Drive Train Analysis and Vehicle Dynamics for the C,Mm,N 2.0

Drive Train Analysis and Vehicle Dynamics for the c,mm,n 2.0

R.P.C. van Dorst, B.J.H van Laarhoven R.A.M Meesters, M.W.F. Mol DCT 2008.142

Master Team Project report

Coaches: dr.ir. I.J.M. Besselink dr.ir. T. Hofman

Supervisor: prof.dr. H. Nijmeijer

Technische Universiteit Eindhoven Department Mechanical Engineering Dynamics and Control Technology Group

Eindhoven, November, 2008 Abstract

The c,mm,n project was initiated in 2005 by the foundation of Nature and Environment (Stichting Natuur en Milieu, SNM) as an answer to the 2005 AutoRAI, where there was little attention for environmentally friendly cars. SNM asked the help of the three universities of technology in the Netherlands to develop a sustainable car for the future. This first phase of the c,mm,n project is called c,mm,n 1.0 and many aspects of the c,mm,n 1.0 car became research topics for graduate students. The results of c,mm,n 1.0 were presented at the 2007 AutoRAI. In November 2007, the c,mm,n 2.0 project was launched. SNM plans to make a new presentation of c,mm,n 2.0 on the 2009 edition of the AutoRAI with the desire to show a driveable prototype. To assist SNM in this task, this report presents a new drive train option which is analyzed and compared to the two c,mm,n 1.0 drive trains. Additionally, the vehicle dynamics of the c,mm,n vehicle are analyzed. The two c,mm,n 1.0 drive trains are a fuel cell supercapacitor hybrid (FCSCH) drive train and an internal combustion engine with cylinder deactivation (ICE) drive train. Because the drive train for an electric vehicle features less energy conversion steps than a hybrid drive train and contains drive train components which all work at high efficiency (>90%), this drive train option was investigated. The new drive train option is therefore an electric vehicle (EV) drive train. It consists of four in-wheel electric motors, a battery pack, power electronics and optionally a solar panel and/or range extender. The electric motors are chosen to meet the requirement that acceleration from 0 to 100 km/h must be possible in under 12 seconds. The size of the battery pack is based on a range requirement which dictates that the autonomous range of the vehicle should be at least 300 km. A range extender which could be placed modularly (i.e. as an additional component that can be added or removed at will) can be an interesting option, because when the c,mm,n is used for transportation to a distant place (e.g. going on vacation), the battery pack range will not be sufficient. For these long distance trips a range extender can be used, such as small fuel cell or an internal combustion engine with an electric generator. To do a simulation of the EV drive train, the QSS Toolbox is used. It can give insight to the influence of regenerative braking on the battery state of charge and the operating points of the electric motor. A drawback of the QSS Toolbox is that not all parameters can be changed easily. It is therefore not possible to simulate with the correct component sizes, which makes the results inaccurate for a quantitative analysis, but still useful as a qualitative analysis. A multi criteria analysis can make clear what drive train option is the preferable drive train for the future. The conclusion of this MCA is that a hydrogen powered vehicle (FCSCH) can be cheaper and more sustainable than an ICE powered vehicle, but this is based on the expectancy that fuel cell prices and hydrogen prices will drop significantly. This will only happen if a global hydrogen economy is realized. When maximizing sustainability the EV has no competition, because of its high well to wheel efficiency. The weak point of the EV is its shorter autonomous range. The vehicle dynamics of the c,mm,n vehicle is investigated by means of simulations using the SimMechanicsTM and Delft-Tyre toolbox of MATLAB R . A SimMechanicsTM model of the EV c,mm,n vehicle simulates the vehicle driving on specific road profiles and some specific manoeuvres. The model contains an active suspension which reduces the pitch and roll motion of the vehicle. Simulation results are compared for a passive suspension setup versus an active suspension setup. The passive suspension setup is identical to the active suspension, but with fixed secondary arm (there is no secondary spring influence). It should be noted that this passive suspension is therefore not the best possible representation of a passive suspension. The analysis does, however, point out the contribution of the active suspension to the vehicle dynamics. In all simulated manoeuvres, the active suspension keeps the vehicle significantly more leveled than the passive suspension does.

1 List of abbreviations

abbreviation description CNG Compressed Natural Gas CO2 Carbon Dioxide DC Direct Current EM Electric Motor ESP Electronic Stability Program EUDC Extra-Urban Driving Cycle EV Electric Vehicle FC Fuel Cell FCSCH Fuel Cell Super Capacitor Hybrid ICE Internal Combustion Engine LiCoO2 Lithium Cobalt Dioxide LiFePO4 Lithium Iron Phosphate MCA Multi Criteria Analysis NEDC New European Driving Cycle NiMH Nickel Metal Hydride PEM Proton Exchange Membrane PLIB Polymer Lithium-Ion Battery PP Power Plant PSD Power Spectral Density QSS Quasi Static Scheduling RAI Rijwiel en Automobiel Industrie RMS Root Mean Square SC Super Capacitor SNM Stichting Natuur en Milieu SOC State of Charge TU/e Technische Universiteit Eindhoven

2 List of symbols

symbol description unit η understeer coefficient − ηcycle cycle efficiency − a distance from front wheels to COG m 2 Af frontal area m b distance from COG to front wheels m C1 cornering stiffness front tyres N/rad C2 cornering stiffness rear tyres N/rad ds suspension damper constant Ns/m dsky skyhook damper constant Ns/m e energy density J/l or J/kg Echarge energy transferred for charging J Econs energy consumption MJ/km Ecost energy cost e/MJ Edemand vehicle energy demand MJ/km Edischarge energy transferred for discharging J Feconomy fuel economy e/km f frequency Hz feig eigen frequency Hz ∆Fz vertical tyre force N g gravitational constant m/s2 ks suspension spring constant N/m kt tyre spring constant N/m m vehicle mass kg ma unsprung mass kg ms sprung mass kg mtank tank mass kg 6 pitch body pitch angle deg 6 roll body roll angle deg s vehicle range km SOC state of charge for battery pack − T torque Nm t time s V vehicle speed km/h Vtank tank volume l xsusp suspension travel mm za unsprung mass displacement m zr road height m zs sprung mass displacement m

3 Contents

1 Introduction 5 1.1 A brief history of c,mm,n...... 5 1.2 The challenges for the c,mm,n 2.0...... 5 1.3 Structure of this report...... 5

2 Drive trains 7 2.1 Design requirements...... 7 2.2 Fuel cell supercapacitor hybrid (FCSCH)...... 8 2.3 Internal combustion engine (ICE)...... 8 2.4 The electric vehicle (EV)...... 10

3 Multi Criteria Analysis 17 3.1 Mass...... 17 3.2 Energy consumption...... 18 3.3 Fuel economy...... 18 3.4 Range...... 20 3.5 Environmental load...... 20 3.6 Lifecycle costs...... 21 3.7 Packaging...... 22 3.8 Conclusion...... 22

4 Vehicle dynamics 23 4.1 Active Suspension...... 23 4.2 Recommendations for further research...... 31

5 Conclusions & recommendations 33

A c,mm,n speciﬁcations 34

B Packaging 36

4 Chapter 1

Introduction

1.1 A brief history of c,mm,n

The foundation for Nature and Environment (”Stichting Natuur en Milieu”, SNM) was the initiator for the project ”A Car in the Future”. The project started in August 2005, by challenging the three universities of technology of the Netherlands (Eindhoven, Delft and Twente) to design a sustainable car for the future. This as an answer to the 2005 AutoRAI, where very little attention was given to cars that are developed to be less harmful to the environment. The upcoming concerns about global warming through CO2 emissions due to cars and the attention SNM wanted to focus on this problem caused them to make a statement to the car industry. SNM wanted them to show an example of a clean, clever and quiet car so as to encourage the car manufacturers to quickly start mass production of green cars. After a short inquiry at the three universities of technology of the Netherlands, it proved to be better to combine the efforts of the three universities instead of having them compete with each other. The car of the future project involves the design of the exterior, interior, suspension system and power train of a future car within the context of the community in 2020. The mechanical engineering division of the Eindhoven University of Technology (TU/e) was asked to develop the complete suspension and power train system of what is called, the c,mm,n vehicle. [1] The result was shown at the AutoRAI 2007 and received a lot of media attention. For more information, the reader may visit http://www.cmmn.eu or http://www.cmmn.org. In November 2007, the c,mm,n 2.0 project was officially launched. In February 2008, the first ”c,mm,n garage” was held. This is an event in which anyone interested in c,mm,n may come and see what it is about and contribute to the project. This first c,mm,n garage coincided with the start of this master team project and visiting this garage showed the variety of different ideas that surround c,mm,n and introduced the people that are active in the c,mm,n project.

1.2 The challenges for the c,mm,n 2.0

SNM plans to make a new presentation of c,mm,n 2.0 on the 2009 edition of the AutoRAI in which they want to show a driveable prototype. To assist SNM in this task, this report presents a new drive train option which is analyzed and compared to the two c,mm,n 1.0 drive trains. Additionally, the vehicle dynamics of the c,mm,n vehicle are analyzed.

1.3 Structure of this report

The core of this report is subdivided into two chapters about the various drive trains and a chapter about vehicle dynamics. A new c,mm,n 2.0 drive train is, whenever possible, compared to the existing c,mm,n 1.0 designs in an MCA. It is therefore a mix of old and new, which may, without further explanation, be confusing to the reader. To prevent such confusion, the remainder of this section should illuminate the structure of this report. In chapter2, three diﬀerent drive trains topologies. Two of these are designed in the c,mm,n 1.0 and one in the c,mm,n 2.0 phase.

5 Structure of this report page 6

Chapter3 is a multi criteria analysis (MCA) in which the performance in terms of mass, energy consumption, fuel economy, range, environmental load, lifecycle costs and packaging is compared for the three diﬀerent drive trains. Chapter4 discusses the vehicle dynamics of the c,mm,n vehicle. This part will mainly consist of several vehicle dynamics simulations. The main goal of this chapter is to identify interesting areas for further research. The conclusions and recommendations are presented in chapter5. Chapter 2

Drive trains

In this chapter three drive trains are presented. A list with design requirements is set up as a guideline and boundary condition for the design of these drive trains. After that, the two c,mm,n 1.0 drive train designs are brieﬂy described and their speciﬁcations are given. The rest of this chapter will discuss a new drive train option and its components in more detail.

2.1 Design requirements

This section is devoted to making clear what is demanded of the c,mm,n 2.0 vehicle. Each requirement will be motivated in order to make the thoughts behind the design process clear to the reader.

• Space for 4(+1) persons

Although the average occupancy of a car is only 25% in the Netherlands [5] and a vehicle for just two persons is easily more eﬃcient than one for 4(+1) persons, the decision for a 4(+1) person vehicle is made, because a c,mm,n car for the common user must be able to transport a family with two to three children. For a family car, 4(+1) persons is a common standard.

• Top speed at least 130 km/h

When driving on the highway in the Netherlands, the allowed maximum speed is 120 km/h. In other European countries, there is an allowed maximum speed of 130 km/h and on some highways in Germany there is no speed limit. To be able to drive at least top speed in most countries implies that the top speed should be at least 130 km/h.

• Autonomous range at least 300 km

The c,mm,n vehicle must be a feasible mobility solution for the daily commuter and the driver should therefore have the possibility to drive at least 100 km to his/her work and then the same distance back home without ”refueling” in between. For large distance traveling (holiday by car, for instance) a diﬀerent approach may be taken, such as public transportation, higher ranged car rental or usage of a range extender.

• Dimensions approximately equal to average family car

The driver and passengers should be able to sit comfortably and therefore the volume of the car will not be signiﬁcantly diﬀerent from the current average family car. To reduce aerodynamic drag, an alternative seat arrangement could be used, but this is intentionally not chosen in order to maintain the image and functionalities of a common family car.

• 0-100 km/h acceleration in a maximum of 12 seconds

7 Internal combustion engine (ICE) page 8

A new technology has to be appealing, before the general public will accept it. A relatively sporty acceleration behaviour is therefore made possible in order to give the c,mm,n an appealing image for a general audience.

• Aim at lowest possible aerodynamic drag, rolling resistance and mass without making the vehicle unstable

As stated in section 1.1, the c,mm,n project is an eﬀort to create a sustainable car for the future. As taking action to reduce drag losses is positive for numerous statistics, such as well-to-wheel eﬃciency, range and top speed, the aim of the c,mm,n vehicle to reduce drag to the lowest value as possible seems a logical one. This report focuses on drive train analysis and vehicle dynamics for c,mm,n and therefore no research is done to improve the exterior of the c,mm,n vehicle in this report. However, this criterion remains important and should be kept in mind in further analyses and attempts to improve c,mm,n.

2.2 Fuel cell supercapacitor hybrid (FCSCH)

One of the options for the drive train, designed by N. Scheffer [1] in the c,mm,n 1.0 project, is the FCSCH. The topology layout is given in figure 2.1. A favourable method to bring energy on board of the vehicle is intermittent material exchange [1]. A material with high energy density is required to keep the vehicle weight as low as possible. For this reason, and because hydrogen is locally clean and has a relatively high energy efficiency of the well-to-wheel path, hydrogen created from renewable energy sources is chosen as energy storage [1]. To store hydrogen a pressurized tank is required. To convert hydrogen into electrical energy a fuel cell is used. A fuel cell is chosen because it has a relatively high efficiency at part load compared to ICE power trains, is very quiet and has an emission consisting of only water vapor. There are different types of fuel cells; for the c,mm,n 1.0 the PEM FC is chosen. This is because the PEM FC has a dry electrolyte (safety, no toxic electrolyte involved) and a low operating temperature (quick start-up and power demand response). Electric machines are needed to convert electric energy into mechanical energy. With minor adaptations it is possible to recuperate brake energy. Because a PEM FC does not work ”in reverse” the recuperated energy needs to be stored in a different device. For the storage of the recuperated energy supercapacitors are chosen, because they have a high (dis-)charge rate, a long life time and a high specific power density. Four in-wheel motors are chosen to convert the electricity into movement. This is because the traction forces are then divided over four instead of two wheels, resulting in less torque per wheel and giving stability control systems the possibility to distribute the power to the wheels ideally. With the use of in-wheel motors drive shafts, differentials and gear sets become obsolete, resulting in more design space and higher efficiency because there are no additional frictional components. To control the energy flow for the fuel cell and supercapacitors and supercapacitors and for controlling the various wheel torques DC/DC converters and a controller are necessary.

Table 2.1: Components of the FCSCH [1] Part Weight Speciﬁcation Hydrogen tank 90 kg 700 bar FC + SC 170 kg 30 kW + 30 kW In-wheel motor 15 kg 10 kW

For more information regarding the FCSCH, the reader is referred to N. Scheﬀers’ report [1]. For more insight in control of a FCSCH, S.A.K. van Loenhout’s report [13] may be useful.

2.3 Internal combustion engine (ICE)

The other c,mm,n 1.0 drive train option, proposed by G. Peters [16], is the application of an adapted internal combustion engine. This option needs to be considered because it currently is the dominant Internal combustion engine (ICE) page 9

Figure 2.1: Topology FCSCH c,mm,n [1]

technology in the automotive world. It is not at all sure yet, that this technology will be succeeded by electrical propulsion because existing ICE motors can, in addition to fossil fuels, also run on renewable sources. These sources can consist of ethanol for Otto-engines and biodiesel (from soybean or algae) for Diesel-engines. However, the production of these biological fuels can, logically, interfere with our food production and this has already caused a food vs. fuel debate. In this drive train option a boxer engine is proposed for reasons of packaging and it is assumed that this engine has some efficiency-improving techniques applied. Conventional improvements are a turbocharger, camless valvetrain and pump-on-demand of the coolant. These improvements have already been applied in the automotive industry for several years. Rather more experimental techniques are cylinder deactivation and hybridization of the vehicle. These are applied in modern engines but not on a large scale yet. The engine operating point can be kept closer to the point of maximum efficiency using cylinder deactivation. The efficiency is often best at high torques so it is better to have one cylinder running with a high torque output than four with low torque output. The topology of the ICE c,mm,n is presented in figure 2.2.

Figure 2.2: Topology ICE c,mm,n [16] The electric vehicle (EV) page 10

Unfortunately no data is available regarding speciﬁc component speciﬁcations in G. Peters’ report [16]. For more information regarding the ICE c,mm,n, the reader is referred to this same report.

2.4 The electric vehicle (EV)

Because the goal of c,mm,n is to create a sustainable vehicle for the future, a drive train design needs to be as energy efficient as possible while being able to satisfy the design specifications mentioned in section 2.1. Because the drive train for an electric vehicle features less energy conversion steps than a hybrid drive train and contains drive train components which all work at high efficiency, the drive train for an all electric vehicle will be introduced in this section. For instance, a series hybrid vehicle converts gasoline or diesel through combustion into kinetic energy of the engine. The kinetic energy of the engine is converted into electrical energy by the generator. This electrical energy is stored in a battery, which is controlled by power electronics that also deliver the electrical energy to an electric motor. The electric motor then powers the wheels either directly or by means of a transmission. It is clear that the tank to wheel efficiency of a series hybrid vehicle is lowered by these six steps from tank to wheel (ICE, generator, PE, battery, PE, EM). In an all electric vehicle only three steps are necessary (battery, PE, EM). The efficiency gain when comparing this EV to a series hybrid is large, because the omission of an internal combustion engine with assumed 25% efficiency [15] already quadruples the overall efficiency. The EV that is considered here is a vehicle consisting of one or multiple electric motors to take care of propulsion and a battery as energy source. The transport of electric energy is handled by the power electronics. As an EV does not have the ability to ”refill” the energy supply in a quick way, the amount of energy that is carried on board must be enough to keep the vehicle driving for the rest of the day so the batteries may be recharged at home during the night. The possibility to charge an EV’s battery by means of connecting it to the electricity grid is called ”plug-in”. In figure 2.3 the topology layout is presented. In the remainder of this section the components will be discussed in detail.

Figure 2.3: Illustration of EV Topology The electric vehicle (EV) page 11

Component speciﬁcations

Electric motors The c,mm,n vehicle will be propelled by four independent in-wheel electric motors, just like the FCSCH. The torque and power combined for these motors should be enough to sufficiently accelerate and to reach a top speed of at least 130 km/h (see section 2.1 for more details). Motors are chosen with a maximum torque of 150 Nm and a maximum power of 15 kW for these reasons. This results in a combined torque of 600 Nm and 60 kW . The benefit of these in-wheel motors (just like any other electric motor) is that maximum torque is instantly accessible from standstill, which results in a good acceleration. An in-wheel motor is more efficient than an ICE and a central electric motor. This is because the in-wheel motor is directly driven. No losses in the gearbox and differential occur. These losses are caused by the design of a gearbox, because it is built to withstand the maximum power of an engine at maximum speeds. All bearings, cogwheels and axes are bigger and heavier than would be necessary to run at nominal load only. Therefore, at nominal load it takes large amounts of energy just to move the gearbox. Although manufacturers often claim that gearbox efficiency is around 95%, this is in fact only the case at peak load. At part load, the efficiency can be as low as 50%. [3] The use of in-wheel motors is also beneficial for the design of the exterior, because the space that is normally occupied by axles, the transmission and the engine can now be used in any way a designer wishes. In figure 2.4 the motor characteristic of the in-wheel motors is shown. Also the road load is shown in this figure to identify the torque reserve and theoretical top speed of 190 km/h.

Figure 2.4: Motor characteristic

In figure 2.5 a graph is shown giving speed versus time at maximum acceleration. The acceleration from 0 to 100 km/h is reached in 12 seconds. This is achieved when addressing the nominal torque. A nice feature of electric motors is that they can be temporarily overloaded. So if faster acceleration is desired, a 0 to 100 km/h acceleration in less than 10 seconds can be reached by briefly overloading the electric motors. When accelerating, the torque is divided over all four wheels, which reduces the torque per wheel and with that the risk of wheel slip. When accelerating on dry roads, the difference between a front/rear wheel drive and a 4-wheel drive is barely noticeable. When roads are wet or slippery, however, (possibly in combination with some road inclination) a 4-wheel drive makes accelerating without wheel slip much easier. These in-wheel motors can be controlled independently, which gives rise to an increase in freedom of The electric vehicle (EV) page 12

Figure 2.5: Full throttle acceleration

controlling stability. Stability systems nowadays (ESP) can only stabilize the vehicle with independent initiation of the brakes. With in-wheel motors, however, the torque can be controlled independently for each wheel, so when the wheel torques are properly controlled, there will be no need for brake initiation. While a brake action feels abrupt (and is a waste of kinetic energy), smooth torque adaptation may stabilize the vehicle without sudden jerks. Another beneﬁt of the use of four in-wheel motors is that regenerative braking on all wheels is possible. Although use of regenerative braking on the front wheels may capture the largest part of the possible re- coverable energy (70%) [20], using regenerative braking on all wheels also results in a larger deceleration. This makes the unrecoverable part of the kinetic energy (the part that still has to be reduced by using disc brakes, thus dissipated to heat) smaller.

Battery pack A polymer lithium-ion battery (PLIB) is an example of a developing battery technology. It is of the lithium-ion type and features higher energy density, lower weight and lower costs than other battery technologies such as NiMH or lead-acid batteries. The latest addition to the PLIB family is the LiF eP O4 type. The advantage of this type is that it is cheaper, safer when used in large battery packs, has a longer cycle life and can be charged in less time than the widely used LiCoO2 type. The LiF eP O4 PLIB has a remarkable cycle efficiency of 99.8% [2]. The definition of cycle efficiency is as follows:

Edischarge ηcycle = (2.1) Echarge where ηcycle is the cycle eﬃciency, Edischarge is the energy transferred when discharging and Echarge is the energy transferred when charging.

All the above mentioned advantages of this LiF eP O4 PLIB makes this the current ”best choice”. Al- though a prediction for the energy density of batteries in 2020 is given in the next subsection, it can not be guaranteed that those batteries will be of the PLIB or even the Lithium-ion type. It may very well be a completely different kind of battery; the ”current” choice for a LiF eP O4 PLIB merely shows that it is probable that future batteries will have a cycle efficiency that is at least in the range of current batteries and that batteries will be used safely and cost effectively in the future. Battery weight determination To create enough range for the c,mm,n vehicle to fulfil the range requirement mentioned in section 2.1, enough energy has to be stored into the battery pack. A driving cycle needs to be defined for calculation The electric vehicle (EV) page 13

Figure 2.6: New European Driving Cycle

of the vehicle range. A typically used driving cycle is the New European Driving Cycle (NEDC). Figure 2.6 is a representation of this driving cycle. The NEDC is a driving cycle consisting of four repeated ECE-15 driving cycles and an Extra-Urban driving cycle, or EUDC. The NEDC is supposed to represent the typical use of a car in Europe. For a distance of 100 km (approximately 9 NEDC cycles) an energy of 20.14 MJ has to be available in the battery pack (figure 3.2). For a minimum acceptable range of 300 km (section 2.1) the energy storage will be at 70.65 MJ or 20 kW h while assuming that regenerative braking is applied with an efficiency of 75%. See section 3.3 for more information about regenerative braking and fuel economy. Since the NEDC is a mild cycle and (most) batteries are not suited to be fully charged and then fully depleted because of battery wear, a correction factor of 1.5 is applied, implying a window of operation 1 of 1.5 = 66%. This results in the need of a battery with a capacity of 30 kW h. With an energy density of 400 W h/kg, a battery weight of approximately 75 kg is needed, see figure 2.7. More details about the determination of this energy density can be found in the subssections below. Determination of energy density Because the battery is at this moment and in the near future still the bottleneck of the electric vehicle, the determination of a realistic value for the energy density is crucial to obtain a realistic value for the battery pack mass of the EV, because vehicle mass influences many dynamics and performance related properties of the vehicle in a negative way. In the remainder of this section, assumptions and consulted sources that lead to the expected value for the energy density in 2020 are presented.

Trends in batteries When looking at figure 2.8[6] a trend of increasing energy density in W h/l can be observed. In the last 15 years the energy density was increased by a factor 5.2. If this increase is maintained until 2020, an energy density of 3000 W h/l is not unthinkable. According to Prof. Dr. Ir. Paul van den Bosch of the department of Electrical Engineering of the TU/e, a factor 3 between W h/l and W h/kg is reasonable, because the batteries in an electric vehicle must be able to handle high incoming and outgoing currents while having a long lifetime and must therefore have a robust construction. When accepting this factor 3, one would arrive at an energy density of 1000 W h/kg or 1 kW h/kg. When comparing this number with different authors that mentioned something about the expected energy density around 2020, the linear extrapolation of figure 2.8 seems somewhat optimistic. For instance, [3] expects that the energy density of a lithium-ion battery in 2020 will be about 103 W h/kg, which is rather pessimistic and even proven wrong, because the Tesla Roadster currently features lithium-ion batteries with an energy density of 125 W h/kg [19]. In [3] the energy density of lithium-ion batteries in 2050 is expected to be about 400 The electric vehicle (EV) page 14

Figure 2.7: Weight of the battery pack for various densities

Figure 2.8: The development of energy density over the years

W h/kg. In [4] the energy density of a PLIB is estimated to be around 400 W h/kg in 2020. A linear extrapolation of figure 2.8 may thus very well not be realistic and therefore the assumed energy density of batteries in 2020 is taken to be 400 W h/kg. In [7] is indicated that the power density of a (polymer) lithium ion battery is in the range of 300-1300 W/kg. Given this range, it is assumed that the power requested by the electric motor(s) will not be limited by the battery, because the size of the battery pack that is needed to fulfill the third design requirement from section 2.1 will be sufficient to also fulfill the power requirement from the electric motor(s). In this report, the energy density is considered to be this fixed parameter and although the future is un- certain and although this parameter greatly influences the feasibility of an EV, a reasonable assumption must be made to be able make a comparison between an EV and the two drive train options from c,mm,n 1.0. The electric vehicle (EV) page 15

Solar panel The rule of thumb for solar panels in Holland is that an annual production of 80 kW h/m2 or 288 MJ/m2 can be reached (source [11]). A solar panel that is placed horizontally, for instance on the roof of a car, is 87 % as efficient as this. A solar panel placed on the roof of the vehicle measuring 3.6 m2 (half the vehicle from a top-view), can therefore deliver 902.0 MJ/year. Given the energy consumption of 23.56 MJ/100km, this will give the c,mm,n,2.0 a solar powered range of about 3800 km/year. This is approximately 40% of the annual mileage of the average current Dutch gasoline vehicle (source:CBS). This figure can be improved if a consumer would decide to place solar panels on the roof (36o to horizon for better efficiency) of his garage to recharge his vehicle with, instead of grid power. Some improvement until 2020 is desirable, because the panels on the roof of the car would currently cost approximately e2000.-, because of the current cost of panels of 550 e/m2 (source: [11]). This is the largest drawback so far, because if you would want to drive the specified 3828.5 km on grid power, it would cost only e50.15 (table: 3.3), giving the panel a payback time of 39.88 years. This means that with current electricity and solar panel prices this option will be reserved for the most environmentally focussed drivers amongst us.[11]

Possibilities for range extension The c,mm,n is preferably used to travel distances up to 300 km. The battery pack is sufficient for those distances. When the c,mm,n is used for transportation to a distant place (e.g. going on vacation), the battery pack range will not be sufficient. When using an EV, charging stops of several minutes will have to be made after every 300 km. For these long distance trips several different range extenders can be used, such as small fuel cell or an internal combustion engine with an electric generator. The range extender should add significant range without weighing too much and costing too much space. The range extender could of course be used at any time, but it is designed to be used for traveling large distances only, because of the extra weight and the loss of efficiency that a range extender introduces. However, most of the time the range extender is not necessary since most of the time vehicles are used for short distances. Therefore, a range extender which could be placed modularly (i.e. as an additional component that can be added or removed at will) can be an interesting option.

Simulation using the QSS Toolbox in Simulink R

For the analysis of the EV on a NEDC cycle, a MATLAB R Simulink R model is made using the QSS Toolbox. Figure 2.9 shows the basic layout of the Simulink model. This way all sorts of data can be analyzed by simulating the c,mm,n drive train on a driving cycle e.g. the state of charge of the battery and the operating points of the electric motors.

Figure 2.9: The Simulink R model

Figure 2.10 shows again the motor torque ﬁeld with the road load torque, but now also the operating points of the vehicle is plotted. This way, a better insight is obtained of how the electric motors are operating for the given NEDC cycle. Figure 2.11 shows the state of charge of the battery for one NEDC. If the line descends, it means that the The electric vehicle (EV) page 16

Figure 2.10: Operating points NEDC for the electric motors

battery is discharging. When the line is ascending it is recharging (recuperating energy from braking).

Figure 2.11: Battery state of charge

A drawback of the QSS Toolbox is that it currently is not very user friendly concerning the change of parameters. To change parameters of the battery for instance, a MATLAB R m-file with no additional description has to be edited. This m-file contains the parameters, but one can not discover what each parameter represents and is therefore unable to get any insight in the workings of this m-file. The simulation is therefore restricted to the use of a standard, current day battery. Adjusting the parameters of the battery for the future predictions (such as a higher cycle efficiency) is too complex. Therefore this QSS toolbox simulations can not really be used for quantitative analysis but could give some qualitative insight of the operating characteristics during a driving cycle. Chapter 3

Multi Criteria Analysis

In this chapter the performance of all three drive trains will be compared in terms of mass, energy consumption, fuel economy, range, environmental load, life cycle costs and packaging. Using the vehicle parameters as presented in appendixA in the QSS toolbox (section 2.4), the energy demand of every drive train to complete an NEDC cycle could be obtained. Using L.Guzella’s book ”Vehicle Propulsion Systems”[10] and adjusting battery eﬃciency to a future prediction of 95% (see section 2.4), the mentioned drive train properties were determined and compared in this chapter. Since this report only deals with the drive train choice, future designers of the vehicle should be encouraged to take a good look at their material choice and application from an environmental point of view. Simply using materials that can be recycled will reduce the future raw material usage (and for instance also give the vehicle a higher trade value when it needs to be replaced). Figure 3.1 shows the c,mm,n implemented in our society, consuming raw materials and leaving waste both from the life cycle and the drive cycle point of view.

Figure 3.1: Energy, cash and pollution ﬂows through c,mm,n.

3.1 Mass

The c,mm,n weighs 650 [kg] without any drive train components installed. Adding the diﬀerent drive trains gives the vehicles masses as given in tabel 3.1. All speciﬁcations can also be found in appendixA.

17 Fuel economy page 18

Table 3.1: Masses of the c,mm,n drive trains

drive train mass total vehicle mass ICE c,mm,n 200 kg 850 kg EV c,mm,n 150 kg 800 kg FCSCH c,mm,n 330 kg 980 kg

3.2 Energy consumption

The energy required per distance traveled varies per vehicle and drive cycle. Since this section focusses on the eﬀects of the drive train choice it is assumed that roll resistance and air drag are equal for each vehicle. The variables then are the mass and eﬃciency of every power train. The NEDC cycle was used because it is a European standard and also previously used in QSS modeling of c,mm,n, see section 2.4.

Using MATLAB R ’s QSS toolbox resulted in the table 3.2 for the energy demand for 100km driven on the NEDC cycle. The energy shown is the total energy dissipated by air drag, rolling resistance and braking. Model parameters were as shown in appendixA and diﬀerences in vehicle performance in table 3.2 originate from diﬀerences in mass and the capability to recuperate brake energy.

Table 3.2: Energy demand in the NEDC cycle

ICE Energy demand 26.13 MJ/100km EV Energy demand (regenerative) 20.14 MJ/100km Energy demand (non-regenerative) 26.00 MJ/100km FCSCH Energy demand (regenerative) 22.22 MJ/100km Energy demand (non-regenerative) 29.64 MJ/100km

In table 3.2, the recuperable energy from regenerative braking is taken to be 75% of the total brake energy, because not all of the energy can be recaptured because of incidental hard braking. More losses occur in the conversion back to electrical energy so the overall efficiency of regenerative braking is lower than 75%. The electric motor can only decelerate as much as it can accelerate and when the required deceleration becomes too high for the in wheel motors, conventional brakes have to be applied. The kinetic energy is then dissipated into heat by these conventional brakes and can not be recuperated. The actual energy consumption depends on the tank-to-wheel efficiency of the drive train. For the ICE c,mm,n a window of 8% improvement on a regular ICE is taken into account for cylinder deactivation and other technologies, proposed in section 2.3. The tank to wheel efficiency is given in figure 3.2. The energy in figure 3.2 is the actual energy a driver of the c,mm,n vehicle needs to buy per 100 km. The exact well-to-tank energy flows will not be calculated, because using for instance the 0.1% conversion efficiency of solar energy to hydro PP energy only makes the comparison needlessly complicated. Instead, well-to-tank efficiency influence will be regarded using energy prices and CO2 emissions.

3.3 Fuel economy

Various types of energy come in various forms at various prices. An engineer will choose the carrier with the highest energy density, an environmentalist the carrier with the lowest environmental load, but the consumer the one that simply costs the least.

Ecost Feconomy = (3.1) Econs

The fuel economy is calculated by dividing the cost per energy (Ecost) unit by the energy consumption per distance unit (Econs), as shown in equation 3.1. Fuel economy page 19

Figure 3.2: Block schedule of energy consumption

For calculating the costs current gasoline prices were taken to be 1.58 e/L and grid power to be 0.20 e/kW h. This is equal to 49.38 e/GJ for gasoline and 55.56 e/GJ for electricity. The future cost of hydrogen is taken to be 4 $/kg [12], equal to 17.70 e/GJ when produced from natural gas. When producing hydrogen through electrolysis the well to wheel eﬃciency becomes 25,7 % because the ”well” in this case becomes grid electricity (equation 3.2). The costs then are at least 4.80 e/100km for a FCSCH c,mm,n.

ηFCSCH = ηcompression · ηelectrolysis · ηfuelcell · ηmotor = 25.7% (3.2)

Where ηcompression= 94%, ηelectrolysis= 76%, ηfuelcell= 40% and ηmotor= 90%, these eﬃciencies can be found in L. Guzella’s ”Vehicle Propulsion Systems” [10].

Table 3.3: Energy prices per 100 km

Source Cost ICE Assumed eﬃcient gasoline engine 5.14 e/100km Current day gasoline engine 7.60 e/100km EV Grid electricity 1.31 e/100km FCSCH Future natural compressed gas 0.43 e/100km Electrolysis by grid electricity 4.80 e/100km

Table 3.3 shows that hydrogen can be a significantly cheaper energy carrier than the alternatives. However the future production of hydrogen from natural gas is not desirable, because this is a fossil fuel. For an economy to be independent of these the energy sources used must be renewable. The feasible sources for the electricity then boil down to solar, wind, tidal, geothermic and nuclear power. It is probable that the future brings more efficient and cheaper technologies for utilizing solar power (through biomass conversion and solar panels) and nuclear power (through nuclear fusion). From this analysis the conclusion can be drawn that, in terms of efficiency, it is not logical to produce hydrogen with electricity instead of storing the electricity directly in batteries (since future battery technology will no longer be a constraining factor, because energy densities rise, charge times drop and costs go down [4]). Table 3.3 then shows that the EV is the cheapest sustainable drive train for the Environmental load page 20 c,mm,n in terms of costs per kilometer. Taking into account future technological improvements it would not be fair to disregard probable changes in the energy prices. Gasoline prices currently are artificially high due to taxes (duties and VAT, currently 61.5 % of the total price in the Netherlands and rising), but these can drop when the demand goes down (for instance when a significant amount of people starts driving EV c,mm,ns). The course of the energy prices can not be predicted.

3.4 Range

The ICE c,mm,n probably1 has a range comparable to most modern gasoline vehicles, because of the high energy density of fossil fuel. When a fuel tank of 30 L, comparable to current small ICE vehicles, is considered, the range of the ICE c,mm,n will be about 900 km.

V × e 30[L] × 31.6[MJ/L] Range = tank = = 911.5[km] (3.3) Econs 1.04[MJ/km] The EV c,mm,n has a range of 300km, chosen by us because it is diﬃcult to carry the energy for long trips in batteries, but more than suﬃcient for home to work commuting. The FCSCH c,mm,n has a range of 770km with the 4kg of hydrogen stored on board.

m × e 4[kg] × 118.8[MJ/kg] Range = tank = = 770[km] (3.4) Econs 0.617[MJ/km]

3.5 Environmental load

CO2 emissions are an increasing concern of today’s society because it is believed that there is a correlation between CO2 concentration in the atmosphere and global temperature. To put a stop to the increasing global warming governments are issuing countermeasures such as CO2 taxes or grants for vehicles with lower than average emissions. Therefore the emissions of a vehicle can become an important selling point as they will more and more influence the purchase and operating costs. L.Guzella [15] gives the total well-to-wheel emissions for various power trains and the combination of these numbers with energy consumption numbers is found in table 3.4. The method from L. Guzella’s ”Vehicle Propulsion Systems” [10] is used to calculate tabel 3.4. First, the ”well-to-miles” energy consumption is calculated and this is related to known CO2 emissions that result from this consumption. For instance: a FC vehicle that has an energy consumption of 50 J/km has a CO2 emission of 12 kg CO2/100 km when the energy source is natural gas and steam refining is used to convert it into hydrogen. The FCSCH c,mm,n with an energy demand of 22.22 MJ/100 km then has a CO2 emission of 5.33 kg CO2/100 km, obtained through scaling, also additional scaling has to be applied for the 8 % more efficient ICE c,mm,n and EV battery efficiencies of 95 %. Concluding from table 3.4, the EV can be seen to have low emissions, only comparable to the ICE when its power is drawn from conventional coal plants. Note that it’s clean PP emission of 2.71 kg CO2/100 km corresponds to 9.33 kg CO2/100 km for the FCSCH when it uses power from the same PP via electrolysis. The ICE just shows the same emissions as current day vehicles have when burning fossil fuel. The assumed clean gasoline engine has the 8% efficiency advantage that was assumed to be possible using cylinder deactivation. The cheap FCSCH (CNG as the source of its hydrogen) shows the disadvantage of using fossil fuels in the form of natural gas or crude oil by no longer being a zero emission vehicle. Comparing the two possible zero emission vehicles with values from table 3.3 it becomes clear that the EV is still the most favorable option. Recycling is another necessity when attempts are made to keep a vehicle as renewable as possible. Most metal components can be easily recycled and most plastics can be recycled in some form as well. Since most lithium systems contain toxic and flammable electrolytes, these can be dangerous to the environment and effort should be made to prevent these batteries from ending up on junk piles instead of recycling them. 1Unfortunately, no specific data can be found in G. Peters’ report [16] Lifecycle costs page 21

Table 3.4: CO2 emissions per 100 km NEDC

Source CO2 ICE Assumed clean gasoline engine 8.91 kg CO2/100 km Current day gasoline engine 13.13 kg CO2/100 km EV Solar or nuclear PP 0 kg CO2/100 km Natural gas (combined cycle) PP 2.71 kg CO2/100 km Coal PP 9.84 kg CO2/100 km FCSCH Electrolysis by grid electricity (nuclear or solar PP) 0 kg CO2/100 km Reﬁning natural gas 5.33 kg CO2/100 km Reﬁning crude oil 8.00 kg CO2/100 km Electrolysis by grid electricity (combined cycle PP) 9.33 kg CO2/100 km Coal PP 33.88 kg CO2/100 km

3.6 Lifecycle costs

Expensive batteries and fuel cells can worsen the bargaining position of the ”ICE rivaling” c,mm,ns. The costs of the operated power components per vehicle will now be included. Batteries cost about 133-200 e/kW h and fuel cells about 1000-1800 e/kW currently, to as little as 38 e/kW [3] if the global economy becomes hydrogen powered. Supercapacitors are cheap compared to fuel cells, costing e0.25-1 cents/F . The production costs of ICEs is a quite constant number; an Otto-engine is slightly cheaper to manufacture than a Diesel-engine, costing e2600 and e4000 respectively. Because of the cylinder deactivation technology, the efficiency of the ICE was granted an 8% improvement of its current efficiency (17 %) and for now it is assumed that the engine price will also increase with an unknown amount, making it approximately e2800. ICEs will become slightly more expensive in the future due to stricter European emission demands. All the components have the potential to outlive the current day vehicles; current lithium-ion batteries have a life of 1000-2000 deep discharge cycles and up to 4000 normal cycles, equivalent to 480,000 km driven since in 1 normal cycle the battery is discharged for about 40%, corresponding to a vehicle range of 120 km. The current day fuel cells have a life of 3500 hours when operated at part load. Driving at an average of 70 km/h this gives the vehicle a life range of 245,000 km. The ICE’s are currently fit for lasting these distances as well and are expected to outlive at least 300,000 km. For simplicity it is assumed that all vehicles will have a life of 300,000 km and service costs are also not taken into account. The purchase costs can then be divided by the total kilometers driven in a lifetime of the vehicle and added to the fuel costs to obtain the total operating costs per kilometer for each vehicle. From table 3.5 can be concluded that the EV is the best alternative to ICE. The only assumption made for the EV is a realistic power density in batteries of 400 W h/kg in 2020. For the FCSCH vehicle to be as cheap as shown in the table, the global economy needs to be hydrogen based and fossil fuel dependent. An option that is still open is the production of hydrogen through reforming biomethanol. If this is possible without compromising the worlds food production the fuel cell vehicle has room for some more improvement. Note however, that small scale production of hydrogen in this way is insufficient because of the ”global hydrogen economy” requirement. Conclusion page 22

Table 3.5: Purchase and lifetime costs Speciﬁcation Cost ICE Purchase 2, 800 e Lifetime cost (eﬃcient motor) 6.07 e/100km EV Purchase future 6, 400 e Lifetime cost future 3.44 e/100km FCSCH Purchase current 54, 000 e Lifetime cost current PP 22.80 e/100km Purchase future 1, 140 e Lifetime cost future CNG 0.82 e/100km Lifetime cost future PP 5.18 e/100km

3.7 Packaging

The EV has a convenient layout due to in-wheel motors and an electric component volume of 45 L. The ICE and FCSCH both have a large fuel tank and an ICE or fuel cell stack, adding up to about 500 L in total, so this requires space in the front and rear of the car. The battery powered c,mm,n only needs one of those areas partially ﬁlled, leaving more luggage area, the choice of where to place 10% of the vehicle mass (to shift the center of gravity) or the possibility to reduce the total vehicle size resulting in lower mass and air drag.

3.8 Conclusion

The information about drive train performance from the previous sections is collected in table 3.6. No actual multi criteria score will be given in this section because the weighing factors needed can not be determined objectively from the research results and the explicit choice was made not to assign subjective factors to the criteria.

Table 3.6: Multi Criteria Analysis of possible drivetrains

MCA ICE Boxer EV (future) FCSCH unit Fuel economy 5.14-7.60 0-1.31 0.43-4.80 e/100km Range 900 300 770 km CO2 emission 8.91-13.13 0-9.84 0-33.88 kg/100km Mass 850 800 980 kg Energy density fuel 32 4.32 6.3 MJ/L Purchase costs 2,800 6,400 1,140 (future) e 54,000 (now) Packaging 0.48 0.10 0.56 m3 + in-wheel motors + in-wheel motors WTW eﬃciency 14.6-21.5 32.1 10.3 (electrolysis) % 18.3 (CNG)

The conclusion is that a hydrogen powered vehicle (FCSCH) is a cheaper and more sustainable one than an ICE powered one, but when maximizing sustainability the EV has no competition, because of its eﬃcient energy storage and conversion. Chapter 4

Vehicle dynamics

In this section the vehicle dynamics behaviour of the c,mm,n vehicle is investigated. This is done by means of simulations using the SimMechanicsTM and TNO Delft-Tyre toolbox of MATLAB R .A SimMechanicsTM model of the EV c,mm,n vehicle simulates the vehicle driving on specific road profiles and some specific manoeuvres. Simulation results will be compared for a passive suspension setup versus an active suspension setup.

4.1 Active Suspension

Current vehicles commonly use a passive suspension system. The unsprung mass (wheel + suspension system) interacts with the sprung mass (car body) by means of a spring and a damper. By tuning the spring and damper characteristics the vehicle behavior is influenced. In passive suspension systems the suspension characteristics are fixed. An active suspension system has got the ability to continuously change its suspension characteristics. The EV and FCSCH vehicles use in-wheel motors. This causes an increase of the unsprung mass. Also the sprung mass is decreased because it contains less drive train components. This generally worsens the comfort and handling behaviour of the vehicle. To maintain a good handling of the vehicle and a comfortable ride an active suspension system is used, proposed by M. Leegwater [14]. The active suspension system is shown in figure 4.1. The active suspension system consists of a trailing arm with primary spring and damper and a secondary arm with secondary pre-tensioned spring. The secondary arm and spring are used as a force actuator. During driving the secondary arm adds a moment around axle A. The magnitude and sign of this moment depend on the angle of the secondary arm around axle B. A positive angle means a positive moment and a negative angle around axle B means a negative moment around axle A. The added moment influences the suspension characteristics of the vehicle.

23 Active Suspension page 24

Figure 4.1: Active suspension (front right wheel) [14]

Ride comfort

The vehicle ride comfort is determined by the intensity of the accelerations of the sprung mass. The sensitivity of human passengers to these acceleration depends on the frequency. For instance the ab- domen has an eigenfrequency of 4-8 Hz so a substantial vertical vibration in this frequency range will be experienced as unpleasant. See ﬁgure 4.2 for a representation of the body as a multibody system with indicated heightened sensitivity for certain frequencies. Because the provided model from Leegwater has got no altitude controller, it can only be used partially for comfort analysis. The model has has got no skyhook damping, which is needed to make any reasonable statements about the ride comfort. Skyhook damping is a damper which connects the sprung mass to the sky and thus make the sprung mass more resistant to vertical acceleration. A schematic representation of skyhook damping is given in ﬁgure 4.3.

Figure 4.2: The human body depicted as a multibody system [17] Active Suspension page 25

Figure 4.3: Schematic representation of skyhook damping [18]

Pitch and roll reduction

In the previously mentioned model the active suspension controls only the pitch and roll motion of the vehicle sprung mass. This has eﬀect on the vehicle behaviour in various driving situations such as cornering and braking. Diﬀerent scenarios will be tested here to analyse the advantage of this active suspension.

Speed bump Figure 4.4 shows the pitch angle over time of the vehicle when driving over a speed bump. It can be seen clearly that the active suspension reduces the pitch angle of the vehicle. There is still a slight variation in pitch because the spring travel will reach its physical limits.

Figure 4.4: Speedbump - Pitch angle versus time, positive angle represents nose up

In the plot of the suspension travel in ﬁgure 4.5 the pitch reduction can be seen in the rear wheel suspension. This suspension has an opposed movement to the passive suspension because the active Active Suspension page 26

Figure 4.5: Speedbump - Suspension travel versus time, positive suspension travel represents wheel extension

Figure 4.6: Speedbump - Vertical wheel load versus time

suspension tries to ’lift’ the rear of the car to keep the body leveled. Note that a positive suspension travel means that the suspension extends downward from the neutral position. Finally, in ﬁgure 4.6 the vertical wheel load is shown. This load can be seen to be oscillatory of nature and the active suspension does not signiﬁcantly change the maximum wheel loads. Active Suspension page 27

Maximum acceleration The vehicle pitch angle as a result of maximum acceleration of the vehicle is shown in ﬁgure 4.7. The pitch angle is not very high for the passive model, but nevertheless reduced to nearly zero by the active suspension. Note that the vehicle body has a negative pitch (nose down) while accelerating due to its trailing arm suspension design.

Figure 4.7: Accelerating - Pitch angle versus time

Figure 4.8: Accelerating - Suspension travel versus time

The suspension travel shown in figure 4.8 is kept to nearly zero by the active suspension. This means that, as already shown in figure 4.7, the vehicle body is kept almost completely leveled. An interesting side observation is that the initial oscillation of the passive suspension is eliminated by the damper. In figure 4.9 it can be seen that the vertical wheel loads have a lower maximum and minimum for the active suspension setup. Also it shows very low oscillatory behaviour which positively influences the Active Suspension page 28

Figure 4.9: Accelerating - Vertical wheel load versus time

vehicle handling, wear and ride comfort.

Braking The pitch angle during braking, shown in ﬁgure 4.10, is much larger than the pitch angle during acceleration. This is because the brake torque can be larger than the maximum electric motor torque, since the torque of additional disc brakes helps the car make an emergency stop. The bigger pitch angle can still be completely eliminated by the active suspension. Again note that the vehicle has a positive pitch (nose up) when braking, because of the trailing arm design.

Figure 4.10: Braking - Pitch angle versus time

In ﬁgure 4.11 it can be seen that the front and rear active suspension have the same travel, because the active suspension is trying to keep the vehicle leveled. The total vehicle will rise for 40 mm because it Active Suspension page 29

Figure 4.11: Braking - Suspension travel versus time

has no altitude controller. The passive vehicle is squatting quite severely. Squatting means that the pitch is positive so the rear end of the vehicle goes down.

Figure 4.12: Braking - Vertical wheel load versus time

The active suspension does not change the vertical wheel load much when braking, but does remove some of the oscillatory eﬀects that occur in the passive model, shown in ﬁgure 4.12. Active Suspension page 30

Making a lane change When making a lane change on the highway the active suspension greatly reduces body roll, keeping the body leveled, shown in ﬁgure 4.13. Also the suspension travel is nearly zero for the actively sprung vehicle because of this, shown in ﬁgure 4.14.

Figure 4.13: Lane change - Roll angle versus time

Figure 4.14: Lane change - Suspension travel versus time

The vertical wheel load, shown in ﬁgure 4.15, is slightly reduced by the active suspension.Also note that the front and rear wheels have nearly equal loads for both the active and passive model, because the model has its center of gravity placed perfectly at the center of its wheelbase. Recommendations for further research page 31

Figure 4.15: Lane change - Vertical wheel load versus time

4.2 Recommendations for further research

Active Suspension

To do a proper comfort analysis, skyhook damping should be added to the model of the active suspension. It should also be decided if an active suspension system is desirable. Furthermore, some research should be done whether it is desirable to reduce body roll and pitch during steering, braking and accelerating. One can imagine that reducing roll and pitch reduces feedback from the vehicle to the driver, which may result in overconﬁdent driving behavior, although it may improve the vehicle’s cornering ability. Also, the trailing arm suspension can be further analyzed: it is observed that the vehicle dives while accelerating and squats while braking, which is opposite to what most vehicles would do. Speciﬁcally, when looking at the passive suspension, there are better options than a trailing arm suspension.

(Independent) 4-Wheel Steering

The application of 4-wheel steering is possible in the FCSCH and EV, and already applied in the FCSCH c,mm,n 1.0 mock-up. Because the boxer engine is placed between the rear wheels in the ICE c,mm,n, G. Peters [16] explicitly states that no rear wheel steering is applied there, for packaging reasons. For 4-wheel steering an extra actuator is needed at both rear wheels, contributing to an increase of mass and cost. There are multiple beneﬁts to being able to control all four wheels of the car independently. Tyre wear at low speeds can be reduced substantially, for instance when parking the car. A dynamic stability controller will steer all four wheels giving the vehicle more stability on the road. Also, because of this increased vehicle stability, narrower tyres can be used without compromising the vehicle stability. Because no substantial research had been done on the mentioned beneﬁts, it is recommended that future participants in the project take a look at the possibilities of 4-wheel steering.

(Independent) 4-Wheel Drive

As with 4-wheel steering, the FCSCH and EV c,mm,n also have the independent 4-wheel drive option while the ICE c,mm,n has not. As can be seen in figure 2.1 of section 2.2 and figure 2.3 of section 2.4, the FCSCH and EV feature four in-wheel motors. The use of 4-wheel drive is beneficial for vehicle performance, see section 2.2. The biggest drawback to the use of a 4-wheel drive using in-wheel motors is the increased price, weight Recommendations for further research page 32 and controller complexity. Further investigation is needed to determine the desirability of four in-wheel motors.

Mass distribution

Vehicle behaviour can be tuned by shifting the location of the drive train components. According to equation 4.1, the vehicle mass distribution inﬂuences under-/oversteer.

mg b a η = ( − ) (4.1) l C1 C2 With η the understeer coefficient. In this equation a denotes the distance from the front wheels to the center of gravity cg, b the distance of cg to the rear wheels and C1 and C2 the cornering stiffnesses of the front and rear tyres respectively. The understeer coefficient determines the magnitude of understeer (η > 0), neutral steer (η = 0) or oversteer (η < 0) of the vehicle. In this report the center of gravity is taken to be exactly into the middle of the vehicle. A proper location of the center of gravity should be examined for the best vehicle behaviour. The drive train component placement can influence the center of gravity and should be examined. Chapter 5

Conclusions & recommendations

The Electric Vehicle (EV) drivetrain In this report the EV as additional drive train option proves to be a favorable and good alternative to the other two existing drive trains for c,mm,n. A distinct ranking of the drive trains can be made in terms of costs and CO2 emissions, in which the EV always performs best. Also, the practicality of the EV is higher in terms of packaging, because of the use of in-wheel motors and limited battery volume. A typical weak point of an EV is the range. A battery pack contains only a limited amount of energy therefore giving it a limited range of around 300 km. Looking at the current battery density trends this weak point should get stronger giving the vehicle a greater range. Note that the energy density of batteries is hard to predict for the year 2020. This is still a critical point for the succes of the EV. Although the autonomous range of approximately 300 km should be large enough in many cases of commuting travel there is an option to extend the range by adding a range extender to the c,mm,n. A rang extender could exist of a fuel cell or a small internal combustion engine with an electric generator. This gives the EV a far greater range, but also adding weight. Overall it gives the vehicle extra efficiency loss making it only necessary for traveling great distances without recharging. The exact effects on marketability of the shorter range of the EV should be investigated. The assumption was made that a range of 300 km is sufficient for everyday use in commuting, but a consumer may decide otherwise. This consumer decision is not in our field of research. Also the assumptions on future technology (on batteries and fuel cells) made in this report should be monitored; a radical breakthrough in one of these fields could make the EV more favorable or it could make other drive trains more favorable. Active suspension In this report the significance of this active suspension was examined by means of comparison with passive suspension. It can be concluded that with the current trailing arm suspension (originally chosen for an active suspension) the active suspension greatly improves the vehicle dynamics. For a proper comparison with a passive suspension there should be chosen for another suspension design than a trailing arm, e.g. a multi-link suspension system could be used. Further research on independent four-wheel steering The benefits of independent four-wheel steering are not yet fully explored in this report. It is interesting to investigate all possibilities of four-wheel steering. Some options that may be considered are: the use of narrower tyres (reducing the rolling resistance) and using stability control by means of four-wheel steering, increasing stability and reducing tyre wear in tight slow corners and facilitating the parking of the c,mm,n vehicle. Further research on independent four-wheel drive The EV and Fuel cell super capacitor hybrid (c,mm,n 1.0) makes use of four in-wheel motors and the independent control of torque to the wheels can be used to increase stability. A controller could be implemented to ensure maximum vehicle performance and safety.

33 Appendix A c,mm,n speciﬁcations

Vehicle speciﬁcations

Table A.1: Vehicle speciﬁcations

Vehicle mass (without drive train 650kg source: [13] components) mv 2 Frontal area Af 2.1m source: [13] Vehicle length 3.75m source: [14] Vehicle width 1.65m source: [14] Vehicle height 1.45m source: [14] Air drag cw 0.23− source: [13] Wheel radius rw 0.3m source: [16] Roll drag cr 0.01− source: [13]

Drive train speciﬁcations

Table A.2: FCSCH speciﬁcations

Vehicle mass 980kg Energy source components mass 170kg source: [1] Fuel mass 4kg source: [1] Fuel tank mass 90kg source: [1] Motor mass 60kg 4 × 15kg source: [1] Power electronics mass 10kg estimation Fuel tank volume 102L source: [1] Energy density fuel 118, 8MJ/kg source: [1] (given in 33000W h/kg) Energy storage (in a full tank) 475, 2MJ source: [1] 118, 8MJ/kg × 4kg Vehicle power 40kW source: [1] Vehicle range 770km Fuel cell power 30kW source: [1] Supercapacitors power 30kW source: [1]

Calculation 1: G.F.A. Peters gives an empty vehicle weight of 850kg, subtracting the bare vehicle mass of 650kg leaves Peters’ combined drivetrain components mass of 200kg.

34 APPENDIX A. C,MM,N SPECIFICATIONS page 35

Table A.3: ICE speciﬁcations

Vehicle mass 850kg Drive train components mass 200kg Calculation 1 (see below) Energy density gasoline (used in 43, 920MJ/kg source: [8] calculations) Energy density diesel 49, 543MJ/kg source: [8] Energy density ethanol (biofuel) 28, 260MJ/kg source: [8] Vehicle range 900km

Table A.4: EV speciﬁcations

Vehicle mass 795kg Battery mass 75kg chosen to provide speciﬁed range of 300km Power electronics mass 10kg estimation Motor mass 60kg 4 × 15kg source: [1] Battery volume 26, 7L 3kg/L source: Prof. dr. ir. Paul van den Bosch (TU/e) Battery costs 6400 e source: [4] Energy density battery 400W h/kg source: [4] Energy storage (on a full charge) 115, 2MJ 1, 44MJ/kg × 80kg Vehicle power 60kW Design Requirements (section 2.1) Vehicle range 300km Speciﬁc battery power 0.3 − 1.5kW/kg source: [7] Appendix B

Packaging

The ICE c,mm,n has its engine and power train between the rear wheels and fuel at the front of the vehicle.

VICE = L · B · H + Vfuel (B.1) = 1.20 · 1.10 · 0.34 + 0.03 = 0.48[m3] (B.2)

VEV = Vbatteries + Vpowerelectronics + Vinwheelmotors (B.3) 3 3 = 0.025 + 0.02 + Vinwheelmotors = 0.045[m ] + Vinwheelmotors[m ] (B.4)

Vpowerelectronics is estimated to be 20 L, to be on the safe side. A designer contest on www.greencarcongress.com required newly designed power electronics for future EV’s to be no larger than 4.6 L. For cooling of the power electronics they should be placed between the rear wheels (outside the chassis) where forced con- vection is naturally present when driving.

VFCSCH = Vfuelcells + Vfuel + Vsupercapacitors + Vinwheelmotors (B.5) 3 = 0.4488 + 0.1026 + 0.0075 + Vinwheelmotors = 0.56[m ] + Vinwheelmotors (B.6)

3 Vfuelcells is 0.4488 m because it occupies the same space as the internal combustion engine, between the rear wheels. The supercapacitors have a power density of 1-1.5 kw/kg, an energy density of 3-5 W h/kg and in terms of volume 20 kW h/m3, so the volume is at most 7.5 L, which is insigniﬁcant compared to the rest of the components (source [1]).

36 APPENDIX B. PACKAGING page 37

Figure B.1: Layout of c,mm,n [14] Bibliography

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