brakesystemassingment-121101153331-phpapp02

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FEDERAL UNIVERSITY OF

TECHNOLOGY MINNA

IN AFFILIATION WITH

FEDERAL COLLEGE OF EDUCATION

(TECH) AKOKA

A TERM PAPER ON

THE METHOD OF ACTUATING THEBRAKES, ACTUATING MECHANISM;

CAUSES AND REMEDIES OF DAMAGES

AUTOMOBILE DEPARTMENT

BY OLORUNFUNMI OLUWASEYI BABATUNDE

2011/3/0006AE&

SALAMI AYODELE .O

2011/3/000

300 LEVEL

LECTURER MR ADEOGUN K.B

COURSE BRAKING SYSTEM


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IntroductionTHE BRAKE

Brake (device), device used to slow and stop a rotating wheel and thus a moving

vehicle. Brakes such as those on automobiles, trucks, trains, and bicycles usefriction between a wheel and another object to slow the motion of the vehicle.The friction created by the rubbing together of two objects generates a largeamount of heat. A brake system must be capable of dissipating the heat asrotating wheels slowly, because ecess heat can cause the brakes to lose their grip and fail.

Automobile braking device!assenger cars and light trucks use a hydraulic brake system to stop motion"uch a system uses a chemical#based li$uid known as brake fluid to transmitpressure from a brake pedal to the brakes on each wheel. Aviator and inventor

%alcolm &onghead, one of the founders of the &ockheed %artin 'orporation,invented hydraulic brakes in *. +our#wheel hydraulic brakes were introducedon the -uesenberg and the 'hrysler automobile models.

To apply the brakes, the driver steps on a brake pedal. The pedal pushes apiston inside an assembly called the master cylinder, which is filled with brakefluid. The master cylinder is connected to the wheel brakes by hollow steel tubescalled brake lines, which are also filled with brake fluid. !ushing the pistons$uee/es the fluid inside the master cylinder, creating hydraulic pressure. "inceli$uid cannot be compressed, the pressure is transmitted through the brake linesto additional pistons inside each brake. These pistons push brake linings against

drums and discs attached to the wheels in order to slow the vehicle down. +or safety purposes, the brake system for the four wheels of a car or truck is dividedinto two separate circuits (each with its own piston inside the master cylinder). 0f a fluid leak in either circuit causes a loss of pressure, the two brakes in the other circuit will still be operational to stop the vehicle. 'ars and trucks use two typesof brakes, called drum brakes and disc brakes, to stop motion.

!rior to 12, all cars and trucks had drum brakes on the front and rear wheels.-rum brakes consist of curved brake shoes that rest within a rotating ironcylinder, or drum, connected to the ale and the wheel. 3hen drum brakes areapplied, hydraulic pressure from the master cylinder pushes a pair of pistons inthe drum against the brake shoes. The shoes then press against the wall of thedrum, slowing the wheel. 3hen the brakes are released, springs pull the shoesback away from the drum. 4arious types of self#adjusting mechanisms withindrum brakes help maintain the correct amount of distance between the shoesand drum.

0n 12 disc brakes were introduced on automobiles. -isc brakes have greater stopping power than drum brakes and are usually installed on the front wheels to


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improve braking during sudden stops. -isc brakes consist of a metal disc, or rotor, that is connected to the wheel. A device called a caliper rests on the edgeof the rotor and holds two friction pads on either side of the rotor. Applying thebrakes causes fluid to push a piston within the caliper, which pinches the brakepads against the rotor and slows the wheel. -isc brakes do not have return

springs, like those in drum brakes, to disengage the brakes. 0nstead, a sealaround the piston bends slightly when the brakes are applied and then retracts topull the piston back away from the rotor when the brake pedal is released. Also,disc brakes rely on a very small amount of wobble, called run out, that is normallypresent in the rotor. 3hen the brakes are released, the run out of the rotor simplypushes the pads away from the rotor.

-isc brakes are considered superior to drum brakes, because disc brakes canhandle higher braking temperatures and dissipate heat more $uickly. Also, discbrakes do not trap water as drum brakes can. 3hen drum brakes become wet,they suffer a decrease in braking, called brake fade, which can happen when

driving through deep puddles. %ost cars and trucks use disc brakes on the frontwheels and drum brakes on the rear wheels, although some cars now featuredisc brakes on all wheels.

-isc brakes generally re$uire added pedal pressure, so most vehicles e$uippedwith these brakes have power#braking systems to reduce a driver5s pedal effort.%ost power#braking systems use a vacuum to increase braking power. Anengine5s pistons create a vacuum as they draw air into the engine. This vacuumis connected by a tube to both sides of a special spring#loaded diaphragmlocated near the master cylinder. 3hen the brake pedal is pressed, ordinary air isallowed to enter on one side of the vacuum diaphragm. The vacuum on the other

side then pulls the diaphragm to one direction with added force. This added forceis sent to the master cylinder, increasing braking power.

Both drum and disc brakes contain several features to dissipate the large amountof heat produced by friction. 0f the heat is not dissipated, the brakes maymalfunction. To dissipate heat more $uickly, many rotors are vented and havecooling fins sandwiched between the faces of the rotor. %ost disc brakes usesemi metallic brake pads that contain chopped steel#wool fiber to aid heatdissipation. The brake linings on drum brakes are made of heat#resistantmaterial. !rior to the introduction of disc brakes, most vehicles had brake liningsthat contained asbestos fiber. Asbestos brake linings were mostly discontinued inthe late *6s because of the health risks posed by asbestos. 7ven so, somereplacement brake linings made by parts manufacturers still contain asbestos.


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Disc and Drum Brakes-isc and drum brakes create friction to slow the wheels of a motor vehicle. 3hena driver presses on the brake pedal of a vehicle, brake lines filled with fluidtransmit the force to the brakes. 0n a disc brake, the fluid pushes the brake padsin the caliper against the rotor, slowing the wheel. 0n a drum brake, the fluidpushes small pistons in the brake cylinder against the hinged brake shoes. Theshoes pivot outward and press against a drum attached to the wheel to slow thewheel.

Anti-lock braking system (A.B.!

0n *2 the first antilock brake system (AB") was introduced for motor vehicles inthe 8nited "tates as a safety feature to give drivers more control when braking.

AB" uses a microprocessor and individual wheel#speed sensors to monitor thebrakes. 9ydraulic control valves for each brake circuit prevent skidding duringpanic stops or when braking hard on wet or slippery surfaces. By 6 AB" wasavailable on about 2 percent of all new cars and trucks. AB" is now available onover 6 percent of all new vehicles.

3heel#speed sensors monitor the rotation of each wheel. 3hen the brakes are

applied, the AB" microprocessor compares wheel speeds. 0f one or more wheelsare rotating more slowly than the others are (a situation that causes wheel lockupand loss of driver control), the system energi/es control valves to isolate theaffected brake circuit. Brake pressure is held momentarily and is then releasedbefore it is reapplied. This cycle allows the wheel to regain traction and preventsskidding. The hold#release#reapply cycle is repeated rapidly for as long asneeded or until the vehicle comes to a stop. The cycling of the AB" controlvalves and pulsating hydraulic pressure can usually be heard and felt through the


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brake pedal. These indicators are designed intentionally to alert the driver thatthe AB" is assisting braking. The driver should maintain firm pedal pressurewhile the AB" is active, as pumping the pedal can defeat the action of the AB"and increase the stopping distance. The AB" does not operate during normalbraking and does not engage unless one or more wheels start to lose traction.

0mprovements in AB" technology now allow some systems to prevent wheel spinwhen accelerating on wet or slippery surfaces. This capability is known astraction control. 3hen the wheel#speed sensors detect that a drive wheel isstarting to spin, the AB" applies the brake on the affected wheel to slow it down."ome of these newer systems also provide additional control when cornering or changing lanes.

The AB" is a four#wheel system that prevents wheel lock#up by automaticallymodulating the brake pressure during an emergency stop. By preventing thewheels from locking, it enables the driver to maintain steering control and to stop

in the shortest possible distance under most conditions. -uring normal braking,the AB" and non#AB" brake pedal feel will be the same. -uring AB" operation, apulsation can be felt in the brake pedal, accompanied by a fall and then rise inbrake pedal height and a clicking sound.

4ehicles with AB" are e$uipped with a pedal#actuated, dual#brake system. Thebasic hydraulic braking system consists of the following:

• AB" hydraulic control valves and electronic control unit

• Brake master cylinder

• ;ecessary brake tubes and hoses

• 9ydraulic 'ontrol 8nit (9'8).

• Anti#lock brake control module.

• +ront anti#lock brake sensors < rear anti#lock brake sensors.

H"# A.B. #"RK

3hen the driver hits the brakes this pressuri/es a hydraulic system which causes

the brake pads to s$uee/e against the discs which causes the car to slow down.

0f the AB" system detects that one wheel is slowing down more rapidly than the

rest (a symptom of wheel#lock) it automatically reduces the brake pressure on

this wheel by opening a pressure release valve in the hydraulic system. AB" also


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has the ability to build the pressure back up via the hydraulic motor. The system

reacts remarkably $uickly, and compared wheel speeds many times a second.

AB" systems can act on just the front wheels (which do most of the braking

work), or all four depending on what car you=re driving.

An AB" system consists of the following components:

• "ome wheel speed sensors

• Brake calipers

• A hydraulic motor

• "ome pressure release valves

• A $uick thinking computer (or control module) which coordinates the whole

process

Anti-lock Brake ystems (AB! o$erates as %ollo&s'


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. 3hen the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the 9'8 inlet ports. This pressure is transmittedthrough four normally open solenoid valves contained inside the 9'8,then through the outlet ports of the 9'8 to each wheel.

. The primary (rear) circuit of the brake master cylinder feeds the frontbrakes.

>. The secondary (front) circuit of the brake master cylinder feeds the rear brakes.

. 0f the anti#lock brake control module senses a wheel is about to lock,based on anti#lock brake sensor data, it closes the normally open solenoidvalve for that circuit. This prevents any more fluid from entering thatcircuit.

2. The anti#lock brake control module then looks at the anti#lock brakesensor signal from the affected wheel again.

1. 0f that wheel is still decelerating, it opens the solenoid valve for that circuit.

?. @nce the affected wheel comes back up to speed, the anti#lock brakecontrol module returns the solenoid valves to their normal conditionallowing fluid flow to the affected brake.

*. The anti#lock brake control module monitors the electromechanicalcomponents of the system.

. %alfunction of the anti#lock brake system will cause the anti#lock brakecontrol module to shut off or inhibit the system. 9owever, normal power#assisted braking remains.

6.&oss of hydraulic fluid in the brake master cylinder will disable the anti#locksystem. liThe #wheel anti#lock brake system is self#monitoring. 3henthe ignition switch is turned to the 8; position, the anti#lock brake controlmodule will perform a preliminary self#check on the anti#lock electricalsystem indicated by a three second illumination of the yellow AB" wantingindicator.

. -uring vehicle operation, including normal and anti#lock braking, the anti#lock brake control module monitors all electrical anti#lock functions andsome hydraulic operations.

.7ach time the vehicle is driven, as soon as vehicle speed reachesapproimately 6 km


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mechanical noise may be heard. This is a normal function of the self#check by the anti#lock brake control module.

>.3hen the vehicle speed goes below 6 km


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• 3hen the brakes overheat to a great degree, the metal in the brake rotors

or drums develops hard spots. These are known as )ot s$ots. The hot spots

resist the friction from the brake shoes and pads. Because the shoes or pads

have nothing they can grasp, there=s no friction. 'onse$uently, braking power is

lost.

• Brakes that s$ueal indicate that the brake pads are wearing thin. By the

time the brakes begin making a grinding sound, they=ve worn down past the pads

to the rotors, which will cost more than pads to replace

,ault +auses Remedies

;oisy brake 3eak shock absorber Ale supports insecureBroken springs

'hangeetightenchange

7rratic brake 3eak road springs

Bad steering geometry

'hange

Alignment

Brake unbalanced • @il or brake fluid

on linings

• -istorted brake

drum

• tyre evenly inflated

• back plate loose

emove, wash

and refit back "traiten or change

0nflate the tyres

e#tight the back

plate

http://auto.howstuffworks.com/auto-parts/brakes/brake-parts/brake-pads.htmhttp://auto.howstuffworks.com/auto-parts/brakes/brake-parts/brake-pads.htm


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on the ale

• worn steering

connection

• bolts connecting

ale suspension

spring loose• lining of different

type or grade

e#change the

steeringconnection

e#tight back

!ut correct grades

and same type

Brake spongy &ow fluid level in

reservoir -efective hose(if

blocked) andleaking

%aster cylinder

main cap worn &eak past master

cylinder secondarycap

Air in the system

• Top up with fluid

• emove and blow

out, change hose

• emove and

replace new one

• emove and

change

• Bleeding to

eradicate air fromthe system

Brake grab • &ining not bedded

in

• 3rong type of

lining

• @il or brake fluidlining

• &oose back plate

on anchor pins

• epaired

• +it in the correct

type

• 3ash with petrol,clean with sandpaper or en#clothand refit

Brake pedal • &ining not bedded

in

• Brake drum

grabbed or wornout

• %aster cylinder

loosed on mount

• epaired

• 'hange

• Dou tight back to it

sitting Brake pedal hard • "ei/ed piston in

wheel cylinder

• @il or brake fluid

on lining

• Binding brake

pedal

• 'hange

• "crub with sand

paper 3ash withfuel, clean andrefit back

• 'lean rust area

and wash with


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fluid and refit

+ar brake pedal

travel• Air in system

• 'racked brakeddrum

• &eak in system

• &ow fluid level in

reservoir

• 7cessive

clearancebetween lining anddrum

• 7cessive

pushrod clearance

• Bleed to eradicate

air from the

system• emove and

change totally

• 'hange part that

causeleakage(pipe,hose)

• Top up the level

with brake fluid

• Adjust

• Adjust the push

rod

Brake drag • !ull off spring

broken or wear

• %aster cylinder by

pass port chocked

•

"ei/ed piston inwheel cylinder

• "hoe sei/ed

piston on anchor pin

• 9and brake

mechanism sei/ed

• !edal return

spring

• Binding pedal

• 9and brake cable

over adjustedpedal to pushrodadjustment toosmall

• 'hange

• emove and clean

•

'hange

• 'hange

• 'hange

• 'hange

• 'hange or clean

rust area and refitback

• e#adjust the

hand brake

Brake inefficient • &ining not bedded

• &ining greasy

• 0ncorrect type of

• 'hange

• 3ash and sand

paper before fit


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lining • emove and

change to correcttype of lining

Re%erences

http:

Documents

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