The suspension system affects both the driver's control of the car and the comfort of the occupants. The springs allow the wheels to move up to absorb bumps in the road and reduce jolting, while the dampers prevent bouncing up and down. Various mechanical links keep the wheels in line.
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Leaf spring
A leaf spring is fixed to the axle by U-bolts that clamp the centre of the stack of steel strips. As the spring deflects , its leaves flatten, make greater contact with one another and stiffen the spring. As the leave flattens, it lengthens so one end has a pivoted shackle.Most cars have steel springs, and the oldest type is the leaf spring . The topmost and longest strip, the master leaf, is curled at each end into an eye by which it is connected to the frame . The leaves below are progressively shorter and less curved.
Leaf springs in action
As the spring deflects, it flattens, causing the second leaf to touch the master leaf, then the third to touch the second. The spring thus becomes progressively stiffer. Such a spring gives a smoother ride than a stiff, plain single leaf could.
In some cars the multi-leaf spring has been replaced by a special single leaf that is tapered in section and has progressive stiffness as it is deflected.
Coil spring
A coil spring is made of resilient steel rod. It extends as the wheel moves down and compresses as the wheel moves up, so the car body remains reasonably level.A coil spring is simply a spiral of resilient steel rod. It is stretched or compressed by the vertical movement of the wheels.
The torsion bar is a length of spring steel with splined or square ends. One splined end is fixed to a lever arm that forms part of the suspension. The bar rotates as the lever arm moves up and down.
Torsion bar
A torsion bar is of spring steel with one end rigidly fixed to the frame. The bar twists as the other end rotates with movements of the suspension lower arm.The other splined end is fixed to the frame. The splines stop the bar turning in its fixings. Instead, the bar has to twist as the suspension deflects.
In all forms of steel spring, the forces set up by road shocks are stored by the spring deflection rather than passed on to the passengers. The forces are then released gradually to restore the car to a level ride.
Rubber springs can perform the same function, but they do not store as much energy and are therefore used on light vehicles only.
A form of hydraulic suspension can be combined with rubber springs to refine the system. Up-and-down movement of the wheel pumps fluid from one chamber to another through a damper valve . Each chamber has a flexible diaphragm with compressed gas on the other side of it.
The gas is compressed further as fluid comes into the chamber through the valve. In effect the gas is acting as a pneumatic spring.
There is usually a link tube through which some of the fluid pumped out of a front-wheel chamber travels to the rear wheel on the same side to equalise the suspension.
Citroen hydraulic suspension can be pumped up and down to raise or lower the car to a desired height.
Springs deflect as the car goes over a bump, then bounce back. The car would continue to bounce up and down if the energy stored in the springs were not dissipated in some way.
Dampers - commonly called shock absorbers - perform this function. A damper has a piston which moves inside a sealed, oil-filled cylinder with the up-and-down movement of the wheel.
There are narrow control passages and one-way valves in the piston, which allow oil to flow through it from one chamber to another - but only very slowly.
This action slows down the spring oscillations and returns the car to a level ride.
There are three types of damper. Telescopic dampers look like telescopes and shorten in the same way. One end is bolted to the axle , the other to the body.
Strut inserts are similar, but are designed to fit inside a MacPherson strut (See Renewing MacPherson-strut inserts ).
Lever-arm dampers resemble hydraulic door closers. The damper, which contains one or two pistons, is fixed to the car body or frame, and a pivoted lever extends from it to the axle.
Some cars have dampers that contain both oil and gas. These act more efficiently than oil-filled dampers.
Hydraulic suspension
Hydraulic suspension combines rubber springs with a damper system linking the front and rear wheel on the same side of the car. As the front wheel rises over a bump, some of the fluid from its suspension unit (known as a displacer unit) flows to the rear-wheel unit and raises it, so tending to keep the car level. In each of the displacer units, the fluid passes through a two-way valve, which provides the damping effect. Once the rear wheel has passed over the bump, the fluid returns to the front displacer unit and the original level is restored.'
20 Jul
ADVICE
How suspension works: Dampers
An integral part of the suspension, dampers are prone to wear and should not be ignored
You may call them shock absorbers, but the hydraulic suspension components that keep a car's springs from bouncing uncontrollably over bumps and potholes are technically known as dampers.
Unseen and often not considered, dampers are one of the keys to your car's on and off-road capability. In fact, they are so important to a vehicle's performance, racing teams around the world spend countless hours and endless dollars fine tuning them.
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But what are dampers? What do they do? How do they work? Why are they important and what are the warning signs they need replacing?
Let's start by explaining what a damper is. It's a long metallic cylinder sealed at both ends, with a piston protruding at one end and they are a major component of the suspension, with one connected to each wheel. In most cases the cylinder is filled with hydraulic fluid. Without getting too technical, there are different types of dampers available, even adjustable ones but essentially, they all do the same job.
What do they do?
Let's start with one thing dampers don't do. They don't support the weight of the car. Instead, that's the job of the springs, another type of major suspension component.
What dampers do is control the bouncing movement of the spring by providing resistance, to ensure the tyres are kept in contact with the road.
Think of it like this: when you bounce a ball and catch it, you are controlling its bounce. If you don't catch it, the ball continues to bounce with each bounce progressively smaller until the ball comes to rest. A car without dampers would behave the same way. After hitting a bump it would bounce up and down continuously, until it finally settled in its normal state.
The damper, like you catching the ball, controls the bounce.
Essentially, dampers do two things. Apart from controlling the movement of springs and suspension, dampers keep your tyres in contact with the ground at all times and whenever a tyre loses contact with the ground, your ability to drive, steer and brake is compromised.
And if the springs are allowed to bounce uncontrollably, the car will wallow and the ride quality will lead the car's occupants to feel sick after a while.
How do they work?
Inside the damper's sealed cylinder are valve passages and hydraulic fluid. As the suspension travels up and down, the piston moves inside the cylinder. As this occurs, the flow of fluid is slowed by the valve passages, which in turn controls the speed of the piston's motion and therefore the movement of the suspension. Dampers automatically adjust to road conditions and the faster the suspension moves the more resistance the dampers provide.
Shock absorbers or dampers are used on all kinds of machinery to cushion the blow
Why are they so important?
Dampers play a vital role in the ride and handling of your car.
Aside from giving you a comfortable ride, dampers help manage a vehicle's stability, cornering, handling, traction, braking, stopping distance, and overall safety.
But dampers tend be one of the most overlooked maintenance items on a car.
Unlike a flat tyre or blown headlight globe, dampers' performance deteriorates gradually over a long period of time, and often unknowingly, drivers adjust their driving style to compensate.
How can you tell they need replacing?
When your car is moving, the dampers are constantly working, so they do wear out. But there are warning signs to tell you your dampers need replacing.
Nose diving or swerving when braking hard indicate that worn dampers can no longer control the weight transfer of the car and the piston in the damper is compressing too rapidly.
After hitting a bump, your car should fall and rise back to its original position and settle after one, or two rebounds at most. If it doesn't, it means the dampers are worn out as they no longer control the bounce of the springs.
When dampers are worn, cars become more unstable, which is magnified in SUVs and LCVs due to their added height and weight.
Rock and roll might be great to listen to but it's no fun when cornering. If your vehicle leans excessively in corners, it's another tell-tale sign that the dampers are worn.
Yet another clue is vibrations through the steering wheel. Often it is simply a wheel out of balance but it could well be one damper is more worn than the other, creating an uneven controlling of the suspension.
Uneven or premature wearing of tyres is another sign of worn dampers caused by the shock's inability to control the suspension, causing the tyre to bounce on the road over bumps and through dips and wear unevenly.
If you have the wheel off and notice there is leakage from the shock, or the bushes are cracked and squashed, then it's time to bin them and get new ones. The same applies if the cylinder is damaged or dented on the outside as there's a good chance they're damaged on the inside and not functioning to their potential.
And when it comes time to replacing dampers, do so in pairs, otherwise uneven controlling of the bounce by one side of the car to the other will occur, causing an uncomfortable and uneven ride and compromise the car's stability.
Connecting your car to the road are four postcard-sized contact areas of the tyres. It is important to have your dampers operating properly to ensure you have the maximum grip and control through these contact patches at all times.
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Written by
Mark Higgins
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