Energy consumption of an off-road modified pick-up and the possibility of hybridisation or electrification

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IN

DEGREE PROJECT VEHICLE ENGINEERING, SECOND CYCLE, 30 CREDITS

STOCKHOLM SWEDEN 2018,

Energy consumption of an off-road modified pick-up and the

possibility of hybridisation or electrification

HÉÐINN HAUKSSON

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Abstract

Arctic Trucks have been modifying vehicles such as the Toyota Hilux, Toyota Land Cruiser, Isuzu D-Max, Nissan Patrol and Nissan Navara for over 25 years for special projects as well as for recreational purposes both in Iceland and other countries. Arctic Trucks started up as a sub-division for Toyota Iceland but became an independent company in 2005. Their capability to make off- road vehicles is well known, the Toyota Hilux AT38 being their flagship. It has been driven to both the magnetic north pole, the south pole and various other remote places and is widely used for logistics in Icelandic highlands as well as other places both during summer and winter time.

This M.Sc. project in vehicle engineering covers measurements of energy consumption of a modified Toyota Hilux AT38 2017 in order to determine if some improvements are possible when it comes to fuel consumption and the vehicles environmental impact by hybridisation or full electrification of the vehicle.

Fuel consumption is measured in various on-road and off-road conditions (gravel, snow and asphalt). Calculations are made to estimate the effect on fuel consumption of the climate control in the vehicle cabin. Air drag coefficent and friction coefficient are estimated based on coast-down tests in real-life conditions. These factors are necessary to evaluate the total running resistance of the vehicle.

These fuel consumption measurements show that the fuel consumption for off-road driving is quite high and since this type of vehicle also needs to be light, the advantages of hybridisation or full electrification need to be examined further. For highway and city driving, hybridisation might be feasible but many factors need to be looked at for that case as well. As of now, battery technology and lack of infrastructure are standing in the way of this type of electric or plug- in hybrid vehicles, since these vehicles are used in environments where electricity or even fossil fuel is hard and expensive to reach.

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Sammanfattning

Arctic Trucks har modifierat fordon såsom Toyota Hilux, Toyota Land Cruiser, Isuzu D-Max, Nissan Patrol och Nissan Navara i över 25 år för speciella pro- jekt såväl som för rekreationsändamål både i Island och i andra länder. Arctic trucks startades upp som en underavdelning av Toyota Island men blev ett självständigt företag 2005. Deras förmåga att göra terrängfordon är välkänt, med Toyota Hilux AT38 som deras flaggskepp. Den har körts till både den magnetiska nordpolen, sydpolen och flera andra avlägsna platser och används ofta för logistik på isländska högländerna samt andra platser både sommartid och vintertid.

Detta examensarbete i fordonsteknik omfattar mätningar av energiför- brukningen för en Toyota Hilux AT38 2017 för att avgöra om det finns möj- lighet till förbättringar av bränsleförbrukningen och fordonets miljöpåverkan genom hybridisering eller full elektrifiering av fordonet.

Bränsleförbrukningen har mäts upp under verkliga förhållande på väg och i terräng för olika underlag (snö, grus och asfalt). Beräkningar har gjorts för att uppskatta effekten på bränsleförbrukningen av klimatkontrollen i fordonshytten.

Utrullningsprov har genomförs för att uppskatta luftmotståndskoefficienten och rullmotståndskoefficienten som är nödvändiga faktorer för att utvärdera fordonets totala färdmotstånd.

Bränsleförbrukningsmätningarna visar att bränsleförbrukningen för ter- rängkörning är ganska hög och eftersom fordonet dessutom behöver vara lätt, måste fördelarna med hybridisering eller full elektrifiering undersökas ytterli- gare. För motorvägs- och stadskörning kan hybridisering vara genomförbar men många faktorer måste utvärderas även i de fallen. Just nu står batteriteknik och brist på infrastruktur i vägen för elektrifiering/hybridisering av denna typ av fordon, eftersom dessa fordon används i miljöer där el eller till och med fossilt bränsle är svårt hitta inom körområdet.

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Acknowledgements

This report is part of my final project to receive a M.Sc. in Vehicle Engineering at KTH Royal Institute of Technology, Stockholm, Sweden. The work has been performed at Arctic Trucks Iceland in Reykjavik.

I would like to express my gratitude to my project supervisor Jenny Jerrelind for her guidance and help through the course of the project.

I would like to offer my special thanks to Hinrik Jóhannsson, R&D manager at Arctic Trucks International for supplying me with an office, test vehicle and general support and interest in the project.

Eiríkur Einarsson, technical manager at Toyota Iceland deserves a special thanks for his support with the data logging equipment.

I wish to acknowledge the help provided by Freyr Þórsson, Kristinn Mag- nússon and Baldur Gunnarsson for supplying me with information regarding the project and general help through the course of the project.

I would also like to thank my girlfriend, Linda Dögg Snæbjörnsdóttir for her encouragement and patience through the course of the project.

Hedinn Hauksson

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List of Figures

1 Toyota Hilux AT38 2017 MY. . . 2

2 Rolling resistance and air drag as a function of vehicle velocity. Combined resistance forces can also be seen [1]. . . 6

3 Range of multiple Nissan Leaf vehicles in cold weather conditions [2]. . . 8

4 Impact of auxiliary load on the range of a Nissan Leaf electric vehicle [3]. . . 8

5 Series hybrid drivetrain setup [4]. . . 9

6 Parallel hybrid drivetrain setup [4]. . . 9

7 Complex hybrid drivetrain setup [4]. . . 10

8 Typical hybrid functions and requirements [5]. . . 11

9 Typical Hybrid electric vehicle battery pack from a Toyota Prius [6]. . . 12

10 Torque curves of an ICE and an electric motor [7]. . . 13

11 Heat balance of an engine with two BMEP values. Engine losses are made up of many factors [8]. . . 14

12 Brake thermal efficiency of three engines equipped with Continu- ously Variable Transmission, Manual Transmission and a Hybrid Vehicle [8]. . . 15

13 Route location, Langjökull to Gullfoss . . . 17

14 Route location at Hamragarðaheiði . . . 18

15 Route location at Þórsmörk . . . 18

16 Screenshot from the data acquisition software for the coast-down test. Many parameters were logged but vehicle speed was only needed for the coast down test. For fuel consumption measurements Injection Volume is used and Engine speed. . . 20

17 The OBDII connector under the steering wheel. . . 21

18 Setup of measurement device in the Hilux. . . 21

19 Specifications for Vehicle Interface Module. . . 21

20 Heat distribution of the rear of a car. By far the biggest part of the heat is lost through the windows [9]. . . 22 21 Heat loss through the windows of a Toyota Hilux as a function

of outside temperature and wind velocity. Inside temperature is

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24 Case 1. Logged fuel consumption over a period of time, average consumption and moving average with 1 min timespan. Tyre pressure 4 psi on soft snow at Langjökull glacier. . . 28 25 Case 2. Fuel consumption over a period of time, average con-

sumption and moving average with 1 and 2 minute timespan, respectively. Tyre pressure 4 psi on soft snow. . . 30 26 Case 3. Fuel consumption over a period of time, moving average

for 1, 5 and 10 minutes. Tyre pressure 4 psi on soft snow. . . 31 27 Case 4. Fuel consumption over a period of time, average fuel

consumption as well as 1, 5 and 10 minute moving average. Tyre pressure 4 psi on soft snow. . . 32 28 Case 5. Fuel consumption over a period of time, average fuel

consumption, 1,2 and 5 min moving averages. Tyre pressure 4 psi on soft snow. . . 33 29 Case 6. Fuel consumption over a period of time, average and 1

and 2 min moving average. Tyre pressure 25 psi on gravel road. . 33 30 Case 7. Fuel consumption over a period of time, average con-

sumption and 1,2 and 5 min moving average. Tyre pressure 25 psi on gravel road. . . 34 31 Case 8. Fuel consumption over a period of time, average con-

sumption and 1,2 and 5 min moving average. Tyre pressure 25 psi on gravel road. . . 35 32 Fuel consumption over a period of time. Tyre pressure 10 psi on

gravel road. . . 36 33 Case 10. Fuel consumption over a period of time, average con-

sumption and 1, 5 and 10 min moving average. Tyre pressure 4 psi on gravel road. . . 37 34 Case 11. Fuel consumption over a period of time. Tyre pressure

3 psi on gravel road. . . 38 35 Case 12. Fuel consumption over a period of time, average con-

sumption and 1,5,10 and 20 min moving average. Tyre pressure 10 psi on gravel road. . . 39 36 Case 13. Fuel consumption over a period of time, average con-

sumption and 1,5,10 and 20 min moving average. Tyre pressure 10 psi on gravel road. . . 39 37 Case 14. Fuel consumption over a period of time, average con-

sumption and 1,5,10 and 20 min moving average. Tyre pressure 25 psi on asphalt. . . 40 38 Fuel consumption over a period of time, average consumption and

1,2,5 and 10 min moving average. Tyre pressure 22 psi on asphalt. 41

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List of Tables

1 Hilux AT 38 specifications (Arctic Trucks, 2018). . . 4 2 Conditions for each measurement case. . . 19 3 Parameters used to calculate heat loss. . . 24 4 Measured velocity values from coast down test at 25 psi tyre

pressure. The average rolling resistance coefficient is 0.032. . . . 26 5 Rolling resistance coefficient fr as a function of tyre pressure on

asphalt. . . 27 6 Logged and calculated energy parameters. Range is calculated

using the assumption that the investigated vehicle is equipped with a 30 kWh battery pack. . . 29 7 Average fuel consumption for the modified Hilux in three different

driving scenarios. . . 41 8 Logged and calculated fuel parameters . . . 42

Abbreviations

A/C Air Condition

CVT Continously Variable Transmission ECU Engine Control Unit

GPS Global Positioning System GTS Global TechStream HEV Hybrid Electric Vehicle ICE Internal Combustion Engine Li-Ion Lithium Ion

NiMH Nickel–Metal Hydride OBDII On-Board Diagnostics II VIM Vehicle Interface Module

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1 Introduction

1.1 Background

Arctic Trucks has converted vehicles from Toyota, Nissan, Isuzu and more for off-road purposes since 1990 and has become a known company worldwide in that aspect. Arctic Trucks started up as a division from Toyota Iceland but became an independent company in 2005. Since then the company has been building special purpose vehicles as well as for recreational purposes both in Iceland and other countries. The company has operations and subsidiaries in many countries including UAE, UK and Norway. The company made the first road legal vehicles to reach the magnetic north pole in association with BBC’s Top Gear in 2007 and they have been involved in numerous research projects on the Antarctica, taking care of logistics problems in the harsh environment [10].

Since these vehicles have proven their worth in these conditions and as the standard for environmental issues such as pollution and emissions becomes more and more important it is of value for Arctic Trucks to monitor and measure the energy usage of their vehicles. This information can then be used to reduce fuel consumption and emissions from the vehicle as well as serve as a basis for further studies on fuel consumption.

1.2 Project aim and approach

The projects aim is two-folded. Firstly, it is to investigate the energy usage of an off-road modified SUV built by Arctic Trucks. Secondly it is to estimate if some advantages can be shown by implementing a hybrid or full electric technology for the investigated vehicle, both for performance, fuel consumption and environmental purposes. As seen in Figure 1, the vehicle studied is a Toyota Hilux 2017 model year modified for off-road driving.

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Figure 1: Toyota Hilux AT38 2017 MY.

The vehicles purpose is to reach remote places, both in Iceland and other countries, safely and efficiently. In order to fulfill the project aim the following parts are to be performed:

1. Review of hybrid electric technology.

2. Log fuel consumption during on-road and off-road driving.

3. Estimate of the energy used to keep the vehicle cabin warm.

4. Estimate of the running resistance of the vehicle.

5. Establish a basis for accurate fuel consumption measurements.

6. Estimate the total energy consumption of the vehicle.

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2 Literature review

The literature review aim is to inform the reader of the background for this thesis. First, a presentation of the studied vehicle is given and then follows an introduction to energy consumption of vehicles such as cabin heating and running resistance. At last, basic hybrid functions are explained and new technology regarding energy consumption in the automotive industry is introduced.

There has been increasing pressure from governments around the world as well as the general public in recent years on vehicle manufacturers to reduce fuel consumption as well as harmful emissions. This is to address energy security, being able to supply energy in any form to society safely and efficiently so there will not be shortage of energy, as well as climate change issues. Vehicle manufacturers have been introducing numerous different solutions to this problem such as Continuously Variable Transmission (CVT), new materials reducing vehicle weight, hybrid vehicles and full electric vehicles.

2.1 Investigated vehicle

Arctic Trucks modifies a number of different types of vehicles but the one chosen for this project is a 2017 Toyota Hilux pickup truck equipped with a 2.4L diesel engine and an automatic gearbox. The vehicle has been modified so that 38/15.5R15 tyres can be fitted. That includes new differentials with lower gear ratios and differential lockers, new fender flares, modified bodywork and new suspension and steering components. This is done so the vehicle can cope with extreme conditions such as the Antarctic/Arctic winter, extreme low temperatures (up to -50^◦C) and snowstorms. The vehicle needs to be able to climb up steep hills and travel over boulder fields to reach its destination. This means the vehicle is heavier and has higher running resistance because of the large tyres.

The four most important factors for an off-road vehicles such as Arctic Trucks manufacture are weight, comfort, performance and transport capacity. The vehicle is equipped with a built-in tyre inflation pump. The outlet for the pump is on the specially built front bumper and the air line comes with the vehicle when modified. The pump is operated with a switch built into the instrument panel. The specifications of a modified model and the original car can be seen in Table 1.

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Table 1: Hilux AT 38 specifications (Arctic Trucks, 2018).

Standard Hilux Hilux AT38

Tyre size 265/65R17 38X12.5R15

Wheel size 17X8 inch 15X12 inch

Front suspension

lift 0 mm 40 mm

Rear suspension

lift 0 mm 20 mm

Front suspension type

Double Wishbone with coilover

Double Wishbone with coilover Rear suspension

type Leaf springs Leaf springs

Height 1815 mm 1995 mm

Width 1855 mm 2144 mm

Wheel base 3085 mm 3085 mm

Track length 1540 mm 1735 mm

Bodywork Original

Fender trimming Fibre glass fender flares Side steps

Final gear ratio 4.10:1 4.88:1

Curb weight 2140 kg 2380 kg

The engine in the Toyota Hilux is a 2GD-FTV 2.4L diesel producing 110 kW of power at 3400 RPM and 400 Nm of torque at 1600-2000 RPM. The maximum thermal efficiency of the engine is 44% but the efficiency is much less for most regular driving scenarios. Therefore the best way is to test the vehicle in real life and measure the efficiency and fuel consumption [11].

2.2 Running resistance

Only a part of the power produced by the engine goes to the wheels to power the vehicle or in other words to overcome its running resistance. Other parts go to overcome friction in mechanical parts such as differential gears and bearings.

This is not the case with electric vehicles. An electric motor has much higher efficiency than an internal combustion engine so almost all the power generated by the electric motor goes to the wheels, no gearboxes or transfer cases are needed since the motor can be controlled in a better way than an ICE and the torque curve complies better with the demand.

For driving, the total running resistance is made up of four forces, rolling resistance, air drag force, climbing resistance and acceleration force to reach the desired vehicle speed. The rolling resistance comes from deformation of tyres which happens at the contact patch between the tyre and ground surface. This

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can be calculated using the following formula:

Fro= fr m g cos(α) (1)

where fris the rolling resistance coefficient between the tyre and surface, m is vehicle mass, g is the gravitational acceleration and α is the gradient angle (road slope).

The rolling resistance coefficient is directly proportional to the deformation of the tyre and inversely proportional to the radius of the tyre so higher and wider tyres mean higher running resistance. The rolling resistance coefficient is also affected by velocity, load and tyre pressure. An example of this can be seen in Figure 2.

The second resistance, aerodynamic drag is calculated using the formula

FAero= 0.5 ρ Cd A(v + v0)² (2) where ρ is the density of air, Cd is the friction or drag coefficient, A is the frontal area of the vehicle, v is the vehicle velocity and v0 is the surrounding wind velocity along the longitudinal axis of the vehicle.

The wind speed is hard to measure in real life since anemometers (equipment to measure wind speed and direction) are hard to mount on a vehicle since the turbulence around the vehicle affects the measurements. The solution would be to mount the anemometers far in front of the vehicle or high above. For this project, the air drag coefficient is evaluated without taking wind into account, that is v0 is assumed zero. The relationship between rolling resistance and air drag can be seen in Figure 2.

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Figure 2: Rolling resistance and air drag as a function of vehicle velocity. Com- bined resistance forces can also be seen [1].

The third resistance, climbing resistance is then defined as:

Fα= m g sin(α) (3)

where α is the inclination of the road. Lastly, the acceleration resistance needs to be defined as:

Fx= (m + mj)a (4)

where m is vehicle mass, mj is the rotational inertias equivalent mass and a is acceleration or deceleration.

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These four factors can then be combined to the total running resistance of the vehicle with the equation

FRR= Fx+ Fro+ FAero+ Fα (5) Then the power needed to overcome these forces can be defined as

PW = FRRv (6)

where v is the velocity of the vehicle. The acceleration of the vehicle is based on the power output of the engine. The power output is then used to overcome the four aforementioned forces [12] [13].

2.3 A/C and cabin heating

Studies have shown that heating and cooling the cabin of vehicles takes a significant amount of energy. There is a strong connection between the cooling capacity of an A/C system and the fuel consumption of the vehicle. The difference between a conventional fossil fueled vehicle and an electric vehicle is that the extra energy produced by the fuel in the engine can be used to heat up the cabin. This is not the case with electric vehicles. Electric vehicles require an external heater which consumes energy from the battery that could otherwise be used to extend the driving range. In arctic conditions this is very important.

The energy used to heat up the vehicle cabin can be a considerable part of the total energy consumption. This is highly variable and depends on weather conditions and other factors [14].

As seen in Figure 3, outside temperature has a large impact on the driving range of an electric vehicle. Both high and low temperature have a bad influence on range since if outside temperature is high the driver will want to use the A/C system and if the temperature is low the driver will want to heat the car up, both of which costs energy. Extremely low or high temperatures also start to effect the battery and how it produces the power needed to drive the vehicle.

The capacity of the battery is also dependent on temperature.

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Figure 3: Range of multiple Nissan Leaf vehicles in cold weather conditions [2].

As seen in Figure 4, auxiliary power load combined with temperature also has an effect on the range and as the load increases the power consumption increases exponentially since the capacity of the battery is temperature dependent as well as load dependent.

Figure 4: Impact of auxiliary load on the range of a Nissan Leaf electric vehicle [3].

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2.4 Hybrid/electric design

There are three types of drivetrain for hybrid vehicles, series, parallel and complex. Series hybrid utilizes the ICE only as a generator to supply the energy to the battery, see Figure 5. The ICE is not mechanically connected to the wheels. This means the ICE runs mostly on optimal operation point which is good in stop&go traffic since the ICE is not efficient in that driving scenario.

The energy from regenerative braking is also stored by the battery pack which can then supply torque to the wheels. The drawback with series hybrid setup is the number of energy conversions in the system. In every step where energy is converted from mechanical or chemical energy to electrical energy some of it is wasted as heat.

Figure 5: Series hybrid drivetrain setup [4].

Parallel hybrid uses the ICE and the electric motor in a parallel setup which means both can supply torque directly to the wheels. This is illustrated in Figure 6.

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The third type of drivetrain, see Figure 7, is the series/parallel or the complex hybrid first introduced in the Toyota Prius. The combination of the two means the wheels can both be driven by the ICE only or fully disconnected from the ICE, thus driven fully by the electric motor. This means the ICE can be driven at near optimum operation more often and across a wider velocity range. The drawback of this setup is that the control system can be complicated since it needs to control both the ICE, electric motor and the combination of the two which also means higher production and design cost [15].

Figure 7: Complex hybrid drivetrain setup [4].

Depending on the driving situation, the drivetrain of a hybrid vehicle should be chosen and designed accordingly. There are ways to improve the efficiency of the drivetrain as well as the whole car. An important part of the design is power-to-weight ratio. This involves more integration of components such as integrating the electric motor into the transmission to reduce packaging and making lighter solutions. Running two powertrain systems (ICE and electric motor) in a car increases the weight, and for modified vehicles the weight is even further increased. As seen in Table 1, the weight of the Hilux is increased by 240 kg by mounting the larger tyres, fender flares and other parts.

In recent years with the focus on emissions, fuel consumption and fuel price, customers have high expectations on hybrid and electric vehicles. They expect hybrids to deliver the same performance as conventional vehicles with considerably less emissions and fuel consumption and additionally the vehicle needs to be able to compete in regard to cost and warranty. This is a tall order, but vehicle manufacturers have made large improvements in regard to power electronics, battery technology and drivetrain technology in recent years [5].

To improve fuel economy of vehicles the hybrid technology is important.

Looking at hybrid technologies and the setup of engine and drivetrain compo-

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nents need to be chosen with respect to the total system. It is also important to optimize those components with respect to the operation which they will be used in. The main functions of a hybrid system can be seen in Figure 8. The classic hybrid functions are start/stop, electric launch, regenerative braking and shifting the operation point of the ICE to higher loads to improve efficiency. In addition some hybrid vehicles enable full electric driving and some high performance vehicles use the hybrid system as a boost or power supply in parallel to the ICE [5].

Figure 8: Typical hybrid functions and requirements [5].

Full electric vehicles are simpler, they require only a large battery (compared to hybrid) and one motor/generator (electric motor) to supply power to the wheels and regenerate the braking energy. Losses in an electric vehicle are much smaller than those through a drivetrain in a conventional vehicle since the electric motor only requires one moving part, the shaft, while the ICE has multiple moving parts which means more energy loss through friction and mechanical inertia.

2.5 Battery and electric motor technology

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Additionally, the weight of the fuel is gradually lost while the battery weight stays constant. Because batteries are heavier and have lower energy density compared to gasoline they may require additional structural strength in the frame of the vehicle but that is dependent on battery and vehicle design [16].

During the last few years there has been rapid development in battery design.

Vehicle manufacturers such as Tesla, Nissan and Toyota have been introducing batteries that are lighter, more energy dense and can deliver more power than previous designs. An example from the Toyota Prius can be seen in Figure 9.

Previously NiMH batteries were used but today Li-Ion batteries are becoming more common since they can be charged and discharged faster than NiMH [17]

[18].

Figure 9: Typical Hybrid electric vehicle battery pack from a Toyota Prius [6].

Electric motors used for HEV’s today are of many types, AC or DC, three phase or single phase, Permanent Magnet (PM) or Induction motor (IM). They need to be able to work both as a generator for regenerative braking and as a motor to supply torque to the wheels. Their power varies depending on whether they are used in hybrid application or in a full electric setup. For a full electric setup the motor in a Nissan Leaf is 110 kW but in Tesla Model S it is up to 568 kW [19] [20]. Although the electric motor can deliver such power, the battery needs to able supply this power, or have a high enough discharge rate, which is more often the problem for such high performance vehicles as the Tesla [21].

For hybrid vehicles, the power of the motor is usually much less since the

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ICE also provides torque to the wheels in most cases. The motor in a Toyota Prius provides 53 kW of power. The biggest advantage of an electric motor compared to an ICE is the shape of the torque curve as seen in Figure 10. The electric motor delivers all the torque available from the beginning of the RPM range while an ICE needs to be in a certain RPM range to deliver full torque.

Figure 10: Torque curves of an ICE and an electric motor [7].

2.6 Thermal efficiency

Internal combustion engines are thermal motors, they use the thermal energy which is the product of fossil fuel burning. This process has some efficiency factor. Most commonly petrol engines are used in hybrids. The Otto thermal cycle is used to describe the process that happens in petrol engines. The thermal efficiency for the Otto cycle (petrol engines) can be described as:

ηth= 1 −1

^κ−1

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κ = Cp

C_v (8)

is the compression ratio, Cv is the specific heat at constant volume and Cp is the specific heat at constant pressure. Increasing the compression ratio or higher specific heat ratio are the only ways to increase the thermal efficiency according

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however increased NOx emissions which are heavily regulated so this can only be used to certain extent. Engine developers are introducing new technologies to take care of these problems but this is a delicate balance [8].

As Figure 11 shows, the losses of an engine are comprised of many factors but the Brake Mean Effective Pressure (BMEP) can be increased by using the engine in a more efficient operation area.

Figure 11: Heat balance of an engine with two BMEP values. Engine losses are made up of many factors [8].

This can be seen in Figure 12, where the HEV uses the engine in a more efficient way than other vehicle configurations, CVT, Manual and HEV [8]. CVT is a type of transmission that is sometimes called shiftless transmission. It is comprised of three main components, primary clutch pulley, secondary pulley and belt connecting the two pulleys. The pulleys have variable diameter [22].

The operational principles of a CVT can be described as:

1. Idle: The engine turns so slowly that the primary pulley does not engage with the belt.

2. Engagement: Engine speed rises sufficiently to cause flyweight centrifugal force to compress the spring in the primary pulley and touch the belt. The belt initially slips on the primary pulley but with increasing engine speed centrifugal forces rise and the belt is compressed between the sheaves of the pulley, eliminating slip. The vehicle starts to move.

3. Straight Shift: When the belt is turning at the same speed as the primary pulley the secondary pulley is turning at a speed in accordance with the lowest gear ratio of the CVT. As power output of the engine increases

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the belt pushes out of its seating area and the diameter of the belt at the primary pulley is increased, simultaneously the diameter of the belt at the secondary pulley is decreased. This means the gear ratio changes continuously through the RPM range of the engine and the speed of the vehicle.

4. Shift out: When the pulleys have been shifted to highest ratio. The pulleys cannot operate faster than peak engine RPM.

Figure 12: Brake thermal efficiency of three engines equipped with Continuously Variable Transmission, Manual Transmission and a Hybrid Vehicle [8].

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3 Measurements

To evaluate the energy consumption of the investigated vehicle the vehicle will be tested in the surroundings and application it is intended for. A typical one day tour will be set up, driving on asphalt, gravel and snow. Fuel consumption will be measured continuously as well as outside and inside temperature. To be able to calculate the energy needed to keep the cabin warm the energy loss must be calculated. For that the inside and outside temperature need to be logged and then the energy can be calculated. The efficiency of the engine of course also needs to be known since the efficiency of an ICE and an electric motor are not similar. First step is to determine the base energy consumption of the vehicle. For this, the base equations shown in Chapter 2.2 are used. The only unknowns in those equations for this vehicle are the rolling resistance coefficient fr and the air drag coefficient Cd. The aftermath and visual representation is done using Matlab and Excel, an example of the Matlab code can be seen in Appendix A.

3.1 Measured cases

Two measurement days were used to gather data on snow and gravel. Asphalt driving was done close to Reykjavik on a separate date. To test the energy consumption of the vehicle the location of Bláfellsháls and Langjökull glacier were chosen. A few kilometers were driven on the glacier to sample data but the weather conditions were quite harsh, temperature −4^◦, snowfall and 10 m/s wind. It was decided to move to a safer place for security reasons. The route back from the highlands to the safer location was also logged as well as a short route that involved some ford-crossing close to Reykjavik. This was done on April 11th 2018. Cases 1 through 8 seen in Table 8 apply to this trip.

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Figure 13: Route location, Langjökull to Gullfoss

A second trip was to decided upon on the 12th of May 2018 which was intended to be logged continuously. The measuring equipment was unfortunately not able to do this. Logging shut of automatically after 2 hours of continuous logging. This was done to get a feeling of how much fuel the car uses during a whole day of driving. The plan was to go to the top of Eyjafjallajökull glacier but due to hard snow conditions and time constraints as well as traveling on a single vehicle this was not possible. The route can be seen in Figure 14. Cases 9-16 seen in Table 8 apply to this trip.

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Figure 14: Route location at Hamragarðaheiði

Later that day a route was logged from Hamragarðaheiði to Þórsmörk. This involved gravel driving with tyre pressure set at 10 psi. The route can be seen in Figure 15.

Figure 15: Route location at Þórsmörk

In the evening the route home was logged as well. The driving conditions were 25 psi tyre pressure on asphalt roads. The specific conditions for each case can be seen in Table 2.

To determine the unknown factors of running resistance, rolling resistance coefficient and air drag coefficient, which are hard to determine it was decided to measure them empirically using the method of coast-down test. This can be done by driving the vehicle on a flat road while logging velocity. The vehicle is driven at constant velocity and then the throttle is released, gearbox is set to neutral and the car rolls freely until the velocity has lowered by 10-15 km/h and the time in which this happens is logged. Two velocity intervals are logged. Then the average velocity and deceleration from those two intervals are calculated from that data and the rolling resistance coefficient and air drag coefficient can be calculated from the equations seen in Chapter 2.2. After these factors have been determined the power needed to drive the vehicle can be determined as a function of velocity [13].

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Table 2: Conditions for each measurement case.

Measurement date

Tyre pressure [psi]

Conditions Time [min]

11/04/18 4 Snowfall, 15 m/s, -4^◦C 1 min 23 sec 11/04/18 4 Snowfall, 15 m/s, -4^◦C 7 min 55 sec 11/04/18 4 Cloudy, 10-15 m/s, 0^◦C 17 min 10 sec 11/04/18 4 Cloudy, 10-15 m/s, 0^◦C 15 min 54 sec 11/04/18 4 Cloudy, 10-15 m/s, 0^◦C 8 min 27 sec 11/04/18 25 Cloudy, 10-15 m/s, 0^◦C 7 min 9 sec 11/04/18 25 Cloudy, 5-8 m/s, 4^◦C 13 min 55 sec 11/04/18 25 Cloudy, rain, 4^◦C 9 min 53 sec 12/05/18 10 Sunny, 10 m/s, 4^◦C 36 min 27 sec 12/05/18 4 Sunny, 10 m/s, 4^◦C 29 min 15 sec 12/05/18 3 Sunny, 10 m/s, 4^◦C 59 min 37 sec 12/05/18 10 Sunny, 10 m/s, 4^◦C 15 min 52 sec 12/05/18 10 Sunny, 5-8 m/s, 12^◦C 1 h 10 min 12 sec 12/05/18 25 Sunny, sleet, rain 1 h 3 min 56 sec 05/04/18 22 Sunny, 5-8 m/s, 4^◦C 12 min 19 sec

3.2 Test equipment and setup

To be able to measure the fuel consumption of the vehicle an OBDII VIM was used, connected via the OBDII port in the vehicle as seen in Figure 17.

The VIM is then connected to a laptop which has installed a GTS (Global TechStream) software which is a PC-based diagnostic tool developed by Toyota Motor Corporation. The laptop was powered by the built in 220V socket in the Hilux [23]. The setup of the measurement equipment (VIM and PC) can be seen in Figure 18. The VIM connects through USB to the PC which stores the GTS Software and then the data can be reconstructed using Excel or Matlab.

The built-in 220V power source in the center console of the Hilux can also be seen in Figure 18. It was used to charge measurement device (laptop). VIM specifications can be seen in Table 19. The logging equipment only has the option to log for 2 hours continuously after pressing the record button.

For the coast down test only vehicle speed and time needed to be logged and from these two parameters the rolling resistance coefficient and air drag coefficient can be estimated. The assumption is that the kinetic energy of the vehicle is absorbed during deceleration by only air drag and rolling resistance

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For fuel consumption, vehicle speed, engine speed and injection volume need to be logged. For data reconfiguration both Matlab and Excel were used. GTS creates a .CSV log file which can be imported to Excel.

Figure 16: Screenshot from the data acquisition software for the coast-down test. Many parameters were logged but vehicle speed was only needed for the coast down test. For fuel consumption measurements Injection Volume is used and Engine speed.

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Figure 17: The OBDII connector under the steering wheel.

Figure 18: Setup of measurement device in the Hilux.

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4 Results

In this chapter results of measurements are presented. Calculations regarding the energy usage for cabin heating as well as energy consumed during driving in the form of diesel fuel are presented. Fuel consumption is measured in various driving conditions.

4.1 Energy usage for heating

To estimate the heat loss of the investigated vehicle, it is assumed that all of the heat is lost through the windows during driving. Since the doors are quite well insulated in modern day vehicles but the windows are 5 mm thick glass this assumption is considered reasonable, as seen in Figure 20. To calculate this heat loss, it is assumed that the air on the inside is 20^◦warm and still. The outside temperature varies from -20^◦to +20^◦. Also, the outside wind speed varies from 0 m/s to 20 m/s.

Figure 20: Heat distribution of the rear of a car. By far the biggest part of the heat is lost through the windows [9].

To calculate the heat loss of the glass windows, the thermal resistance of the system needs to to determined. There are two types of heat transfer ways hap- pening in this situation, convection on either side of the window and conduction

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through the glass. The thermal resistance of convection can be described as

Rt,conv=Ts− T∞

q = 1

hA (9)

where T_sis the window surface temperature, T_∞is the cabin temperature or the outside temperature and h is the convection coefficient which is quite hard to determine. It is affected by boundary conditions, the type of fluid motion and other fluid and thermodynamical properties and is therefore the most important factor when studying convection. For this case, an empirical equation was used [24]:

h = 10.45 − v + 10 ·√

v (10)

where v is the relative wind velocity. Since it is assumed the air is stationary inside the vehicle, the inside convection coefficient, hin, is constant. Outside, the convection coefficient h_out is a function of wind velocity and therefore varies.

When h is determined as a function of velocity, the thermal conduction resistance can be determined using

R_t,cond= T_in− Tout

qx

= L

kA (11)

These resistance values are similar to electrical resistances so the total thermal resistance of the system can be described as

R_tot= R_t,cond+ R_t,conv=

1 hin

+L k + 1

hout

1

A (12)

and then the total heat loss through the windows is

Q = T_in− T_out Rtot

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calculation parameters and their values can be seen in Table 3. Equations and methods are taken from [25].

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Table 3: Parameters used to calculate heat loss.

Symbol Value Unit Parameter

A 2.1 [m²] Surface area of windows

t 0.005 [m] Thickness of windows

Tin 20 [^◦C] Inside temperature

T₀ 0 [^◦C] Window surface temperature

T_∞ -20 to 20 [^◦C] Outside temperature

k_g 1.4 [W/mK] Conduction coefficient of glass hin 10.45 [W/m² K] Convection coefficient of air (inside) h_out 35.17136 [W/m² K] Max convection coefficient (wind speed)

Vin 0 [m/s] Wind velocity inside

Vout 0-20 [m/s] Wind velocity outside

Figure 21: Heat loss through the windows of a Toyota Hilux as a function of outside temperature and wind velocity. Inside temperature is set at 20^◦C.

Since the vehicles for this project are more exposed to low temperatures, the energy used for heating is considered. The cooling of air using an air conditioner also takes quite a lot of energy as already mentioned in Chapter 2.3. Although these results show that only 0.7 kW are needed to withhold the temperature inside the cabin, this is a very simplified example and studies have shown that the energy needed for auxiliary power (total power usage besides driving wheels) can be up to 5 kW as seen in Figure 4. This means the range of an electric vehicle

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with a 30 kWh battery pack (2017 Nissan Leaf) would be reduced significantly if auxiliary load is continuous.

According to these calculations, it is assumed that temperature is constant, so if the door was opened for 30 seconds, the car would needed to be heated up again which costs much more energy than maintaining an already achieved temperature. Another factor worth mentioning here is that humans inside a vehicle radiate large amounts of heat so that needs to be taken into account.

Studies have shown that they have a big impact on heat in a vehicle cabin as seen in [26] [25].

4.2 Energy usage for driving

4.2.1 Air drag and rolling resistance coefficients

To calculate the rolling resistance function and the air drag coefficient the basic equations from Chapter 2.2 and the method obtained from [12] are used. The equation of motion for this case can be simplified to:

Fx= Fro+ FAero (14)

where Fxis the deceleration force which is only countered by the air drag force and the rolling resistance of the tyres. The results of this test can be seen in Table 4. hs1 stands for high speed interval 1. ls1 stands for low speed interval 1. This is used to measure mean velocity and deceleration during high speed coast down and low speed coast down. From that, using the equations of motion as seen in [12], the air drag coefficient and rolling resistance coefficient can be determined. For one value of the rolling resistance coefficient and the air drag coefficient both the high speed and low speed intervals are needed, so four tests give four values of each coefficient. As seen in the table, some unrealistic values for the air drag coefficient was obtained. It was decided to use the official value of 0.394 and the coast down test was performed four times and the average rolling resistance coefficient of 0.032 was obtained.

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Table 4: Measured velocity values from coast down test at 25 psi tyre pressure.

The average rolling resistance coefficient is 0.032.

Coast down

test 25 psi hs1 hs2 hs3 hs4 ls1 ls2 ls3 ls4

va [km/h] 89 84 82 70 34 40 46 45

vb [km/h] 61 64 63 51 24 24 27 30

t [s] 15.49 11.79 9.44 11.78 10.81 16.00 17.91 14.14 meanv

[km/h] 75.0 74.0 72.5 60.5 29.0 32.0 36.5 37.5

meana

[km/h²] 1.81 1.70 2.01 1.61 0.92 1.00 1.06 1.06

cw 0.84 0.71 1.11 1.12

f 0.021 0.024 0.021 0.020

µ 0.034 0.031 0.041 0.034 0.024 0.025 0.026 0.026

The results of the air drag measurements and rolling resistance estimations described in Chapter 3.1 can be seen in Figure 22.

Figure 22: Total running resistance due to air drag and rolling resistance as a function of velocity of a Toyota Hilux AT38.

This proved to be problematic since the calculated values of Cdproved to be quite high and the friction coefficient (fr) quite low, as seen in Table 4. Since Cd

of the unmodified vehicle is 0.394 according to [27], it was decided to use that value for the equations based on the thought that the drag coefficient would not change significantly and only calculate the frsince the increased contact patch and larger tyres would have a larger impact on the running resistance compared to bigger fender flares, but of course, this is always a combination of factors.

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According to [13], there are many ways to estimate these factors and given the time constraints for this project these values obtained from Toyota and the coast down test, Cd value of 0.394 and fr value of 0.032 were used. For reference, since these vehicles are often driven on snow with low tyre pressure it was decided to measure the resistance of the tyres with low pressure. This was done in the same manner as the previous test but high speed driving with 4 psi in the tyres was not considered safe so only low speed interval was used for that. The results of these tests can be seen in Table 5. As seen from the values in Table 5, the lower tyre pressure contributes to high rolling resistance, as is expected.

Table 5: Rolling resistance coefficient fras a function of tyre pressure on asphalt.

Rolling resistance coefficient Tyre pressure [psi]

0.03 25

0.036 10

0.052 4

Since the measurement equipment only logs velocity with ±0.5 km/h and because of the changes in gear ratio it was uncertain that the velocity measurement was accurate. Since GPS measurement are more accurate than typical vehicle speedometers it was decided to test the comparison of the vehicle speedometer.

Since this showed no significant error it was decided to use the velocity data as obtained from the vehicle ECU. The GPS measurement can be seen in Figure 23 and it showed good correlation between GPS and vehicle speedo.

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4.2.2 Fuel consumption in various conditions

The measured fuel consumption in real life situations with the investigated vehicle can be used as a basis to estimate the usage of a hybrid or a full electric setup. As described earlier, the vehicle had been out for testing for two days on two different locations with different driving scenarios. The earlier date involved snow driving in harsh weather conditions with new, soft snow while driving in the track of another vehicle.

The second day involved driving a new track in heavy, wet snow. The energy needed to make new tracks in soft or wet snow is significantly more compared to driving in tracks that have been treaded as seen in Figure 24, where the conditions are harsh and the vehicle is barely moving. Since this was only a short test to see if the equipment worked, the results of the test are quite unreliable, the time span is only 1.2 minutes, but it gives an idea of the energy consumption of the vehicle during short periods under high load, for example getting the vehicle loose from snow or mud, as was the case here.

Figure 24: Case 1. Logged fuel consumption over a period of time, average consumption and moving average with 1 min timespan. Tyre pressure 4 psi on soft snow at Langjökull glacier.

For Case 1, the calculated fuel consumption in L/100km is 73.1 L/100km but the measured distance is only 104 meters and the fuel consumption 0.076L

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and as mentioned earlier the speedometer of the vehicle only shows speed with the accuracy of +- 0.5 km/h and when the speed of the vehicle is only 3-6 km/h the error is significant, especially in such a short time. This has a large impact on the final consumption number. 73.1 L/100km is a high number but taken into consideration that the vehicle is barely moving and with low tyre pressure in soft snow, the motion resistance is quite high. Other factor that needs to be taken into account with distance measurements from the speedometer is that in slippery snow the vehicle slips or slides quite often. This translates to an error in the distance measurement. To solve this problem it would be possible to use GPS to accurately measure the distance traveled by the vehicle, not just wheel spin.

To estimate the energy usage of the vehicle during that time, the energy content of diesel fuel is 38.6 MJ/L according to [28], so the energy going into the engine is known. However, the thermal efficiency of the engine is not constant but is stated by Toyota to be maximum 44% as stated in Chapter 2.1. The efficiency map of the engine is not available to public and it is a lot of work to measure it and calculate it by hand. Therefore, to estimate the consumption of the vehicle it is assumed that the efficiency is 44% all the time. Based on those assumptions, the energy usage of the vehicle during this period is 2.72 MJ but only 1.20 MJ is delivered to the wheels. This is equal to 0.33 kWh. Total energy consumption of all the cases can be seen in Table 6.

Table 6: Logged and calculated energy parameters. Range is calculated using the assumption that the investigated vehicle is equipped with a 30 kWh battery pack.

Driving case

Fuel energy [MJ]

Max thermal efficiency [%]

Energy usage [MJ]

Range [km]

1 2.7 0.44 1.2 9.4

2 9.6 0.44 4.2 9.4

3 37.7 0.44 16.6 22.4

4 55.5 0.44 24.4 29.6

5 24.8 0.44 10.9 35.3

6 18.7 0.44 8.2 43.5

7 65.7 0.44 28.9 60.8

8 13.6 0.44 6.0 26.3

9 107.8 0.44 47.4 19.0

10 93.1 0.44 41.0 9.1

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The benefit of an electric motor is that it has high efficiency (>95%) which means the battery would only have to deliver 1.2 MJ (0.33 kWh) to the motor to drive the same distance. This would mean the range of an electric vehicle with 30 kWh battery capacity (2017 Nissan Leaf) would be 14.8 km which is not enough for the investigated vehicle, but as stated earlier, for such a short time and short distance there is much uncertainty in the measurements. Using the same reasoning, it is possible to estimate the average power needed which is for Case 1 15.3 kW which is quite low. The max power delivered to the wheels in Case 1 is 50 kw.

Figure 25: Case 2. Fuel consumption over a period of time, average consumption and moving average with 1 and 2 minute timespan, respectively. Tyre pressure 4 psi on soft snow.

Case 2, seen in Figure 25, the timespan is longer which gives the possibility of having accurate results. In this case the logged fuel consumption is 72.6 L/100km, which is similar to Case 1 which also means the range of the similar electric vehicle should be similar. The average power needed is 9.3 kW and max is 30 kW. The same applies to Case 2, the vehicle was almost stuck in deep, soft snow so the velocity measurements are not accurate.

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Figure 26: Case 3. Fuel consumption over a period of time, moving average for 1, 5 and 10 minutes. Tyre pressure 4 psi on soft snow.

For the test shown in Figure 26 there is a different scenario. The driving route is down the glacier at first, lowering altitude, but then the route goes uphill which explains the high consumption towards the end, which leads to higher average consumption than in Case 2. It is natural that driving such a vehicle uphill, in wet snow with such low tyre pressure increases the rolling resistance severely. As seen in minutes 12-15 the injection volume is quite high which means the engine is under high load to maintain appropriate vehicle speed, it is important for an off-road vehicle to maintain its velocity when driving uphill since if it stops when driving uphill it can be hard to get started and get the vehicle moving again. For Case 3 the average power needed is 17.1 kW and max is 101 kW.

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Figure 27: Case 4. Fuel consumption over a period of time, average fuel consumption as well as 1, 5 and 10 minute moving average. Tyre pressure 4 psi on soft snow.

For Case 4 as shown in Figure 27, the vehicle is driving on relatively flat surface at higher velocity compared to Case 3 (approx. 20 km/h compared to 10 km/h for Case 3) although the fuel injection volume is quite variable. The variations are load dependent as well as throttle position and since the surface is very variable and the tyre pressure is low, the load frequently changes. The average power needed for this case is 27 kW which is explained by the higher velocity. Max power is 104 kW. Case 5 shown in Figure 28 shows the transition phase from snow to gravel road. The transition can be seen as the injection volume becomes lower because of less running resistance on gravel as well as increased tyre pressure.

As seen on the graph (2 min avg) the max fuel injection in that period is approximately 1.5 · 10⁻⁴ L/min and then drops down to 0.5 · 10⁻⁴ L/min approximately towards the end of the period. Another inherent part of the lowering of fuel consumption is that the transition zone is directly linked to altitude so when transitioning from snow to gravel it is fairly likely that the vehicle is going downhill so less power is needed for driving. At that point the tyre pressure had also been increased to 25 psi which makes a big difference in running resistance. Also, the tyres can easily be damaged when driving on gravel roads with tyre pressure less than 5 psi. The tyres can be torn on the sides

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if they rub against sharp rocks or get punctured if they get jammed between a sharp rock and the rim.

Figure 28: Case 5. Fuel consumption over a period of time, average fuel consumption, 1,2 and 5 min moving averages. Tyre pressure 4 psi on soft snow.

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Case 6 shown in Figure 29 shows the descend down from the highlands. It clearly shows lower fuel consumption than the previous cases, except for Case 5, since the tyre pressure has been increased to 25 psi as well as the route descends in altitude so the combination accounts for low fuel consumption. Another factor when driving on gravel road is the condition of the road which has an impact on how fast the vehicle can drive. For this case, this stretch of road was very bumpy, meaning the average velocity is lower so less fuel is used. The average power needed for this case is 35 kW which is fairly low but the expected range of an electric vehicle, similar in size as the investigated vehicle, equipped with a 30 kWh battery pack would be 60 km.

Figure 30: Case 7. Fuel consumption over a period of time, average consumption and 1,2 and 5 min moving average. Tyre pressure 25 psi on gravel road.

For Case 7 shown in Figure 30, the descend slowly fades out to flat road but it continued to be very bumpy in the beginning until asphalt was reached and the consumption decreases. The calculated maximum power used for this case was 115 kw which is more than the official vehicle power, but since the assumption is that the engine always has its max efficiency (44%) there is a chance of error for these calculations. This is natural since more power is needed to drive on higher speeds on asphalt compared to driving slowly on gravel. The range of an electric vehicle would be 73 km although the consumption is higher but it is more efficient when driving on higher speeds on asphalt.

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Figure 31: Case 8. Fuel consumption over a period of time, average consumption and 1,2 and 5 min moving average. Tyre pressure 25 psi on gravel road.

Case 8 seen in Figure 31 was recorded at another location in Mosfellsdalur close to Reykjavik. The temperature was higher than on the glacier (approx.

5^◦C) and it was raining. The route contained different types of surface including fine gravel roads as well as very rough tracks, which explains the variations in fuel consumption. Mean power for this case is very low, only 10.3 kW which is understandable since this was in large driving very slowly on rough tracks, crossing small rivers and driving on steep hills, up, down and sideways. The average fuel consumption for this case was 26.1 L/100km which is fairly high, but as stated earlier it involved some low range driving which means consumption increases. When travelling very slowly, the load on the engine is fairly low most of the time, but the baseline consumption always needs to be fulfilled so that contribution becomes more important the lower speed you travel.

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Figure 32: Fuel consumption over a period of time. Tyre pressure 10 psi on gravel road.

For Case 9 seen in Figure 32, data was recorded at May 12th 2018. The plan was to reach the summit of Eyjafjallajökull in the south of Iceland. Due to time constraints and the fact that the weather conditions at the top were not good (fog) only the edge of the glacier was reached. The beginning of the route was a gravel road and a steep uphill section which explains the high consumption during the first 6-7 minutes. The elevation at that time goes from 10 m above sea level to approximately 400 m above sea level. When the most uphill section is done the surface flattens a bit but still slowly increases elevation. The gravel road gets rougher so the vehicle slows down.

The baseline consumption of the vehicle can be seen in the end of this graph, the baseline consumption of the vehicle is 0.14x10⁻⁴L/min. This case also goes into the transition zone between snow and gravel as mentioned earlier. As seen between minute 30 and 35 on the graph, the consumption increases since then the vehicle is being driven on wet snow so the running resistance is very high, so high that the vehicle became stuck. Then it was time to reduce the tyre pressure to 4 psi to be able to drive on top of the snow. Average power for this section was 23.0 kW.

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Figure 33: Case 10. Fuel consumption over a period of time, average consumption and 1, 5 and 10 min moving average. Tyre pressure 4 psi on gravel road.

For Case 10 shown in Figure 33 the conditions were getting harder, as the vehicle drove closer to the glacier and with higher elevation the snow got heavier and the wheel spin increased again. This had an effect on the distance measurement as stated earlier. Although the motion resistance increases with heavier snow the fuel consumption doesn’t necessarily increase accordingly. The velocity of the vehicle decreases but consumption stays similar. This of course means that the range decreases because the vehicle is able to drive less kilometers on the same amount of fuel but the load on the engine stays similar or even decreases. Case 11 can be seen in Figure 33. The mean power is also quite low for that kind of driving, 27.9 kW in this case.

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Figure 34: Case 11. Fuel consumption over a period of time. Tyre pressure 3 psi on gravel road.

As the snow got heavier and the rolling resistance increased with increasing altitude the tyre pressure needed to be lowered even further to be able to drive in these tough conditions. The vehicle was frequently getting stuck on small hills.

After the tyre pressure was lowered by 1 psi it was easier to drive. It could have been lowered even more to increase the contact patch even further but since traveling with a single vehicle that was considered unsafe. The risk with low tyre pressure is that when driving sideways on a hill the tyre can become loose from the rim and lose all the pressure and damage the wheel assembly.

As seen on the graph, the average fuel consumption is quite low. This can be explained by the low speed at which the vehicles travels by in such conditions.

By trying to drive faster, the wheels slips more and sinks deeper so it slows down the vehicle. The average power needed for such driving is therefore very low, only 16.9 kW. Due to these bad driving conditions it was decided to turn back. That explains the lower fuel consumption towards the end of the period, when transitioning again from snow to gravel.

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Figure 35: Case 12. Fuel consumption over a period of time, average consumption and 1,5,10 and 20 min moving average. Tyre pressure 10 psi on gravel road.

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Case 12 as seen in Figure 35 was driving on gravel road with 10 psi tyre pressure, just for comfort of the passengers and to minimize vibrations and harsh movements for the vehicle. The gravel road was flat and in good condition. As seen from Figure 35, the consumption for this period is fairly even, although there are spikes in the beginning. For this period, there are sections when driving at constant speed and the fuel consumption is fairly constant. Other sections involve crossing small rivers so the velocity is low. The load on the engine is fairly low in these conditions, driving at constant velocity or driving slowly on flat road. The average consumption for Case 12 is also quite low, only 14.4 L/100km which is approximately the average consumption of the vehicle, but the tyre pressure is only 10 psi.

For the case seen in Figure 36, Case 13, it is very similar, driving the same route in the other direction. Slightly less average fuel consumption on the route back, but that can be explained by the slight incline on the route, driving upwards in Case 12 seen in 35 and downwards in Case 13 seen in Figure 36.

Figure 37: Case 14. Fuel consumption over a period of time, average consumption and 1,5,10 and 20 min moving average. Tyre pressure 25 psi on asphalt.

Case 14 seen in Figure 37 is exclusively highway driving on the southcoast of Iceland. Only variable for that case is the weather, which went from +12^◦ C and sunny, to 0^◦C and snowfall back to +10^◦C. This did not seem to have any effect on consumption, it stayed fairly constant. The road surface was fairly flat

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and elevation stayed similar and as seen on the graph the average consumption is fairly even. Fuel consumption for highway driving on this car is measured 10.2 L/100km compared to 7.0 L/100km which is the official Toyota value.

Case 15 seen in Figure 38 is similar to Figure 37, asphalt driving close to Reykjavík.

Figure 38: Fuel consumption over a period of time, average consumption and 1,2,5 and 10 min moving average. Tyre pressure 22 psi on asphalt.

To conclude these results, Table 7 shows the mean fuel consumption in L/100 km for the three different driving scenarios, driving on snow with 4 psi tyre pressure, gravel with 10 psi and asphalt with 25 psi.

Table 7: Average fuel consumption for the modified Hilux in three different driving scenarios.

Fuel consumption Average L/100km

Snow 4 psi 49.4

Gravel 10 psi 18.9

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Table 8: Logged and calculated fuel parameters Driving

case

Consumption

L/100km Distance [km] Fuel [L]

1 73.08 0.104 0.076

2 72.55 0.367 0.267

3 30.61 3.436 1.052

4 23.17 6.68 1.549

5 19.41 3.56 0.692

6 15.77 3.32 0.523

7 11.27 16.27 1.834

8 26.09 1.46 0.38

9 36.09 8.33 3.01

10 75.47 3.45 2.6

11 51.2 6.2 3.17

12 11.72 2.12 0.25

13 13.32 26.75 3.56

14 10.16 84.4 8.57

15 9.39 14.61 1.37

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5 Discussion and conclusions

As stated earlier, the projects aim is two-folded. Firstly, it is to investigate the energy usage of an off-road modified SUV built by Arctic Trucks. Secondly it is to estimate if some advantages can be shown by implementing a hybrid or full electric technology for the investigated vehicle, both for performance, fuel consumption and environmental purposes. In order to fulfill the project aim the following parts were identified to be:

1. Log fuel consumption of a Toyota Hilux modified for offroad driving.

2. Estimate the energy used to keep the vehicle cabin warm.

3. Estimate the running resistance of the vehicle.

4. Look into hybrid electric technology.

5. Establish a basis for accurate fuel consumption measurements.

6. Estimate the total energy consumption of the vehicle.

The methods used to test or estimate these factors have produced the following results:

1. Logged fuel consumption on snow, asphalt and gravel roads in various conditions with various tyre pressure.

2. Estimation of the heat loss through the cabin windows.

3. Coast-down tests with various tyre pressure to estimate running resistance and drag coefficient for the modified vehicle.

4. An overview of hybrid and fully electric technologies.

5. A method to calculate and measure fuel consumption.

6. Energy consumption of the vehicle in various conditions.

According to the results, the fuel consumption of the vehicle is quite high when driving on snow, as was expected. For the gain of hybridizing such a vehicle, the regenerative function would be very inefficient, low speed, low tyre pressure and high running resistance so the vehicle stops almost immediately

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the Discussion would be to come loose from slush or mud pits with the small electric motor. For some driving scenarios including much waiting time (engine idle) hybridisation might be feasible.

For driving on gravel, the consumption is considerably less. Increased tyre pressure and much less running resistance contribute to that. Hybridisation might be desirable for this case since considerable energy could be generated with the regeneration function.

For asphalt driving, the consumption is fairly low compared to many other offroad vehicles, but still considerably higher than an unmodified version of the same car. For that case a hybrid version could save considerable amount of fuel or even a full electric version for testing might be feasible in coming years. For better and more reliable results more measurements would need to be done in more scenarios. These are only short measurements and many unknowns can occur in these situations. More measurements would provide a better idea of the real energy consumption. To get a better feeling of the fuel consumption it would have been good to test it in such a way that it could be comparable.

For example, logging 5 km of gravel, snow and asphalt and then comparing the conditions (soft snow, hard snow, wet snow, powder snow, rough gravel, fine gravel and so on) and from that create a fuel consumption map with the variables being distance, fuel consumption and conditions.

When designing a hybrid or electric vehicle there are many factors that need to be considered and for environmental purposes the "big picture" needs to be looked at. If the plan was to make all vehicles fully electric meaning they would emit zero CO2 and produce the electricity using coal or fossil fuel that would not change much. According to [29], producing electricity is approximately 50%

more efficient than burning diesel in an ICE. Of course this is an improvement but when taking into consideration pollution from battery factories and so on the image changes again. As stated earlier, battery technology is improving fast so maybe in time electric vehicles will be environmentally friendly.

As mentioned in Chapter 2.1, the four most important factors for an off-road vehicles such as Arctic Trucks manufacture are weight, comfort, performance and transport capacity.

For weight, hybridisation is bad since it usually adds weight and takes up space for transport capacity. However, the batteries are becoming lighter and it is possible that the weight of a conventional drivetrain for this type of vehicle (without an extra transfer case for low-low range as is common) might be comparable in weight as a parallel hybrid setup including a small battery pack.

This can be examined further. A hybrid could be more powerful and offer func- tionalities that might be desirable for off-road vehicle. There is one function worth mentioning which might be good for an off-road vehicle from a hybrid