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POLITECNICO DI TORINO

Master of Science in Automotive Engineering

Master degree Thesis

Fuel consumption and performance analysis

of TTR hybrid 4WD vehicles

Academic Tutors: Author:

Nicola Amati Chowdhury Foyz Ahamed Polas

Andrea Tonoli

Luca Castellazzi

December 2016

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Acknowledgements

I would like to thank family for their continuous support, and love throughout my whole

life. Special thank goes to my brother for always being there for me. Without them it

wouldnt be possible for me reach where I am today.

I would also like to express my deepest appreciation to Luca Castellazzi for his

continuous support and assistance throughout the development of this thesis. Also

thanks to Di Donato Stefano for helping me out with various problems in the thesis.

Big shout to my friends for always sticking with me in good and bad times.

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Abstract

One of the biggest concerns in the automotive industry today is the fuel consumption of

the vehicle due the destructive environmental effect of the carbon emission and the

increase of fossil fuel price. One of best solution today to reduce the fuel consumption

of vehicles is the hybrid-electric vehicle technology, which uses electric power in

conjunction with the combustion engine to drive the vehicle. The use of the electric

motor reduces the use of the internal combustion engine, thus reducing the fuel

consumption.

Most of the companies today are trying to develop HEVs instead of traditional ICE

based vehicles. The problem in the development of the HEVs is the high amount of

modification required in the vehicle chassis to support the components of the electric

powertrain.

The Through The Road (TTR) HEV is a variation of 4WD parallel HEV architecture

that allows total mechanical decoupling of the ICE, which propels one axle, and the

EM, which propels the others axle of the vehicle. The TTR architecture does not require

total redesign of the vehicle chassis as the ICE and the EM are totally separate and work

independently.

The main objective of this thesis is to develop a flexible and modular model of a TTR

HEV as the first step of vehicle development. The battery and motor dimensioning is

the principle goal as the front axle components (ICE, gearbox and differential) are

standard. The modelling is done using the Matlab and Simulink framework. The vehicle

model is created based on the longitudinal dynamics (supposing that the vehicle moves

in a straight line on a planar surface), using only the main powertrain components (ICE,

EM, gearbox, clutch, battery, differential, wheels etc.) that are required to drive the

vehicle.

A controller interprets the throttle and brake power required by the driver. The control

algorithm/strategy splits the power and torque between the ICE and EM based on the

constraints on battery current, SOC, temperature, and EM characteristics. The first step

is to find out the optimum power split strategy. The second step is to find out a suitable

battery capacity that maximizes the electric motor use and provides the power to all the

electric accessories, while minimizing the fuel consumption of the vehicle.

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Throughout this thesis the following goals are tried to be achieved

To satisfy the drivers power demand,

Dimension a suitable electric drive-train (battery and electric motor),

Minimize the fuel consumption and emission,

Maintain a reasonable level of battery SOC for self sustaining operation (no

external charging),

Recover maximum amount of brake energy.

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Contents

1 Introduction ............................................................................................................. 11

1.1 Hybrid Electric Vehicles (HEV) ...................................................................... 12

1.1.1 Based on the architecture .......................................................................... 12

1.1.2 Based on hybridization ratio ..................................................................... 14

1.2 Through The Road (TTR) HEV ....................................................................... 15

2 Vehicle Model ......................................................................................................... 17

2.1 Driver ............................................................................................................... 18

2.1.1 Throttle and brake pedal control ............................................................... 18

2.1.2 Clutch control and gear selection .............................................................. 19

2.2 Drive train ..................................................................................................... 20

2.2.1 Front axle .................................................................................................. 21

2.2.2 Rear axle ................................................................................................... 26

2.2.3 Brakes ....................................................................................................... 32

2.2.4 Wheels ...................................................................................................... 33

2.3 Vehicle dynamics ............................................................................................. 34

3 Energy storage system (ESS) .................................................................................. 36

3.1 Battery technology ........................................................................................... 36

3.2 Battery modelling ............................................................................................. 38

3.2.1 Charge and discharge model ..................................................................... 39

4 Control strategy ....................................................................................................... 42

4.1 Traction and brake torque calculation .............................................................. 43

4.2 Maximum electric motor torque calculation .................................................... 44

4.2.1 Current limitation ...................................................................................... 45

4.2.2 SOC limitations ......................................................................................... 46

4.2.3 Temperature limitation ............................................................................. 47

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4.3 Clutch position control ..................................................................................... 48

5 Model validation ..................................................................................................... 49

5.1 Pure ICE mode ................................................................................................. 50

5.2 EV mode ........................................................................................................... 52

5.3 HEV mode ........................................................................................................ 53

5.4 Energy validation .................................................................................................. 56

6 Simulation and results analysis ............................................................................... 59

6.1 Velocity limit with no constraint on the battery usage .................................... 60

6.2 Velocity limit with current constraint .............................................................. 61

6.3 Fuel consumption ............................................................................................. 67

6.4 Electric accessories .......................................................................................... 71

6.5 Fuel consumption with alternator connected to the ICE .................................. 75

6.6 Summary of the results ..................................................................................... 79

7 Conclusion .............................................................................................................. 82

8 Model limitations and future work ......................................................................... 84

9 Bibliography ........................................................................................................... 92

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1 Introduction

August 8, 2016, Earth Overshoot Day, the day we began to use more from nature than

our planet can renew in the whole year [1]. Fossil fuel account for 85% of worlds

energy needs [2], simply because they are the worlds least expensive source of energy

and today almost half of it is being used in the automotive industry. In 2010 the number

of motor vehicles in the world crossed the 1 billion mark [3] and the emission from

these vehicles is one of the biggest reasons of some very concerning issues, such as

global warming, deforestation, and air pollution. In 2016 the danger is more evident

than ever as this year has been the hottest year in the recent history [4]. If the oil

discovery and consumption follows the current trend, in less than 50 years we are going

to be out of fossi