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<ul><li><p>Brakes</p></li><li><p>Purpose of a Brake</p><p> When a vehicle is accelerated, energy supplied by theengine causes the vehicle speed to increase.</p><p> Some of this energy is instantly used up in overcomingfrictional and tractive resistances, but a large amountremains stored in the vehicle as kinetic energy (can be seenin neutral).</p><p> The vehicle does not immediately come to rest; instead, ittravels for a considerable distance before it becomesstationary.</p><p> In this case, the stored energy is slowly being convertedand used to drive the vehicle against the resistances thatoppose the vehicle motion, which is not feasible.</p><p> So an additional resistance, called a brake, is needed toconvert the energy at a faster rate. The purpose of a brakeis to convert kinetic energy to heat energy.</p></li><li><p> The speed of the energy conversion controls the rate ofretardation of a vehicle (i.e. its rate of deceleration).</p><p> Heat generation at the brake is obtained by rubbing a fixedpad or shoe against a rotating object driven by the motionof the vehicle.</p><p>Purpose of a Brake</p></li><li><p>Stopping Distance and Tyre Adhesion</p><p> The strength of the force pressing a shoe against a wheelgoverns the resistance to rotation of a road wheel.</p><p> During this operation the road surface has to drive thewheel around.</p><p> The limit of this driving force is reached when theresistance of the brake equals the maximum frictional forcethat is produced between the tyre and road.</p><p> The latter is called the adhesive force and can be calculatedfrom the expression:</p><p> Adhesive force = Load on wheel x Coefficient of friction</p></li><li><p> When the limit is reached, the wheel starts to skid.</p><p> So extra force on the brake shoe will not produce anyincrease in the rate of vehicle slows down, no matter howgood the braking system.</p><p> This situation is apparent when a vehicle is braked on aslippery surface: slight pressure on the brake soon locks upthe wheel and very poor braking results.</p><p> Road adhesion is affected by: type of road surface,condition of surface (wet, dry, icy, greasy), design of tyretread, composition of tread material and depth of tread.</p><p>Stopping Distance and Tyre Adhesion</p></li><li><p> With respect to method of braking contact Internal expanding brakes</p><p> Drum brakes</p><p> External contracting brakes Disc Brakes Band Brakes</p><p> With respect to mechanism Mechanical brakes Power brakes</p><p> With respect to application Foot Brake Hand Brake</p><p>Types of Brakes System</p></li><li><p> With respect to number of wheels Two wheel brake Four wheel brake</p><p> With respect to method of applying braking force Single acting Double acting</p><p> With respect to nature of power employed Vacuum brakes Pneumatic brakes Hydraulic brakes Electric brakes Magnetic brakes</p><p>Types of Brakes System</p></li><li><p>Drum Brake This internal expanding type of brake uses two shoes that</p><p>are attached to a back-plate, which is fixed to stub axle oraxle tube.</p><p> Each shoe has a T section and a friction lining is riveted orbonded to the outer face of the shoe.</p><p> At one end of the shoe is a device for expanding the shoewhen the brake pedal is depressed.</p><p> In a simple brake, a cam is used as a shoe expander, butmodern cars hydraulically operated pistons is used.</p><p> A shoe anchor is rigidly attached to the back-plate, takesthe form of a large pin that passes through the shoes (actas pivot).</p><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p> Simple arrangements of springs are used to pull thebrake shoes return the shoes to the off position afterthe brake has been applied.</p><p> The inner cylindrical surface of the cast iron drum isground to give a smooth surface on to which the brakelinings can rub.</p><p> Drums should be exposed to good flow of air todissipate the heat.</p><p> Some form of adjuster is provided at each brake to takeup excessive clearance due to wear of the frictionfacing.</p><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p>Types of shoe mountings Sliding and Pinned The end of each shoe locates at a fixed point on the brake</p><p>back plate can be mounted in two ways:</p><p>- Sliding - In the sliding (or floating) shoe type the end of theshoe has a radius, which can roll or slide on a flat surface. Itis held against the surface by the shoe return springs.</p><p>- Pinned - In the pinned shoe type the shoe pivots about apost mounted on the back plate.</p><p>- Sliding shoes give a degree of self-alignment so the liningscan be efficiently held against drum with minimum wear.</p><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p>da</p><p>Sliding Pinned</p><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p> Leading and trailing shoes(Pinned)</p><p> Which shoe is ahead of itspivot point, is called leadingshoe.</p><p> Similarly the shoe trailsbehind its pivot point and iscalled a trailing shoe.</p><p> There is an importantdifference in the way leadingand trailing shoes act underbraking.</p><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p> One key advantage of thedrum brake (pinned) systemover other systems is that itprovides a self-servo action.</p><p> When the force is applied onleading shoe. Notice that thefrictional drag force has amoment about the pivot point.</p><p> This increases the input loadand hence increases the drag.In other words, there is a self-servo action, which increasesthe braking effect.</p><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p> But when force is applied ontrailing shoe. The moment ofthe frictional drag force aboutthe pivot point opposes theinput load, thereby reducingthe drag and the braking effect.</p><p> For many years, vehiclemanufacturers used drumbrakes as the main brakingsystem on both front and rearaxles because of their simplicityand low manufacturing costs.</p><p> To take more advantage thisproblem some modificationswere came into picture.</p><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p>Types - Method of Braking ContactDrum Brakes - Duo-Servo Brake (Sliding)</p><p> This system is often called a self-energizing brake, which isvery powerful brake.</p><p> The operating principle is based on the use of drum energyto considerably boost the force applied by the driver.</p><p> When the leading shoe is pushed out into contact with theforward-moving drum, the frictional force causes it torotate partially with the drum.</p><p> The shoe movement produced by this self-wrapping actionis transmitted through a floating adjuster to the trailingshoe, which brings the shoe into contact with the drum.</p><p> So by this way now rotation of drum helps the brakeapplication for both shoes irrespective to leading andtrailing shoe arrangement.</p></li><li><p> To minimize the delaybefore the self-energizingassistance comes intoaction, the trailing shoe isheld on the anchor pin bya stronger return spring,by this means expanderonly moves the leadingshoe.</p><p> In this case only, theleading shoe is called theprimary shoe, becausethe shoe is made tocontact the drum beforethe secondary shoe.</p><p>Types - Method of Braking ContactDrum Brakes - Duo-Servo Brake (Sliding)</p></li><li><p> Before the universal adoption of the disc for front brakes,the 2LS was commonly used.</p><p> Each shoe had its own expander, which is positioned so thatboth shoes were subject to a self-servo action.</p><p> An interlinking pipe behind the back-plate provided anequal hydraulic pressure to each single-acting cylinder.</p><p> The cylinder housings acted as a shoe anchor for thefloating shoes, so the cylinders were rigidly attached to theback-plate.</p><p>Types - Method of Braking ContactDrum Brakes - Twin leading shoe brake (2LS)</p></li><li><p>Types - Method of Braking ContactDrum Brakes - Twin leading shoe brake (2LS)</p><p>Self Energizing action </p></li><li><p>Types - Method of Braking ContactDrum Brakes - Twin leading shoe brake (2LS)</p></li><li><p> Compared with a leading and trailing shoe brake, the 2LStype had the following advantages:</p><p>1. Equal self-servo there were two effective shoes so amore powerful, stable brake was obtained.</p><p>2. Even lining wear because both shoes did an equalamount of work, a longer life was achieved,</p><p>3. Greater resistance to fade less reliance was placed onone shoe to do the major share of the braking, so the self-servo action on this shoe could be reduced. This resultedin a more progressive brake and as a result, it was lesssensitive to heat.</p><p>Types - Method of Braking ContactDrum Brakes - Twin leading shoe brake (2LS)</p></li><li><p> One disadvantage of the 2LS type showed up duringreversing, because both shoes became trailing shoes whenthe car travelled backwards.</p><p>Types - Method of Braking ContactDrum Brakes - Twin leading shoe brake (2LS)</p></li><li><p> A shoe-type brake assembly uses two single-acting type wheel cylinders to expand the shoes in a twin leading shoe brake and a double-acting type for a leading and trailing shoe brake. </p><p> Wheel cylinders are fitted with a valve at the highest part to allow air to be bleed from the system. </p><p>Types - Method of Braking ContactDrum Brakes Wheel Cylinder</p></li><li><p> A major disadvantage of the drum brake operation is brake fade.</p><p> This condition occurs when the temperature between thetwo friction linings increases so much during braking that itcauses a reduction in the braking performance.</p><p> This condition normally arises when the vehicle is driven forlong periods and the brakes have been used regularly or ondownhill movement.</p><p> The driver then has to apply greater pressure to the brakepedal to try to obtain the same braking efficiency.</p><p> This is because in drum brakes the heated regions areshrouded by metal hence poor heat dissipation.</p><p>Types - Method of Braking Contact(Drum Brakes)</p></li><li><p> The disc brake was developed tominimize the fade problem seen indrum brakes.</p><p> They consist of an exposed disc, whichis attached to the hub flange and thetwo friction pads are pressed on to thisdisc to give a braking action.</p><p> The pads are moved by hydraulicpistons working in cylinders formed in acalliper that is secured to a fixed part ofthe axle.</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p> When hydraulic pressure isapplied to the two cylindersheld in the calliper, the pistonsmove; this action forces thefriction pads into contact withthe rotating disc that is oftenmade from cast iron or othermaterials, such as carbon orceramic on high performancevehicles.</p><p> The sandwiching action of thepads on the disc gives aretarding action and heatgenerated from the energy ofmotion is conducted to thedisc.</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p> As a large part of the disc is exposedto the air, heat is easily radiated, thisenable the brake to be usedcontinuously for long periodswithout serious fade occurs.</p><p> Hence this type of brake is not sosensitive to heat build-up.</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p>Different types of callipers</p><p>- Two-piston calliper each shoe have individual piston.</p><p>- Four-piston calliper each shoe have </p><p>2 pistons</p><p>- Single piston calliper single piston used.</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p> The limited road wheel-to-disc clearance on vehicleswith a steering geometry based on the negative offset(negative scrub radius) principle is often insufficient toaccommodate a calliper having two opposed pistons.</p><p> In these cases, a single-piston calliper is used.</p><p> The piston housing is keyed to the pad housing, whichis bolted to the wheel suspension member.</p><p> Hydraulic pressure moves the piston in one directionand the piston housing in the opposite direction.</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p> Brake Disc</p><p> Brake discs are generally manufactured from grey cast iron and come in a number of different diameters.</p><p> The discs rotate at the same speed as the road wheels.</p><p> Brake discs have two frictional surfaces that the brake pads grip when brake pedal pressure is applied. </p><p> The radiated heat produced is dissipated throughout the disc frictional surface and housing area.</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p> Types of Brake Discs</p><p>- Solid disc Used where the less braking force is there. Less manufacturing cost.</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p>- Ventilated Disc</p><p> Like solid discs, ventilated discs alsohave two frictional surfaces, butthese are separated by an air space.</p><p> The frictional surfaces are joined byfins that are designed to draw coolair into the centre of the disc when itis rotating.</p><p> This enables the cooling of the discwhen high temperatures aregenerated during braking, thereforepreventing brake fade.</p><p> Ventilated discs are commonly usedon the front braking system</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p> Cross drilled disc</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p> Brake Pads</p><p> The pad is usually made by bonding africtional surface to a steel backing plate.</p><p> The brake pads are held in place by abrake calliper and are arranged in pairson each wheel.</p><p> The steel backing plates are mountedinto the calliper with the frictionalsurface facing the brake disc.</p><p> Earlier asbestos is used, but nowcellulose, mineral fibres, aramid,chopped glass, steel, copper fibres andceramics are in use.</p><p>Types - Method of Braking Contact(Disc Brakes)</p></li><li><p>1. The disc surface on which heat is generated is directlyexposed to the air, allowing easier dissipation of heat andgiving a greater resistance to fade.</p><p>2. Independence of self-servo effect. The non-assisted brakemay require more effort but its action is progressive (i.e.the brake gives a braking torque proportional to theapplied force).</p><p>3. The brake is not so sensitive to friction changes.4. Self-adjusting linings or pads are used, which are easily</p><p>replaced.5. Pedal travel does not increase as the disc heats up </p><p>heating a drum causes expansion that increases pedaltravel.</p><p>6. Weight of disc brake arrangements is generally lighterthan drum.</p><p>Types - Method of Braking ContactDisc Brakes vs Drum Brakes</p></li><li><p> This is simplest arrangement also called mechanicallyoperated braking system.</p><p> Four adjustable rods or cables link the brakeshoe operatinglevers to a transversely mounted cross-shaft.</p><p> The footbrake and handbrake controls are connected to thecross-shaft by links.</p><p> In this system, each brake will receive its share of the brakepedal force only when the mechanism is balanced (i.e. setup so that each shoe contacts the drum simultaneously).</p><p> If one brake has a much smaller shoe-drum clearance thanthe others, all of the drivers force will be directed to thatbrake; as a result, the unbalanced braking action will causethe vehicle to pull violently to that side.</p><p>Types With Respect to MechanismMechanical Brakes</p></li><li><p>Types With Respect to MechanismMechanical Brakes</p></li><li><p> Single-line hydraulic layout used to operate a drum and discbrake system.</p><p> When the driver applies brake pedal pressure to thesystem, the master cylinder feeds hydraulic fluid to each ofthe wheel cylinders.</p><p> Each cylinder then operates and moves the brake shoesoutwards towards the brake drum.</p><p> The master cylinder has an integral reservoir to store anadditional amount of fluid to support the systemsdemands.</p><p>Types With Respect to MechanismHydraulic Brakes</p></li><li><p>Types With Respect to MechanismHydraulic Brakes</p></li><li><p>Types With Respect to MechanismHydraulic Brakes</p></li><li><p> Regulations demand that a separate mechanical parkingbrake (handbrake) system must be provided on at least tworoad wheels.</p><p> This then enables the driver to stop the vehicle in the eventof the hydraulic system failing.</p><p>Types With Respect to MechanismHydrauli...</p></li></ul>