Christof Schernus & Peter Janssen JörgSeibel Lu …...Hybrid Electric Vehicle Performance Modeling using GT-DRIVE GT-SUITE User’s Conference 2006 MercureHotel Frankfurt Airport,

FEV_SAIC_HEV_Modelling / Schernus (FTO), Jassen (CVG) 1

FEV_SAIC_HEV_Modelling / Schernus (FTO), Jassen (CVG)

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Hybrid Electric Vehicle Performance

Modeling using GT-DRIVE



© by FEV – all rights reserved. Proprietary and Confidential

Hybrid Electric Vehicle Performance Modeling using GT-DRIVE

GT-SUITE User’s Conference 2006

Mercure Hotel Frankfurt Airport, 2006-10-09, Frankfurt/Main, Germany

The Dearborn Inn, 2006-11-14, Dearborn, Michigan, U.S.A.

Christof Schernus & Peter JanssenFEV Motorentechnik GmbH, Aachen

Jörg SeibelInstitute for Combustion Engines, RWTH Aachen University

Lu Lianjun & Meng Tao Automotive Engineering Academy of SAIC Motor Co. Ltd., Shanghai

Further Acknowledgements:

G. Fialek, R. Keribar, B. Luptowski @ GTI

- A Study on a new HEV Powertrain

Good morning,

In this paper we want to show you results from a simulation study on a new Hybrid

Electric Vehicle powertrain, that FEV and SAIC carried out in cooperation. Thanks

are due to my co-authors Peter Janssen at FEV, Jörg Seibel at the Aachen University

and to Dr Lu and Dr Tao at SAIC in Shanghai.

I also wanted to thank for the support by Greg Fialek, Rifat Keribar and Brian

Luptowski at Gamma Technologies.



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Contents

Introduction

Electrically controlled Planetary Gear Set

Vehicle model and features

Performance simulations

Fuel consumption simulation

Conclusions

After the introduction, the presentation will continue with a brief description how a

planetary gear set can be used to replace a torque converter creating a hybrid electric

powertrain.

Then the GT-DRIVE model of the vehicle will be shown highlighting a few

important features.

That model is used for performance simulations as well as for fuel consumption

prediction.

The presentation will end with conclusions.



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Introduction

Motivation for HEV

Improved Fuel Economy

� Green house effect: target CO2 emission ≤ 140 g/km

� ACEA: MY2008

� JAMA+KAMA: MY2009

� Reduced dependency on oil producing countries

Emission legislation

� ZEV credits (depending on ZEV range)

One of the major benefits we can expect from a hybrid electric vehicle is a

significant improvement of fuel consumption.

Aiming at a reduction of greenhouse gas emissions, the European automakers 1)

have committed to reduce the carbon dioxide emission to an average of 140 g/km

for MY 2008.

The same target was adopted by the automotive industry in Japan and Korea for

MY2009.

An overall reduction of fuel consumption also raises hopes for less dependency on

foreign countries producing oil.

Depending on the pure electric mileage of the HEV, the car builder also earns Zero

Emission Vehicle credits in the US.

1) ACEA: Association des Constructeurs Européens d’Automobiles



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Introduction

Motivation for HEV

Improved Fuel Economy

� Green house effect: target CO2 emission ≤ 140 g/km

� ACEA: MY2008

� JAMA+KAMA: MY2009

� Reduced dependency on oil producing countries

Emission legislation

� ZEV credits

Fun to drive

� Enables downsizing with impressing

low-end torque

� Silent driving

Extended functionality

� Hill hold

� Extended on-board availability of electric energy for driver assistance and comfort

systems

Last but not least, there are always two ways to use a new technology.

The combination of an electric motor with high torque at low speed with a

combustion engine enables a downsizing concept with impressing low-end torque.

That means, you can deploy a smaller turbo combustion engine and overcompensate

its weaker starting torque by the electric motor. As a consequence you will enjoy a

true punch in drive away situations.

But not only power is fun, it may also be enjoyable to drive electrically almost

without a sound. Not to mention further benefits from hybridization like extended

functionality and large battery capacity.



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Introduction

Approach

Replacement of hydraulic TC with e-motor controlled PGS

⇒⇒⇒⇒ Parallel HEV with ability of

� Recuperative braking

� Boosting by e-motor

� Operating point shift for regeneration

� Start/stop

� Electric driving

Internal

Combustion

Engine

Planetary

Gear

Set

Automatic

Trans-

Mission

Motor-Generator

The hybridization concept in our study replaces the hydraulic torque converter by a

double pinion planetary gear set. This is used as a continuously variable

transmission with speed ratios between zero and infinity; and the gear ratio is

controlled by the electric motor-generator on the sun gear. Furthermore, the entire

planetary gear set can be locked by a clutch. In that case, its gear ratio will be one

and electric motor and internal combustion engine operate at the same speed. We

would call that “parallel mode”; and this is the typical mode of operation. It allows

electric power boosting, battery regeneration and recuperative braking.

Using the planetary gear set as CVT would be called “PGS mode”. And this is used

for idle operation at standstill, drive away from standstill or purely electric driving.



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Contents

Introduction





Conclusions

Let us go more into details of the electrically controlled PGS…



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TR NT,R

TC

TSNT,S

Single PGS

TSTC

NT,R

TR

NT,S

Double PGS


Vehicle: Double Pinion Planetary Gear Set (DPGS)

GT-DRIVE model: Single Planetary Gear Set (SPGS)

How to obtain dynamic equivalence?

rpmSunCarrierRing

As mentioned before, the powertrain concept features a Double Pinion Planetary

Gear Set, i.e. a carrier holding two planet gears between the central sun gear and the

outer ring gear. But GT-DRIVE has only a building-block available for a Single

Planetary Gear Set. I will now show you how we can use the single PGS model of

GT-DRIVE for a double pinion PGS.

In a single PGS, the speeds of the sun, carrier and ring can be plotted as points on a

straight line, like on a lever with the carrier as a pivot. This lever is horizontal if all

speeds are the same.



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SunCarrierRing

TR NT,R

TC

TSNT,S

Single PGS

TSTC

NT,R

TR

NT,S

Double PGS


Vehicle: Double Pinion Planetary Gear Set (DPGS)

GT-DRIVE model: Single Planetary Gear Set (SPGS)

How to obtain dynamic equivalence?

� NT,R/NT,S of SPGS = (NT,R-NT,S)/NT,S of DPGS

� The part connected to the Ring of the DPGS has to be connected to the Carrier of the

SPGS and vice versa

rpm

SunRingCarrier

If the carrier stands still, sun and ring will rotate in opposed directions and the ratio

of speeds is reciprocal to the number of teeth.

When the carrier accelerates, its speed rises the lever as a whole.

For a double pinion PGS, we have to switch the connections of the carrier and the

ring.

Furthermore, the number of teeth of sun and ring gear has to be readjusted according

to this formula to obtain a kinematical equivalence. And to obtain a good dynamic

correlation we must take care the inertias accelerate at the same rate in model and

hardware. Therefore, we keep the gear inertias linked to the identical external

connections.



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Double Pinion Planetary Gear Set Schematic

Transmission at Stand Still (Engine Start or Idle Speed)

Note: Gear ratios not to scale, selected for animation purposes only

The kinematical equivalence is highlighted by a few animations.

This one shows the operation at idle speed in standstill. The transmission input

speed is zero, and therefore, the ring of the double pinion PGS and the carrier of the

single PGS do not rotate.

The e-motor on the sun gear rotates at the same speed in both cases and the

combustion engine rotates in the opposite direction at a the speed defined by the

gear ratio.



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Engine at Stand Still (Electric Driving)

This will show electric driving. Now the combustion engine is locked by a brake.

Hence, the carrier of the double pinion PGS and the ring of the single PGS do not

rotate.

The e-motor on the sun gear rotates at the same speed in both cases and the

transmission input shaft rotates in the same direction.



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Lockup Clutch Closed (Parallel Driving)

And in parallel mode, the entire PGS is locked by a clutch just like a torque

converter would be locked to avoid slip at higher engine speeds.

Therefore, all parts rotate at the same speed in the same direction.



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Contents

Introduction





Conclusions

Next, I want to show you the GT-DRIVE vehicle model and some features therein.



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Hybrid Electric Vehicle – GT-DRIVE Simulation Model

Top Level Overview

The model consists of a vehicle body, connected to the road by front and rear axle

and tires. The front axle is driven by a shaft coming from the automatic

transmission. On the right hand side, there is the internal combustion engine that can

be held at zero speed by a one way clutch or brake for electric driving. And between

transmission and engine we see the planetary gear set with the electric motor-

generator connected to it. Further, we have the battery, the driver controlling the

vehicle speed and a quite a few of control functions hiding in the sub assemblies on

top of the screen.

As we talked about the switched connections of the PGS before, I want to go into

that detail here:



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HEV Powertrain – GT-DRIVE Model

Planetary Gear Set

DPGS replaced by SPGS model

building block of GT-DRIVE

� Connections of Ring Gear and Carrier flipped

� Note: Inertias must remain associated to

identical external parts, i.e.

� Flywheel inertia remains at Combustion

Engine side (SPGS: “Ring” Gear)

� Gear box connecting shaft inertia remains

at Transmission side (SPGS: “Carrier”)

� Number of teeth of ring and sun gear adjusted

to maintain DPGS gear ratio

To use the single PGS building block of GT-DRIVE for a Double pinion PGS, we

made all internal inertias external ones before flipping the connections of ring and

carrier. Therefore, you see the ring gear inertia connected to the carrier port of the

PGS part and the carrier inertia linked to the ring port. Between carrier inertia and

sun inertia there is the clutch to lock up the CVT in parallel mode.

And for sure, the number of teeth of ring and sun gear were adapted according to the

formula shown on slide #6.



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Hybrid Electric Vehicle – GT-DRIVE Simulation Model

Top Level Overview

The next example feature I wanted to display is the PGS mode controller.



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HEV Powertrain – GT-DRIVE Model

Top Level Overview

Slip of Torque converter in drive away is performed in “PGS mode”

� ICE and EM operating at different speeds

� ICE RPM target is generated

� Electric motor torque used to minimize ICE RPM control error

PGS mode controller can be disabled

� For purely electric driving or

� For parallel mode driving (PGS lockup clutch closed)

� By setting by input = target value of PID controller object used as P-controller (KI,KD=0)

For drive away the PGS has to fulfill the function of the torque converter it replaced.

As shown in the animation before, engine and e-motor rotate at different speeds and

in different directions in stand still, allowing to run the combustion engine at true

idle conditions torque-flow separated from the transmission.

For drive away, a target engine speed is generated, and the e-motor torque is

adjusted by a PID controller to strut the transmission against the ICE. Both together

will accelerate the transmission input shaft and, consequently, the vehicle.



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Contents

Introduction





Conclusions

The function of this PGS controller is highlighted as part of the performance

simulation.



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Drive Away from Stand Still

Operation in PGS Mode until PGS Lock Up

The upper diagram displays the rotary speed of internal combustion engine ICE, e-

motor and transmission input shaft. The lower plot shows normalized torque in a

drive away situation.

Starting from standstill, the difference between e-motor and engine speed will first

increase.

This is also indicated by the increasing tilt of the lever. As the car accelerates, the

PID-controller tries to limit the engine speed to a certain level. The nice thing about

this acceleration mode is, that the e-motor regenerates some battery charge, as long

as it rotates in the negative direction and provides positive torque to adjust the

engine speed. Contrary to that, the slip of a torque converter always is subject of

losing energy or converting it into heat, respectively.

The electric motor speed changes from negative to positive direction and accelerates

further until it catches up with the combustion engine. At that point the clutch is

closed, the powertrain enters the parallel operation mode and all three rotary speeds

are equal.

As the acceleration continues, the speed lever moves upward in a horizontal

position.



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Acceleration 0-100 km/h

Comparison HEV vs. Conventional Vehicle

HEV and conventional

car equipped with the

same turbo engine

Significant increase in

performance due to

electric boost

t = 0 s

t = 5.0 s

t = 7.8 s

Now, we want to compare the acceleration performance of the hybridized vehicle

with its conventional competitor. The comparison looks a bit unfair, because the

HEV has the e-motor torque on top of the conventional engine‘s full load curve. But

you should remember that also the TC has a torque amplification in the take-off

phase, so it is not that unfair.

The animation will give you an impression how much the hybrid vehicle

performance is improved. The red rectangle symbolizes the conventional car, the

blue one the HEV.

From standstill, the HEV pulls away quickly; and it reaches the target speed of 100

km/h in less than 8 seconds and about 120 meters distance. The conventional car

needs more time and distance to get to the target speed.



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Contents

Introduction





Conclusions

As last result, the benefit of hybridization is shown in drive cycle fuel consumption.



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Comparison of fuel consumed by conventional and

hybrid vehicle concepts

Fuel consumption

at standstill

Torque

converter

“idle”

Comparison

� Conventional vehicle

with automatic

transmission and torque

converter

� HEV with different

degree of hybridization

� Base: only e-PGS

instead of TC

� e-PGS + Start/stop

� e-PGS + Start/stop

+ electric driving

+ recuperative

braking

NEDC operation

� Importance of stand still

and idle

In this slide, we compare the conventional vehicle to hybrid powertrains with

stepwise increased degree of hybridization. The upper diagram indicates vehicle

speed and also phases in which the combustion engine is shut off including electric

driving. The lower plot indicates the roundtrip average fuel consumption in liters per

100 km from the start to the indicated time. The curves are normalized with the

NEDC end value of the conventional vehicle.

Operating a conventional vehicle in a drive cycle like the New European Drive

Cycle (NEDC), it consumes an awful lot of fuel in the frequent standstill phases.

One of these standstills is highlighted with the blue frame. In case of the automatic

transmission, the torque converters does not allow for a complete separation of

engine and transmission, so you need always to keep your foot on the brakes to

prevent the car from creeping. This causes a certain engine load and thus a fuel

consumption as indicated by the tangent to distance specific fuel consumption.



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Comparison of fuel consumed by conventional and

hybrid vehicle concepts

HEV Benefits:

� PGS cancels TC power

dissipation

� Idle operation is true idle

like with an open clutch

and not “milling” torque

converter oil

� PGS mode stores and

uses electric energy

more efficiently than

torque converter

operation

� Start/stop cancels any

fuel consumption at

standstill

� Additional benefits from

electric driving and

(moderate) recuperative

braking

Fuel consumption

at standstill

Start/stop

PGS idle

Electric driving

+ brake recup.

Replacing the torque converter by the electrically controlled PGS allows for a total

separation of engine and transmission. The engine runs at true idle, i.e. zero BMEP

and therefore consumes less fuel than with the torque converter. Further advantages

are due to avoiding slip wherever possible using the PGS, but that could be achieved

with a different lockup strategy of the torque converter, too.

The next reduction of fuel consumption is provided by deploying a start/stop

strategy. This shuts off the ICE at stand still and cancels its fuel consumption as

indicated by the horizontal green tangent.

Introducing moderate recuperative braking and electric driving to cancel ICE

operation at unfavorably low loads would be a further step, but removing the torque

converter and introducing start/stop seem the most important steps toward lower fuel

consumption and less CO2 emission.



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Contents

Introduction





Conclusions

To finish the presentation …



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Conclusions

GT-DRIVE useful as a virtual prototype to study hybrid vehicle fuel

consumption and performance

Hybridization with e-PGS =

� Downsizing without drive-away drawbacks

� More fun2drive with green conscience

Fuel consumption reduced by

� Replacing the hydraulic torque converter with e-PGS

� Start/stop

� Electric driving

� Recuperative braking

Full use of regenerative braking requires a brake-by-wire system

� Load shift is also beneficial, especially if electric driving is extended to cancel ICE operation at low load (i.e. low efficiency)

…we found GT-DRIVE very useful in our study as a virtual prototyping platform to

predict the HEV fuel consumption and full load performance.

We can conclude that hybridizing a conventional vehicle the way we propose allows

to deploy downsizing without drive-away drawbacks. The vehicle performance is

improved, but not at the cost of fuel consumption. The fuel mileage is improved due

to replacing the torque converter by our e-PGS and by introducing a start/stop

strategy. Further improvements are expected from electric driving whenever the

combustion engine efficiency would be bad and by recuperative braking.

To recuperate most or all available brake energy, a brake-by-wire system is

required, the development of which is a complex and expensive task.

Load shift is also helpful, if the electric driving is used to cancel unfavorable ICE

operation points.

Documents

Christof Schernus & Peter Janssen JörgSeibel Lu …...Hybrid Electric Vehicle Performance Modeling using GT-DRIVE GT-SUITE User’s Conference 2006 MercureHotel Frankfurt Airport,