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Electronically Controlled Braking System

TRUCKABS/EBS

Prosp. Truck ABS/EBS -E 27.07.2004 10:49 Uhr Seite 1

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WABCO Truck ABS/EBS

Introduction

The ABS specifications situation

ABS control unit family

The WABCO ABS/ASR modular system

Basic version ABS from

4S/3M to 4S/4M

ABS/ASR

Frame assembly

EBS in tests

EBS cost-effective, safe and innovative

Compatibility betweentractor and trailer vehicles

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6

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CONTENTS 3


Introduction

Figure 1

4 TRUCK ABS/EBS

the first system of this kind and was launched into volume production in com-mercial vehicles back in 1981. Europeanlegislation recognized the tremendousimprovement in safety standards achievedby the ABS system, making ABS a man-datory requirement for certain vehicletypes.

Over the past few years, virtually noother aspect of commercial vehicletechnology has changed as much asthe brakes.

In this area of technology, the designerhas to take into consideration a widerange of vehicles – from vans throughlight-duty trucks to heavy-duty truckswith trailers, or semitrailers and buses – in which various braking systems areused. Furthermore, different usagedemands are to be satisfied. And last

but not least, there are various possibleservice brake designs. Other systemsand functions will also be added over thenext few years.

Viewed historically, the past few decadeshave seen a vast number of major deve-lopments and changes. The introductionof the dual circuit compressed air brakein the 1960s or the launch of the automa-tically load-dependent braking powergovernor in the 1970s are just two ofmany examples.

We are now experiencing the 1980s and1990s as the decades of electronic vehi-cle feedback control systems which alsomade their mark on vehicle brakingsystems. The anti-lock system (ABS) was


TRUCK ABS/EBS 5

Fig. 2: ABS & EBS – step-by-step more safety and economic viability

The aim of this brochure is to provide anoverview of the function and structure ofthe various ABS and EBS systems aswell as of new parts and amendments tolegislation.

In 1987, ABS was then extended toinclude anti-slip control (ASR) wherebytraction was improved significantly bymeans of brake intervention.

The increasing pressure of competition inthe transport trade also increased therequirements placed on the brakingsystem.

This was followed by the introduction ofthe electronically controlled brakingsystem (EBS) in 1996. This step repre-sented a considerable increase in safetylevels and a notable increase in vehicleeconomic viability.

Attempts to improve the rollover resis-tance of commercial vehicles have beenachieved through extending the functionsof ABS and EBS. Dynamic Drive Controlcombined with EBS delivers yet another increase in vehicle safety.

Economy

Vehiclesafety

ABS/ASR for tractorunits and trailers

EBS – For tractorunits and buses

EBS – For trailers

ESC – ElectronicStability Control

ACC – AdaptiveCruise Control


The ABS regulations situation

Figure 3

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advice, ABS had been phased in progres-sively as a mandatory requirement for allother vehicles by 31.03.2001, wherebyvans and light-duty buses in excess of 5 twill also belong to the ABS club.

Standard specifications apply to allvehicles used within Europe. Theregulations for braking systems incl.ABS can be found in ECE-R13 andCouncil Directive 71/320/EEC.

The ECE rulings are accepted throughoutEurope and exist in parallel to the EUDirectives. For various reasons, differentdates for introducing the EC and ECEregulations have however been estab-lished so that different usage dates wererequired for ABS (refer to Figure 3).

Heavy commercial vehicles > 16 t (categories N3, …) should be fitted withABS as standard as of October 1991. Following the latest round of specialist

TRUCK ABS/EBS

01.10.91 MANDATORY for road registrationN3 > 16 t and suitable for towing trailers (O4)

N3 > 16 t and suitable for towing trailers (O4)

O4

O4

M2, M3N2, N3O3

N2 < 7.5 tO3 < 5 t

M2, M3N2 > 7.5 tO3 > 5 t

N3

31.03.2001 MANDATO-RY for road registration

01.10.99 new type approval




01.04.01 manda-tory, see above

01.04.00 mandatory, see above

01.10.98 mandatory, see above

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E-R

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ABS man

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Figure 4

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Basic version ABS from4S/3M to 4S/4M

In order to satisfy extreme cost require-ments even in the light-duty vehicle ranges, WABCO has defined a basic ABSversion. This satisfies all statutory ABSrequirements and is designed for 4S/3Mand 4S/4M applications (in special in-stances, also available as 4S/2M). The E generation is also available with ASRand EBL (Electronic Brake Limiter).

The WABCO ABS/ASR modular system

Modified vehicle concepts, the desire forgreater optimisation of functionality andongoing reductions in system costs have resulted in the development of theABS/ASR E generation. This describes awhole system family. WABCO provides

vehicle manufacturers with different con-trol unit installation options ranging fromdriver’s cab to frame mounted, dependingon the vehicle concept.

All versions of the modular system alsosatisfy the most stringent of statutoryrequirements and at the same time pro-vide the manufacturer with the options ofe.g. selecting between a pure ABS appli-cation right up to the greatest ABS/ASRscope of function.

TRUCK ABS/EBS



Figure 5

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Frame assembly

Some driver’s cab concepts – especiallyin US vehicles – prefer fitting theABS/ASR control unit on the frame. Inthese instances, WABCO provides a spe-cial housing suitable for this purpose. Atpresent, this family is only designed for12 V applications.

ABS/ASR

The traditionally familiar ABS/ASR controlunit version is fitted in the driver’s cab.These various ABS versions are availablein a flexible modular system:

■ From 4S/3M to 6S/6M

■ With and without ASR

■ For 12 V or 24 V voltage supply

■ CAN bus in accordance with SAE J 1939

■ Trailer interface in accordance with SAE J 2497 PLC 4 Truck

■ RSC

■ Diagnosis interfaces in accordancewith SAE J 1587, ISO 9141,KWP 2000

■ Diagnosis via flashing code

TRUCK ABS/EBS


EBS in tests

Figure 6

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■ The conventionally braked trailer is also controlled by the EBS. How does this affect tractor trailer balance?

■ How resistant to failure have you found the EBS system to be?

EBS has been used in volume production runs since 1996.

It is important for us to know what ourcustomers say about our products. Isthere anything they would like us toimprove?

■ How do you find the braking feeling in comparison with a conventional braking system?

■ Can you feel the shorter braking distance of the EBS?

■ What have been your experiences with regard to brake lining wear?

■ How does the EBS behave in terms of actuation and pedal feel?

140.000 km and no noticeable

wearyes! 100 %

very good! perfect

simplyexcellent

as reliableas a Swiss watch

small amountof force required

The brake iseffective immediately,

without any delay

brakes similar to thoseof a passenger car

TRUCK ABS/EBS


EBS – cost-effective, safe and innovative

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Innovative as a result of extensive dia-gnosis and self-diagnosis tools.

Innovative as a result of new functionscombined with other vehicle systems,such as continuous braking integrationand drag torque control.

EBS electro-pneumatically controls thebraking pressure levels of the front andrear axle as well as the trailer controlpressure. Redundant pressure control isalso available if the vehicle electrics fail.

EBS from WABCO offersa wide range of attractivebenefits

Cost-effective for the manufacturerthrough the use of standard componentsand simple assembly.

Cost-effective for the operator throughthe minimized and even spread of wearon the front and rear axles and throughgood tractor-trailer balance.

Safe thanks to improved ABS and ASRfunctions which are integral componentsof the system.

Safe thanks to convenient braking, virtu-ally comparable with braking in cars.

Trailer control valve

Brake signal transmitter

Central module

Proportionalrelay valve

ABS valve

Back-up valve

Rear axle modulator

Figure 7

TRUCK ABS/EBS


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■ System functionsEBS has a multitude of functions which reduce operating costs, increase braking comfort levels and improve safety.

■ Brake management functionsContinuous brake integration is responsible for correct usage of the brakes available. It ensures that the zero-wear brakes – retarder, engine brake – take on a maximum degree of braking work for the entire roadtrain during every instance of braking. Thisleaves the wheel brakes cold and saves brake linings and drums and/or brake discs.

EBS features

■ A brake signal transmitter which creates both an electrical and a pneumatic nominal retardation value from driver pedal actuation

■ A proportional relay valve for controlling the front axle braking pressure with rear-mounted ABS control valves

■ An axle modulator for controlling the braking pressure on the rear axle

■ An electro-pneumatic trailer control valve for controlling the trailer control pressure

■ A digital data interface to trailers with EBS

■ A central control unit for primary brake management functions, for front axle and trailer pressure control, for evaluating sensor signals and for communicating with other vehicle systems

1 Pneumatic group

2 Brake signal transmitter

3 Central control unit

4 Proportional relay valve

5 Axle modulator

6 ABS control valve

7 Sensors

8 Trailer control

9 Auxiliary/parking brake

10 Back-up valve

TRANSMISSION ECAS RETARDER

ENGINE

Figure 8: EBS system

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2

3

4

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7

89

10

1

11

1

1

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TRUCK ABS/EBS


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EBS – cost-effective, safe and innovative

With regard to ABS, the modified indivi-dual control system (MIR) on the frontaxle ensures a tremendous ability to con-trol the vehicle, while independent controlof the rear axle minimises all braking travel to that actually required.

The braking force distribution function is responsible for the correct distri-bution of braking force to the axles of the towing vehicle and trailer. The braking force distribution function adaptively adapts to the loading ratios of the towing vehicle. The correct braking pressure is therefore automa-tically applied adaptively to each axle.

At the same time, the integrated trailer control determines the correct bra-king pressure for the towed vehicle. Good compatibility is therefore ensured even with ever changing vehicle combinations. The brake management functions are perfec-

ted by the addition of the retardation control function. This determines possible deviations between the desired and actual retardation and compensates for this in a manner barely perceptible to the driver. All in all, this provides for a braking feeling comparable with that of a car.

■ ABS and ASR The ABS and ASR functions are integrated in the EBS system. Through the use of information which is available only to an EBS unit, such as nominal retardation value, engine torque or the actual braking pressure levels, it has been possible to further improve control quality and comfort when compared with conventional systems.

pedal codebraking force

pedalhysteresis

feeling curvereference

retardation

actuation braking force

retardation controlreference and actual

retardation

balanceof hysteresis

Zeit

braking forcedistribution control

pressure FA, RA

reference retardation

trailer controlpressure pm

reference retardation

actual retardation

Figure 9: Sequence of EBS Functions

TRUCK ABS/EBS


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■ Diagnosis functions The EBS uses a multitude of functionsto test itself. In the event of a mal-function, such as a defective electricalwire, EBS reports it via the relevantwarning device. Such an error can berapidly determined with the assistanceof diagnosis tools. The EBS will alsoat the same time inform you as towhether the issue is actually a wireinterrupt or short circuit. It goes withoutsaying that the EBS also reducesundesirable workshop visits.

Figure 10

TRUCK ABS/EBS


Compatibility between tractor and trailer vehicles

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In order to ensure that there is sufficientbalanced of braking force between tractor and trailer vehicles, ECE R13 andCouncil Directive 71/320 specify mini-mum threshold times for the buildup ofpressure on the coupling head and anassignment of deceleration z to pressureon the coupling head pm.

These rulings were adapted in 1998 forvehicles with EBS. The situation requiredof tractor vehicles is described in ECE-R13 §5.2.1.28.5.


For reasons associated with safety andcost effectiveness, a well-balanced bra-king force between the tractor and trailervehicles is needed at all times. A towingprocess is considered to be well balan-ced if there are only slight differences inthe dead time and activation pressurecharacteristics of the powered vehicleand trailer vehicle and if the braking forces are distributed in accordance withthe loading. The distribution of brakingforce is ideal if the dynamic deceleration

of the related axles of one combination isthe same, i.e. each axle in the combina-tion retards their own dynamic share ofmass in accordance with the decelerationspecified by the driver. This ideal distribu-tion of braking force is shown in Figure 11.

As can be seen in the Figure, the ratio ofbraking force and axle load or the decele-ration angle α of all axles is the same. Insuch instances, ideal coupling forcesexist between the tractor and trailer vehi-cles. With road trains, the towbar forceequals zero. With semitrailer trains, theratio of horizontal force to vertical forceon the fifth wheel ideally corresponds tothe deceleration angle α.

Figure 11: Ideal distribution of braking force between the axles

TRUCK ABS/EBS

ideal retardation: tan αi = = Z ; αi on all axlesa–g



Figure 12: Example basic layout of vehicles

in compatibility band

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Figure 13: Compatibility control function

out. Right from the first instance of bra-king after starting a journey, the differencein braking characteristics is detected and,as is shown in Figure 13, corrected. Itcan be clearly seen that the brakingcharacteristics of the tractor vehicle areadapted to that of the trailer vehicle withregard to the braking pressure on thecoupling head brake (pm). The compari-son is undertaken again with everyinstance of deceleration and further cor-rections undertaken if required. Tractortrailer compatibility is therefore con-tinuously improved.

Although new vehicles with ABS onlyhave to satisfy the compatibility bandwhen fully laden, vehicle manufacturersare attempting to achieve good compati-bility for all loading statuses. As far as istechnically possible, a central band posi-tion is striven for. If combinations arechanged frequently, on average satisfac-tory wear characteristics are thereforeachieved for all vehicles involved.Furthermore, the combination has goodbalanced braking characteristics duringsevere retardation. In reality, more andmore complaints relating to tractor-trailercompatibility are however lodged. Thiscan in particular be explained by the diffe-rent levels of brake lining wear.

Thanks to WABCO EBS and automaticcompatibility control function, these complaints have increasingly become athing of the past. Differences between thebraking characteristics of the tractor andtrailer vehicles are detected by the EBS in the tractor vehicle and automaticallyreduced. This feedback control takesplace in every instance of deceleration.Figures 12 and 13 show the function ofautomatic compatibility control functionon a sample vehicle.

Figure 13 contains the familiar diagramsused for checking compatibility, firstlyshowing the braking characteristics of atypical conventional trailer vehicle and anEBS tractor vehicle by way of basic lay-

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

00 1 2 3 4 5 6 7

pm in [bar]

TM/P

M a

nd T

R/P

R in

[-]

Typical, conventionaltrailer vehicle

EBS tractor vehicle:basic layout

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

00 1 2 3 4 5 6 7

pm in [bar]

TM/P

M a

nd T

R/P

R in

[-]

Typical conventionaltrailer vehicle


EBS tractorvehicle: adapted

to trailer

Compatibilitycontrol function

TRUCK ABS/EBS



Figure 14: Possible control range of EBS-braked tractor vehicle

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was therefore to ensure better brakingbalance between tractor and trailer vehicleeven in the aforementioned instance.Compatibility is improved through theadoption of the following measures:

The automatic compatibility control func-tion always pursues the aim of reducingthe coupling forces between the vehiclesto the ideal level. On this basis, it is per-missible for the tractor vehicle to exit theoriginal band limits of ECE-R13. This isalso necessary when you take intoaccount particularly old or poorly maintai-ned trailer vehicles which only satisfy theintended band situation at lower brakingpressure levels. Figure 14 shows theusual control range of a tractor vehiclewith EBS. This range would however onlybe fully utilised if the trailer vehicle were tomake this necessary.

Further problems may arise if the tractorand trailer vehicles are fitted with differentbrakes. Tractor vehicles are increasinglyfitted with disc-type brakes, whereas themajority of trailer vehicles still have drumbrakes. Since disc-type brakes are sub-ject to less thermal fading than drum bra-kes, the braking force in such brakes fallsless considerably at high temperatures.During long periods of braking, brakingenergy could therefore be increasinglytransferred from the trailer vehicle (fittedwith drum brakes) to the tractor vehicle(fitted with disc-type brakes). One of themain objectives of EBS developments

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

00 1 2 3 4 5 6 7

pm in [bar]

TM/P

M in

[-]


Lower limit(ECE-R 13; 5.2.1.28.5)

Upper limit(ECE-R 13; 5.2.1.28.5)

Possiblecontrol range

TRUCK ABS/EBS



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Figure 15

The best results are of course achievedwhen both tractor vehicle and trailer vehi-cle have WABCO EBS. By transferringadditional data through the standardisedelectrical connection, it is then possiblefor the ideal tractor-trailer balance to beestablished.

A combination of these measures resultsin the retardation characteristics of bothvehicles of the combination being virtuallyidentical in the range of lower brakingpressure levels and highly synchronouswear characteristics are achieved bet-ween the two parts of a tractor-trailer unit.

■ The basic layout of EBS tractor vehicles corresponds to the mean band position of laden vehicles over the entire deceleration range. Retar-dation feedback control therefore allows the assignment of vehicle retardation to the coupling head pres-sure to be re-compared again and again during travel.

■ The basic layout of EBS trailer vehi-cles with WABCO EBS has also been designed for the mean band position as was standard in previous trailer vehicles. The starting point in the EC Band, i.e. the activation pressure, is therefore defined as 0.7 bar.

■ As a result of fitting automatic compatibility control function in the tractor vehicle EBS, differences in the braking characteristics of tractor and trailer vehicles are automatically learnt and minimised. If the differences in braking characteristics are compen-sated for, all wheel brakes of the vehi-cle combination should make contact at the start of braking. The predomi-nance function of the standard trailer control valve is therefore substituted by an electropneumatic adaptation function which is automatically activated when trailers are changed.

TRUCK ABS/EBS



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If you would like more informationabout WABCO Truck EBS, have anyfurther questions or are interested inindividual advice, please contact yourWABCO field service staff directly atone of our Service Centers or callWABCO at +49 (0)511-922-0.

In addition to this, overall wear levels arereduced because the average temperatu-re level of the wheel brakes is reduced asa result of the better distribution of bra-king force. New tractor vehicles with EBSusually have a greater braking force thanprevious vehicles. However, this is notachieved by a steeper characteristicscurve in the EC band, but by increasingthe permanently available supply pressurewith the aid of introduced constant pres-sure systems. The characteristics curve istherefore extended over the 6.5 bar com-puted pressure to 8.5 bar. All trailer vehi-cles, even older ones which are operated

behind these new tractor vehicles, alsoprovide more braking force because theyare supplied with 8.5 bar of constantpressure and around 8 bar is availablewhen the brakes are fully actuated.

The present standard design of trailerbraking systems where z = 0.55 ... 0.6 at pm = 6.5 bar should therefore be retained in principle.

Therefore, it generally makes no difference whether the trailer vehiclesare fitted with drum- or disc-type brakes.

TRUCK ABS/EBS

Braking Situation

partial braking range

stability range

max breaking ratio zsupply 3rd circuit 6.5 bar

partial braking range

stability range

max breaking ratio zsupply 3rd circuit 8.5 barconstant pressure

Towing Vehicle

conventional

EBS

conventional

-

frequently different response pressures

deferred responseof trailer brake

towing vehicle and trailerapprox 0.55 ... 0.6

+

adaptation through towingvehicle EBS

improved response of trailer brake


EBS

o

improved adaptation to towingvehicle by setting parameters

improved response of trailerbrake


++

best possiblesynchronization

best possiblesynchronization


Trailer


19TRUCK ABS/EBS


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WABCO, the vehicle control systems busi-ness of American Standard Companies, isthe world’s leading producer of electronicbraking, stability, suspension and trans-mission control systems for heavy duty com-mercial vehicles. WABCO products arealso increasingly used in luxury cars andsport utility vehicles (SUVs). Customersinclude the world’s leading commercialtruck, trailer, bus and passenger car man-ufacturers. Founded in the US 135 years

ago as Westinghouse Air Brake Company,WABCO was acquired by AmericanStandard in 1968. Headquartered inBrussels, Belgium, the business todayemploys nearly 6500 people in 29 officeand production facilities worldwide. In2003, WABCO contributed US$ 1.358 billion to American Standard’s total salesof US$ 8.568 billion.

Website: www.wabco-auto.com

Vehicle Control SystemsAn American Standard Company

WABCO WORLDWIDE


prosp. truck abs/ebs -e 27.07.2004 10:49 uhr seite ... - · pdf filewabco truck abs/ebs...

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