Chapter 1

Vehicle powertrain concepts

Table of Contents
1.1 Powertrain efficiency ........................................................................................................................ 3
1.1.1 Well to wheels approach ........................................................................................................... 4
1.1.2 Conventional powertrains ......................................................................................................... 5
1.1.3 Vehicle performance ................................................................................................................. 6
1.1.4 Hybrid powertrains ................................................................................................................. 12
1.2 Powertrain components ................................................................................................................... 16
1.3 Driver behaviour ............................................................................................................................. 18
1.4 Role of modelling ........................................................................................................................... 20
1.5 Aim of book .................................................................................................................................... 22
1.6 Further reading ................................................................................................................................ 23
1.7 References ....................................................................................................................................... 23
1.1 Powertrain efficiency

Over the past 100 years, vehicles have changed our lives; they have provided mobility

which we exploit in all out commercial activities around the globe and they have also provided

millions of us with new opportunities afforded by personal transportation. At the very heart of

vehicle design is the powertrain system; it is the engineering of the powertrain system which

provides driving force behind the mobility.

The output from the power source – to date dominated by the internal combustion (IC)

engine – is controlled by a transmission system and driveline to deliver tractive effort to the

wheels. And all these components, collectively referred to as the powertrain system, are

controlled by the driver. Drivers, who are also viewed as discerning customers by the vehicle

manufacturers, have a range of performance criteria; acceleration, top speed, fuel economy,

gradeability, and towing capacity are some of the more obvious quantitative features. But

subjective judgements such as driveability, fun to drive, refinement and driving pleasure play a

huge part in the commercial success of vehicles. On the other hand, society imposes different

performance demands – with a huge recent emphasis on emissions and CO2 usage of vehicles.

And governments have gone as far as imposing overall emissions control targets on

manufacturers’ fleets of vehicles.

In order to meet all these conflicting demands, engineers need to master the complete

powertrain system. If there is one underlying theme to this book, it is that in order to understand

vehicle mobility one must analyse the entire system together – driver, engine, transmission,

driving cycles etc. The aim of this chapter is to provide the background to this theme.
 The key issue at the heart of this textbook is to adopt a systems approach to hybrid

electric vehicle powertrain design. In simple terms, this means collecting together all the

individual components in the powertrain – or drivetrain as it is sometimes called – and analysing

how they combine and interact. The ultimate aim is, of course, to predict the overall vehicle

behaviour in terms of speed, acceleration, gradeability, fuel economy etc.

1.1.1 Well to wheels approach

First, the behaviours of the powertrain components are analysed – and then these

components are combined together as a complete system to capture the overall vehicle driveline

from the prime mover, through the transmission – clutch, gears, differential etc – to the final

drive at the wheels. The important theme is that it is only by taking a system level view of the

powertrain that the vehicle designer can achieve the desired goals of vehicle performance. In a

systems approach to any problem, it is important at the outset to define the system boundaries.

So, for example, if we wish to study the overall usage of energy in passenger car transportation,

the system would look like that shown in Figure 1.1 – in which the energy is tracked from its

original source through to its final usage in propelling a vehicle. This overview is important in

the context of powertrain system design, and is now commonly referred to as the Well-to-Wheels

analysis of energy consumption.

 Well
Pump
000
0
000
0

Pipeline

Fuel refinery Road transport Fuel tank

Fossil fuel reservoir (a) Well-to-Tank

Wheels

Driveline
Fuel tank
Engine

(b) Tank-to-Wheels

Figure 1.1 Overall energy conversion process in vehicle transportation – the Well-to-Wheels idea

1.1.2 Conventional powertrains

This book concentrates mainly on what are commonly referred to as conventional

powertrains – in which an IC engine drives the vehicle wheels through a transmission

incorporating a gearbox and final drive unit. A typical structure for a front-engined, rear wheel

drive (RWD) car is shown in Figure 1.2, with a notation of how the chapters in this book are

mapped on to the powertrain system. The most common layout for small passenger cars is front-

engined, front wheel drive (FWD) but the principles associated with powertrain analysis are

exactly the same.

 Fuel economy Chapter 5 Driveline dynamics
Chapter 6

Chapter 3 Chapter 2 Engine

Vehicle performance
Driving force

Resistive forces
Clutch Gearbox Driveshaft Differential
Transmission Chapter 4

Figure 1.2 Overview of vehicle powertrain system and related book chapters

The world’s total population of cars and light trucks is estimated in 2009 at around 900

million, with a production of new cars and light trucks of about 61 million in the same year. The

vast majority of these – more than 99% - employ conventional powertrains as described above.

Hence, despite the enormous interest from 2000 onwards in alternative powertrains, described

under the general heading of Low Carbon Vehicles (LCVs), it is clear that the principles of

analysing and understanding conventional powertrain systems as described in this textbook will

certainly be of interest for several more decades.

1.1.3 Vehicle performance

Ever since the first usable road vehicles appeared on the roads - built by, for example,

Daimler, Benz, Peugeot and Panhard & Levassor in the 1890s and 1900s – people have quoted

performance Figures as a means of comparing vehicles. In the first instance, these were usually

top speed and range; then came other performance measures as more powerful engines were

installed – acceleration, gradeability and towing performance. Performance could be predicted

based on very simple models using Newton’s Second Law. For example, in Kerr Thomas’ 1932
book (6), a chapter on the ‘Mechanics of a Moving Vehicle’ shows how to calculate speeds and

accelerations based on knowledge of the engine torque and speed characteristics, gearbox ratios

and estimates of the rolling resistance and aerodynamic drag terms.

According to a review paper in 1936 by the pioneering automobile engineer, Olley (7), the

typical American car of that period weighed around 2 tons (2000 kg) and had an engine power of

around 100 horsepower (75 kW), resulting in a typical acceleration of about 10 ft/s2 (~3 m/s2), a

gradeability of about 11% and a top speed around 85 m.p.h. (38 m/s ~ 140 km/h). The accuracy

of these performance predictions gradually improved from the 1930s onwards as measurement

techniques for engine performance (8), tyre rolling resistance characteristics (9) and aerodynamic

drag effects (10) improved. An example to illustrate approximately where all the energy is used

in vehicle longitudinal performance is shown in Figure 4 for typical urban and highway

conditions.
 100 %

19 %
-3% 13 %
Aerodynamic
- 17 %
100 % Standby
-6%
Fuel tank Driveline
13 % - 62 % 19 % 13 %
Engine
Driving -2%
Energy Accessory
-6%
Braking
-4%
Rolling
(a) Urban driving
100 %

25 %

- 11 % 20 %
Aerodynamic
-4%
100 % Standby
-5%
Fuel tank Driveline
20 % - 69 % 25 % 20 %
Engine
Driving -2%
Energy Accessory
-2%
Braking
-7%
Rolling (b) Highway driving

Figure 1.4 Example of typical energy flows during urban (a) and highway (b) driving

In the 1970s, there was a massive shift in interest in vehicle performance to focus on fuel

economy calculations. In the USA, this was prompted by the Corporate Average Fuel Economy

(CAFE) regulations first enacted by Congress in 1975; these were federal regulations intended to

improve the average fuel economy of cars and light trucks sold in the U.S. in the wake of the

1973 oil crisis. Basically, it was a sales-weighted average fuel economy of a manufacturer's
range of passenger cars or light trucks, manufactured for sale in the United States. This signalled

the start of a huge amount of interest around the world in both fuel economy and the linked topic

of emissions – and governments became very active in legislating for the measurement and

control of both these aspects of vehicle performance.

Over recent decades, the highly competitive commercial environment for selling cars has

meant that consumers require data and performance figures to compare different manufacturers’

models. Longitudinal performance – maximum speeds, acceleration, hill climbing, towing

abilities etc – are straightforward to measure and fairly non-controversial. In contrast, however,

comparative data on fuel economy, and hence emissions – has proved extremely controversial.

The established method of quantifying a vehicle’s fuel economy is to subject the vehicle,

mounted on an instrumented dynamometer, to a standard drive cycle. The drive cycle simply

consists of a set of data points which specify a speed vs distance travelled profile. Different drive

cycles have been developed to simulate different types of vehicle operation – for example, extra-

urban, urban, highway, and combined urban-highway.

Although this approach is internationally accepted, substantial detailed differences have

emerged in different countries and different regions of the world. Thus, global comparisons of

the fuel economy of vehicles are fraught with difficulties! Broadly speaking, the current range of

standard drive cycles has emerged from the world’s big 3 automotive markets – Europe, USA

and Asia – and the differences to some extent reflect different driving patterns in those regions.

An excellent overview of the comparative driving cycles is reported in (11). The situation is

further complicated by the fact that different countries or regions have developed different
targets for fuel economy and emissions – which of course, makes life difficult for global

manufacturers in meeting different standards for different markets.

Because of these regional differences, drive cycle testing has been a source of

considerable controversy in the industry. But it has also proved extremely controversial from the

consumer’s point of view, because in real world driving it has proved virtually impossible to

achieve the ideal figures obtained under the standard test conditions. To the engineering

community, this is an expected outcome – the tests and measurements are carried out in

laboratory conditions over a repeatable drive cycle which can only be ‘typical’ of millions of real

driving conditions. The key advantage is, of course, that vehicles are at least compared under fair

and repeatable conditions. Nevertheless, consumer organizations and popular car publications

continue to argue that the quoted figures – which now usually have to be displayed in the vehicle

windscreen during sale – should reasonably be achievable in practice.

In the European Union, the fuel economy of passenger vehicles are commonly tested

using two drive cycles, referred to as 'urban' and 'extra-urban'. The urban test cycle (ECE-15)

was introduced in 1999 and simulates a 4 km journey at an average speed of 18.7 km/h and

maximum speed of 50 km/h. The extra-urban cycle (EUDC) simulates a mixture of urban and

highway running; it lasts 400 seconds with an average speed of 62.6 km/h and a top speed of

120 km/h. In the USA, the testing procedures are administered by the Environmental Protection

Agency (EPA) and were updated in 2008 to include 5 separate tests – which are then weighted

together to give an EPA City and Highway figure that must be quoted in car sales information. It
is claimed – with some justification – that these figures are a better reflection of real world fuel

economy performance than the EU figures.

Just to add to the confusion, fuel economy continues to be quoted in different units

around the world. For example, both the US and the UK use miles per gallon (mpg) – although

even these are not comparable since the US gallon is 0.83 of an imperial gallon! In Europe and

Asia, fuel consumption is quoted in units of l/100km. Note that both lower (l) and upper case (L)

can be used for litres. This is effectively an inverse of the mpg approach and a large mpg is

comparable to a small l/100km – so for example 30 mpg = 9.4 l/100km and 50 mpg = 5.6

l/100km.

However, most vehicle analysts agree that overall, the drive cycles are all less aggressive

than typical real world driving; in practice, this means that they include lower values of

acceleration and deceleration than typically used in normal driving situations. With the upsurge

of interest in hybrid powertrains over the first two decades of 2000, there has inevitably been an

enormous interest in promoting their potential fuel economy relative to conventional

powertrains. This has generated an on-going debate about whether the drive cycles tend to favour

HEV powertrains over conventional ICE based powertrains. The underlying principle is that

HEVs offer the biggest scope for improvement under stop-start driving conditions in heavy city

traffic for example; hence, it is argued that since most drive cycles have their bias towards urban

operation and inclusion of idle periods, they can distort the potential benefits available from

hybrid powertrains – but again, there are a wide range of views!

 In relation to emissions, there are two aspects; both of them are commonly referred to as

‘tailpipe emissions’ for the rather obvious reason that they emerge from the exhaust pipe as

products of the combustion process. The first issue is the pollutant emissions – these include

Carbon Monoxide (CO), unburnt Hydro Carbons (HC) and oxides of nitrogen (NOx). In Europe,

engine emission standards were introduced in the early 1990s to reduce all these pollutants from

vehicles. It led to significant improvements in harmful emissions from passenger cars. Euro 5 is

due to come into effect for passenger cars in 2011 and a further tightening of the regulations,

Euro 6, is planned after that for both commercial vehicles and cars.

The second issue is the Carbon Dioxide (CO2) emission levels of vehicles. These have

assumed increasing attention during the early part of the 21st century due to global concerns

about the environment – and they form part of the Carbon Footprint calculations which have

become embedded in all aspects of life. In the UK from 2001, the vehicle tax was linked to the

CO2 emissions of new vehicle, so that vehicle emitting less than 100g/km were actually free of

road tax. And in 2008, an ambitious piece of legislation was passed which committed European

car manufacturers to cut average CO2 emissions from new cars to 130g/km by 2015.

1.1.4 Hybrid powertrains

During the late 1800s and early 1900s when engineers became fascinated with the

opportunities for personal transportation provided by the motor car, there were three competing

technologies for the powerplant – steam, electric and petrol. Each of these had their own merits

and disadvantages, and it was not at all clear at the time which was likely to dominate in the

longer term. In fact, a 1900 census in the eastern US states (5) showed that each of these
technologies shared about a third each of the emerging market – however, horse drawn carriages

still dominated in terms of total vehicles!

Steam had a longer history of development and there was no problem installing sufficient

power to give good performance. But fuel economy was poor, the boiler needed firing up prior to

a journey and both water storage and usage were problems. Electric vehicles looked extremely

promising – they were quiet, clean and remarkably easy to operate. Range was the major

problem limited by the available energy storage in the battery – a problem which remains to this

day! Gasoline cars in that period were less well developed and appeared extremely troublesome

– they were difficult to start and when running they were noisy, dirty and pretty unreliable. But

their fundamental advantage – which of course is obvious now – was the energy density of

gasoline which was about 300 times better than a lead-acid battery. This meant it was worthwhile

investing in the engineering refinement of the gasoline-based powertrain – and this approach of

relentless development and refinement has continued to the present day.

Given these discussions at the time about the best way forward for the automobile

powerplant, it is not surprising that several forward-thinking engineers suggested combining two

powerplants in order to extract the benefits of each – and hence, the notion of a hybrid vehicle

was born around the turn of the 19th century. They were not called ‘hybrid’ at the time, but it is

nevertheless remarkable that, for example, the 1902 Woods gas-electric car (5) had realised the

potential of what we now know as a series-electric hybrid layout. The vehicle was driven by a

motor which doubled as a generator, it could run on battery power alone at low speeds, the
down-sized gasoline engine could be used to charge the battery and it featured regenerative

braking.

Although there are a substantial number of different powertrain architectures for hybrid

vehicles, at the time of writing this book in 2011 there are three of particular interest, all linked

to commercially available vehicle models. These three types are summarised in Figure 1.3 and

are:

(i) Plug-in Electric Vehicle (EV) e.g. Nissan Leaf

(ii) EV with Range Extender e.g. Chevrolet Volt

(iii) Hybrid Electric Vehicle (HEV) e.g. Toyota Prius

 External
recharging source
Electrical power flow
Battery pack
Motor/
Generator

(i) Plug-in Electric Vehicle

Generator

External Engine
recharging source

Battery pack
Electrical power flow
Motor/
Generator

(ii) Electric Vehicle with range extender and Plug-in facility

Engine Power split

device
Battery pack

Motor/ Generator

(iii) Hybrid Electric Vehicle- tractive power provided by engine, motor

or a combination of both

Figure 1.3 Three types of typical hybrid/electric vehicle architectures available in 2011

This book contains a chapter which introduces highly topical subject of hybrid vehicle

powertrains. It is not intended to provide a comprehensive treatment of the rapidly changing

subject of hybrid vehicle technology – there are many excellent references already written on this

topic and they are referenced at the end of Chapter 7. Rather, the chapter is intended to show

how the same principles of powertrain systems analysis which is the core of the textbook can be

applied to different technologies. The aim is to show how the systems approach to the analysis of
so-called conventional powertrain components can readily be applied to powertrains built up of

different components such as batteries, motor-generators, fuel cells, supercapacitors etc.

1.2 Powertrain components

The components in the powertrain are described in detail in each of the following chapters

in the book – and references for further reading of the best books are also provided. Needless to

say, all these components are subject to relentless efforts to improve their performance –

efficiency, emissions control, refinement – as well as their overall cost effectiveness. The most

recent trends in powertrain component engineering are summarised below:

Engine

 Stratified Charge combustion

 Lean burn combustion

 HCCI (Homogeneous Charge Compression Ignition) combustion

 Variable valve timing

 Supercharging or twincharging (when coupled with a downsized engine)

 Turbocharged Direct Injection diesel engines

 Gasoline direct injection petrol engines

 Common Rail diesel engines

 Variable geometry turbocharging

Transmission

 Lower-friction lubricants (engine oil, transmission fluid, axle fluid)

  Locking torque converters in automatic transmissions to reduce slip and power losses in

the converter

 Continuously variable transmission (CVT)

 Automated manual gearbox

 Dual clutch gearbox

 Increased the number of gearbox ratios in manual or automatic gearboxes

Vehicle structure

 Reducing vehicle weight by using materials such as aluminium, fiberglass, plastic, high-

strength steel and carbon fiber instead of mild steel and iron

 Using lighter materials for moving parts such as pistons, crankshaft, gears and alloy

wheels

 Replacing tyres with low rolling resistance models

Systems operation

 Automatically shutting off engine when vehicle is stopped

 Recapturing wasted energy while braking (regenerative braking)

 Augmenting a downsized engine with an electric drive system and battery (mild hybrid

vehicles)

 Improved control of water-based cooling systems so that engines reach their efficient

operating temperature sooner

1.3 Driver behaviour

Although the focus of this textbook is entirely on the vehicle and the engineering of its

powertrain system, it is important to recognise that whenever a vehicle is used on the road, the

complete system actually involves both the vehicle and its driver. The complete system is shown

in Figure 1.5, in which the driver effectively acts as a feedback controller – monitoring the

performance of the vehicle and feeding back this information to compare with his demand

signals to the accelerator, brake, gear selection etc. Thus, from a dynamics point of view, we are

in practice dealing with a control system. In designing the vehicle engineering system, therefore,

we must be aware of the driver preferences as a controller.

Fuel input
Distance travelled
Gear selection (Drive cycle)
Target Accelerator Acceleration
Driver Vehicle
Driving Cycle Brake Speed

Emissions Fuel usage

Figure 1.5 Overview of the driver-vehicle system governing vehicle longitudinal performance

In subjective terms, drivers tend to prefer systems which are:

 Responsive

 Controllable

 Repeatable

 Stable

 Involve minimum time lags

  Linear

 Free from jerks or sudden changes

The study of drivers’ assessments of the longitudinal control of the vehicle is called ‘driveability’

and it is emerging as a crucial feature of vehicle refinement to assess the customer acceptance of

new powertrain components. For example, it has been used in the industry from 2000 onwards to

assess the smoothness of gear changes in new transmissions developments such as dual clutch

gearboxes and continuously variable transmissions (CVTs). Indeed, procedures for the

assessment of the highly subjective perception of the driver have been incorporated on

specialized vehicle software packages such as AVL-DRIVE (12). The idea is to generate an

objective measure which is based on subjective judgments made by drivers using a range of

vocabulary such as – jerk, tip-in, tip-out, kick, response delay, oscillations, ripple, backlash etc –

some of which have more obvious interpretations than others.

There are occasions in vehicle performance calculations and simulations in which it is

necessary to include a mathematical model of the driver in the complete system shown in Figure

5. In the so called ‘forward-facing’ simulation, discussed in the next section, it is necessary to a

driver model which attempts to follow the specified driving cycle by applying appropriate

signals to the accelerator and brake inputs. The approach used in this case is often a simple PID

(Proportional Integral Derivative) model. This is good for tracking the speed profile, but not

necessarily representative of actual driver behaviour which is likely, for example, to include

some element of look-ahead preview.

1.4 Role of modelling

The whole ethos of this book is based on a modelling approach to analysing and

understanding powertrain system design. The underlying aim is to explain how components

function and then represent their behaviour through mathematical models based on the physics of

their operation. Then, the components can be combined together as a complete powertrain

system – and the resulting model should provide an important tool to contribute to vehicle

design. Thus, although an analytical approach is used in order to understand the fundamental

behaviour, the results are always aimed at being of practical value to vehicle engineers.

The models used throughout the text are relatively simple – and examples are provided in

which the models are expressed and solved in the MATLAB/SIMULINK environment. Thus, it

should be easy to follow the complete process from the derivation of the governing equations,

through to their coding in MATLAB/SIMULINK to their solution and presentation of results.

Since the book is based on fundamental issues, it is felt important that the reader – whether a

student or a practising engineer can follow this whole procedure and try it out for themselves.

In calculations of vehicle performance over a specified driving cycle, there are two

fundamentally different approaches – which are often not well understood by newcomers to the

subject area. The most common simulation is called a ‘backwards facing’ calculation. This

means that at each point on the speed vs distance profile, the current values of both the vehicle

speed and acceleration are known and using these it is possible to work backwards through the

powertrain to calculate the speeds, accelerations, torques and powers of all the components. This

process is simply repeated for all the points on the driving cycle and the results summed together
at the end. This is the simplest and most commonly used method of predicting vehicle

performance over a drive cycle.

The other approach is called a ‘forward-facing’ simulation; this requires a driver model in

addition to the vehicle model. The drive cycle is a target trajectory which the driver tries to track

via inputs to the vehicle system. The simulation is performed a then as a conventional time

history simulation, involving integration of the dynamic equations. This approach is required

when developing control systems for the powertrain elements in order to simulate how the

controller would actually behave in real time on the vehicle.

For more detailed analyses of powertrain components and systems, there are several

commercial packages available. These are used extensively of vehicle design offices around the

world, and whilst they undoubtedly offer increased fidelity in their representation of the

engineering systems involved, they are less informative of the underlying mechanics. Examples

of such packages include;

ADVISOR – (ADvanced VehIcle SimulatOR) was created by the U.S. Department of Energy's

National Renewable Energy Laboratory's (NREL) Center for Transportation Technologies and

Systems in 1994. It was a flexible modelling tool that rapidly assesses the performance and fuel

economy of conventional, electric, hybrid, and fuel cell vehicles. It was acquired by AVL in

2003 (12).

AVL CRUISE - Vehicle and driveline system analysis for conventional and future vehicle

concepts (12).
AVL-DRIVE – Assessment of driveability (12).

CarSim – Vehicle performance in response to braking, steering and accelerating inputs (13).

IPG CarMaker – Vehicle performance in response to braking, steering and accelerating inputs

(14).

Dymola – A multibody systems dynamics packages with automotive as well as other industrial

applications (15).

WAVE – 1D engine and gas dynamics simulation; also includes a drivetrain model to allow full

vehicle simulation (16).

SimDriveline – Blocks to characterise driveline components to include in Simulink environment

(17).

Easy5 – Multi-domain modelling and simulation of dynamic physical systems (18).

1.5 Aim of book

The overall aim of this book is to provide a comprehensive and integrated overview of the

analysis and design of vehicle powertrain systems.

This involves the following objectives:

 To present a summary of the systems approach to vehicle powertrain design

 To provide information on the analysis and design of powertrain components, in

particular:-

– Internal combustion engine

– Transmissions

– Driveline components

 To analyse the longitudinal dynamics of the vehicle in order to predict performance

  To analyse and discuss the fuel economy performance of vehicles

 To analyse the torsional dynamics behaviour of the driveline system

 To describe the fundamentals of hybrid electric components and the architecture of their

usage in a hybrid vehicle powertrain

 To present examples – some with worked solutions – throughout the text

 To present case studies of powertrain performance using MATLAB as an analysis tool

1.6 Further reading

The books listed as references (1) to (5) all provide excellent background information on

the history of automotive engineering, IC engine, transmissions and hybrid vehicle

developments. They are all worth reading to set the scene for powertrain systems analysis.

1.7 References

1. SAE. The automobile; a century of progress. ISBN 0-7680-0015-7, 1997

2. Eckermann, E. World history of the automobile. SAE, ISBN 0-7680-0800-X, 2001

3. Daniels, J. Driving Force: The Evolution of the Car Engine. Haynes Manuals, 2nd ed,

ISBN 978-1859608777, 2003

4. Gott, P.G. Changing gears; the development of the automatic transmission. SAE, ISBN 1-

56091-099-2, 1991

5. Fuhs, A.E. Hybrid vehicles and the future of personal transportation. CRC Press, ISBN

978-1-4200-7534-2, 2009

6. Kerr Thomas, H. Automobile Engineering Vol 1, Sir Isaac Pitman & Sons, 1932
7. Olley, M. National influences on American passenger car design. Proc Institution of

Automobile Engineers, Vol XXXII, pp509-541, 1936

8. Plint, M.J. Engine Testing (Third Edition). SAE International, ISBN: 978-0-7680-1850-9,

2007

9. Clark, S.K. (ed) Mechanics of pneumatic tyres. DOT HS 805 952, U.S. Dept of

Transportation, Washington, 1981

10. Hucho, W-H. (ed) Aerodynamics of road vehicles. 4th edition, SAE, ISBN 0-7680-0029-7,

1998

11. Samuel, S.; Austin, L.; Morrey, D. Automotive test drive cycles for emission measurement

and real-world emission levels - a review. Proceedings of the Institution of Mechanical

Engineers, Part D: Journal of Automobile Engineering, Volume 216, Number 7, pp 555-

564, 2002

12. www.avl.com (last accessed March 2011)

13. www.carsim.com (last accessed March 2011)

14. www.ipg.de (last accessed March 2011)

15. www.dymola.com (last accessed March 2011)

16. www.ricardo.com (last accessed March 2011)

17. www.mathworks.com (last accessed March 2011)

18. www.mscsoftware.com (last accessed March 2011)