ABSTRACTThe current tendencies in automotive industry need intensive investigation in problems of interaction of active safety systems with brake system equipments. At the same time, the opportunities to decrease the power take-off of single components, disc brake systems. Disc brakes sometimes spelled as "disk" brakes, use a flat, disc-shaped metal rotor that spins with the wheel. your fingers$, slowing the wheel. The disc brake used in the automobile is divided into two parts% a rotating a&is symmetrical disc, and the stationary pads. The hydraulic disc brake is an arrangement of braking mechanism which uses brake fluid, typically containing ethylene glycol, to transfer pressure from the controlling unit, which is usually near the operator of the vehicle, to the actual brake mechanism, which is usually at or near the wheel of the vehicle. The frictional heat, which is generated on the interface of the disc and pads, can cause high temperature during the braking process. 'ence the automobiles generally use disc brakes on the front wheels and drum brakes on the rear wheels. The disc brakes have good stopping performance and are usually safer and more efficient than drum brakes. The four wheel disc brakes are more popular, swapping drums on all but the most basic vehicles. (any two wheel automobiles design uses a drum brake for the rear wheel. )rake technology began in the *+,s as a serious attempt to provide adequate braking for performance cars has ended in an industry where brakes range from supremely adequate to downright phenomenal. -ne of the first steps taken to improve braking came in the early *.,s when manufacturers, on a widespread scale, switched from drum to disc brakes. /ince the ma#ority of a vehicle*s stopping power is contained in the front wheels, only the front brakes were upgraded to disc during much of this period. /ince then, many manufacturers have adopted four-wheel disc brakes on their high-end and performance models as well as their low-line economy cars. -ccasionally, however, as in the case of the 0111 (a!da 2rot3g34s, a manufacturer will revert from a previous four-wheel disc setup to drum brakes for the rear of the car in order to cut both production costs and purchase price. 1 hen the brakes are applied, a calliper squee!es the brake pads against the disc "#ust as you would stop a spinning disc by squee!ing it between CHAPTER-1 INTRODUCTION A brake is a mechanical device which inhibits motion. (ost commonly brakes use friction to convert kinetic energy into heat, though other methods of energy conversion may be employed. 5or e&le regenerative braking converts much of the energy to electrical energy, which may be stored for later use. -ther methods convert kinetic energy into potential energy in such stored forms as pressuri!ed air or pressuri!ed oil. 6ddy current brakes use magnetic fields to convert kinetic energy into electric current in the brake disc, fin, or rail, which is converted into heat. /till other braking methods even transform kinetic energy into different forms, for e&le by transferring the energy to a rotating flywheel. )rakes are generally applied to rotating a&les or wheels, but may also take other forms such as the surface of a moving fluid "flaps deployed into water or air$. /ome vehicles use a combination of braking mechanisms, such as drag racing cars with both wheel brakes and a parachute, or airplanes with both wheel brakes and drag flaps raised into the air during landing. /ince kinetic energy increases quadratically with velocity " $, an ob#ect moving at 0, m7s has 0,, times as much energy as one of the same mass moving at 0 m7s, and consequently the theoretical braking distance, when braking at the traction limit, is 0,, times as long. 8n practice, fast vehicles usually have significant air drag, and energy lost to air drag rises quickly with speed. Almost all wheeled vehicles have a brake of some sort. 6ven baggage carts and shopping carts may have them for use on a moving ramp. (ost fi&ed-wing aircraft are fitted with wheel brakes on the undercarriage. /ome aircraft also feature air brakes designed to reduce their speed in flight. 9otable e&les include gliders and some orld ar 88-era aircraft, primarily some fighter aircraft and many dive bombers of the era. These allow the aircraft to maintain a safe speed in a steep descent. The /aab ) 0. dive bomber used the deployed undercarriage as an air brake. 2 5riction brakes on automobiles store braking heat in the drum brake or disc brake while braking then conduct it to the air gradually. use their engines to brake. hen the brake pedal of a modern vehicle with hydraulic brakes is pushed, ultimately a piston pushes the brake pad against the brake disc which slows the wheel down. -n the brake drum it is similar as the cylinder pushes the brake shoes against the drum which also slows the wheel down. hen travelling downhill some vehicles can HISTORY OF DISC BRAKE 6ver since the invention of the wheel, if there has been "go" there has been a need for "whoa." As the level of technology of human transportation has increased, the mechanical devices used to slow down and stop vehicles has also become more comple&. 8n this report 8 will discuss the history of vehicular braking technology and possible future developments. )efore there was a "horse-less carriage," wagons, and other animal drawn vehicles relied on the animal4s power to both accelerate and decelerate the vehicle. 6ventually there was the development of supplemental braking systems consisting of a hand lever to push a wooden friction pad directly against the metal tread of the wheels. 8n wet conditions these crude brakes would lose any effectiveness. The early years of automotive development were an interesting time for the designing engineers, "a period of innovation when there was no established practice and virtually all ideas were new ones and worth trying. :uite rapidly, however, the design of many components stabili!ed in concept and so it was with brakes; the ma#ority of vehicles soon adopted drum brakes, each consisting of two shoes which could be e&panded inside a drum." 3 8n this chaotic era is the first record of the disc brake. Dr. 5. . <anchester patented a design for a disc brake in 01,= in 6ngland. 8t was incorporated into the <anchester car produced between 01,+ through 010>. These early disc brakes were not as effective at stopping as the contemporary drum brakes of that time and were soon forgotten. Another important development occurred in the 01=,4s when drum brakes were used at all four wheels instead of a single brake to halt only the back a&le and wheels such as on the 5ord model T. The disc brake was again utili!ed during orld ar 88 in the landing gear of aircraft. The aircraft disc brake system was adapted for use in automotive applications, first in racing in 01?=, then in production automobiles in 01?+. @nited /tates auto manufacturers did not start to incorporate disc brakes in lower priced non-highperformance cars until the late 01+,4s. 4 CHAPTER-2 CHARACTERISTICS )rakes are often described according to several characteristics including% Peak force A The peak force is the ma&imum decelerating effect that can be obtained. The peak force is often greater than the traction limit of the tires, in which case the brake can cause a wheel skid. Cont n!o!" #o$er % "" #at on A )rakes typically get hot in use, and fail when the temperature gets too high. The greatest amount of power "energy per unit time$ that can be dissipated through the brake without failure is the continuous power dissipation. Bontinuous power dissipation often depends on e.g., the temperature and speed of ambient cooling air. Fa%e A As a brake heats, it may become less effective, called brake fade. /ome designs are inherently prone to fade, while other designs are relatively immune. 5urther, use considerations, such as cooling, often have a big effect on fade. S&oot'ne"" A A brake that is grabby, pulses, has chatter, or otherwise e&erts varying brake force may lead to skids. 5or e&le, railroad wheels have little traction, and friction brakes without an anti-skid mechanism often lead to skids, which increases maintenance costs and leads to a "thump thump" feeling for riders inside. Po$er A )rakes are often described as "powerful" when a small human application force leads to a braking force that is higher than typical for other brakes in the same class. This notion of "powerful" does not relate to continuous power dissipation, and may be confusing in that a brake may be "powerful" and brake strongly with a gentle brake application, yet have lower "worse$ peak force than a less "powerful" brake. Pe%a( fee( A )rake pedal feel encompasses sub#ective perception of brake power output as a function of pedal travel. 2edal travel is influenced by the fluid displacement of the brake and other factors. Dra) A )rakes have varied amount of drag in the off-brake condition depending on design of the system to accommodate total system compliance and deformation that e&ists under braking with ability to retract friction material from the rubbing surface in the off-brake condition. 5 D!rab ( t* A 5riction brakes have wear surfaces that must be renewed periodically. ear surfaces include the brake shoes or pads, and also the brake disc or drum. There may be tradeoffs, for e&le a wear surface that generates high peak force may also wear quickly. +e )'t A )rakes are often "added weight" in that they serve no other function. 5urther, brakes are often mounted on wheels, and unsprung weight can significantly hurt traction in some circumstances. " eight" may mean the brake itself, or may include additional support structure. No "e A )rakes usually create some minor noise when applied, but often create squeal or grinding noises that are quite loud. 2,1 T*#e" of Brak n) S*"te&"-)rakes may be broadly described as using friction, pumping, or electromagnetic. -ne brake may use several principles% for e&le, a pump may pass fluid through an orifice to create friction% Fr ct ona( brake" are most common and can be divided broadly into "shoe" or "pad" brakes, using an e&plicit wear surface, and hydrodynamic brakes, such as parachutes, which use friction in a working fluid and do not e&plicitly wear. Typically the term "friction brake" is used to mean pad7shoe brakes and e&cludes hydrodynamic brakes, even though hydrodynamic brakes use friction. 5riction "pad7shoe$ brakes are often rotating devices with a stationary pad and a rotating wear surface. Bommon configurations include shoes that contract to rub on the outside of a rotating drum, such as a band brake; a rotating drum with shoes that e&pand to rub the inside of a drum, commonly called a "drum brake", although other drum configurations are possible; and pads that pinch a rotating disc, commonly called a "disc brake". -ther brake configurations are used, but less often. 5or e&le, 2BB trolley brakes include a flat shoe which is clamped to the rail with an electromagnet; the (urphy brake pinches a rotating drum, and the Ausco <ambert disc brake uses a hollow disc "two parallel discs with a structural bridge$ with shoes that sit between the disc surfaces and e&pand laterally. P!&# n) brake" are often used where a pump is already part of the machinery. 5or e&le, an internal-combustion piston motor can have the fuel supply stopped, and then internal pumping losses of the engine create some braking. /ome engines use a valve override called a Cake brake to greatly increase pumping losses. 2umping brakes can dump 6 energy as heat, or can be regenerative brakes that recharge a pressure reservoir called a hydraulic accumulator. E(ectro&a)net c brake" are likewise often used where an electric motor is already part of the machinery. 5or e&le, many hybrid gasoline7electric vehicles use the electric motor as a generator to charge electric batteries and also as a regenerative brake. /ome diesel7electric railroad locomotives use the electric motors to generate electricity which is then sent to a resistor bank and dumped as heat. /ome vehicles, such as some transit buses, do not already have an electric motor but use a secondary "retarder" brake that is effectively a generator with an internal short-circuit. Delated types of such a brake are eddy current brakes, and electro-mechanical brakes "which actually are magnetically driven friction brakes, but nowadays are often #ust called Eelectromagnetic brakesF as well$. Brake" are one the key parts of any vehicle, without which it is virtually not possible to use the vehicle for travel. Blearly, a brake, which serves to slow down the vehicle, should not be too weak. )ut interestingly, when designing a brake system, it should also be taken care that it4s not too efficient. A too strong a brake would e&pose us continuously to the ill effects of a sudden brake application in bus or car. 8f a vehicle is stopped abruptly or strongly, the passenger may hit the front seat or whatever is there. 'ence, too efficient a brake system is not requiredG The braking system is strongly relation to 9ewton4s laws of motion. 8ndeed, the above phenomenon is linked to 9ewton4s second law of motion, which states EA body continues to be in its state of rest or of motion unless e&ternal force acts on the sameF. -n the other hand, if a brake system is too weak, the stopping distance would increase and hence may lead to accidents. Thus, a brake system should be perfect enough to stop the vehicle at minimum safe distance, without affecting the comfort of the passenger. 8n an endeavour to achieve this there have been a lot of developments in the brake system technology, right from (echanical brakes to Air brakes in automobiles. 8n this article we would like provide the relevant information regarding the same CHAPTER-. 7 +ORKING OF A BRAKE e all know that pushing down on the brake pedal slows a car to a stop. )ut we do not how does this happen, how does our car transmit the force from our leg to its wheels and how does it multiply the force so that it is enough to stop something as big as a car. 5ig 0% )raking A fundamentals Fr ct on an% 'o$ t a##( e" to a!to&ob (e" A brake system is designed to slow and halt the motion of vehicle. To do this, various components within the brake system must convert vehicle4s moving energy into heat. This is done by using friction. 5riction is the resistance to movement e&erted by two ob#ects on each other. Two forms of friction play a part in controlling a vehicle% Hinetic or moving, and static or stationary. The amount of friction or resistance to movement depends upon the type of material in contact, the smoothness of their rubbing surfaces and the pressure holding them together. Thus, in a nutshell a car brake works by applying a static surface to a moving surface of a 8 vehicle, thus causing friction and converting kinetic energy into heat energy. The highlevel mechanics are as follows. As the brakes on a moving automobile are put into motion, rough-te&tures brake pads or brake shoes are pressed against the rotating parts of vehicle, be it disc or drum. The kinetic energy or momentum of the vehicle is then converted into heat energy by kinetic friction of the rubbing surfaces and the car or truck slows down. hen vehicle comes to stop, it is held in place by static friction. The friction between surfaces of brakes as well as the friction between tires and roads resists any movement. To overcome the static friction that holds the car motionless, brakes are released. The heat energy of combustion of in engine is converted into kinetic energy by transmission and drive train, and the vehicle moves. 5ig =% Typical )raking /ystem CHAPTER-/ 9 BRAKE BASICS hen you depress your brake pedal, your car transmits the force from your foot to its brakes through a fluid. /ince the actual brakes require a much greater force than you could apply with your leg, your car must also multiply the force of your foot. 8t does this in two ways% • • 0ec'an ca( a%1anta)e 23e1era)e4 H*%ra!( c force &!(t #( cat on The brakes transmit the force to the tires using fr ct on, and the tires transmit that force to the road using friction also. )efore we begin our discussion on the components of the brake system, let*s cover these three principles% 3e1era)e H*%ra!( c" Fr ct on /,1 3E5ERA6E The pedal is designed in such a way that it can multiply the force from your leg several times before any force is even transmitted to the brake fluid. 10 5ig I% <everage 8n the figure above, a force 5 is being applied to the left end of the lever. The left end of the lever is twice as long "=J$ as the right end "J$. Therefore, on the right end of the lever a force of =5 is available, but it acts through half of the distance "K$ that the left end moves "=K$. Bhanging the relative lengths of the left and right ends of the lever changes the multipliers. /,2 HYDRAU3IC SYSTE0S The basic idea behind any hydraulic system is very simple% 5orce applied at one point is transmitted to another point using an nco&#re"" b(e f(! %, almost always an oil of some sort. (ost brake systems also multiply the force in the process. /,. FRICTION 5riction is a measure of how hard it is to slide one ob#ect over another. Take a look at the figure below. )oth of the blocks are made from the same material, but one is heavier. 8 think we all know which one will be harder for the bulldo!er to push. 11 5ig > % 5riction force versus weight To understand why this is, let*s take a close look at one of the blocks and the table% 5ig ?% Blose look at one of the blocks 6ven though the blocks look smooth to the naked eye, they are actually quite rough at the microscopic level. hen you set the block down on the table, the little peaks and valleys get squished together, and some of them may actually weld together. The weight of the heavier block causes it to squish together more, so it is even harder to slide. Different materials have different microscopic structures; for instance, it is harder to slide rubber against rubber than it is to slide steel against steel. The type of material determines the coefficient of friction, the ratio of the force required to slide the block to the block*s weight. 8f the coefficient were 0., in our e&le, then it would take 0,, pounds of force to slide the 0,,-pound ">? kg$ block, or >,, pounds "0L, kg$ of force to slide the >,,-pound block. 8f the coefficient were ,.0, then it would 12 take 0, pounds of force to slide to the 0,,-pound block or >, pounds of force to slide the >,,-pound block. /o the amount of force it takes to move a given block is proportional to that block*s weight. The more weight, the more force required. This concept applies for devices like brakes and clutches, where a pad is pressed against a spinning disc. The more force that presses on the pad, the greater is the stopping force. A SI0P3E BRAKE SYSTE0 The distance from the pedal to the pivot is four times the distance from the cylinder to the pivot, so the force at the pedal will be increased by a factor of four before it is transmitted to the cylinder. The diameter of the brake cylinder is three times the diameter of the pedal cylinder. This further multiplies the force by nine. All together, this system increases the force of your foot by a factor of I+. 8f you put 0, pounds of force on the pedal, I+, pounds "0+= kg$ will be generated at the wheel squee!ing the brake pads. There are a couple of problems with this simple system. hat if we have a leakM 8f it is a slow leak, eventually there will not be enough fluid left to fill the brake cylinder, and the brakes will not function. 8f it is a ma#or leak, then the first time you apply the brakes all of the fluid will squirt out the leak and you will have complete brake failure. 13 CHAPTER-7 TYPES OF BRAKES TYPES OF BRAKES 0. DD@( )DAH6/ =. D8/B )DAH6/ "BA<<826D )DAH6/$ 5ig +% Types of )rakes 7,1 DRU0 BRAKES The drum brake has two brake shoes and a piston. hen you hit the brake pedal, the piston pushes the brake shoes against the drum. This is where it gets a little more complicated. as the brake shoes contact the drum, there is a kind of wedging action, which has the effect of pressing the shoes into the drum with more force. The e&tra braking force provided by the wedging action allows drum brakes to use a smaller piston than disc brakes. )ut, because of the wedging action, the shoes must be pulled away from the drum when the brakes are 14 released. This is the reason for some of the springs. -ther springs help hold the brake shoes in place and return the ad#uster arm after it actuates. 7,2 DISC BRAKE The disc brake has a metal disc instead of a drum. 8t has a flat shoe, or pad, located on each side of the disc. To slow or stop the car, these two flat shoes are forced tightly against the rotating disc, or rotor. 5luid pressure from the master cylinder forces the pistons to move in. This action pushes the friction pads of the shoes tightly against the disc. The friction between the shoes and the disc slows and stops the disc. 15 CHAPTER-6 TYPES OF DISC BRAKES The Three Types of Disc )rakes Are%0. 5<-AT89N BA<826D D8/B )DAH6/ =. 58J6D BA<826D D8/B )DAH6/ I. /<8D89N BA<826D D8/B BA<826D 8,1 F3OATIN6-CA3IPER DISC BRAKES The calliper is the part that holds the brake shoes on each side of the disc. 8n the floating-calliper brake, two steel guide pins are threaded into the steeringknuckle adapter. The calliper floats on four rubber bushings which fit on the inner and outer ends of the two guide pins. The bushings allow the calliper to swing in or out slightly when the brakes are applied hen the brakes are applied, the brake fluid flows to the cylinder in the calliper and pushes the piston out. The piston then forces the shoe against the disc. At the same time, the pressure in the cylinder causes the calliper to pivot inward. This movement brings the other shoe into tight contact with the disc. As a result, the two shoes EpinchF the disc tightly to produce the braking action 16 5ig .% 5loating calliper Disc )rake 8,2 FI9ED-CA3IPER DISC BRAKE This brake usually has four pistons, two on each side of the disc. The reason for the name fi&ed-calliper is that the calliper is bolted solidly to the steering knuckle. hen the brakes are applied, the calliper cannot move. The four pistons are forced out of their calliper bores to push the inner and outer brake shoes in against the disc. /ome brakes of this type have used only two pistons, one on each side of the disc 17 5ig L% 5i&ed Baliper Disc )rake 8,. S3IDIN6-CA3IPER DISC BRAKE The sliding-calliper disc brake is similar to the floating-calliper disc brake. The difference is that sliding-calliper is suspended from rubber bushings on bolts. This permits the calliper to slide on the bolts when the brakes are applied. 2roper function of the brake depends on "0$ the rotor must be straight and smooth, "=$ the calliper mechanism must be properly aligned with the rotor, "I$ the pads must be positioned correctly, ">$ there must be enough "pad" left, and "?$ the lever mechanism must push the pads tightly against the rotor, with "lever" to spare. (ost modern cars have disc brakes on the front wheels, and some have disc brakes on all four wheels. This is the part of the brake system that does the actual work of stopping the car The most common type of disc brake on modern cars is the single-piston floating calliper. 18 0AIN PARTSThe main components of a disc brake are% • • • The brake pads The calliper, which contains a piston The rotor, which is mounted to the hub BRAKE PAD 5ig 1% )rake 2ad CA3IPER AND ROTOR 5ig 0,% Baliper and Dotor 19 CHAPTER-: CO0PONENTS OF HYDRAU3IC DISC BRAKE 9ow that we understand hydraulics let*s take a look at the different parts which make up the hydraulic brake. The entire braking system can be broken down into the following main parts% 0. (aster cylinder "<ever$ =. <ines I. 5luid >. /lave cylinder "Balliper$ ?. 2ads +. Dotor 9e&t we will e&plain these components in more detail. 20 5ig 00% The layout of a typical brake system :,1 0ASTER CY3INDER Bonverts mechanical force from the brake pedal, power booster and push rod into hydraulic pressure Bontain pistons, piston seals, return springs and internal brake fluid ports. Also has a fluid reservoir that may either be an integral part of the unit or remotely mounted. The reservoir itself will have a removable cap with a rubber diaphragm seal that must be in good condition to seal properly. 21 (ost reservoirs also have a low brake fluid level switch to alert the driver of a low fluid condition. 0a"ter C*( n%er;3e1er The master cylinder, mounted to the handlebar, houses the brake lever and together they produce the input force needed to push hydraulic brake fluid to the slave cylinder "or calliper$ and cause the brake pads to clamp the rotor. The lever stroke can be divided into I categories% 1, Dea%-"troke - This is the initial part of the lever stroke when the primary seal pushes fluid toward the reservoir before it goes on to push fluid on to the calliper via the brake lines. 2, Pa% 6a# Stroke - This is the part between the calliper beginning to push the pistons out of their housings and the pads contacting the disc "as the dead space between the pads and rotor is taken up$. ., Contact < 0o%!(at on - The pads are now clamping the rotor and by stroking the lever further, additional brake power will be generated. (odulation is rider controlled and not necessarily a characteristic of the braking system; however some brakes may allow the rider to better modulate or control the braking forces than others. :,2 0ASTER CY3INDER - OPEN OR C3OSED (aster cylinder systems can be categori!ed into two groups - open and closed. An open system includes a reservoir and bladder which allow for fluid to be added or removed from the braking system automatically during use. Deservoirs are the overflow for fluid which has e&panded due to heat produced by braking. The bladder has the ability to e&pand and contract therefore as the fluid e&pands the bladder will compensate without any adverse effects on the *feel* of the brake. Deservoirs also provide the additional fluid needed as the pads begin to wear resulting in the need for the pistons to protrude further to compensate for the reduced pad material. A closed system also utili!es a reservoir of brake fluid however the lack of an internal bladder to compensate for the e&pansion in brake fluid and also to compensate for pad 22 wear means that any ad#ustments to the levels of brake fluid within the working system need to be made manually. :,. BRAKE 3INES 'ydraulic brake lines or hoses play the important role of connecting the two main working parts of the brake, i.e. the master cylinder and slave cylinder. e*ve already mentioned that hydraulic systems can be very versatile in that their lines or hoses can be routed almost anywhere so let*s take a closer look. Ho"e Con"tr!ct on 'ydraulic hoses are multi-layered in their construction and usually consist of I layers% 1, Inner T!be - This layer of tubing is designed to hold the fluid. Teflon is usually the material of choice here as it does not react or corrode with brake fluid. 2, Ara& % 2Ke1(ar4 3a*er - provides the strength and structure of the hose. This woven layer is fle&ible and handles the high pressures of the hydraulic system efficiently in that it should not e&pand. Hevlar is also very light, which is a desirable attribute for any cycle component, and also it can be cut easily and re-assembled using standard hose fittings. ., O!ter Ca" n) - /erves as a protection layer for both the Hevlar layer and the bike frame to reduce abrasions. 23 5ig 0=% The layers that make up an average hydraulic brake line Stee( Bra %e% Brake 3 ne" /teel braided hoses can provide some advantages over standard hydraulic hoses. /teel braided hoses are also usually a I-layer construction, the inner most layer contains the brake fluid and there is an outer most layer which provides protection against abrasions. The key difference is in the middle layer which is made up of a stainless steel braid. This stainless steel layer is designed to be more resistant against e&pansion than that of standard lines. This can be an advantage because when the brake lever is applied we want all of the force we put in to be transferred to the calliper to cause braking. Any e&pansion in the hydraulic line due to the pressures within will mean that some of that pressure will not be transferred to the calliper. This will be wasted effort and will require additional lever input by the rider to compensate. /teel braided lines may also be more appealing aesthetically. (any riders believe that they look better than the standard, boring black hoses that are supplied with the vast ma#ority of brakes on the market. 24 5ig 0I%=,00 5ormula D0 brake with braided brake lines :,/ BRAKE F3UID 'ydraulic braking systems typically use one of two types of brake fluid - D-T fluid or mineral oil. An important thing to note before we get into the properties of each is that the two fluids should never be mi&ed. They are made up of very different chemicals and the seals within the braking system are suited to either fluid or not both; therefore mi&ing or replacing one fluid with the other is likely to corrode the internals of your brake. -n the other hand, mi&ing fluid from the same family is allowed but not generally advised. 5or e&le you may mi& D-T > fluid with D-T ?.0 without harming your braking system. DOT Brake F(! % D-T brake fluid is approved and controlled by the Department of Transportation. 8t has to meet certain performance criteria to be used within braking systems and is classified by its performance properties - mainly its boiling points. D-T I, > and ?.0 brake fluids are glycol-ether based and are made up of various solvents and chemicals. Nlycol-ether brake fluids are hygroscopic, which means they absorb water from the environment even at normal atmospheric pressure levels. The typical absorption rate is quoted to be around IO per year. This water content within the brake fluid will affect the performance by reducing its boiling points that is why it is recommended to change brake fluid every 0-= years at most. 25 The table below shows D-T brakes fluid in its various derivatives with its corresponding boiling temperatures. et boiling point refers to fluid with water content after 0 years* service. DOT F(! % DOT . DOT / DOT 7 DOT 7,1 Dr* Bo ( n) Po nt =,? PB ">,0 P5$ =I, PB ">>+ P5$ =+, PB "?,, P5$ =., PB "?0L P5$ +et Bo ( n) Po nt 0>, PB "=L> P5$ 0?? PB "I00 P5$ 0L, PB "I?+ P5$ 01, PB "I.> P5$ D-T brake fluid is commonly used in Avid, 5ormula, 'ayes and 'ope brakes. DOT 7 Brake F(! % D-T ? brake fluids "not to be mistaken for D-T ?.0$ are very different from other D-T fluids as it is silicone based and not glycol-ether based. This silicone based brake fluid is hydrophobic "non water absorbing$ and must never be mi&ed with any other D-T brake fluid. D-T ? can maintain an acceptable boiling point throughout its service life although the way in which it repels water can cause any water content to pool and free!e7boil in the system over time - the main reason that hygroscopic fluids are more commonly used. 0 nera( O ( (ineral oil is less controlled as a brake fluid, unlike D-T fluid which is required to meet a specific criteria, therefore less is known regarding its performance and boiling points from brand to brand. (anufacturers such as /himano and (agura design their brakes around their own brand of mineral oil and should never be introduced to D-T brake fluid as this will likely have an adverse effect on the brake*s seals. An advantage of mineral oil is that, unlike most D-T fluids, it does not absorb water. This means that the brake will not need to be serviced as often, but any water content within the braking system could pool and free!e7boil adversely affecting the performance of the 26 brake. (ineral oil is also non-corrosive meaning handling of the fluid and spillages are less of a concern. :,7 S3A5E CY3INDER;CA33IPER The brake callipers reside at each wheel and respond to the lever input generated by the user. This lever input is converted to clamping force as the pistons move the brake pads to contact the rotor. Ballipers can be fi&ed by a rigid mount to the frame or floating. 5i&ed callipers are combined with a fi&ed rotor which offers the only way of achieving !ero free running drag one drawback of this design is that it is much less tolerant of rotor imperfections. 5loating callipers slide a&ially and self-centre with each braking application. Con"tr!ct on Balliper construction can fall into two categories - mono-block and two piece. The difference here is the *bridge* design, the bridge is the part of the calliper above the pistons which connects the two halves together and provides the strength to endure the clamping forces generated by the pistons. 1, 0ono-b(ock - A mono-block calliper is actually a one piece design formed from one piece of material. This can offer a unique design and usually a lighter calliper as there is no need for steel bolts #oining both halves as in a two piece design. Also the lack of a transfer port seal means there is one less opportunity for fluid leaks at the half way seam. /ervicing a mono-block calliper can be tricky however and manufacturing and assembly are usually more difficult. 2, T$o # ece - These two piece callipers are constructed as two separate halves and are then held together with steel bolts which can provide additional strength over a monoblock design. /ervicing, manufacturing and assembly are simplified. /teel bolts and additional seals are a means of additional weight and can be problematic during servicing. 27 5ig 0>% 6&ploded view of an Avid two-piece calliper design P "ton" The pistons are the cylindrical components housed within the calliper body. @pon lever input they protrude to push the brake pads which contact the rotor. The number of pistons within a calliper or brake can differ. (any hydraulic mountain bike brakes have = piston callipers, some may have > pistons. hereas some automobile brake callipers have + or even L pistons. 8t is an important note that brake power is not determined by piston quantity. A more reliable indicator would be total piston contact area, e.g. > smaller pistons can be #ust as powerful as = larger pistons. 2istons can be either opposed or single sided. -pposed pistons both protrude with lever input to push the brake pads equal amounts to meet the rotor at both sides. hereas single sided calliper pistons stroke on one side and float the rotor to the opposite pad. :,8 BRAKE PADS Bhoosing the right brake pads can mean the difference between a great and a poor performing brake. ith the sheer diversity of brake pad materials out there it is quite easy to get it wrong when the time comes to replace the pads. <et*s #ump right in and take a look at the different pad materials available and their properties. 28 Or)an c -rganic brake pads contain no metal content. They are made up of a variation of materials which used to include asbestos until its use was banned. These days you will commonly find materials such as rubber, Hevlar and even glass. These various materials are then bonded with a high-heat-withstanding resin. An advantage of organic pads is that they*re made up of materials that don*t pollute as they wear. They are also softer than other brake pads and as a result quieter. Also they inflict much less wear upon the brakes* rotor. 'owever organic pads wear down faster and they perform especially poorly in wet gritty conditions "@H readers take note$. -rganic pads then are probably more suited to less aggressive riding in mostly dry conditions . 5ig 0?% -rganic )rake pads Se& -&eta(( c The metallic content of semi-metallic pads can vary from anything between I,O and +?O. The introduction of metal content into the friction material changes things slightly. 8t can improve the lifespan of the pad quite significantly as metal wears slower than organic materials. Also heat dissipation is improved as it is transferred between the pad material and the backing plate. /ome disadvantages can include increased noise during use and the harder compound means increased wear on the rotor. 29 5ig 0+% /emi-metallic pads S ntere% /intered brake pads are made up of hardened metallic ingredients which are bound together with pressure and high temperature. The advantages of this compound are better heat dissipation, a longer lasting pad, better resistance to fading and superior performance in wet conditions. The trade-offs are more noise, longer bed-in time and a poor initial bite until the friction material has chance to warm. 5ig 0.% /intered )rake pads 30 Cera& c Beramic brake pads are now seen more and more as an alternative7upgrade mountain bike brake pad. Traditionally ceramic brake pads would only be seen on high performance racing cars with brakes which need to perform under intense heat. 'eat like that is not usually a problem for the average mountain bike brake and therefore for most people ceramic pads would be overkills however they might have other desirable properties. The advantages of a ceramic material then is one which can cope with e&treme heat and keep performing strongly; this is in part down to its great dissipating abilities. They also last longer than other pads and noise is less of an issue. They*re also easier on brake rotors and produce a lot less dust that other brake pad compounds. 5ig 0L% Beramic )rake pads :,: ROTORS Dotor si!e has a direct effect on braking power. The larger the brake rotor the more power will be produced for any given input. This can be a concern with larger rotors as they tend to have more of a *grabby* feel making the brake more difficult to modulate. (ountain bike rotors tend to range in si!e from 0+,mm to =,Imm, with smaller rotors geared toward JB type riding and larger rotors designed for downhill riding. 31 Rotor De" )n 8mportant specifications of rotor design include hardness, thickness and rub area. The material used to manufacture rotors must be hard and durable due to the aggressive forces inflicted upon them from the pad friction material. This has a direct impact on rotor wear. Dotors must also have no thickness variations. Differences in thickness around the circumference of the rotor can have undesired effects on the braking system including pulsing as thicker and thinner sections pass between the pads. Dotors also need to run true. Any lateral wobble in the rotor during use can cause the brake to contact the pads intermittently during riding. 5ig 01% <eft to right% 5ormula <ightweight, Avid NI Blean /weep, AshimaAiDotor A rotor*s rub area can take the form of many different designs. The three rotors above show this in detail. Dub area design can affect the weight and strength of the rotor. 8t also has a direct effect on pad lifetime. TYPES OF ROTORS The two types of rotor on the market today are 8/- standard +-bolt rotors and Benter<ock rotors. )oth have their pros and cons. 8 Bo(t - Deadily available and interchangeable between many brake models, this is the most common rotor fi&ing system in use today and was adopted by all manufacturers in the late 011,*s. ith no shortage of hub options, cross-compatibility with other products is rarely a problem. 'owever installation of si& fi&ing bolts can be cumbersome and there is always the risk of stripping a thread on fi&ing bolts and hub mounting points. 32 Center3ock - The /himano Benter<ock system eliminates the risk of stripping threads as there are no bolts to worry about, #ust one centre locking ring. 8nstallation and removal is also simplified, although you will need a Benter<ock tool. <ack of mass-market adoption means that hub choices are limited and brake choice may also be limited due to odd si!ed rotors. Benter<ock rotors are also generally slightly heavier and can come at a price premium. 5ig =,% <eft to right% 8/- standard +-bolt, /himano Benter<ock 2-P ece Rotor" =-2iece rotors are supplied as standard with some higher priced brake sets and can also be bought separately as an upgrade. 8n contrast to standard stainless steel rotors, =-piece rotors combine a stainless steel rub area with an aluminium carrier "or spider$. The advantage of the alloy carrier is a cooler running disc as aluminium has superior heat dissipation qualities to that of stainless steel. This will also help to keep your pads, calliper and fluid cooler. Aluminium is also lighter than stainless steel so a reduction in weight can be e&pected. 33 5ig =0% 5ormula =-2iece /tainless /teel 7 Aluminium Dotor Rea"on $'* Brake" Fa ( 'ydraulic brakes can fail or temporarily stop working for numerous reasons such as a simple "but potentially catastrophic$ fluid leak or eventual brake fade after prolonged use. Hnowing the causes of brake failure can be valuable knowledge in curing the problem and preventing future episodes. As we know there are a couple of important principles behind hydraulic brakes. 'ydraulics relies on pressure within the system and brakes rely on friction. Absence of either will result in failure of the system. 5or e&le, a loss of brake fluid will decrease the pressure within the system as the lever has nothing to transfer the input forces to. -n the other hand if brake fluid contacts the brake pads or rotor, a loss of friction will occur due to the lubricating nature of brake fluid. The above e&les should be obvious to most but what about the less obvious causes of brake failureM 6arlier we mentioned brake fade, a term which 8 bet many of you have heard, however did you know that there are multiple types of brake fadeM )elow is an overview of the three different types. Pa% Fa%e All friction material "the stuff your pads are made of$ has a coefficient of friction curve over temperature. 5riction materials have an optimal working temperature where the coefficient of friction is at its highest. 5urther hard use of the brake will send the friction material over the optimal working temperature causing the coefficient of friction curve to decline. 34 This high temperature can cause certain elements within the friction material to melt or smear causing a lubrication effect; this is the classic gla!ed pad. @sually the binding resin starts to fail first, and then even the metallic particles of the friction material can melt. At very high temperatures the friction material can start to vapori!e causing the pad to slide on a layer of vapori!ed material which acts as a lubricant. The characteristics of pad fade are a firm, non-spongy lever feel in a brake that won*t stop, even if you are squee!ing as hard as you can. @sually the onset is slow giving you time to compensate but some friction materials have a sudden drop off of friction under high temperatures resulting in sudden fade. 6reen Fa%e Nreen fade is perhaps the most dangerous type of fade which manifests itself on brand new brake pads. )rake pads are made of different types of heat resistant materials bound together with a resin binder. -n a new brake pad these resins will cure when used hard on their first few heat cycles and the new pad can hydroplane on this layer of e&creted gas. Nreen fade is considered the most dangerous as it can catch users unaware given its quick onset. (any people would consider new brake pads to be perfect and may be used hard from the word *go*. Borrect bedding-in of the brake pads can prevent green fade. This process removes the top layer of the friction material and keys the new pad and rotor together under controlled conditions. F(! % Fa%e 5luid fade is caused by heat induced boiling of the brake fluid in the callipers and brake lines. hen used under e&treme conditions heat from the pads can transfer to the calliper and brake fluid causing it to boil, producing bubbles in the braking system. /ince bubbles are compressible this results in a spongy lever feel and prevents the lever input from being sent to the calliper. The ma#or cause of fluid fade is absorbed water from the air under normal atmospheric conditions which reduces the boiling temperature of the brake fluid. D-T brake fluid has an affinity for absorbing water from the air around it, especially in hot humid conditions. This is the main reason why we replace brake fluid on an annual basis. 5ortunately fluid fade has a gradual onset giving the user time to compensate for potential loss of braking. 35 CHAPTER-= +ORKIN6 OF HYDRAU3IC DISC BRAKES 5ig ==% orking of hydraulic disc brakes The master cylinder is where the brake fluid starts. The pedal is attached to the master cylinder plunger. hen the pedal is depressed it pushed the plunger which pushes the brake fluid down the brake lines. The brake lines are connected to the slave cylinders. hen the brake fluid reaches the slave cylinders it presses out a piston to which is attached a brake pad. The brake pad then clamps against the rotor. All air must be bled from the system. "Air is compressible and if you have any in the system you will have a soft pedal.$ As oil is virtually uncompressible it works as a solid link from pedal to brake. 36 =,1 THE 0ASTER CY3INDER IN ACTION As you can see in figure there are two pistons "primary and secondary$ and two springs inside the master cylinder. hen the brake pedal is pressed, a push rod moves the primary piston forward which begins to build pressure in the primary chamber and lines. As the brake pedal is depressed further, the pressure continues to increase. 5luid pressure between the primary and secondary piston then forces the secondary piston forward and pressuri!es the fluid in the secondary circuit. 8f the brakes are operating properly, the pressure will be the same in both circuits. 5ig =I% )rakes released 37 5ig =>% )rakes applied 8f there is a leak in one of the brake circuits, that circuit will not be able to maintain pressure. 5igure shows what happens when one of the circuits develops a leak. 8n this e&le, the leak is in the primary circuit and the pressure between the primary and secondary pistons is lost. This pressure loss causes the primary piston to mechanically contact the secondary piston and the master cylinder now behaves as if it has only one piston. The secondary circuit will continue to function correctly, however the driver will have to press the pedal further to activate it. 8n addition, since only two wheels now have pressure, the braking power will be reduced. 38 5ig =?% 5unctioning of the brakes =,2 CO0PENSATIN6 PORTS /mall holes those are located between the master cylinder reservoir and the front side, or pressure side, of the master cylinder pistons. hen the master cylinder pistons are in the at-rest position "no braking-figure 1$, the piston seals uncover the compensating ports and open the passages between the reservoir and the wheel brake channel. Allow for the normal e&pansion and contraction of brake fluid due to changes in temperature. 39 5ig =+% Bompensating 2orts Assist in fluid return after brake release "/ee )ypass 2ort section below$. Notehen the brakes are released, the piston seals on both the primary and secondary pistons are located between the compensating port and the bypass port. During braking, the piston seals close the compensating port passages to the reservoir which prevents high pressure fluid from entering the reservoir. =,. BYPASS PORTS The bypass ports, like the compensating ports, are passages that are open between the reservoir and the master cylinder chambers "fig. 0,$. 'owever, the bypass ports are open to the low pressure or back side of the pistons. Allow the master cylinder pistons to return to the at-rest position rapidly. 40 5ig =.% )ypass 2orts During brake release, the following occurs% Q /trong springs in the master cylinder force the pistons back to the at-rest position faster than the brake fluid can return through the hydraulic channels. The pistons must return rapidly so they can be ready for another forward stroke, if necessary. This rapid piston return movement could create a vacuum in the master cylinder high pressure chambers, which would delay brake release. Q The bypass ports allow brake fluid from the reservoir to fill the low-pressure piston chambers. Q )rake fluid from the low pressure chambers then passes through holes in the pistons and bypasses the piston lip seals. The pistons can then return without any EdraggingF. /ince this Ereturn actionF causes additional fluid to be moved to the front of the piston, it results in an e&cess amount of fluid being present there, as even more fluid returns from the callipers and wheel cylinders. This e&cess fluid is easily returned to the reservoir through the now-open compensating ports. Note- E2iston draggingF can also occur if the seals are installed backward. 41 5ig =L% (aster Bylinder Deturn -peration% applied "left$; releasing "right$ =,/ SE3F AD>UST0ENT OF DISC BRAKESDisc brakes are self ad#usting. 6ach piston has a seal on it to prevent fluid leakage. hen the brakes are applied, the piston moves toward the disc. This distorts the hen the brakes are released, the seal rela&es and returns to its original piston seal. position. This pulls the piston away from the disc. As the brakes linings wear, the piston over travels and takes a new position in relation to the seal. This action provides selfad#ustment of disc brakes. =,7 E0ER6ENCY BRAKES8n cars with disc brakes on all four wheels, an emergency brake has to be actuated by a separate mechanism than the primary brakes in case of a total primary brake failure. (ost cars use a cable to actuate the emergency brake. 42 5ig =1% 6mergency )rakes /ome cars with four-wheel disc brakes have a separate drum brake integrated into the hub of the rear wheels. This drum brake is only for the emergency brake system, and it is actuated only by the cable; it has no hydraulics. 43 CHAPTER-? BRAKE FADE Rehicle braking system fade, or brake fade, is the reduction in stopping power that can occur after repeated or sustained application of the brakes, especially in high load or high speed conditions. )rake fade can be a factor in any vehicle that utili!es a friction braking system including automobiles, trucks, motorcycles, airplanes, and even bicycles. )rake fade is caused by a build-up of heat in the braking surfaces and the subsequent changes and reactions in the brake system components and can be e&perienced with both drum brakes and disc brakes. <oss of stopping power, or fade, can be caused by friction fade, mechanical fade, or fluid fade. )rake fade can be significantly reduced by appropriate equipment and materials design and selection, as well as good cooling. )rake fade occurs most often during high performance driving or when going down a long, steep hill. -wing to their configuration fade is more prevalent in drum brakes. Disc brakes are much more resistant to brake fade and have come to be a standard feature in front brakes for most vehicles. ?,1 BRAKE 0ODIFICATION TO REDUCE FADE 'igh performance brake components provide enhanced stopping power by improving friction while reducing brake fade. 8mproved friction is provided by lining materials that have a higher coefficient of friction than standard brake pads, while brake fade is reduced through the use of more e&pensive binding resins with a higher melting point, along with slotted, drilled, or dimpled discs7rotors that reduce the gaseous boundary layer, in addition to providing enhanced heat dissipation. 'eat build-up in brakes can be further addressed by body modifications that direct cold air to the brakes. The "gaseous boundary layer" is a hot rod mechanics e&planation for failing self-servo effect of drum brakes because it felt like a brick under the brake pedal when it occurred. To 44 counter this effect, brake shoes were drilled and slotted to vent gas. 8n spite of that, drum brakes were abandoned for their self-servo effect. Discs do not have that because application force is applied at right angles to the resulting braking force. There is no interaction. Drum brake fade can be reduced and overall performance enhanced somewhat by an old "hot rudder" technique of drum drilling. A carefully chosen pattern of holes is drilled through the drum working section; drum rotation centrifugally pumps a small amount air through the shoe to drum gap, removing heat; fade caused by water-wet brakes is reduced since the water is centrifugally driven out; and some brake-material dust e&its the holes. )rake drum drilling requires careful detailed knowledge of brake drum physics and is an advanced technique probably best left to professionals. There are performance-brake shops that will make the necessary modifications safely. ?,2 DISC BRAKE 5ENTS 5ig I,% )rake (odification to Deduce 5ade 45 A moving car has a certain amount of kinetic energy, and the brakes have to remove this energy from the car in order to stop it. 'ow do the brakes do thisM 6ach time you stop your car, your brakes convert the kinetic energy to heat generated by the friction between the pads and the disc. (ost car disc brakes are vented. )rake fade caused by overheating brake fluid "often called 2edal 5ade$ can also be reduced through the use of thermal barriers that are placed between the brake pad and the brake calliper piston. These reduce the transfer of heat from the pad to the calliper and in turn hydraulic brake fluid. /ome high-performance racing callipers already include such brake heat shields made from titanium or ceramic materials. 'owever, it is also possible to purchase aftermarket titanium brake heat shields that will fit your e&isting brake system to provide protection from brake heat. These inserts are precision cut to cover as much of the pad as possible. These Titanium )rake shims are an easy to install, low cost solution that are popular with racers and track day enthusiasts. Another technique employed to prevent brake fade is the incorporation of fade stop brake coolers. <ike titanium heat shields the brake coolers are designed to slide between the brake pad backing plate and the calliper piston. They are constructed from a high thermal conductivity, high yield strength metal composite which conducts the heat from the interface to a heat sink which is e&ternal to the calliper and in the airflow. They have been shown to decrease calliper piston temperatures by over twenty percent and to also significantly decrease the time needed to cool down. @nlike titanium heat shields, however, the brake coolers actually transfer the heat to the surrounding environment and thus keep the pads cooler. 46 CHAPTER-1@ AD5ANTA6ES 1@,1 AD5ANTA6ES OF DISC BRAKES O5ER DRU0 BRAKES As with almost any artifact of technology, drum brakes and disc brakes both have advantages and disadvantages. Drum brakes still have the edge in cheaper cost and lower comple&ity. This is why most cars built today use disc brakes in front but drum brakes in the back wheels, four wheel discs being an e&tra cost option or shouted as a high performance feature. /ince the weight shift of a decelerating car puts most of the load on the front wheels, the usage of disc brakes on only the front wheels is accepted manufacturing practice. Drum brakes had another advantage compared to early disc brake systems. The geometry of the brake shoes inside the drums can be designed for a mechanical selfboosting action. The rotation of the brake drum will push a leading shoe brake pad into pressing harder against the drum. 6arly disc brake systems required an outside mechanical brake booster such as a vacuum assist or hydraulic pump to generate the pressure for primitive friction materials to apply the necessary braking force. All friction braking technology uses the process of converting the kinetic energy of a vehicle4s forward motion into thermal energy% heat. The enemy of all braking systems is e&cessive heat. Drums are inferior to discs in dissipating e&cessive heat% "The common automotive drum brake consists essentially of two shoes which may be e&panded against the inner cylindrical surface of a drum. The greater part of heat generated when a brake is applied has to pass through the drum to its outer surface in order to be dissipated to atmosphere, and at the same time "the drum is$ sub#ect to quite severe stresses due to the distortion induced by the opposed shoes acting inside the open ended drum. 47 The conventional disc brake, on the other hand, consists essentially of a flat disc on either side of which are friction pads; equal and opposite forces may be applied to these pads to press their working surfaces into contact with the braking path of the discs. The heat produced by the conversion of energy is dissipated directly from the surfaces at which it is generated and the deflection of the braking path of the disc is very small so that the stressing of the material is not as severe as with the drum." The result of overheated brakes is brake fade...the same amount of force at the pedal no longer provides the same amount of stopping power. The high heat decreases the relative coefficient of friction between the friction material and the drum or disc. Drum brakes also suffer another setback when overheating% The inside radii of the drum e&pand, the brake shoe outside radii no longer matches, and the actual contact surface is decreased. Another advantage of disc brakes over drum brakes is that of weight. There are two different areas where minimi!ing weight is important. The first is unsprung weight. This is the total amount of weight of all the moving components of a car between the road and the suspension mounting points on the car4s frame. Auto designs have gone to such lengths to reduce unsprung weight that some, such as the 6-type Caguar, moved the rear brakes inboard, ne&t to the differential, connected to the drive shafts instead of on the rear wheel hubs. The second "weighty" factor is more of an issue on motorcycles% gyroscopic weight. The heavier the wheel unit, the more is gyroscopic resistance to changing direction. Thus the bike4s steering would be higher effort with heavier drum brakes than with lighter discs. (odern race car disc brakes have hollow internal vents, cross drilling and other weight saving and cooling features. (ost early brake drums and discs were made out of cast iron. Burrent -6( motorcycle disc brakes are usually stainless steel for corrosion resistance, but after-market racing component brake discs are still made from cast iron for the improved friction qualities. -ther e&otic materials have been used in racing applications. Barbon fibre composite discs gripped by carbon fibre pads were common in formula one motorcycles and cars in the early 011,4s, but were outlawed by the respective racing sanctioning 48 organi!ations due to sometimes spectacular failure. The carbon7carbon brakes also only worked properly at the very high temperatures of racing conditions and would not get hot enough to work in street applications. A recent Ducati concept show bike uses brake discs of selenium, developed by the Dussian aerospace industry, which claim to have the friction coefficient of cast iron with the light weight of carbon fibre. Another area of development of the disc brake is the architecture of the brake calliper. 6arly designs had a rigidly mounted calliper gripping with opposed hydraulic pistons pushing the brake pads against a disc mounted securely to the wheel hub. <ater developments included a single piston calliper floating on slider pins. This system had improved, more even pad wear. (ost modern automobiles and my 01L= Hawasaki motorcycle use this type calliper. Burrent design paradigm for motorcycle brakes have up to si& pistons, opposed to grip both sides of a thin, large radius disc that is "floating" on pins to provide a small amount of lateral movement; two discs per front wheel. 8mprovements in control have been made available with the application of Anti<ock )rake technology. heel sensors convey rotation speed of each wheel to a computer that senses when any of them are locked up or in a skid, and modulates individual wheel brake hydraulic pressure to avoid wheel skidding and loss of vehicular control. The use of e&otic materials for additional weight savings would be likely for the future of motor vehicle braking. Discs mounted to the wheel4s rim gripped by an internally located calliper are not necessarily a new design "2orsche, 01+I$ but could be a futuristic looking option for motorcycle wheels. 6lectric vehicles of the future will likely utili!e regenerative braking, the electric motors become generators to convert kinetic energy back to electricity to recharge the batteries. As production vehicles become increasingly quicker, the need for "whoa" will always accompany the "go". 49 1@,2 REASON FOR HI6H EFFICIENCY OF DISC BRAKES 5lat brake disc "a&ial brake$ under high pressure versus round brake drum "radial brake$ during braking 5ull friction surface of the brake pad on the plane brake disc. 9o loss of brake power due to overheating or partial contact from brake drum parts e&pansion. Disc brakes can withstand higher loads and its efficiency is maintained considerably longer even under the highest stresses 'igher residual brake force after repeating braking )rake discs can withstand e&tremely high temperatures 5ull contact of brake pads achieves ma&imum effect. 9o verification of brake pads. Dangerous fading or slipping is almost completely eliminated. 1@,. BETTER BRAKING BEHAVIOUR OF HYDRAULIC DISC BRAKES Driver friendly braking behaviour. /ensitive braking in all situations and better /ensitive brake application and better brake feeling @niform braking from small fluctuations in brake forces Detardation values retained even under heavy stresses (inimal "pulling to one side" due to uneven brake forces Disc brake a&ial arrangement permits a simple and compact design <inear characteristics lead to an even progression of brake force )asic design principle makes for higher efficiency <ow hysteresis is particularly suitable to A)/ control cycles 1@,/ HI6HER SAFETY RESER5ES 50 (inimal braking effect from high temperatures and e&treme driving requirements (inimal heat fading 9o brake disc distortion from e&treme heat due to internal ventilation with directional stability and large power reserve under high stress The decisive safety aspects of the disc brake design are shorter braking distances 'igh power and safety reserves for emergencies Bonstant braking power under high stresses /hortened braking distance under emergency braking with considerably improved directional stability 51 CHAPTER-11 3I0ITATIONS The limitations of hydraulic disc brakes% )raking systems fails if there is leakage in the brake lines. The brake shoes are liable to get ruined if the brake fluid leaks out. 2resence of air inside the tubing ruins the whole system. 2ad wear is more. 'and brakes are not effective if disc brakes are used in rear wheels also. "'and brakes are better with mechanical brakes$. 52 CHAPTER-12 APP3ICATIONS The applications of 'ydraulic Disc )rakes are% 'ydraulic Disc brakes are used primarily in motor vehicles, tanks, but also in machinery and equipment, and aircraft, bicycles, carriages and railway. The disc brakes have been widely used in cars and trucks, especially in the premium sedan. The disc brakes on the new mine hoist brake. The disc brake inertia is small, fast action, high sensitivity, and ad#ustable braking torque. The multi-rope friction hoist all use disc brakes. 53 II, CONC3USION (any trucks and buses are equipped with hydraulic actuated disc brakes. The high contact forces are transmitted mechanically via needle mounted actuating device. 8n view of the fact that the air can circulate freely between the disc and the brake shoe, disc brakes are cooled much better, especially since it is possible to do so ventilated discs e&tra holes. The gases resulting from friction, dust, dirt, do not stay on the working surfaces. These brakes are not sticky. The disc brakes have been widely used in cars and trucks, especially in the premium sedan. The disc brakes on the new mine hoist brake. The disc brake inertia is small, fast action, high sensitivity and ad#ustable braking torque. 54 III, REFERENCES TechBenter )y Harl )rauer, 6ditor in Bhief, 6dmunds.com http%77cars.about.com7od7thingsyouneedtoknow7ig7Disc-brakes http%77en.wikipedia.org7wiki7DiscSbrake http%77www.kobelt.com7pdf7brochureSbrake.pdf http%77auto.howstuffworks.com7auto-parts7brakes7brake-types7disc-brake.htm http%77www.sae.org7searchMsearchfieldTbrakeO=,system http%77www.hinduonnet.com7thehindu7=,,,7,?7=?7ceramic brake disc Automotive 6ngineering 8nternational -nline Nlobal Riewpoints, 9ovS 0111 55