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By

PRATEEK M NAIK

1RE08ME036

MECHANICAL DEPARTMENT

REVA ITM

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INTRODUCTION

Vehicle skid can be defined as the loss of traction between a

vehicles tires and the road surface due to the forces acting on the

vehicle. This skid of car causes loss of control and resulting in

OVERSTEER and UNDERSTEER problem.

To reduce OVERSTEER and UNDERSTEER effect on a

motor vehicle , modern technologies such as ANTILOCK BRAKING

SYSTEM , ELECTRONIC STABILITY PROGRAM , TRACTION CONTROL

SYSTEM & ELECTRONIC BRAKE FORCE DISTRIBUTION systems are

utilized . The thesis displays the use of such system on vehicle

stability and remedial measures to be taken.

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OVERSTEER

A car that oversteer turns very sharply, moving the rear of the car to slide outside

of a corner while its front points towards the inside.

Oversteer occurs when a cars front tires have more traction than the rear tyres,particularly with rear wheel drive cars.

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UNDERSTEER

When a car understeer, the front end of the car slides to the outside of a turn

instead of taking the turn.

Understeer occurs when the rear tires have more traction than the front tires, whichoften happens with frontwheel drive cars.

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VEHICLE SKID

CONTROL

The Vehicle Skid Control (VSC) is made possible by the combination of different

electronic and mechanical components.

Main objective is to , sense the onset of traction loss and keep the driver on track.

These skid control systems are often integrated with the engine management

system to cut power in even more tricky situations.

Here a complex system of sensors and microprocessors that continually monitor

the vehicle for any signs of instability.

Once detected (usually in the form of a slide or skid), the system automatically

applies selective braking to specific wheels thereby stabilizing the vehicle.

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Yaw rate sensor

G-sensor

Steering angle sensor

Electronic throttle control

Slip indicator

Computer

COMPONENTS OF

Vsc

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ANTILOCK BRAKING

SYSTEM

An anti-lock braking system (ABS, from German: Antiblockiersystem) is a safety

system that allows the wheels on a motor vehicle to continue

interacting tractively with the road surface as directed by driver steering inputs

while braking , preventing the wheels from locking up (that is, ceasing rotation)

and therefore avoiding skidding.

An ABS generally offers improved vehicle control and decreases stopping

distances on dry and slippery surfaces for many drivers; however, on loose

surfaces like gravel or snow-covered pavement, an ABS can significantly increase

braking distance, although still improving vehicle control

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COMPONENTS OF ABS

There are four main components to an ABS:

SPEED SENSOR

ABS VALVES

ABS PUMP

ABS ACTUATORS

ABS CHANNEL

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WORKING OF ABS

The ECU constantly monitors the rotational speed of each wheel; if 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.

Conversely, if the ECU detects a wheel turning significantly faster than the others,

brake hydraulic pressure to the wheel is increased so the braking force is reapplied,

slowing down the wheel. This process is repeated continuously and can be

detected by the driver via brake pedal pulsation.

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TYPES OF ABS

FOUR CHANNEL , FOUR SENSOR ABS

THREE CHANNEL , FOUR SENSOR ABS

THREE CHANNEL , THREE SENSOR ABS

ONE CHANNEL , ONE SENSOR ABS

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ELECTRONIC STABILITY

PROGRAM

ESP systems are an evolution of the ABS concept. Here, a minimum of two

additional sensors are added to help the system work: these are a steering wheel

angle sensor, and a gyroscopic sensor.

When the gyroscopic sensor detects that the direction taken by the car does not

coincide with what the steering wheel sensor reports, the ESC software will brake

the necessary individual wheel(s) , so that the vehicle goes the way the driver

intends.

The steering wheel sensor also helps in the operation of Cornering Brake Control

(CBC), since this will tell the ABS that wheels on the inside of the curve should

brake more than wheels on the outside, and by how much.

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A traction control system (TCS), also known as anti-slip regulation (ASR), is typically

(but not necessarily) a secondary function of the anti-lock braking system (ABS) on

production motor vehicles, designed to prevent loss of traction of driven road

wheels.

When invoked it therefore enhances driver control as throttle input applied is mis-

matched to road surface conditions (due to varying factors) being unable to

manage applied torque.

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OVERSTEER & UNDERSTEER CAUSED BY TRACTION LOSS

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When the traction control computer detects one or more driven wheels spinningsignificantly faster than another, it invokes ABS ecu to apply brake friction to wheels

spinning with lessened traction.

Braking action on slipping wheel(s) will cause power transfer to wheel axle(s) with

traction due to the mechanical action within a differential.

All-wheel drive AWD vehicles often have an electronically controlled coupling

system in the transfer case or transaxle engaged (active part-time AWD), or locked-

up tighter (in a true full-time set up driving all wheels with some power all the

time) to supply 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.

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Electronic brake force distribution (EBD or EBFD), Electronic brake force limitation

(EBL) is an automobile brake technology that automatically varies the amount of

force applied to each of a vehicle's brakes, based on road conditions, speed,

loading, etc.

Always coupled with anti-lock braking systems, EBD can apply more or less braking

pressure to each wheel in order to maximize stopping power while maintaining

vehicular control.

The front end carries the most weight and EBD distributes less braking pressure to

the rear brakes so the rear brakes do not lock up and cause a skid.

In some systems, EBD distributes more braking pressure at the rear brakes during

initial brake application before the effects of weight transfer become apparent

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EBD may work in conjunction with ABS and Electronic Stability Control ("ESC") tominimize yaw accelerations during turns.

ESC compares the steering wheel angle to vehicle turning rate using a yaw rate

sensor. "Yaw" is the vehicle's rotation around its vertical center of gravity

If the yaw sensor detects more/less yaw than the steering wheel angle shouldcreate, the car is understeering or oversteering and ESC activates one of the front

or rear brakes to rotate the car back onto its intended course

If a car is making a left turn and begins to understeer (the car plows forward to the

outside of the turn) ESC activates the left rear brake, which will help turn the car

left.

The sensors are so sensitive, and the actuation is so quick that the system may

correct direction before the driver reacts. ABS helps prevent wheel lock-up and EBD

helps apply appropriate brake force to make ESC work effectively.

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ADVANTAGEs &

DISADVANTAGEs

ADVANTAGES

Monitors each wheel independently maximizing the performance of the car.

Increases comfort, both physical and psychological.

Improves safety aspects of the car and the driver.

Helps save money long term.

Enhances the ability to dodge a renegade object in its pathways.

DISADVANTAGES

High initial costs.

Overdependence.

Not perfect.

Repairing cost may be high.

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REMEDIAL MEASURES

In each case, the cause can be removed by taking the foot off the accelerator or brake

and depressing the clutch. The reasons are as follows:-

By decelerating, the vehicles speed is lowered, which in turn will start to reduce the

magnitude of the skid.

Relaxation of the pressure on the brake pedal will unlock the wheels and allow the tyres

to regain traction, enabling the vehicle to be steered.

Depressing the clutch pedal has 3 beneficial effects:

(i) The engine will not stall, enabling the vehicle to be moved quickly from the danger

area.

(ii) The link between engine & transmission is broken, there is no drive to any of the

wheels, therefore the vehicle is no longer a front, rear or four wheel drive model.

(iii) A very slippery surface can cause the drive to lock up which in turn causes the wheels to

lock, keeping the vehicle in a skid situation.

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conclusion

Latest generation of stability control systems offer drivers increased protection

for both themselves and the vehicle, they can never overcome poor judgment or

the laws of physics

When we drive, it not only affects our safety but the safety of

everyone around us whether driving or not. With increasing development in the

field of automobiles, it is only imperative that we go for vehicles that have these

technologies installed in them. Vehicle Skid Control would not, in anyway,

eliminate all road accidents; however it would lower the percentage of crashes

thereby lowering the number of fatalities.

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BIBLIOGRAPGHY

www.experiencemad.co.uk

www.trailer-bodybuilders.com

www.graham-sykes.co.uk

www.lexus.com

www.howstuffworks.com

Heitner Joseph,Automobile Mechanics,2nd ed ,East West press, New

Delhi, 2001

Sing Harbans , The Automobile,1st editions Chand, New Delhi,2001

http://www.experiencemad.co.uk/http://www.trailer-bodybuilders.com/http://www.graham-sykes.co.uk/http://www.lexus.com/http://www.howstuffworks.com/http://www.howstuffworks.com/http://www.lexus.com/http://www.graham-sykes.co.uk/http://www.graham-sykes.co.uk/http://www.graham-sykes.co.uk/http://www.trailer-bodybuilders.com/http://www.trailer-bodybuilders.com/http://www.trailer-bodybuilders.com/http://www.experiencemad.co.uk/

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