S a f e t y D r i v e s U s

SYSTEMS ANDCOMPONENTS

For Buses

2

ECAS Elektronische NiveauregelungElectronically Controlled Air Suspension

ESAC Elektronisch gesteuerte FahrwerksdämpfungElectronic Shock Absorber Control

EBS Elektronisches BremssystemElectronic Brake System

ESC Elektronische Überwachung der FahrstabilitätElectronical Stability Control

IVTM ReifendrucküberwachungIntegrated Vehicle Tire Pressure Monitoring

MTS Modulare Türsteuerung

ATC Automatische KlimasteuerungAutomatic Temperature Control

6

10

12

16

18

20

24

Table of Contents

CONTENTS 3

Answers to Your Questions

For many years now, WABCO has beensupplying various units and systemswhich have enabled buses to performtheir tasks reliably and safely. Whereas inthe past these components were straight-forward mechanical items, today’s rangeincludes diverse electronic systems whichare making bus travel even more safe andcomfortable for passengers and driversalike. This document contains a brief description of the systems supplied byWABCO for modern buses.

Please refer to the relevant system booklets for further information.

+800 43 89 22 26 (+800 GET WABCO)

The WABCO premises

Naturally, you can also address yourquestions to our employees, for exampleat WABCO Direct on (49) (1802) 232 337.

The WABCO Service Team can adviseyou on all technical matters and settleany doubts you may have regarding pro-duct selection. In case an item does notfunction as you would expect it to, theteam will be happy to advise you on diagnosis, provide help regarding repairor can put you in touch with expert tech-nicians. Just give us a call.

4 Service DirectWABCO

Safety Drives Us

Taken together, they represent systemsolutions from a single supplier whichmake driving more economical, morecomfortable and more environmentallyfriendly thanks to their active and passivesafety features. Play it safe – check outthe entire range on www.wabco-auto.com.

Innovation and perfection are factorswhich have made WABCO into an inter-national leader in brake and controlsystem technology for commercial vehi-cles. For more than 100 years now, wehave been developing and implementingcreative ideas which bring us closer andcloser to the vision of safe long distancegoods traffic for people and technology.

We deal with the technologies which youencounter safely on the road day in, dayout, perhaps without realizing it. And notjust in buses. This process started withABS and also includes the electronicbrake system and intelligent driving dyna-mics tools. From the conventional gear-box control unit through to componentssuch as compressors, sensors or plugconnectors.

Service Direct WABCO 5

Linking the system with the door controlsystem is just as easy to imagine as acti-vating the bus-stop brake when the busis kneeling or implementing a crush pointguard using signals from external sensorsunder the vehicle. All these potential functions lead to increased safety whenpassengers are getting on and off.

There are additional decisive advantagescompared to previous air suspensionsystems. The significantly reduced airconsumption and the concomitant energysaving not only save costs but also re-duce the environmental impact. It is pos-sible to alter the parameters of the elec-tronic control unit in a wide variety ofways. This allows vehicle manufacturersto adopt a very flexible approach to setting up the system and means theycan easily respond to many wishes oftheir customers.

It goes without saying that ECAS includesa comprehensive safety concept andoffers extensive diagnostic functions.

ECAS is an air suspension systemdeveloped by WABCO which offersincreased driving comfort as well asa wide range of practical functions.

Air suspension systems have been usedin commercial vehicles for more than 50 years now. Above all in the bus sector,air suspension has almost completelyreplaced the classic steel spring. WithECAS, WABCO is offering one of the mostmodern level control systems. ECAS is afurther development of the former air sus-pension systems which only had mecha-nical components controlling their function.Mechanical control has been replaced byan electronic control unit which governsthe valves, amongst other things.

More than 1.3 million commercial vehicles havebeen equipped with ECASsystems from WABCOsince 1986. This figureincludes well over 75.000buses which utilize thebenefits of this maturesystem.

As well as increasing thecomfort of travel for pas-sengers, air suspension

offers a consistent entry height irrespec-tive of the bus load.

In contrast to conventional systems, the clear modular system structure and the fact that the majority of componentsare standardized mean that additionalfunctions can easily be implemented withECAS. For example, the bus can belowered when at a standstill making iteasier for passengers to get on and off. If required, additional controls can beused to set any particular ride heights ina straightforward fashion, for example inorder to negotiate an obstacle, or evenselect a different ride height. The fact thatthe valves have large nominal diametermeans that these level changes are com-pleted within a very short time.

ECAS – Comfort and Safety

6 Electronically Controlled Air SuspensionECAS

example, solenoid valves are used inmany buses which combine all the func-tions in a single valve block.

All that is needed is to connect the fourair lines from there to the bellows and thereservoir pressure line, and to install twoor three electrical cables.

Future ECAS systems will also includecontrolling the traction help on 3-axlebuses as well as a load sensing function.

The setpoint level used for normal drivingis referred to as the normal level. As wellas this basic function, ECAS may alsopossess many other options, dependingon which ECU is used, for example:

■ Kneeling on one side

■ Kneeling of the entire bus

■ Kneeling of one axle

■ Kneeling of one wheel

■ Lifting and lowering the entire bus

■ Changing the level on a selected axle

■ Selecting a 2nd ride height (e.g. to afford greater ground clearance)

■ Compensating for tire deflection

With ECAS electronic control units whichare designed for conventional cabling, allthat is needed in order to use these func-tions is to modify any necessary parame-ter settings and to connect the relevantcontrols. An additional pressure sensor isonly required in order to compensate fortire deflection.

The latest electronic control units areequipped with the SAE J 1939 CAN databus and offer even more functions.Installing ECAS air suspension has beenkept as uncomplicated as possible. For

ECAS offers comfort combined withease of installation and maximumfunctions.

In developing the ECAS air suspensionsystem, WABCO not only focused onachieving a high degree of flexibility in thesystem but also on providing the userwith a product that could be installed inexisting air suspension systems asstraightforwardly and inexpensively aspossible.

The principle of ECAS air suspension hasbeen kept as simple as possible. Inductiveposition sensors measure suspension travel. There are usually two sensors onthe rear axle and one on the front axle.The measured actual values are sent tothe ECU (electronic control unit) and com-pared with the setpoint values. If there isa discrepancy between the values, the airpressure in the corresponding air bellowsis increased or decreased in order to re-establish the specified ride height.

ECAS – System Structure and Funktions

123Basic systems:

1 ECU (electronic

control unit)

2 Position sensor

3 Solenoid valve

4 Air bellows

4

Distance

between

axle and

body

ECAS 7

Different valve blocks may be used inthree-axle buses. Combined with currentCAN electronic control units, they make itpossible to implement a traction helpfunction within the scope of statutoryregulations which operates by increasingthe load on the driven axle and reducingthe load on the trailing axle.

Naturally, it is in most cases possible touse a separate, less complicated valveblock for each axle. In the final analysis,the devices which are used depend onthe function required, the available instal-lation space and the wishes of the parti-cular vehicle manufacturer.

The electronic control unit is the centralcomponent of ECAS air suspension. It isinstalled inside the bus. As well as amicroprocessor, it contains various me-mory modules which store all the dataneeded to operate the system. WABCOsupplies the ECU with a software programstored in the read only memory. There isa configurable memory area available forthe user to make individual adaptations tothe system by setting various individualparameters.

The ECU permanently receives currentdata from the connected sensors. Theseactual values are compared to the pro-grammed setpoints for the set level. If adeviation violates the tolerance range, theECU intervenes and activates the appropriate solenoid valve.

Furthermore, the ECU stores any faultswhich occur during operation. This infor-mation can be evaluated when thesystem is serviced. In addition, routinesfor system self-diagnosis are also provi-ded. These make it even easier for usersto take their ECAS air suspension intooperation.

The solenoid valves used have been spe-cially developed for ECAS air suspension.Several valves are grouped together in ablock. This reduces the volume of thesystem and minimizes the work involvedin connecting it up. The valves have largecross sections which means rapid fillingor venting of the air bellows is assured.

WABCO offers different types of valveblocks. For example, units are availablecombining all the functions needed for a4x2 bus including lateral kneeling in a single item.

ECAS – Components and Their Functions

ECAS can be adapted to almost anytype of vehicle by using differentmodules. It can easily be set up inany constellation.

8 Electronically Controlled Air SuspensionECAS

compensation makes it possible to over-come this problem and ensure a consis-tent entry height and ground clearance.

In three-axle buses, the bellows pressureinformation can be processed by ECASelectronic control units with a CAN databus to implement the traction help function.

In many ECAS applications, one or morepressure sensors are used as well. In thiscase, the electronic control unit gets ananalog signal from the sensor correspon-ding to the pressure in the relevant airbellows. This signal is used for the tyredeflection compensation function (REK),for example. When a vehicle is fully laden,its tyres are compressed more than whenit is unladen. This means the entry heightis reduced although the distance betweenthe axle and the body remains constantthanks to ECAS control. Tyre deflection

The position sensors used by WABCOmeasure the distance between the busbody and the axle. The sensor is moun-ted on the bus frame and is mechanicallylinked to the axle via a lever. The positionof this lever changes depending on theheight of the bus. This changes the levelof inductance in the coil and this value isevaluated by the ECU in defined time slices. In this way, the electronic controlunit continuously receives informationabout the current distance between theaxle and the body.

ECAS 9

ESAC – The Logical Next Step After ECAS

As far back as 1987, WABCO estab-lished a milestone in commercialvehicle air suspension systems withECAS. ESAC is the logical develop-ment of this innovation. This adaptiverunning gear control system was in-troduced in trucks in 1995 in coope-ration with ZF Sachs (shock absorbermanufacturer).

ESAC offers the solution to the conflictinginterests of driving comfort and safety.The properties of the vehicle are influencedby adapting the shock absorber settings.For example

■ vibration comfort

■ forces acting on passengers and cargo

■ carriageway wear

■ roll properties

■ pitch properties

■ handling properties

are set to optimum levels.

The following illustration shows by way ofexample that ESAC leads to

■ roll angles when driving on winding roads and

■ suspension travel on the front axle when braking (brake diving)

which are significantly less than in vehi-cles without ESAC.

without

with

Driving on winding roads

Time (s) 0 1 2 3 4 5 6

1

0.5

0

- 0.5

- 1

20

10

0

- 10

- 20

- 30

- 40

Time (s) 0 1 2 3 4 5

Front – rear suspension travel during braking

10 Electronical Shock Absorber ControlESAC

ESAC = ECAS + Software + Variable Shock Absorbers

■ reduced pitching behavior when braking or sitting back when accelerating away,

■ improved driving comfort by setting the shock absorbers as soft as pos-sible, thereby reducing the forces acting on passengers, cargo and the carriageway.

The ECU parameters and the shockabsorber installation must be adapted tothe particular vehicle in order to achieveoptimum conditions. Subsequent road trials are also essential.

Operation of ESAC is measurable andcan be felt. It offers

■ greater driving stability thanks to reduced rolling when cornering or during major steering maneuvers (e.g. when the driver is forced to change lanes quickly) and thereby also

■ faster driving for vehicles with a high center of gravity (e.g. double-decker buses, buses with gas tanks in the roof) on winding roads,

The ESAC ECU receives sensor informa-tion from other systems via the vehicledata bus (CAN bus), e.g.: transverseacceleration, brake pedal position, acce-lerator pedal position, road speed. Inte-grating ESAC into ECAS offers advanta-ges because it uses the existing sensorsfor measuring the suspension travel. Thesignals for these sensors are used toobtain information about the roll and pitchcharacteristics as well as to recognize the carriageway properties.

In addition,

■ the driver’s actions, e.g. moving the steering wheel, braking, accelerating and road speed,

■ driving conditions such as vehicle load, current ECAS control, vehicle type and, in cargo vehicles, the position of the lifting axle,

■ vehicle responses such as pitching or rolling on poor carriageways, cornering, braking, accelerating or side wind,

■ composition of the carriageway

are used for evaluation purposes.

A special calculation algorithm (fuzzy con-troller) is used to determine the optimumdamping setting and the calculated para-meters are set in the infinitely variableshock absorbers (CDC shock absorbers= Continuous Damping Control, ZF Sachs).

ESAC 11

EBS represents a yardstick for safety andfar exceeds the criteria demanded inlegislation. As well as having redundantbrake circuits, it also implements an exten-sive diagnostic program which immedia-tely informs the driver of any impairmentin the operation of the brakes. It goeswithout saying that ABS (anti-lock brakes)and ASR (traction control) are also inte-grated.

On request, EBS can detect differentlevels of wear on the wheel brakes andcompensate for this at suitable moments.This ensures that all brake pads wearevenly and reduces the number of timesthe vehicle has to be taken into theworkshop. The serviceability of the vehi-cle is increased and the cost/benefit calculation is improved.

The quality of the brake system isprobably the most significant factorin determining how safe a vehicle ison the road.

WABCO has set itself the task of develo-ping a brake system which will make driving even safer and optimize brake padwear. The result is an electronic brakesystem – EBS.

EBS Increases Road Safety andReduces Operating Costs

12 Electronic Brake SystemEBS

vehicle with maximum deceleration evenif there is an electrical power failure.

An extensive diagnostic process monitors the operational status of thebrake circuits and the individual wheelbrakes. Malfunctions are immediately displayed to the driver. They are stored ina fault memory so that workshop staffcan read out the information and localizethe problem.

During normal operation, the brake pres-sures at the front and rear axles are moni-tored by a control unit. If the setpointpressure specified via the electrical circuitis not available, both the front axle brakecircuit and the rear axle brake circuit arecapable of generating the setpoint pres-sure by pneumatic means alone.

The safety concept developed by WABCOtherefore makes it possible to brake the

An ingenious safety concept makesWABCO EBS one of the safest brakesystems in the commercial vehiclemarket. It provides several redundantbrake circuits so that you can be surethe vehicle can always be brakedeven when individual faults occur.

The brake signal transmitter actuated bythe driver controls one electropneumaticcircuit and two separate pneumatic circuits.

EBS – Safety Concept andRedundancy Process

Speedsensor

Brake signal transmitter

Central module

Proportionalrelay valve

ABS valve

Redundant valve

Rear axle modulator

EBS 13

The electrical signals are used for con-trolling the brake system electrically. Thepneumatic signals are only required asredundant backups and, in such a case,they fulfill the same function as performedpreviously by the electrical system althoughwith certain restrictions.

The electrical signal is sent to the centralmodule (1) via the system’s own databus. There, the appropriate setpoint pres-sures for the individual brake cylinders arecalculated with regard to the load level ofthe vehicle. These pressures are thenused for braking the vehicle. The calcula-ted value is sent to the proportional relayvalve and the rear axle modulator.

The system used is referred to as a 2P/1E system. This means one electrical circuit is superimposed ontwo pneumatic brake circuits.

The system’s reservoir tanks are filledwith compressed air. The reservoir pres-sure in two separate circuits is applied to the brake signal transmitter (2), the proportional relay valve (3), the rear axle modulator (5) and the redundant valve (6). In the event that one of the circuits malfunctions, it is still assured that thesecond circuit can brake the vehicle to a standstill.

The brake signal transmitter generatestwo electrical and two pneumatic signals,one of each for the front and rear axles,depending on the pedal setting.

How Does EBS Work?

1

3

6

54

78

2

14 Electronic Brake SystemEBS

EBS

TRANSMISSION ECAS RETARDER

ENGINE

controlled by the corresponding electro-nic control unit. As a result, the brake canstill be used under full load and there isno risk of loss of braking in the vehicle.The failure of the electronic control unit isindicated to the driver on a display, allo-wing the driver to adapt to the alteredbraking characteristics of the vehicle.

Thanks to extensive diagnostic functions,the central module continuously receivesinformation about the current status ofthe brake system. Faults are immediately

detected when they occur. They are thenlogged and signaled to the driver. A diagnostic memory can be read out whenthe vehicle is inspected in the workshop.This enables faults to be picked up andrectified as soon as possible.

control unit via a CAN interface. Thisreduces the engine output accordingly,which ensures the acceleration of thevehicle is controlled.

Wear sensors (8) detect the abrasion ofthe individual brake pads. Different levelsof wear are evaluated in the central mo-dule and this information is incorporatedin the setpoint calculation for the individualbrake cylinder pressures. If the setpoint islow, the brake pressure is slightly shiftedaway from pads where there is greater

wear to ones which have worn down less.This reduces the wear of the pads andimproves the serviceability of the vehicle.

The pneumatic signals from the brake signal transmitter are not considered further in normal circumstances. Only ifthe electronic control unit fails are theusual electrical signals replaced by pneu-matic ones. The part of the brake systemdivided into two circuits largely corres-ponds to the setup in a conventional bus.

The brake signal transmitter sends thesetpoint pressure value to the proportionalrelay valve and, via the second circuit, tothe redundant valve. These control pres-sures pneumatically operate the samesolenoid valves which would normally be

The rear axle modulator contains an inde-pendent electronic control unit which isprogrammed with the control algorithmsfor the rear axle wheels. The algorithmsfor the front axle are handled by the central module itself.

The respective electronic control unitsallow the air pressure to flow into the indi-vidual brake cylinders (4) via proportionalsolenoid valves. Sensors measure theactual value and send this back to theappropriate control algorithms.

Inductive sensors measure the speed of the individual wheels. As a result, anytendency of the front axle to lock is picked up at an early stage by the centralmodule and of the rear axle by the axlemodulator. The brake pressure for thecorresponding cylinder is reduced by theABS valve (4) and the axle modulator. Aspart of this process, various control algo-rithms ensure that the vehicle remainsstable and, if possible, is braked with thespecified setpoint.

Traction control can be integrated usingthe speed sensors, without the need foradditional hardware. If there is any indica-tion that one or more wheels are spin-ning, the central module detects this factand passes the information to the engine

EBS 15

ESC is an expansion of the EBS electronic brake system. The systemcan detect when physical limits havebeen reached and promptly inter-venes in the control of the brakes.

After EBS, ESC sets the next milestone in the control of electrical brake systems.While EBS prevents the wheels from locking, ESC goes one step further.

When negotiating tight bends or makingsudden steering maneuvers, there is arisk that the driver could lose control ofthe vehicle. The higher a vehicle’s centerof gravity, the greater the risk that it willbe unable to make it round that tightbend, veer or even tip over during stee-ring maneuvers. Under such situations,pressing the brake pedal is a natural res-ponse – although not necessarily onewhich will improve matters.

The ESC electronic stability control inter-venes in such cases. It specifically brakesindividual wheels, reduces the input torque and keeps the vehicle stable. Indoing so, ESC goes right up to the limitsof what is physically possible. Often, ESCcan prevent a serious accident and there-fore represents a guardian angel for thedriver, passengers or cargo.

In practice, extreme situations such asthese occur again and again. With ESC,the possible consequences can be

avoided. EBS with integrated ESC electronic stability control guaranteesoptimum braking of the vehicle in everysituation.

The system makes a further contributionto safety and, by preventing damage,also plays its part in maintaining the effi-ciency of a vehicle or a fleet.

ESC – Brake Control for Physical Limits

16 Electronic Stability ControlESC

additionally if necessary. This makes itpossible to take the bend without anaccident. Of course, ESC control cannotgo beyond the limits of what is physicallypossible. It will prevent the vehicle fromtipping over if it is being driven too fast;however, the vehicle's ability to negotiatethe bend can only be guaranteed as longas the physical limits are not reached.

In the development of ESC, particularemphasis was placed on ensuring thatthe system could easily be integrated inWABCO EBS brake systems. The elec-tronic control units communicate inaccordance with the CAN bus specifica-tion so they can be integrated into theoverall vehicle communication network.

towards the outside of abend. The rear wheel on theinside of the bend and, ifnecessary, the inside frontwheel as well are braked inorder to keep the vehiclestable.

An oversteer situation isdetected if the vehicle iscornering more tightly thanthe direction set by the dri-ver. Stabilization is achievedby braking the front wheelon the outside of the bendand, if necessary, the out-side rear wheel as well.

These two phenomena are more likely to occur on wet or muddy road surfaces,in other words when the coefficient of friction of the carriageway is low. Undergood road conditions, the coefficient offriction of the carriageway is higher andthe risk of oversteer or understeer isreduced. However, ESC can come inhandy even then.

Frequently, drivers try to take corners toofast, particularly at motorway exits. Onroad surfaces with a high coefficient offriction, this can lead to the vehicle tip-ping over in the worst-case scenario. Thetransverse acceleration sensor in the ESCsystem can detect such a situation andintervene. The control system reduces theengine torque and brakes the vehicle

Ideally, ESC should never have to operate. However, experience hasshown that this is not the case inpractice.

ESC is triggered whenever the vehicledoes not follow the steering angle set bythe driver, e.g. in understeer or oversteersituations. In addition, ESC can tell if thevehicle is threatening to tip over whencornering too fast.

The ability to recognize such a situation inthe vehicle initially calls for various sen-sors. The steering direction set by the dri-ver is picked up by a steering angle sen-sor. This information is compared with theactual situation in the vehicle.

Two more sensors detect the actual situ-ation in the vehicle. A rate of yaw sensormeasures the turning motion of the vehi-cle about its perpendicular axis while atransverse acceleration sensor measuresthe acceleration of the vehicle at rightangles to the direction of travel. This in-formation is evaluated in the stabilitymodule and compared with the setpointvalues.

If there is any discrepancy between therequired driving direction and the real dri-ving direction, ESC control takes effect. Itintervenes in the brake control and enginecontrol systems.

Understeer causes the vehicle to veer

without ESC with ESC

Corneringof a trailer

Economy

Vehiclesafety

ABS/ASR for tractiveunits and trailers

EBS – For tractiveunits and buses

EBS – For trailers

ESC – ElectronicStability Control

ACC – AdaptiveCruise Control

ESC 17

When and How Does ESC Operate?

In addition, IVTM means there is no lon-ger any need for staff to go to the timeand trouble of checking the air pressuremanually directly at the tire inflating valve.With IVTM, the pressures of all tires canbe displayed on a dashboard display atthe push of a button.

Ease of installation and straightforwardoperation make IVTM the ideal system forretrofitting in buses. It makes a majorcontribution to the safety and mobility ofthe vehicle as well as significantly lowe-ring operating costs.

WABCO has cooperated withMichelin to develop a tire pressuremonitoring system which has beenspecially developed for use in commercial vehicles.

More than a quarter of all commercialvehicle accidents come down to tiredamage, making tires the second highestcause of accidents. One in two commer-cial vehicle tires on the road is not infla-ted adequately – and this not infrequentlyhas serious consequences. Only in about15 % of cases does a tire fail due to sudden and extensive damage. 85 % oftire failures are preceded by a slow pres-sure loss which goes unnoticed by thedriver, in particular in a commercial vehicle.

IVTM measures the tire pressure at regular intervals and warns the driver ingood time before any critical pressureloss occurs. This enables the risk of asudden tire failure to be significantly reduced.

As well as all the credit on the safetyside, avoiding even a single breakdownand all the associated costs means thatthe system has usually paid for itself.

However, IVTM also saves costs in normal operation. A tire which is alwaysinflated to the optimum pressure presentsa lower rolling resistance and thereforecuts the vehicle's fuel consumption.Furthermore, the service life of the tire issignificantly extended.

IVTM – The Tire Pressure Monitoring System for Commercial Vehicles

Fuel

co

nsum

pti

on

in p

erce

nt

Deviation from nominal tire pressure in percent

Red

ucti

on

in s

ervi

ce li

fe in

per

cent

Deviation from nominal tire pressure in percent

10

8

6

4

2

0

-2

-4

-60 -50 -40 -30 -20 -10 0 10 20 30 40 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30

0

-5

-10

-15

-20

-25

-30

-35

-40

-45

-50

18 Integrated Vehicle Tire Pressure MonitoringIVTM

Under-pressure

Over-pressuer

Under-pressure

Over-pressuer

a diagnostic interface. In the same way, it is possible to read out operating andsystem faults stored in a fault memory,which means that any problems canquickly be located and rectified.

WABCO is already a leading systemssupplier of electronic safety systems to allmajor commercial vehicle manufacturers.This product represents a further expan-sion to WABCO’s product range and is adecisive safety component in commercialvehicles. Furthermore, IVTM makes animportant contribution towards achievinga significant reduction in vehicle operatingcosts and the time it spends off the road.

The module is connected to the inflatingvalve by a hose pipe. This means there isno need to take the tire off the rim whenfitting the system. Also, there is no needto reconfigure the system when changinga wheel or a tire.

The wheel module contains a pressuresensor and the values it measures are

IVTM – Mode of Function and Components

regularly sent to the IVTM ECU via a 433MHz radio link. The electronic control unitemploys an evaluation algorithm speciallydeveloped for commercial vehicle tires by Michelin experts. It detects criticaldeviations from the nominal tire pressu-res. The driver gets an audible warningwhile a display shows which is the wheelwith the low pressure and what the pressure value is.

In total, one ECU is able to monitor up to twelve wheels. The antenna integratedin the ECU ensures that the pressure signals are picked up clearly, even in 18 meter long articulated buses.

The system can easily be configuredusing a notebook computer connected to

A wheel module is mounted on thewheel studs of every wheel in order to monitor the tire pressure permanently.

IVTM system structure

Electronic control unitWheel modules Display

IVTM 19

MTS – The Further Development ofElectronic Door Control (ETS)

With MTS, WABCO is offering a doorcontrol system which breaks newground in terms of safety and opera-ting comfort.

This door control system has been available from WABCO since 1998. Today(2002) more than 30.000 systems areinstalled. MTS is the successor to ETS(electronic door control). The ETS system

has been used successfully in about30.000 busses since 1987. Lengthy ex-perience with the system made it possibleto expand its functions as well as makingit even safer and easier to use. As well as conventional cabling, users can nowchoose to have a CAN interface for con-trolling the doors. The system is com-patible with all types of door, with electricor pneumatic drive. A simple teach-inprocedure initializes the entire controlsystem extremely quickly and makes anycalibration work unnecessary. The ETSvalve and cylinders have also been re-worked and their function made even moreeffective. Sensors register movements ofthe door panels and thereby permit theelectronic control unit to trigger safetyfunctions in hazardous situations.

It goes without saying that the systemincorporates a diagnostic function whichcan be called up via the CAN bus or a K-line.

20 Modular door controlMTS

The valve/cylinder combination offered byWABCO incorporates an ingenious circuitto prevent the door from slamming shutuncontrollably. This can be caused by asudden pressure buildup in the cylinderand it is only possible to prevent it fromhappening by means of carefully thought-out return procedures.

The teach-in procedure for MTS can becarried out extremely quickly and withoutdifficulty by users. The first electroniccontrol unit stores the limit positions ofeach door when the doors are movedthrough their full travel range on oneoccasion. In addition, the system detectshow many electronic control units areinstalled and what are the operatingmodes of the doors.

The diagnostic function allows all of theteach-in parameters to be checked viathe vehicle’s CAN or the K-line. Further-more, faults can be detected and located.

A sensor is installed in each door panel.This sensor can either be a potentiometermounted directly on the swivel post or, ifelectric drive is employed, an encoderintegrated in the motor. This sensor pro-vides a continuous stream of informationto the electronic control unit concerningthe current door position. If the currentposition does not match the position setin the electronic control unit, the systemimmediately detects this fact and stopsthe movement of the door. The door canthen be moved to the required limit posi-tion manually or by repeating the controlcommand.

The door can also be moved manuallyafter the emergency tap is operated.However, this condition cannot be revokedby repeating the control command. It isfirst necessary to return the emergencytap to its original position.

A clever system layout means thenumber of components has beenreduced. This produces costs savingsand also means that the greatestnumber of door types can be supported.

MTS requires an electronic control unit on each door. The unit on the first doorsends control commands to the otherelectronic control units via the system’sCAN bus. The first electronic control unitcan be connected to the vehicle's CANbus or, alternatively, to a conventionalwiring system. In addition, the first elec-tronic control unit manages all the para-meter data needed for operating thedoors used. As a result, it is possible toreplace all other door electronic controlunits without any problems.

It is possible to use up to five electroniccontrol units in an MTS system. EachECU is responsible for one door or twodoor panels of any design. The centralsignal processing system effectively redu-ces the number of components neededwhile the system's CAN bus cuts downthe amount of cabling work required.

2

2 12 1

2

1 1

2 1

2

1

1 1

1

MTS 21

MTS – Fewer Components,Greater Flexibility

MTS Door Valve with Electrically Operated Limit Position Damping

Door closing – no damping Door closing – with damping

2

31

2

31

a

b

a

b

A BA BA BA B

22 Modular door controlMTS

Emergency tab closed open Emergency tab closed open

position. Valves 2 and 3 are energized (valves 1 and 2 for the closing movement). This means the pistons remain in their current position, although the diameter of the outlet opening is additionally reduced.

■ The electronic control unit immediately switches to opening if an obstacle is detected when the door is closing.

The zero-force function is also used for emergency tap reset.

When the emergency tap is operated,reservoir pressure is initially directed be-tween the two pistons and thus the twoouter limit positions of the pistons are set.The cylinders are also vented. When theemergency tap is reset, reservoir pressureonce again acts on the valve and bothcylinder chambers are pressurized due tothe initial position of the pistons. As aresult, the door cannot move inadver-tently.

■ First of all, solenoid valve 3 is activated with a brief electrical pulse.

■ This means the reservoir pressure is directed to piston B in good time and both pistons are moved to their left-hand limit position.

■ The reservoir pressure now flows past the narrow point of the piston and into chamber a of the cylinder.

■ The door opens.

■ The electronic control unit detects if this procedure is delayed or stopped by an obstacle in the door, and it energizes solenoid valve 2.

■ The pistons are moved to their outer limit position and the full reservoir pres-sure flows into both cylinder chambers. This means there is no force acting on the door and it can be moved manually.

■ A new control command from the elec-tronic control unit can be directly con-verted into the required movement.

■ The electronic control unit also detects when the door is reaching its limit

The tried-and-tested door valve usedin ETS could scarcely be improved,and was initially adopted “as is”during the development of MTS. Theonly modification involved the air outlet control of the cylinders.

The valve is operated by three solenoidpilot valves. Depending on the energiza-tion of the solenoids, pistons A and B aremoved to one or another of their limit po-sitions and the reservoir pressure accor-dingly flows through the narrow point ofthe piston into chambers a and/or b ofthe cylinder. The electronic control unitmonitors the movement of the door anddetects when it is approaching its limitposition. The flow volume of the outlet airis reduced before the door reaches itslimit position, and therefore the speed ofthe door's movement is reduced. As aresult, it has been position to dispensewith the damping elements formerly inte-grated in the cylinders and to improve the functions of the system even more.

The way in which the valve and the doorcontrol operates can be made apparentby examining an opening cycle:

MTS 23

ATC – Heating, Ventilation and ClimateControl for City Buses and Coaches

In a luxury double-decker coach, how-ever, it is possible to use up to six substations with additional sensors and actuators connected to them.

NTC sensors connected to the controlelement and the substations record awide range of temperatures. The control-ler in the control element processes thesensor values and sends appropriatecontrol signals to the actuators such asflap servomotors and finely adjustablelinear water valves. In this way, the tem-perature in the vehicle can be kept at theset level.

The climate of the passenger compart-ment is controlled fully automatically andcan be switched on or off at the controlelement. The driver's area can be set andcontrolled in accordance with the driver’spersonal requirements.

Depending on the expansion level, ATCoffers a high level of comfort in terms ofventilation and air conditioning throughoutthe entire vehicle. At the same time, itkeeps the windows clear for the driverand passengers.

ATC offers heating, ventilation andclimate control for city buses andcoaches, involving the minimum ofdistraction for the driver.

Nowadays, climate control is part of thestandard equipment for coaches, andincreasingly in city buses too. In ATC,WABCO has developed a climate controlsystem which can be adapted to particu-lar applications by means of various con-trol elements and expansion levels. ATCoffers comfort for the driver and passen-

gers. As well as the control element, thesystem contains up to eight substationswhich are connected together via thesystem’s CAN bus. For example, the con-trol element can be operated as a stand-alone unit in a city bus, controlling theblower speed and heating temperature(air conditioning) for the driver’s area andthe passenger compartment.

24 Automatic Temperature ControlATC

Pressing the Smog button shuts off thefresh air supply to the entire bus. The roofhatches and fresh air flaps are closed andthe air inside the bus is recirculated. These settings are automatically reversedafter a time interval which can be set inthe parameters.

The “Reheat” function of ATC has provedto be very useful. In this mode, the freshair is initially cooled down using the airconditioning system before being heatedup again. This process lowers the moistu-re content of the fresh air and thereforereduces the degree of misting of the windows.

Depending on the potentiometer setting,the air is directed to the footwell, to thefootwell and the windscreen or only to thewindscreen. Air is also directed solely tothe windscreen in the “Defrost” position,however in this case the air temperatureand air flow are both set to maximum.

The coach system also offers additionalsetting options to enable the climate inthe passenger compartment to be setmore easily. Nominal temperature andblower output values can be set withgreat accuracy using rocker switches,and the values are shown on a centraldisplay in the dashboard. The air condi-tioning system can also be switched on and off at the control element.

As well as climate control, the ATCsystem developed by WABCO offerslots of extras for the user whichprove to be extremely useful in every-day service.

The ATC system for city buses is designedso the driver only needs to set the climatecontrol for the driver's area. The parame-ters for the temperature in the passengercompartment are set once and then thistemperature is maintained constantly. Of course, it is possible to alter the nomi-nal value subsequently, but this is notessential.

Using the two potentiometers on the control element, the driver can set the airsupply temperature and the speed of theblower in the driver’s area. There is a thirdpotentiometer for controlling the flaps atthe outlet nozzles of the air supply.

ATC Controls More Than Just the Climate

ATC 25

The maximum temperature at the air out-let from the heaters is limited to a valueset in the parameters, e.g. 60 °C, in orderto provide heating with a comfortabletemperature. An auxiliary heater can beinstalled in order to achieve a requirednominal temperature even when the out-side temperature is very low. This is alsoswitched on and off at the control ele-ment. In coaches, the auxiliary heater canalso be activated using the integrated 7-day timer switch, and therefore opera-ted as an independent heater.

The control element can be linked to thevehicle communication network via aCAN interface. It obtains information suchas the cooling water temperature, road speed and outside temperature in order to achieveoptimum temperature control. In addition,signals are received about door move-ments. The speeds of all blowers arereduced when the last door is being clo-sed in order to make it easier for the doorto close.

As well as these functions, the ATCsystem also supports diagnostic func-tions. There are various possibilities forsetting parameters while, in addition,faults can be read out of a memory andlocated. Also, practical help for installationwork can be called up.

Fresh air

Recirculatingor heated air

Heated air, fresh air or air conditioning air

Recirculating air

Exhaust air

26 Automatic Temperature ControlATC

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WABCO is an international group of companies and co-operation partnerslocated in Austria, Belgium, Brazil, China,Czech Republic, France, Germany, GreatBritain, Hungary, India, Italy, Japan,Korea, Poland, Russia, South Africa, Spain,Sweden, Switzerland, The Netherlands, USA and other countries.

Our detailed communication connections are in the Internet under:

www.wabco-auto.com E-mail: info@wabco-auto.com

Vehicle Control SystemsAn American Standard Company

WABCO WORLD-WIDE