drive train analysis and vehicle dynamics for the c,mm,n 2 · drive train analysis and vehicle...

Drive Train Analysis and VehicleDynamics for the c,mm,n 2.0

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

DCT 2008.142

Master Team Project report

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

Supervisor: prof.dr. H. Nijmeijer

Technische Universiteit EindhovenDepartment Mechanical EngineeringDynamics 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 Natuuren Milieu, SNM) as an answer to the 2005 AutoRAI, where there was little attention for environmentallyfriendly cars. SNM asked the help of the three universities of technology in the Netherlands to developa sustainable car for the future. This first phase of the c,mm,n project is called c,mm,n 1.0 and manyaspects of the c,mm,n 1.0 car became research topics for graduate students. The results of c,mm,n 1.0were presented at the 2007 AutoRAI.

In November 2007, the c,mm,n 2.0 project was launched. SNM plans to make a new presentation ofc,mm,n 2.0 on the 2009 edition of the AutoRAI with the desire to show a driveable prototype. To assistSNM in this task, this report presents a new drive train option which is analyzed and compared to thetwo 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 internalcombustion engine with cylinder deactivation (ICE) drive train.

Because the drive train for an electric vehicle features less energy conversion steps than a hybrid drivetrain and contains drive train components which all work at high efficiency (>90%), this drive trainoption was investigated. The new drive train option is therefore an electric vehicle (EV) drive train. Itconsists of four in-wheel electric motors, a battery pack, power electronics and optionally a solar paneland/or range extender. The electric motors are chosen to meet the requirement that acceleration from0 to 100 km/h must be possible in under 12 seconds. The size of the battery pack is based on a rangerequirement 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 addedor removed at will) can be an interesting option, because when the c,mm,n is used for transportationto a distant place (e.g. going on vacation), the battery pack range will not be sufficient. For these longdistance trips a range extender can be used, such as small fuel cell or an internal combustion engine withan electric generator.

To do a simulation of the EV drive train, the QSS Toolbox is used. It can give insight to the influenceof regenerative braking on the battery state of charge and the operating points of the electric motor. Adrawback of the QSS Toolbox is that not all parameters can be changed easily. It is therefore not possibleto simulate with the correct component sizes, which makes the results inaccurate for a quantitativeanalysis, but still useful as a qualitative analysis.

A multi criteria analysis can make clear what drive train option is the preferable drive train for thefuture. The conclusion of this MCA is that a hydrogen powered vehicle (FCSCH) can be cheaper andmore sustainable than an ICE powered vehicle, but this is based on the expectancy that fuel cell pricesand 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 simulatesthe vehicle driving on specific road profiles and some specific manoeuvres. The model contains an activesuspension which reduces the pitch and roll motion of the vehicle. Simulation results are compared for apassive suspension setup versus an active suspension setup. The passive suspension setup is identical tothe active suspension, but with fixed secondary arm (there is no secondary spring influence). It should benoted 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 thepassive suspension does.

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List of abbreviations

abbreviation descriptionCNG Compressed Natural GasCO2 Carbon DioxideDC Direct CurrentEM Electric MotorESP Electronic Stability ProgramEUDC Extra-Urban Driving CycleEV Electric VehicleFC Fuel CellFCSCH Fuel Cell Super Capacitor HybridICE Internal Combustion EngineLiCoO2 Lithium Cobalt DioxideLiFePO4 Lithium Iron PhosphateMCA Multi Criteria AnalysisNEDC New European Driving CycleNiMH Nickel Metal HydridePEM Proton Exchange MembranePLIB Polymer Lithium-Ion BatteryPP Power PlantPSD Power Spectral DensityQSS Quasi Static SchedulingRAI Rijwiel en Automobiel IndustrieRMS Root Mean SquareSC Super CapacitorSNM Stichting Natuur en MilieuSOC State of ChargeTU/e Technische Universiteit Eindhoven

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List of symbols

symbol description unitη understeer coefficient −ηcycle cycle efficiency −a distance from front wheels to COG mAf frontal area m2

b distance from COG to front wheels mC1 cornering stiffness front tyres N/radC2 cornering stiffness rear tyres N/radds suspension damper constant Ns/mdsky skyhook damper constant Ns/me energy density J/l or J/kgEcharge energy transferred for charging JEcons energy consumption MJ/kmEcost energy cost e/MJEdemand vehicle energy demand MJ/kmEdischarge energy transferred for discharging JFeconomy fuel economy e/kmf frequency Hzfeig eigen frequency Hz∆Fz vertical tyre force Ng gravitational constant m/s2

ks suspension spring constant N/mkt tyre spring constant N/mm vehicle mass kgma unsprung mass kgms sprung mass kgmtank tank mass kg6 pitch body pitch angle deg6 roll body roll angle degs vehicle range kmSOC state of charge for battery pack −T torque Nmt time sV vehicle speed km/hVtank tank volume lxsusp suspension travel mmza unsprung mass displacement mzr road height mzs sprung mass displacement m

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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

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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 initiatorfor the project ”A Car in the Future”. The project started in August 2005, by challenging the threeuniversities of technology of the Netherlands (Eindhoven, Delft and Twente) to design a sustainable carfor the future. This as an answer to the 2005 AutoRAI, where very little attention was given to carsthat are developed to be less harmful to the environment. The upcoming concerns about global warmingthrough CO2 emissions due to cars and the attention SNM wanted to focus on this problem caused themto make a statement to the car industry. SNM wanted them to show an example of a clean, clever andquiet car so as to encourage the car manufacturers to quickly start mass production of green cars. After ashort inquiry at the three universities of technology of the Netherlands, it proved to be better to combinethe efforts of the three universities instead of having them compete with each other. The car of thefuture project involves the design of the exterior, interior, suspension system and power train of a futurecar within the context of the community in 2020. The mechanical engineering division of the EindhovenUniversity of Technology (TU/e) was asked to develop the complete suspension and power train systemof 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,ngarage” was held. This is an event in which anyone interested in c,mm,n may come and see what it isabout and contribute to the project. This first c,mm,n garage coincided with the start of this masterteam project and visiting this garage showed the variety of different ideas that surround c,mm,n andintroduced 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 theywant to show a driveable prototype. To assist SNM in this task, this report presents a new drive trainoption which is analyzed and compared to the two c,mm,n 1.0 drive trains. Additionally, the vehicledynamics 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 aboutvehicle dynamics. A new c,mm,n 2.0 drive train is, whenever possible, compared to the existing c,mm,n1.0 designs in an MCA. It is therefore a mix of old and new, which may, without further explanation, beconfusing to the reader. To prevent such confusion, the remainder of this section should illuminate thestructure of this report.

In chapter 2, three different drive trains topologies. Two of these are designed in the c,mm,n 1.0 and onein the c,mm,n 2.0 phase.

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Structure of this report page 6

Chapter 3 is a multi criteria analysis (MCA) in which the performance in terms of mass, energy consump-tion, fuel economy, range, environmental load, lifecycle costs and packaging is compared for the threedifferent drive trains.

Chapter 4 discusses the vehicle dynamics of the c,mm,n vehicle. This part will mainly consist of severalvehicle dynamics simulations. The main goal of this chapter is to identify interesting areas for furtherresearch.

The conclusions and recommendations are presented in chapter 5.

Chapter 2

Drive trains

In this chapter three drive trains are presented. A list with design requirements is set up as a guidelineand boundary condition for the design of these drive trains. After that, the two c,mm,n 1.0 drive traindesigns are briefly described and their specifications are given. The rest of this chapter will discuss a newdrive 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 requirementwill 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 twopersons is easily more efficient than one for 4(+1) persons, the decision for a 4(+1) person vehicle ismade, because a c,mm,n car for the common user must be able to transport a family with two to threechildren. 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 otherEuropean countries, there is an allowed maximum speed of 130 km/h and on some highways in Germanythere is no speed limit. To be able to drive at least top speed in most countries implies that the topspeed 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 shouldtherefore have the possibility to drive at least 100 km to his/her work and then the same distanceback home without ”refueling” in between. For large distance traveling (holiday by car, for instance) adifferent approach may be taken, such as public transportation, higher ranged car rental or usage of arange 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 notbe significantly different from the current average family car. To reduce aerodynamic drag, an alternativeseat arrangement could be used, but this is intentionally not chosen in order to maintain the image andfunctionalities of a common family car.

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

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Internal combustion engine (ICE) page 8

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

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

As stated in section 1.1, the c,mm,n project is an effort to create a sustainable car for the future. Astaking 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 seemsa logical one. This report focuses on drive train analysis and vehicle dynamics for c,mm,n and thereforeno research is done to improve the exterior of the c,mm,n vehicle in this report. However, this criterionremains 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]. Amaterial 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 apressurized tank is required.

To convert hydrogen into electrical energy a fuel cell is used. A fuel cell is chosen because it has arelatively high efficiency at part load compared to ICE power trains, is very quiet and has an emissionconsisting of only water vapor. There are different types of fuel cells; for the c,mm,n 1.0 the PEM FC ischosen. This is because the PEM FC has a dry electrolyte (safety, no toxic electrolyte involved) and alow operating temperature (quick start-up and power demand response).

Electric machines are needed to convert electric energy into mechanical energy. With minor adaptationsit is possible to recuperate brake energy. Because a PEM FC does not work ”in reverse” the recuperatedenergy needs to be stored in a different device. For the storage of the recuperated energy supercapacitorsare 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 tractionforces are then divided over four instead of two wheels, resulting in less torque per wheel and givingstability control systems the possibility to distribute the power to the wheels ideally. With the use ofin-wheel motors drive shafts, differentials and gear sets become obsolete, resulting in more design spaceand higher efficiency because there are no additional frictional components.

To control the energy flow for the fuel cell and supercapacitors and supercapacitors and for controllingthe 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 barFC + 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 moreinsight 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 adaptedinternal 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 byelectrical propulsion because existing ICE motors can, in addition to fossil fuels, also run on renewablesources. These sources can consist of ethanol for Otto-engines and biodiesel (from soybean or algae) forDiesel-engines. However, the production of these biological fuels can, logically, interfere with our foodproduction 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 thisengine 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 inthe automotive industry for several years. Rather more experimental techniques are cylinder deactivationand hybridization of the vehicle. These are applied in modern engines but not on a large scale yet. Theengine 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 torqueoutput 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 tobe as energy efficient as possible while being able to satisfy the design specifications mentioned in section2.1.

Because the drive train for an electric vehicle features less energy conversion steps than a hybrid drivetrain and contains drive train components which all work at high efficiency, the drive train for an allelectric vehicle will be introduced in this section. For instance, a series hybrid vehicle converts gasolineor diesel through combustion into kinetic energy of the engine. The kinetic energy of the engine isconverted into electrical energy by the generator. This electrical energy is stored in a battery, which iscontrolled by power electronics that also deliver the electrical energy to an electric motor. The electricmotor then powers the wheels either directly or by means of a transmission. It is clear that the tank towheel 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). Theefficiency gain when comparing this EV to a series hybrid is large, because the omission of an internalcombustion 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 careof propulsion and a battery as energy source. The transport of electric energy is handled by the powerelectronics. As an EV does not have the ability to ”refill” the energy supply in a quick way, the amountof energy that is carried on board must be enough to keep the vehicle driving for the rest of the day sothe batteries may be recharged at home during the night. The possibility to charge an EV’s battery bymeans 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 bediscussed in detail.

Figure 2.3: Illustration of EV Topology


Component specifications

Electric motorsThe 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 reacha top speed of at least 130 km/h (see section 2.1 for more details). Motors are chosen with a maximumtorque of 150 Nm and a maximum power of 15 kW for these reasons. This results in a combined torqueof 600 Nm and 60 kW . The benefit of these in-wheel motors (just like any other electric motor) is thatmaximum 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-wheelmotor is directly driven. No losses in the gearbox and differential occur. These losses are caused by thedesign 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 loadonly. Therefore, at nominal load it takes large amounts of energy just to move the gearbox. Althoughmanufacturers often claim that gearbox efficiency is around 95%, this is in fact only the case at peakload. 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 isnormally occupied by axles, the transmission and the engine can now be used in any way a designerwishes.

In figure 2.4 the motor characteristic of the in-wheel motors is shown. Also the road load is shown in thisfigure 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 from0 to 100 km/h is reached in 12 seconds. This is achieved when addressing the nominal torque. A nicefeature 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 electricmotors.

When accelerating, the torque is divided over all four wheels, which reduces the torque per wheel andwith that the risk of wheel slip. When accelerating on dry roads, the difference between a front/rearwheel drive and a 4-wheel drive is barely noticeable. When roads are wet or slippery, however, (possiblyin combination with some road inclination) a 4-wheel drive makes accelerating without wheel slip mucheasier.

These in-wheel motors can be controlled independently, which gives rise to an increase in freedom of


Figure 2.5: Full throttle acceleration

controlling stability. Stability systems nowadays (ESP) can only stabilize the vehicle with independentinitiation of the brakes. With in-wheel motors, however, the torque can be controlled independently foreach 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 maystabilize 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 usingdisc brakes, thus dissipated to heat) smaller.

Battery packA polymer lithium-ion battery (PLIB) is an example of a developing battery technology. It is of thelithium-ion type and features higher energy density, lower weight and lower costs than other batterytechnologies such as NiMH or lead-acid batteries. The latest addition to the PLIB family is the LiFePO4

type. The advantage of this type is that it is cheaper, safer when used in large battery packs, has a longercycle life and can be charged in less time than the widely used LiCoO2 type. The LiFePO4 PLIB has aremarkable cycle efficiency of 99.8% [2]. The definition of cycle efficiency is as follows:

ηcycle =Edischarge

Echarge(2.1)

where ηcycle is the cycle efficiency, Edischarge is the energy transferred when discharging and Echarge isthe energy transferred when charging.

All the above mentioned advantages of this LiFePO4 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 notbe guaranteed that those batteries will be of the PLIB or even the Lithium-ion type. It may very well bea completely different kind of battery; the ”current” choice for a LiFePO4 PLIB merely shows that it isprobable that future batteries will have a cycle efficiency that is at least in the range of current batteriesand that batteries will be used safely and cost effectively in the future.

Battery weight determinationTo 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


Figure 2.6: New European Driving Cycle

of the vehicle range. A typically used driving cycle is the New European Driving Cycle (NEDC). Figure2.6 is a representation of this driving cycle. The NEDC is a driving cycle consisting of four repeatedECE-15 driving cycles and an Extra-Urban driving cycle, or EUDC. The NEDC is supposed to representthe typical use of a car in Europe. For a distance of 100 km (approximately 9 NEDC cycles) an energyof 20.14 MJ has to be available in the battery pack (figure 3.2). For a minimum acceptable range of 300km (section 2.1) the energy storage will be at 70.65 MJ or 20 kWh while assuming that regenerativebraking is applied with an efficiency of 75%. See section 3.3 for more information about regenerativebraking and fuel economy.

Since the NEDC is a mild cycle and (most) batteries are not suited to be fully charged and then fullydepleted because of battery wear, a correction factor of 1.5 is applied, implying a window of operationof 1

1.5 = 66%. This results in the need of a battery with a capacity of 30 kWh. With an energy densityof 400 Wh/kg, a battery weight of approximately 75 kg is needed, see figure 2.7. More details about thedetermination of this energy density can be found in the subssections below.

Determination of energy densityBecause 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 thebattery pack mass of the EV, because vehicle mass influences many dynamics and performance relatedproperties of the vehicle in a negative way. In the remainder of this section, assumptions and consultedsources that lead to the expected value for the energy density in 2020 are presented.

Trends in batteriesWhen looking at figure 2.8 [6] a trend of increasing energy density in Wh/l can be observed. In the last15 years the energy density was increased by a factor 5.2. If this increase is maintained until 2020, anenergy density of 3000 Wh/l is not unthinkable. According to Prof. Dr. Ir. Paul van den Bosch of thedepartment of Electrical Engineering of the TU/e, a factor 3 between Wh/l and Wh/kg is reasonable,because the batteries in an electric vehicle must be able to handle high incoming and outgoing currentswhile having a long lifetime and must therefore have a robust construction. When accepting this factor3, one would arrive at an energy density of 1000 Wh/kg or 1 kWh/kg. When comparing this numberwith different authors that mentioned something about the expected energy density around 2020, thelinear extrapolation of figure 2.8 seems somewhat optimistic. For instance, [3] expects that the energydensity of a lithium-ion battery in 2020 will be about 103 Wh/kg, which is rather pessimistic and evenproven wrong, because the Tesla Roadster currently features lithium-ion batteries with an energy densityof 125 Wh/kg [19]. In [3] the energy density of lithium-ion batteries in 2050 is expected to be about 400


Figure 2.7: Weight of the battery pack for various densities

Figure 2.8: The development of energy density over the years

Wh/kg. In [4] the energy density of a PLIB is estimated to be around 400 Wh/kg in 2020. A linearextrapolation of figure 2.8 may thus very well not be realistic and therefore the assumed energy densityof batteries in 2020 is taken to be 400 Wh/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 powerrequested by the electric motor(s) will not be limited by the battery, because the size of the battery packthat is needed to fulfill the third design requirement from section 2.1 will be sufficient to also fulfill thepower 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 assumptionmust be made to be able make a comparison between an EV and the two drive train options from c,mm,n1.0.


Solar panelThe rule of thumb for solar panels in Holland is that an annual production of 80 kWh/m2 or 288 MJ/m2

can be reached (source [11]). A solar panel that is placed horizontally, for instance on the roof of acar, is 87 % as efficient as this. A solar panel placed on the roof of the vehicle measuring 3.6 m2 (halfthe vehicle from a top-view), can therefore deliver 902.0 MJ/year. Given the energy consumption of23.56 MJ/100km, this will give the c,mm,n,2.0 a solar powered range of about 3800 km/year. This isapproximately 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 horizonfor 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 costapproximately e2000.-, because of the current cost of panels of 550 e/m2 (source: [11]). This is thelargest drawback so far, because if you would want to drive the specified 3828.5 km on grid power, itwould cost only e50.15 (table: 3.3), giving the panel a payback time of 39.88 years. This means thatwith current electricity and solar panel prices this option will be reserved for the most environmentallyfocussed drivers amongst us.[11]

Possibilities for range extensionThe c,mm,n is preferably used to travel distances up to 300 km. The battery pack is sufficient for thosedistances. When the c,mm,n is used for transportation to a distant place (e.g. going on vacation), thebattery pack range will not be sufficient. When using an EV, charging stops of several minutes willhave to be made after every 300 km. For these long distance trips several different range extenders canbe used, such as small fuel cell or an internal combustion engine with an electric generator. The rangeextender should add significant range without weighing too much and costing too much space. The rangeextender could of course be used at any time, but it is designed to be used for traveling large distancesonly, 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 shortdistances. Therefore, a range extender which could be placed modularly (i.e. as an additional componentthat 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 QSSToolbox. Figure 2.9 shows the basic layout of the Simulink model. This way all sorts of data can beanalyzed by simulating the c,mm,n drive train on a driving cycle e.g. the state of charge of the batteryand 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 operatingpoints of the vehicle is plotted. This way, a better insight is obtained of how the electric motors areoperating 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


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 ofparameters. To change parameters of the battery for instance, a MATLAB R© m-file with no additionaldescription has to be edited. This m-file contains the parameters, but one can not discover what eachparameter represents and is therefore unable to get any insight in the workings of this m-file. Thesimulation is therefore restricted to the use of a standard, current day battery. Adjusting the parametersof the battery for the future predictions (such as a higher cycle efficiency) is too complex. Therefore thisQSS toolbox simulations can not really be used for quantitative analysis but could give some qualitativeinsight 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, energyconsumption, fuel economy, range, environmental load, life cycle costs and packaging. Using the vehicleparameters as presented in appendix A in the QSS toolbox (section 2.4), the energy demand of everydrive train to complete an NEDC cycle could be obtained. Using L.Guzella’s book ”Vehicle PropulsionSystems”[10] and adjusting battery efficiency to a future prediction of 95% (see section 2.4), the mentioneddrive train properties were determined and compared in this chapter. Since this report only deals withthe drive train choice, future designers of the vehicle should be encouraged to take a good look at theirmaterial choice and application from an environmental point of view. Simply using materials that can berecycled will reduce the future raw material usage (and for instance also give the vehicle a higher tradevalue when it needs to be replaced). Figure 3.1 shows the c,mm,n implemented in our society, consumingraw 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 drivetrains gives the vehicles masses as given in tabel 3.1.

All specifications can also be found in appendix A.

17

Fuel economy page 18

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

drive train mass total vehicle massICE c,mm,n 200 kg 850 kgEV c,mm,n 150 kg 800 kgFCSCH 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 focusseson the effects of the drive train choice it is assumed that roll resistance and air drag are equal for eachvehicle. The variables then are the mass and efficiency of every power train. The NEDC cycle was usedbecause 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 onthe NEDC cycle. The energy shown is the total energy dissipated by air drag, rolling resistance andbraking. Model parameters were as shown in appendix A and differences in vehicle performance in table3.2 originate from differences in mass and the capability to recuperate brake energy.

Table 3.2: Energy demand in the NEDC cycle

ICEEnergy demand 26.13 MJ/100km

EVEnergy demand (regenerative) 20.14 MJ/100kmEnergy demand (non-regenerative) 26.00 MJ/100km

FCSCHEnergy demand (regenerative) 22.22 MJ/100kmEnergy 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 brakeenergy, because not all of the energy can be recaptured because of incidental hard braking. More lossesoccur in the conversion back to electrical energy so the overall efficiency of regenerative braking is lowerthan 75%. The electric motor can only decelerate as much as it can accelerate and when the requireddeceleration becomes too high for the in wheel motors, conventional brakes have to be applied. Thekinetic 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 ICEc,mm,n a window of 8% improvement on a regular ICE is taken into account for cylinder deactivationand 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% conversionefficiency 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 withthe highest energy density, an environmentalist the carrier with the lowest environmental load, but theconsumer the one that simply costs the least.

Feconomy =Ecost

Econs(3.1)

The fuel economy is calculated by dividing the cost per energy (Ecost) unit by the energy consumptionper 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 0.20e/kWh. This is equal to 49.38 e/GJ for gasoline and 55.56 e/GJ for electricity. The future costof hydrogen is taken to be 4 $/kg [12], equal to 17.70 e/GJ when produced from natural gas. Whenproducing hydrogen through electrolysis the well to wheel efficiency becomes 25,7 % because the ”well” inthis case becomes grid electricity (equation 3.2). The costs then are at least 4.80 e/100km for a FCSCHc,mm,n.

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

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

Table 3.3: Energy prices per 100 km

Source CostICE

Assumed efficient gasoline engine 5.14 e/100kmCurrent day gasoline engine 7.60 e/100km

EVGrid electricity 1.31 e/100km

FCSCHFuture natural compressed gas 0.43 e/100kmElectrolysis by grid electricity 4.80 e/100km

Table 3.3 shows that hydrogen can be a significantly cheaper energy carrier than the alternatives. Howeverthe future production of hydrogen from natural gas is not desirable, because this is a fossil fuel. For aneconomy to be independent of these the energy sources used must be renewable. The feasible sourcesfor the electricity then boil down to solar, wind, tidal, geothermic and nuclear power. It is probablethat the future brings more efficient and cheaper technologies for utilizing solar power (through biomassconversion 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 producehydrogen with electricity instead of storing the electricity directly in batteries (since future batterytechnology will no longer be a constraining factor, because energy densities rise, charge times drop andcosts 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 changesin the energy prices. Gasoline prices currently are artificially high due to taxes (duties and VAT, currently61.5 % 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 energyprices can not be predicted.

3.4 Range

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

Range =Vtank × e

Econs=

30[L]× 31.6[MJ/L]1.04[MJ/km]

= 911.5[km] (3.3)

The EV c,mm,n has a range of 300km, chosen by us because it is difficult to carry the energy for longtrips 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.

Range =mtank × e

Econs=

4[kg]× 118.8[MJ/kg]0.617[MJ/km]

= 770[km] (3.4)

3.5 Environmental load

CO2 emissions are an increasing concern of today’s society because it is believed that there is a correlationbetween CO2 concentration in the atmosphere and global temperature. To put a stop to the increasingglobal warming governments are issuing countermeasures such as CO2 taxes or grants for vehicles withlower than average emissions. Therefore the emissions of a vehicle can become an important sellingpoint as they will more and more influence the purchase and operating costs. L.Guzella [15] gives thetotal well-to-wheel emissions for various power trains and the combination of these numbers with energyconsumption 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 resultfrom this consumption. For instance: a FC vehicle that has an energy consumption of 50 J/km has aCO2 emission of 12 kg CO2/100 km when the energy source is natural gas and steam refining is used toconvert it into hydrogen. The FCSCH c,mm,n with an energy demand of 22.22 MJ/100 km then has aCO2 emission of 5.33 kg CO2/100 km, obtained through scaling, also additional scaling has to be appliedfor 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 whenits power is drawn from conventional coal plants. Note that it’s clean PP emission of 2.71 kg CO2/100km corresponds to 9.33 kg CO2/100 km for the FCSCH when it uses power from the same PP viaelectrolysis. 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 usingcylinder deactivation. The cheap FCSCH (CNG as the source of its hydrogen) shows the disadvantageof 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 theEV is still the most favorable option.

Recycling is another necessity when attempts are made to keep a vehicle as renewable as possible. Mostmetal components can be easily recycled and most plastics can be recycled in some form as well. Sincemost lithium systems contain toxic and flammable electrolytes, these can be dangerous to the environmentand effort should be made to prevent these batteries from ending up on junk piles instead of recyclingthem.

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

ICEAssumed clean gasoline engine 8.91 kg CO2/100 kmCurrent day gasoline engine 13.13 kg CO2/100 km

EVSolar or nuclear PP 0 kg CO2/100 kmNatural gas (combined cycle) PP 2.71 kg CO2/100 kmCoal PP 9.84 kg CO2/100 km

FCSCHElectrolysis by grid electricity (nuclear or solar PP) 0 kg CO2/100 kmRefining natural gas 5.33 kg CO2/100 kmRefining crude oil 8.00 kg CO2/100 kmElectrolysis by grid electricity (combined cycle PP) 9.33 kg CO2/100 kmCoal 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. Thecosts of the operated power components per vehicle will now be included.

Batteries cost about 133-200 e/kWh and fuel cells about 1000-1800 e/kW currently, to as little as 38e/kW [3] if the global economy becomes hydrogen powered. Supercapacitors are cheap compared to fuelcells, costing e0.25-1 cents/F . The production costs of ICEs is a quite constant number; an Otto-engineis slightly cheaper to manufacture than a Diesel-engine, costing e2600 and e4000 respectively. Becauseof the cylinder deactivation technology, the efficiency of the ICE was granted an 8% improvement ofits current efficiency (17 %) and for now it is assumed that the engine price will also increase with anunknown amount, making it approximately e2800. ICEs will become slightly more expensive in thefuture due to stricter European emission demands.

All the components have the potential to outlive the current day vehicles; current lithium-ion batterieshave a life of 1000-2000 deep discharge cycles and up to 4000 normal cycles, equivalent to 480,000 kmdriven since in 1 normal cycle the battery is discharged for about 40%, corresponding to a vehicle rangeof 120 km.

The current day fuel cells have a life of 3500 hours when operated at part load. Driving at an averageof 70 km/h this gives the vehicle a life range of 245,000 km. The ICE’s are currently fit for lasting thesedistances as well and are expected to outlive at least 300,000 km. For simplicity it is assumed that allvehicles will have a life of 300,000 km and service costs are also not taken into account. The purchasecosts can then be divided by the total kilometers driven in a lifetime of the vehicle and added to the fuelcosts 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 madefor the EV is a realistic power density in batteries of 400 Wh/kg in 2020. For the FCSCH vehicle to beas 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 ispossible without compromising the worlds food production the fuel cell vehicle has room for some moreimprovement. Note however, that small scale production of hydrogen in this way is insufficient becauseof the ”global hydrogen economy” requirement.

Conclusion page 22

Table 3.5: Purchase and lifetime costs

Specification CostICE

Purchase 2, 800 eLifetime cost (efficient motor) 6.07 e/100km

EVPurchase future 6, 400 eLifetime cost future 3.44 e/100km

FCSCHPurchase current 54, 000 eLifetime cost current PP 22.80 e/100kmPurchase future 1, 140 eLifetime cost future CNG 0.82 e/100kmLifetime 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. TheICE and FCSCH both have a large fuel tank and an ICE or fuel cell stack, adding up to about 500 L intotal, so this requires space in the front and rear of the car. The battery powered c,mm,n only needs oneof those areas partially filled, leaving more luggage area, the choice of where to place 10% of the vehiclemass (to shift the center of gravity) or the possibility to reduce the total vehicle size resulting in lowermass and air drag.

3.8 Conclusion

The information about drive train performance from the previous sections is collected in table 3.6. Noactual multi criteria score will be given in this section because the weighing factors needed can not bedetermined objectively from the research results and the explicit choice was made not to assign subjectivefactors to the criteria.

Table 3.6: Multi Criteria Analysis of possible drivetrains

MCA ICE Boxer EV (future) FCSCH unitFuel economy 5.14-7.60 0-1.31 0.43-4.80 e/100kmRange 900 300 770 kmCO2 emission 8.91-13.13 0-9.84 0-33.88 kg/100kmMass 850 800 980 kgEnergy density fuel 32 4.32 6.3 MJ/LPurchase costs 2,800 6,400 1,140 (future)

54,000 (now)e

Packaging 0.48 0.10+ in-wheel motors

0.56+ in-wheel motors

m3

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 thanan ICE powered one, but when maximizing sustainability the EV has no competition, because of itsefficient 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 bymeans of simulations using the SimMechanicsTM and TNO Delft-Tyre toolbox of MATLAB R©. ASimMechanicsTM model of the EV c,mm,n vehicle simulates the vehicle driving on specific road pro-files and some specific manoeuvres. Simulation results will be compared for a passive suspension setupversus an active suspension setup.

4.1 Active Suspension

Current vehicles commonly use a passive suspension system. The unsprung mass (wheel + suspensionsystem) interacts with the sprung mass (car body) by means of a spring and a damper. By tuning thespring and damper characteristics the vehicle behavior is influenced. In passive suspension systems thesuspension characteristics are fixed. An active suspension system has got the ability to continuouslychange its suspension characteristics.

The EV and FCSCH vehicles use in-wheel motors. This causes an increase of the unsprung mass. Alsothe sprung mass is decreased because it contains less drive train components. This generally worsensthe comfort and handling behaviour of the vehicle. To maintain a good handling of the vehicle and acomfortable 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 trailingarm with primary spring and damper and a secondary arm with secondary pre-tensioned spring. Thesecondary arm and spring are used as a force actuator. During driving the secondary arm adds a momentaround axle A. The magnitude and sign of this moment depend on the angle of the secondary arm aroundaxle B. A positive angle means a positive moment and a negative angle around axle B means a negativemoment 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. Thesensitivity 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 beexperienced as unpleasant. See figure 4.2 for a representation of the body as a multibody system withindicated heightened sensitivity for certain frequencies. Because the provided model from Leegwater hasgot no altitude controller, it can only be used partially for comfort analysis. The model has has got noskyhook damping, which is needed to make any reasonable statements about the ride comfort. Skyhookdamping is a damper which connects the sprung mass to the sky and thus make the sprung mass moreresistant 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]


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 thevehicle sprung mass. This has effect on the vehicle behaviour in various driving situations such as corner-ing 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 seenclearly that the active suspension reduces the pitch angle of the vehicle. There is still a slight variationin 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 wheelsuspension. This suspension has an opposed movement to the passive suspension because the active


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

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 suspensiontravel 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 natureand the active suspension does not significantly change the maximum wheel loads.


Maximum acceleration

The vehicle pitch angle as a result of maximum acceleration of the vehicle is shown in figure 4.7. Thepitch angle is not very high for the passive model, but nevertheless reduced to nearly zero by the activesuspension. Note that the vehicle body has a negative pitch (nose down) while accelerating due to itstrailing 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 meansthat, as already shown in figure 4.7, the vehicle body is kept almost completely leveled. An interestingside 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 theactive suspension setup. Also it shows very low oscillatory behaviour which positively influences the


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 accel-eration. This is because the brake torque can be larger than the maximum electric motor torque, sincethe torque of additional disc brakes helps the car make an emergency stop. The bigger pitch angle canstill 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 theactive suspension is trying to keep the vehicle leveled. The total vehicle will rise for 40 mm because it


Figure 4.11: Braking - Suspension travel versus time

has no altitude controller. The passive vehicle is squatting quite severely. Squatting means that the pitchis 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 someof the oscillatory effects that occur in the passive model, shown in figure 4.12.


Making a lane change

When making a lane change on the highway the active suspension greatly reduces body roll, keepingthe body leveled, shown in figure 4.13. Also the suspension travel is nearly zero for the actively sprungvehicle 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 thatthe front and rear wheels have nearly equal loads for both the active and passive model, because themodel 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 shouldbe 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 mayresult in overconfident driving behavior, although it may improve the vehicle’s cornering ability. Also, thetrailing arm suspension can be further analyzed: it is observed that the vehicle dives while acceleratingand squats while braking, which is opposite to what most vehicles would do. Specifically, when lookingat 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 FCSCHc,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 massand 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 dynamicstability controller will steer all four wheels giving the vehicle more stability on the road. Also, becauseof 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 futureparticipants 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 optionwhile 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 featurefour 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-wheelmotors.

Mass distribution

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

η =mg

l(b

C1− a

C2) (4.1)

With η the understeer coefficient. In this equation a denotes the distance from the front wheels to thecenter of gravity cg, b the distance of cg to the rear wheels and C1 and C2 the cornering stiffnesses of thefront and rear tyres respectively.

The understeer coefficient determines the magnitude of understeer (η > 0), neutral steer (η = 0) oroversteer (η < 0) of the vehicle. In this report the center of gravity is taken to be exactly into themiddle of the vehicle. A proper location of the center of gravity should be examined for the best vehiclebehaviour. The drive train component placement can influence the center of gravity and should beexamined.

Chapter 5

Conclusions & recommendations

The Electric Vehicle (EV) drivetrainIn this report the EV as additional drive train option proves to be a favorable and good alternative to theother two existing drive trains for c,mm,n. A distinct ranking of the drive trains can be made in termsof costs and CO2 emissions, in which the EV always performs best. Also, the practicality of the EV ishigher in terms of packaging, because of the use of in-wheel motors and limited battery volume. A typicalweak point of an EV is the range. A battery pack contains only a limited amount of energy thereforegiving it a limited range of around 300 km. Looking at the current battery density trends this weakpoint should get stronger giving the vehicle a greater range. Note that the energy density of batteriesis hard to predict for the year 2020. This is still a critical point for the succes of the EV. Although theautonomous range of approximately 300 km should be large enough in many cases of commuting travelthere is an option to extend the range by adding a range extender to the c,mm,n. A rang extender couldexist of a fuel cell or a small internal combustion engine with an electric generator. This gives the EV afar greater range, but also adding weight. Overall it gives the vehicle extra efficiency loss making it onlynecessary for traveling great distances without recharging.The exact effects on marketability of the shorter range of the EV should be investigated. The assumptionwas made that a range of 300 km is sufficient for everyday use in commuting, but a consumer maydecide otherwise. This consumer decision is not in our field of research. Also the assumptions on futuretechnology (on batteries and fuel cells) made in this report should be monitored; a radical breakthroughin one of these fields could make the EV more favorable or it could make other drive trains more favorable.

Active suspensionIn this report the significance of this active suspension was examined by means of comparison with passivesuspension. It can be concluded that with the current trailing arm suspension (originally chosen for anactive suspension) the active suspension greatly improves the vehicle dynamics. For a proper comparisonwith 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 steeringThe benefits of independent four-wheel steering are not yet fully explored in this report. It is interestingto investigate all possibilities of four-wheel steering. Some options that may be considered are: the useof narrower tyres (reducing the rolling resistance) and using stability control by means of four-wheelsteering, increasing stability and reducing tyre wear in tight slow corners and facilitating the parking ofthe c,mm,n vehicle.

Further research on independent four-wheel driveThe EV and Fuel cell super capacitor hybrid (c,mm,n 1.0) makes use of four in-wheel motors and theindependent control of torque to the wheels can be used to increase stability. A controller could beimplemented 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 traincomponents) mv

650kg source: [13]

Frontal area Af 2.1m2 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 980kgEnergy 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 estimationFuel tank volume 102L source: [1]Energy density fuel 118, 8MJ/kg source: [1] (given in

33000Wh/kg)Energy storage (in a full tank) 475, 2MJ source: [1] 118, 8MJ/kg × 4kgVehicle power 40kW source: [1]Vehicle range 770kmFuel 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 massof 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 850kgDrive train components mass 200kg Calculation 1 (see below)Energy density gasoline (used incalculations)

43, 920MJ/kg source: [8]

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 795kgBattery mass 75kg chosen to provide specified range

of 300kmPower electronics mass 10kg estimationMotor 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 400Wh/kg source: [4]Energy storage (on a full charge) 115, 2MJ 1, 44MJ/kg × 80kgVehicle power 60kW Design Requirements (section

2.1)Vehicle range 300kmSpecific 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 thevehicle.

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)

= 0.025 + 0.02 + Vinwheelmotors = 0.045[m3] + Vinwheelmotors[m3] (B.4)

Vpowerelectronics is estimated to be 20 L, to be on the safe side. A designer contest on www.greencarcongress.comrequired newly designed power electronics for future EV’s to be no larger than 4.6 L. For cooling of thepower 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)

= 0.4488 + 0.1026 + 0.0075 + Vinwheelmotors = 0.56[m3] + Vinwheelmotors (B.6)

Vfuelcells is 0.4488 m3 because it occupies the same space as the internal combustion engine, between therear wheels.

The supercapacitors have a power density of 1-1.5 kw/kg, an energy density of 3-5 Wh/kg and in termsof volume 20 kWh/m3, so the volume is at most 7.5 L, which is insignificant compared to the rest of thecomponents (source [1]).

36

APPENDIX B. PACKAGING page 37

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

Bibliography

[1] N. Scheffer, Design and optimization of a FC-SC Hybrid, Department of MechanicalEngineering, Section Automotive Engineering Science - Power Trains, TU/e, (2007)

[2] DN Power Electronic Technology Co.,LTD, General Knowledge about Polymer Lithium-ion Battery (PLIB), http://www.dn-power.com/v2/Battery/PLIB-intro.asp, (2006), vis-ited on april 16th 2008

[3] Thomas Kruithof, Driving the Future - Techno-economic comparison of fuel cell, serialhybrid and internal combustion engine drivetrains for light duty vehicles, Master The-sis Sustainable Development, Energy and Resources, Copernicus Institute University ofUtrecht, (2007), 37-42

[4] T. Hofman, Storage Systems for hybrid vehicle drive trains, Lecture notes 2 of ”Designof hybrid drive trains” (4N840), Department of Mechanical Engineering, Section Auto-motive Engineering Science - Power Trains, TU/e, (2008), 11-34

[5] Jaap Kwadijk, Trends in mobiliteit, http://www.nl.capgemini.com/m/nl/f2f/innovation/04 mobiliteit.pdf (2007), 1, visited on May 20th 2008

[6] Battery association of Japan, Sheet of presentation obtained from T. Hofman, MatsushitaBattery Industrial Co., Ltd., (2006)

[7] Wikipedia, Lithium ion battery, http://en.wikipedia.org/wiki/Lithium ion, (2008), vis-ited on May 26th 2008.

[8] Energy density wiki, Energy density, http://wiki.xtronics.com/index.php/Energy density,(2008), visited on May 26th 2008.

[9] Source from c,mm,n CD, Technische gegevens Cmmn en Cito.doc, (2006)

[10] L. Guzzella, A. Amstutz, The QSS Toolbox Manual, ETH - IMRT, (2005)

[11] Floris Wouterlood, Photovoltaic solar PV panels in The Netherlands,http://www.zonnepanelen.wouterlood.com, (2008), visited on May 27th 2008.

[12] F. David Doty, A Realistic Look at Hydrogen Price Projections,http://www.dotynmr.com/PDF/Doty H2Price.pdf, (2004), visited on May 31st2008.

[13] S.A.K. van Loenhout, Real-time control for a Fuel Cell Hybrid Vehicle with the EquivalentConsumption Minimization Strategy, Section Automotive Engineering Science - PowerTrains, TU/e, (2007)

[14] M.S.P. Leegwater, An active suspension system - capable of economically leveling a carduring cornering, Department of Mechanical Engineering, Section Automotive Engineer-ing Science - Vehicle Dynamics, (2007)

[15] L. Guzzella, A. Sciaretta, Vehicle Propulsion Systems - Introduction to Modeling andOptimization, Springer, (2007)

[16] G.F.A. Peters, Cylinder deactivation on 4 cylinder engines: A torsional vibration anal-ysis, Department of Mechanical Engineering, Section Automotive Engineering Science -Power Trains, TU/e, (2007)

38

BIBLIOGRAPHY page 39

[17] I. Rericha, Methoden zur objektiven bewertung des fahrkomforts, AutomobilIndustrie,2/86:175-182, (1986)

[18] R.S.G. Baert, I.J.M. Besselink e.a., Introduction to Automotive Technology (4N820),Eindhoven University of Technology, Department of Mechanical Engineering, (2006)

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[20] T. Hofman - Introduction (New), Lecture notes 1 of ”Design of hybrid drive trains”(4N840), Department of Mechanical Engineering, Section Automotive Engineering Sci-ence - Power Trains, TU/e, (2008), 37

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