brakes amol.ppt

7/29/2019 brakes amol.ppt

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The Basic Concepts

Hydraulic layouts

Component functions

Brake Balance Stopping Distance


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Kinetic energy = heat

F = ma.

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The brake system converts the kineticenergy of vehicle motion into heat


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A vehicle weighing 290 kg. (639 lbs.)

At 90 kph (55.9 mph) has kinetic energy of:

Stopping the vehicle at .9G takes 2.9 Seconds

This is equal to 31 kilowatts (42 HP).

OR 90,770N-M.


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Kinetic Energy as a Function of Speed and Mass

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

30 60 90 120Speed kph

EnergyN-M

200 kg

250 kg

290 kg


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Basic System Model

Brake Force


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There are two layouts of hydraulic brake systems used

in cars and light trucks.

Front/Rear hydraulic split:Also called axle by axle, vertical, and some times blackand white.

Diagonal Split:Also called criss-cross.

The type of split is only significant in theevent of a hydraulic system failure.


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Front Axle

Rear Axle

TMC


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In a diagonal split system, one brake line is run to

each rear brake and one to each front brake.

The connections are such that the left front and

the right rear brake are on one circuit and the rightfront and left rear are on the other circuit

Front/Rear split hydraulic System

Diagonal Split System


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Right front

left rear

Left front

right rear


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Brake Component Function


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Actuation sub-system

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Foundation sub-system


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Brake Pedal

Master Cylinder

Brake Lines

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Driver Input

Output to master cylinder

100 N and 144 mm

400 N and 36 mm4:1 Nominal

Pedal Ratio


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Output Pressure

Input Force

A master cylinder is just a simple piston

inside a cylinder


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Operated

Mechanically Bottoms Against

Secondary Piston

Pressure for

Normal

Secondary

System

Function


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Bottoms at End of Cylinder Bore

Pressure for Normal Primary System Function


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Brake Lines

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Double wall steel tubing (Bundy Tubing) is industry

standard.

3/16 o.d. is standard size.

Very robust, can take a lot of abuse

Use SAE 45 inverted flare (J533 and J512) joints

if you can.


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Disc Brakes

Linings


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Brake linings are probably the most mis-understood partof a brake system.

The output of any brake is directly related to thecoefficient of friction () between the lining and the disc

or drum.The challenge is knowing what the instantaneous valueof is during any given stop.

Any design calculations you do, go right out the window

if the lining you use does not have the value youassumed.

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Remember the equation for a disc brake

The best method for determining the actual value of for

a given lining is from a dynamometer test.


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Not good if you are on a curved road

You cant steer

OK, if you must hit something

The vehicle goes straight


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The front wheels track straight ahead Then the rear wheels deviate to the side

Until the vehicle cant track straight anylonger and the rear starts to spin around the

front


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If there is more front brake torque than dynamic front weight

The front wheels will lock up before the rears

20%80% 40% 60%

Brake torque

distribution

Dynamic weight

distribution


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If there is more rear brake torque than dynamic rear weight;

The rear wheels will lock up before the fronts

40% 60% 20% 80%

Brake torque

distribution

Dynamic weight

distribution


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Optimum braking is achieved when brake torque

distribution matches dynamic weight distribution

Weight Distribution

No Braking Hard Braking

40%60%

20%80%


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Does not Depend on:

Type of brakes

Size of brakes

Does Depend on:

Tire to road friction

Vehicle balance

Skill of driver

System Reaction Time


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Brake fade is the loss of performance resulting

from the lining friction decreasing as the lining

and rotor or drum rises in temperature


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THAKN YOU FOR

KEEPING PATIENCE.

brakes amol.ppt

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