2015 aug 14 Automotive Brakes

H R A M A S U B R A M A N I A N( H R S )

An awareness

EVOLUTION OF AUTOMOTIVE BRAKES

Started with solid wheelsNo brakes. Only the bullock is controlled to slow

down or stop the cart.Horse drawn cart. Faster than bullock carts.

2Automotive Brakes & Braking Systems

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EVOLUTION OF AUTOMOTIVE BRAKESSince the speed is more, it was difficult to slow

down or stop the cart within the distance.They realised the need for an external force to

slow down or stop the cart.They designed a wooden block and a lever as a

brake for the cart.The wooden block wear was more and required

to replace very often.The metal ring gave comparatively uniform

friction than simple wooden wheels.




As you know, you need more contact area of friction to reduce the wear.

Instead of holding the wheel periphery, holding a drum is simpler.

They designed a metal band and a lever as a brake for the cart.

Friction materials were developed and pasted inside the band to make brakes more effective.

Instead of single band, hinged two piece bands were developed, next.




These technology were used for quite some time.Even today, bullock carts are used without brake

which you can see, in Chennai itself.Instead of wooden wheels, tyres are used today.

That makes the bullock’s life easier.If it is two wheeled cart, the load on the bullock /

horse is more.With four wheels, more load can be pulled.



WHY DO YOU NEED BRAKES?

Newton’s law of motion

First Law:

Every object in a state of uniform motion tends to remain in that state of

motion unless an external force is applied to it.

Second Law:

The relationship between an object’s mass m, its acceleration a, and the

applied force F is F=ma

Third Law:

For every action there is an equal and opposite reaction.



WHAT HAPPENS WHEN YOU APPLY BRAKES?The simple answer: They slow you down or stop

The complex answer: The common misconception is that brakes squeeze

against the drum or disc, the pressure of squeezing action is what slows

you down.

This, in fact, is only part of the equation.

Brakes are essentially a mechanism to change the energy types.

When you are travelling at speed, your vehicle has kinetic energy.

When you apply the brakes, the pads or shoes that press against the rotor or

drum convert that energy into thermal energy through friction.

The cooling of brakes dissipates the heat and the vehicle slows down.

First law of thermodynamics or law of conservation of energy.



BRAKING SYSTEM



BASICS OF BRAKE SELECTION



Static Front Axle weight (FAW)

Static Rear axle weight (RAW)

Gross Vehicle weight (W)

Height of CG (h)

Wheel Base (L)

Brake applied at ‘a’ deceleration

Weight transfer from rear to front

=(W x a x h)/L

Dynamic Front Axle weight FAW + W.a.h/L

Dynamic Rear Axle weight RAW – W.a.h/L

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DYNAMIC WEIGHT TRANSFER

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TYPES OF BRAKING SYSTEM

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Cable Operated

Solid Bar Operated


TYPES OF BRAKING SYSTEM

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Single Circuit Hydraulic Dual Circuit Hydraulic


MECHANICAL ADVANTAGE – HYDRAULIC SYSTEM



BRAKING SYSTEM



TYPES OF BRAKES & THEIR FUNCTION

Drum Brake




Drum Brake

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Single Leading

Forward Rotation Reverse Rotation



Drum Brake

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Double Leading




Drum Brake

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Double Leading




Drum Brake

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Duo Servo



TYPES OF BRAKES

Disc Brake



TYPES OF BRAKESDisc Brake



WHY DISC BRAKE?

Brakes are generallySpeed SensitiveLoad SensitiveTemperature Sensitive

Compared to drum brakes, disc brakes are, Less speed sensitiveLess temperature sensitiveLess load sensitive.

Consistent performance even at high temperature and speedDrum brake – curved MuDisc brake – flat MuPositive clampingFaster responseSelf adjustingSelf cleaningMinimal regular maintenanceEasier lining change



HOW DISC BRAKE WORKS?When brake is applied, the

hydraulic pressure from themaster cylinder pushed thepiston, thus moving the padagainst the rotor. Once thepad is pressed against therotor, the reaction force actson the caliper body and slidesin the opposite directionmoving the fist. Thus the padon the other side of the rotoris pressed against the rotor.Thus a clamp force isgenerated the rotor is sloweddown or stopped fromrotation.

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When the brake is released, the pressure is released. The reaction force becomes zero and the pads move away from the rotor leaving an air gap. Thus the rotor starts rotating again.


REQUIREMENTS

Safety Critical Parts of an AutomobileTyreSteeringBrakes

o Reliabilityo Consistencyo Directional Stabilityo Heat Dissipationo Fade Resistanceo Less Weighto Serviceabilityo Longer Life



HISTORY OF DEVELOPMENT




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2015 aug 14 Automotive Brakes

Automotive

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