Brakes&

Braking system

Dr. 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 MUST

•Stop 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 driver’s 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. 1. RF= 6.76 kN, RR = 5.23kN, Deceleration = 7.28 m/s2, distance = 19.086 m2. RF= 6.49 kN, RR = 5.01kN, Deceleration = 6.47 m/s2 , distance = 21.47 m3. RF= 7.50kN, RR = 4.0kN, Deceleration = 9.48 m/s2, distance = 14.656 m

Types of brakes

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

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

III. On the basis of driver’s 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 type

Floating expander, fixed and floating anchor type

Types of drum brakes

Disc brakes

Swinging caliper type Sliding caliper type

Types of Disc brakes

Description

1 Life of friction material

2 Visibility of wear from outside3 Heat dissipation4 Replacement of friction materials

5 Weight6 Cooling7 Water and duct collection

8 Braking effect

Description

9 Temperature effect

10 Self energizing action

11 Brake pedal efforts

12 Behavior of hydraulic system in released state

13 Force needed to apply brake

14 Nature of wear

15 Shape of friction lining

Description Drum brake Disc brake

1 Life of friction material Reasonable (about 1500 km)

Reasonable (about 2500 km)

2 Visibility of wear from outside Not possible Can be seen at a glance

3 Heat dissipation Inferior Better4 Replacement of friction materials Troublesome and time

takingEasy and rapid

5 Weight Bulky Lighter6 Cooling Very slow Efficient7 Water and duct collection Accumulates Self cleaning

8 Braking effect Generally inconsistent Consistent

Description Drum brake Disc brake

9 Temperature effect Severe Unaffected10 Self energizing action Exists absent11 Brake pedal efforts Higher Proportional to

retardation12 Behavior of hydraulic system in

released stateSome pressure always exists

No hydraulic pressure on piston

13 Force needed to apply brake Comparatively less More, since brakes are not self energizing

14 Nature of wear Non uniform Uniform15 Shape of friction lining Curved Straight

Mechanical brakes

Hydraulic brakes

Types of Master Cylinder

1. Single cylinder (a)For drum brakes (b) for disc brakes

2. Double master cylinder

3. Tandem master cylinder

Master cylinder

Tandem Master cylinder

Working

Responses when fluid is leaking

Conventional braking system Axle by axle split system

Upper and lower wheel cylinder system Diagonal split system

Pneumatic brakes

Braking limitations

Stopping Distance

Sudden Braking

Braking on Slippery surface

Antilock Braking System

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