INTRODUCTION TO BRAKING SYSTEM

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BRAKE Abrake is amechanicaldevice whichinhibits motion.

WORKING OF BRAKES A COMMON MISCONCEPTION ABOUT BRAKES IS THAT BRAKES SQUEEZEAGAINST A DRUM OR DISC, AND THE PRESSURE OF THE SQUEEZING ACTIONSLOWS THE VEHICLE DOWN. THIS IS IN FACT A PART OF THE REASON FORSLOWING DOWN A VEHICLE. ACTUALLY BRAKES USE FRICTION OF BRAKE SHOES AND DRUMS TO CONVERTKINETIC ENERGY DEVELOPED BY THE VEHICLE INTO HEAT ENERGY. WHEN WE APPLY BRAKES, THE PADS OR SHOES THAT PRESS AGAINST THE BRAKEDRUMS OR ROTOR CONVERT KINETIC ENERGY INTO THERMAL ENERGY VIAFRICTION.THUS BRAKES ARE ESSENTIALLY AMECHANISM TO CHANGE ENERGYTYPES

TYPES OF BRAKES MECHANICAL BRAKESDRUM BRAKESDISC BRAKES HYDRAULICBRAKES POWER BRAKESAIR BRAKES AIR HYDRAULIC BRAKES VACCUM BRAKES ELECTRIC BRAKES

BRAKE SYSTEM COMPONENTS

HYDRAULIC BRAKES Hydraulics is the use of a liquid under pressure totransfer force or motion, or to increase anapplied force. The pressure on a liquid is called HYRAULICPRESSURE. And the brakes which are operated by meansof hydraulic pressure are called HYDRAULICBRAKES. These brakes are based on the principle ofPascal’s law.

PASCAL’S LAW The pressure exertedanywhere in a mass ofconfined liquid is transmittedundiminished in all directionsthroughout the liquid. Applied in hydraulic lifts,hydraulic brakes etc.

MASTER CYLINDER IN ACTION When we press the brake pedal, it pushes on primarypiston through a linkage. Pressure is built in the cylinder and the lines as the brakepedal is depressed further. The pressure between the primary and secondarypiston forces the secondary piston to compress the fluidin its circuit. If the brakes are operating properly, the pressure wll besame in both the circuits. If there is a leak in one of the circuits, that circuit will notbe able to maintain pressure.

MASTER CYLINDER

USE OF LIQUIDS INSTEAD OF GASES Liquids are used in hydraulic systems because liquidsare incompressible. If we use a gas, on increasing the pressure, the gas willbe compressed into a smaller volume due to whichthere will be no transmission of force or motion.

ADVANTAGES OF HYDRAULIC BRAKES Equal braking effort to all the four wheels Less rate of wear (due to absence of joints compared tomechanical brakes) Force multiplication (or divisions) very easily just by changingthe size of one piston and cylinder relative to other.

DISADVANTAGES OF HYDRAULIC BRAKES Evenslight leakage of air into the breaking systemmakes it useless. Thebrake shoes are liable to get ruined if the brakefluid leaks out.

DISC BRAKES In a disc brake, the fluid from themaster cylinder is forced into acaliper where it presses against apiston. The piston in turn squeezes twobrake pads against the disc (rotor),which is attached to wheel, forcingit to slow down or stop.

DISC BRAKE AND BRAKE OF A BICYCLE Similar to a bicycle brake where two rubber pads run againstthe wheel rim creating friction. But in a disc brake, the brake pads squeeze the rotor insteadof the wheel, and the force is transmitted hydraulicallyinstead of through a cable.

DRUM BRAKES The drum brake has a metalbrake drum that encloses thebrake assembly at eachwheel. Two curved brake shoesexpand outward to slow orstop the drum which rotateswith the wheel.

WORKING OF DRUM BRAKES Drum brakes work on the same principle as thedisc brakes. Shoes press against a rotating surface. In this system that surface is called a drum. Drum brake also has an adjuster mechanism, anemergency brake mechanism and lots of springs. The shoes are pulled away from the drum by thesprings when the brakes are released.

DRUM BRAKE ADJUSTER For the drum brakes to function correctly, thebrake shoes must remain close to drum withouttouching it. If they get too far away from the drum (as theshoes wear down), the piston will require morefluid to travel that distance and the brakepedal will sink closer to the floor when we applybrakes. That is why most drum brakes have anautomatic adjuster.

DISK BRAKE AND DRUM BRAKE

SOME MORE POINTS Most modern cars have disc brakes on front wheels and drum brakes onrear wheels and some wheels have disc brakes on all four wheels. To increase safety, most modern car brake systems are broken into twocircuits, with two wheels on each circuit. If a fluid leak occurs in one circuit, only two of the wheels will loose theirbrakes and the car will still be able to stop when we press the break pedal.

EMERGENCY BRAKES In cars with disc brakes on all four wheels, anemergency brake has to be actuated by aseparate mechanism than the primary brakes incase of a total primary break failure. Most cars use a cable to actuate the emergencybrake. Some cars with four wheel disc breaks have aseparate drum brake integrated into the hub ofthe rear wheels. This drum brake is only for emergency breaksystem, an is actuated only by the cable. It has nohydraulics.

BRAKE FLUIDS One of the important characteristics of brakefluid is its BOILING POINT. Hydraulic systems relyon incompressible fluid to transmit force. Liquids are generally incompressible whilegases are compressible. If the break fluid boils (becomes a gas), it willloose most of its ability to transmit force. This may partially or completely disable hebrakes.

TYPES OF BRAKE FLUIDSDOT 3GLYCOL BASED(ABSORBWATER)DOT 4FLUIDSSILICON BASED(DOESN’TABSORB WATER)DOT 5

PRECAUTIONS As a DOT 3 or DOT 4 brake fluid absorbs water, its boiling point decreases. Itcan absorb water from air, that is why we should avoid opening the car’sbrake fluid reservoir and the container of the brake fluid should be tightlysealed. Also DOT 3 and DOT 4 brake fluids eat paint. None of the different types of brake fluids should be mixed. They can reactbadly with each other and corrode the brake system.

As a DOT 3 or DOT 4 brake fluid absorbs water, its boiling point decreases. It can absorb water from air, that is why we should avoid opening the car’s brake fluid reservoir and the container of the brake fluid should be tightly sealed. Also DOT 3 and DOT 4 brake fluids eat paint. None of the different types of brake fluids should be mixed .