car suspension system

8/8/2019 Car Suspension System

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ByAmit Saini


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When people think ofautomobile performance, they normally

think of horsepower, torque and zero-to-60 acceleration. But allof the power generated by a piston engine is useless if thedriver can't control the car. That'swhy automobileengineersturned their attention to thesuspension system almost assoonas they had mastered thefour-stroke internal combustion

engine. Thestudy of theforces atwork on a moving car is

called vehicle dynamics, and you need to understand someofthese concepts in order to appreciatewhy a suspension is

necessary in thefirstplace


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Somebasics tooverviewPrinciple Definition Goal Solution

Road IsolationThe vehicle's ability toabsorb or isolate road

shock from the passenger

compartment

Allow the vehicle body to

ride undisturbed while

traveling over rough roads.

Absorb energy from road bumps

and dissipate it without causing

undue oscillation in the vehicle.

Road Holding

The degree to which a car

maintains contact with the

road surface in various

types of directional

changes and in a straight

line (Example: The weight

of a car will shift from the

rear tires to the front tires

during braking. Because

the nose of the car dips

toward the road, this type

of motion is known as

"dive." The opposite effect

-- "squat" -- occurs during

acceleration, which shiftsthe weight of the car from

the front tires to the back.)

Keep the tires in contact

with the ground, because it

is the friction between the

tires and the road that

affects a vehicle's ability to

steer, brake and accelerate.

Minimize the transfer of

vehicle weight from side to

side and front to back, as

this transfer of weight

reduces the tire's grip on

the road.

CorneringThe ability of a vehicle to

travel a curved path

Minimize body roll, which

occurs as centrifugal force

pushes outward on a car's

center of gravity while

cornering, raising one side

of the vehicle and loweringthe opposite side.

Transfer the weight of the

car during cornering from

the high side of the vehicle

to the low side.


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Howsuspension system work

According to Newton's laws of motion,all forces have bothmagnitude and direction. A bump inthe road causes the wheel to move upand down perpendicular to the roadsurface. The magnitude, of course,depends on whether the wheel is

striking a giant bump or a tiny speck.Either way, the car wheel experiencesa vertical acceleration as it passes

over an imperfection.Without an intervening structure, allof wheel's vertical energy istransferred to the frame, which movesin the same direction. In such a

situation, the wheels can lose contactwith the road completely. Then, underthe downward force of gravity, thewheels can slam back into the roadsurface. What you need is a systemthat will absorb the energy of thevertically accelerated wheel, allowingthe frame and body to ride

undisturbed while the wheels followbumps in the road.


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1. The frame - structural, load-carryingcomponent thatsupports the car'sengine and body,which are in turn

supported by thesuspension2. The suspension system - setupthatsupportsweight, absorbs anddampensshock and helps maintaintire contact

3. The steering system - mechanismthatenables the driver to guide anddirect the vehicle

4. The tires and wheels - componentsthat make vehicle motion possiblebyway ofgrip and/orfriction with theroad


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With thisbig-pictureoverview inmind, it's time to look at thethreefundamental components

ofany suspension:springs,dampersandanti-sway bars.


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Dampers: Shock AbsorbersUnless a dampening structure is present,

a car spring will extend and release theenergy it absorbs from a bump at anuncontrolled rate. The spring willcontinue to bounce at its naturalfrequency until all of the energyoriginally put into it is used up. Asuspension built on springs alone wouldmake for an extremely bouncy ride and,

depending on the terrain, anuncontrollable car.

the shock absorber, or snubber, a devicethat controls unwanted spring motionthrough a process known as dampeningShock absorbers work in two cycles --the compression cycle and the extension

cycle. The compression cycle occurs asthe piston moves downward,compressing the hydraulic fluid in thechamber below the piston. The extensioncycle occurs as the piston moves towardthe top of the pressure tube,compressing the fluid in the chamberabove the piston


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Anti-sway Bars

Photo courtesyH

SW ShopperAnti-sway bars

Anti-sway bars (also known asanti-roll bars) are used along withshock absorbers or struts to give amoving automobile additionalstability. An anti-sway bar is ametal rod that spans the entire

axle and effectively joins eachside of the suspension togetherWhen the suspension at onewheel moves up and down, theanti-sway bar transfers movementto the other wheel. This creates amore level ride and reduces

vehicle sway. In particular, itcombats the roll of a car on itssuspension as it corners. For thisreason, almost all cars today arefitted with anti-sway bars asstandard equipment, although ifthey're not, kits make it easy to

install the bars at any time.


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Coil springs - This is the most common typeofspring and is, inessence, a heavy-duty torsion bar coiled around an axis. Coil springs

compress and expand to absorb the motion of thewheels

Photo courtesy Car Domain

Coil springs


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Leaf springs - This typeofspring consistsofseveral layersofmetal (called "leaves") bound together to act as a single unit. Leafsprings werefirst used on horse-drawn carriages and werefound on

most American automobiles until 1985. They arestill used today onmost trucks and heavy-duty vehicles

Photo courtesy

Leaf spring


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y

Torsion bars- Torsion bars use

the twisting propertiesofa steel barto provide coil-spring-likeperformance. This ishow they work:Oneend ofa bar is anchored to thevehicleframe. Theotherend isattached to a wishbone,which actslike a lever that moves perpendicularto the torsion bar. When thewheelhits a bump, vertical motion istransferred to thewishbone and then,through the levering action, to thetorsion bar. The torsion bar then

twists along its axis to provide thespring force. European carmakersused thissystem extensively, as didPackard and Chrysler in the UnitedStates, through the1950s and 1960s.

Photo courtesyTorsion bar


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Air springs -Airsprings,whichconsistofa cylindrical chamberofair

positioned between thewheel andthe car'sbody, use the compressivequalitiesofair to absorbwheelvibrations. The concept is actuallymore than a century old and could befound on horse-drawn buggies. Air

springsfrom thisera were madefromair-filled, leather diaphragms, muchlike a bellows; they werereplacedwith molded-rubber airsprings in the1930s Photo courtesy HSW Shopper

Air springs


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Typesofsuspension systems

Suspension Types: Front

Dependent Front Suspensions

Independent Front Suspensions

Suspension Types: Rear

Dependent Rear Suspensions

Independent Rear Suspensions


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Dependent Front Suspensions Dependent front suspensions have a rigid front axle that

connects the front wheels. Basically, this looks like a solid barunder the front of the car, kept in place by leaf springs andshock absorbers. Common on trucks, dependent frontsuspensions haven't been used in mainstream cars for years.

Independent Front SuspensionsIn this setup, the front wheels are allowedto move independently. The MacPhersonstrut, developed by Earle S. MacPherson ofGeneral Motors in 1947, is the most widelyused front suspension system, especially in

cars of European origin.The MacPherson strut combines a shockabsorber and a coil spring into a single unit.

This provides a more compact and lightersuspension system that can be used for

front-wheel drive vehicles.The double-wishbone suspension, also

known as an A-arm suspension, is another

common type of front independentsuspension


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Specialized Suspensions: TheBaja Bug

Baja BugsTheVolkswagen Beetle, or Bug, was destined to become a favoriteamong off-road enthusiasts. With a low center of gravity and engineplacement over the rear axle, the two-wheel-drive Bug handles off-road conditions as well as some four-wheel-drive vehicles. Of course,

the VW Bug isn't ready for off-road conditions with its factoryequipment. Most Bugs require some modifications, or conversions, toget them ready for racing in harsh conditions like the deserts of BajaCalifornia.

One of the most importantmodifications takes place in the suspension. The torsion-barsuspension, standard equipment on the front and back of most Bugsbetween 1936 and 1977, can be raised to make room for heavy-duty,

off-road wheels and tires. Longer shock absorbers replace thestandard shocks to lift the body higher and to provide for maximumwheel travel. In some cases, Baja Bug converters remove the torsionbars entirely and replace them with multiple coil-over systems, anaftermarket item that combines both the spring and shock absorber inone adjustable unit. The result of these modifications is a vehicle thatallows the wheels to travel vertically 20 inches (50 cm) or more ateach end. Such a car can easily navigate rough terrain and oftenappears to "skip" over desert washboard like a stone over water.


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Specialized Suspensions:Formula One Racers

. Unlike road cars, however,the shock absorbers and coilsprings of a Formula Oneracecar don't mount directly

to the control arms.Instead, they are orientedalong the length of the carand are controlled remotelythrough a series of pushrodsand bell cranks. In such anarrangement, the pushrodsand bell cranks translate the

up-and-down motions of thewheel to the back-and-forthmovement of the spring-and-damper apparatus.

Formula One racecar


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car suspension system

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