Engine Design, Sizing and Operation in Hybrid Electric Vehicles

Mike Duoba

Argonne National Laboratory

Presentation at University of Wisconsin-Madison

ERC – 2011 Symposium

June 8, 2011

Question to Engine Experts: “Are your days numbered?”

“take a look

under the hood”

“It is my dream to see our roads with at least 90% EVs

so that there's more efficient use of our energy and

resources. The internal combustion engine is one of

the most wasteful machines ever invented and we all

should prepare the world for the energy crisis we will

face when crude oil extraction enters the decline

phase.”

- Ricardo Parker, reader blog, Seattle PI

2

Answer: NoEVs Can Not Be The Primary Household Vehicle.Consumer Acceptance is Limited (with current technology)

Engines Needed

3

Hybrid Vehicle Sales Going Up!Predicted to Top 4 Million by 2015.

- Consumer Reports: 39 percent are considering a hybrid or electric

power type for their next new car

- Other analysts say “~50 HEV models by year 2015,” “10% of sales”

4

Engine Design, Sizing and Operation in HEVs

Discussion Outline

� Introduction: Powertrains and Hybrids

� Engine Start and Re-start: Emissions and fuel concerns

� Peak Efficiency: Engine maps, transmissions, load points (CVTs, EVT)

� Sizing: Downsizing for hybrids?

� HEVs and Thermal State: Reducing fuel use with thermal management

� PHEVs: Unique operation and challenges (blended, not blended, US06,

EREV engines)

5

IntroductionPowertrains, Hybrids, Operation

6

Argonne State-of-the-Art Laboratory for Research in Vehicle Systems Analysis

Advanced Powertrain Research Facility (APRF)

� Custom multi-input data acquisition specific to hybrid vehicle instrumentation

� Staff at cutting edge of test procedures for new advanced vehicles

� Inventing new and novel instrumentation techniques

Novel Sensor DevelopmentAdvanced Powertrain Research Facility (APRF)

In-House Data Acquisition

Tested Nearly All Hybrids in USA

Climate-Controlled 4WD Chassis Dynamometer

7

Powertrains: Torque and Speed to Drive at the Wheel

Urban CyclePrius

Veh Wt: 3250 lbs

Road Load Force

F = A + Bv + Cv2

A= 25

B= 0.139

C= 0.0164

Mismatch is only a problem for

engines. Motors can in fact be

8

engines. Motors can in fact be

designed to satisfy wheel

demands.

Compare Wheel Requirements to Engine Capability

Engine Operation Space

Wheel Wheel

Operation Operation

SpaceSpace

9

Compare Wheel Requirements to Engine Capability ���� Transmission and Brake System

4:1 Drive Ratio

8:1 Drive Ratio

16:1 Drive Ratio

10

Braking Torque Device Needed

Terminology for “Electrified Vehicles”

Vehicle Type Electric

Power

Electric

Storage

Grid Connected

Electric

Driving

Mild HEV Low Low No No

Full HEV Med Low No Very

limited

Blended

PHEVMed Med Yes Limited

Civic HEV

Escape HEVPrius HEV

VUE HEV

Hymotion Prius

11

PHEV

Intermediate

PHEV

Med+ Med Yes UDDS

cycle

E-REV

PHEV

High High Yes FullPerformance

BEV High High Yes Full Performance

Toyota PHEV

GM Volt

RAV-4 EVEV1

Volt

Plug-In

Vehicles

Hybrid Architectures

WheelFinal

Drive

Gen-

erator

MotorEngine

Torque-

Split Gears

T

0.28T

0.72T

IClutch

IClutch

Push

Power-Split

- Toyota Prius�

- Ford

- GM complex 2-Mode has

fixed gear capability

Honda System

12

Engine

I

M

A

Manual

5-Speed

Final

DriveWheelEngine

I

M

A

Manual

5-Speed

Final

DriveWheel

Final

DriveWheel

Final

DriveWheel

Push

Belt

CVTB

AS

Auto

6-SpeedMo

tor

Honda System

- Insight, Civic, CR-Z �

Hyundai System

- Sonata “1-motor” �

- Nissan has slightly

different 1-motor design

EngineEngine

Hybrid and Advanced Powertrain Operational Features

Method Examples

Engine Idle Stop

Best Line in Map

Engine Downsizing

(all hybrids)Mazda 3

(non-hybrid)

PriuseAssist

Prius Insight

CVT

(BAS)

CVTEVT

13

Engine Downsizing(electric assist)

Low-Load Electric Driving

Regenerative Braking

Transient Smoothing

Hybrids: Engine smaller or Performance Up

(full hybrids)

Prius

Power-split

Fusion

Power-split

Sonata

Parallel

All Hybrids (Full HEV recovers most)

All Hybrids

(more power = more torque authority)

Engine Start and Re-StartEmissions and Fuel Concerns

14

THS Initial Engine-Start Strategy“Cold-Start” UDDS

� Hill 1 of UDDS requires low

driving loads. Motor handles

driving while engine employs

controlled warm-up strategy.

� Conservative cold-start

strategy employed in 2001

Prius. No shut-down

eng rpm/100

Batt kW

veh mph

2001 Prius

2001 Prius2001 Prius 2004 Prius2004 Prius

Key Start

Prius. No shut-down

between hills 1 and 2.

� 2004 Prius delays engine

start after key start

� 2004 Prius shuts down

engine between hills 1 and 2

15

Batt kW

2004 Prius

Key Start

Cold Hybrid Engine Start Strategy AnalysisMY 2010 Prius uses a unique cold-start/catalyst warm-up strategy

Catalyst Warm-up Continued Vehicle Warm-up

16

Fast catalyst warm-up with

minimal fueling

Reduced engine speed variability

during vehicle warm-up

Hybrid Operation Different Between Mild and Full Hybrids- Different trade-offs in achieving low emissions and high fuel efficiency

18

2006 Civic Hybrid

17

# Engine stops = 45

2001 Prius Hybrid

Hybrid Engine Thermal Conditions Also Different

- In transient driving, full hybrid engines spend considerable time OFF.

- Cylinder, head/port temperatures, fueling strategies different

- Catalyst temperature management strategies different

2010 Prius

18

~90 C activation temp.

UDDS CS UDDS HS

Prius exhaust-to-coolant heat exchanger for improved warm-up.

19

* Figures from TMC Prius Manual

At higher coolant temps.

bypass is activated

Coolant circulates

around exhaust

Prius exhaust heat recovery system

Peak EfficiencyEngine maps, transmissions, load points (CVTs, EVT)

20

700

800

900

Engine Efficiency Map, , MY99 P rius

0.3

5

0.35

0.35

0.3

40

. 33

0.3

2

“Best Line” shown on

engine efficiency map

Power-Split Design Enables Variable Ratio Ratio of infinity possible – launch capability

1000 1500 2000 2500 3000 3500 4000 45000

100

200

300

400

500

600

700

RP M

En

gin

e B

ME

P (

kP

a)

0.350.35

0.34

0.340.34 0.33

0.330.33 0.32

0.320.32

0.31 0.310.31

0.31

0.28 0.280.28

0.2

8

0.25 0.25 0.25

0.2 0.2 0.2

0.15 0.15 0.15

Test results using in-situ

torque sensor

Source: ANL data

Location of Peak Efficiency

o Electric assist allows engine to operate in

high torque region at given speed• Minimal “torque reserve”

o For EVT operation, peak system

efficiency may not be peak eng eff• Assist can keep engine in efficient zones

during transients

o No enrichment zone in map

Atkinson Cycle Engine - Prius

22

Conventional Engine

Conventional Engine

Low Load Electric Driving Eliminates Lowest Efficiency Operation

0.2530

0.35540.3642

20%

25%

30%

35%

40% 36.42%Interesting Side Note:

Low-load electric driving affects engine sizing

- Honda Insight and Civic (1.3L)

- Prius (1.5-1.8L)

Smaller engines are more efficient at low

loads

Prius avoids <30% engine operation

23

0%

5%

10%

15%

20%

0 5 10 15 20 25 30 35 40 45

Engine Output [kW]

Engine-Off Load

Engine SizingIs smaller = Better?

24

Conventional Wisdom,smaller always better?

Smaller engine = Higher MPG!

Hybrids allow more engine downsizing while maintaining performance

?

Downsized

engine:

1.2L, 200HP

Volt engine:

1.4L, 84HP

35 MPG Mustang with 1.0L engine?

25

Downsizing Limits ���� Baker Grade- Hybrids boost for seconds, not minutes- Over-downsized hybrid will be a traffic hazard!

26

Regen Level Determines Optimum Level of Hybridization

MP

G �

Battery/Motor system size that

can fully recover regen braking on

UDDS cycle

Best cost/performance point

27

From Toyota.com

Traction Battery Type:

Sealed Nickel-Metal Hydride

Power Output: 36 hp (27 kW)

Voltage: 201.6V

27kW

Level of Hybridization �

Peak Efficiency – Atkinson CycleWith respect to peak power, Atkinson Cycle is downsizing

� 2011 Prius 1.8L – 142 N-m

� Toyota Matrix 1.8L – 169 N-m

� Honda Civic 1.8L – 174 N-m

28

Downsizing? In 2010, Prius Engine Got BIGGER!MPG: 46 ���� 50

29

Off<8kW

Off<8kW

MPG Improvement Comes From Several Changes

- Same power achieved at lower RPM- Larger high-efficiency window

30

Plug-In HEVs (PHEV)More challenges, more departures from “conventional”

31

Two Types of PHEV Operation During Testing

EV

Mode

SO

C

Sustain Mode

EREV: Defined as having the ability

to drive all-electric under driving

style (max power in electric)

x

miles EV

range = Engine-on

(start of day)

“Charge-

Sustaining”

“Charge-

Depleting”

32

SO

C

Depleting

Mode

Sustain

Mode

Blended: Does not have a “full

performance” electric drive

system. Engine operation needed

during some or all test cycles.

Although small electric drive,

blended PHEVs can displace a

significant amount of fuel use.

(start of day)

x

miles CD

range

“Charge-

Sustaining”

“Charge-

Depleting”

EREV

Intermediate “Urban-Capable”

Blended

Wheel Power Requirements Show When

Electric Dive Can Displace Engine Operation W

he

el

kW

Both electric-capable in this cycle

33

04Prius

Full Accel

Wh

ee

l kW

Engine Temperature Never Reaches Operating Temp

Charge Sustaining UDDS

� Early engine temp rise

comes from hot coolant

purging from storage

canister (emissions

feature of Gen 2 Prius)

� Normal engine On/Off

keeps engine temp low

(70-75 C)

60703067veh mph

Ah*10

eng temp

THC

Charge Depleting UDDS

� Late start controls

� Temperature only reaches

~40 C

� Engine is cooling from

infrequent operation

34

60612031

eng rpm/100

eng temp

THC

Engine Operation

– Large emissions spike at first engine

operation

– Google staff ironically referred to

delayed-start calibration as the “low-

emissions” calibration

UDDS Emissions Can Suffer from Too Much EV Operation

Aftermarket PHEV Prius

Cold Start

Production Prius

Cold Start

35

Emissions Control Possible After Long Periods of Engine-Off

Cold-Start Urban

Hymotion Prius

No emissions after long shut-downNormal cold-start

emissions

36

Normal

emission

control

>700s (~12min) of EV operation

Engine speed (/100)

Emissions (HC, CO, NOx)

Future Engine Technology in Hybrids – Any Synergies?

� Diesels and Hybrids

– Old Assumption = Diesel or Hybrid, never diesel-hybrid

– New lesson = Peugeot 3006 full hybrid with diesel engine

� HCCI Engines (and other advanced combustion)

– Design and control suited for limited operation regime

– HEV configuration with very controllable load and speeds

� Lean Burn and Other Combustion Strategies� Lean Burn and Other Combustion Strategies

– Decoupling engine load from driving demands offer more opportunities

for care and feeding of advanced after-treatment controls

– Diesel DPF regen and rich events for lean-burn better controlled

� Less Demanding Engine Design Requirements

– Turbo lag less important

• Eliminate expensive anti-turbo-lag technology in modern small turbos

– Optimize peak efficiency at low loads, less compromises for peak power / liter

� More Demanding Idle-Stop Requirements

– Emissions concerns in restart

– DI engines may be better suited for idle-stop

37

Conclusions

� Complexity: Engines are parts of a complex powertrain that are designed, sized,

and controlled to meet very specific requirements.

� Optimization: By optimizing the whole system, engine design can be better suited

for operation that can be very different than for conventional vehicles

� Peak Efficiency: Hybrid assist allow high peak efficiency during normal driving.

Efficiency not important at idle and off-idle loads.Efficiency not important at idle and off-idle loads.

� Engine Sizing: Downsizing only goes so far in hybrids.

� Thermal Management: Attention must be given for keeping engine warm to

reduce losses and lower fuel consumption.

38

For More Information

Google Search:

� Argonne Transportation

� Downloadable Dynamometer Database (open to anyone)

� Advanced Powertrain Research Facility

39

This work was supported by DOE’s FreedomCAR and Vehicle

Technology Office under the direction of Lee Slezak.