brakes and braking system

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Brakes& Braking systemDr. Chetan S. Mistry

BRAKES

Principle Braking distance Braking efficiency Weight transfer Wheel skidding Principle and working of various types of brakes Anti-lock Brake systems (ABS)

Braking requirements:

It MUSTStop the vehicle within smallest possible distance. Act instantaneously in case of an emergency. Strong enough to sustain sudden braking force. Neither slip nor should cause any skid the vehicle.Brake lining should have longer life. Operate with the least effort.

Frictional Resistance and Coefficient of Friction

The value of Coefficient of friction depends on several factors:Road surface condition. Tyre tread pattern. Inflation pressure (Correct, over or under inflated.) Material of road surface.

Braking Efficiency

Let aBr = Braking retardation g = Acceleration due to gravity

Highly efficient brakes produce greater deceleration (retardation) which may cause

Injury to passenger due to their sudden forward shifting. Goods collide among themselves, or collide with drivers cabin. Rapid wear of tyre tread. Faster wear of the brake linings and the brake drum. Driver to lose control of the vehicle.

As per international standard braking function term is use which is equal to

Stopping distance

Braking Effect : Weight transfer

Example:A Maruti car moving at 80kmph takes 32 m to stop when the brakes are applied on it under standard test conditions. How much is its braking efficiency? Also determine the retardation produced during braking.

Ans: v=22.2 m/s BE =87.2 % deceleration =8.55 m/s2

Climbing- up a inclined road

Brakes applied to front wheels only

Brakes applied to rear wheels only

Brakes applied on all the four-wheels

Daewoo car has kerb weight of 970 kg and wheelbase of 2520mm. Its CG is 1250 mm in front of the rear axle and 655 mm above the level road. The coefficient of road-wheels adhesion is 0.6. If the car is moving upward on a road inclined at an angle of 25 deg with horizontal, calculate the load distribution on the front and rear axles, the acceleration or retardation, and the stopping distance when, while moving at 60kmph (1) the front brakes are applied (ii) rear brakes are applied and (iii) all the four-brakes are applied. The seating capacity of the vehicle is for 5 passengers including driver. Take weight of each person as 600 N.Ans. RF= 6.76 kN, RR = 5.23kN, Deceleration = 7.28 m/s2, distance = 19.086 mRF= 6.49 kN, RR = 5.01kN, Deceleration = 6.47 m/s2 , distance = 21.47 mRF= 7.50kN, RR = 4.0kN, Deceleration = 9.48 m/s2, distance = 14.656 m

Types of brakesOn the basis of purpose served1. Main (Service or primary) operational brakes2. Parking (or secondary ) brakes

On the basis of location in the vehicle1. Wheel mounted brakes2. Transmission mounted brakes

III. On the basis of drivers Ergonomics1. Foot brakes2. Hand brakes

IV. On the basis of Actuating method1. Mechanical brakes2. Hydraulic brakes3. Pneumatic brakes (a) Compressed air brakes (b) vacuum brakes4. Electric brakes

V. On the basis of construction1. Drum brakes 2. Disc brakes3. Band brakes

VI. On the basis of application of braking effort1. Manual brakes2. Servo (power-assisted) brakes3. Power (power-operated) brakes

VII. On the basis of action of brake shoes1. Internal expanding brakes2. External contracting brakes

VIII. On the basis of combinations1. Drum and disc combination brakes2. Mechanical and hydro combination brakes

IX. On the basis of speciality1. Engine exhaust gas operated brake2. Pneumatic-hydro brake3. Hill-holding brake

Drum brakes : Construction and working

Types of drum brakes

Articulate anchored typeFloating expander, fixed and floating anchor typeTypes of drum brakes

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Disc brakes

Swinging caliper typeSliding caliper typeTypes of Disc brakes

Description

1Life of friction material2Visibility of wear from outside3Heat dissipation4Replacement of friction materials5Weight6Cooling7Water and duct collection8Braking effect

Description

9Temperature effect10Self energizing action11Brake pedal efforts12Behavior of hydraulic system in released state13Force needed to apply brake14Nature of wear15Shape of friction lining

DescriptionDrum brakeDisc brake1Life of friction materialReasonable (about 1500 km)Reasonable (about 2500 km)2Visibility of wear from outsideNot possibleCan be seen at a glance3Heat dissipationInferiorBetter4Replacement of friction materialsTroublesome and time takingEasy and rapid5WeightBulkyLighter6CoolingVery slowEfficient7Water and duct collectionAccumulatesSelf cleaning8Braking effectGenerally inconsistentConsistent

DescriptionDrum brakeDisc brake9Temperature effectSevereUnaffected10Self energizing actionExistsabsent11Brake pedal effortsHigherProportional to retardation12Behavior of hydraulic system in released stateSome pressure always existsNo hydraulic pressure on piston13Force needed to apply brakeComparatively lessMore, since brakes are not self energizing14Nature of wearNon uniformUniform15Shape of friction liningCurvedStraight

Mechanical brakes

Hydraulic brakes

Types of Master Cylinder

Single cylinder For drum brakes (b) for disc brakes

2. Double master cylinder

3. Tandem master cylinderMaster cylinder

Tandem Master cylinder

Working

Responses when fluid is leaking

Conventional braking systemAxle by axle split systemUpper and lower wheel cylinder systemDiagonal split system

Pneumatic brakes

Braking limitations

Stopping DistanceSudden Braking

Braking on Slippery surface

Antilock Braking Systemhttp://www.nhtsa.gov/cars/problems/equipment/absbrakes/page1-doom-04-26-2013.htmlhttp://www.drivingfast.net/technology/abs.htm