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Les Rencontres Scientifiques d'IFP Energies nouvelles - Int. Scient. Conf. on hybrid and electric vehicles RHEVE 20116-7 December 2011 Proceedings Copyright 2011, IFPEN

Assessment by Simulation of Benefits of New HEVPowertrain Configurations

Namdoo Kim and Aymeric Rousseau

Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL, 60439-4815, USA

e-mail: [email protected], [email protected]

Abstract During the past couple of years, numerous powertrain

configurations for hybrid electric vehicles (HEV) have been introduced into the

marketplace. The current dominant architecture is the power-split configuration

with the input split (single-mode) from Toyota and Ford. General Motors recently

introduced a two-mode power-split configuration for applications in sport utility

vehicles. Also, the first commercially available Plug-In Hybrid Electric Vehicle

(PHEV) the GM Volt was introduced into the market in 2010. The GM Volt

uses a series-split powertrain architecture, which provides benefits over the series

architecture, which typically has been considered for Electric-Range Extended

Vehicles (E-REV). This paper assesses the benefits of these different powertrain

architectures (single-mode vs. multi-mode for HEV) (series vs. GM Voltec for

PHEV) by comparing component sizes, system efficiency, and fuel consumption

over several drive cycles. On the basis of dynamic models, a detailed component

control algorithm was developed for each configuration. The powertrain

components were sized to meet all-electric-range, performance, and grade-

capacity requirements. This paper presents and compares the impact of these

different powertrain configurations on component size and fuel consumption.

INTRODUCTION

Various hybrid electric vehicle (HEV)architectures have been proposed one of theearliest and most commercially successful

systems has been the power split, as used on allthree generations of the Toyota Prius (as well asother Toyota/Lexus models) and on the FordEscape. The powertrain configuration of thepower-split hybrid system, sometimes referredas the parallel/series hybrid, combines theprevious two configurations with a power-splitdevice. It is appealing because with a propercontrol strategy, it can be designed to takeadvantage of both parallel and series typeswhile avoiding their disadvantages. A majoradvantage of this configuration is the potential tode-couple the ICE and wheel speed as long as

the output power demand is met, which offersgreater flexibility in terms of choosing the ICEworking point to optimize fuel consumption [1,2].

However, in the power-spilt configuration, theinternal power circulation occurs along theclosed loop (depending on the speed ratio), andsometimes the circulated power increasesenormously. This power circulation can lead tohigh losses and, as a result, low efficiency of the

power transmission. Such drawbacks can beaddressed by combining several EVT (electro-mechanical infinitely variable transmission)modes into one multi-mode hybrid system,thereby increasing the number of mechanical

points and allowing greater operation flexibility.Various multi-mode EVT design configurationshave been proposed, as indicated by patentsand publications [37].

In an HEV, because the battery is charged onlyby the engine and not by plugging it into anexternal power source, electric driving range islimited because of the batterys relatively smallcapacity. Compared to the common HEV, aplug-in hybrid electric vehicle (PHEV) hasgreater potential for improved fuel efficiency andreduced emissions because it allows full electric

driving and can easily use electric powerprovided by the home electricity grid [8]. APHEV is also capable of long-distance travelbecause of its HEV function. PHEVs are gainingmore attention in the automobile industrybecause of their advantages, but there havebeen few comparative studies on theirpowertrains because they require a differentcontrol algorithm than HEVs, depending on theconfiguration of the PHEV.

IFP Energies nouvelles - RHEVE 2011 - 1 -
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Les Rencontres Scientifiques d'IFP Energies nouvelles - RHEVE 2011

When a vehicle is designed for a specificapplication, the goal is to select the powertrainconfiguration that maximizes the fuel displacedand yet minimizes the sizes of components. In

the first part of this study, we evaluate thebenefits of several multi-mode powertrainconfigurations with regard to size and fuelconsumption for HEVs. Each powertrain is sizedto represent a small-size sport utility vehicle(SUV) application, following the same vehicletechnical specifications, such as accelerationand gradeability. In the second part, acomparative study is conducted on a GM Voltand a series plug-in hybrid for a PHEV. Twovehicle-powertrain configurations are sized toachieve similar performance for all-electricrange (AER) approaches, on the basis of a mid-sized vehicle application. The component sizesand the fuel economy of each option areexamined.

1 DESCRIPTION OF POWERTRAIN

SYSTEM

1.1 HEV powertrain system

1.1.1 Single-mode EVT

Figure 1 is a schematic diagram of the single-mode power split transmission (TM) with areduction gear (RG). Because the input powerfrom the ICE is split at the planetary gear, whichis located at the input side, and the powertransmission characteristic is represented by asingle relationship for the whole speed range,this power-split configuration is called the input-split type or single-mode EVT. This input-splitconfiguration consists of two planetary gearsand two electric machines (MC1 and MC2). Thelarger electric machine on the right (MC1) isconnected to the output shaft through thesecond planetary gear and does not affect thespeed ratio. Therefore, for this particular EVTarrangement (which maximizes the output

torque), the speed of the output is the weightedaverage of the speed of the input and the speedof MC2. The second planetary gear setmultiplies the torque from the input and both ofthe electric motors during input-split operation.For comparison, the single-mode powertrainwithout RG is also investigated in this study.

Figure 1: Schematic of the single-mode EVT

In Figure 2, the electro-mechanical power ratioand the EVT system efficiency () are plottedwith respect to the speed ratio (SR). In thisanalysis, it is assumed that there is no power

loss through the all-mechanical path and onlyelectric machine loss is considered by using theefficiency maps of electric machines. The powerratio is defined as the ratio of the electro-mechanical power to the ICE input power, andthe SR is defined as the ratio of the ICE inputspeed to output speed. In high SR range, thesystem efficiency is low because the electricalmachines have relatively low efficiency. This lowsystem efficiency can be avoided by propellingthe vehicle by using the electric motor directlyinstead of using the engine. When SR=0.7, theelectro-mechanical power ratio becomes 0, and

all the power is transmitted through themechanical part. This point is called themechanical point (MP). The system efficiencyshows the highest value at the MP. For SR

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Les Rencontres Scientifiques d'IF

P Energies nouvelles - RHEVE 2011


0 0.5 1 1.5 2 2.5 3-1.5

-1

-0.5

0

0.5

1

ower

ato

The ratio P-elect to P-eng (@ W-eng=1500rpm, T-eng=100Nm)

EVT1

0 0.5 1 1.5 2 2.5 30.5

0.6

0.7

0.8

0.9

1

SR, the ratio of W-eng to W-out

Eff.

Efficienc y (@ W-eng=1500rpm, T-eng=100Nm)

EVT1

Figure 2: Power characteristics of the single-mode EVT

1.1.2 Two-mode EVT with fixed-gear ratios

Figure 3: Schematic of the two-mode EVT with FGs

Figure 3 is a schematic of the two-mode hybrid,

which is called the General Motors AdvancedHybrid System2 (AHS2) for front-wheel drive(FWD) [5]. This system has an additionalstationary clutch and an additional rotatingclutch. Through engaging or disengaging thefour clutches, this system realizes six differentoperation modes, including two EVT modes andfour fixed-gear (FG) modes. When operated inany of the four fixed-gear modes, the vehicle iscomparable to a parallel pre-transmission HEV.

0 1 2 3 40.4

0.5

0.6

0.7

0.8

0.9

1


Eff.

Efficien cy (@ W-eng=1500rpm, T-eng=100Nm)

EVT1

EVT2

0 1 2 3 4-1.5

-1

-0.5

0

0.5

1

1.5

ower

ato

The ratio P-elect to P-eng (@ W-eng=1500rpm, T-eng=100Nm)

EVT1

EVT2

Figure 4: Power characteristics of the two-mode EVT with

FGs

In Figure 4, the two-mode EVT already has anative fixed gear ratio, the synchronous shiftratio, in which the action of two clutches at thesame time provides a fixed ratio. For the two-mode hybrid, one fixed gear was added within

the ratio range of the first EVT mode, and twomore fixed gears were added within the ratiorange of the second EVT mode. So, for the two-mode hybrid, the native fixed gear between thetwo EVT modes is fixed gear 2 (FG2). The topfixed gear ratio, fixed gear 4 (FG4), was addedby putting a stationary clutch on one of themotors that regulates the speed ratio throughthe transmission, MC1. Fixed gear 1 (FG1) andfixed gear 3 (FG3) were both added with arotating clutch. The FG1 comes from locking upthe input-split mode, so the speed, torque, andpower from the engine go through the torquemultiplication of the second planetary gear set.The FG3 comes from locking up the compound-split mode, and so the speed, torque, and powerfrom the engine are coupled directly to theoutput. This study also investigates theadditional two-mode EVT with fixed gears, whichis called AHS2 for rear-wheel drive (RWD) [5,7].

A two-mode EVT with both an input-split modeand a compound-split mode fundamentallylowered the requirement for motor power, thus

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allowing the EVT to be selected as a soundbasis for large cars and trucks.

1.1.3 Equations

To develop the plant model and the controller ofthe multi-mode hybrid system, we need to useequations that describe the operations of thesystem. To provide ease of use, the equationsare simplified versions of the more complexones. In the case of an EVT mode, only twodifferential equations are required to representthe powertrain system, since there are only twoindependent state variables engine speed

(e) and vehicle velocity (V). With mathematicalmanipulation, the dynamic equations can beobtained as follows by using four factors, ,

, r , and , that are specific to mode

jp

jq j js j :

uX = & (1)

where

,][,][ 12T

LMCMCe

T

e FTTTuVX ==

,21

2

2

2

12

121

2

2

2

++++

+++

=

t

w

MCjMCjMCjjMCjj

MCjjMCjjMCjMCje

R

JJsJqMJsrJqp

JsrJqpJrJpJ

= 10

01

jj

jj

sq

rp

where is the inertia of the ICE, and

are the inertia of the electric machine, is the

wheel inertia, is the tire radius,

eJ 2MCJ

J

1MCJ

w

tR M is the

vehicle mass, and is the road load.LF T and

denote the torque and speed of each

component. The parameters are defined inAppendix Table A-1, as well as in AppendixTable A-2. From Eq. (1), the dynamics of theEVT hybrid powertrain can be represented in a

state-space equation as follows:

+=

+=

uDXCY

uBXAX& (2)

where

,,0,][ 112 === BAVY TMCMCe

0,10

01=

= D

sq

rpC

T

jj

jj

In the case of a fixed gear mode, the speed andtorque relationships are similar to those of aconventional multispeed transmission. They aregiven as follows:

1122 MC

i

MCMC

i

MCe

i

eo TkTkTkT ++= (3)

=

=

=

o

i

MCMC

o

i

MCMC

o

i

ee

k

k

k

11

22

(4)

whereooT / is the output torque/speed of the

transmission, and is the multiplication ratio foreach component, as given in AppendixTable A-3.

i

k

1.2 PHEV powertrain system

1.2.1 GM Volt powertrain system

The series engine configuration is oftenconsidered to be closer to a pure electric vehiclewhen compared to a parallel configuration. Inthis case, the vehicle is propelled solely from theelectrical energy. Engine speed is completelydecoupled from the wheel axles, and its

operation is independent of vehicle operations.As a result, the engine can be operatedconsistently in a very high efficiency area.

Figure 5: Schematic of the GM Voltec

GM Volt system employs a planetary gear as itspower-split device. The GM Volt is an output

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split-type vehicle, with engine power split at theoutput. Unlike the plug-in series, two clutchesand one brake are applied in the powertrainsystem, which allows multiple driving modes for

the vehicle. The structure of GM Volt is shown inFigure 5. The engine and MC2 are connectedthrough clutch CL1, and MC2 is connected tothe ring gear through clutch CL2. The ring gearis also connected to brake, BL1. MC1 isconnected to the sun gear, and the carrier isconnected to the vehicles final reduction gear.

Table 1: System operation schedule of GM Volt [10]

SystemOperationScheduleMode BK1 CL1 CL2

EV1 On Off Off

EV2 Off Off On

Series On On Off

Powersplit Off On On

By setting the engagement and disengagementof the clutches and brake as shown in Table 1,the GM Volt is driven in four modes: the EV1,EV2, series, and power-split modes. The EV1and EV2 modes are called charge-depleting(CD) modes, while the series and power-splitmodes are called charge-sustaining (CS)

modes [9]. In the CD mode, the battery is theonly power source, and the vehicle operationdepends on the energy from the battery. In theCS mode, the engine serves as the main powersource while sustaining the battery SOC.

In Figure 6, in low SR range, the systemefficiency is low because the electrical machineshave relatively low efficiency. This low systemefficiency can be avoided by propelling thevehicle by using the series mode instead of thesplit mode.

0 0.5 1 1.5 2 2.5 3 3.5 4-1.5

-1

-0.5

0

0.5

1

PowerRatio

The Ratio P-elect to P-eng (@W-eng=1500rpm, T-eng=100Nm)

EVT1 (Outpu t Split)

0 0.5 1 1.5 2 2.5 3 3.5 40.5

0.6

0.7

0.8

0.9

1


EFf.

Efficienc y (@W-eng=1500rpm, T-eng=100Nm)

EVT1 (Output Split)

Figure 6: Power characteristics of the GM Voltec

1.2.2 Equations

The speed relationship of the powertraincomponents and the vehicle dynamic modelswas obtained by using the following equations:

t

d

MCMCoutR

NVba =+= 21 (5)

where is the final reduction gear ratio.dN

The dynamic models of the transmission in theGM Volt for the EV1 and EV2 modes werederived as follows:

outMCMCout Ja

Ta

T &= 12111 (6)

212121

11MCMCoutMCMCout J

a

bJ

aT

aT && += (7)

In the series mode, the dynamic equation ofMC1 was the same as that shown in equation(6), and the dynamic equation of the engine andMC2 was obtained as follows:

22 )( MCeeMCe TTJJ +=+ & (8)

In the power-split mode, the dynamic equation ofMC1 was the same as that shown in equation(7), and the dynamic equation was derived as:

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12

1212

2

2 )(

MCMCe

outMCeMCMCe

Ta

bTT

Ja

bJ

a

bJJ

+=

++ && (9)

2 COMPONENT SIZING

2.1 Modeling the vehicle in Autonomie

Autonomie is a forward-looking modeling toolthat can simulate a broad range of powertrainconfigurations [11]. The driver model computesthe torque demand needed to meet the vehiclespeed trace. The torque demand is interpretedby a high-level controller that computes thecomponents torque demands while ensuringthat the system operates within its constraints.Detailed transmission models were developed

by using SimDriveline, including specific lossesfor gear spin and hydraulic oil [12], as shown inFigure 7. Such a level of detail is necessary toproperly assess the trade-off betweencomplexity and efficiency.

Figure 7: Transmission model for the AHS2 FWD

2.2 Mode selection during acceleration

The powertrain must be operated in such a way

that the output shaft can transmit the maximumtorque from the powertrain to the final drive. Thiscan be regarded as an optimization problem,and it is solved for the corresponding vehiclespeed. An off-line computation was used togenerate the maximum powertrain torque thatcould be used in Simulink, indexed by gearboxoutput speed and battery power. To computethat look-up table, a brute-force algorithm is

used, possibly several hundreds of times, alongan output speed grid ranging from 0 to itsmaximum.

The maximum powertrain torque curves areobtained along the scheme and displayed inFigure 8. In acceleration simulations, the modethat allows the maximum output torque isselected. Figure 8 shows the tractive capabilityof the system with fixed gears, on the basis ofthe optimum selection of engine speed, toprovide the highest level of tractive output. Fromthis graph, in Figure 8a, it can be seen that FG1increases the vehicle tractive capabilitysignificantly in the range of 1045 mph. The useof FG1 over a large range of vehicle speedseliminates the need to use the motors forprocessing engine power, thereby freeing upcapacity to boost acceleration.

0 20 40 60 80 100 120 140 1600

200

400

600

800

1000Max Torqu e (AHS2 FWD)

Vehicle Speed, mph

GB

TorqueOut,Nm

EVT1

EVT2

FG1

FG2

FG3

FG4

AHS2 FWD

Figure 8a: Max torque during acceleration Two-mode EVT

with FGs (AHS2 FWD)

0 20 40 60 80 100 120 140 1600

200

400

600

800

1000

1200

Vehicle Speed, mph

GB

TorqueOut,Nm

Max Torque (GM Voltec)

EV1

EV2

Series

Split

GM Voltec

Figure 8b: Max torque during acceleration GM Voltec

2.3 Sizing process

To quickly size the component models of thepowertrain, an automated sizing process wasused [13]. The sizing process defines the peak

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mechanical power of the electric machine asbeing equal to the peak power needed to followthe acceleration constraints. The peak dischargepower of the battery is then defined as the

electrical power that the electric machinerequires to produce its peak mechanical power.The sizing process then calculates the peakpower of the engine by using the power of thedrivetrain required to achieve the gradeabilityrequirement of the vehicle.

As detailed previously, the componentscharacteristics determine the constraints. Themain vehicle characteristics used in this studyare summarized in Table 2. In particular, theratios of planetary gear sets are derived frompatents and references. The 060-mphperformance requirement for the vehicle issatisfied implicitly by the constraints on the peakmotor power and the peak engine power. Thepower required by the motor for the vehicle tofollow the UDDS cycle added to the powerrequired by the engine for the vehicle to drive upa 13% grade at 65 mph exceeds the power thatthe vehicle needs to go from 0 to 60 mph in7.8 s.

Table 2: Specifications of the small-size SUV for HEV

Body andchassis

mass

1180 kgFrontal

area2.64 m

2

Dragcoefficient

0.37Wheelradius

0.3423m

Final driveratio

Single mode: 4.11Multi mode: 3.02

PGs ratio(Zr/Zs)

Single mode: 2.6Single mode with RG: 2.4, 2.0

AHS2 FWD: 2.36, 2.24AHS2 RWD: 1.93, 1.97, 2.6

To meet the all-electric range (AER)requirements for a PHEV, the battery power issized to follow the Urban Driving DynamometerSchedule (UDDS) driving cycle while in all-

electric mode. We also ensure that the vehiclecan capture the entire energy from regenerativebraking during decelerations on the UDDS.Finally, battery energy is sized to achieve therequired AER of the vehicle. The AER is definedas the distance the vehicle can travel on theUDDS until the first engine start. Note that aspecific control algorithm is used to simulate the

AER. This algorithm forces the engine to remain

off throughout the cycle, regardless of the torquerequest from the driver.

The selected vehicle class for PHEV represents

a midsize sedan. The main characteristics aredefined in Table 3.

Table 3: Specifications of the mid-size sedan for PHEV

Body andchassismass

950.2 kgFrontal

area2.22 m

2

Drag

coefficient0.275

Wheel

radius0.317 m

Final driveratio

Series PHEV: 4.44GM Voltec: 3.02

PGs ratio(Zr/Zs)

Series PHEV (Manual 2spd): 1.86, 1GM Voltec: 2.24

The components of the different vehicles forPHEV were sized to meet the following vehicleperformance standards:

060 mph < 9 s Gradeability of 6% at 65 mph Maximum speed > 100 mph

2.4 Sizing results

2.4.1 Single-mode EVT vs. multi-mode EVT

The sizing results for HEV are summarized in

Figure 9 and Appendix Table A-4. Forcomparison, two single-mode EVT hybridsystems and two multi-mode EVT hybridsystems are investigated, and the results arepresented. As noted in the introduction, themulti-mode system results in significantimprovements in dynamic performance atreduced capacities of the electro-mechanicalpower. As can be seen in Figure 9, thecapacities saved by the multi-mode systemrange from 31.7% to 64.3%, relative to thesingle-mode system. The main contributor is theaddition of the EVT mode, which causes the

difference between the single-mode and multi-mode systems.

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Figure 9: Component sizing results

2.4.2 Series PHEV vs. GM VOLTEC

The main characteristics of the sized vehiclesare described in Table 4. Note that enginepower is similar for the series and GM Voltec.The sizing result shows that the GM Voltecpowertrain requires lower component power tomeet the VTS than does a series systembecause of the use of an additional drivingmode. Because the electric machine is the onlycomponent used in the series to propel thevehicle, its power is also higher than that in theGM Voltec configuration.

Table 4: Component size 400-mi AER case

Parameter Plug-inSeries

GM Voltec

Engine Power (kW) 77.1 69.9

MC1 Power (kW) 129.4 125.8

MC2/Generator (kW) 74.8 69.9

Battery Capacity (kWh) 17.6 16.8

Vehicle Mass (kg) 1900 1865

3 CONTROL STRATEGY

3.1 Mode shift strategy

0 20 40 60 80 100 120 140 1600

100

200

300

400

500

600

700

800

900

1000Mode Shift Map

Vehicle Speed, mph

GB

TorqueOut,Nm

EVT1

EVT2

FG1FG2

FG3

FG4

Figure 10a: Mode shift maps for AHS2 FWD

0 20 40 60 80 100 120 140 160

100

200

300

400

500Mode Shift Map

Vehicle Speed, mph

GB

TorqueOut,Nm

EVT1

EVT2

FG1

FG2

FG3

FG4

Figure 10b: Mode shift maps for AHS2 FWD

To evaluate the benefits of several multi-mode

powertrain configurations from the standpoint offuel consumption, a control strategy is requiredfirst. One of the major challenges of the multi-mode control strategy is to properly select theoperating mode. To develop a mode shiftstrategy, a brute-force algorithm is used. Thealgorithm generates an optimal input speed andtorque for each EVT mode, indexed by gearboxoutput speed, battery power, and gearboxoutput torque. By knowing these parameters, wecan compute the fuel power and compare it withthat in the other EVT modes [14, 15].Meanwhile, a candidate input set for FGs is

obtained in the conventional way. Figure 10adepicts the optimal mode selections for variousoutput load conditions. If we convert theseresults into a new map by using vehicle speedand engine speed indexes, the mode selectionrule is defined on the basis of the speed ratio.The reason for this is because the selectedoptimal mode could be divided according to thespeed ratio, which is defined as the ratio of thetarget engine speed to the output speed. Whenin propelling mode, the target engine speed hasbeen previously computed by the simplifiedoptimal system operating line for driver powerdemand. In Figure 10b, the FG2 mode appearsin the transition area between the EVT1 andEVT2 modes. The FG2 mode is inherent in themodes needed for the synchronous shiftbetween the two EVT modes. The FG4 modesupplements the EVT2 mode. The logic wasvalidated for both single-mode and two-modehybrid systems by using vehicle test data [16].Similar algorithms were implemented for the GMVoltec configurations.

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3.2 Energy management strategy forPHEV

According to sizing results, the average all-

electric range of the PHEV is almost 40 mi. Toachieve this electric driving range, an energymanagement strategy must be developed.

0 10 20 30 40 500.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Distance

SOC

Figure 11: Control strategy SOC behavior

The developed energy management strategy isshown in Figure 11. When the battery is beingcharged, the upper SOC threshold is set at 0.9because of the efficiency problem. When theinitial battery SOC is 0.9, the vehicle is driven inthe CD mode at engine start. In the CD mode,the GM Voltec is driven in the EV1 or EV2mode, depending on the driving conditions. Thebattery is the only power source in the CD

mode. When the battery SOC decreases andreaches 0.25, the vehicle operation modeswitches to the CS mode. The engine nowworks as the power source. The engine suppliesthe demanded vehicle power and maintains thebattery SOC at around 0.25. When the batterySOC reaches 0.3, the driving mode of thevehicle is reverted back to the CD mode. Byusing this algorithm, as much electric energy ascan be consumed is consumed to obtain betterfuel efficiency.

For the GM Voltec configuration, driving mode is

an integral part of the energy managementstrategy. For the CD mode, the transmissionefficiency map of EV1 and EV2 mode can becalculated by considering the motor efficiencyand transmission loss. On the basis of theefficiency map, the shift map can be constructedfor the CD mode. As a result, the EV1 orEV2 mode can be selected by the battery SOC,vehicle velocity, and drive demand torque.

4 SIMULATION RESULTS

4.1 Comparative analysis of HEVs

Figure 12: Fuel economy summary

With the transmission models and controllerdescribed in the previous section, the vehiclewas simulated on standard drive cycles: theurban dynamometer driving schedule (UDDS);the highway fuel economy test (HWFET) cycle;the new European driving cycle (NEDC); a moreaggressive urban cycle with some short highwaycycles (LA92); and a highly aggressive cycle,predominantly at high speed (US06). The fueleconomy results are reported in Figure 12. Forurban driving, the single-mode hybrid systemhas relatively high fuel economy compared withthe multi-mode hybrid system. On the other

hand, the trend shown by the different cyclesindicates that the higher the speed of the drivingpattern, the greater the advantage of the multi-mode hybrid system. As a consequence, the

AHS2 FWD provides a greater advantage interms of fuel consumption for the vehicleapplication considered on the small-size SUVspecification.

0 10 20 30 40 50 600

50

100

150

Vehicle Speed, mph

EngineSpeed,

rad/s

HWFET - Operating points (HEV and propelling)

M.P.

MP

Single-mode

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0 10 20 30 40 50 600

50

100

150

200

Vehicle Speed, mph

EngineSpeed,rad/s

HWFET - Operating points (HEV and propelling)

M.P.1

M.P.2

FG1

FG2

FG3

FG4

EVT1

EVT2

FG3

FG4

FG2

(MP1)FG3

FG4

(MP2)AHS2 FWD

Figure 13: Operating points for HWFET

Figure 13 reports the operating points of thepowertrain for urban and highway driving. It isremarkable how the vehicles operate in theregions of higher efficiency to reduce fuelconsumption. As shown in Figure 13, the single-mode hybrid system has relatively lower systemefficiency in the primary operating region, forhighway driving. This occurs because theelectro-mechanical power increases sharply asthe transmission reaches higher overdrive. Theoperating points of the multi-mode hybrid systemare between the mechanical points to achievethe high EVT efficiency. For the multi-modehybrid system, highway cycles favor the use offixed gears.

Table 5 shows the efficiencies of all three powersources and powertrains. The transmissionefficiency refers only to the all-mechanical path.The single-mode hybrid system has the highesttransmission efficiency, since there is no needfor more planetary gears or clutches. For themulti-mode system with the fixed gear, it isinteresting to note that the efficiencies of the ICEare not particularly high. This effect is due to thefixed gear, which improves the highway fueleconomy by avoiding the lower systemefficiency region to maintain holding torque atthe second mechanical point.

Table 5: Component average efficiencies (%)

UDDS S1 S2 M1 M2

Engine 33.3 33.4 30.9 31.1

MC1 87.0 87.5 86.5 86.7MC2 86.2 86.1 86.0 86.0

TM 96.1 96.4 90.5 89.5

PT 33.5 33.6 31.6 30.9

HWFET S1 S2 M1 M2

Engine 33.8 33.7 31.6 30.6

MC1 91.4 89.9 86.6 87.2

MC2 86.5 86.5 86.6 86.6

TM 94.7 93.4 89.0 88.9

PT 25.9 26.0 26.7 26.2

(S1: single mode; S2: single mode with RG; M1: AHS2 FWD;

M2: AHS2 RWD; TM: transmission; PT: powertrain)

4.2 Comparative analysis of PHEVs

The series is mainly driven in the EV and HEVmodes, but the GM Voltec has four drivingmodes. In the CD mode, GM Voltec has the EV1and EV2 modes to drive the vehicle at low andhigh speed. In the GM Voltec, only MC1 is usedto propel the vehicle, and MC2 does not work inthe EV1 mode. Furthermore, MC2 and MC1propel the vehicle together in the EV2 mode. InFigure 14a, it can be seen that the MC1 torqueshows a similar performance, even if the vehicleis driven in a different driving mode. This shows

that the MC1 torque of the GM Voltec isdetermined only by the demanded wheel torqueand is operated regardless of the driving mode,which implies that MC1 should have a powercapacity that is large enough to drive the vehiclewhile satisfying the demanded power. Thisexplains why the capacity of MC1 in the GMVoltec is 125 kW, which is similar to the capacityof MC1 in the plug-in series. In the plug-inseries, as shown in Figure 14a, in the EV mode,only MC1 is used to propel the vehicle, and MC2does not work.

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P Energies nouvelles - RHEVE 2011


Figure 14a: Comparison of component torque Initial SOC =

80%, (top = series, bottom = GM Volt)

160 180 200 220 240 260 280 300 320 340-300

-200

-100

0

100

200

Time, sec

Torque,Nm

Component Torque

Veh Spd, kph

Eng Trq, Nm

Gen Trq, Nm

Mot Trq, Nm

160 180 200 220 240 260 280 300 320 340-200

-150

-100

-50

0

50

100

150

200

Time, sec

Torque,Nm

Component Torque

Veh Spd, kph

Eng Trq, Nm

Mot2 Trq, Nm

Mot1 Trq, Nm

GM Mode, x10

Figure 14b: Comparison of component torque Initial SOC =

30%, (top = series, bottom = GM Volt)

In the CS mode, GM Voltec has the series andpower-split modes at low and high vehiclespeeds. When the GM Volt is driven in theseries mode, MC2 works as a generator and

supplies the electric power required for MC2 topropel the vehicle. In the power-split mode, evenif MC2 can be used for optimal engine operationfor both PHEV, the role of MC2 in the GM Voltecis different from that in the plug-in series. In theGM Voltec, MC2 assists the engine to producethe demanded torque at the ring rear andpropels the vehicle together with MC1. In theplug-in series, MC2 works as a generator togenerate electric power, while MC1 is only usedto propel the vehicle.

The J1711 procedure is used to calculate thefuel economy of PHEVs. Table 6 shows theelectrical consumption and fuel economy resultsfor each powertrain configuration. TheGM Voltec provides the more efficient electricalconsumption in CD mode. The higher efficiencyof the power transfer from engine to wheelsbenefits the plug-in series because of the use oftwo electric machines. The GM Voltec also hasthe better fuel economy in CD mode. The seriesconfiguration suffers from dual powerconversion from mechanical (engine) toelectrical (generator) and back to mechanical(electric machine). The GM Voltec configurationperforms better in highway driving than in urban

driving because of the power-split operation.The power split allows the engine to be operatedclose to its most efficient point without theengine sending all of its power through bothelectric machines. High engine efficiency andthe ability to send mechanical power directly tothe wheel allow this configuration to providebetter CS fuel economy.

Table 6: PHEV fuel economy results

Electrical Consumption &

Fuel Economy

Plug-in

Series

GM

Voltec

CD Wh/mi 265.0 251.7

CS MPG 44.5 46.8

Wh/mi 195.0 185.9UDDS

CD+CSMPG 111.3 117.0

CD Wh/mi 250.7 240.3

CS MPG 44.5 49.4

Wh/mi 197.2 193.1HWFET

CD+CSMPG 120.1 133.6

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5 CONCLUSION

This paper examines the several powertrainconfigurations, including single-mode EVT,multi-mode EVT, series and GM Voltec, and

vehicle-level controls developed in Autonomie.Detailed transmission models were implementedto allow a fair assessment of the benefitsassociated with these different powertrainarchitectures by comparing component sizes,system efficiency, and fuel consumption overseveral drive cycles.

First, single-mode EVT and multi-mode EVTwere sized to represent a small-size SUV HEVapplication, following the same vehicle technicalspecifications, such as acceleration andgradeability. The results predicted that the multi-

mode system would have better accelerationthan a single-mode system, since the additionalEVT modes significantly lower the requirementfor the electric machine power. In addition,simulations were performed on a small-sizeSUV to characterize the impact on componentoperating conditions and fuel consumption forseveral driving cycles. It was determined that themulti-mode system has an advantage in terms offuel economy during the high-speed cyclebecause of relatively higher system efficiency.

A comparative study between the PHEV

GM Voltec and series powertrains was alsoperformed. The sizing results show that theGM Voltec powertrain requires lower componentpower to meet the VTS than a series systembecause of the many component efficienciesbetween the engine and the wheel. In addition,simulations were performed on a midsizevehicle to characterize the impact on componentoperating conditions and fuel consumption onurban and highway driving. The series mode inthe GM Voltec implies that a relatively largerMC2 is required for the vehicles powerrequirement. In the power-split mode, MC2 isused to assist the engine in the GM Voltec, while

in the plug-in series, the MC2 works as agenerator. It was determined that the GM Voltecpowertrain achieved lower fuel consumptionduring all driving condition modes, compared toa pure series configuration.

6 ABBREVIATIONS

AHS advanced hybrid systemBK brakeCL clutch

EV electric vehicleEVT electro-mechanical infinitely

variable transmissionFG fixed gearFWD front-wheel driveHEV hybrid electric vehicleHWFET highway fuel economy testICE internal combustion engineMC electric machine/motorMP mechanical pointNEDC new European drive cyclePG planetary gearPHEV plug-in hybrid electric vehicle

PT powertrainRG reduction gearRWD rear-wheel driveSOC state-of-chargeSR speed ratioSUV sport utility vehicleTM transmissionUDDS urban dynamometer driving

schedule

REFERENCES

1. M. Schulz, Circulating Mechanical Power in a

Power-split Hybrid Electric VehicleTransmission, Proc. Instn. Mech. Engrs., Part D:J. Automobile Engineering 218, 2004, pp. 14191425.

2. M. Duoba, H. Lohse-Busch, R. Carlson,T. Bohn, and S. Gurski, Analysis of Power-splitHEV Control Strategies Using Data from SeveralVehicles, SAE paper No. 2007-01-0291, 2007.

3. A. Holmes and M. Schmit, Hybrid ElectricPowertrain Including a Two-mode ElectricallyTransmission, US Patent, US006478705, 2002.

4. A. Holmes, M. Schmit, and D. Klemen,Electrically Variable Transmission with SelectiveFixed Ratio Operation, US Patent,US007220203, 2007.

5. M. Schmit and D. Klemen, Two-modeCompound-split, Hybrid Electro-mechanicalTransmission having Four Fixed Ratios,US Patent, US006953409, 2005.

8/13/2019 26_Kim_RHEVE2011

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6. A. Holmes, M. Schmit, and B. Conlon, Three-mode Electrically Variable Transmission,US Patent, US007645206, 2010.

7. T. Grewe and B. Conlon, A. Holmes, Definingthe General Motors 2-Mode HybridTransmission, SAE 2007-01-0273, 2007.

8. L. Situ, Electric Vehicle Development: Thepast present & Future, 3rd InternationalConference on Power Electronics Systems and

Applications, K210509135, 2009

9. M. Miller, A. Holmes, B. Conlon, andP. Savagian, The GM Voltec 4ET50 Multi-ModeElectric Transaxle, SAE 2011-01-0887

10. http://www.chevrolet.com/volt/

11. R. Vijayagopal, N. Shidore, S. Halbach,L. Michaels, and A. Rousseau, AutomatedModel based Design Process to Evaluate

Advanced Component Technologies, SAE 2010-0-0936, 2010.

12. H. Kitabayashi, C. Li, and H. Hiraki, Analysisof the Various Factors Affecting Drag Torque inMultiple-Plate Wet Clutches, SAE 2003-01-1973, 2003.

13. P. Sharer, R. Rousseau, S. Pagerit, andP. Nelson, Midsize and SUV Vehicle SimulationResults for Plug-in Component Requirements,SAE 2007-01-0295, 2007.

14. K. Ahn and S. Cha, Developing Mode ShiftStrategies for a Two-mode Hybrid Powertrainwith Fixed Gears, SAE 2008-01-0307, 2008.

15. D. Karbowski, J. Kwon, N. Kim, andA. Rousseau, Instantaneously OptimizedController for a Multi-mode HEV, SAE 2010-01-0816, 2010.

16. N. Kim, R. Carlson, F. Jehlik, andA. Rousseau, Tahoe HEV Model Developmentin PSAT, SAE 2009-01-1307, 2009.

ACKNOWLEDGMENTS

This work was supported by DOEs VehicleTechnology Office under the direction of David

Anderson and Lee Slezak. The submittedmanuscript has been created by UChicago

Argonne, LLC, Operator of Argonne NationalLaboratory (Argonne). Argonne, a U.S.Department of Energy Office of Sciencelaboratory, is operated underContract No. DE-AC02-06CH11357. TheU.S. Government retains for itself, and othersacting on its behalf, a paid-up nonexclusive,irrevocable worldwide license in said article toreproduce, prepare derivative works, distributecopies to the public, and perform publicly anddisplay publicly, by or on behalf of the

Government.

APPENDIX

Table A-1: Definitions of ratio variables

Config-uration

EVT jp jq

jr

js

Singlemode

- 1+a az 0 z

Singlemodew/RG

- 1+a az 0 bz

1 a bcz 0 cz AHS2FWD

2bd

a

1 bd

bcz

1

bd

ad

1 bd

cz

1

1bc

a

1 bc

bdez

1

0 ez

AHS2RWD

2 a bz d

ac d

zbc )1(

whereradiusWheel

ratiodriveFinalz =

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Table A-2: Definitions of simplified factors Table A-4: Component sizing results

Config-

urationa b c d e f

Singlemode 1

R - - - - -

Singlemodew/RG

1R 2R - - - -

AHS2FWD 1

R 11R 12 +R 2R - -

AHS2RWD 1

R 11+R

Config-

uration

ICE

(kW)

MC2

(kW)

MC1

(kW)

Battery

(Cells)

Mass

(kg)

Singlemode

131.5 91.7 91.2 180 1953

Singlemodew/RG

131.1 80.9 88.2 173 1940

AHS2FWD

124.8 58.1 47.2 170 1875

AHS2RWD

125.3 62.6 52.2 171 1883

31 R+ 3R

2

2

1 R

R

+ 21

1

R+

GMVoltec

- - - -11 R

1

+ 11 R

R

+1

where , , and are the planetary gear

ratios of PG1, PG2, and PG3.1R 2R 3R

ik 2

ik 1

Table A-3: Fixed gear ratios

Configuration FGsi

ek MC MC

1 c c c

2a

bc 0 c

3 1 1 1AHS2 FWD

4ad

c d

c 0

1 e e e

2ac

ed +bd 1 c

ed1e

3 1 1 1AHS2 RWD

4ac

bc 1

c

10

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