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M.P.Khond BRAKESLecture11,12,13, Introduction INTRODUCTION:Braking is the mechanism in the motor vehicle which is usedto slowing down and stopping the vehicle to rest in the shortest possible distance.Principle of Braking system: While operating the braking system the KINETIC ENERGY of moving vehicle is converted in to HEAT ENERGY.Functions of Brakes: Brakes have the following functions.1.It is used to stop the vehicle in the shortest possible time 2.It is used to control the speed where and when required.3.It is used to control the vehicle while descending along the slope.4.To park the vehicle and held it in stationary position without the presence of Driver.Requirement of braking system Requirements of Automobile Brakes:1.It should work efficiently irrespective of road condition and quality.2.The retardation must be uniform throughout its application.3.The pedal effort must be within the convenient capacity of the driver.4.It must be reliable and should not be effected by heat water and dust.5.It should be in minimum weight.6.It should have long life.7.It should be easy to maintain and adjust.8.Noise and vibrations are to be minimum.9.There should be provision for secondary brake or parking brake. The capacity of brakeThe capacity of brake is depends upon-Unit pressure between the braking surfacesCoefficient of friction between braking surfaces.The peripheral velocity of braking drum.The projected area of friction surfacesThe ability of brake to dissipate heat equivalent to the energy being stored Brake Pedal DesignAdvantage by LeverageFirst Mechanical Advantage is Drivers footLength of Lever determines force applied Uses FulcrumPedal Ratio

1025:12.5 inches50.5 inchStopping distance and Braking efficiency:For practical measure for braking efficiency that of the minimum distance in which it can be brought in to rest after the brake is applied.The stopping distance depends upon1.Grip between the tyre and road surface.2.Tyre tread condition.3.Tyre inflation.4.Nature of road surface.The stopping distance is calculated byD=kv2Where D=stopping distance in kilometers.K=Constant depending upon the road and tyre inflation.V=velocity of the vehicle per hour.The value of k is 1/25 for 4 wheel braking system.1/12 for 2 wheel braking system.The braking efficiency is calculated by the equation:=V2/3D where v=velocity of the vehicleD=stopping distance.Condition of Brake Braking efficiency in %1.Perfect 90%2.Excellent 77%3.Good 70%4.Fair 60%5.Poor 50%6.Bad 37%7.Very bad 30%Below Fair is very danger.Factors controlling the stop of an AutomobileSpeed and loadRoad surfaceTyre treadsGradientNumbers of wheels brakingCoefficient of friction braking surfacesBraking force of enginePressure applied through the energization Weight transferClassification of Brakes: The following are the classifications of Brakes:1.By method of powera) Mechanical brakesb) Hydraulic brakesc) Vacuum brakesd) Air brakese) Electrical brakesf) Magnetic brakesg) Air assisted hydraulic brakes2.By method of application:a) Service or foot brakesb)Parking or hand brakes3.By method of operation:a) Manualb) Servoc) Power operationBy method of Braking contacta. Internal Expanding Brakesb. External Contracting Brakes.5. By Method of Applying Brake force:a. Single Acting Brakes.b. Double Acting Brakes.ConstructionThe main components of drum brakes are1. Brake drum2. Back plate3. Brake shoes4. Brake Liners5. Retaining Springs6. Cam7. Brake LinkagesDrum Brake System

In this system the wheel is attached to drum. There are brake shoes used to contact the rotating drum for braking operation. The shoes provide lining on their outer surface. The cam is used to lift the brake shoes at one end, other end is connected by some method so as to make as the brake sleeve come into contact in the brake drum. The retaining spring is provided for bringing the brake shoes back to its original position, after releasing the brake pedal.All these parts are fitted in the back plate and enclosed with brake drum. Working: When the pedal is pressed the cam moves the shoes outwards through linkages, there by coming in frictional contact with the rotating drum.As soon as the brake pedal is released the retaining springs help the brakeshoes to brought back and release the brakes.

Disc brakes:Disc brakes: There are two types of disc brakes:1. Spot Typea. Swinging Caliper Typeb. Sliding caliper type2. Clutch TypeConstruction: The discs are made of gray cast Iron. The brake pressure incase of disc brakes have to be much lighter than the drum brakes.It consists of rotating disc and two friction pads which are actuated bythe four hydraulic wheel pistons contain in two halves of an assembly is called a caliper. The caliper assembly is secured to the steering knuckle in a front wheel brakes. The road wheel is fashioned to the outer surface of the disc.The friction pads rides freely on each side of the discs. They are in positionbeing the hydraulic systems.

Disc Brake Caliper Assembly

Sliding CaliperApplies pressure to two pads on opposite sides of rotorCaliperSliding FixedFriction Material exposed to air

Fixed CaliperApplies two pistons to opposite sides of rotorCaliper stays stationaryDisc Brakes require higher hydraulic pressure

Working:When the brakes is applied hydraulic pressure is supply to the fluid inlet tube, due to which the wheel cylinder piston force the friction pads against the rotating disc. In the released piston, the spring hold the piston pads so that they maintain contact with disc surface.Advantages of Disc BrakesLighter than drum brakesBetter cooling Since braking surface is directly exposed to air.Offer better resistance to fadeUniform Pressure distribution.Brakes pad can easily replacedThese brakes are self adjusting by design Disadvantages of Disc BrakesCostlier than drum brakesFor stopping the vehicle higher pedal pressure is required.It is difficult to install adequate parking attachment.There is no servo action in these brakesConstruction and Working of Hydraulic systems:

Hydraulic brakes make used of hydraulic pressure to force brake shoesout words against the brake drum based on PASCALS LAW.Construction: The main components of the system is1. Master Cylinder 2. Wheel CylinderTheThe hydraulic pressure is the same, but the applied force can be changed by changing the piston size.

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The figure shows the master cylinder is connected by tubing to thewheel cylinder, at each of the four wheels. The system is filled with the liquidunder light pressure when the brake is not in operation. The brake fluidgenerally a mixture of glycerin and alcohol or caster oil, denatured alcoholand some additives.The brakes shoes which are mounted on the inner side of the brakedrum and do not rotate. The brake liners are fitted on the outer surface of the brake shoes. The brake pedal is connected to the master cylinder piston by means of a piston rod.When the brake pedal is pressed the piston is forced in to themaster cylinder, the hydraulic pressure is applied equally to all wheelcylinders. The pistons in the wheel cylinders pushed outwards against thebrake drum.When the driver release the brake pedal, the piston in the mastercylinder returns back to its original position due to the return spring pressure.Thus the pistons in the wheel cylinder come back in its original inward position.Thus the brakes are releasedMaster Cylinder

Master CylinderThe is the heart of the hydraulic brakesystem. It consists of two main chambers. The fluid reservoir which containsthe fluid to supply to the brake system, and the compression chamber inwhich the piston operates. The reservoir supplies fluid to the brake system through two ports. The larger port is called the filler or intake part and is connected to the hollow portion of the piston between the primary and secondary cups which act as piston seals. The smaller port is called the relief, bypass or compensating port which connects the reservoir directly with the cylinder and lines when the piston is in the released position.When the brake pedal is depressed, the master cylinder piston movesforward to force the liquid under pressure into the system. The relief port issealed out of the system. The liquid pressure is conducted to the wheel cylinders, where it forces the wheel cylinder pistons out wards. These pistons force the brake shoes out against the brake drums.When brake pedal is released, the return spring quickly forces themaster cylinder piston back against the piston stop. Because the fluid in thelines returns rather slowly, a vacuum tends to form in the cylinder in front ofthe piston. This causes the primary cup to collapse to allow the liquid to flowfrom the reservoir through the filter port past the piston to fill the vacuum.WHEEL CYLINDER:Wheel cylinder is the second important hydraulic brakesystem. It consists of two pistons which can move in opposite directions by thefluid pressure. It is rigidly mounted on the brake shield or backing plate. Theboots protect the cylinders from foreign substances. Bleeder valves areprovided in the cylinder to permit air and liquid to be pumped out of thesystem during of the bleeding operation .Piston cup fits tightly in the cylinder against each piston and seal themechanism against leakage of the brake fluid. A Spring serves to hold thecups against the piston when the pressure is decreased.When the brakes are applied the brake fluid enters the cylinder from abrake line connection inlet between the two pistons. It causes to force outthe two pistons in opposite directions. This motion is transmitted to the brakeshoe. Directly or through links force them against the brake drum, thusapplying the brake.Advantages of Hydraulic systemEqual braking effort to all the four wheels Accurate and less wearSelf lubricatingHigh mechanical advantageFlexibility in brakes linesThe Hydraulic brakes can also provide differential braking action between the front and rear brakes by using the wheel cylinder of different size for the front and rear wheels .Disadvantages of Hydraulic systemEven slight leakage of air into the braking system make it useless.The brake shoes are liable to get ruined if the brake fluid leak outThis system is suitable only for applying brakes intermittently, for parking purpose separate rate Mechanical linkages has to be applied Hydraulic Brake fluidShould be non CompressibleMust remain fluid at low temperatureShould not rust corrodeChemically stableMust act as lubricantDurability

Bleeding of hydraulic brakeThe process of eliminating or removing air out of braking system of an automobile is called bleeding Tandem master CylinderIn this master cylinder there are two pistons in the and hydraulic pressure developed in two chambers one for the front left, and rear rightbrakes and other for the front right and rear left brakes.In tandem master cylinder one cylinder operates the front brakes while the other cylinder operates the rear brakes.Air brake systemThe air brake system consists of two-stage air-compressor driven by the crankshaft or gearbox shaft. It takes air from atmosphere, compresses it and delivers to the air reservoir through un-loader valve. Where the pressure of the reservoir reaches the maximum degree, the un- loader valve opens to the atmosphere. Then the compressed air is directed in to the atmosphere directly.Each of the four wheels fitted with brake chambers consists of a diaphragm, and which the air pressure is applied and pushes it. This force operates the cam actuating lever and applies the brake. Each of the brake chamber is connected to the brake pedal, and air filter is also fitted between the brake valve and reservoir.

WorkingWhen the brake pedal is pushed the brake valve opens andcompressed air is allowed in to the brake chamber. The brake valve consistsof three passages.1. Air intake 2. Exhaust 3. Brake chamberWhen the brake pedal is pressed the exhaust passage will be closedand Air intake passage open and compressed air goes back to the chamber.During return stroke the exhaust passage opens while intake closes and used air goes to the atmosphere. This system fitted with an emergency mechanical brake, which can be used when air supply fails the air brake system, which is called air assisted hydraulic braking system.Advantages and Disadvantages of Air Brakes

Advantages:1. This system used in heavy vehicles because they are more powerful than hydraulic or mechanical brakes.2. It simplifies the chassis design3. The compressed air is used for purposes like tyre inflation; for horn, windscreen wiper etc.Disadvantages:If there is any leakage in passage the entire system will be fail. Therefore sealing of air is very difficult.Electric BrakesIn an Electric brake the current from battery is utilized to energize an electromagnet within the brake drum.This actuates a cam to expand the brake shoes.When the current stops the cam and brake shoe are returned to the release position by retractor springs. The severity of braking is controlled by means of rheostat, which is operated by driver through the foot pedal Advantages of Electric BrakesElectric Brakes claim the following advantages-Simple in design and installationSimplified operating linkagesLess time lag between the pressing of pedal and application of brakes on the wheels.Much better control over the braking effortsAbsence of grabNo adjustment required during its lining life

Exhaust brakeAn exhaust brake is a means of slowing a diesel engine by closing off the exhaust path from the engine, causing the exhaust gases to be compressed in the exhaust manifold, and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards, slowing down the vehicle. The amount of negative torque generated is usually directly proportional to the back pressure of the engine. BenefitsThe biggest benefit of the exhaust brake is that they add slowing power to the regular brakes, preventing them from heating up and glazing, which dramatically decreases their effectiveness. When towing heavy loads, these brakes can save lives. These brakes do not damage the engines, and therefore they can be used over and over safely.WarningWhile an exhaust brake can significantly increase slowing and stopping duties, it is by no means a primary braking system. Also, check local ordinances regarding these brakes, because some can create substantial noise and may be illegal. An exhaust brake is not the same as the Jake Brakes used on semi-trucks, but is similar in idea. Some exhaust brakes may lack power at lower RPMs as well, and are mostly used in full-speed applications.

Trouble shooting chart SYMPTOMCAUSESREMEDIESNoisy BrakesUnder adjustmentAdjustLack of LubricationLubricateBroken Brake ComponentsReplace ComponentsIncorrect Brake ComponentsCorrectLocking BrakesLoose, Bent or Broken Brake ComponentsReplace ComponentsUnder AdjustmentAdjustOut-of-Round Brake DrumsMachine or ReplacePulls to One SideIncorrect Tire PressureInflate Evenly on Both Sides to Req. PressuresUnmatched Tires on Same AxleMatch Tires on AxleRestricted Brake Lines or HosesRepair or ReplaceMalfunctioning Cylinder AssemblyCheck for Stuck or Sluggish PistonsDefective or Damaged Shoe and LiningInstall New Shoe and Lining-complete AxleOne Side Out-of-AdjustmentAdjustDraggingImproper FluidReplace Rubber Parts Fill with DOT4 FluidBlocked Master CylinderOpen with Compressed Air or Replace CylinderParking Brake Cable FrozenFree Cable and LubricateImproper Lining Thickness or LocationInstall New Shoes and LNo BrakesBroken or Kinked Brake LineRepair or ReplaceSevere Under adjustmentAdjust BrakesMalfunctioning Actuation SystemTroubleshoot SystemSurging BrakesGrease or Oil on LiningsClean or ReplaceOut of Round Drums or Cracked DrumsMachine or ReplaceHarsh BrakesBrake Adjustment Not CorrectManual-Adjust Brakes Automatic-Make Several Reverse StopsGrease or Fluid on LiningsReplace Shoes and LiningWeak BrakesBrake Adjustment Not CorrectManual-Adjust Brakes Automatic-Make Several Reverse StopsExcessively Worn Brake LiningsReplace Shoes and LiningIncorrect LiningInstall Correct Shoe and LiningGrease or Fluid Soaked LiningRepair Grease Seal or Wheel Cylinder. Install New Shoe and Lining.Frozen Master Cylinder or Wheel Cylinder PistonsRecondition or Replace All Cylinders, Brake FluidGlazed LiningReburnish or ReplaceExcessive Drum WearReplaceTrapped Air in LinesBleed SystemOverloaded TrailerCorrectMalfunctioning Actuating SystemTroubleshoot SystemHard Brake Pedal Check for engine vacuum, make sure manifold is open and clear of carbon build up. Use a vacuum gauge to check the vacuum at the booster. Do not guess. Check vacuum hoses for soft spots, deterioration or collapse_(replace hose if in doubt). Check brake pedal for binding. Check the condition of the foundation brakes - drums, linings, _brake shoes for binding. Check air in hydraulic system. Check for any line restrictions.Pedal Kickback Check for dirt or foreign matter in hydraulic system. Before replacing the booster, remove the master cylinder to clean out any dirt. Clean out the rest of the hydraulic system also.

Brake Will Not Release Be sure a brake booster with residual check valve is not used with_master cylinder with check valve. On remote mounted boosters, disconnect the line between the master cylinder _and the brake booster. If the brakes release, the trouble is in the Master Cylinder_(possibly the brake pedal is binding). If brakes do not release, disconnect the line from the booster to the wheel _cylinders. If the brakes release, the problem will be in the booster. If the brakes still do not release, the problem is in the foundation brakes. If the brakes will not release on firewall mounted brake booster, disconnect the _hydraulic line to the wheels. If the brakes release, the problem is in the booster or master cylinder _(Be sure the brake pedal is not binding).

Low Brake Pedal Make sure master cylinder reservoir is full. Check for air in the hydraulic system. Make sure there are no leaks in the wheel cylinders, lines or fittings. Check the foundation brakes for proper adjustment, cracked or over-sized drumsSample Questions Short Answer Questions:Explain the function of brakes?What are the requirements of Automobile brakes?What are the classifications of brakes?What does stopping distance mean?Explain about braking efficiency?Why brakes are designed so that braking efforts are more on front wheels?What is bleeding ?What is fading of brakes?What is the advantages of using aluminum brake drums?Why fading cannot occur in case of disc brake?What is meant by brake binding ?What is brake drag?Long Answer Questions:1. What are the types of mechanical brakes explain any one of them?2. Explain the construction and working of Hydraulic brakes?3. Explain the Construction and working of Air brakes?4 What are the factors affecting on controlling the stop of an Automobile?