a new parallel-type hybrid electric-vehicle

8/8/2019 A New Parallel-type Hybrid Electric-Vehicle

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A new parallel-type hybrid electric-vehicle

K. David Huang a, Sheng-Chung Tzeng b,*

a Graduate School of the Vehicular Engineering, Dayeh University, Changhua

500, Taiwan, ROCb Department of Mechanical Engineering, Chien Kuo Institude of Technology, Changhua

500, Taiwan, ROC

Accepted 2 December 2003

Available online 28 January 2004

Abstract

This new system promises an internal-combustion engine that always maintains optimal

operating conditions. The system comprises two parts: (1) an internal-combustion power-distribution device and (2) an integrated design involving the engine and electronic motor. The

internal-combustion power-distribution device provides an engine capable of constantly op-

erating in an optimal fashion, minimizing emissions and maximizing thermal-efficiency. The

electric motor can generate extra power. Notably, the integrated torque design comprises three

helical gears. This design can release the power of the engine or electric motor separately, or

can integrate these two different powers into a hybridized power system.

2004 Elsevier Ltd. All rights reserved.

Keywords: Hybrid electric-vehicle; Power-distribution device; Hybridized power system

1. Introduction

The continued sluggish development of pure electric vehicles (EVs) results from a

lack of significant developments in battery technology. However, pure electric ve-

hicles still exhibit some limitations in battery capacity. Recently, many investigations

have examined the construction of hybrid-power systems. Most research on these

is focused on how to avoid high pollution and fuel consumption in internal-

* Corresponding author. Tel.: +886-4-7111111x3132; fax: +886-4-7357193.

E-mail address: [email protected] (S.-C. Tzeng).

0306-2619/$ - see front matter 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.apenergy.2003.12.001

www.elsevier.com/locate/apenergy

Applied Energy 79 (2004) 5164

APPLIED

ENERGY
http://mail%20to:%[email protected]/http://mail%20to:%[email protected]/


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combustion engines running at low speeds. The environmental problems are wors-

ening, and more countries are paying increased attention to environmental issues,

leading to the aggressive development of new-generation transportation with char-

acteristics of energy saving and low pollution. Numerous new technologies have been

developed over the past few decades. However, many problems remain impossible to

solve using these technologies. Pure EVs were initially the focus of development in the

field of new-generation transportation [1,2]. However, pure EVs suffer from the

following technological limitations that prevent their mass-production, namely: Low battery-energy density causing poor driving durability for EVs and

motorcycles.

Nomenclature

1/SOC battery-charge stateDc1 pulley diameter of the final power-output axle (mm)

Dd pulley diameter of the magnetic clutch (mm)

De pulley diameter of the first pulley (mm)

Dg pulley diameter of the second pulley (mm)

Es fixed battery internal-voltage (V)

i discharge current (A)

im input current (A)

Ialt alternators output-current (A)

Ifld alternators exciting-current (A)

Im motor inertiaK resistor (X)

Ki torque constant value

Lfld alternators exciting-inductance (H)

Q battery capacity (A h)

R linear resistor (X)

Rfld alternators exciting-resistance (X)

Tc1 final power-output axle torque

Td magnetic-clutch torque

Tg alternators loaded torque

Tm motors output torque

Vb battery voltage (V)

Vfld alternators exciting-voltage (V)

Vsys alternators output-voltage (V)

Greek symbols

xalt alternator speed (RPM)

xe engines input-speed

xm motors input-speed

xo output speed

52 K. David Huang, S.-C. Tzeng / Applied Energy 79 (2004) 5164


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Slow battery-charging speed preventing rapid mass charging.

Difficulty in accurately displaying the residual energy of the battery.

Used batteries cause significant environmental pollution.

The environment lacks equipment such as convenient and quick-charging devicesto facilitate the use of EVs.

From the late 1990s, numerous studies have addressed hybrid electric vehicles

[311]. Consequently, more immediate possibilities lie in hybrid electric vehicle

(HEV) transportation, with the most popular combination involving an internal-

combustion engine combined with an electric motor power output.

In general, two types of HEV exist: serial and parallel. The advantage of the serial

type of hybrid-power system lies in its simple construction. The internal-combustion

engine is the only method used to generate electrical power in the serial type system,

while the power required to drive the vehicle comes entirely from the electric motor.

Consequently, the disadvantage of the serial-type system results from the enginepower being dedicated to the electric motor only, meaning that its horsepower

output and efficiency are worse than those of the parallel-type. By contrast, the

parallel-type system employs two power sources, and thus has a higher application

efficiency than the serial type. The most notable feature of the parallel-type of HEV

is that the engine and motor can output power simultaneously when the vehicle is

carrying a heavy-load or climbing. The two power sources then are combined

through the torque-integrated mechanism, generating significantly more power to

drive the vehicle. When the engine offers sufficient power to drive the vehicle, then

the alternator is also driven to charge the battery concurrently. The engine does not

operate in starting and low-speed driving, and thus the vehicle power source then

comes from the motor. Therefore, compared with the serial type, the parallel-type

hybrid-power system can apply two power sources efficiently, so the system can be

operated in various ways according to different driving requirements. Although the

mechanism of the parallel-type is considerably more complicated than that of the

serial type, all output efficiencies are better than for the internal-combustion engine

or the serial type. The outputs of internal-combustion engines, that employ the

current parallel-type hybrid-power system, are required to adjust their operation

range according to vehicle loading. Consequently, the engine of the parallel-type

cannot be set for its best operating range, meaning that its emission and thermalefficiency are worse than those of the serial type.

To overcome the disadvantage of current parallel-type hybrid-power systems, this

investigation considers a new parallel-type hybrid-power system. With its simple,

efficient, and reliable design, not only can the new system maintain an engine in its

optimum operating-range once it is started, but it can also combine two power

sources smoothly to comply with any driving requirement.

2. System design

Fig. 1 illustrates the complete system: it is equipped with two power sources,

namely an internal-combustion engine, and the motor. The middle conjunction

K. David Huang, S.-C. Tzeng / Applied Energy 79 (2004) 5164 53


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mechanism is a twin torque integrated mechanism as shown in the upper section of

Fig. 1. The first and second helical gears are installed onto the final power-output

axles, and one-way clutches are installed so that the two helical gears are kept rotating

in the same direction. Meanwhile, the third helical gear axle is placed on the final

power-output axle, and meshes with the first and second helical gears. Consequently,

when the first and second helical gears are driven by different input powers, the finalpower-output axle can be driven through the third helical gear. Gear-ratio analysis

reveals that the rpm of the final power-output axle of the third helical gear is half

those of the first and second helical gears. Therefore, when the final power-output

axle is required to output much more power and torque, this system drives the first

and second helical gears through both the internal-combustion engine and the electric

motor, so that the final power-output axle is offered more power and torque owing to

the third helical gear being driven first, while the second helical gears are driven

synchronously. When only a single power-source input is running, for example either

the engine or motor, this system can still smoothly output energy to the final power-

output axle, and does not lose energy owing to power source reversal.The optimum setting of the internal-combustion engine is when the engine

torque distribution device is applied (as displayed in the middle section of Fig. 1.).

Fig. 1. Design of the new parallel-type hybrid-electric-power system.



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This device can control the diameters of the first and second pulley sets to adjust

the output energy onto the final power-output axle to comply with the driving

requirements. Additionally, extra energy can be inputted into the alternator.

However, the total engine load is maintained in the torque output of the bestperformance operation point to ensure that constant optimal engine performance.

When the engine power is outputted to the final power-output axle, through the

first pulley set and pulley belt, the power-control module (PCM) operates to

engage the first clutch, while the second clutch is disengaged if the required load

of the final power-output axle is less than the consistent torque output of the

engine. The PCM then actuates the servomotor of the first and second pulley sets

to hold or loosen to adjust the diameter of these pulleys. This mechanism allows

surplus engine-power to be shifted to the alternator via the engine output axle,

first clutch, and second pulley belt, as well as the second pulley set, thus charging

the battery.In reverse, if the required load of the final power-output axle exceeds the con-

sistent torque output of the engine, the PCM actuates to disengage the first clutch

and the motor, and also adjusts the output torque of the motor via the torque-in-

tegrated mechanism through the third pulley belt.

3. System features

Based on the above statement, the features of the new parallel-type hybrid-elec-

tric-power system are described as follows:

3.1. Internal-combustion engine-performance is optimized

Fig. 2 presents the brake specific fuel consumption (BSFC) of the internal-com-

bustion engine. The horizontal-axle indicates the engine speed, the vertical-axle

represents the torque output, and the contour line stands for the BSFC. Fuel-con-

sumption requirements for each unit of energy output decrease with decreasing

distance to the contour-line center.

In the system, the engines energy-distribution mechanism applies with a stable

load for the internal-combustion engine. Furthermore, the system is designed to set

the engine speed and acceleration so as to minimize the fuel consumption (Point A,

Fig. 2). This approach enhances fuel efficiency and minimizes emissions such as HC

by reaching the physical limitations of the fuel. Also, the engine intake, exhaust,

injection, ignition, combustion, lubrication, cooling and noise can be designed to

achieve optimization. This approach can significantly reduce the development diffi-

culty, time taken, and costs for this internal-combustion engine.

3.2. Multi-selection for engine fuel

The internal-combustion engine used in this system has a fixed optimal perfor-

mance and consistent loading, so reducing the importance of fuel characteristics.



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Consequently, different fuels can be applied such as methanol or natural gas, which

have low energy densities and are relatively clean alternative-fuel sources. Moreover,

the engine is designed to have its optimal performance under a fixed load, so not

affecting the overall systems performance.

3.3. Stable and continuous speed transfer via the pulley set

The pulley set in the energy distribution mechanism is likely to employ a con-

tinuous variable transmission (CVT) [12]. The main feature of this pulley set is that it

involves incurring lower shocks, and, owing to the precise control of the servomotor,

the pulley set does not have the disadvantage of lack of control associated with the

roller-type pulley.

3.4. One-way clutch prevents reverse rotation

In the energy-integrated mechanism, a one-way clutch is installed at the junction

of the two power source output ends and the helical gears to prevent these two

powers from driving each other so causing energy loss and device damage.

3.5. Difference of rotating speed is balanced by the helical gear

The helical gear sets in the energy-integrated mechanism can integrate two dif-

ferent speed power sources into a larger power source, as well as offering speed re-duction. Consequently, the system does not require a complicated speed-reduction

mechanism to adjust the torque output via the first and third pulley belts.

TORQUE(N-m

)

A

RPM

Fig. 2. BSFC of the internal-combustion engine.



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4. Mathematical description of the behaviour of each component

In this work, the behaviours of the components of the parallel-type HEV are

described as follows:

4.1. Alternator [13]

Ialt fxalt;Ifld; Vsys 1

The relationship of exciting current and exciting voltage is

LflddIfld

dtRfldIfld Vfld 2

The relationship of both the alternator exciting-current and the rotating speed of the

alternator can be obtained from formulae (1) and (2). Fig. 3 displays the speed

torque character curve of the alternator that was applied in the system simulation.

4.2. Battery

The Modified Shepherd Model formula of the behaviour of the lead-sulfuric-acid

battery [14] is stated below

Vb Es iR ki Cln d QQ

Ridt

3

and

Q

Q Ridt

1

SOC; 4

where SOC represents the state-of-charge of the battery. Also, the SOC must be the

same as for the practical operating condition.

Fig. 3. Speedtorque character curve of the alternator applied in the system simulation.



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4.3. Motor

The system is applied using a brushless DC motor, which combines the advan-

tages of compact size and powerful output. This motor thus is suitable as a vehiclepower source. The torque formula of the brushless DC motor [13] is

Tm Kiim Imdx

dt5

Consequently, the motor output torque can be adjusted by changing the im value in

formula (5).

4.4. Energy-distribution mechanism

The energy-distribution mechanism can list the following three formulae for the

middle section of Fig. 1.

Te Tc1De

Dc1 Td; 6

Tg TdDd

Dg; 7

and

xo xe xm

2: 8

These formulae assume no friction, thermal energy loss or belt slipping. While the

engine output can be maintained at optimal torque performance, the torque of the

final power-output axle and alternator can be adjusted according to the variation of

the De and Dg diameter-ratio.

5. Analysis and evaluation of the systems kinetic simulation

The systems kinetic simulation involves three conditions. The electrical motor

provides the system power when the system is in its light-duty mode; the internal-

combustion engine offers system power in the medium-duty mode; and both the

motor and engine supply power to the system in the heavy-duty mode. The varia-

tions of the speed and power output of each power axle are simulated over time.

5.1. Electrical motor alone provides system power in the light-duty mode

When the internal-combustion engine was stopped, and an outer torque load,

10 sin 10t N m was applied in accordance with time change to the final power-output axle, only the electrical motor provided power to meet the systems needs.

The lower line in Fig. 4 denotes the speed of the final power-output axle, while the



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upper line represents the motor speed. Notably, the speed of the final power-output

axle is half that of the motor.

Fig. 5 displays the power output of both the final power-output axle and the

motor. From the simulation results, although the final power-output axle is sub-

jected to different torque loadings, its speed can still be kept stable. The energy

variation required by the final power-output axle can be satisfied by simply con-trolling the current and rotating speed of the motor. The simulation results also

demonstrate that the designed functions of the system comply with substantial re-

quirements of the torque-integrated mechanism. The power of the final output axle is

significantly higher than the motors output-power.

Fig. 5. Power output of each component in the light-duty mode.

Fig. 4. Correspondence of variations in the motor speed with the speed of the final power-output axle.



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5.2. Internal-combustion engine alone provides system power in the middle-duty mode

When the electrical motor stopped, the outer torque load, 20 sin 10t Nm, is

applied in accordance with the time change to the final power-output axle, and atthis point, the internal-combustion engine alone powers the system. A function is

designed in this system that can control the diameters of the first and the second

pulleys to adjust the range and freedom and thus permit simple and easy control.

However, if the diameter variation of the first pulley is sufficient, then the system

requirements can be satisfied by adjusting the diameter of the first pulley alone.

The system attempted to transfer most of the power from the engine to the final

power-output and axle is illustrated in Figs. 6 and 7. The torque is maintained at

20 sin 10tN m. The speed of the final power-output axle is thus very high, and theaxle receives much energy. However, the alternator receives low energy only and also

has a low speed. Based on the simulation result, although the final power-output axleis applied with different torque loadings, its speed and energy output remain stable.

During the initial stage, the speed and energy output of the engine were influenced by

different loads, but the output can be kept stable quickly by adjusting the engines

energy-distribution mechanism. Simulation results also demonstrate that the engines

energy-distribution mechanism can maintain the optimal engine-performance ac-

cording to different system output requirements. The control strategy used for the

system provides the most simple feedback-control. Thus, a significantly more

accurate control strategy can markedly reduce the feedback time of the engines

energy-distribution mechanism, so producing an engine that is quick running and

has optimum performance.

An attempt was made to transfer the power from both the engine and the motor

to the final power output axle, as is illustrated in Figs. 8 and 9. Meanwhile, the

Fig. 6. Speed of each component when most of the energy is transferred from the engine to the final

power-output axle in the medium-duty mode.



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torque was maintained at 20 sin 10tN m. From the two figures, it can be seen thatthe rotating speeds of the first helical gear and the alternator were similar. However,

the vibrations were reduced after 30 s, and eventually converted to the same rotating

speeds for the first helical gear and the alternator. Although the final power output

was applied with different torque loads, and vibration occurred during the initialstage, system stability can quickly be achieved. The distributions of engine speed and

energy output can be quickly stabilized using the engines energy-distribution

Fig. 8. Speed of each component when approximately 50% of the energy is transferred from the engine to

the final power-output axle in the medium-duty mode.

Fig. 7. Power output of each component when most of the energy is transferred from the engine to the

final power-output axle in the medium-duty mode.



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mechanism. Therefore, the engine energy-distribution mechanism can optimize en-

gine performance under such conditions.

5.3. Both motor and engine supply power to the system in the heavy-duty mode

The final power-output axle was applied with outer torque load, 20 sin 10tN m,in accordance with time change to the power output. Both the internal-combustion

Fig. 10. Speed of each component in the heavy-duty mode.

Fig. 9. Output of each power component when around 50% of the energy is transferred from the engine to

the final power-output axle in the medium-duty mode.



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engine and the electrical motor concurrently provide power to meet the systems

needs. The alternator was disengaged and did not generate power. Heavy-duty

starting initially caused vibrations and consequent instability. But, the motor quickly

reached a stable speed during the initial 5 s, as presented in Figs. 10 and 11.

6. Conclusions

The new parallel-type hybrid-electric-power system comprises an engines energy-

distribution and a torque-integrated mechanism (specifically including an engine, a

motor/alternator, a CVT device, and an PCM as well as a 3-helical gear set). To let

the engine achieve maximum thermo-efficiency with minimum emissions, the ser-

vomotors adjust the diameter size of the pulley to control the engine output for the

final power-output axle and the alternator. The system is applied with a stable

engine-load to maximize operating performance. The vehicle is driven by the motoralone in the light-duty mode. Meanwhile, in the medium-duty mode, power comes

from the engine, with extra energy being used for battery charging. Finally, in heavy-

duty mode, both the engine and motor together power the vehicle. The engine output

is fixed, but the motor output power can be controlled.

Based on a simulation analysis, the new system meets the final power-output axle

requirements, and the engine performance was maximized under different driving

conditions. The advantages of the system can be summarized as follows:

Engine performance can be optimized, removing the need for rapid acceleration

or deceleration. Consequently, engine wear is also reduced and the engines life

is prolonged. Additionally, since the engine operates at a specific speed and undermaximum fuel-economy, the air/fuel mixture can be completely burned, thereby

markedly reducing air pollution and saving energy.

Fig. 11. Power output of each component in the heavy-duty mode.



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The speed and load of the internal-combustion engine conform to single values.

Consequently, engine design and manufacture are simple and economic.

The engine outputs and distributes power to the alternator according to the im-

posed load conditions, thus charging the battery. The engine can be assisted by the motor for driving the final power-output axle,

thus obtaining more power and torque.

The motor and alternator can be integrated into a single unit, so reducing the sys-

tems weight and size, but can be separated to save the need for one set of clutches.

Both the engines energy-distribution mechanism and the torque-integrated mech-

anism are qualified with a speed reduction function, thereby saving the system

from needing to install additional complicated transmission equipment.

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a new parallel-type hybrid electric-vehicle

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