simulation based comfort evaluation for vehicles with automated transmissions

HOCHSCHULE KONSTANZ TECHNIK, WIRTSCHAFT UND GESTALTUNG

UNIVERSITY OF APPLIED SCIENCES

hofer-pdc GmbH

MASTER THESIS Simulation Based Comfort Evaluation for Vehicles with

Automated Transmissions

Ahmad Hakim Mohd Sorihan

Automotive Systems Engineering

28.02.2013

Supervisors:

Prof. Dr.-Ing Uwe Kosiedowski

Dr. Mathias Lutz

Ahmad Hakim Mohd Sorihan i

Abstract

In the last few years, the design variation of automated transmission is becoming more and more

diverse. Some examples besides the well-known automatic transmission with torque converters and

planetary gears are the Dual Clutch Transmission (DCT) and the Automated Manual Transmission

(AMT), to name a few. These transmission variations are further divided according to their

realisation concept, such as the Dry Dual Clutch and Wet Dual Clutch Transmission.

The very diverse design of a transmission causes different driving experience and influences the

driving comfort. This comfort perception is evaluated in a subjective way by the driver. The aim of

this master thesis is to reproduce comfort-relevant driving situations in simulation models and to

evaluate the driving situations with both proven and newly defined evaluation criteria. The

evaluation steps and result obtaining were automated with programming scripts for convenience.

The long term aim of this thesis is to provide a knowledge of simulation based comfort evaluation.

In den letzten Jahren wchst bei den automatisierten Getrieben die Vielfalt der Getriebetypen.

Neben den bekannten Wandlerautomatgetrieben mit Planetenradstzen sind das automatisierte

Schaltgetriebe (AMT) und das Doppelkupplungsgetriebe (DCT) zu nennen. Zu den verschiedenen

Getriebetypen existieren verschiedene Realisierungskonzepte, wie z.B. Getriebe mit nasser und mit

trockener Doppelkupplung.

Die verschiedenen Realisierungskonzepte und Getriebetypen verursachen unterschiedliches

Fahrerlebnis. Das Fahrerlebnis wird subjektiv von Fahrer wahrgenommen. Das Ziel dieser Arbeit ist

die verschiedenen komfortrelevanten Fahrsituationen realistisch in Simulationsmodellen

nachzubilden und die Situationen mit sowohl bewhrten als auch mit neu entwickelten Kriterien zu

bewerten. Die Bewertungsschritte wurden durch programmierte Skripte automatisiert. Das

langfristige Ziel dieser Arbeit ist das Bereitstellen von Kenntnissen fr die simulationsbasierte

Komfortbewertung.

Ahmad Hakim Mohd Sorihan ii

Declaration of Confidentiality

We, the University of Applied Sciences Konstanz, hereby acknowledge and agree to comply that this

master thesis entitled

Simulation Based Comfort Evaluation for Vehicles with Automated Transmissions

and the all the information contained in this thesis are not to be revealed to a third person or made

public without the written approval of hofer-pdc GmbH.

hofer-pdc GmbH Prof. Dr. Ing. Uwe Kosiedowski

Stuttgart, Konstanz,

Ahmad Hakim Mohd Sorihan iii

Declaration of Originality

I hereby declare that this master thesis entitled

Simulation Based Comfort Evaluation for Vehicles with Automated Transmissions

submitted as the final thesis of the master program Automotive Systems Engineering of University

of Applied Sciences Konstanz is written on my own and not made use of the work of any other party

or students past or present without acknowledgement, except those indicated by referencing.

____________________

Stuttgart, 28.02.2012

Ahmad Hakim Mohd Sorihan

Ahmad Hakim Mohd Sorihan iv

Acknowledgement

This master thesis for the final thesis of the Master course Automotive Systems Engineering would

not have been possible without the generous support and guidance of several individuals who in one

way or another contributed their valuable assistance in the preparation and completion of this

study.

First and foremost, I would like to express my gratitude to my supervisors Prof. Dr. Ing. Uwe

Kosiedowski of HTWG Konstanz and Dr Mathias Lutz of hofer-pdc GmbH for the opportunity as well

as the continuous assistance and supervision during my 5 month Master Thesis at hofer-pdc GmbH.

I would also like to thank Mr Jens Schfer and Mr Matteo Mocchi for the assistance in regards to the

software AMESim and DIAdem as well for the helpful advises for this thesis. My gratitude also goes

to Ms Elke Gamper and Ms Julia Hendrich for the help in reviewing this thesis.

Finally, I would like to thank the whole Simulation Department of hofer-pdc GmbH for the

comfortable and friendly atmosphere from the start till the end of my master thesis.

Ahmad Hakim Mohd Sorihan v

Table of Contents

1 Introduction .................................................................................................................................... 1

1.1 Motivation ............................................................................................................................... 1

1.2 Scope of Work ......................................................................................................................... 2

2 Simulation Software Used ............................................................................................................... 3

2.1 LMS Imagine.Lab AMESim....................................................................................................... 3

2.2 DIAdem ................................................................................................................................... 5

3 Theoretical Foundations ................................................................................................................. 6

3.1 Automotive Transmission and Powertrain ............................................................................. 6

3.1.1 Dual Clutch Transmission ................................................................................................ 7

3.1.2 Powertrain .................................................................................................................... 12

3.2 Subjective Evaluation of Driving Situation ............................................................................ 13

3.3 Objectification of Comfort Criteria ....................................................................................... 14

3.3.1 Driving Capability vs. Driving Tasks ............................................................................... 14

3.3.2 Driving Situations and the Respective Comfort Evaluation Criteria ............................. 15

3.3.3 Summary of the Driving Situations ............................................................................... 23

4 Simulation Model Setup and Parameterisation ............................................................................ 25

4.1 Overview of the Complexity of the Simulation Model ......................................................... 25

4.2 Simulation Components in AMESim ..................................................................................... 26

4.3 Reference Car ........................................................................................................................ 27

4.4 Reference Transmission: Getrag Powershift 6DCT250 ......................................................... 29

4.4.1 Dry Dual Clutches .......................................................................................................... 29

4.4.2 Electromechanical Actuator of the Dual Clutches ........................................................ 31

4.4.3 Gears and Gear Actuators ............................................................................................. 34

4.5 Reference Engine: 1.6 Ti-VCT ................................................................................................ 38

4.6 Control System ...................................................................................................................... 40

4.6.1 Launch / Moving Off ..................................................................................................... 42

4.6.2 Upshift ........................................................................................................................... 45

4.6.3 Downshift ...................................................................................................................... 48

5 Evaluation of Results ..................................................................................................................... 54

5.1 Script/Apps for Evaluation of Results ................................................................................... 54

5.2 Evaluation of Simulation Results........................................................................................... 55

5.2.1 Launch/Moving Off ....................................................................................................... 55

Ahmad Hakim Mohd Sorihan vi

5.2.2 Upshift ........................................................................................................................... 65

5.2.3 Downshift ...................................................................................................................... 76

5.3 Comparison of Simulated Driving Situations with the Real Measurement Data .................. 82

6 Conclusions and Future Improvements ........................................................................................ 85

7 Reference Index ............................................................................................................................ 87

8 Appendix ....................................................................................................................................... 89

8.1 AMESim Submodels Used in Simulation ............................................................................... 89

8.2 Table for Subjective Evaluation of Driving Situations ........................................................... 93

8.3 Simulation Model Basis ......................................................................................................... 95

8.4 App Interfaces ....................................................................................................................... 98

8.5 Python Code Snippets ......................................................................................................... 102

Ahmad Hakim Mohd Sorihan vii

List of Figures

Figure 1: LMS Imagine.Lab AMESim ....................................................................................................... 3

Figure 2: App Designer in AMESim ......................................................................................................... 4

Figure 3: Gear ratio ................................................................................................................................. 6

Figure 4: Schematic of a dual clutch transmission [1] ............................................................................ 7

Figure 5: Dry dual clutch with external torsion damper (left) and friction disk integrated damper

(right) [2] ................................................................................................................................................. 8

Figure 6: Electromechanical actuator of a dry dual clutch [4] ................................................................ 9

Figure 7: Concentric (left) and parallel design (right) of a multi disk wet dual clutch [1] ...................... 9

Figure 8: Wet dual clutch [2] ................................................................................................................. 10

Figure 9: Single cone synchroniser unit [5] ........................................................................................... 11

Figure 10: Gear shifter unit [1].............................................................................................................. 11

Figure 11: Powertrain structure of a commercial vehicle [1] ............................................................... 12

Figure 12: Driving capability vs. driving task ......................................................................................... 14

Figure 13: Launch, tL and launch hesitation, tLH .................................................................................... 16

Figure 14: Jerk during gear upshift 1 to 2 ............................................................................................. 18

Figure 15: Upshift from gear 1 to 2 ....................................................................................................... 19

Figure 16: Power on downshift from gear 4 to 3 .................................................................................. 20

Figure 17: Judder during clutch harmonisation .................................................................................... 22

Figure 18: Change of mind (let off) ....................................................................................................... 23

Figure 19: Rotary load in AMESim ........................................................................................................ 26

Figure 20: AMESim model of the b-segment car .................................................................................. 28

Figure 21: Getrag Powershift 6DCT250 Transmission [7] ..................................................................... 29

Figure 22: Cross-section view of Getrag 6DCT250 dry dual clutches [7] .............................................. 30

Figure 23: Dry dual clutch model in AMESim ........................................................................................ 31

Figure 24: LuK actuator unit for Ford 6DCT250 dual clutch transmission [8] ....................................... 31

Figure 25: Lever concept (left) and clutch actuator unit (right) [4] ...................................................... 32

Figure 26: Clutch actuator (for launch) ................................................................................................. 32

Figure 27: Clutch actuator for launch and gearshift ............................................................................. 33

Figure 28: Complex model of the clutch actuator ................................................................................ 34

Figure 29: Getrag Powershift 6DCT250 transmission layout [7] ........................................................... 35

Figure 30: Transmission model in AMESim ........................................................................................... 36

Figure 31: Gear actuator of Getrag Powershift 6DCT250 Transmission [7] ......................................... 36

Figure 32: Gearshift diagram for gear 1 to gear 4 ................................................................................ 37

Figure 33: 1.6 Ti-VCT engine [11] .......................................................................................................... 38

Figure 34: Engine torque characteristic curve ...................................................................................... 39

Figure 35: Engine model in AMESim ..................................................................................................... 39

Figure 36: Direct control system ....................................................................................................... 40

Figure 37: Control system with AMESim Sequential Function Chart .................................................... 41

Figure 38: Engine speed controller ....................................................................................................... 42

Figure 39: Desired engine speed curve ................................................................................................. 42

Figure 40: Control stages during launch in flowchart view .................................................................. 43

Figure 41: Launch from creep ............................................................................................................... 44

Ahmad Hakim Mohd Sorihan viii

Figure 42: Launch from brake ............................................................................................................... 45

Figure 43: Control stages during upshift from gear 1 to gear 2 in flowchart view ............................... 46

Figure 44: Engine torque controller ...................................................................................................... 47

Figure 45: Upshift from gear 1 to gear 2 ............................................................................................... 47

Figure 46: Gearshift diagram areas ....................................................................................................... 48

Figure 47: Control stages during power on downshift for gear 4 to gear 3 in flowchart view ............. 50

Figure 48: power on downshift for gear 4 to gear 3 ............................................................................. 51

Figure 49: Control stages during power on downshift for gear 2 to gear 1 in flowchart view ............. 52

Figure 50: Power off downshift for gear 2 to gear 1............................................................................. 53

Figure 51: Form window for base App (right) and scripted App for evaluation (left) .......................... 54

Figure 52: Launch from creep with simple clutch actuator model (see chapter 4.4.2) ........................ 56

Figure 53: Launch from creep with the complex clutch actuator model (see chapter 4.4.2) .............. 58

Figure 54: Launch from brake with simple clutch actuator model ....................................................... 60

Figure 55: Launch from brake with complex clutch actuator model .................................................... 61

Figure 56: Launch on hill with simple actuator model .......................................................................... 63

Figure 57: Comparison of upshift of gear 1 to gear 2 between the simple and complex actuator

model .................................................................................................................................................... 65

Figure 58: Upshift from gear 1 to gear 2 for accelerator pedal position 40 %, 70 %, 100 % ................ 67

Figure 59: Jerk of upshift from gear 1 to gear 2 for accelerator pedal position 40 %, 70 %, 100 % ..... 68





Figure 64: Power on downshift from gear 4 to gear 3 .......................................................................... 77

Figure 65: Jerk of power on downshift from gear 3 to gear 4 for different accelerator pedal position

change ................................................................................................................................................... 78

Figure 66: Power off downshift for gear 4 to gear 3............................................................................. 80

Figure 67: Jerk during power off downshift from gear 4 to gear 3 and gear 2 to gear 1 ..................... 80

Figure 68: Launch comparison between measured data and simulation ............................................. 82

Figure 69: Upshift gear 1 to gear 2 comparison between measured data and simulation .................. 83

Figure 70: Comparison of acceleration between measured and simulation ........................................ 84

Figure 71: Simulation model basis for launch ....................................................................................... 95

Figure 72: Simulation model basis for upshift ...................................................................................... 96

Figure 73: Simulation model basis for downshift ................................................................................. 97

Figure 74: App interface for launch with simple actuator model ......................................................... 98

Figure 75: App interface for launch with complex actuator model ...................................................... 98

Figure 76: App interface for upshift (shift time) ................................................................................... 99

Figure 77: App interface for upshift (jerk) ............................................................................................ 99

Figure 78: App interface for power on downshift (shift time) ............................................................ 100

Figure 79: App interface for power on downshift (jerk) ..................................................................... 100

Figure 80: App interface for power off downshift (shift time) ........................................................... 101

Figure 81: App interface for power off downshift (jerk)..................................................................... 101

Figure 82: Code snippet for basic plotting app class .......................................................................... 102

Figure 83: Code snippet for basic LED display of calculated values.................................................... 103

Ahmad Hakim Mohd Sorihan ix

List of Tables

Table 1: Subjective evaluation widely used by Automakers [1] ........................................................... 13

Table 2: Summary of the driving situations .......................................................................................... 24

Table 3: Overview of the simulation model complexity ....................................................................... 25

Table 4: Overview of the variable parameters and evaluation criteria for the simulation .................. 26

Table 5: Technical data of the reference b-segment car ...................................................................... 27

Table 6: Technical data of Getrag Powershift 6DCT250 transmission [7] ............................................ 29

Table 7: Gear ratio of Getrag Powershift 6DCT250 Transmission ........................................................ 35

Table 8: Technical data of the reference engine [9] [10] ...................................................................... 38

Table 9: Evaluation criteria for launch from creep with simple actuator model .................................. 57

Table 10: Evaluation criteria for launch from creep with complex actuator model ............................. 59

Table 11: Evaluation criteria for launch from brake with simple actuator model ................................ 60

Table 12: Evaluation criteria for launch from brake with simple actuator model ................................ 62

Table 13: Evaluation criteria for launch on hill with simple actuator model ........................................ 64

Table 14: Jerk of upshift from gear 1 to gear 2 for accelerator pedal position 40 %, 70 %, 100 % ...... 68

Table 15: Jerk of upshift from gear 2 to gear 3 for accelerator pedal position 40 %, 70 %, 100 % ...... 71

Table 16: Evaluation criteria for upshift from gear 3 to gear 4 for accelerator pedal position 40 %, 70

%, 100 % ................................................................................................................................................ 74

Table 17: Evaluation criteria for power on downshift for gear 4 to gear 3 .......................................... 78

Table 18: Evaluation criteria for power off downshift for gear 4 to gear 3 and gear 2 to gear 1 ........ 81

Table 19: AMESim Signal and Control library ....................................................................................... 90

Table 20: AMESim Mechanical library .................................................................................................. 91

Table 21: AMESim Powertrain library ................................................................................................... 92

Table 22: AMESim Sequential Functional Chart (SFC) library ............................................................... 93

Ahmad Hakim Mohd Sorihan x

List of Abbreviations

AMESim LMS Imagine.Lab AMESim

AMT Automated Manual Transmission

DCT Dual Clutch Transmission

CVT Continuous Variable Transmission

App Application

ICE Internal combustion engine

OSS Output shaft sensor

ISS Input shaft sensor

Acc pedal Accelerator pedal

CAN Controlled Area Network

SFC Sequential Functional Chart

c1, c2 Clutch 1, clutch 2

Tc1, Tc2 Torque of clutch 1, torque of clutch 2

Fc1, Fc2 Actuation force on clutch 1, actuation force on clutch 2

hofer hofer-pdc GmbH

VW Volkswagen AG

Introduction

Ahmad Hakim Mohd Sorihan 1

1 Introduction

1.1 Motivation

In the last few years, the number of passenger vehicles with automated transmission is increasing

rapidly. At the same time, the design variation of automated transmission is becoming more and

more diverse. Besides the well-known automatic transmission with torque converter and planetary

gear wheels, other types of transmission such as the continuous variable transmission (CVT),

automated manual transmission (AMT) and the dual clutch transmission (DCT) are becoming more

popular in the passenger car market. The listed automated transmission types can be further

classified according to their realisation concept, such as the wet and the dry variation type of the

dual clutch transmission.

As a result of the differences in the concept implementation of the listed transmissions, the driving

experience also varies according to the different transmission concept. The driving dynamics, as well

as the comfort perception are evaluated by the driver in a subjective way. As a way to improve the

development of the transmission, objectification of the drivers subjective perception is the way

forward. As an example, the power interruption period during acceleration with an automated

transmission can be used as an evaluation criterion, since the transmission does not allow a power -

interruption-free shifting.

A lot of evaluation criteria such as the one mentioned above are already put into used in the early

stages of simulation-based evaluation. The challenge however lies in the complete evaluation using

the objective criteria defined, without relying on the subjective perception of the driver. It is also

important to make sure that the parameters as well as the control strategies used in the simulation

can be implemented realistically on the real transmission.

Introduction


1.2 Scope of Work

The aim of this master thesis is to evaluate the subjective perception of comfort in different driving

situations by means of simulation. These driving situations are focused on vehicles with automated

transmission.

To start off, a variety of driving situations was listed and defined. In order to evaluate the listed

situations, suitable evaluation criteria were determined to produce the required objective results,

i.e. representing and explaining the evaluated driving situations in an accurate matter, in other

words, to objectify the subjective perception of comfort during driving. To help the author of the

thesis to understand more about the driving situations, several test drives were performed.

Subsequently, suitable driving situations were chosen considering the time constraint of the master

thesis and the difficulty to realise such driving situations on a simulation program.

The chosen driving situations were simulated using the simulation program LMS Imagine.Lab

AMESim, or simply AMESim. Depending on the necessity, other programs such as Diadem were used

to assist the simulation and evaluation process. The simulation model parameters were calibrated to

the reference transmission. The simulation model in the early stage was relatively simple and

uncomplicated. Depending on the results of the early stage simulation, improvements were made

where deemed necessary by increasing the complexity of the model.

Using the measurement methods determined in the first part of the task, objective results were

obtained and evaluated. By comparing the simulation results achieved from the hofer benchmark,

results from the simulation would then be compared with the measurement data from hofer,

further improvements of the simulation were made where deemed necessary. Additionally, in order

to facilitate the evaluation process of the obtained results, several programming scripts were

written. In the end, conclusions are made according to the comparisons and evaluation of the

results.

Simulation Software Used


2 Simulation Software Used

To carry out the tasks of the thesis smoothly, it is required that the student were able to use the

software products such as AMESim and DIAdem. Since both software programmes were not familiar

to the student, an introduction time to learn and familiarise with the software was needed. The

software products used to carry out this Master Thesis are described in the following sub chapter.

2.1 LMS Imagine.Lab AMESim

LMS Imagine.Lab AMESim or simply AMESim is an element or component based simulation software

for the modelling and simulation of one-dimensional systems developed and distributed by LMS

International. The software package offers a 1D simulation suite to model and analyse the hydraulic,

pneumatic, electrical and mechanical behaviour of the 1D system. In its usage AMESim is similar to

Simulink.

For modelling of the system, AMESim is equipped with approximately 30 libraries. Due to the

partnership of hofer-pdc GmbH with LMS, the complete library package is provided. The important

libraries for this thesis are controls, mechanical, pseudo-mechanical, hydraulics, electrical,

thermodynamics and powertrain. More about the elements used for the simulation in this thesis can

be read under appendix.

Figure 1: LMS Imagine.Lab AMESim

The figure 1 shows a standard interface of AMESim. The modelling and simulation of a system is

done in four steps: sketch, submodel, parameter and run. These four steps are represented or

highlighted by the 4 panels on the left side of the screen. The four steps are:



Sketch mode: Components are selected from the library and are linked together to form a

system. Drag-and-drop functionality simplifies and accelerates modelling processes.

Submodel mode: Physical submodel associated to each component is chosen.

Parameter mode: The parameters for each submodel of the system are set and compiled.

Run mode: The simulation is run. The run mode also includes the pre-processing mode. The

needed curves which show the behaviour of the system (e.g. displacement vs. time) can be

viewed after the simulation ended.

AMESim also provides an App Designer. The App Designer is a pre and post-

processing IDE (Integrated Development Environment) that can be used to create user interfaces

(which are also called App) for the users specific needs, use and reuse them within AMESim. The

App Designer uses the already known QT-Platform with several modifications by AMESim to

accommodate its users. Normal users can use the available widgets to assist their work. Advanced

python users can additionally design their own widgets by writing their own python scripts (e.g. to

enable them to automate the obtaining and evaluation of the simulation results).

Figure 2: App Designer in AMESim

The simulations in this thesis are done using this software program. The App Designer is used

automate the repeating steps taken to obtain the simulation results.



2.2 DIAdem

DIAdem is a technical software for managing, analysing, and reporting technical data developed by

National Instruments. It is used to analyse data sets that are obtained from test drive equipment,

provided by National Instrument. With this software it is also possible to use mathematical functions

on a data set or a curve such as the average, integration and differentiation function and in the end

graphically present it in a report.

This software program is used to read and edit the results obtained from the test drives.

Theoretical Foundations


3 Theoretical Foundations

3.1 Automotive Transmission and Powertrain

A transmission plays a very important role in passenger and commercial vehicles. The main task of a

transmission is to convert the traction supplied from the power source, mainly the internal

combustion engine, to satisfy the requirements of the driving situations performed by the driver. A

transmission consists of sets of gears to provide different gear ratios for the mentioned different

driving situations. As an example, during start up or launch of a vehicle from stationary, the driver

might want to accelerate from stationary to the desired speed. Hence, a combination of gears which

provide a high gear ratio is needed to convert the supplied torque from the engine and accelerate

the vehicle. In addition, a transmission also plays an important role in respect to fuel consumption,

reliability and safety.

The following figure depicts a simple gear set in a schematic view. Gearwheel 1 is connected to shaft

1 and gearwheel 2 to shaft 2 respectively. The letters n stands for rotation per minute, T stands for

the torque and z stands for the gear teeth number.

Figure 3: Gear ratio

The gear ratio of a gear set can be calculated as follows:

(3.1)

As mentioned, an automotive transmission consists of several gear sets as depicted above to provide

suitable gear ratios respective to driving situations and fuel consumption. In general, an automotive

transmission may be in the form of manual transmission, automatic transmission or automated

manual transmission.

Shaft 1

Shaft 2

n1, T1

n2, T2

z1

z2



3.1.1 Dual Clutch Transmission

To understand this thesis, it is important to get to know the type of transmission used in the test

drive and for the simulation. The evaluation of the comfort criteria would be done using a dual

clutch transmission (see chapter 4.4).

Dual clutch transmissions (DCT) are categorised as automatic transmission with various gear ratios

due to their similarities with respect to control and functionality [1]. A DCT combines the

characteristics of a manual transmission, such as a high level of efficiency, a broad range of gear

ratios and sportiness, with the ease of handling and shifting without power interruption from an

automatic transmission.

A DCT generally consists of two sub-gearboxes, each connected to the engine through its own clutch.

One sub-gearbox contains the odd gears (1, 3, 5) while the other contains the even gears (2, 4, 6).

The following figure shows a schematic design of a DCT.

Figure 4: Schematic of a dual clutch transmission [1]

With the help of the figure above, a basic gear shifting process can be explained as follows. While

accelerating in the first gear, the idle second gear is preselected and engaged. Since clutch 2 is not

engaged during the idle gear synchronisation process, there is no interruption to the torque supplied

by the engine. The driver does not notice the synchronisation process. When the speed for the

upshift from first gear to second gear is reached, clutch 1 disengages at the same time when the

clutch 2 engages. This phase is known as the cross-fading phase. This enables a power-interruption-

free gear shifting. Once the shifting process ends, the next gear, the third gear, can be preselected,

while the first gear is disengaged and the same steps is repeated for upshift. This principle is

basically the same for upshift and downshift.

The dual clutch built in a DCT can be further divided into two variant types, namely the wet dual

clutch and the dry dual clutch transmission.



Dry Dual Clutches

Dry dual clutches are normally used in small vehicle with low engine torque not more than 250 Nm.

A clutch of a dry dual clutch transmission usually consists of a single friction plate and the torque is

transmitted via pressure plate and friction plate of the clutch, like a normal clutch of a manual

transmission. However, there are some design differences compared to the clutch of a manual

transmission, such as the dry clutch is normally designed to be in open position (disengaged) when

no force is applied to the clutch. It is designed that way to fulfil the safety requirement, which

requires the clutch to open automatically when the clutch actuation system fails. Another difference

is, because of the high actuation force of dual clutches, direct linkage and bearing support on the

crankshaft is not feasible due to the high load. So, the clutch needed to be supported at one of the

two shafts of the transmission.

There are further two known variants of support design on the shaft. The position of the support

bearing is preferred to be on the hollow shaft. What differs here is the position of the damper to

eliminate or reduce unwanted oscillation between the engine and the clutches. In variant 1, the

torque damper is mounted on the crankshaft, and the crankshaft is linked to the clutch via a drive

gear. This drive gear is preloaded in circumference direction and can also compensate axial tolerance

between the engine and the transmission shafts. In variant 2, torque dampers are integrated to each

friction plate of each clutch. The crankshaft is connected to the transmission shafts via a flywheel

with a cardanic function. The cardan joint is made of elastic elements which can compensate radial

and axial tolerance between the engine and the transmission shafts [2].

Figure 5: Dry dual clutch with external torsion damper (left) and friction disk integrated damper (right) [2]



Figure 6: Electromechanical actuator of a dry dual clutch [4]

The figure above presents the electromechanical actuation concept of a dry clutch. The dry clutch is

actuated by an E-Motor by means of engagement lever. When the E-Motor is supplied with power,

its shaft-rotation would be converted to translational displacement by the ball screw. The roller on

the ball screw here acts as a variable pivot. The apply spring supplies the preload on one lever end.

By varying the position of the pivot, different actuation can be achieved on the other end of the

lever.

Wet Dual Clutches

Wet dual clutches are used in vehicles with high engine output, typically 250 Nm and above. The

typical design of wet dual clutches consists of multiple friction disks, to accommodate the high input

load. They are mounted directly on the transmission shafts or in an external clutch carrier connected

directly to the transmission. Most of the wet dual clutches currently in the market are actuated by

hydraulic means [2]. There are two typical wet dual clutch designs known implemented by

automakers, which are

concentric design (also called radial arrangement)

parallel design (also called axial arrangement)

Figure 7: Concentric (left) and parallel design (right) of a multi disk wet dual clutch [1]



Concentric clutches are advantageous for short installation spaces. In a vehicle which uses the

concentric design, the outer clutch is preferred as master clutch due to its higher thermal capacity,

suitable for low gears which need to transfer high input torque. The cooling oil flows first through

the outer clutch to the inner clutch. In the contrary, parallel design are applied in transmission which

has limited space in the radial direction. The parallel design enables the first gear to be controlled by

either the outer or the inner clutches. Another advantage of such arrangement is that the cooling oil

can be supplied separately to each clutch.

The following figure presents a dual clutches in concentric design. From the figure, it can be

identified that the torque damper are arranged in the dry space between the engine and the dual

clutch. Another alternative to this design is to integrate the torque damper to the dual clutch plates

in the wet chamber, similar to the dry dual clutch design. To actuate the clutches

electrohydraulically, an external hydraulic pack is necessary. The hydraulic pack consists of a

hydraulic pump, which pumps the cooling oil and the oil to actuate the clutches, and a valve block

for controlling. The actuation oil from the pump would flow through the rotary oil passages to the

pressure chambers. Parallel to the pressure chambers are compensation chambers, which are

needed to compensate the influence of centrifugal oil pressure that builds up from the rotation.

Figure 8: Wet dual clutch [2]

Synchronizer and Gear Actuation

In simpler words, synchronisation of a gear in a vehicle with dual clutch transmission can be defined

as firstly, friction coupling with non-planar friction plane, that follows with form locking of an idle

gear to a sub-gearbox shaft, to transfer power from the input shaft via the now engaged idle gear

and sub-gearbox shaft, to the output shaft. Depending on the application in vehicles (passenger



vehicle and commercial vehicle), a synchronizer unit may differ in terms of the number of non-planar

friction plane (also known as cone) involved during synchronisation process. In practice there can be

up to 3 non planar friction planes in a synchroniser unit (single cone, double cone or triple cone). The

number of cones is a multiplication factor for the synchronisation capability of a synchronizer [5].

The figure below depicts a single cone synchronizer.

Figure 9: Single cone synchroniser unit [5]

The same or similar synchroniser unit can also be found on each sub-gearbox shaft in a dual clutch

transmission. However, in a dual clutch transmission, the far left and far right idle gears should be

consecutive either odd or even number gears (e.g. 1st gear and 3rd gear or 2nd gear and 4th gear) so

that gear pre selection during upshift and downshift can be achieved. During gear change, the

gearshift sleeve would be shifted to the desired shift position. The gearshift sleeve is connected to a

gear shifter, which can be seen in the figure 10 below.

Figure 10: Gear shifter unit [1]



Gear shifter can be actuated by means of hydraulics or electric. The gear shifter presented above is a

hydraulic operated gear actuator of a dual clutch transmission. As mentioned under the previous

chapter (3.1.1 Dry Dual Clutches), a hydraulic operated actuator is preferred for wet dual clutch

transmission and hydraulically operated DCT-systems. The same applies to eletromechanically

operated DCT-systems. One distinguished feature of a hydraulic gear shifter is the locking element,

which is needed to supply the locking force to the synchronisation force from the hydraulic piston.

3.1.2 Powertrain

In general, the torque supplied by the engine in a vehicle must pass through several components

before the output at the vehicle tyres. The engine torque is converted through multiplication of each

gear ration from these components. The whole combination of the components is called powertrain.

A powertrain mainly consist of 4 sections, which is the engine, the coupling element, the

transmission and the final drive, as depicted below.

Figure 11: Powertrain structure of a commercial vehicle [1]

The total ratio iA is the multiplication product of the ratio of each the coupling element, the selector

gearbox and the final drive.

(3.2)

It is important to understand how the powertrain works, since the output torque at the tyres are

influenced by the components in each section, as can be seen above.



3.2 Subjective Evaluation of Driving Situation

The evaluation of comfort by a driver, which consists of noise, visible and sensible oscillation, can

be developed through his or her subjective perception. Since every drivers perception can differ

from one another, it is important to evaluate how comfortable the driving experience through a

group of trained evaluators and a group of customers and taking the average marks from each

group. The following table presents one of the ways to summarise the evaluation given by the

evaluators that is normally used by the major automakers. The scale used is 1 to 10, with 10

representing the best mark and 1 the worst.

Marks Flaw detection Evaluation

10 Not detectable by trained evaluators Excellent

Marketable 9 Detectable by trained evaluators Very good

8 Detectable only by critical customers Good

7 Detectable by all customers Satisfying

6 Sensed by some customers as disturbing Acceptable

Not marketable

5 Sensed by all customers as disturbing Not acceptable

4 Sensed by all customers as faulty Faulty

3 Complained and claimed by customers Fail

2 Only partly functioning Bad

1 Not functioning Very bad

Table 1: Subjective evaluation widely used by Automakers [1]

The subjective evaluation data are already available as reference for this thesis. However, to

increase the understanding of how the subjective evaluation is carried out, a simple subjective

evaluation was done by the student as an example. The test was carried out using a VW Passat 2.0

which is also equipped with a dual clutch transmission. The evaluation table used by hofer can be

found under appendix.



3.3 Objectification of Comfort Criteria

To evaluate how comfortable a person driving is actually a very difficult task because there are no

objective guidelines to it. The feeling of comfortable is very subjective depending on different

person. Therefore, this chapter would elaborate on the objectification of subjective feelings that

would be used to evaluate the driving situation chosen.

3.3.1 Driving Capability vs. Driving Tasks

Before proceeding with the objectification of the subjective criteria, it is important to determine the

target type of drivers. The type of driver is typically differentiated in two categories, the sporty

driver and the driver that prefers comfortable driving. One way to differentiate between the two

types of drivers is by using the following driving capability vs. driving tasks curve.

Figure 12: Driving capability vs. driving task

A drivers capability is determined by:

competence: Driving licence, extra training, experience

psychological factors: feelings (under stress, anxiety)

substance: under alcohol or drug influence

and many more. Whereby driving tasks are determined by the following factors:

increase with increasing driving resistance (air resistance, slope, rolling resistance,

acceleration)

secondary factors: pedestrian, road regulations and many more [6].



From the curve, we can clearly conclude that a comfortable driver is a driver that feels that they

have the vehicle under control by having more capabilities than tasks, while a sporty driver is a

driver that likes to prefer using their own capabilities to take on the driving tasks.

Our target driver is the comfortable driver. This means that the drivers in this category would like to

have, to some extent, driving assistance to have a smooth and unburdening driving. An example of

such driver is a driver that prefers automatic transmission with smooth gear shifts without

vibrations.

3.3.2 Driving Situations and the Respective Comfort Evaluation Criteria

Driving situations that affect the comfort of driving were determined, before an appropriate method

of evaluating can be assigned. The following driving situations were identified as having most effect

on the driving comfort and needed to be evaluated.

Launch

Creep

Gear upshift and downshift

Hill hold

Judder

Change of mind

To assist the simulation process regarding the driving situations, it also makes sense to identify the

participating sub-systems as well as the measurement instruments (sensors and actuators) used for

each driving simulations. This information is to be summarised in a table and suitable driving

situations can be chosen based on the information of each driving situations.

Launch

In a non-technical term, launch is understood as start-up or moving off of a vehicle from stationary

condition to the desired speed. In this thesis, launch is further divided into two sub-definition, that is

launch and launch hesitation. The definitions used in launch are as following:

Launch hesitation, tLH: Period between accelerator pedal actuation and maximum vehicle

acceleration

Launch, tL: Period between maximum vehicle acceleration and full clutch engagement

Total time, tT: Sum of launch and launch hesitation

The sub-systems taking part during launch are:

Accelerator pedal



Transmission, which includes first gear and final drive ratios and inertias

Clutch, including clutch actuator and clutch control

Engine, including inertia and engine control strategy

Road profile, for plane and hill launch

Figure 13 can help present the definitions of launch and launch hesitations. The upmost curve shows

the engine speed in red and shaft 1 speed in green. The middle curve shows the acceleration of the

vehicle while the last curve shows the accelerator pedal actuation signal.

Figure 13: Launch, tL and launch hesitation, tLH

To determine the exact time where each section (launch and launch hesitation) starts, a method of

quantification is needed. The right parameters must first be determined, and then the respective

signals from the respective sensors can be obtained, either from the Transmission Control Unit or

through external built sensors.

In this case, the accelerator pedal potentiometer can provide the start time of the launch. The time

where maximum acceleration is reached, which signals the end of launch and start of launch

hesitation, is calculated through the speed signal of the output speed sensor (OSS). The speed of

each sub-gearbox is obtained from its own sensors while the input speed sensor (ISS) provides the



engine speed. Therefore, the moment of the speed harmonisation of the engine and shaft 1 can be

calculated at the time when both speeds reach a common speed with a constant micro slip.

Creep

Creep is normally associated with automated transmission. At start-up, when the driver shifts the

gear lever into drive mode (D) but without following up by actuating the accelerator pedal or the

brake pedal, the vehicle would accelerate on its own until it reaches a certain creeping speed and

moves forward constantly with this speed. This phenomenon is called creep. Creep in a vehicle with

dual clutch transmission is usually achieved by actuation of the clutch with a certain amount of slip

(the clutch is not 100% closed).

Creep is simulated together with launch. Hence, the sub-systems taking part are almost the same as

during launch, except that an extra creep control strategy which control the clutch slip during

creeping is needed.

The figure 13 also shows creep of the vehicle. If the driver still has not actuated the accelerator

pedal after 1 s, the vehicle would start accelerating until it reaches the creep speed. This can be seen

through the shaft 1 speed (green curve) of the upmost curve in the figure. The speed difference

between the engine speed and the shaft 1 speed can be seen here, which indicates the micro slip in

the clutch.

Gear Upshift and Downshift

One of the main reasons of the introduction of dual clutch transmission into the automotive market

was to improve the smoothness of gear shifting. The key to determining the evaluation parameter is

the change felt by the driver. When a driver is driving at a constant speed, he or she would not feel

any significant vibration with his or her body. Only when the driver is accelerating would the driver

feel the change with his body. Therefore, peak to peak acceleration, app, as an example, can be used

as a criterion for objectification of the subjective comfort feeling felt by the driver during gear

shifting.

Another criterion widely used by the automakers to evaluate shifting smoothness is shock intensity

or jerk (J). Shock intensity or jerk is defined as rate of change of longitudinal acceleration.

(3.3)

It is widely accepted by automakers that jerk value of 5 m/s3 as comfortable to drivers.



Figure 14: Jerk during gear upshift 1 to 2

The figure above shows the acceleration (top) and jerk (bottom) during upshift from gear 1 to gear 2.

The acceleration which falls almost instantaneously during the cross-fading from around 6.3 s to

6.62 s (labelled A) causes average jerk (in green) of approximately -6 m/s3. As the engine speed is

reduced to match the shaft 2 speed, the vehicle is moving with a constant acceleration, hence the

constant jerk, labelled with B. As the engine speed reaches the speed of the shaft 2, the matching up

of the two speeds causes a slight increase in acceleration hence an average jerk around 5 to 10 m/s3

(labelled with C).

Besides the named criteria above, it is also plausible to take into account the torque phase time,

speed phase time and the total shifting time [3]. These parameters can be defined as follows.



Torque phase time, tTP: The period between start of torque reduction of the off going clutch

and until the oncoming clutch fully engaged (also known as clutch cross-fading). It can also

be approximately measured from the acceleration curve, from the fall of acceleration until

the minimum acceleration (area labelled as A in figure 14)

Speed phase time, tSP: The period of the deceleration of the engine speed to oncoming shaft

speed. It can approximately be measured starting from the minimum acceleration until the

acceleration rise again (area labelled as B in figure 14)

Shifting time, tS: Total shifting time which is the sum of torque phase time and speed phase

time.

The two phases of gear upshift (torque phase and speed phase) are explained in detail in chapter

4.6.2. The following figure presents the evaluation parameters mentioned above, which are torque

phase time, speed phase time and shift time.

Figure 15: Upshift from gear 1 to 2

For power on downshift, the order of the tTP and tSP is reversed. The reason is further discussed in

chapter 4.6.3. The following figure depicts the evaluation parameters for power on downshift of

gear 4 to 3.



Figure 16: Power on downshift from gear 4 to 3

The sub-systems taking part during upshift and downshift are:

Accelerator pedal

Transmission, which includes first gear and final drive ratios and inertias

Transmission control unit, which is responsible for transmission control strategies

Clutch, including clutch actuator and clutch control

ICE , including inertia and engine control strategy

ICE control unit, which is responsible for ICE control strategies

Road profile

Engine speed, shaft 1 and shaft 2 speeds are provided by their own sensors respectively. The vehicle

speed is obtained from the OSS and then differentiated by means of evaluation software programs

such as DIAdem or even MS Excel to get the evaluation parameters acceleration and jerk

respectively. From the acceleration curve, the torque phase time and speed phase time can be

calculated.



Hill Assist Control

Hill assistant is a mechanism that prevents the vehicle from rolling backwards down a hill when the

brake pedal is released by the driver. The aim of the mechanism is to increase driving comfort during

hill launch. The implementation of hill hold mechanism for a vehicle with a dry dual clutch

transmission is particularly complicated, since the dry clutch would be closed when the brake pedal

is released on hill. If the hill is too steep or the time taken to actuate the accelerator pedal is too

long, the clutch would get hot and subsequently lose its friction coefficient. To avoid any defect on

the clutch, most of the hill hold strategy used by the automakers is to disengage the clutch and let

the vehicle roll backwards.

It is plausible to measure the hill hold time, tH, of a vehicle on different angle of slope. Hill hold time

can be defined as period between releasing the brake pedal until the vehicle starts rolling

backwards. Generally it is preferable to drivers that a vehicle has a long hill hold time, so that a

driver could switch from brake to accelerator pedal without rushing, hence avoiding mistakes such

as rollback or engine stalling.

An additional element which is important for hill hold is the slope sensor. One of the requirements

of the activation of the hill start is that the vehicle needs to be on a slope. However, if the slope

angle is more than the critical angle, the hill hold mechanism would not be activated at all to avoid

hot clutch. The moment when the vehicle starts to roll backwards can be determined from the

speed signal provided by the OSS.

Judder

Judder can be defined as vertical oscillation of a vehicle. Judder usually happens during vehicle

motion at low speed and low accelerator pedal actuation level, which is normally lower than 30%.

Vehicle controls nowadays are optimised to avoid judder at every speed; hence it is very difficult to

get a vehicle to judder intentionally. Evaluation parameters that can be used to measure judder are

the peak to peak values of the vehicle speed oscillation and its frequency. Low amplitude judder can

however be easily detected at sub-gearbox-shafts mainly during engagement of the clutch due to

the unoptimised controller settings.



Figure 17: Judder during clutch harmonisation

Figure 17 shows a low amplitude judder during clutch harmonisation at launch. The shaft oscillation

does not cause the vehicle to judder, as can be seen from the speed curve of the vehicle most

probably due to the damping in the powertrain.

Change of Mind

Change of mind can be divided further into two sub categories, which is tip in and let off.

Tip in can be defined as quick sudden pressing of the accelerator pedal during deceleration. This can

occur in situation such as when a driver, who is on a branch road, is decelerating to find a gap in

between vehicles on the main road, and as soon as a gap was found, the driver would press the

accelerator pedal quickly to drive his or her vehicle into the gap. The tip in time, tTI, which is the time

between the actuation of the accelerator pedal and the moment when the vehicle starts

accelerating, can be used as a criterion to evaluate tip in.

In contrary to tip in, let off is defined as the sudden releasing of accelerator pedal when accelerating

(pressing of accelerator pedal). This can occur when a driver suddenly sees an obstruction in front of

him that needs to be avoided, and quickly releasing the accelerator pedal to actuate the brake pedal.

At this moment the vehicle control unit should be able to detect the drivers request and react as

fast as it can to reduce the vehicle speed. The let off time, tLO, is the time period between the release

of the accelerator pedal and the moment when the vehicle starts decelerating.



The following figure depicts the change of mind driving situation, namely sudden the let off of the

accelerator pedal during driving. As can be seen from the figure, the vehicle only starts to slow down

after 2 s letting off of the accelerator pedal.

Figure 18: Change of mind (let off)

3.3.3 Summary of the Driving Situations

The driving situations explained in the previous sub-chapters are summarised in the table below.

Driving situation

Description Measurement instruments

Measurement method & quantification

Root causes / corresponding subsystems

Test data

Launch & launch

hesitation

Launch hesitation: defined as the period between acc pedal actuation and the moment when the vehicle reaches peak acceleration Launch: period from the moment of peak acceleration until clutch is fully closed Total time: Launch hesitation + launch test variation: -on plane & on slope -from creep & from brake

-Acc pedal potentiometer -OSS -ISS -Sensors on sub-gearboxes

Potentiometer (sensor) at acc pedal provides time when acc pedal is pressed, Output speed sensor provides time of acceleration begin. 'Intersection' of engine speed and shaft speed to detect closed clutch. Sensor at sub-gearbox shaft provides shaft speed, input speed sensor (ISS) provides engine speed. Signals from sensors acquired from TCU/ECU through CAN

Acc pedal -Transmission - Clutch - Clutch Actuation (electromot. or hyd.) -Road profile -Engine - Inertia - Delays from ECU (incl. discreteness) - ICE control strategy (ICE speed by control of torque)

Yes



Driving situation

Description Measurement instruments

Measurement method & quantification

Root causes / corresponding subsystems

Test data

Creep

Creep: Vehicle moves forward when driver shifts to 1st gear, without pressing acc pedal Variation: -zero pedal, from brake release -on fixed grade

-OSS -ISS

Creep speed and acceleration provided by the OSS

-Engine -Acc pedal -Transmission - Clutch controlled in Slip mode? - Control towards target speed?

Yes

Gearshift (up-/

downshift)

Upshift from gear 1 to gear 6 / downshift from 6 to 1 under normal condition.

-Acc pedal potentiometer -OSS -ISS -Sensors on sub-gearboxes

Evaluation of shifting through 'jerk' and velocity curve of the car

-Acc pedal -Transmission - Clutch - Clutch control (slip) -Road profile (flat road) -Engine - Inertia - ICE sontrol strategy (ICE speed by control of torque)

Yes

Hill hold & hill assist control

Hill hold: Vehicle does not slip down when driver switch from brake pedal to acc pedal on hill Measure maximum holding time at certain slope Variation of strategy: -closing of clutch - brake assistance

-Slope sensor -Acc pedal sensor -OSS -ISS -Sensors on sub-gearboxes -Brake signal

Slope sensor,OSS provides time when the vehicle begins to slip. Signal from acc pedal must be zero! Indentify brake assistance strategy through brake signal, clutch closing through shaft speed sensor and ISS

-Transmission - Thermal model for clutch -Road profile -(brake/brake assistance)

Yes

Judder

Judder: Vibration during idle and low vehicle velocity

-Acc pedal sensor -OSS -ISS -Sensors on sub-gearboxes (-Slope sensor)

Evaluation of shifting through 'jerk' and velocity curve of the car

- Transmission - Clutch with "capability for judder"

Yes

Change of mind -tip in -let off

Tip in: Quick sudden pressing of the acc pedal during deceleration. Instead of shifting down, stay at the same gear and anticipate next move of the driver. Let off: Qquick sudden releasing of the acc pedal during acceleration. Instead of shifting up, stay at the same gear and anticipate next move of the driver.

-Accelerator pedal potentiometer -OSS -ISS -Sensors on sub-gearboxes

Period between tipping the accelerator pedal until the car starts accelerating is calculated. Measurement same as 'launch hesitation'. Period between let off of the accelerator pedal until the car starts decelerating is calculated. Measurement same as 'launch hesitation'.

-Acc pedal -Transmission - Shift Strategy -(Engine)

Partially avail-able

Table 2: Summary of the driving situations

After careful consideration regarding the time frame of the thesis and the workload, the driving

situations launch, creep, upshift and downshift were chosen to be simulated.

Simulation Model Setup and Parameterisation


4 Simulation Model Setup and Parameterisation

This chapter deals with the modelling of the simulation sub-systems by using the chosen reference

vehicle. Besides the model setup, variable parameters used and model complexity variations are also

presented in the following chapters. This chapter would be the prerequisite to understanding

chapter 5, which presents the simulation results.

4.1 Overview of the Complexity of the Simulation Model

The following table depicts the overview for the simulation done for this thesis. There are a total of 5

submodels that needed to be modelled, which are the engine, clutch actuator, car, gears and

synchronizers, and the control system.

Launch Upshift Downshift

from Brake

From Creep

Launch on

slope

1-4 Power off Power on

(gear 2-1) (gear 4-3)

Engine Basic x x x x x x

Extended x x x

Complex

Clutch-Actuator Basic x x x x x x

Extended

Complex x x

x (gear 1-2)

Car Basic

Complex x x x x x x

Gears & Synchronizer Basic x x x x x x

Control

Direct x x

Flow diagram x x x x x x

Table 3: Overview of the simulation model complexity



The variable parameters and the evaluation criteria for each driving situations are listed in table 4.

Launch Upshift Downshift

from Brake

From Creep Launch on slope

1-4 Power off Power on

(gear 2-1) (gear 4-3)

Variable parameters

Acc pedal position (1,0 - 0,3)

x x x x

x

Slope

x

Friction coefficient x x x

Evaluation criteria

Launch x x x

Launch hesitation x x x

Cross-fading time

x x x

Total shift time

x x x

Jerk

x x x

Max. creep speed x x x

Max. slope x x x

Table 4: Overview of the variable parameters and evaluation criteria for the simulation

4.2 Simulation Components in AMESim

Simulation components in AMESim are called submodel and usually consist of one or more ports. It

is important to understand that the number of ports does not necessarily represent the number of

input or output. A port can consist of multiple numbers of input or output and at the same time the

combination of both input and output.

Figure 19: Rotary load in AMESim

Figure 19 shows as an example a rotary load with two shafts and friction in AMESim. The two shafts

represent the ports of the submodel. As can be seen, the both shafts consist of inputs and outputs at

the same time. The left shaft has an input torque and provides an output angular speed, whereby

the right shaft has an input torque, which can occur because of reaction force from other connected

component, and an output angular acceleration.



4.3 Reference Car

The car that is used as a reference for the simulation is one of a b-segment class car. Some of the

examples in this class include VW Polo, Ford Fiesta and Peugeot 206. Further information about the

engine, transmission and other submodels are presented together with their simulation models in

the following sub-chapters.

The general information of the car is summarised in the following table. The information is provided

by hofer internal.

Curb weight 1110 kg

Maximum speed 190 km/h

Acceleration 1-100 km/h 10.0 s

Drag coefficient cw 0.3

Front cross-section area AF 2.2 m2

Fuel type Gasoline

Fuel consumption urban/outside urban/combined 7.8/4.5/5.8 (litre/100 km)

CO2 Emission 133 g/km

Tyres 195/50 R 15 H

Power density 0.09 kW/kg

Table 5: Technical data of the reference b-segment car

The following figure presents the vehicle model in Amesim. The vehicle submodel is a 2D submodel

with 3 degrees of freedoms due to its longitudinal, vertical and pitch translation. Basic geometrical

parameters of the vehicle such as its mass, centre of gravity position, pitch inertia, wheelbase and

track dimensions, cross-section area and drag coefficient were set in this submodel. The inputs into

the vehicle part are the headwind speed, longitudinal forces partly due to the road profile and drive

torque from the powertrain via the tyres and shock absorbers. The vehicle submodel provides the

output of distance, speed and acceleration of the vehicle in all three degrees of freedoms. Spring

and damping coefficient of the car suspensions were set in the respective model, while parameters

such as tyre types and tyre dynamic rolling radius were set in the wheel and tyre submodel. The

wheel and tyre submodel has the outputs of drive torque on the road and longitudinal and vertical

forces on the vehicle carbody. Its inputs are torque from the powertrain, input torque resulting from

the friction with the road and the brake signal (can be set as brake torque, brake force or in %). The

road profile also enables the user to set the inclination and the condition of the road, such as dry or

slippery road.



Figure 20: AMESim model of the b-segment car

The inertia of the tyres and wheels as well as the car suspension stiffness and damping were set as

following.

Wheel and tyres: J = 1 kgm2; rdyn = 0.270 m

Car suspension: c = 20000 N/m; d = 2000 Ns/m



4.4 Reference Transmission: Getrag Powershift 6DCT250

Figure 21: Getrag Powershift 6DCT250 Transmission [7]

The reference transmission used to investigate the comfort criteria of a DCT is the Getrag Powershift

6DCT250 Transmission. It is developed together by Getrag and Ford, and is mainly targeted for the B-

and C-segment vehicles. The main target of its development is to achieve better fuel consumption

than any other automatic transmission. It is claimed that this transmission shows 10-20%

improvement of fuel consumption compared to the state of art planetary automatic transmission

with torque converter. Besides better fuel consumption, by using electromechanical concept for the

clutches and gear actuations, a reduction in CO2 emission is achieved.

The Getrag 6DCT250 is a three shaft design transmission developed for B and C-segment vehicles of

Ford and Renault vehicles with front-transverse engine position. Since the transmission uses the dry

dual clutch system, the torque capacity of the transmission is limited to maximum 250 Nm. No

additional cooling system for the dry dual clutches is required. The important information of this

transmission is summarised in the table below.

Weight 75kg (without EM)

Length 350-380 mm

Clutches Dry single plate dual clutches

Clutch actuation Electromechanical

Clutch torque capacity 250 Nm

Gears 6 forward gears, 1 reverse gear

Drive mode Automatic, manual (sequential)

Oil Volume 1.7-1.9 litre

Table 6: Technical data of Getrag Powershift 6DCT250 transmission [7]

4.4.1 Dry Dual Clutches

The dual clutches in the Getrag transmission were designed according to variant 2 of dry dual clutch

(see chapter 3.1.1 Dry Dual Clutches), which uses friction plate integrated with torque damper for

each clutch. This design is favourable for applications with low engine excitation such as for petrol



application. The clutches are axially supported by a support bearing on the hollow shaft and radially

supported on the crankshaft.

Figure 22: Cross-section view of Getrag 6DCT250 dry dual clutches [7]

Figure 23 describes the dual clutch model in AMESim. The clutch is modelled as two rotating bodies

with a common rotation axis. It uses the coulomb friction model which is represented as follows. The

input of the clutch is set to normal force, Fnormal.

(4.1)

The coulomb friction model is extended with the tanh function that helps eliminate the difculty in

determining the friction force at zero sliding speed both at start up and at direction change. This

model is more numerically stable than the coulomb-viscous friction model [12]. The friction force

developed at the contact can be described as following.

[

] (4.2)

Whereby Vrel is the relative speed of the two rotating bodies and dV is the rotating speed threshold.

Fdyn is the coulomb friction force and can be calculated from the input normal force Fnormal and

coefficient of friction dyn [13].

An inertia-element is connected to each clutch, and this inertia represents the reduced inertia of the

clutch and the involving gears on each subgearbox-shaft. Appropriate viscous friction value can also

be set if needed. The parameters of the inertia are set as below.

Friction disks

Pressure plate 2

Pressure plate 1

Flywheel

Flexplate

Torque dampers Support bearing

Cover



Reduced inertia, J = (0.005 0.01) kgm2

Viscous friction coefficient, d = (0.0 0.001) Nm/(rev/min)

Figure 23: Dry dual clutch model in AMESim

4.4.2 Electromechanical Actuator of the Dual Clutches

Figure 24: LuK actuator unit for Ford 6DCT250 dual clutch transmission [8]

Figure 24 shows the arrangement of the clutch actuator motors on the dual clutch unit. The actuator

motor, also known as electronically commutated motor (or simply EC-Motor), has a range of power

from 110-170 Watt. However, the limit of continuous loading is approximately 20 Watt of electrical



energy input to avoid thermal overload of the EC-Motor. The dual clutch actuator, together with the

dual clutch unit, is developed by LuK and uses a simple lever actuator concept.

The mechanism of the lever actuator can be explained using the following figure of a simple lever. A

preloaded spring will provide the spring force Fspring on one end of the lever. By varying the position

of the pivot by means of the EC-Motor via a ball screw (see also chapter 3.1.1 Dry Dual Clutches),

variable clutch actuation force on the other end of the lever can be achieved.

Figure 25: Lever concept (left) and clutch actuator unit (right) [4]

Thus, by referring figure 25 (left) the clutch actuator force, Fclutch, can be calculated as following.

(4.3)

Figure 26: Clutch actuator (for launch)

At the early phase of the simulation, a simple PID controller was used to model the slip controlled

clutch actuation (figure 26). The actual slip is calculated from the difference between feedback



engine speed and shaft speed. The desired slip input is given. The desired slip is located at the

negative port to make sure that the input value into the PID controller is positive to further avoid

negative output force from the controller. The limiter also serves the same purpose. A PT1-Filter is

connected at the output to smoothen the output clutch force.

To simulate gear shifting during driving, the clutch actuator was enhanced to include torque

controller during clutch cross-fading phase. The torque controller also uses a PID-controller with the

input of error between actual and desired torque and the output of clutch actuator force.

Figure 27: Clutch actuator for launch and gearshift

A more complex model of the clutch actuator was later built to take the power limit of the actuator

motor and the friction force caused by the normal force acting on the lever pivot into account. The

actuator is still slip-controlled; hence using the same input as the previous actuator model. A torque

limiter was placed for the actuator motor. The upper and lower torque limit, TU/L is calculated as

follows, whereby the maximum power of the actuator motor is set as 110W and the actuator shaft

rotation speed, nEM, can be read from the rotational speed sensor element connected to its shaft.

|

| (4.3)

The friction torque acting on the pivot is a function of the output clutch force is calculated as

follows.

(4.4)



These defined equations were set as a function in the new actuator model. The implementation of a

variable PID-controller enables the user to use only one PID-controller for both slip control as well as

cross-fading control. Only the input to the controller needed to be switched using the signal switch

element (input error from torque during cross-fading, input error from slip during other condition).

Endstop elements were added to set the maximum distance of the actuator. The following figure

presents the more complex clutch actuator modelled for the simulation.

Figure 28: Complex model of the clutch actuator

4.4.3 Gears and Gear Actuators

The Getrag 6DCT250 transmission is a 3 shaft design type transmission, which enables a compact

design for small and medium size vehicles. It has 6 forward gears and 1 reverse gear. The low gears

(1st and 2nd gears), which requires high torque capacity transfer, are synchronised with double cone

synchronisers whereas the rest of the gears are synchronised with single cone synchronisers. The

intermediate gear required to change the direction of the vehicle in reverse gear is integrated

together with the idle 2nd gear, thus saving space of an extra shaft for the reverse gear.

The input shaft 1, which is actuated by clutch 1, is responsible for the actuation of the odd gears (1st,

3rd and 5th gear) while the input shaft 2 for the even gears (2nd, 4th and 6th gear). The idle gears of the

1st, 2nd, 5th and 6th gear are located on the output shaft 1 while the idle gears of the 3rd, 4th and

reverse gear are on the output shaft 2. Both output shafts are connected to the differential. Thus,

while driving in a certain gear, the power flows from the ICE through the clutch and input shaft,

depending either on odd or even gear, and then through the respective output shaft to the



differential and the tyres. An exception for the reverse gear, the power flows firstly through the

intermediate gear which is integrated to the idle 2nd gear on output shaft 1, to the idle reverse gear

on output shaft 2 and lastly to the differential and tyres. Thus, a change of direction can be achieved.

Figure 28 presents the layout of the Getrag 6DCT250 transmission.

Figure 29: Getrag Powershift 6DCT250 transmission layout [7]

The following table summarises the location of each idle gear, the gear ratios for each gear and the

total ratio of each gear after multiplication with the final drive ratio.

Input Gears Output Gear ratio Final drive ratio Total ratio

Input shaft 1 (Clutch 1)

1 Output shaft 1 3.92 3.89 15.2488

3 Output shaft 2 1.44 4.35 6.264

5 Output shaft 1 0.87 3.89 3.3843

Input shaft 2 (Clutch 2)

2 Output shaft 1 2.43 3.89 9.4527

4 Output shaft 2 1.02 4.35 4.437

6 Output shaft 1 0.70 3.89 2.723

R Output shaft 2 3.51 4.35 15.2685

Table 7: Gear ratio of Getrag Powershift 6DCT250 Transmission

The transmission gear sets were modelled using the 3 ports gear submodel and the 4 ports idle gear

submodel. The idle gear submodel must be used with together with the half synchroniser submodel

for it to fully function. By using the gear submodels provided by AMESim, the user can set the

geometry of the gears, as an example the working transverse pressure angle, tw and helix angle, .

However, the parameters used for the simulation in this thesis were only the working radius and the

constant gear efficiency. As mentioned before, the inertia for the participating gear is reduced to a

single inertia for each shaft (see chapter 4.4.1). The differential is not modelled for the simulation



since the driving situations simulated were assumed to have been done on a straight road; hence no

influence from the differential. The differential ratio is already included in the final ratio gear. The

powertrain model is built as the following in AMESim.

Figure 30: Transmission model in AMESim

The Getrag 6DCT250 transmission uses an electromechanical gear actuator, which comprises two

actuator motors, one for each output shaft. A shift drum, which is designed with groove around it, is

linked to the actuator motor via two intermediate gears. Each shift drum with groove is responsible

for two shift forks on its respective output shaft. During actuation, because of the groove design, the

rotating shift drum would slide the shift fork axially and the shift fork, which is attached to the

synchronizer, will engage the desired idle gear.

Figure 31: Gear actuator of Getrag Powershift 6DCT250 Transmission [7]

Actuator motors

Intermediate gears

Shift drums Shift forks



Due to the pre-select gear mechanism of the dual clutch transmission, gear synchronisation does not

have a big influence on the comfort during gear shifting. So, the gear pre-engage and disengaging

mechanism was simplified with a logic function of binary signal (0/1) as an input for the AMESim

synchroniser model. Attention should be paid to the gear pre-select logic, so that there is no double

overlapping of pre-select, to avoid unnecessary energy loss due to the extra inertia.

The following figure shows the gear shift diagram for upshift and downshift of the transmission from

gear 1 to 4 and vice versa. The input parameters are accelerator pedal position and the actual

vehicle speed. The gear shift diagram is designed so that gear upshift occurs at low rpm for low

accelerator pedal actuation for a fuel efficient drive. At high accelerator pedal position, which signals

a need for high load, the gear upshift occurs at high rpm. The normal lines represent upshift curves

while the dotted lines represent the downshift curves.

Figure 32: Gearshift diagram for gear 1 to gear 4



4.5 Reference Engine: 1.6 Ti-VCT

Figure