Post on 10-Apr-2018
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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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