DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERINGSri Venkateshwara College of Engineering

PRESENTED BY,

RAGHAVENDRA. B USN : 1VE11EC069 DEPT OF E&CE, SVCE

UNDER THE GUIDANCE OF,

MRS. DEVI. SASST. PROF,

DEPT OF E&CE,SVCE

ANTI-LOCK BREAKING SYSTEMS

CONTENTS

Safety methods.

Why ABS ?

Introduction to ABS.

Motivation for ABS development.

Background.

Components overview.

Working principle of ABS.

Advantages and disadvantages.

References.

SAFETY METHODS IN DRIVING

1) ACTIVE SAFETYActive driving safety refers to devices and systems that help

keep a car under control and prevent an accident. These devices are usually automated to help compensate for human error -- the single biggest cause of car accidents. For example:

• Anti-lock brakes prevent the wheels from locking up when the driver brakes, enabling the driver to steer while braking.• Traction control systems prevent the wheels from slipping while the car is accelerating.• Electronic stability control keeps the car under control and on the road.

SAFETY METHODS IN DRIVING

2) PASSIVE SAFETYPassive driving safety refers to systems in the car that

protect the driver and passengers from injury if an accident does occur.

• Air bags provide a cushion to protect the driver and passengers during a crash.• Seat belts hold passengers in place so that they aren't thrown forward or ejected from the car.• Rollover bars protect the car's occupants from injury if the vehicle rolls over during an accident.• Head restraints prevent the driver and passengers from getting whiplash during a rear-end collision.

WHY ABS ?

Statistics show that approximately 40 % of automobile accidents are due to skidding.

Skidding , vehicle instability, steer inability and long distance stopping are the problems commonly occurring on vehicle with conventional brake system, which can be avoided by adding devices called ABS.

An ANTI-LOCK BRAKING SYSTEM (ABS) prevents skidding, reduces stopping distance and allows you to steer your vehicle around obstacles you'd otherwise hit. The system engages when it detects a wheel has locked and starts to skid. It then 'pumps' the brake (applying and releasing it) much quicker than you can.

INTRODUCTION TO ABS

Anti-lock braking system (ABS) is an automobile safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to driver inputs while braking, preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding.

ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces; however, on loose gravel or snow-covered surfaces, ABS can significantly increase braking distance, although still improving vehicle control.

INTRODUCTION TO ABS

The Antilock braking system controls braking force by

controlling the hydraulic pressure of the braking system, so

that the wheels do not lock during braking.

The Antilock braking system prevents wheels locking or

skidding, no matter how hard brakes are applied, or how

slippery the road surface. Steering stays under control and

stopping distances are generally reduced.

MOTIVATION FOR ABS DEVELOPMENT

BACKGROUND

A mechanical anti lock system was originally developed for use on aircrafts in the late 1920s.

Approximately 30 years later, some of the same ideas were used on motorcycles to reduce stopping distances and prevent skidding, which was a significant factor in many accidents.

The mechanical system was used in limited instances on vehicles in the 1960s, but never saw widespread use due to its high price tag and unreliability.

A computerized system was developed and used by Chrysler in the early 1970s. Ford followed suit, and truly began to refine the system. It worked well, and similar systems began appearing on vehicles across manufacturers.

Anti lock brakes are now a standard feature on most vehicles, and provide many expanded functions.

BACKGROUND

COMPONENTS OVERVIEW

Component Purpose

Speed SensorMonitors for quick decelerations which indicate the wheel is about to lock up

Valves Control brake lines; typically has three positions

Pump Restores pressure to brake line

Controller Interprets data from speed sensors; controls valves and pump

COMPONENTS OVERVIEW

CONTROLLER SPEED SENSORS MODULATOR/VALVES

PUMPS

WORKING PRINCIPLE OF ABS

When the brake pedal is depressed during driving, the wheel speed decreases and the vehicle speed does as well. The decrease in the vehicle speed, however, is not always proportional to the decrease in the wheel speed. The non-correspondence between the wheel speed and vehicle speed is called “slip” and the magnitude of the slip is expressed by the “slip ratio” which is defined as follows:

WORKING PRINCIPLE OF ABS

Slip ratio = (Vehicle speed – Wheel speed)/Vehicle speed × 100%

When the slip ratio is 0%, the vehicle speed corresponds exactly to the wheel speed. When it is 100%, the wheels are completely locking (rotating at a zero speed) while the vehicle is moving.

WORKING PRINCIPLE OF ABS

λ ----------- Slip.µ ----------- Road Friction.

λ = v – wr / v -------------- 1

Where,V--------- Vehicle Speedµ = Wr------- Wheel Speed

Figure . Illustration of the relationship between braking coefficient and wheel slip

WORKING PRINCIPLE OF ABS

Figure shows the relationship between braking co-efficient and wheel slip. It

is shown that the slide values for stopping/traction force are proportionately

higher than the slide values for cornering/steering force. A locked-up wheel

provides low road handling force and minimal steering force.

λ = v – wr / vλ = 1 – wr / vλ = 1 – 0.8

Wr / v = 0.8Wr = 0.8 v

i.e., Wheel Velocity = 80% of Vehicle Velocity.

• The best braking action occurs at between 10-20%.

• If vehicle speed and wheel speed is the same wheel slippage is 0%

• A lock-up wheel will have a wheel slippage of 100%

WORKING PRINCIPLE OF ABS

(A) Slip ratio (B) Coefficient of friction between tire and road surface

(1) Icy road(2) Asphalt-paved road(3) Control range by ABS

Sensors at each of the four wheels sense the rotation of the wheel. Too much brake application wheel stop rotating Sensors ECU releases brake line pressure wheel turns again. Then ECU applies pressure again stops the rotation of the wheel releases it again and so on

This releasing and re-application or pulsing of brake pressure happens 20-30 times per second or more.This keeps the wheel just at the limit before locking up and skidding no matter

WORKING PRINCIPLE OF ABS

ABS SYSTEM DIAGRAM

DEMONSTRATION VIDEO

ADVANTAGES & DISADVANTAGES

Advantages:

1. It allows the driver to maintain directional stability and control over steering during braking.

2. Safe and effective.

3. Automatically changes the brake fluid pressure at each wheel to maintain optimum brake performance.

4. ABS absorbs the unwanted turbulence shock waves and modulates the pulses thus permitting the wheel to continue turning under maximum braking pressure.

ADVANTAGES & DISADVANTAGES

1. Expense. An ABS can be expensive to maintain. Expensive sensors on each wheel can cost hundreds of dollars to fix if they get out of calibration or develop other problems. For some, this is a big reason to decline an ABS in a vehicle.

2. Delicate systems. It's easy to cause a problem in an ABS by messing around with the brakes. Problems include disorientation of the ABS, where a compensating brake sensor causes the vehicle to shudder, make loud noise or generally brake worse.

Disadvantages :

REFERENCES

[1] H. Mirzaeinejad, M. Mirzaei, ‘A novel method for non-linear control of wheel slip in anti-lock braking systems’, Control Engineering Practice vol. 18, pp. 918–926, 2010

[2] S. Ç.baslamisli, I. E. Köse and G Anlas, ‘Robust control of anti-lock brake system’, Vehicle System Dynamics, vol. 45, no. 3, pp. 217-232, March 2007

[3] S. B. Choi, ‘Antilock Brake System with a Continuous Wheel Slip Control to Maximize the Braking Performance and the Ride Quality’, IEEE Transactions on Control Systems Technology, vol. 16, no. 5, September 2008

[4] K.Z. Rangelov, SIMULINK model of a quarter-vehicle with an anti-lock braking system, Master’s Thesis -Eindhoven: Stan Ackermans Institute, 2004. - Eindverslagen Stan Ackermans Institute, 2004102