Team Teaching Presentation How Car Suspension Works

7/30/2019 Team Teaching Presentation How Car Suspension Works

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Anthony AloyRick Anderson

Bronco Meeks

Car Suspension


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How Car Suspension Works

When people think of automobile performance, they normally think of horsepower,torque and zero-to-60 acceleration. But all of the power generated by a pistonengine is useless if the driver can't control the car. That's why automobileengineers turned their attention to the suspension system almost as soon as theyhad mastered the four-stroke internal combustion engine.

The job of a car suspension is to maximize the friction between the tires and theroad surface, to provide steering stability with good handling and to ensure thecomfort of the passengers.

William, H. (2005). How Car Suspensions Work. [On-Line]. Available: http://auto.howstuffworks.com/car-suspension.htm.

Photo courtesy Honda Motor Co., Ltd.Double-wishbone suspension on

Honda Accord 2005 Coupe


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Vehicle Dynamics If a road were perfectly flat, with no irregularities, suspensions wouldn't be

necessary. But roads are far from flat. Even freshly paved highways have subtleimperfections that can interact with the wheels of a car. It's these imperfectionsthat apply forces to the wheels. According to Newton's laws of motion, all forceshave both magnitude and direction. A bump in the road causes the wheel tomove 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. Eitherway, the car wheel experiences a vertical acceleration as it passes over animperfection.



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Vehicle Dynamics Contd

Without an intervening structure, all of wheel's vertical energy istransferred to the frame, which moves in the same direction. Insuch a situation, the wheels can lose contact with the roadcompletely. Then, under the downward force of gravity, thewheels can slam back into the road surface. What you need is asystem that will absorb the energy of the vertically acceleratedwheel, allowing the frame and body to ride undisturbed while thewheels follow bumps in the road.

The study of the forces at work on a moving car is called vehicledynamics. Most automobile engineers consider the dynamics of

a moving car from two perspectives:

Ride - a car's ability to smooth out a bumpy road

Handling - a car's ability to safely accelerate, brake and corner



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Springs

Today's springing systemsare based on one of fourbasic designs:

Coil springs - This is themost common type ofspring and is, in essence, aheavy-duty torsion bar

coiled around an axis. Coilsprings compress andexpand to absorb themotion of the wheels.Photo courtesy Car Domain

Coil springs

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Springs Contd

Leaf springs - This type of spring consists of several layers

of metal (called "leaves") bound together to act as a single

unit. Leaf springs were first used on horse-drawn carriagesand were found on most American automobiles until 1985.

They are still used today on most trucks and heavy-duty

vehicles.


Longhurst, C. (1994). The Suspension Bible. [On-Line]. Available: http://www.chris-longhurst.com/carbibles/suspension_bible.html.


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Springs Contd

Air springs - Air springs,which consist of a cylindricalchamber of air positionedbetween the wheel and thecar's body, use the

compressive qualities of air toabsorb wheel vibrations. Theconcept is actually more than acentury old and could be foundon horse-drawn buggies. Airsprings from this era were

made from air-filled, leatherdiaphragms, they werereplaced with molded-rubberair springs in the 1930s. Photo courtesy HSW Shopper

Air springs

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Springs Contd

The stiffness of the springs affects how the sprung massresponds while the car is being driven. Loosely sprung cars, suchas luxury cars (think Lincoln Town Car), can swallow bumps andprovide a super-smooth ride; however, such a car is prone todive and squat during braking and acceleration and tends toexperience body sway or roll during cornering. Tightly sprungcars, such as sports cars (think Mazda Miata), are less forgivingon bumpy roads, but they minimize body motion well, whichmeans they can be driven aggressively, even around corners.

So, while springs by themselves seem like simple devices,designing and implementing them on a car to balance passengercomfort with handling is a complex task. And to make mattersmore complex, springs alone can't provide a perfectly smoothride. Why? Because springs are great at absorbing energy, butnot so good at dissipating it. Other structures, known asdampers, are required to do this.



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Historical Suspensions

Sixteenth-century wagons and carriages tried to solve the problemof "feeling every bump in the road" by slinging the carriage bodyfrom leather straps attached to four posts of a chassis that lookedlike an upturned table. Because the carriage body was suspendedfrom the chassis, the system came to be known as a "suspension" --

a term still used today to describe the entire class of solutions. Theslung-body suspension was not a true springing system, but it didenable the body and the wheels of the carriage to moveindependently.

Semi-elliptical spring designs, also known as cart springs, quickly

replaced the leather-strap suspension. Popular on wagons, buggiesand carriages, the semi-elliptical springs were often used on boththe front and rear axles. They did, however, tend to allow forwardand backward sway and had a high center of gravity.



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Dampers: Shock Absorbers



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Dampers: Shock Absorbers

Unless a dampening structure is present, a car spring will extend and release the energy itabsorbs from a bump at an uncontrolled rate. The spring will continue to bounce at itsnatural frequency until all of the energy originally put into it is used up. A suspension builton springs alone would make for an extremely bouncy ride and, depending on the terrain,an uncontrollable car.

A shock absorber is basically an oil pump placed between the frame of the car and thewheels. The upper mount of the shock connects to the frame (i.e., the sprung weight), whilethe lower mount connects to the axle, near the wheel (i.e., the unsprung weight).

When the car wheel encounters a bump in the road and causes the spring to coil anduncoil, the energy of the spring is transferred to the shock absorber through the uppermount, down through the piston rod and into the piston. Orifices perforate the piston andallow fluid to leak through as the piston moves up and down in the pressure tube. Becausethe orifices are relatively tiny, only a small amount of fluid, under great pressure, passesthrough. This slows down the piston, which in turn slows down the spring. When the carwheel encounters a bump in the road and causes the spring to coil and uncoil, the energyof the spring is transferred to the shock absorber through the upper mount, down through

the piston rod and into the piston. Orifices perforate the piston and allow fluid to leakthrough as the piston moves up and down in the pressure tube. Because the orifices arerelatively tiny, only a small amount of fluid, under great pressure, passes through. Thisslows down the piston, which in turn slows down the spring.



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Dampers: Struts



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Dampers: Struts Contd

Another common dampening structure is the strut -- basically ashock absorber mounted inside a coil spring. Struts perform two

jobs: They provide a dampening function like shock absorbers,and they provide structural support for the vehicle suspension.That means struts deliver a bit more than shock absorbers, which

don't support vehicle weight -- they only control the speed atwhich weight is transferred in a car, not the weight itself.

Because shocks and struts have so much to do with the handling

of a car, they can be considered critical safety features. Wornshocks and struts can allow excessive vehicle-weight transferfrom side to side and front to back. This reduces the tire's abilityto grip the road, as well as handling and braking performance.

http://auto.howstuffworks.com/tire.htmhttp://auto.howstuffworks.com/brake.htmhttp://auto.howstuffworks.com/brake.htmhttp://auto.howstuffworks.com/tire.htm


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Dampers: Anti-sway Bars

Anti-sway bars (also known as anti-roll bars) are used along with shock absorbers or strutsto give a moving automobile additional stability. An anti-sway bar is a metal rod that spansthe entire axle and effectively joins each side of the suspension together.

When the suspension at one wheel moves up and 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 its suspension as it corners. For this reason,almost all cars today are fitted with anti-sway bars as standard equipment, although ifthey're not, kits make it easy to install the bars at any time.



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Suspension Types: Rear

Rear Suspension - DependentSystemsIf a solid axle connects the rearwheels of a car, then thesuspension is usually quite

simple -- based either on a leafspring or a coil spring. In theformer design, the leaf springsclamp directly to the drive axle.The ends of the leaf springsattach directly to the frame,

and the shock absorber isattached at the clamp thatholds the spring to the axle.



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Rear Suspension - Independent

Suspensions If both the front and back

suspensions are independent,then all of the wheels aremounted and sprungindividually, resulting in what

car advertisements tout as"four-wheel independentsuspension." Any suspensionthat can be used on the front ofthe car can be used on therear, and versions of the front

independent systemsdescribed in the previoussection can be found on therear axles.



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The Future of Car Suspensions

Bose -- the same Bose known for itsinnovations in acoustic technologies.Some experts are going so far as to saythat the Bose suspension is the biggestadvance in automobile suspensionssince the introduction of an all-independent design.

The Bose system uses a linear

electromagnetic motor(LEM) at eachwheel instead of a conventional shock-and-spring setup. Amplifiers provideelectricity to the motors in such a waythat their power is regenerated with eachcompression of the system. The mainbenefit of the motors is that they are notlimited by the inertia inherent inconventional fluid-based dampers. As a

result, an LEM can extend and compressat a much greater speed, virtuallyeliminating all vibrations in the passengercabin.


Longhurst, C. (1994). The Suspension Bible. [On-Line]. Available: http://www.chris-longhurst.com/carbibles/suspension_bible.html.
http://auto.howstuffworks.com/framed.htm?parent=car-suspension.htm&url=http://qualitysound.bose.com/pg/learning/project_sound/suspension_challenge.jsphttp://auto.howstuffworks.com/framed.htm?parent=car-suspension.htm&url=http://qualitysound.bose.com/pg/learning/project_sound/suspension_challenge.jsp

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Team Teaching Presentation How Car Suspension Works