Abs Project Report Penny

PROJECT REPORT PROJECT REPORT

ONON

“ DESIGN AND FABRICATION OF ANTI-LOCKDESIGN AND FABRICATION OF ANTI-LOCK BRAKING SYSTEM”BRAKING SYSTEM”

(AUG 2010 – DEC 2010)

SUBMITTED FOR THE PARTIAL FULFILMENT OF THE AWARD OFSUBMITTED FOR THE PARTIAL FULFILMENT OF THE AWARD OFDEGREE OFDEGREE OF

B.TECH (MECHANICAL & AUTOMATION ENGINEERING)B.TECH (MECHANICAL & AUTOMATION ENGINEERING)

Prepared by:

NAVEEN KUMAR SHARMA 210/BTECH/MAE/ASET/08 GAUTAM KUMAR 060/BTECH/MAE/ASET/07 AMIT KUMAR MANAV 069/BTECH/MAE/ASET/07 PUNEET CHAUHAN 066/BTECH/MAE/ASET/07 ASHISH BANSAL 064/BTECH/MAE/ASET/07

UNDER THE GUIDANCE OF MR. SUDEEP KUMAR SINGH

DEPARTMENT OF MECHANICAL & AUTOMATION ENGINEERING

AMITY SCHOOL OF ENGINEERING & TECHNOLOGYAMITY SCHOOL OF ENGINEERING & TECHNOLOGY

BIJWASAN, NEW DELHI-110061

Affiliated to

GURU GOBIND SINGH INDRAPRASTHA UNIVERSITYGURU GOBIND SINGH INDRAPRASTHA UNIVERSITYKASHMERE GATE, NEW DELHI-110006

CERTIFICATECERTIFICATE

This is to certify that the Final Year Project entitled, “DESIGN &

FABRICATION OF ANTI-LOCK BRAKING SYSTEM” has been

submitted to the Department of Mechanical & Automation Engineering of

Amity School of Engineering & Technology, New Delhi, by the following

listed students for the partial fulfillment of the award of degree, Bachelor of

Technology in Mechanical & Automation Engineering. The work is a

record of genuine work carried out by them under our guidance and

supervision and fulfills all requirements for the submission of the thesis,

which has required standard.

The matter embodied in this dissertation has not been submitted in part or

full to any other university or institute for the award of any degree or

diploma.

Mr. Sudeep Kumar Singh Dr. Prem Prakash

Project Guide HOD. MAE.

Deptt. of MAE. ASET

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ACKNOWLEDGEMENT

Final year project is an indispensable part of any engineering curriculum.

It provides the students with an opportunity to gain experience on the

practical application of their technical knowledge.

We express our gratitude to Dr. Prem Prakash, Department of

Mechanical and Automation Engineering, Amity School of Engineering &

Technology and all the faculty members at Amity School of Engineering

and Technology (ASET) who have helped us at every juncture of our

project. We have no doubt that this project has helped us gain much

practical knowledge and the experience has been unique.

We would like to thank Mr. Sudeep Kumar Singh, Lecturer,

Department of Mechanical and Automation Engineering for giving us

this opportunity to work under his guidance on this project. His technical

help and goal oriented approach has been unique and a stepping stone

towards the successful completion of our project.

We would also like to thank, Mr. B.S. Mehta of the Mechanical Lab

at ASET for guiding us and helping us on many occasions during the

design and manufacturing of our project.

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ABSTRACT

Design and Fabrication of Anti-Lock Braking System

“An anti-lock brake system is a feedback control system that modulates brake pressure in response to measured wheel deceleration, preventing the controlled wheels from becoming fully locked.”

Anti-Lock Braking Systems (ABS) are designed to maintain driver control and stability of the car during emergency braking. Locked wheels will slow a car down but will not provide steering ability. ABS allows maximum braking to be applied while retaining the ability to 'steer out of trouble‘. The operation of ABS can slightly reduce stopping distance in some cases like on wet road surfaces, but it can increase the stopping distance in others, as may be the case in deep snow or gravel.

An ABS system monitors four wheel speed sensors to evaluate wheel slippage. Slip can be determined by calculating the ratio of wheel speed to vehicle speed, which is continuously calculated from the four individual wheel speeds. During a braking event, the function of the control system is to maintain maximum possible wheel grip on the road - without the wheel locking - by adjusting the hydraulic fluid pressure to each brake by way of electronically controlled solenoid valves.

While ABS offers improved vehicle control in some circumstances, it can also present disadvantages including increased braking distance on slippery surfaces such as ice, packed snow, gravel, steel plates and bridges, or anything other than dry pavement. ABS has also been demonstrated to create a false sense of security in drivers, who may drive more aggressively as a result.

Since initial widespread use in production cars, anti-lock braking systems have evolved considerably. Recent versions not only prevent wheel lock under braking, but also electronically control the front-to-rear brake bias. This function, depending on its specific capabilities and implementation, is known as electronic brakeforce distribution (EBD), traction control system, emergency brake assist, or electronic stability control.

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INDEX

ACKNOWLEDGEMENT………………………………………..………………...I CERTIFICATE………… …………………………………………..……………...II ABSTRACT………………………………………………………………………...III

1.1. GENERAL INTRODUCTIONGENERAL INTRODUCTION1.11.1 Definition of ABS………………………………………………..1Definition of ABS………………………………………………..11.21.2 Need and procedure……………………………………………...5Need and procedure……………………………………………...51.31.3 Working principle………………………………………………..7Working principle………………………………………………..7

22. EXPERIMENTAL SETUP. EXPERIMENTAL SETUP 2.1 ABS components overview……………………………………..102.2 Diagrammatic representation…………………………………...12

3. DESIGN 3.1 Design and selection of components……………………………..15 3.2 Design procedure………………………………………………....18 3.3 Material selection………………………………………………....20

4. FABRICATION 4.1 Wheel Speed Sensors………………………………………….....22 4.2 Electronic Control Unit…………………………………………..24 4.3 Hydraulic Modulator Unit………………………………………..26 4.4 Valves and Brakes………………………………………………..28

5. CALCULATIONS 5.1 Force Analysis………………………………………………........29 5.2 Energy absorbed by the Brakes…………………………………..33 5.3 Stress Analysis…………………………………………………....35

6. CASE STUDY………………………………………………………..34

7. FUTURE SCOPE……………………………………………………36

8. REFERENCES……………………………………………………… 37

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INTRODUCTION

An anti-lock braking system (ABS) is a safety system that prevents the wheels on a motor vehicle from locking up (or ceasing to rotate) while braking.

A rotating road wheel allows the driver to maintain steering control under heavy braking by preventing a skid and allowing the wheel to continue interacting tractively with the road surface as directed by driver steering inputs. ABS offers improved vehicle control and decreases stopping distances on dry and especially slippery surfaces for many drivers, but on loose surfaces like gravel and snow-on-pavement it can significantly increase braking distance, while still improving vehicle control.

Since initial widespread use in production cars, anti-lock braking systems have evolved considerably. Recent versions not only prevent wheel lock under braking, but also electronically control the front-to-rear brake bias. This function, depending on its specific capabilities and implementation, is known as electronic brake force distribution (EBD), traction control system, emergency brake assist, or electronic stability control.

The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake).

A typical ABS is composed of a central electronic control unit (ECU), four wheel speed sensors — one for each wheel — and two or more hydraulic valves within the brake hydraulics. The ECU constantly monitors the rotational speed of each wheel, and when it detects a wheel rotating significantly slower than the others — a condition indicative of impending wheel lock — it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel. The wheel then turns faster; when the ECU detects it is turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied and the wheel slows. This process is repeated continuously, and can be detected by the driver via brake pedal pulsation. Some anti-lock system can apply and release braking pressure 16 times per second.The ECU is programmed to disregard differences in wheel rotative speed below a critical threshold, because when the car is turning, the two wheels towards the center of the curve turn slower than the outer two. For this same reason, a differential is used in virtually all road going vehicles.

If a fault develops in any part of the ABS, a warning light will usually be illuminated on the vehicle instrument panel, and the ABS will be disabled until the fault is rectified.

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TRACTION CONTROL

The ABS equipment may also be used to implement a traction control system(TCS) or Anti-Slip Regulation (ASR) on acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is regained. Manufacturers often offer this as a separately priced option even though the infrastructure is largely shared with ABS] More sophisticated versions of this can also control throttle levels and brakes simultaneously.

When the traction control computer (often incorporated into another control unit, like the anti-lock braking system module) detects one or more drive wheels spinning significantly faster than another, it will use the ABS to apply brake friction to the wheels that are spinning too fast. This braking action on the slipping wheel(s) will cause power to be transferred to the wheels that are not due to the mechanical action within a differential. all-wheel drive vehicles also often have an electronically controlled coupling system in the transfer case or transaxlethat is engaged (in an active part time AWD), or locked up tighter (in a true full-time set up that drives all the wheels with some power all the time) to supply the non-slipping wheels with (more) torque.

This often occurs in conjunction with the powertrain computer reducing available engine torque by electronically limiting throttle application and/or fuel delivery, retarding ignition spark, completely shutting down engine cylinders, and a number of other methods, depending on the vehicle and how much technology is used to control the engine and transmission.

Traction control is not just used for improving acceleration under slippery conditions. It can also help a driver to corner more safely. If too much throttle is applied during cornering, the drive wheels will lose traction and slide sideways. This occurs as understeer in front wheel drive vehicles and oversteer in rear wheel drive vehicles. Traction control can prevent this from happening by limiting power to the wheels. It cannot increase the limits of grip available and is used only to decrease the effect of driver error or compensate for a driver's inability to react quickly enough to wheel slip.

Automobile manufacturers state in vehicle manuals that traction control systems should not encourage dangerous driving or encourage driving in conditions beyond the drivers' control.

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AUTOMOBILE BRAKING SYSTEM

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DESIGN AND SELECTION OF COMPONENTS

Brake is a device that slows or stops a machine according to operators will. It is that part of a machine or vehicle that slows it down or stops it. In friction brakes this is achieved by transforming the K.E. of the vehicle into heat energy released when friction brakes are applied.

Given the required reliability, it is illustrative to see the choices made in the design of the ABS system. Proper functioning of the ABS system is considered of the utmost importance, for safeguarding both the passengers within, and people outside of the car. The system is therefore built with some redundancy, and is designed to monitor its own working and report failures. The entire ABS system is considered to be a hard real-time system, while the sub-system that controls the self diagnosis is considered soft real-time. As stated above, the general working of the ABS system consists of an electronic unit, also known as ECU (electronic control unit), which collects data from the sensors and drives the hydraulic control unit (HCU), mainly consisting of the valves that regulate the braking pressure for the wheels.

The communication between the ECU and the sensors must happen quickly and at real time. This is usually done by using analog cable connection between the wheel sensor and the ECU, where the voltage or current signal has sine form, with a frequency proportional to the rotation speed of the wheel. In addition to telling the speed, the ABS ECU also performs complex analysis of the working condition of the sensor and if error is detected the system stops functioning. The communication with the valves of the HCU is usually not done this way. The ECU and the HCU are generally very close together. The valves, usually solenoid valves, are controlled directly by the ECU. To drive the valves based on signals from the ECU, some circuitry and amplifiers are needed (which would also have been the case if the CAN-bus was used). Due to the fact, most of the Automotive ECUs use 500K baud rate, it provides sufficient bandwidth for real time communication between ECUs, many Engine ECU now rely wholly on the ABS ECU for speed information, especially when the USA government requires all 2008 and later automotive sold in USA must equip CAN bus.

The sensors measure the position of the tires, and are generally placed on the wheel-axis. The sensor should be robust and maintenance free, not to endanger its proper working, for example an inductive sensor. These position measurements are then processed by the ECU to calculate the differential wheel rotation.

The hydraulic control unit is generally integrated with the ECU (or the other way around), and consists of a number of valves that control the pressure in

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the braking circuits. All these valves are placed closely together, and packed in a solid aluminum alloy block. This makes for a very simple layout, and is thus very robust.

The central control unit generally consists of two microcontrollers, both active simultaneously, to add some redundancy to the system. These two microcontrollers interact, and check each other's proper working. These microcontrollers are also chosen to be power-efficient, to avoid heating of the controller which would reduce durability.

The software which runs in the ECU has a number of functions. Most notably, the algorithms that drive the HCU as a function of the inputs, or control the brakes depending on the recorded wheel spin. This is the obvious main task of the entire ABS-system. Apart from this, the software also needs to process the incoming information, e.g. the signals from the sensors. There is also some software that constantly tests each component of the ABS system for its proper working. Some software for interfacing with an external source to run a complete diagnosis is also added.

As mentioned before the ABS system is considered hard real-time. The control algorithms, and the signal processing software, certainly fall in this category, and get a higher priority than the diagnosis and the testing software. The requirement for the system to be hard real-time can therefore be reduced to stating that the software should be hard real-time. The required calculations to drive the HCU have to be done in time. Choosing a microcontroller that can operate fast enough is therefore the key, preferably with a large margin. The system is then limited by the dynamic ability of the valves and the communication, the latter being noticeably faster. The control system is thus comfortably fast enough, and is limited by the valves.

The Insurance Institute for Highway Safety (IIHS) has conducted several studies trying to determine if cars equipped with ABS are involved in more or fewer fatal accidents. It turns out that in a 1996 study, vehicles equipped with ABS were overall no less likely to be involved in fatal accidents than vehicles without. The study actually stated that although cars with ABS were less likely to be involved in accidents fatal to the occupants of other cars, they are more likely to be involved in accidents fatal to the occupants of the ABS car, especially single-vehicle accidents.

There is much speculation about the reason for this. Some people think that drivers of ABS-equipped cars use the ABS incorrectly, either by pumping the brakes or by releasing the brakes when they feel the system pulsing. Some people think that since ABS allows you to steer during a panic stop, more people run off the road and crash.

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DESIGN PROCEDURE

1. Need

2. Design Concept

3. Material Selection

4. Block Diagram

5. Analysis of Forces

6. Energy Absorbed by the Brake

7. Calculation of Braking Torque

8. Stress Analysis

9. ABS Component Overview

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MATERIAL SELECTION

1. High Coefficient of Friction with Minimum fading.

2. Low wear rate.

3. High heat resistance.

4. High heat dissipation capacity .

5. Low coefficient of thermal expansion.

6. Adequate mechanical strength.

7. Cast iron, Bronze, steel, wood on cast iron & fibre, cork, leather, asbestos on metal.

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ADVANTAGES

1. It helps to maintain steering ability.

2. It avoids skidding while braking.

3. It prevents the wheel of a motor vehicle from locking while braking.

4. It prevents the vehicle from over turning.

5. Brakes are applied in pulses to reduce the jerks felt by the driver.

6. But it increases the braking distance.

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ABS COMPONENTS OVERVIEW

Typical ABS Components:

Wheel Speed Sensors (up to 4)

Electronic Control Unit (ECU)

Brake Master Cylinder, Hydraulic Modulator Unit with Pump and Valves

Vehicle’s Physical Brakes

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WORKING PRINCIPLE

1. Sensing the rate of rotation of the wheels.

2. Transmitting signals regarding the rate of wheel angular rotation to one or more controlling devices which interpret those signals and generate responsive controlling output signals and

3. Transmitting those controlling signals to one or more modulatordevices which adjust brake actuating forces in response to those

signals.

The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake).

A typical ABS is composed of a central electronic control unit (ECU), four wheel speed sensors — one for each wheel — and two or more hydraulic valves within the brake hydraulics. The ECU constantly monitors the rotational speed of each wheel, and when it detects a wheel rotating significantly slower than the others — a condition indicative of impending wheel lock — it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel. The wheel then turns faster; when the ECU detects it is turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied and the wheel slows. This process is repeated continuously, and can be detected by the driver via brake pedal pulsation. Some anti-lock system can apply and release braking pressure 16 times per second.

The ECU is programmed to disregard differences in wheel rotative speed below a critical threshold, because when the car is turning, the two wheels towards the center of the curve turn slower than the outer two. For this same reason, a differential is used in virtually all roadgoing vehicles.

If a fault develops in any part of the ABS, a warning light will usually be illuminated on the vehicle instrument panel, and the ABS will be disabled until the fault is rectified.

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DIAGRAMMATICAL REPRESENTATION OF WORKING

PRINCIPLE

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WHEEL SPEED SENSORS

The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information. Teeth on the sensor ring rotate past the magnetic sensor, causing a reversal of the magnetic field polarity, resulting in a signal with frequency related to the angular velocity of the axle.

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ELECTRONIC CONTROL UNIT

The signal from the WSS is proportional to angular velocity. By differentiating this signal, acceleration of each wheel is known. If a wheel

is decelerating too quickly the brake pressure is modulated.

A fifth input to the ECU is from a brake pedal switch. This signal can shift program execution from a standby to an active state The controller is an ECU type unit in the car which receives information from each individual wheel speed sensor, in turn if a wheel looses traction the signal is sent to the controller, the controller will then limit the brake force (EBD) and activate the ABS modulator which actuates the braking valves on and off.

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HYDRAULIC MODULAR UNIT

The hydraulic modulator unit contains the ABS pump as well as solenoid valves for each brake line. The fifth line - far right - is from the brake master cylinder, which is connected to the brake pedal.

The hydraulic brakes are applied with the liquid pressure. The pedal force is transmitted to brake shoe by means of a confined liquid through a system of force transmission. The system is based upon “PASCAL’s principle” which states that “The confined liquid transmits pressure without loss equally in all directions”.

The hydraulic brake system consists essentially of two main components:Master Cylinder

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Master cylinder is connected by tubing to the wheel cylinders, which is connected by tubing to the wheels. When the brake pedal is pressed, it pushes on the primary piston through a linkage. Pressure builds in the cylinder and lines as the brake pedal is depressed further. The pressure between the primary and secondary piston forces the secondary piston to compress the fluid in its circuit. If the brakes are operating properly, the pressure will be the same both circuits.

The most common vehicle uses of master cylinders are in brake and clutch systems. In brake systems, the operated devices are cylinders inside of brake calipers and/or drum brakes; these cylinders may be called wheel cylinders or slave cylinders, and they push the brake padstowards a surface that rotates with the wheel (this surface is typically either a drum, or a disc, a.k.a. a rotor) until the stationary brake pad(s) create friction against that rotating surface (typically the rotating surface is metal or ceramic/carbon, for their ability to withstand heat and friction without wearing-down rapidly). In the clutch system, the device which the master cylinder operates is called the slave cylinder; it moves the throw out bearing until the high-friction material on the transmission's clutch disengages from the engine's metal (or ceramic/carbon) flywheel. For hydraulic brakes or clutches alike, flexible high-pressure hoses or

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inflexible hard-walled metal tubing may be used; but the flexible variety of tubing is needed for at least a short length adjacent to each wheel.

WHEEL CYLINDER

Each wheel brake consists of a cylinder which is mounted on the inner side of the wheel and revolves with it and two brakes shoes which are mounted inside the brake drums and do not rotate. When the driver pushes the pedal with a small force, the piston in the master cylinder applies pressure to the brake fluid, which is then transmitted through the hydraulic lines to the caliper cylinders. Consequently, a great amount of force is applied which stops the wheels.

A wheel cylinder is a component in a drum brake system. It is located in each wheel and is usually at the top, above the shoes. Its responsibility is to exert force onto the shoes so they can contact the drum and stop the vehicle with friction. What connects these wheel cylinders to the shoes are usually small rods shaped like a birds beak. It is very similar to amaster cylinder and functions in pretty much the same way, consisting of just a simple little plunger on the inside. On older vehicles these will begin to leak and hinder the performance of the brakes, but are normally inexpensive and easy to replace

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VALVES AND BRAKES

There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:

In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.

In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.

In position three, the valve releases some of the pressure from the brake.

The valves modulate the brake pressure up to 20 times per second, effectively realizing the ideal tire slip percentage. ABS ‘pumps’ the brakes much faster than any driver could.

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ANALYSIS OF FORCES

Forces Acting on a brake Application

P = Force applied at the end of lever. Rn = Normal force pressing the brake block on the wheel. Ft = Tangential braking force or frictional force acting at the contact surface of the block. Tb = Braking torque r = Radius of the wheel. 2θ = Angle of contact surface of the block. µ = Coefficient of friction.

1. Ft = (µ x Rn)

2. Tb= Ft x r = (µ x Rn) x r

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Case 1. When the line of action of (Ft) passes through fulcrum ‘O’ of the lever. Then taking moment about the fulcrum ‘O’, We have

Rn x X = P x L or Rn = (P x L) / X

Tb = µ x Rn x r = (µ x P x L x r) / X

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Case 2. When the line of action of (Ft) passes through a distance (‘a’) below the fulcrum ‘O’, then taking moment about the fulcrum ‘O’

(Rn x X) + (Ft x a) = P x L

Or Rn = (P x L) / (X+µ x a)

Tb = µ x Rn x r = (µ x P x L x r) / (X +µ x a)

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Case 3. When line of action of (Ft) passes through a distance ‘a’ above the fulcrum ‘O’, then taking moments about O, we have

Rn x X = (P x L) + (Ft x a) = (P x L) + (µ x Rn x a) Rn= (P x L) / (X - µ x a)

Tb = µ x Rn x r = (µ x P x L x r) / (X - µ x a)

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ENERGY ABSORBED BY THE BRAKE

Case 1. When the motion of the body is pure translation. Change in kinetic energy of vehicle of mass (m) moving with velocity (V1) is reduced to velocity (V2),

E1 = ½ x m x [(V1)2 – (V2)2]

If the vehicle is stopped after applying brake, then E2 = ½ x m x (V1)2

Case 2. When the motion of the body is pure rotation. When the body of mass moment of inertia ‘I’ is rotating about an axis with angular velocity ‘ω’ is reduced to ‘ω’rad/s after applying the brake. Therefore change in kinetic energy

E1 = I = ½ x L x [(ω1)2 –(ω2)2]

If the rotating body is stopped after applying E2 = I = ½ x L x (ω1)2

Case 3. When the motion of the body is both translation and rotation .

Therefore , Total kinetic energy to be absorbed by the brake, E=E1+E2

N1= Speed of the brake drum before brake is applied N2= Speed of the brake drum after brake is applied N = Mean speed of brake drum = N1+N2/2

Total energy absorbed by the brake must be equal to the work done by frictional force, therefore

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E = (Ft x pi x d x N x t)

Or Ft = E / (pi x d x N x t)

CASE STUDY

To stop a vehicle of 1200kg in a distance of 50m which is moving down the hill at a slope of 1:5 at 72km/h. How much would be the average braking torque required.

We have,

M =1200kg; slope = 1:5; v=72km/h=20m/s; h=50m

Average braking torque to be applied to stop the vehicle

We know that kinetic energy of the vehicle

Ek =( ½ x m x V2 )= ½ x 1200 x (20)2 = 240000N-m

The Potential energy of the vehicle,

Ep = (m x g x h) x slope = (1200 x 9.81 x 50) x 1/5 = 117720N-m

Total energy of the vehicle or energy absorbed by the brake,

E = Ek + Ep = 240000 + 117720 = 357720N-m

Tangential braking force to stop the vehicle in a 50m distance,

Ft = 357720 / 50 = 7154.4N

Average braking torque to be applied to stop the vehicle,

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Tb = Ft x r = 7154.4 x 0.3 = 2146.32N-m

STRESS ANALYSIS

Rectangular Projected Area Brake shoe

Width of Brake Shoe, W= 155mm

Length of Brake shoe, L = 250mm

Projected Bearing Area of brake Shoe,

A = 38750mm2

Ft = 7154.4N

Stress on brake shoe, σb = Ft / A = 7154.4 / 38750

= 0.1846N/mm2

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FUTURE SCOPE

By 2020 Australian study by Monash University Accident Research Centre found that ABS:

Reduced the risk of multiple vehicle crashes by 18 percent, Reduced the risk of run-off-road crashes by 35 percent.

On high-traction surfaces such as bitumen, or concrete, many (though not all) ABS-equipped cars are able to attain braking distances better (i.e. shorter) than those that would be easily possible without the benefit of ABS. In real world conditions even an alert, skilled driver without ABS would find it difficult, even through the use of techniques like threshold braking, to match or improve on the performance of a typical driver with a modern ABS-equipped vehicle. ABS reduces chances of crashing, and/or the severity of impact. The recommended technique for non-expert drivers in an ABS-equipped car, in a typical full-braking emergency, is to press the brake pedal as firmly as possible and, where appropriate, to steer around obstructions. In such situations, ABS will significantly reduce the chances of a skid and subsequent loss of control.

In gravel, sand and deep snow, ABS tends to increase braking distances. On these surfaces, locked wheels dig in and stop the vehicle more quickly. ABS prevents this from occurring. Some ABS calibrations reduce this problem by slowing the cycling time, thus letting the wheels repeatedly briefly lock and unlock. Some vehicle manufacturers provide an "off-road" button to turn ABS function off. The primary benefit of ABS on such surfaces is to increase the ability of the driver to maintain control of the car rather than go into a skid, though loss of control remains more likely on soft surfaces like gravel or slippery surfaces like snow or ice. On a very slippery surface such as sheet ice or gravel, it is possible to lock multiple wheels at once, and this can defeat ABS (which relies on comparing all four wheels, and detecting individual wheels skidding). Availability of ABS relieves most drivers from learning threshold braking.

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REFERENCES

1. Bhandari V.P, Design of Machine Elements, Tata Mc Graw Hill, 11th

Edition,2000.

2. Giri N.K , Automobile Engineering, Khanna Publications, 2nd Edition,2007.

4. Gerald J. S. Wilde , Haynes Anti lock brake system, 3rd Edition, 1994.

5. www.auto.howstuffworks.com

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