lab sheet (anti-lock braking system)

8/18/2019 Lab Sheet (Anti-lock Braking System)

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Anti-Lock Braking System Trainer Experiment Manual / BS-ABS-2

3

BASIC THEORY

This chapter is begun by introducing the braking system and its components. After

introducing the braking system, the theory goes on to Anti-lock Braking System (ABS)

and its components. At the end of the chapter, questions about ABS are discussed.

3.1. BRAKING SYSTEM

Braking systems hae the task of reducing the speed of a ehicle, bringing it to a halt or

holding it stationary if it is at a standstill. Braking systems are thus essential for the

operation of a motor ehicle and its safety in road traffic.

All braking systems of a ehicle form the braking equipment as a !hole. Braking systems

can be classified according to their use and the type of energy used.

3.1.1. Classification according to t! "s!

"n the basis of legal regulations, the braking equipment in ehicles is subdiided into

three braking systems#

1. Servicing Braking

System

"n the one hand, the serice braking system (foot brake) reduces the speed of the ehicle

or keeps it constant !hen driing do!n hill and, on the other, brings the ehicle to a halt.

The system seres for normal operation of the ehicle. $t can be operated gradually by the

foot and acts on all four !heels.

2. Parking Brake

System

The parking brake system (hand brake) is the third system in the braking equipment

installation. $t must hold the ehicle stationary, een on a slope and in the absence of

the drier. %or safety reasons, there must be a continuous mechanical connection bet!een

the control deice and !heel brake in the parking brake system, e.g. by means of a rod

linkage or brake cable assembly. The parking brake system is actuated from the

drier seat, normally by means of a hand brake leer or, in some ehicles by means of

a foot pedal. This braking system can be operated gradually and acts on the !heels of only

one a&le.

3.1.#. Classification in accordanc! $it t%&! of !n!rg% "s!d

'epending on !hether a braking system is operated completely, partially or not at all by

muscular energy, a distinction is dra!n bet!een#

.

Muscular Energy Braking

System

$n this system, !hich is fitted in passenger cars and on motorcycle, th e actie muscular

energy on the foot pedal or hand brake leer is transmitted to the brakes either mechanically

(by rod linkage or brake cable) or hydraulically.

Energy Assisted Braking Systemnergy assisted braking systems are fitted in passenger cars and light commercial ehicle.

This system boosts the muscular energy in the brake booster by means of an au&iliary force

generated by acuum or a hydraulic fluid. The force is transmitted hydraulically to the !heel

brakes ('ig"r! 3.1.1.)


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'ig"r! 3.1.1. Example of energy assisted braking system of a passenger car

! Brake "edal# 2 $acuum Brake Booster# % Tandem Master &ylinder# ' Brake (luid )eser*oir# + ,isc

Brake

(ront.# Braking (orces "roportioning ,e*ice# 0 ,rum Brake

)ear.

Non-muscular Energy Braking (Power System

The on-muscular energy braking systems generally used in commercial ehicles are

occasionally used in large passenger cars and in passenger cars !ith integrated ABS. *ere,

the serice brake is operated e&clusiely by non-muscular energy.

The system operates !ith hydraulic energy (based on fluid pressure) and !ith hydraulic

transmission. The hydraulic fluid is stored in energy accumulators in !hich gas (mostly

nitrogen) is compressed. The gas and fluid are separated from each other by an elastic bladder

(bladder accumulator) or a piston !ith a rubber seal (piston accumulator). A hydraulic pump

generates the fluid pressure, !hich is al!ays in equilibrium !ith the gas pressure in the

energy accumulator. A pressure regulator s!itches the hydraulic pump to idle operation as

soon as the ma&imum pressure is reached.

The hydraulic fluid has the adantage that it is considered to be incompressible in practical

application, i.e. it does not change its olume !hen it is e&posed to pressure. +onsequently,

small quantities of hydraulic fluid can transfer high pressures and the brake assemblies are

characteried by being compacted and small sied. *o!eer, a disadantage is that hydraulic

fluid can leak if the system is not sealed, !hich finally leads to e&haustion of the energy

medium.


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3.1.(. Bra)ing *!canics

According to the definition in the standard, the term braking mechanics coers all

phenomena occurred bet!een the start of actuation of the (brake) control deice and the end

of braking. The braking mechanics are characteried by different phases ('ig"r! 3.1.#)#

%ig"r! 3.1.#. ,eceleration during braking

t 1 Start of Braking t !-t 1 )esponse and build up time

t ! -t 1 3nitial response time t % -t 2 "ortion of 4mean fully de*eloped deceleration5

t !-t ! "ressure build up time t ' -t ! Acti*e braking time

Ac tua ti ng ti m e t1The start of part moements of the control deice (on !hich the control force acts)

starts.

$nitial res ponse time t!-t1lapsed time bet!een the moments !hen the component of control deice (on

!hich the control force acts) starts to moe and moment !hen the braking force

takes effect.

Build up time t!/-t!lapsed time bet!een the moments !hen the braking force takes effect and the

moment !hen this force reaches a certain alue (corresponds to 012 of the brake

pressure).

Total braking time t'-t1lapsed time bet!een the moment !hen the control deice component (on !hich

the control force acts) starts to moe and the moment !hen the braking forceceases. $f the ehicle stops before the braking force ceases, the time of the

moement end constitutes the end of the total braking time.

Actie braking time t'-t!lapsed time bet!een the moment !hen braking force takes effect and the moment

at !hich it ceases. $f the ehicle stops before the braking force ceases, the time of

moement end constitutes the end of the actie braking time.

Sec ti on of the m ean fu ll y dee lo p ed dec e ler a ti on t%- t23ean alue of the deceleration in a section of the fully deeloped deceleration.


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3.1.+. ,%sical &rinci&l!s

ery body attempts to either remain in its rest condition or to presere its state of moement.

%orce must be e&panded or transmitted in order to cause a change in the respectie state. $f an

attempt is made to brake in a cure on an icy road, for e&ample, the ehicle slides on straight

ahead !ithout becoming noticeably slo!er or reacting to steering moements.

%orces, !hich act on a moing ehicle, are# graity, air force (air resistance) and tire force

(rolling resistance).

A desired moement or change in a moement can be achieed in a specific !ay only by

means of the tire force. The tire force consists of the follo!ing components ('ig"r! 3.1.3)#

4eripheral force ( 6 caused by the drie.

5ateral force ( S caused by the steering. ormal force ( 7 as a result of the ehicle !eight.

( 7 7ormal (orce

'ig"r! 3.1.3. Tire (orce

( 6 "erip8eral (orce "ositi*e9 ,ri*ing (orce# 7egati*e9 Braking.

( S Lateral (orce

The peripheral force ( 6 acts on the road plane and allo!s the drier to accelerate the car

using the accelerator pedal and to brake it using the brake pedal. The lateral force ( S , !hich is

perpendicular to ( 6 , transfer the steering moement to the road and causes the ehicle to turn.

The normal force ( 7 is determined by the !eight of the ehicle and its load, i.e. it is the

!eight component acting perpendicularly on the road. The degree to !hich the forces can

actually come into effect depends on the condition of the road and tires and on the !eather

conditions, i.e. on the friction force bet!een the tires and road surface.

The safety systems of the ABS (anti-lock braking system) make optimum use of this

aailable friction adhesion.


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3.1.-. 'riction forc!

The friction force ( ) is proportional to the normal force

( 7 #

( ) 6 : B & ( 7

The factor : B is the braking force coefficient (or coefficient of friction or adhesion

coefficient). $t describes the characteristics of the different tire7 road material pairings andall influences to !hich these pairings are e&posed. The braking force coefficient isthus a measure of the transferable braking force. %or ehicle tires, the braking forcecoefficient reaches its ma&imum alues on a dry and clean road surface and itslo!est on ice. $ntermediate media such as !ater and dirt reduce the baking force coefficient.

&ample#

Road condition Bra)ing forc! co!ffici!nt B

'ry 8.9 : 9;et 8.< : 8.=1

$cy 8.881 : 8.9

The braking force coefficient depends greatly on the speed. This applies $ particular on !et

road surfaces. ;hen braking at high speeds, and under certain road conditions, the !heels

may lock if the braking force coefficient is so lo! that the adhesion of the !heels to the

road surface can no longer be maintained. $f a !heel locks, it ceases to transfer lateral

forces and the ehicle can no longer be steered.

Sli&

;hen a !heel rolls under the effects of driing or braking forces, comple& physical phenomena occur in the contact area of the tire !ith the road. The rubber elements of the tire

become distorted and e&posed to partial sliding moements, een if the !heel has not yet

locked. This slip can be generated either by the tire>s rotational speed being greater or less

than the ehicle speed . The measure of the sliding component of the rolling moement is the

slip ?#

? 6 ($ ( -$ 6 )7 $ (

!here $ ( is the ehicle speed and $ 6 the circumferential speed of the !heel ('ig"r! 3.1.+).

a. (reely rolling ;8eel# b. Brake ;8eel

$ ( 9 $e8icle speed at t8e ;8eel center

point M# $ 6 9 "erip8eral ;8eel speed T8e

angle of rotation < becomes less per time

unit for t8e braked ;8eel slip..

'ig"r! 3.1.+. )olling mo*ement of t8e ;8eel

The formula state that brake slip occurs as soon as the !heel start s to rotate or slo! do!n its

speed !hich corresponds to the driing speed. Braking force can be generated only in thiscondition (an analog situation to acceleration).

Braking force coefficients often sho!n as a function of brake slip, may possess different

alues, depending on the road conditions.

http://en.wikipedia.org/wiki/Tirehttp://en.wikipedia.org/wiki/Tire


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3.3. ANTI/0OCK BRAKING SYSTEM ABS2

'eelopment in the field of passenger-car brakes has led to efficient and reliable braking

systems !hich can decelerate cars optimally een at high speeds. The systems permit a car to

be braked reliably and rapidly or brought to a halt under normal road conditions. $f on the

other hand, driing conditions are critical (!et or slippery road, sudden shock reaction of the

drier as the result of an unforeseen obstacle, incorrect behaior of other road users etc.), the

!heels may lock during braking, !ith the result that the ehicle can no longer be steered andstarts to skid, and may een leae the road.

$n such a situation, the anti lock braking system ABS interenes. $t immediately recognies

any tendency of one or more !heels to lock and instantaneously ensures that the brake

pressure is kept constant or reduced. The ehicle is steerable, it remains stable and it is

optimally braked. Because it helps the drier to master difficult braking situations ( 'ig"r!s

3.3.1a and 3.3.1), ABS thus makes a decisie contribution to road safety.

a. b.

'ig"r! 3.3.1. Braking effect

a. Braking effect ;it8out ABS T8e tracks s8o; t8at t8e ;8eels 8a*e locked and t8e *e8icle 8as

broken a;ay

b. Braking effect ;it8 ABS T8e *e8icle retains full steer ability and keeps to its course e*ent of

panic braking

3.3.1. 4!*ands on ABS

ABS must satisfy e&tensie requirements. This applies particularly to all safety requirements,

!hich relate to braking dynamics and brake-assembly engineering#

@ The braking control system must guarantee stability and steer ability under all road

conditions (!hich can range from a dry road proiding good grip to a road coered !ith

ice).

@ ABS must optimally e&ploit the braking capability of the !heels on the road, !hereby

driing stability and steer ability hae priority oer reduction in the braking distance. $t

must be irreleant !hether the drier slams on the brakes abruptly or slo!ly increases

the brake pressure up to the locking limit.

@ The braking control system must operate throughout the !hole of the speed range

ehicle right do!n to !alking pace. $f the !heels lock at this lo! speed, the remaining

trael of the ehicle until it comes to a halt is uncritical.

@ The braking control system must adapt itself quickly to change in road adhesion, e.g. on

dry road !ith occasional patches of ice, the possible locking of the !heels must be

restricted to such short periods that driing stability and steer ability are not impaired.

"n the other hand, ma&imum use must be made of the adhesion on the dry part of theroad.


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3.(. ABS COM,ONENTS

3.(.1. 5!!l/s&!!d s!nsors

The !heel-speed sensors ('ig"r! 3.(.1) signal the !heel speed to the +. The pole pin (1)

of the !heel-speed sensor is surrounded by a !inding () and is located directly oer the

sensor ring (=), a gear !heel, !hich is attached to the !heel hub (in special cases, the !heel-

speed sensor is installed in the differential). The pole pin is connected to a permanent magnet(


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3.+. TRACTION CONTRO0 SYSTEM

TCS2

;hat is traction, and !hat does traction control do on my car !hile $ drieC Traction is the

grip that your car/s tires hae on the road, !hich is needed to accelerate, turn and brake.

$f your car, or more specifically, your tires hae little or no gripD your car !ill not

accelerate, turn or brake and !ill skid. Traction control deices in the car !ill help preentthis loss of grip so your tires !ill hae traction to accelerate, turn and brake.

The interention can consist of any, or all, of the

follo!ing#

9. Eetard or suppress the spark to one or more cy li n d ers


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ABS ;it8 T&S Trainer Experiment Manual / BS-ABS-%

#.+. Saf!t% ,r!ca"tions

9. 'o not connect the Humper into any test points because it could damage the electronic

system.


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+.1. NORMA0 BRAKING

OB8ECTI9E

pon completion of this e&periment the students should be able to e&plain ho! the normal

braking system !orks (!ithout ABS) and the students should be able to understand the

!orking principle of main braking components such as electric hydraulic brake booster, brake

master cylinder, disc brake, and brake fluids.

E:6I,MENT

9. Anti-5ock Braking System (ABS) !ith T+S Trainer (BS-ABS-F)

bser*e (igure

belo; for becoming more familiar ;it8 t8e ABS/T&S electric brake pump module and

master cylinder

'ig"r!.+.1/1. ABS 8ydraulic brake booster and ABS/T&S actuator unit

. 3ake sure the !heel is not turning and all electric motors are in sto& condition.

1. Apply braking system by pressing the brake pedal. "bsere each slae cylinder

pressure at the pressure gauge ne&t to the corresponding !heel and record the readings.

The pressure at front left (%5) !heel slae cylinder (J9) is ::.. psi

The pressure at front right (%E) !heel slae cylinder (J


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9995ABT(+*


+.#. S644EN BRAKING 5ITH AN4 5ITHO6T ABS

OB8ECTI9E

pon completion of this e&periment the students should be able to e&plain the function of

ABS to preent rapid deceleration that caused by sudden braking or panic breaking.

E:6I,MENT9. Anti-5ock Braking System Trainer !ith Traction +ontrol System (BS-ABS-

F)


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99


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99F5ABT(+*


+.3. BRAKING IN 4RY AS,HA0T

ROA4

OB8ECTI9E

pon completion of this e&periment the students should be able to e&plain the behaior of

ABS !hen braking on dry asphalt road surface.

E:6I,MENT

9. Anti-5ock Braking System Trainer !ith Traction +ontrol System (BS-ABS-F)


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=. Set the initial speed appro&imately 08 km7hour and let the !heels speed up to the initial

speed.

0. "bsere that the !heels are accelerating to achiee a simulation of a ehicle running at 08

km7h.

K. 3ake sure the ABS7T+S is in =On> position. Apply sudden full braking and hold the brake

pedal.L. "bsere the pressure gauges, feel the pulsation on the braking pedal.

98.The four !heel start to decrease in speed, obsere the 0-segment display to monitor either

the braking time or the stopping distance.

;hen the !heels stop, !rite do!n the braking time and stopping distance.

Braking time 6 ::::: seconds

Stopping distance 6 ::::: meters

Eelease the brake.

99.Set the initial speed appro&imately 918 km7hour

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+.(. BRAKING IN 5ET AS,HA0T ROA4

OB8ECTI9E

pon completion of this e&periment the students should be able to e&plain the behaior of

ABS !hen braking on !et asphalt road surface.

E:6I,MENT

9. Anti-5ock Braking System Trainer !ith Traction +ontrol System (BS-ABS-F)


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+.+. BRAKING IN ICY


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rear left (E5) - (JF)

rear right (EE) - (J)

master cylinder - (J1)


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=. Set the initial speed appro&imately 08 km7hour and let the !heels speed up to the initial

speed.

0. "bsere that the !heels are accelerating to achiee a simulation of a ehicle running at 08

km7h.

K. 3ake sure the ABS7T+S is in =On> position. Apply sudden full braking and hold the brake

pedal.L. "bsere the pressure gauges, feel the pulsation on the braking pedal.

98.The four !heel start to decrease in speed, obsere the 0-segment display to monitor either

the braking time or the stopping distance.

;hen the !heels stop, !rite do!n the braking time and stopping distance.

Braking time 6 ::::: seconds

Stopping distance 6 ::::: meters

Eelease the brake.

99.Set the initial speed appro&imately 918 km7hour

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lab sheet (anti-lock braking system)

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