ieee-potentials-hev-2004

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The design of the propulsion systems for

automobiles and other transportation

products is going through a major evolu-

tion...perhaps one of the biggest changes

since the early part of the 1900s. An

exciting feature of this change is that it

centers on electrifying the powertrain of

the automobile using technology near

and dear to electrical engineers.

Hybrid-electric is a term used more

and more frequently in automotive con-versations. A decade ago you could not

buy a hybrid electric vehicle (HEV).

About the only examples were in the

labs and shops of university project

teams getting ready for design competi-

tions. Today several major companies

have vehicles on the market, and there

are over 200,000 satisfied

customers driving them.

Most of them are in North America.

Whats more, students have played a

significant role in developing and bring-

ing HEV to the forefront.

Why the change?The major motivating factors for

using electric propulsion and the other

hybrid-electric features is concern for

our energy supplies and the environ-

ment. The automobile and other modes

of transportation consume two-thirds of

the petroleum used in the US. As the

economy of China and other develop-

ing countries mature, the worlds

automotive population is projected

to be five times larger by mid-century.

But t petroleum is a finite resource and

gasoline will probably become a veryexpensive energy source in the future.

Also, the consumption of hydrocar-

bon fuels releases carbon dioxide into

the atmosphere. Carbon dioxide is the

major greenhouse gas (GHG) raising

concern about global warming.

California is now working on a man-

date to regulate the GHG emissions

from automobiles. Adopting automotive

propulsion technologies that improve

the efficiency of energy usage and

reduce transportations impact on global

warming can have a significant impact

on the future quality of life.Several initiatives have accelerated

the research and commercialization of

hybrid-electric and other advanced

automotive propulsion technologies.

Californias air resource board issued a

mandate in 1990 challenging auto man-

ufacturers to sell a required percentage

of zero emissions vehicles (ZEV) in the

Los Angeles basin. This challenge

resulted in the development and public

offering of a few thousand capable elec-

tric vehicles (EV) like General Motors

EV-1, and Honda and Toyota EVs.

But the mandate has been amended

over the years. Also, most EVs have been

pulled back from their leases and none

are available for purchase today. The lim-

ited range due to battery energy storage

capacity is often cited as the Achilles

heel of the battery-electric automobile.

However, some manufacturers now offergasoline fueled partial zero emission

vehicles (PZEV) that emit no more regu-

lated pollutants than an electrical gener-

ating plant would in providing the elec-

tricity to recharge an EVs battery.

The electric drive technology devel-

oped in response to the California man-

date has matured and become an

enabling factor in the hybrid-electric

vehicle (HEV) evolution. The federal

government decided to collaborate on

research with the big three auto compa-

nies in the 1990s. Called the Partnership

for Next Generation Vehicles (PNGV),

one of its goals is to increase the fueleconomy of the family sedan by a fac-

tor of three, or to about 80 miles per

gallon (MPG). Reduced weight, reduced

aerodynamic drag and HEV propulsion

are the means of achieving this goal.

In this decade, the focus of this col-

laborative research has shifted to fuel

cells and hydrogen fuel with the current

FreedomCAR initiative. The viability of

the hybrid-electric concept and electric

propulsion as major ways to improve

energy efficiency and reduce the auto-

mobiles environmental effects has been

demonstrated through this initiative.

Besides the energy consumption and

environmental impact advantages of

HEVs, they can be performance

enhancers. The buying public typically

wants high peak power available in the

cars they are looking at. The sum of the

powers available from both the internalcombustion engine (ICE) and the elec-

tric motor of a HEV permit larger peak

power. Also, the efficiency and environ-

mental benefits are still present.

Lets not overlook the fact that we

engineers enjoy playing with and

implementing new technologies that

can help society. Electronics and com-

puterized engines and drive train man-

agement have made monumental

impacts on cleaning up the ICE and

making the conventional car much

more reliable and drivable. The devel-

opments of EVs and HEVs provide atechnology bridge to the electric

propulsion technologies needed for the

fuel cell cars of the future.

The marketplaceTwo major automotive manufacturers

have several years experience with

HEVs in the marketplace, and others

are introducing products. Toyota was

the first to offer a HEV for sale. They

placed their Prius model on the market

in Japan in late 1997. Honda was the

first to market a HEV in the US, intro-

ducing the Insight in late 1999. Toyotaintroduced a slightly updated

version of the Prius in the

North America and Europe markets in

late 2000. Honda introduced a hybrid

version of their Civic sedan in 2003.

Toyota introduced an improved Prius

for the 2004 model year. Ford intro-

duced a HEV version of their Escape

sport utility vehicle (SUV) for the 2005

model year.

Through its Allison Transmissions

subsidiary, General Motors has devel-

oped a hybrid-electric transmission

product that is the heart of a diesel-elec-tric hybrid city bus. The transmission

significantly reduces pollution and ener-

gy consumption for the start and stop

driving prevalent in urban mass trans-

portation. The technology is scaleable

and will be showing up in their pick-up

and SUV products in the future.

Europe has been reluctant to adopt

HEV technology due to its added cost,

relying instead on the improved tech-

40278-6648/04/$20.00 2004 IEEE IEEE POTENTIALS

Robert D. Strattan

future

automobile

Theelectrifying

ofthe

hybrid

DIGITALVISION/MKCCOMPOSITE:MKC


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nology diesel engine. Nearly half of all

passenger cars sold in Europe are fuel-

efficient diesels. Diesels popularity is

increasing in the United Kingdom, also.

Hybrid-electric technologyHybrid electric vehicles can have

many configurations as with any engi-

neering design exercise. The principal

features of a HEV are:

1) Multiple power sources, usuallytwo; an internal combustion engine

(ICE) and an electric motor.

2) A means to combine and select

the power produced by each of the

sources.

3) An energy storage system (ESS),

usually a battery, but ultra-capacitors,

flywheels and hydraulic accumulators

are other possibilities.

4) An intelligent control system to

transparently manage the power flow.

A simple way to think of a HEV is to

imagine a battery-electric car that takes

advantage of the energy efficient start-

stop characteristics of an EV. But it car-

ries its own ICE driven generator to

recharge the batteries. This recharging

ability overcomes the range limitations

of the battery. This configuration is

referred to as a Series HEV, since the

power flow is serial from the ICE

through the electric generator andmotor to the wheels.

An alternate configuration is the

Parallel HEV. Here the electric motor

and ICE both have a direct power flow

path to the wheels. The Parallel HEVs

advantage is that each power source

can be smaller, with the overall power

to the wheels being the combined total.

The electric motor for the Series HEV

must be large enough to handle the

peak power demand to the wheels

alone. The series configuration is sim-

pler to visualize and build, but does not

have the ultimate efficiency advantages

of the parallel configuration. The cou-

pling mechanism for the parallel config-

uration may be complex and difficult to

build, or it may be quite simple but

then it may not be as effective in

achieving the HEV goals.

All of the HEV passenger cars in themarketplace today use variations of the

parallel configuration. The Honda prod-

ucts use an integrated motor assist

(IMA) configuration: an electric motor-

generator is connected directly to the

ICE crankshaft. The powerplant is then

coupled to the wheels through a con-

ventional transmission arrangement,

either a clutch and manual transmission

or a continuously variable automatic

transmission (CVT).

While this system is simple, it does

not provide a means of moving the car

in an electric-only mode. The electric

motor-generator however gives a power

boost to the ICE, starts the ICE,

recharges the battery and converts brak-

ing action into electrical energy. This

energy can be stored in the battery dur-

ing the regenerative braking mode.

The Toyota and Ford products use a

version of the parallel configuration,called power-split, to couple the power

sources to the wheels. The setup also

provides an electrically implemented

and controlled continuously variable

automatic transmission (ECVT) for cou-

pling the ICE to the drive wheels. The

ICE, two electric motor-generators, and

the wheels are coupled using a plane-

tary gear set as the power splitter. A

planetary gear set is a 3-port mechani-

cal coupling device. One of the electric

motors is connected to the output port

along with the wheels, and provides an

electric only propulsion mode as wellas the regenerative braking mode. The

ICE is connected to one of the input

ports, and the other electric motor is

connected to the other port.

By controlling the speed and

torqueand thus the power flow of

each of the motorsany mechanical

torque advantage or speed ratio

between the ICE and wheels is possi-

ble. The result is an ECVT that allows

for the ICE being off during electric

only propulsion, or feeding power to

the wheels through any electrically reg-

ulated transmission ratio without usingany of the clutches or belts required for

a conventional CVT. One of the electric

motors also serves as the ICE starter

motor for automatic shut-off and start.

Electrical power is transferred between

the motors and the battery as needed

by the power electronics controller.

A HEV saves fuel and reduces emis-

sions through three basic processes:

1) Each power source is used under

its most functional operating conditions.

The ICE is most efficient and cleanest

when used at a constant speed and

moderate to full load power conditionssuch as highway cruising, hill climbing

and accelerating to highway speeds.

The electric motor is superior to the ICE

for: launching from a start, frequent

start-stop cycles, creeping through city

traffic, coasting and low speed driving

and braking.

2) Automatic shut-off of the ICE

when it is not needed. Examples are

stopped at a traffic light, in line for the

AUGUST/SEPTEMBER 2004 5

Fig. 1 Series HEV Layout

Series HEV Layout(or Fuel Cell Hybrid Vehicle)

ICE Gen.

Tran.Elect.Motor

ESS(Battery)

Fig. 2 Parallel HEV Layout

Parallel HEV Layout

ESS(Battery)

M/G

ICE Coupling

Tran.

GM Hy-wire & AUTOmony FCHV Concepts

Hy-Wire Interior/Controls

AUTOnomy Skateboard Fuel Cell Chassis


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drive-up window, creeping in slow traf-fic or cruising for a mall parking spot.

3) Regenerative braking where thekinetic energy of the vehicle is capturedand stored in the ESS for reuse laterrather than being wasted as heat by the

friction brakes.The HEV improved fuel efficiency

advantage is most pronounced duringurban driving conditions. There is noHEV advantage during highway cruisingsince the ICE is doing all of the workand is at its best during this condition.In fact, there is actually a slight disad-vantage due to the added weight of theadditional electrical components. Butthis downside is offset by the improvedefficiency of a smaller ICE. This smaller

size is possible thanks to the electricalpower boosts available for peak power

demand conditions. The ICEand thetransmission required to adapt the ICEstorque-speed characteristics to start-stop-creep urban drivingis notorious-ly inefficient during city driving condi-tions. Only about an eighth of the ener-gy content of the gasoline fuel becomesuseful propulsion energy in a conven-tional automobile.

The strength of the hybridization isanother design variable when classifying

HEVs. The IMA implementation of theHonda products is considered a mild

HEV design approach. The power ratingof the electric motor relative to the ICEis small (13.4/85 hp-electric/ICE powerrating for the Civic Hybrid) and an elec-tric-only driving mode is not available.

The power split configuration ofToyota products is considered a strongHEV design approach. The power rat-

ing of the electric motor relative to theICE is larger (67/76 hp - electric/ICEpower rating for the Prius) and anelectric-only driving mode is available.

Another classification is the plug-inHEV. Current products such as the CivicHybrid and Prius have no provision forcharging the battery from an externalelectrical source. They maintain their

charge from on-board generationderived from the gasoline fuel. By usinglarger capacity batteries and providing acharging port for connecting to an exter-nal electrical source, a significant elec-

tric-only range is possible. This allowsthe car to be used as a battery-electricvehicle for short urban driving distances while retaining the cross-country high-way cruising range afforded by the ICE.Electricity now becomes an alternatefuel. Expect the plug-in HEV conceptbecome more popular.

The HEV requires no breakthroughtechnologies. The technical challengeis to bring the existing electro-technolo-

gies together in the optimum way tosatisfy the demands of an efficient, reli-able, desirable and affordable automo-

bile. Advances in power electronics andelectric motors such as variable fre-quency inverters, flux vector inductionmotor control and brushless direct cur-rent motors are enabling technologies. Advanced battery technologies such asnickel-metal-hydride (NiMH) with lower weight, higher power capacity andhigher cycle life are important in theESS design. The integrated control ofthe many HEV subsystems requires theuse of many embedded microcon-trollers and communications networks.

EPA mileage ratingsThe urban advantage of the HEV is

apparent by examining the EPA mileageratings. For a conventional car, the cityMPG rating will be less than the highwayrating. This fact is contrary to the energydemand predictions of simple physics.That is, it takes less energy to move a car agiven distance at low speeds than at highspeeds due to the aerodynamic drag forceincreasing as the square of the speed.

However, the city MPG ratings of aHEV typically will be greater than thehighway ratings. Also, the highway MPGratings of HEVs are higher than compara-

ble conventional cars due to improvedefficiency in the ICEs plus a smaller ICEcan be used. Table 1 shows the city andhighway MPG ratings of the CivicHybrid, the conventional automatic Civicand a 2004 model Toyota Prius are com-

pared to a similar sized Camry with anautomatic transmission.

Alternative fuelsTable 1 also compares the estimated

GHG emissions in tons per year of car-bon dioxide. All three cars use conven-tional gasoline fuel. The difference issimply based on the amount of carboncontained in the fuel consumed. The

more fuel-efficient cars use less fuel toperform a given mission. They, therefore,release less GHG into the atmosphere.

A companion technology is the use of

alternate fuels in automobiles. Fuels madefrom biomass, such as biodiesel madefrom soybeans, provide a significantreduction in net GHG emissions. Thisadvantage is due to the upstream creditgiven for the carbon dioxide removedfrom the atmosphere by the photosynthe-sis process of growing vegetation used asfeedstock for the fuel production.

A biomass-sourced fuel is renewable,or sustainable, and reduces the demandon our finite fossil fuel sources. Diesel-electric hybrids are probably one of the

6 IEEE POTENTIALS

Fig. 3 Honda Hybrid System

Honda Hybrid SystemIntegrated Motor Assist (IMA)

Motor-Generator

Electronic Controller Bat tery

Clutch andTransmission

or CVT

Wheels and Differential

InternalCombustion

Engine

Fig. 4 Toyota Hybrid System. For morediscussion and a diagram, checkout

Toyota Hybrid System(Power Split - ECVT)

Motor-Generator #1

Planetary GearPower Splitter Battery

ElectronicController

Motor-Generator #2

Wheels and Differential

InternalCombustion

Engine

GlossaryHEV Hybrid electric vehicle

EV Electric vehicle,also battery-electric vehicle

ZEV Zero emissions vehiclePZEV Partial zero emissions vehicleSUV Sport util ity vehicleICE Internal combustion engineESS Energy storage system,

usually a batteryIMA Integrated motor assist,

similar to a milder integratedstarter alternator (ISA) design

CVT Continuously variableautomatic transmission

ECVT Electrically implemented

continuously variableautomatic transmissionNiMH Nickel metal hydrideMPG Miles per gallonEPA Environmental Protection

AgencyPNGV Partnership for New

Generation VehiclesSAE SAE International is a

professional-technical

society for the mobility

industry. The acronym name

comes from its Society of

Automobile Engineers heritage.


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next developments to reach the market

place. Hydrogen used as a fuel produces

no GHG. The only byproduct of burning

hydrogen in an ICE or converting elec-

tricity in a fuel cell is water vapor.

However, hydrogen fuel is difficult to

produce and transport. The net benefit is

only slightly better than that achieved by

a strong HEV when the complete well-

to-wheels process is considered.

The universities roleUniversity students through engineering

design competitions have made significant

contributions to the development and

adoption of HEV concepts. For instance,

solar car competitions renewed the appeal

of propelling cars with electrical drives and

alternate renewable energy sources.

Unfortunately, there isnt enough real estate

on a practical passenger car to hold all of

the photo-voltaic cells that are needed.

With the 80 MPG goal in mind, the

US Department of Energy, the big three

US auto manufacturers and SAE spon-sored a series of design competitions for

engineering student teams. The contests

focused on improved fuel economy and

reduced emissions. The first one was

the HEV Challenge hosted by Ford at

their Dearborn, MI research & develop-

ment center in 1993. This competition

phase ran for three years. It featured

both scratch-built prototype HEVs and

conversions of conventional cars to HEV

operation. Nearly all of the HEVs in the

world were designed and built by uni-

versity students during these early years.

For the next several years, theFutureCar competitions demonstrated

the feasibility of the PNGV 80 MPG goal

through the HEV conversion of Taurus-

Lumina-Concorde sedans by 15 select

university teams. The next competition

phase was the FutureTruck demonstra-

tions of the HEV technology in improv-

ing the efficiency of Suburban and

Explorer SUVs. The Challenge X is the

next phase. The three-year run goes

from 2005 through 2007. Emphasis will

be placed on using systems engineering

processes to demonstrate and incorpo-

rate these technologies into the newChevrolet Equinox crossover SUV.

The Tour de SolThe Great

American Green Transportation Festival

and Competition provides a venue for

universities and other teams to demon-

strate many versions of sustainable

energy transportation concepts. The

Michelin Bibendum (meeting this

October in China) also provides a

venue for university and commercial

ventures to showcase their achieve-

ments in designing fuel efficient and

environmentally friendly vehicles. These

events help benchmark progress and

educate the public and professional

decision makers on HEV technology.

Personal experienceThe University of Tulsa is a small pri-

vate school located away from the

motor city hub of the automotive indus-try. However, we fortunately, have

been able to participate in this electrify-

ing evolution of automotive design. We

began shortly before the HEV Challenge

with a student initiative to build a new

t e c hno l ogy

p r a c t i c a l

vehicle.

An initial

EV concept

soon evolved

into an HEV

one when we

realized therange limita-

tions of batteries. It was an obvious

transition to change our goals toward

the HEV Challenge, where we compet-

ed with our scratch-built fiberglass chas-

sis series HEV Hybrid Hurricane. After

three years in that competition, and fail-

ing to make the cut into the FutureCar

competition, we choose to pursue the

PNGV 80 MPG goal on our own.

We decided we needed a parallel

HEV powertrain design to fully exploit

the potential of the HEV propulsion

concept. We set out to develop it byconverting a 1992 Geo Metro hatchback

into a powertrain development test

mule. This vehicle, the ParaDyne,

proved to be a success and has partici-

pated in the Tour de Sol five times,

winning the prototype HEV class using

both gasoline and ethanol fuels. We are

now competing in the Tour de Sol with

our third generat ion vehicle, the

Proxima. The Proxima is a lightweight

carbon and glass fiber sports car chassis.

It is powered by an improved version of

the parallel HEV powertrain developed

in the ParaDyne test mule. Our nextphase is to participate in Challenge X.

When the HEV was first offered to

the public as a commercial product in

2000, I could not resist the temptation. I

was one of the early adopters of a

Toyota Prius HEV. It has been my daily

driver for nearly four years with zero

problems over 50,000 miles. My lifetime

fuel economy is 45 MPG for all types of

driving including interstate cruising and

city driving with the air conditioner on.

I entered it into the Tour de Sol compe-

tition in the production class, with

repeat wins on my record.

The futureIt is risky to predict the future. But

the trends indicate that more of the

propulsion force will be the result of

electrical motors. Computerized engine

management has cleaned up the ICEregulated emissions to an acceptable

level while improving the efficiency and

drivability. With HEV, some of the trac-

tion forces are now coming from elec-

tric motors.

Some would have you believe that

the car of the future is the hydrogen

powered fuel cell electric car. However,

this is really a series HEV with the fuel

cell replacing the ICE and generator.

Prototype fuel cell hybrids are now in

the hands of a few select fleet operators.

Some manufacturers suggest that

hybrid versions will be available

throughout their product line within the

decade. As an electrical engineer, it is

rewarding to see electro-technology

positively impact on a product so dearand relied upon by so many.

About the authorThe author Robert D. Strattan is

Emeritus Professor of Electrical

Engineering and Adjunct Professor of

Mechanical Engineering at the

University of Tulsa. He has been a fac-

ulty co-advisor to the universitys

Hurricane Motor Works hybrid electric

vehicle project for 13 years. For further

details, see or

contact him at .

AUGUST/SEPTEMBER 2004 7

Table 1 Comparison of Conventional and HEV Fuel

Efficiency and GHG Emissions

Vehicle Technology Trans- City Highway GHG

mission MPG MPG (Tons/Yr

Honda Civic Hybrid

Honda Civic

Toyota Prius

Toyota Camry

HEV (mild)

Conventional

HEV (strong)

Conventional

CVT

AT

ECVT

AT

48

35

60

23

47

40

51

32

4.1

5.2

3.5

7.2

Check the web http://auto.howstuffworks.com/hybrid-car.htm http://www.transportation.anl.gov/ hybrids http://www.transportation.anl.gov/competitions http://www.eere.energy.gov/vehiclesandfuels/ http://www.fueleconomy.gov/feg http://www.nesea.org/transportation /tour/ http://www.challengebibendum.com/challenge/

front/affich.jsp?&lang=EN http://evworld.com/

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