Electronic Transmission Control ETC 2004

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Published by:© Robert Bosch GmbH, 2004Postfach 1129,D-73201 Plochingen, Germany.Automotive Aftermarket Business Sector,Department AA/PDT5.Product Marketing,Diagnostics & Test Equipment.

Editor-in-chief:

Dipl.-Ing. (FH) Horst Bauer.

Editorial staff:

Dipl.-Ing. Karl-Heinz Dietsche.

Authors:

(in alphabetical order)Dipl.-Ing. D. Fornoff(Development AST Actuators),D. Grauman(Sales AST Transmission Actuators),E. Hendriks(Product Management CVT Components),Dipl.-Ing. T. Laux(Product Management Transmission Control),Dipl.-Ing. T. Müller(Product Management Transmission Control),Dipl.-Ing. A. Schreiber(Development ECUs),Dipl.-Ing. S. Schumacher(Development Actuators and Modules),Dipl.-Ing. W. Stroh(Development ECUs)and the editorial team in co-operation withthe responsible technical departments atRobert Bosch GmbH.

Unless otherwise indicated, the above are

employees of Robert Bosch GmbH, Stuttgart.

Reproduction, duplication and translation of thispublication, either in whole or in part, is permis-sible only with our prior written consent andprovided the source is quoted.Illustrations, descriptions, schematic diagramsand the like are for explanatory purposes andillustration of the text only. They cannot be usedas the basis for the design, installation, or speci-fication of products. We accept no liability forthe accuracy of the content of this documentin respect of applicable statutory regulations.Robert Bosch GmbH is exempt from liability,Subject to alteration and amendment.

Printed in Germany.Imprimé en Allemagne.

1st Edition, March 2004English translation of the 1st German editiondated: June 2004(1.0)

Imprint


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ElectronicTransmission Control ETC

Robert Bosch GmbH


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4 Transmissions forMotor Vehicles

4 Transmission in the Drivetrain6 Transmission Requirements7 Manual Transmission8 Automated Shift Transmission

(AST)12 Dual-Clutch Transmission (DCT)13 Automatic Transmission (AT)22 Continuously Variable Transmission

(CVT) Toroid Transmission

30 Electronic Transmission Control30 Drivetrain Management31 Market Trends32 Control of Automated Shift

Transmission36 Control of Automatic

Transmissions52 Control of Continuously Variable

Transmission

54 Sensors54 Application in Motor Vehicles55 Transmission Speed Sensors56 Micromechanical Pressure

Sensors59 Temperature Sensors60 Position Sensors

61 Sensor-Signal Processing

62 Electronic Control Unit (ECU)

62 Operating Conditions, Design,Data Processing

68 ECUs for Electronic TransmissionControl

75 Thermo-Management77 Processes and Tools Used in ECU

Development78 Software Development

92 Electrohydraulic Actuators92 Application, Function,

and Requirements93 Design and Operating Concept94 Actuator Types

103 Simulation in Development

106 Modules for TransmissionControl

106 Application107 Module Types

111 Technical Terms andAbbreviations

111 Technical Terms114 Abbreviations

Contents


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The drivetrain is designed to transfer the energy generated by the engine to the wheelsof the vehicle with the minimum possible loss of energy. To do this, the drivetraincomponents – engine, transmission, clutch, and brakes – must be matched as well aspossible. The best results are achieved using electronic transmission control (ETC).Electronic transmission control can coordinate overall control of the individualsystems and components with convenient and energy-saving shifting strategies.

The automated shift transmission (AST) is a manually shifted transmission with elec-

tric or electrohydraulic actuators for operating the clutch and the gearshift mechanism.In conjunction with suitable shifting strategies, the AST is so economical that it is now used in the first 3-liter automobile.

Gearshift sophistication (ease of shifting) can be increased with a dual-clutch trans-mission (DCT). This transmission prevents interruption of the tractive force duringgearshift operation. The advantageous fuel consumption values are retained.

New electronically controlled automatic transmissions (AT) open up a whole new field of potential for reducing fuel consumption by selecting the best operating point.They can also lock up the hydraulic converter within broad ranges. Their differentshifting strategies can even shape the character of the vehicle – from economical tosporty requirements.

The continuously variable transmission (CVT) also offers a high degree of conve-nience in conjunction with favorable fuel-consumption figures. Its electronic controlsystem can operate the engine in either the optimum fuel-consumption range or theultimate high-performance range.

This volume of the Automotive Engineering Technical Know-How series introduces

you to the various transmission types together with the accompanying variants of elec-tronic transmission control and its components. The table of contents and the detailedindex of technical terms will help you to find the individual subject areas, and the listof abbreviations sets out the abbreviations commonly used in the field of electronictransmission control.


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Transmissions for Motor Vehicles Transmission History 1 5

1 Engine2 Belt drive to

intermediate shaft3 Bevel gear4 Crankshaft with

flywheel5 Chain drive to

powered axle

1 2

5

3 4

Transmission History 1

Benz patent motor carriage from 1886 withbelt and chain drivesWhen Daimler, Maybach, and Benz launchedtheir first road vehicles, pioneers of motivepower engineering had already developed themachine parts required for power transmissionto a considerable extent. Names such asLeonardo da Vinci, Dürer, Galileo, Hooke,Bernoulli, Euler, Grashof, and Bach had playeda significant role in these developments.

Power transmission in an automobile mustguarantee the functions of starting and engine-speed and torque conversion for forward andreverse travel. These functions call for actuatorsand shifting elements which intervene in thepower-flow and perform engine-speed andtorque conversion.

The first operational Benz patent motor car-riage appeared in 1886. It was the first three-wheel vehicle to be conceived in its entiretyspecifically for motorized road traffic. It may well

have had just one gear, but it did not have astart-up clutch. In order to get the carriage mov-ing at all, it was necessary to push it or crank itwith the flywheel.

A single-cylinder four-stroke engine with adisplacement of 984 cc and a power output of0.88 HP (0.65 kW) served as the drive unit forthis Benz three-wheeler.

Benz utilized the following machine parts totransfer the motive force of his engine to theroad:

The end of the engine’s crankshaft held theflywheel, which ensured that the engine ran moresmoothly and which could also be used to crank the engine. Since the engine was built over therear axle, a bevel gear arranged at right anglestransmitted power in a small space to a beltdrive, which reduced the rotational speed slightlyto an intermediate shaft. Finally, a chain drive re-duced the speed further to the powered axle.

The belt and chain drives dating from the ori-gins of the automobile were gradually replacedby a gear train. But, today, they are experiencinga renaissance in the form of the continuouslyvariable transmission (CVT). A CVT transmis-sion consists of a variator with two V-pulleysand a flexible steel push-belt. As soon as thepressure of the transmission oil displaces themoving V-pulley halves, this changes the posi-

tion of the steel push-belt between the two pul-leys and with it the gear ratio. This technologyallows continuous adjustment of the gear ratiowithout interrupting the power transmission andoperation of the engine in its most favorablepower range.

Benz patent motor carriage from 1886 with its machine parts (source: DaimlerChrysler Classic)

æ U T S 0 3 5 5 Y

æ U T S 0 3 5 4 Y


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Transmission RequirementsEvery motor vehicle places quite specificdemands on its transmission. Each of thetransmission types differ in terms of designand associated features. The objectives ormain points of emphasis in transmissiondevelopment can be divided into the follow-ing categories:

comfort and convenience,fuel consumption,

driveability,installation space, andproduction costs.

Comfort and ConvenienceEssential requirements in terms of comfortand convenience are, in addition to a smoothgear change without engine-speed jumps,comfortable gearshifts irrespective of engineload and operating conditions, and a low level of noise. Nor should there be any loss of

convenience over the entire lifetime of thetransmission.

Fuel ConsumptionThe following transmission characteristicsare essential in keeping fuel consumption aslow as possible:

large transmission-ratio range,high mechanical effi-ciency,“intelligent”shiftingstrategy,low power forcontrol,low weight, andstand-by control,torque converterlockup clutch,low churning losses(resistance of thetransmission oilpassing through thegears), etc.

DriveabilityThe following transmission functions ensuregood driveability:

shifting points adapted to the relevantdriving situation,recognition of the type of driver,high accelerating performance,engine braking action during downhilldriving,suppression of gear change duringcornering at high speed, and

recognition of winter road conditions.

Installation SpaceDepending on the type of drive, there aredifferent stipulations for the space available:

Thus, the transmission for a rear-wheeldrive should be as small as possible in termsof diameter, while the transmission for afront-wheel drive should be as low as possi-ble in overall length. There are also precisely defined specifications for satisfying require-

ments in a crash test.

Production CostsThe preconditions for the lowest productioncosts possible are:

production in large-scale numbers,simple control-system layout andautomated assembly.

6 Transmissions for Motor Vehicles Transmission Requirements

Fig. 11 Input shaft2 Main shaft3 Shifting elements4 Countershaft5 Output shaft

1 2

4

53

Manually shifted transmission (section, source: DaimlerChrysler)1

æ U T S 0 2 1 9 Y


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Manual TransmissionApplicationManually shifted transmissions are the sim-plest and most inexpensive transmissions forcar drivers (final users). For this reason, they still dictate the market in Europe.

Due to increasing engine performance andhigher vehicle weight together with decreas-ing c d values, 5-speed manual transmissions

have been superseding the previously domi-nant 4-speed manual transmissions sincethe beginning of the 1980s. And now the6-speed transmission is virtually standard.

This development provided, on the onehand, safe starting and good accelerationand, on the other hand, lower engine speedsat higher road speeds, and thus reduced fuelconsumption.

DesignThe design of a manually shifted trans-mission (Figures 1 and 2) incorporates

a single-plate dry clutch as the powertake-up element and for interrupting thepower-flow during gear changes,gears mounted on two shafts,positive clutches as shifting elements,actuated via a synchronizer assembly.

Features

The main features of the manualtransmission are:

high efficiency,compact, light design,economical construction,absence of comfortable operation(clutch pedal, manual gear changing),driver-dependent shifting strategy,interruption of tractive force duringgearshifting.

Transmissions for Motor Vehicles Manually Shifted Transmission 7

1s t gea r

2nd ge a r

3r d gea r

4th gear

5th gear

Rever se gear

Power-flow in a standard drive (5-speed transmission)2

æ U T S 0 2 2 0 E


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Automated ShiftTransmission (AST)ApplicationAutomated shift transmissions (AST), orautomated manual transmissions (AMT),help to simplify transmission operation andincrease economic operation. They are anadd-on solution to conventional manualtransmissions. The previously manualgearshifts are now performed by pneumatic,

hydraulic, or electrical means. Bosch favorsthe electrical solution described below (Figure 1).

Design and Operating ConceptThe AST is made possible by electronicclutch management (ECM), supplementedby two servomotors (selection and shiftingmotors) for selection and shifting. Depend-ing on the system used, the required electri-cal control signals can be issued directly from

a shift lever actuated by the driver or from anintermediate electronic control system.

Thanks to the electric-motor-drivenactuators of the AST concept, it is possibleat little expense to achieve automation of thetransmission complete with the associatedincrease in convenience. An important argu-ment for the transmission manufacturershere is the ability to reuse existing produc-tion facilities.

In the simplest system, the mechanical link-age is merely replaced by a remote switch.The shift lever (tip lever or switch with Hgearshift pattern) just outputs electricalsignals. Power take-up and clutching areperformed as in the manual transmission,partly linked to a gearshift recommendation.

In fully automatic systems, the transmissionand power take-up element are automated.A lever or tip switch is the control element

for the driver. The driver can skip the auto-matic facility with a manual setting or with+/– buttons. Automatically controlling amultispeed transmission requires a complex shifting strategy which also takes into ac-count the present total running resistance(determined by load and road profile).

To support the synchronization process inthe interruption of tractive force during thegearshift operation, an electronic engine-control facility (depending on the shift type)

automatically closes the throttle briefly.

The design of automated shift transmissionsis characterized by the following features:

basic design as for manual transmissions,actuation of clutch and gear change by actuators (pneumatic, hydraulic orelectric-motor-driven), andelectronic control.

Features

The main features of the automated shifttransmission are:

compact design,high efficiency,adaptation to existing transmissionpossible,more competitively priced than automaticor CVT transmissions,simple operation,suitable shifting strategies for achievingoptimum fuel consumption and bestconsumption figures, andinterruption of tractive force duringgearshifting.

8 Transmissions for Motor Vehicles Automated Shift Transmission (AST)

RND

with ASTConventional

Declutching replaced by Clutch servo unit

Selection andshifting motors

replaced bySelectionand shifting

Automated shift transmission as add-on solution formanual transmission

1

æ U T S 0 2 2 1 E


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Examples of AST in Series ProductionAST Electric-Motor-DrivenOpel Corsa (Easytronic, Figure 2a),Ford Fiesta (Durashift),

AST with ElectromechanicalDrum TransmissionSmart.

AST ElectrohydraulicDaimlerChrysler Sprinter(Sequentronic, Figure 2b),BMW-M with SMG2,Toyota MR2,Ford Transit,VW Lupo,Ferrari, Alfa,BMW 325i/330i.

Transmissions for Motor Vehicles Automated Shift Transmission (AST) 9

Fig. 2a Easytronic

(Opel Corsa)b Sequentronic

(DaimlerChrysler)1 Transverse

transmission2 Clutch servo unit

with integrated ECU3 Tip lever4 Shifting/

selection motor5 Longitudinal

transmission6 Shifting/

selection motor7 Shift lever

b

6 75

1

2 3

4

a

Series examples of AST (sources: Opel, DaimlerChrysler)2

æ U T S 0 2 2 2 Y


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AST ComponentsThe components of an AST must be able towithstand high loads in terms of tempera-ture, leak-tightness, lifetime, and vibration.Table 1 lists the most importantrequirements.

Clutch Servo UnitThe clutch servo unit (Figures 4 and 5) withintegrated electronic control unit (ECU) (Fig-ure 3) serves to actuate the clutch. The entire

AST function is also incorporated in the elec-tronics.The clutch servo unit comprises

integrated ECU,housing with cooling function,DC motor,helical gear,push rod, andreturn spring.

DC Motors for Gear Selectionand EngagementThere are two types of DC motor for AST(Figures 5 and 6):

The selector motor has a short

response time.The shift motor has a highrotational force.

The transmission types for the selector motorand the shift motor can be set up symmetri-cally (left and right), and different mountingbores are also possible. The layout of the6-pin connector can be chosen as desired.

10 Transmissions for Motor Vehicles Automated Shift Transmission (AST)

Fig. 31 Monitoring computer2 Flash memory3 Microcomputer

(16-bit)4 Travel-sensor

contacts5 DC converter6 Driver stage for

electric motors7 Bridge driver

Table 1

Fig. 411 Actuator motor12 ECU13 Worm14 Worm gear15 Worm-gear shaft

16 Pin17 Position sensor18 Compensation

spring19 Push rod10 Master cylinder

Demands placed on AST components1Temperature 105°C permanent

125°C brieflyWinding andcommutation system

Leak-tightness Steam jetSplash waterTransmission fluid

Operating life 1 million shift cyclesVibrations 7...20 g sine

Armature mountingElectrical / electroniccomponentsElectronics PCB

10 9 8 7 6

1 2 3 4 5

Clutch servo unit (section)4

æ U T S 0 2 2 4 Y

2

1

3 4 5 6 7

Integrated ECU (view)3

æ U A E 0 9 4 9

- 1 Y


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Dual-Clutch Transmission(DCT)ApplicationDual-clutch transmissions, DCT (Figure 1),are seen as the further development of theAST. They operate without interruption of tractive force, a major drawback of the AST.

The DCT’s main benefit lies in its lowerfuel consumption compared with auto-mated shift transmissions.

The dual-clutch transmission was usedfor the first time in 1992 in motor racing(Porsche). However, owing to the highcomputation effort required in the controlsystem to ensure a comfortable overlappinggearshift, it failed to make it into massproduction.

With the availability of high-powercomputers, several manufacturers (e.g. VW,Audi) are now working on introducing dual-clutch transmissions for mass production.

Since its requirements profile matches thatof an automatic transmission in terms of convenience and functionality, it has foundits niche in the superior, luxury vehiclecategories.

Dual-clutch transmissions also match thewishes of vehicle manufacturers for modularconcepts since both manually shifted andautomated shift transmissions can be manu-factured on the same production line.

DesignThe design of dual-clutch transmissions ischaracterized by the following features:

basic design as for manual transmissions,gears mounted on three shafts,two clutches,actuation of clutch and shifting elementsvia transmission-shift control andactuators.

12 Transmissions for Motor Vehicles Dual-Clutch Transmission (DCT)

Fig. 111 Output for right

front wheel12 Bevel-gear drive for

rear axle13 Parking lock 14 Oil cooler15 Output shaft 116 Input shaft 2

17 Mechatronic module18 Input shaft for oil

pump19 Return shaft10 Input shaft 111 Dual clutch

2

1011 9 8 7

3 4 51 6

Dual-clutch transmission, DCT (cutaway view, source: VW)1

æ U T S 0 2 2 7 Y


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Automatic Transmission (AT)ApplicationAutomatic power-shift transmissions, orsimply automatic transmissions (AT) per-form power take-up, select the gear ratios,and carry out the gearshifts themselves. Ahydrodynamic converter acts as the powertake-up element.

Design and Operating Concept

Transmission with Ravigneaux Planetary-Gear SetThe four-shaft planetary-gear set known asthe Ravigneaux set is the basis of many auto-matic 4-speed transmissions. Figure 1 showsthe schematic, the shifting logic, and a speed-ladder diagram for this transmission. Thetransmission schematic clearly shows the lay-out of the gear wheels and shifting elements.

Sun gears B, C and planetary-gear carrier Scan be connected via clutches CB, CC and CS

to shaft A, which is guided by the converterturbine into the transmission. Shafts S and Ccan be connected with the aid of brakes BSand BC to the transmission housing.

A planetary-gear set of this type has a kine-matic degree of freedom of 2. This meansthat, when two speeds are specified, all theother speeds are established. The individualgears are shifted in such a way that via twoshifting elements the speeds of two shaftsare defined either as drive speed n dr or ashousing speed n C = 0 rpm.

The speed-ladder diagram clearly shows thespeed ratios in the transmission. The speeds

are entered upwards on the speed ladders forthe individual shafts of the overlapping orshift transmission. The gaps of the speedladders are derived from the gear ratios ornumbers of teeth such that the speeds be-longing to a particular point of operationcan be connected by a straight line.

At a specific drive speed, the five referencelines characterize the speed ratios in fourforward gears and one reverse gear.

Only the three shafts B, C and S between theinput shaft “in” (corresponding to A) andthe output shaft “out” are available for thedifferent gearshifts. All three shafts can be

14 Transmissions for Motor Vehicles Automatic Transmission (AT)

Fig. 1a Transmission

schematicb Shifting logicc Speed-ladder

diagram

0

3,000

–3,000

6,000rpm

E n g

i n e s p e e

d

Shifting range

Sun = C Bridge = S Ring gear = out Sun = B

4

321R

1 2 3

2 3 41 2 3 4

1 2 3 4

Gear

Gear steps withsimple gearshifts

CC CS CB BS BC itot–2.550

2.800

1.508

1.000

0.718

R

N1

2

3

4

a c

b

CB

A

T PWL S

C B

TCC

in out

CC BC BSCS

4-speed automatic transmission based on Ravigneaux planetary-gear set1

æ U T S 0 2 2 9 E


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connected to input shaft A, but thenconstructively only two shafts can still beconnected to the transmission housing.

The simultaneous shifting of two brakes isnot useful for gearshifts as this blocks thetransmission. Of equally little use is thesimultaneous connection of one shaft to thehousing and to the input shaft. The simulta-neous shifting of two clutches always resultsin the direct gear ( i = 1).

This retains exactly the five gears shownin the shifting logic and in the speed dia-gram. Beyond the numbers of teeth that arepossible within the framework of the instal-lation conditions, the designer still has theoption of changing the individual gearratios, where a direct gear is always specifiedwith i = 1.

Finally, these transmissions still make it pos-sible with simple gearshifts to skip gears by

cutting in one shifting element and cuttingout another shifting element. It is possible toshift from 1st gear into 2nd or 3rd gear, andfrom 4th gear into 3rd or 2nd gear. From2nd and 3rd gear, all other gears can bereached with simple gearshifts.

However, it is not possible to shift more thanfour forward gears with the Ravigneaux set.An automatic transmission with five gearstherefore requires either another basictransmission or a front-mounted or rear-mounted range-change unit to expand theRavigneaux set. But such an expansion stagerequires at least two shifting elements.

An example of this is the 5HP19 auto-matic transmission from ZF, which has threeclutches, four brakes, and a one-way clutchto shift only five forward gears.Obviously, it is also possible to attain morethan 5 gears with range-change units butshifting effort then becomes increasingly more pronounced and gearshifts of severalshifting elements for one gear change cannotbe avoided.

Transmission withLepelletier Planetary-Gear SetA more elegant way of shifting five andmore gears was devised by the Frenchengineer Lepelletier. He expanded theRavigneaux set to include a range-changetransmission for only two shafts of theRavigneaux set in order to drive them withmeans other than the drive speed.

The unusual feature of the Lepelletier plane-

tary-gear set as set out in Figure 2 (followingpage) lies in the fact that the additionalthree-shaft planetary-gear set reduces thespeed of shaft D in respect to that of shaft A.In the first three gears of this 6-speed auto-matic transmission, the shifting logic corre-sponds to the logic of the 4-speed Ravi-gneaux set. The gear ratios are greater by theorbit ratio of the internal gear to the carrierat the fixed sun gear of the additional plane-tary-gear set.

In 4th and 5th gears, shaft S is connected viaclutch KS to shaft A. It rotates faster thanshafts B and C. The transmission ratios areproduced from the gearshifts in 4th gear:S = A and B = D and in 5th gear S = A andC = D. Without the additional transmissionfrom A to D, the gear ratios in 3rd, 4th and5th gears would be identical and all i = 1.

The 6th gear of this 6-speed automatictransmission corresponds in terms of theshifting logic again to the 4th gear of the4-speed automatic transmission. Even thegearshifts of the reverse gears are identicalin these 4-speed and 6-speed automatictransmissions.

Transmissions for Motor Vehicles Automatic Transmission (AT) 15


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The 6-speed automatic transmission(Figure 3) also makes possible wide gearsteps with simple gearshifts, which can benecessary particularly in the case of rapiddownshifts.

The Lepelletier planetary-gear set thereforediffers from the Ravigneaux set only in thatit has an additional planetary-gear set with afixed gear ratio. The number of shifting ele-ments remains the same. They are simply

used repeatedly for the additional gears. Interms of space, weight, and cost, this trans-mission is more suitable than a 5-speed au-tomatic transmission. With the numbers of teeth shown in Figure 2, this 6-speed auto-matic transmission achieves a setting rangeof = 6 with easily shiftable gear spacings.

The additional planetary-gear set consists of sun gear E, internal gear A, and planetary-gear carrier D and is used in reverse gear and

the first 5 gears as a fixed ratio stage. Shaft E ispermanently connected as reaction memberto the transmission housing. If this connec-

tion were removed and replaced by an addi-tional brake BE, the vehicle could be startedwith this brake instead of the converter.

Power Take-Up ElementsIn the majority of automatic transmissionswhich are geared towards convenience, ahydrodynamic converter adopts the powertake-up function. A hydrodynamic converteris an ideal power take-up element because of the way it works as a turbo element. In order

to minimize converter losses during vehicleoperation, it is however (as often as is possi-ble) locked up with the torque converterlockup clutch (TCLC).

When used with very high-torque turbo-diesel engines, the converter can no longerbe designed to achieve optimum results forall operating states. A drive of this typerequires a relatively soft converter character-istic for safe starting in cold conditions. The

maximum pump torque may only have aneffect at high speeds so that the drag lossesdo not stall the weak engine without suffi-


Fig. 2a Transmission

schematicb Shifting logicc Speed-ladder

diagram

1 2 3 4

4 5 6

3 4 5 6

2 3 4 5 6

1 2 3 4 5

1 2 3 4

Gear CC CS CB BS BC itot–3.400

4.171

2.340

1.5211.143

0.867

0.691

R

N1

2

34

5

6

a

b

CB

A

D

E

T PWL S

C B

TCLC

in out

CC BC BSCS

0

3,000

6

53

21R

–3,000

6,000rpm

E n g i n e s p e e

d

Shifting range

Sun = C Bridge = S Ring gear = out Sun = B

4

c

6-speed automatic transmission based on Lepelletier planetary-gear set2

æ U T S 0 2 3 1 E


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cient charge-air pressure. At normal operat-ing temperatures and at speeds at which suf-ficient charge-air pressure is available, a hardconverter characteristic with a steep rise inpump torque as engine speed increases isadvantageous.

Series applications with fast and accuratepressure control now also make it possible tostart up comfortably with friction clutches.A good example of this is the Audi A6 withthe continuously variable Multitronic trans-

mission.Pressure control and heat dissipation can

be better achieved with a brake than with aclutch. It should therefore also be possible toobtain comfortable starting with the brake.Even during the gear changes, a slipping brakecan remove the load from the other shiftingelements in the same way as a converter.

Automatic Transmission Fluid (ATF)Automatic transmissions place exacting

demands on the ATF ( automatic trans-mission f luid):

increased pressure-absorption capability,good viscosity-temperature characteristics,high resistance to aging,

low foaming tendency,compatibility with sealing materials,These requirements must be guaranteed

in the oil pan in a temperature range of –30...+150°C. Temperatures of up to 400°Care briefly and locally possible between theclutch plates during a gearshift.The transmission fluid is specially adaptedfor fault-free operation of the automatictransmission. A series of chemical sub-stances (additives) is added to the basic oil

for this purpose. The main additives are:friction modifiers, which influence thefrictional behavior of the shiftingelements,antioxidants for reducing thermo-oxidative aging at high temperatures,dispersants for preventing deposits in thetransmission,foam inhibitors for preventing thebuildup of oil foam,corrosion inhibitors for preventing

corrosion of transmission componentswhen condensation water is formed, andseal-swell agents, which control theswelling of sealing materials (elastomers)under the influence of oil to defined levels.


Fig. 31 Transmission input

from engine2 Torque converter

lockup clutch3 Turbine

4 Converter5 Multiplate clutches6 Module for

transmission control7 Planetary-gear set8 Transmission output

1 2 3 54 6 87

ZF 6-speed 6HP26 automatic transmission (source: ZF Friedrichshafen)3

æ U T S 0 2 3 0 Y


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GM established the first specification forATF back in 1949. Typical technical data forSAE viscosity classes in accordance withDIN 51512 are:Flash point (> 180°C)Pour point (< –45°C)Viscosity index (VI > 190)Kin. viscosity: 37 cSt (at +40°C)

17 cSt (at +100°C)Dyn. viscosity: 17000 cP (at –40°C)

13300 cP (at –30°C)

11000 cP (at –20°C)

In the meantime, automatic transmissionsare increasingly being filled with lifetimefluid, thus rendering unnecessary a changeof fluid.

Oil PumpThe transmission requires an oil pump (Fig-ure 4) to build up a control pressure. Thispump is driven by the engine. At the same

time, the oil-pump drive power reduces thetransmission efficiency. The following equa-tion applies here:

Pump output = pressure flow

Figure 5 shows the output characteristicsof a gear pump (1) and a radial pistonpump (2) in comparison. Possibilities foroptimization in the oil-pump range areoffered by a variable flow or a controllablepump pressure:

Variable Pump Flow The particular features of variable pumpflow are as follows:

The design creates a sufficiently high flow

to fill the clutch at idle speed.An additional displacement at higherspeeds causes a loss of output.The variable-capacity pump enables thepump output to be adapted as required.However, variable pump flow has thedrawback of being expensive and suscep-tible to failure.

Controllable Pump PressureThe particular features of controllable pump

pressure are as follows:The pump pressure is adapted to thetorque to be transferred in each case.Main-pressure control allows effectiveoperation (by means of the actuator)close to the clutch slipping point.


Fig. 41 Pressure outlet2 Crescent3 Internal gear4 Suction side5 External gear,

driven by engine

6 Drive lug

Fig. 51 Gear pump2 Radial piston pump

2

5

3 41

6

Crescent oil pump (section)4

æ S T S 0 2 3 2 Y

Engine speed n E

kW

10

8

6

4

2

00 2,000 4,000 6,000 rpm

P u m p o u

t p u

t P P

1

2

Oil pumps (pump outputs in comparison)5

æ S T S 0 2 3 3 E


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No free radial forces occur in the plane-tary-gear set. Rolling bearings can bereplaced by cost-effective plain bearings.Multiplate clutches, multiplate brakes,band brakes, and one-way clutches can bearranged concentrically to the planetary-gear set, thus providing more space for thehydraulic control system.

Different planetary-gear set combinationsare used in transmissions:

Simpson (3-speed, two systems),Ravigneaux (4-speed, two systems),Wilson (5-speed, two systems).

Two types of planetary-gear set have beensuccessfully used in automatic transmissionsand are characterized by the following easy-to-distinguish features:

Ravigneaux SetIn the Ravigneaux set (Figure 11), two dif-ferent planetary sets and sun gears operatein a single internal gear.

Simpson Set

In the Simpson set (Figure 12), two plane-tary sets and internal gears run on one jointsun gear.

Parking LockThe function of the parking lock (Figure 13)is to secure the vehicle against rolling off. Itsreliable operation is therefore fundamentalto safety.

The driver must press the brake pedalbefore the selector lever can be moved from

the P (Park) position. This mechanism pre-vents the vehicle from being set in motionby accidental operation of the selector lever.


Fig. 111 Internal gear2 Sun gear and

planetary-gear set 13 Planetary-gear set 24 Sun gear 2

Fig. 121 Planetary-gear set 1

and internal gear 12 Planetary-gear set 23 Internal gear 2

4 Sun gear

Fig. 131 Pawl2 Parking-lock gear

21 1 43Simpson set (schematic)12

æ U T S 0 2 3 8 Y

1 2

Parking lock 13

æ U T S 0 2 3 9 Y

21 2 43

Ravigneaux set (schematic)11

æ U T S 0 2 3 7 Y


24/116

Continuously VariableTransmission (CVT)ApplicationDrive concepts with continuously v ariabletransmissions (CVT) are characterized by high driving convenience, outstanding ridecharacteristics, and low fuel consumption.

VDT (Van Doorne’s Transmissie) has formany years specialized in developing CVTcomponents and prototype transmissions.

Since its takeover of VDT in 1995, Boschnow covers the entire field of CVT systemdevelopments through to complete drive-train-management systems. All the continu-ously variable automatic transmissions listedin Table 1 are operated with a push-belt(Figure 1). One exception is the Audi Multi-tronic with a link-chain manufactured by LuK (Figure 2).

The main components of a CVT can beactivated by an electrohydraulic module. In

addition to the push-belt – in mass produc-tion since 1985 – pulleys, pumps, and electro-hydraulic modules are being developed forvolume production launch. There are differ-ent types of push-belt for mid-range enginetorques up to 400 Nm (e.g. Nissan MuranoV6 with 3.5 l displacement and max. 350 Nmat 4000 rpm, with converter).

The know-how within theBosch Group provides thesoftware for optimum CVTactivation. Naturally there isfull flexibility with regardto software sharing so thatvehicle manufacturers canalso develop and imple-ment special functionsthemselves.

22 Transmissions for Motor Vehicles Continuously Variable Transmission (CVT)

Fig. 11 Torque converter2 Pump

3 Planetary-gear setwith forward/reverseclutch

4 Push-belt5 Variator6 Control module

Current availability (worldwide) of vehicleswith CVT

1

Vehiclemanufacturer

CVT designation Vehicle

Audi Multitronic A4, A6

BMW CVT Mini

GM CVT Saturn

Honda Multimatic Capa, Civic,HR-V, Insight,Logo

Hyundai CVT Sonata

Kia CVT Optima

Lancia CVT Y 1.2l

MG CVT F, ZR, ZS

Mitsubishi CVT Lancer-Cedia,Wagon

Nissan Hyper-CVT Almera,ICVT Avensis,Extroid-CVT Bluebird,

Cube Micra,Murano, Primera,Serano, Tino,Cedric Gloria

Rover CVT 25/45

Subaru ICVT Pleo

Toyota Super-CVT Previa,Hybrid-CVT Opa Prius

1

6

23

5

4

CVT for front-wheel drive, transverse (section)1

æ U T S 0 2 4 0 Y


25/116


26/116

Figure 5 shows the me-chanical adjustment of the gear ratio from “low”to “overdrive”. The controlsetup shown in Figure 6 isused for this purpose.

The model-basedvariator control systemfeatured in Figure 7processes the followingoperations:

Adjustment of primary speed or gear ratio withPI controller.Adjustment of contactpressure for the primary and secondary pulleys.Coupling of the controlof gear ratio and con-tact-pressure controland control of thepump.Adaptive function forcompensating toler-ances.


Fig. 5a “Low” ratiob “Overdrive” ratio

1 Input (primary)pulley

2 Push-belt or chain3 Output (secondary)

pulley

a 1, b 1 “Low” ratioa 2, b 2 “Overdrive” ratio

1

2

3

a ba 1 a 2

b1 b2

Mechanical variator adjustment (schematic)5

æ U T S 0 2 4 4 Y

Command signalpressure force

Secondary pressure

Command signal ratio

Secondary speed

Primary speedPrimary pulley

Secondary pulley

Primarypressure

Model-basedvariatorcontrol

Variator adjustment (control principle)6

æ U T S 0 2 4 5 E

Nominal speed

Secondary speed

Gear ratio

Engine torque

Clutch / CC

Engine speed

Temperature

Primarytorque

Nom. pressureMax. adjust-

ment speed

Nominal ratio

–

Ratiocontroller

Secondary-pressurecontroller

Primarycurrent

Adaptivefunction

Secondarypressure

Pumpcontrol

Secondarycurrent

Model-based variator adjustment7

æ U T S 0 2 4 6 E


27/116

DesignThe converter or the multiplate clutch actsas the power take-up element, and the re-verse gear is shifted via a planetary-gear set.

The gear ratio is continuously varied withV-pulleys and a belt or a chain (variator).

High-pressure hydraulics provide the neces-sary contact pressure and variator adjust-ment.

All the functions are controlled by the elec-trohydraulic control system. The variouscomponents of the CVT transmission aredepicted in Figure 8.

FeaturesOne advantage of CVT transmissions is thatthey do not cause any interruption of trac-tive force when the gear ratio is changed.These transmissions offer a high level of con-venience since gearshifts are not necessary.

In the entire engine map, operation ismatched to optimum fuel consumption/maximum acceleration. A high ratio span isalso possible.

Although the high-pressure pump requires acertain level of drive power, the overall effi-ciency is satisfactory.

Transmissions for Motor Vehicles Continuously Variable Transmission (CVT) 25

Fig. 811 Engine12 Pump13 Converter14 Planetary-gear set15 Push-belt16 Input (primary)

pulley17 Output (secondary)

pulley18 Differential19 Electronic engine

management

10 Electrohydraulicmodule (hydraulicvalves, sensors,actuators)

11 Vehicle wiringharness

1 2

3 4 5

6

7 8

9

11

10

Model-based variator control8

æ U T S 0 2 4 7 Y


28/116

CVT ComponentsVariatorThe variator consists of two V-pulleys whichmove in relation to each other (Figures 9and 10).

The pressure p of the transmission fluidmoves the moving parts of the variator (1)in relation to each other. This alters the posi-tion of the push-belt (3) between the twopulleys and changes the gear ratio.

As power transmission is based solely on

the friction between the belt and the varia-tor, this type of adjustment requires a highsystem pressure.

Push-BeltThe company Van Doorne’s Transmissieholds a worldwide patent for the push-belt.Figure 11 shows the different types of beltand their areas of application in relation tothe engine torque to be transferred.

The push-belt (Figure 12) consists of pushelements 2 mm thick and 24...30 mm wide,which are arranged at an inclination angleof 11° to each other. The chain is held by

two packs, each with 8 to 12 steel belts.The coefficient of friction of the chain isat least 0.9.


Fig. 101 Moving pulley2 Fixed pulley3 Push-belt4 Spring p Pressure of

transmission

fluid applied

Fig. 12

1 Push element2 Steel-belt pack

2

1

3

4

p

p

Variator (schematic)10

æ U T S 0 2 4 9 Y

1

2

Push-belt (view with excerpt)12

æ U T S 0 2 5 1 Y

Variator (view)9

æ U T S 0 2 4 8 Y

Compactclass

Mid-rangeclass

300

400

Nm

T o r q u e

200

100

0Luxury-classvehicles

VDTbelt

24/924/12 30/9

30/9

30/12

Product range of push-belts11

æ U T S 0 2 5 0 E


29/116

The following nomenclature is used for thebelt designations:

24/12/1.5/208.8Belt diameter

Thickness of beltsNumber of belts

Width of push elements in mm

Link-chain

Instead of the push-belt usually used in CVTtransmissions, Audi uses a link-chain manu-factured by the company LuK in its Multi-tronic transmission (this chain is based onthe pin chain manufactured by the company P.I.V. Reimers).

This link-chain is made completely of steel and yet is almost as flexible as a V-belt.It is composed of various positions of linksnext to each other and therefore of suchrobust design that it can transfer very

high torques (transferable engine torque350 Nm) and forces.

The chain (Figure 13) consists of 1025 indi-vidual links, each with 13...14 chain linkslined up next to each other. Pins with awidth of 37 mm and an inclination angle of 11° connect the links (1) to each other. Theends of the pins (2) press against the conicalsurfaces in the variator.

The tractive force of the chain is trans-ferred to the variator pulleys at the supportpoints created. The mini slip created in theprocess is so minimal that the pins are subject to wear of no more than one to twotenths of a millimeter over the entire work-ing life of the transmission.

The link-chain has the further advantagethat it can be routed over a circumferencethat is smaller still than other belts. By run-ning on this minimum wrap diameter, it hasthe capacity to transfer maximum forces andtorques. In this event, only nine pairs of pinsare in contact with the inside surfaces of thepulleys. However, the specific contact pres-sure is so high that they do not slip evenunder maximum load.

CVT Oil PumpSince the process of adjusting the pulleysin the CVT requires a high fluid pressure,a high-power oil pump is used to generatethis pressure (Figure 14).

Transmissions for Motor Vehicles Continuously Variable Transmission (CVT) 27

Fig. 131 Links2 Pin

CVT oil pump14

æ U T S 0 2 5 3 Y

2 1

Link-chain for Audi Multitronic (source: Audi)13

æ U T S 0 2 5 2 Y


30/116

Toroid TransmissionApplicationThe toroid transmission is currently only used in Japan in the Cedric and Gloriamodels built by Nissan.

DesignAs a special type of continuously variabletransmission (Figures 1 and 2), the toroidtransmission is also known as a friction-gear

CVT. It is characterized by the followingdesign features:

converter as power take-up element,reverse gear via planetary-gear set,power transmission via torus wheels withintermediate rollers,continuously variable change of ratioby hydraulic angle adjustment of inter-mediate rollers,

high-pressure hydraulics for preloadingthe torus wheels, andelectrohydraulic control.

FeaturesThe main features are as follows:

no interruption of tractive force,no gearshifts (high convenience),adapted operation in the engine map foroptimum fuel consumption/maximumacceleration,

can be used for high torques,rapid ratio adjustment,high drive power for the high-pressurepump (overall efficiency therefore only satisfactory), andspecial ATF (automatic transmissionf luid) with high shear strength required.

28 Transmissions for Motor Vehicles Toroid transmission

Fig. 1

a Half toroidb Full toroid

1 Input wheel2 Variator3 Output wheel4 Output

Fig. 21 Input wheel2 Variator3 Output

a

13

2

b

4

1 3

2

4

Toroid transmission (schematic)1

æ

U T S 0 2 5 4 Y

1 2 3

Toroid transmission (version)2

æ U T S 0 2 5 5 Y


31/116

Transmissions for Motor Vehicles Transmission History 2 29

1 Transmission inputwith bevel clutch

2 Sliding-gearcluster 1

3 Sliding-gearcluster 2

Daimler/Maybach Steel-Wheel Carriage from1889 with Four-Speed TransmissionPower transmission in an automobile mustguarantee the functions of starting, engine-speed, and torque conversion for forward andreverse travel. These functions call for actuatorsand shifting elements which intervene in thepower-flow and perform engine-speed andtorque conversion.

In the very early days of automobile history,

many vehicles transferred their engine’s motiveforce to the road with belt and chain drives.Only in the output stage, the final drive, weregear and chain drives soon to be in use due tothe high torques involved.

The steel-wheel carriage from Daimler andhis designer Maybach from 1889 was the first four-wheel vehicle with an internal-combustionengine not to be simply a converted horse-drawn carriage, but to be conceived in itsentirety specifically for motorized road traffic.The power-flow of its vertically mounted two-cylinder V-engine with a power output of 2 HP(1.45 kW) was already transferred to the pow-ered axle with a clutch, a four-speed manuallyshifted gear transmission, and a differential. Agear transmission could specifically carry outthe conversion of rotational speed, torque, anddirection of rotation in the tightest of spaces.

The four-speed transmission to be operatedusing two shift levers consisted of differentstraight-toothed gear pairs, one pair of whichcould always be engaged with the aid of twosliding-gear clusters. The top speed that couldbe reached ranged between 5 km/h (1st gear)and 16 km/h (4th gear). For the purpose ofstarting and shifting, the power transmissionfrom the engine to the transmission could beinterrupted with a bevel clutch.

Despite the introduction of the variable-ratiogear transmission, the belt drive maintained itsposition for some time as the power take-up ele-ment in the subsequent course of vehicle devel-opment because it permitted a certain startingslip and a greater spacing to the other drivetraincomponents. There were also combinations ofbelt drives, manual gear transmissions, andchain drives. The chain drive remained in usein passenger cars until roughly 1910. But asengine power output continued to increase,there was no longer any way past the variable-ratio gear transmission with bevel clutch onaccount of the high forces that were created.

After 1920 the positive connection (withconstantly engaged gears) was established bydisplacing dog clutches with low displacementtravel. Then helical gears and synchronizationbecame standard in manually shifted transmis-sions. Finally, there came the introduction ofautomatic transmissions, which are usually fittedwith planetary-gear sets on account of the highpower density.

Daimler/Maybach steel-wheel carriage from 1889with its four-speed transmission(source: DaimlerChrysler Classic)

æ U T S 0 3 5 6 Y

Transmission history 2

1

2

3

æ U T S 0 3 5 7 Y


32/116

In complicated traffic situations, unfamiliarsurroundings, or poor weather conditions(e.g., heavy rain, snow, or fog), manualgear changing can distract car drivers tosuch an extent as to create situations thatare difficult to control. This also applies tothe annoying, incessant process of engaging and disengaging the clutch when driving instop-and-go traffic.Automatic transmis-sions with electronic control assist drivers inthese and other traffic situations so that they

can concentrate fully on the road conditionsand what is happening around them.

Drivetrain Management

As the number of electronic systems in thevehicle increases, so too does the complexity of the overall network of the various ECUs.Controlling such networked structures re-quires hierarchical order concepts, such as,for example, the “Cartronic” system from

Bosch. Coordinated drivetrain manage-ment is integrated as a substructure in the“Cartronic”system. It facilitates optimally matched management of the engine andtransmission in the various vehicle operat-ing conditions.

The engine is operated as often as possiblein the fuel-saving ranges of its programmap. If the driver adopts a sporty drivingstyle, however, the high, less economicalspeed ranges are increasingly utilized. Such asituation-dependentmode of operation pre-supposes on the one handthat the driver commandis recognized and on theother hand that its imple-mentation is left to theelectronic drivetrain-management system anda higher-level drivingstrategy. When the driverpresses the acceleratorpedal, the system inter-prets this action as anacceleration request.From this request, the

drivetrain-management system calculatesthe conversion into torque and engine speedand implements them. In order for such astrategy to be implemented, it is essential forthe system to be equipped with an electri-cally actuated throttle valve (drive by wire).

Figure 1 shows the organizational structureof drivetrain management as part of theoverall vehicle structure. The vehicle coordi-nator forwards the requested propulsion

movement to the drivetrain coordinatorwhile taking into account the power require-ments of other vehicle subsystems (e.g.,body or electrical-system electronics). Thedrivetrain coordinator distributes the powerdemand to the engine, converter, and trans-mission. In the process, the various coordi-nators may also have to solve conflicts of in-terest that arise in accordance with definedpriority criteria. A whole range of differentexternal influencing factors (such as envi-

ronment, traffic situation, vehicle operatingstatus, and driver type) plays a role here.

The Cartronic concept is based on anobject-oriented software structure withphysical interfaces, e.g., torque as an inter-face parameter of drivetrain management.

30 Electronic Transmission Control Drivetrain Management

Electronic Transmission Control

Slip Converter

Torque

Drive

Provision of propulsionpower and power for otherloads/consumers

Engine

Gear ratio Trans-mission

C o o r

d i n a

t o r

Vehicle

Vehiclemotion

Electricalsystem

C o o r

d i n a

t o r

Body andinterior

Environmentalvariables

Driving-conditionvariables

Vehiclevariable

Uservariables

?

?

?

?

Monitoring architecture of monitored drivetrain management1

æ S T S 0 2 5 6 E


33/116

Market TrendsThe statutory requirements relating to fuelconsumption and exhaust-gas emissions willplay a significant role in transmission devel-opment over the next few years. There fol-lows a brief comparison of the requirementsof the main markets for this purpose.

ACEA, JAMA and KAMAThe ACEA (Association des Constructeurs

Européens d’ Automobiles, i.e. Association of European Automobile Manufacturers) hasagreed to reduce the corporate average inCO2 emissions in the period from 2002 to2008 from 170 mg CO 2 to 140 mg CO 2(Figure 1).

The Japanese and Korean manufacturers’ as-sociations (JAMA and KAMA) have adoptedthe same limits for the year 2009. In orderfor this target to be achieved, the next few

years will see an increased acceptance of transmission types such as the 6-speedtransmission CVT ( continuously v ariabletransmission) and AST ( automated shifttransmission).

CAFE RequirementsIn contrast to Europe, the USA, the mostimportant market for automatic transmis-sions, has seen no change in the CAFE fuel-consumption requirements ( corporate aver-age f uel efficiency) since 1990 (Figure 2). Allattempts to bring about a tightening of theserequirements have proven unsuccessful.

Electronic Transmission Control Market Trends 31

Year

0

5

10

15

20

25

30FE/mpg

1978

Standard

1990 2000

Current value

F u e

l c o n s u m p

t i o n

CAFE fuel-consumption requirements (passenger cars, light commercial vehicles not included)2

æ S T S 0 2 5 8 E

Year

2002100

120

140

160

180

200g/km

2000 2004 2006 2008 2010 2012

C O

2 e m

i s s

i o n

165…170

140

Consumption leaderVW Polo 3l

Current fieldof values

CO 2-emission requirements1

æ S T S 0 2 5 7 E


34/116

Control of Automated ShiftTransmission ASTRequirementsCurrent market developments reveal amarked trend towards an increase in in-carsafety and operating comfort and conve-nience. This is accompanied by an increasein vehicle mass and in the final analysis anincrease in fuel consumption. The emissionguidelines laid down by legislators (140 g/km

CO2 by 2008) only intensify the situation.

The automated shift transmission (AST)combines the advantages of a manually shifted transmission with the functions of an automatic transmission. The automatedversion of the classic manual transmissionis characterized by its high efficiency. Sliplosses do not occur as in conventionaltorque-converter transmissions.

Specific fuel consumption in the auto-

matic mode is below the low level of themanual transmission.

AST development is founded on theknowledge and findings gained in connec-tion with electric-motor clutch management(ECM).

Electric-Motor Clutch Management(ECM)ApplicationFollowing initial experiences with hydraulicclutch management, users are now concen-trating their efforts on the use of electricmotors as clutch actuators in the small-carsegment. This new approach allows for sav-ings to be made on costs and weight, as wellas providing a higher degree of integration.Corresponding ECM systems are used in theMercedes A-Class, the Fiat Seicento, and theHyundai Atoz.

Design and Operating ConceptThe most important step in minimizingcosts was switching from a hydraulic actua-tor to an electric-motor actuator. This stepremoved the need for a pump, an accumula-tor, and valves as well as the need for a travel

sensor in the clutch-release system. Insteadthe clutch-travel sensor is integrated in theelectric-motor actuator.

The small electric motor offers a low power density in comparison with ahydraulic pump and accumulator. Theelectric-motor actuator is therefore only suitable if it can achieve sufficiently shortdeclutching times for rapid gearshifts.

Shifting without Torque Correction

In the conventional system without torquecorrection (Figure 1), the clutch torque is farin excess of the engine torque. The reasonbehind this is that the dry clutch, which hasto transfer at least the engine torque underall extreme conditions, normally offers areserve of 50 to 150%. The engine torquedrops when the driver wishes to change gearand at the same time takes his foot off theaccelerator pedal. Operating the shift leverinitiates the intention to change gear, and

the clutch must now be moved from thefully closed to the fully open position. Thisdefines the declutching time.

If the declutching time is too long, the clutchwill still transfer torque while the next gear isbeing synchronized, a process which may re-sult in rattling or damage to the transmission.

32 Electronic Transmission Control Control of Automated Shift Transmission AST

Fig. 1M C Clutch torqueM E Engine torquet D Declutching timeS 1 Signal for gearshift

command

1̄00

100

200

300

400Nm t D

M C

M E

S 1

0 2 4 6 8 s

0

Time t

T o r q u e

Shifting without torque correction1

æ S T S 0 2 5 9 E


35/116

Shifting with Torque Correction The most technically sophisticated solutionfor avoiding transmission damage is tocombine a reduced-force clutch with torquecorrection.

Figure 2 shows the shifting operation withtorque correction, in which the clutchtorque is only marginally above the enginetorque. When the driver takes his foot off the accelerator pedal to change gear, theclutch torque drops as well as the engine

torque. When the intention to change gearis initiated, the clutch is thus already almostopen and the remaining declutching opera-tion follows very rapidly.

Figure 3 features a schematic representa-tion of electric-motor clutch management(ECM) as a partial-automation solution,and the automated shift transmission (AST)as the complete automation of the manualtransmission, both as add-on systems.

Electric-Motor Automated ShiftTransmission ASTApplicationToday the AST is used primarily in the lowertorque classes (e.g., VW Lupo, MCC Smart,Opel Corsa Easytronic, see also chapter enti-tled “Transmission Types”), where, in com-parison to the fully automatic transmission,the cost benefit makes up for the downsideof the interruption in tractive force.

Design and Operating Concept The electric-motor AST features the auto-mated clutch operation of the ECM system.With an additional electric-motor actuatorfor the transmission, the driver is able tochange gear without there being a mechani-cal connection between the selector leverand the transmission (shift by wire).

In the case of the AST, all modifications to thetransmission are to be avoided.This will en-

able the transmission manufacturer to mounteither manual transmissions or ASTs on theproduction line. As the hardware for thissystem (e.g., for the Opel Corsa Easytronic),Bosch supplies the electric motors for clutchengagement, shifting, and selection (see chap-ter entitled “Transmission, Automated ShiftTransmission”), and the ECU.Automatedand cost-effective mass production is madepossible by the use of standard componentsin all AST applications.

Electronic Transmission Control Control of Automated Shift Transmission AST 33

Fig. 2

M C Clutch torqueM E Engine torquet D Declutching timeS 1 Signal for gearshift

command

Fig. 3a ECMb AST

1 Available signals2 Clutch actuator with

integrated ECMECU

3 Gear recognition4 Shift-intention

recognition on

shift lever5 Clutch actuator with

integrated AST ECU6 Transmission

actuator7 Selector lever

1̄00

100

200

300

400Nm t D

M C

M E

S 1

Time t

0 2 4 6 8 s

0

T o r q u e

Shifting with torque correction2

æ S T S 0 2 6 0 E

1

b

ECM

AST

a

1

2

5

4

3

7

6

ECM and AST as add-on systems3

æ S T S 0 2 6 1 E


36/116

Software SharingThe vehicle manufacturer (OEM), the sup-plier and if necessary a system integratorshare the AST software tasks. The operatingsystem, signal conditioning, and the hard-ware-specific routines for activating theactuators are provided by Bosch. Bosch’sextensive knowledge and experience in thefield of automatic transmissions is alsoapplied in establishing the AST target gears.This includes, among others, driver recogni-

tion, uphill/downhill recognition, corneringrecognition, and other adaptive functions(see also chapter entitled “Adaptive Trans-mission Control, ATC”).

The tasks of activating the transmission andcoordinating the gearshift sequence (clutch,engine, transmission) are the responsibility of the OEM or the system integrator.

This also applies to clutch control, signifi-

cant parts of which can be taken over fromthe ECM system. Each vehicle manufacturerbrings its marque-specific philosophy regarding shifting time, shifting points,and shifting sequences to bear.

Shifting Operation and Interruption of Tractive ForceThe basic problem associated with the ASTis the interruption of tractive force. This isrepresented in Figure 4 by the “hollow” of the vehicle acceleration between the twoshifted gears. In terms of what is requiredof the actuators, these phases can be dividedinto two blocks:

phases which have an effect on the vehicleacceleration,

phases which represent pure responsetimes.

In the phases which have an effect on thevehicle acceleration, it transpires that athrottle action is needed because excessively quick changes in vehicle acceleration are feltto be unpleasant. The optimum interactionof engine, clutch, and transmission interven-tion results in the best possible performance.

The synchromesh can be supported forexample by double-declutching. In theresponse times, however, the maximum speedof the actuators is demanded. It is importanthere that the synchromesh does not experi-ence too hard a shock after the gear has beendisengaged and the following rapid phase.

34 Electronic Transmission Control Control of Automated Shift Transmission AST

Fig. 41 Current gear2 Next gear

∆ M 1 Torque reduction∆ M 2 Torque increaset 0 Tractive-force

interruption

t 1 Shifting operationt 2 Accelerationt 3 Disengage and

select geart 4 Synchronizationt 5 Shift through gear

t 0

∆ M 1

∆ M 2

t 2

t 1

t 3 t 4 t 5

Time t

1

2 A c c e

l e r a

t i o n a

Phases of AST shifting operation4

æ S T S 0 2 6 2 E


37/116

Figure 5 shows a comparison of the shiftingtimes that can be achieved with a hydraulicsystem and an electric-motor system and theshifting time necessary for a comfortableshifting operation. The bar lengths equate tothe times required for the individual phasesand the same shading schemes are used.

When the capacity of the actuators isexploited to maximum effect, the electric-motor system only demonstrates a time

disadvantage compared with its hydrauliccounterpart in the clutch-operation phase.This could be reduced in particular in thetorque-reduction phase by an intelligent

control strategy such as torque correction orby the interaction of the engine and theclutch.

It is important to highlight here that thereis hardly any difference between the twosystems in the phases for response time, geardisengagement, and gear engagement. Theresponse times are not extended practically,even in the case of comfortable shifting.However, the phases relevant to acceleration

must be two to four times as long as in theextreme case, both for the hydraulic and theelectric-motor actuator systems.

Electronic Transmission Control Control of Automated Shift Transmission AST 35

Fig. 61 Engine electronics

(EDC)2 Transmission

electronics3 Transmission

actuator4 Diesel engine5 Dry interrupting

clutch6 Clutch servo unit7 Intarder electronics8 Display9 Driving switch

(selector lever)10 ABS/TCS

11 Transmission12 Air supply

___ Electrics- - - - Pneumatics ___ CAN communication

Torquereduction

Comfortable

Maximumelectronic force

Maximumhydraulic force

Torqueincrease

Gearout

Synchro-nization

Gearin

100 ms

Comparison of achievable shifting times5

æ S T S 0 2 6 3 E

1 8 2 119 3

7

10

654

CAN

12

Automated shift transmission (AST) in a diesel vehicle (example: system diagram)6

æ U T S 0 2 0 7

- 1 Y


38/116

Control of AutomaticTransmissionsRequirementsThe control system for an automatic trans-mission must fulfill the following essentialrequirements or functions:

always shifting the correct gear or settingthe correct gear ratio as a function of assorted influencing variables,executing the shifting operation through

adapted pressure characteristics as com-fortably as possible,implementing additional manual inter-ventions on the part of the driver,detecting maloperations, e.g. by prevent-ing non-permitted gearshifts,providing ATF oil for cooling, lubricationand for the converter.

Current control systems are exclusively electrohydraulic in nature.

Hydraulic ControlThe main function of the hydraulic-controlsystem (Figures 1 and 2) is to regulate,boost, and distribute hydraulic pressuresand volumetric flows. This includes generat-ing the clutch pressures, supplying the con-verter, and providing the lubricating pres-sure. The housings of the hydraulic-controlsystem are made from diecast aluminumand contain several precision-machinedslide valves and electrohydraulic actuators.

36 Electronic Transmission Control Control of Automatic Transmissions

Exploded view of a hydraulic-control system (example: GM HYDRA-MATIC 4L60-E)1

æ U T S 0 2 6 4 Y

Main control with hydraulic valves2

æ U T S 0 2 6 5 Y


39/116


40/116


41/116

for the clutches (Figure 8). This means thatwhile clutch 1 opens for gear x, clutch 2 mustclose for gear y. Since this type of control isvery elaborate and time-critical, it is neces-sary to provide considerably higher comput-ing power in the ECU than for the simpleshifting sequences with one-way clutch shifts(see also chapter entitled “ECUs”).

The most important features of overlapcontrol are:

low mechanical complexity,minimal space requirement,multiple use for different gear stepspossible,high control precision for load transferrequired,high software complexity for torquecontrol,in event of incorrect control: excessivespeed (engine races) or onset of a brak-ing torque (extreme case: transmission

blocking).

Adaptive Pressure ControlThe function of adaptive pressure control isto achieve a consistently good shift quality over the entire working life of the transmis-sion and the accompanying changes in thefriction coefficients at the clutch surfaces.It also compensates for any potential devia-tion of the calculated torque or the torquetransferred by the engine which can occuron account of changes to the engine ormanufacturing tolerances.

In this case, an important role is played by pressure adaptation with the aid of the shift-ing times applied by the manufacturer. Tothis end, the applied shifting times are com-pared with the real shifting times that occur.If the measurements are repeatedly outside apre-specified tolerance range, the pressureparameters pertaining to the shifting opera-tion are incrementally adapted. A distinctionis made here between the fill time and theslip time of the clutch.

Fill-Time Measurement The fill time t fill(Figure 9) is the time fromthe start of the gearshift t shift to the start of synchronization (a drop in speed is identi-fied during the upshift [US]):

t fill= t vertex – t shift

Slip-Time Measurement The slip time t slip (Figure 10) of the clutch isthe time from recognition of the speed vertex (start of synchronization) to complete syn-chronization of the speed in the new gear.

Electronic Transmission Control Control of Automatic Transmissions 39

Fig. 8 p 1 Pressure,

cutting-in clutch p 2 Pressure,

cutting-out clutchn E Engine speedM Torque

Time t

S p e e

d n

p1

p2

nE

M

T o r q u e M

P r e s s u r e p

Overlap control US8

æ S T S 0 2 7 1 E

t shift t vertexTime t

T u r b

i n e s p e e

d n t

u∆ntu

t fill

ntu

Fill time9

æ S T S 0 2 7 2 E


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t slip = t sync – t vertex

The speed thresholds used for measuring theslip time t slip (Figure 10) are calculated inadvance of the start of shifting, where thefollowing relationship applies to upshifts:Start of fill-time measurement = start of shifting

Vertex: A decrease in the turbine speed n tu by at least n tu (vertex) revolutions is detected.

n tu (t –1) – n tu (t ) > n tu (diff)

Synchronization speed:An increase in theturbine speed n tu by at least n tu (sync) revo-lutions is detected.

n tu (t ) – n tu (t – 1) > ∆ n tu (sync)

Pressure Correction Pressure adaptation is only permitted withinspecific limits on account of operational re-liability. The typical adaptation width lies inthe range of ±10% of the modulation pres-sure calculated for the shift. The correctionvalues are also still distinguished accordingto speed bands.

The adaptation values are stored in a non-volatile memory so that the optimum mod-ulation pressure can be reapplied when thevehicle is restarted. The overall pattern of pressure adaptation can also be evaluated asa sign of changes in the transmission.

Shifting-Point SelectionConventional Shifting-Point SelectionIn the majority of automatic transmissionscurrently available, the driving program isselected using a selector switch or a button.The following driving programs are gener-ally available in this respect:

Economy (very economical),Sport, orWinter.

The individual programs differ in the posi-tion of the shifting points in relation to theposition of the accelerator pedal and the dri-ving speed. The Economy and Sport shiftingmaps of a 5-speed transmission are usedhere as examples (Figure 11).

If the current driving speed or the accelera-tor-pedal position corresponding to thedriver command (accelerator-pedal value)intersects the shift curve, a gearshift is trig-

gered. A requested gearshift can be eithercanceled or converted into a double shiftwithin a specific period of time (whichdepends on the hydraulic system of theautomatic transmission)

For example, the driver is driving in fifthgear on an interstate highway and would liketo overtake. To do so, he presses the accelera-tor pedal to the floor, whereupon a down-shift is requested.


Fig. 11

1 UpshiftXE Economy modeXS Sport mode

t vertex t syncTime t

T u r b

i n e s p e e

d n t

u

∆ntu(sync)

ntu

t slip

Slip time10

æ S T S 0 2 7 3 E

A c c e

l e r a

t o r - p e

d a

l p o s

i t i o n

Vehicle speed υ F

00

50

100

%

50

1

km/h

2-1 RSXE XS

1-2 HSXE XS

US and DS characteristics in Economy mode (XE)and Sport mode (XS)11

æ S T S 0 2 7 4 E


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When the accelerator pedal is firmly pressedto the floor, the 4-3 DS shift curve is inter-sected directly after the 5-4 DS shift curve,and a 5-3 double downshift is performedinstead of a sequential downshift. Specialshifting points for kickdown (forced down-shift) allow the maximum possible enginepower to be utilized at this point.

Adaptive Transmission Control (ATC)All newer transmission-control systems have

– instead of active driving-program selectionby the driver – software which enables thedriver to adapt to the special ambient condi-tions while driving. This includes first andforemost driver-type recognition and dri-ving-situation recognition. Examples whichare currently in use are adaptive transmissioncontrol (ATC) from BMW and the d ynamicshift program (DSP) from Audi.

Driver-Type Recognition

A driver type can be identified by means of an evaluation of the actions he or sheperforms. This includes:

kickdown operation,brake operation, andrestriction via selector lever.

For example, the kickdown evaluator countsthe number of times the driver engages kick-down during a presettable period of time. If the counter exceeds a specific threshold, thedriver-type recognition facility selects thenext, more sporty driving program. It auto-matically switches back to a more economicaldriving program once this time has elapsed.

Driving-Situation Recognition For driving-situation recognition, differenttransmission-control input variables arelinked to conclusions about the presentdriving condition. The following situationscan generally be recognized:

uphill driving,cornering,winter operation, andASC operation.

Uphill Driving Recognition of uphill driving by comparingthe current acceleration with the requestedacceleration by way of the engine torque,results in upshifts and downshifts at higherengine speeds and thus prevents gearshifthunting.

Cornering This facility uses the difference in wheelspeeds to calculate whether the vehicle is in a

curve or bend. With active cornering recog-nition, requested shifts are delayed or pro-hibited in order to increase vehicle stability.

Winter Recognition Winter operation is recognized on the basisof slip detection from analysis of the wheelspeeds. This serves primarily to

prevent the wheels from spinning andselect a higher gear during starting so thatless torque is transferred to the drive

wheels, thereby preventing prematurewheel spin.

ASC Operation If the system detects while driving that theASC ECU (anti- slipping control or tractioncontrol s ystem, TCS) is in control mode,requested gearshifts are suppressed in orderto support the ASC function.



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Engine InterventionApplicationA precisely controlled time characteristic of engine torque during the shifting operationsof an automatic transmission offers the pos-sibility of optimizing transmission controlwith regard to gear-shift sophistication(convenience), clutch service life, and trans-ferrable power. The engine managementsystem implements the torque command(reduction) of the transmission control by

retarding the moment of ignition.The theoretical principles, processes, and

measurement results are presented using theexample of engine intervention in ignition.

Symbols and Abbreviations C Spring stiffness of drivetraini Gear ratio J Mass moment of inertiak ConstantM Engine torquen Rotational speedq Specific lost work Q Lost work t TimeW Running resistancex Spatial coordinateδ Temperatureω Angular velocity Φ Angle of rotation

Angle of rotation, linearized

Indices O OutputV Vehiclelimit Permitted limit valueC Clutch (friction element)kin Kinetic shareE Engine (transmission input)red Reduced values Slip timecom Share of combustion energy

(engine torque)Reference variable

1 Clutch drive side2 Clutch output side

Requirements The ever-increasing demand for more eco-nomical fuel consumption in motor vehiclesdictates to a significant degree the develop-ment objectives in the field of automatictransmissions as well. In addition to mea-sures for improving the efficiency of thetransmission itself (such as, for instance, thetorque converter lockup clutch), these objec-tives include introducing transmissions withmore gears. However, additional gear steps

inevitably call for increased shift frequency.This in turn results in increased demandsplaced on gear-shift sophistication (conve-nience) and the load capacity of the frictionelements.

Engine intervention takes into accountboth requirements and institutes an addi-tional degree of freedom for controlling anautomatic transmission. “Engine interven-tion”covers all those measures which allow the engine torque generated by the combus-

tion process during the shifting operation inthe transmission to be specifically influ-enced and in particular reduced. Engineintervention can be used in both upshiftsand downshifts.

The primary aim of engine interventionin upshifts is to reduce the lost energy thatoccurs in the friction elements during theshifting operation. This is done by reducingthe engine torque during synchronizationwithout interrupting the tractive force. Themargin acquired in this process can be usedto:

Increase the service life by shortening theslip time (if all other operating parame-ters in the transmission, such as clutchpressure and number of plates, remainunchanged).Improve the convenience by reducing theclutch torque, brought about by loweringthe clutch pressure during the slip phase.Transmit higher power, provided themechanical strength of the transmissionpermits this; in most cases, however, thepower loss in the clutches is the limitingfactor.



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Naturally, it is also possible to adopt a sensiblecombination of these measures within theframework of the specified margin.

The aim of engine intervention in down-shifts is to reduce the jolt which occurs whenthe one-way clutch or a friction elementengages at the end of the synchronizationprocesses. This results in

improved convenience andsupported and improved synchronization

in transmissions without one-way clutches.

Interventions in the Mechanical ShiftingSequenceThe following explanations illustrate whichpossibilities present themselves for interven-tion in the mechanical shifting sequence.The individual phases of upshifts and down-shifts are described in the section entitled“Shifting-Sequence Control”.

Upshifts Engine intervention is discussed using theexample of an upshift from the direct gear(i = 1) to overdrive ( i < 1). The followingsimplifications serve to illustrate the physicalrelationships more clearly:

The influence of the torque converter isdisregarded.There is no overlap of friction elements,i.e., only one friction element participatesin the gearshift.The engine torque remains constant dur-ing the gearshift, thereby providing linearspeed characteristics.The vehicle speed during the gearshift istaken to be constant.The heating of the friction linings by briefly successive shifting operations isdisregarded.

Upshifts take place without an interruption of the tractive force.Synchronization of engineand transmission takes place via a frictionelement in slipping-intervention operation.The following relative speed ensues betweenthe drive and output side of the clutch:

∆ ω = ω1 – ω2 (1)

In relation to the lost energy which mustbe absorbed or forwarded by the frictionelements during the shifting operation, thefollowing equation applies:

t sQ = M C (t ) · ∆ ω(t ) · dt (2)

0

Furthermore, the angular-momentum prin-

ciple applies to the drive and output sides of the clutch. For the rotational masses of thedrive side:

1– i M E – M C∆ ω = ωO · + · t (3)i J O

Under the above-mentioned preconditions,this produces:

∆ ω = ωE – ωO = ωE (t =0 ) – ωO + ωE ·t

or

1– i M E – M C t 2SQ = M C ωO · · t s + ·i J E 2

From (1), (2), and (3), this produces for atime-constant clutch torque the lost energy as a function of the shifting-sequence para-meters.

J 1 · ω.

1 = M E – M C

The slip time itself is dependent on theclutch and engine parameters, where

ωO 1 – i 1– i J Et s = · = ωO · · (4)ω. E i i M E – M CThis produces the lost energy to be absorbedby the friction element

1 M C · J E 1 – i Q = · · ω2O 2 (5)2 M E – M C i

i.e., the lost energy is dependent only on theclutch and engine torques, the driving speed,and the gear ratios.

When the clutch torque determined by (4)is applied in (5), this produces the lost energy



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as the sum of a share of the kinetic energy which is released when the rotational massesare braked to the synchronization speed anda share of the engine combustion energy:

ω2O 1–i ω O 1–i

Q = Qkin+Qcom = J E · · 2+M E ·t S · · (6)2 i 2 i Both these shares are roughly of thesame order of magnitude.At speeds of n = 3000 rpm and typical values for the gearstep and the engine-drag torque ( i = 0.8,

J E = 0.3 kg · m2, M E = 100 Nm, t S = 500 ms),this produces:

Qcom/Qkin ≈ 1...4

This clearly shows the possibilities of engineintervention for reducing the power loss inthe friction elements.

A further significant aspect is derived from(6): Only the share of lost energy stemming

from the combustion energy is dependenton the slip time t S. The decisive factor is theproduct of the engine torque and the sliptime. This means, however, that the slip timecan be extended accordingly when the en-gine torque is reduced without an increasein the total lost energy. In actual fact, thewear of the friction elements even decreaseswith constant total lost energy when the sliptime is extended. The temperature of thefriction linings corresponds to the load onthe friction elements.

Figure 12a shows the lost energy absorbedby the friction element as a function of theengine torque and the slip time. The maxi-mum permitted lost energy Q limitand theengine torque to be transferred during thisgearshift determine the maximum slip time,for instance in accordance with point S. Themaximum permitted energy Q limitcorre-sponds in accordance with (5) to the clutchtorque determined by the slip time M Climit(point 1 in Figure 12b).

To reduce the lost energy, the clutchtorque in relation to point S would have tobe increased and thereby the slip time short-ened. However, this would lead in equal

measure to a reduction in gear-shift sophis-tication (convenience). A reduction of theclutch pressure is not permitted in this case,as otherwise Q limitwill be exceed

Electronic Transmission Control ETC 2004

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