Principles and Springs Suspension Principles and Springs

Why To protect the passengers from bumps in the road. To protect the vehicle from damage To keep the wheel in contact with the road surface Control pitch, roll and braking forces

How Fitting a spring between the road wheels and the chassis Fitting a Pneumatic tyre to the wheel Fitting Springs to seating

What Leaf Springs Coil Springs Rubber mountings Torsion Bars Pneumatic Hydragas Tyres

Tyres Tyres are the first point of contact for the suspension system. The rubber tyre flexes when it comes into contact with a bump in the road and the air inside the tyre will compress to absorb some of the shock and travel

Laminated or Leaf Springs The main leaf is rolled at each end to for eyes and has a number of leaves clamped to it. Leaves are graduated in length to ensure a constant stress Rebound clips transfer the load to some of the lower leaves to reduce the need to add too many springs Rubber mountings absorb shock and noise A swinging shackle is fitted to accommodate the alterations in spring length.

Stiffness rate The lower the rate the softer the ride The force required to deflect the spring effects ride comfort and payload. Length – the shorter the spring the higher the rate Width – the wider the higher the rate Thickness – the thicker the higher the rate Number – more leaves the higher the rate Force required, length, width, thickness , number

Friction As the leaves flex they rub against each other causing friction. Although this does have a desirable damping effect it does create a hard ride, noise and wear. In older vehicles the leaves would be periodically sprayed with penetrating oil. These days special features have been added to prevent the need for servicing. Various methods of reducing the friction

Friction reduction Synthetic rubber buttons Reducing the number of leaves or using a single tapered leaf Inter-leaf plates of low friction material

Transverse Leaf Spring Triumph Herald used a transverse leaf spring which had the effect of drawing the wheels in wards when the weight was taken off them.

Coil Spring

Coil Spring Usually used with independent suspension and some rear axle assemblies. Although the coil is better at storing energy it does require more components to be fitted which can add to the weight. Rate is governed by thickness and length of the spring. The length is determined by the diameter and number of active coils.

McPherson Strut Double Wishbone Trailing Arm

Dampers Convert Kinetic energy to heat energy When a spring is compressed it stores energy When the energy is released the spring will extend beyond it’s normal length This also stores energy which is released and compresses the spring This characteristic is known as oscillation A damper is fitted to reduce the oscillations and improve ride comfort and road holding.

Shock absorbers work in two cycles -- the compression cycle and the extension cycle. The compression cycle occurs as the piston moves downward, compressing the hydraulic fluid in the chamber below the piston. The extension cycle occurs as the piston moves toward the top of the pressure tube, compressing the fluid in the chamber above the piston. A typical car or light truck will have more resistance during its extension cycle than its compression cycle. With that in mind, the compression cycle controls the motion of the vehicle's un-sprung weight, while extension controls the heavier, sprung weight.

Torsion bars Behaves like a coil spring One end attached to the frame and the other to the control arm The control arm rises and falls with the road wheel and the torsion bar twists and untwists to absorb the movement. A damper is used to control the oscillations

assembly

Air Springs A throwback again to the horse and carriage where leather bellows type airbags where used. Changed to rubber air springs in the 1930’s Not so much used at all today

Hydrolastic Suspension The front and rear suspension units have Hydrolastic displacers These are interconnected by a small bore pipe. Each displacer incorporates a rubber spring damping of the system is achieved by rubber valves when a front wheel is deflected, fluid is displaced to the corresponding suspension unit. That pressurises the interconnecting pipe which in turn stiffens the rear wheel damping and lowers it The rubber springs are only slightly brought into play and the car is effectively kept level and freed from any tendency to pitch

Hydragas Suspension With Hydragas, the rubber spring is removed completely. The fluid still exists but above the fluid there is now a separating membrane or diaphragm, and above that is a cylinder or sphere which is charged with nitrogen gas. The nitrogen section is what has become the spring and damping unit whilst the fluid is still free to run from the front to the rear units and back.

Beam Axle A dead Axle (non-driving) Designed to reduce the sprung-weight of the rear axle in front wheel drive cars A panhard rod is used to prevent lateral (side to side) movement of the assembly

Control Blade Ford’s new suspension lowers centre of gravity and separates suspension components from handling components.

Conclusion A suspension system separates the payload of a vehicle from the variations in road surface It maintains maximum contact between the tyres and the road surface Absorbs and controls pitch and roll from accelerating, cornering and braking forces.

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