Car Suspension - An Introduction!

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Car suspension - An introduction!


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Basics :-

The basic job of the car suspension is to maximizethe friction between the road surface and the tiresand body roll is minimized. Greater the friction

more stable would be the steering and handling ofthe car. It allows the car to travel smoothly overbumps in the road by absorbing and dissipatingkinetic energy from the point of contact.

Furthermore, a suspension system allows the car toturn corners without rolling by shifting the car'scentre of gravity to maintain balance.


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If the roads were perfect we wouldnt need any kind

of suspension. But it is not so. Hence suspension has

a great importance.


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What actually happen when a car

move over an imperfection?

A bump in the road causes the wheel to move

up and down perpendicular to the road surface.

The magnitude, of course, depends on whether

the wheel is striking a giant bump or a tiny

speck. Either way, the car wheel experiences a

verticalacceleration as it passes over an

imperfection.


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Without an intervening structure, all of wheel'svertical energy is transferred to the frame, whichmoves in the same direction. In such a situation,

the wheels can lose contact with the roadcompletely. Then, under the downward force ofgravity, the wheels can slam back into the roadsurface. Hence we need a system that will absorb

the energy of the vertically accelerated wheel,allowing the frame and body to ride undisturbedwhile the wheels follow bumps in the road.


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These two characteristics can be further described

in three important principles-


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A key part of the suspension system is the shockabsorber. Its job is to convert kinetic energy intoheat that can be absorbed by the shock's hydraulic

fluid.

Another key component of the suspension is theanti-sway bar (also known as an anti-roll bar), which

connects the two sides of a car's suspension alongthe axle. If one side of the car moves up or down toany extent, the anti-sway bar is able to minimize theroll of the car by distributing the movement to the

other side of the car. This means the car won't swaytoo much in either direction and will remain morelevel. The anti-sway bar is of particular use whengoing around corners, especially sharp ones.


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Race car suspension systems make for an interesting

contrast with standard cars. Although it's better and

safer for both racing cars and standard cars to haveall of their wheels in contact with the track or road

at all times, and both use independent suspensions,

the reasons they use them differ. The race car driver

wants all four wheels to be on the track for stability,

and so the wheels take advantage of the engine's

power. The race car's suspension has to handle

extreme acceleration and turns taken at high speedsand sudden stops, all of which are more than a

standard car is built to deal with. The standard car's

suspension, on the other hand, only has to deal with

balancing comfort and performance


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CAR CHASSIS PARTS:-

The suspension of the car is basically a part ofchassis which has 4 main components:-


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Frame - structural, load-carrying component

that supports the car's engine and body, which

are in turn supported by the suspension.

Suspension system - setup that supports

weight, absorbs and dampens shock and helpsmaintain tire contact.


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Steering system - mechanism that enables the driver to

guide and direct the vehicle.

Control arm - components that make vehicle motion

possible by way of grip and/or friction with the road.


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COMPONENTS OF

SUSPENSIONSYSTEM :-

Fundamental components of any suspension

system are :-

1. Springs

2. Dampers and

3. Anti-sway bars.


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SPRINGS:-

There are four basic designs

1.Coil springs:-

This is the most common type of spring and is,

in essence, a heavy-duty torsion bar coiled

around an axis. Coil springs compress and

expand to absorb the motion of the wheels.


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2. Leaf spring

This type of spring consists of several layers ofmetal (called "leaves") bound together to act as a

single unit. These are use on most trucks and

heavy-duty vehicles.


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3. Torsion bar

A steel bar that is twisted to support the weight of

the vehicle. Torsion bars are used in place of coil orleaf springs on some vehicles, and allow ride heightto be adjusted to compensate for sage that occursover time. Torsion bars use the twisting properties of

a steel bar to provide coil-spring-like performance.One end of a bar is anchored to the vehicle frame.The other end is attached to a wishbone, which actslike a lever that moves perpendicular to the torsionbar. When the wheel hits a bump, vertical motion is

transferred to the wishbone and then, through thelevering action, to the torsion bar. The torsion barthen twists along its axis to provide the spring force.


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A long spring steel rod or flat bar attached in such a way

that one end is anchored while the other is free to twist.

One end is fastened to the frame at one end and to a

suspension part at the other. If an arm is attached at right

angles, to the free end, any movement of the arm will

cause the rod or bar to twist the bars resistance to twisting

provides a spring action. The torsion bar replaces both Coil

spring and Leaf springs in some suspension systems. The

main advantage of the torsion bar over the Coil spring in

the Front suspension is the ease of adjusting frontsuspension height. Some are mounted longitudinally (i.e.,

front of car to back of car) or transversely (i.e., from the

left side to right side of the car).


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4. Air spring:-

A Suspension system using air rather than metal

springs to support the vehicle and control ride

motions. Air springing results in a smoother ride,

because the natural frequency of vibration of an airspring does not vary with loading as it does with

metal springs. Air springs can be made very soft for

the lightly loaded condition and the pressure

automatically increased to match any increase in

load, thus maintaining a constant sprint vibration

period any load.


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SPRUNG AND UNSPRUNG MASS

Based on where springs are located on a car --

i.e., between the wheels and the frame. It is

classified as sprung and unsprung mass.The sprung mass is the mass of the vehicle

supported on the springs, while the unsprung

mass is loosely defined as the mass between theroad and the suspension springs


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The stiffness of the springs affects how the

sprung mass responds while the car is being

driven. Loosely sprung cars, such as luxury cars

can swallow bumps and provide a super-smooth

ride; however, such a car is prone to dive and

squat during braking and acceleration and tendsto experience body sway or roll during cornering.

Tightly sprung cars, such as sports cars are less

forgiving on bumpy roads, but they minimizebody motion well, which means they can be

driven aggressively, even around corners.


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Loosely sprung car

Provide super-smooth ride but may roll on steep turns

Tightly sprung car

Good turning but less forgiving on bumpy roads.


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DAMPERS (SHOCK ABSORBERS):-

Springs by themselves seem like simple devices,

designing and implementing them on a car to

balance passenger comfort with handling is a

complex task. And to make matters more complex,

springs alone can't provide a perfectly smooth ride.

It is because springs are great at absorbing energy,

but not so good at dissipating it. Other structures,

known as dampers, are required to do this.


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Unless a dampening structure is present, a car

spring will extend and release the energy it

absorbs from a bump at an uncontrolled rate.The spring will continue to bounce at its natural

frequency until all of the energy originally put

into it is used up.A suspension built on springs alone would make

for an extremely bouncy ride and, depending on

the terrain, an uncontrollable car.


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To overcome this problem dampers are used. Shock

absorbers or dampers slow down (or damp) and

reduce the magnitude of vibratory motions by turning

the kinetic energy of suspension movement into heat

energy that can be dissipated through hydraulic fluid.


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A shock absorber is basically an oil pump placed

between the frame of the car and the wheels.

The upper mount of the shock connects to theframe (i.e., the sprung weight), while the lower

mount connects to the axle, near the wheel (i.e.,

the unsprung weight). In a twin-tube design, the

upper mount is connected to a piston rod, which

in turn is connected to a piston, which in turn

sits in a tube filled with hydraulic fluid. The inner

tube is known as the pressure tube, and theouter tube is known as the reserve tube. The

reserve tube stores excess hydraulic fluid.


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When the car wheel encounters a bump in the

road and causes the spring to coil and uncoil,

the energy of the spring is transferred to theshock absorber through the upper mount, down

through the piston rod and into the piston.

Orifices perforate the piston and allow fluid toleak through as the piston moves up and down

in the pressure tube. Because the orifices are

relatively tiny, only a small amount of fluid,

under great pressure, passes through. This slows

down the piston, which in turn slows down the

spring.


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Shock absorbers work in two cycles

compression cycle &

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 asthe piston moves toward the top of the pressure tube,compressing the fluid in the chamber above the piston. Atypical car or light truck will have more resistance during

its extension cycle than its compression cycle. With that inmind, the compression cycle controls the motion of thevehicle's unsprung weight, while extension controls theheavier, sprung weight.


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STRUTS:-

A single, self-contained pivoting suspension unit

that integrates a coil spring with a shock absorber.

Struts are used on front wheel drive automobiles.

They provide a dampening function like shock

absorbers, and they provide structural support for

the vehicle suspension. That means struts deliver abit more than shock absorbers.


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Because shocks and struts have so much to do with thehandling of a car, they can be considered critical safetyfeatures. Worn shocks and struts can allow excessive

vehicle-weight transfer from side to side and front toback. This reduces the tire's ability to grip the road, aswell as handling and braking performance.


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ANTI-SWAY / ANTI-ROLL BARS:-

Anti-sway bars are used along with shock

absorbers or struts to give a moving automobileadditional stability. An anti-sway bar is a metalrod that spans the entire axle and effectively

joins each side of the suspension together.When the suspension at one wheel moves upand down, the anti-sway bar transfersmovement to the other wheel. This creates a

more level ride and reduces vehicle sway. Inparticular, it combats the roll of a car on itssuspension as it corners.


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It also affects handling. A front anti-roll bar

increases understeer and a rear bar increasesoversteer.


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SUSPENSION TYPES

1. SOLID BEAM AXLE (front suspension dependentsystem):-

In the beam axle setup both of the front wheels areconnected to each other by a solid axle. It is basically a

solid bar under the front of the car, kept in place by leafsprings and shock absorbers. This style was carried overto the first automobiles from the horse drawn carriagesof the past. New developments in springs, roll bars, and

shocks have kept the solid axle practical for someapplications. If we look at the front end of a semi orheavy duty truck, we wouldve noticed that both of the

front wheels are connect by a solid axle.


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They haven't been used on mainstream cars for years forthree main reasons:

Shimmy - because the wheels are physically linked, the

beam can be set into oscillation if one wheel hits a bumpand the other doesn't. It sets up a gyroscopic torque aboutthe steering axis which starts to turn the axle left-to-right.Because of the axle's inertia, this in turn feeds back to

amplify the original motion. Weight - or more specifically unsprung weight. Solid front

axles weigh a lot and either need sturdy, heavy leaf springsor heavy suspension linkages to keep their wheels on the

road. Alignment - simply put, you can't adjust the alignment of

wheels on a rigid axis. From the factory, they're perfectlyset, but if the beam gets even slightly distorted, you can't

adjust the wheels to compensate


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2. SWING AXLE:-

Swing axle suspension, as the name suggests,

set up so that the axles pivot about a location

somewhere near the centre of the car and allow

the wheels to travel up and down through theirrespective arcs. This system was eventually

adapted for rear suspensions as can be found on

the old beetles.


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Old beetle suspension


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FRONT SUSPENSION

INDEPENDENT SYSTEMS

The front wheel's suspension systems are

independent of each other (except where joinedby an anti-roll bar) . These are of two types:-

1.MacPherson Strut or McPherson strut

2.Double wishbone suspension systems.

1 MacPherson Str t or McPherson


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1. MacPherson Strut or McPherson

strut

The system basically comprises of a

strut-type spring and shock absorbercombo, which pivots on a ball joint on

the single, lower arm. At the top endthere is a needle roller bearing on

some more sophisticated systems. Thestrut itself is the load-bearing member

in this assembly, with the spring andshock absorber merely performing

their duty as oppose to actually

holding the car up.

.


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The steering gear is either connected

directly to the lower shock absorber

housing, or to an arm from the frontor back of the spindle . When you

steer, it physically twists the strut

and shock absorber housing (and

consequently the spring) to turn thewheel. The spring is seated in a

special plate at the top of the

assembly which allows this twisting

to take place


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2 D bl i hb i t


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2.Double wishbone suspension systems.

In this design the suspension is supported by a

triangulated A-arm at the top and bottom of theknuckle. The earliest designs of the A-arm suspensionincluded equal length upper and lower arms mountedparallel to the ground. Each wishbone, which has twomounting positions to the frame and one at the wheel,bears a shock absorber and a coil spring to absorbvibrations. Double-wishbone suspensions allow formore control over the camber angle of the wheel,which describes the degree to which the wheels tilt inand out. They also help minimize roll or sway andprovide for a more consistent steering feel


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In order to determine a way for the suspension to gain

negative camber as it was compressed unequal length

double A-arm suspension was born.

By using an upper control arm that is shorter than the lower

one, as the wheel travels up it tips in, gaining negative

camber. This is because the upper arm swings through ashorter arc than the lower and pulls in the top of the tire as

the wheel travels upwards. The advantage in this negative

camber gain is that as the chassis rolls against the wheels,

the increasing negative camber on the outside wheel helps

keep the wheel upright against the road surface and allows

the tire to generate the maximum possible cornering force.

By adjusting the length of the arms and their respective angles to


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By adjusting the length of the arms and their respective angles to

the ground, there are infinite possibilities in the design of a vehicles

roll centre height and swing arm length. This flexibility gives

suspension designers unlimited options on how to best setup thesuspension.


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REAR SUSPENSION

Dependent Rear Suspensions

If a solid axle connects the rear wheels of a car,

then the suspension is usually quite simple -- based

either on a leaf spring or a coil spring. In the former

design, the leaf springs clamp directly to the drive

axle. The ends of the leaf springs attach directly to

the frame, and the shock absorber is attached at the

clamp that holds the spring to the axle.

S i


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Independent Rear Suspensions

If both the front and back suspensions are

independent, then all of the wheels are mounted andsprung individually, resulting in "four-wheel

independent suspension."

In the rear of the car, the steering rack -- the assembly

that includes the pinion gear wheel and enables the

wheels to turn from side to side -- is absent. This

means that rear independent suspensions can be

simplified versions of front ones, although the basic

principles remain the same.

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Car Suspension - An Introduction!