cross section, and number of leaves are determined by the loads carried.

Leaf Spring Fixings The top leaf is called the main leaf and each end of this leaf is rolled to form an eye. This is for attachment to the vehicle chassis or body. The leaves of Details of a leaf spring the spring are clamped together by a bolt or pin known as the centre bolt. The spring eye allows movement about a shackle and pin at the rear, allowing the spring to flex. The vehicle is pushed along by the rear axle through the front section of the spring, which is anchored, firmly to the fixed shackle on the vehicle chassis or body. The curve of leaf springs straightens out when a load is applied to it, and its length changes.

Shackles ฀฀฀Because of the change in length as the spring moves, the rear end of a leaf spring is fixed by a shackle bolt to a swinging shackle. As the road wheel passes over a bump, the spring is compressed and the leaves slide over each other. As it returns to its original shape, the spring forces the wheel back in contact with the road. The leaf spring is usually secured to the axle by means of U bolts. As the leaves of the spring move, they rub together. This produces interleaf friction, which has a damping effect.

Single Leaf Spring A single leaf spring, as the name implies, consists of one uniformly stressed leaf. The spring varies in thickness from a maximum at the centre to a minimum at the spring eyes. Tapered single leaf This type of leaf spring is made to work in the same way as a multi-leaf spring. Advantages of this type of spring are:

Simplified construction Constant performance over a period,

because interleaf friction is eliminated Reduction in unsprung mass.

Torsion Bars This type of suspension uses a metal bar, which provides the springing effect as it is twisted. It has

Torsion bar in a guide tube

the advantage that the components do not take up too much room. The torsion bar can

be round or square section, solid or hollow. The surface must be finished accurately to eliminate pressure points, which may cause cracking and fatigue failure. They can be fitted longitudinally or laterally.

Torsion Bar Features Torsion bars are maintenance free but can be adjusted. They transmit longitudinal and lateral forces and have low mass. However, they have limited self-damping. An anti-roll bar is a torsion spring