E L S E V I E R JSAE Review 18 (1997) 393- 399 O Development of test system for motor of hybrid electrical vehicle

Eiji Yamada, Yasutomo Kawabata EV Motor Studio Group, In[ormation Technology and Engineering Division, Toyota Motor Corporation, Teiho 7, Teiho-cho, Toyota-shi, Aichi, 47l Japan

Received 14 January 1997

Abstract

The motor units of hybrid electric vehicles (HEVs) have been developed with the aim of achieving good fuel economy and low emissions. We have developed a system for evaluating the performance of an HEV motor unit under various driving patterns. We review the function and performance of this system. © Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V.

1. Introduction

In recent years, there has been increasing concern about global environmental issues such as global warm- ing, urban air pollution, and acid rain caused by exhaust gases emitted through the combustion of fossil fuels, as well as the problem of the collapse in the balance of supply and demand for fossil fuels. In particular, these issues are focused on the automobile. For example, in the US, the state of California has started taking positive measures such as enacting state laws requiring auto- makers to sell zero-emission vehicles (ZEVs) and equiva- lent zero-emission vehicles (EZEVs). To address the ZEV requirements, automobile manufacturers and relevant parts manufacturers are making tremendous efforts to develop EVs (electrical vehicles) and related parts. How- ever, numerous issues concerning EVs remain unsolved, such as the problem of the cost performance of batteries, and the fact that drivable distance per charge is far less than the distance that can be covered by vehicles with conventional engines.

Meanwhile, to accommodate the EZEV requirements, automakers are energizing their development efforts to create a hybrid electrical vehicle (HEV) that aims for lower fuel consumption and lower pollution by combin- ing an internal combustion engine (ICE) and an electric motor.

Figure 1 shows the drivetrain model of a typical HEV system. Eliminating the clutch and the transmission of the conventional vehicle, the system comprises a

generator, a drive motor, and batteries. The system achieves a considerable increase in fuel economy by oper- ating the engine constantly in its high-efficiency range and by enabling the drive motor to regenerate electricity during braking.

The major issues that the HEV presents are the increase in vehicle weight by the replacement of the conventional transmission with motors, batteries, and a control device, and the life of the batteries, their high cost, and maintenance. To resolve these issues, the indi- vidual, detailed technical issues that are encountered in the process of achieving the target must be clearly identified.

The authors have developed a test system that provides the test condition settings and data measure- ment/analysis functions that are necessary for evaluat- ing the motor units of HEVs. This paper reports on the test system's principal functions and evaluation results.

2. Previous methods and problems in testing motor units

In our previous methods for testing motor, we meas- ured a motor's efficiency and heat generation at a given torque and speed at representative points (Fig. 2). The resultant data was used in simulations in which efficien- cies were estimated. The mode driving pattern is shown in Fig. 3. These methods included numerous error elements such as the transient charges in the energy

0389-4304/97/$17.00 1997 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved Pll S 0 3 8 9 - 4 3 0 4 ( 9 7 ) 0 0 0 3 8 -6 JSAE9735871

394 E. Yamada, X Kawabata / JSAE Review 18 (1997) 393-399

An additional problem was the difficulty of precisely measuring the vehicle data, such as the energy of generation, drive and battery charging/discharging, that are needed for optimizing the evaluation of the HEV control algorithm and the adjustment of control para- meters. It was also difficult to obtain data that could be replicated.

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Batteries

Fig. 1. HEV drivetrain model.

w v

• Measurement point

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• • • • • • • • •

I I I I I I I I i

Motor speed (rpm)

3. Functions needed to evaluate HEV motors

Table 1 summarizes the functions that are needed to evaluate HEV motors. In particular, the evaluation functions needed are those that can faithfully simulate a prescribed driving pattern, such as a mode driving pattern, so that measurements relating to the efficiency of the motors and to the charging/discharging of the batteries can be evaluated under essentially the same operating conditions as those found in actual driving situations.

Furthermore, functions to evaluate the responsiveness and stability of the motor control, which influence the vehicle's smooth acceleration and quiet operation, are also important. A function is also required to monitor how the control CPU executes control in relation to the dynamically changing accelerator command.

Fig. 2. Previous measurement points. 4. Configuration of the test system

transmission efficiency or in the charging/discharging efficiency of the batteries which were difficult to estimate. Therefore, it was difficult to carry out a realistic efficiency evaluation.

Figure 4 shows the configuration of the test system that we developed. The system consists of a mechanical portion, a motor control portion and a data measure- ment portion.

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Fig. 3. Mode driving pattern (LA4).

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E. Yamada, Y. Kawabata / JSAE Review 18 (1997) 393 399

Table 1 Functions required for evaluating HEV motor system

395

Evaluation item Description Function required for evaluation

Operation condition setting Measurement function

Component evaluation

t <

Entire motor system evaluation

~2

~z

Pattern driving evaluation

Durability and reliability evaluation

Evaluating the efficiency and heat generation of the generator and the drive motor

Evaluating the total efficiency and heat generation of the generator and drive motor and batteries combined

Evaluating the efficiency and heat generation when the motors are driven in accordance with a mode driving pattern

Evaluating the durability of the motor under excess load condi- tions such as sudden takeoffs and steep uphills

A function to individually operate the generator and the drive motor at a prescribed speed and torque

A function to simultaneously operate the generator and drive motor at a prescribed speed and torque

A function to generate acceleration torque in accordance with a speed pattern. A function to enable the engine-equivalent motor to create torque in accordance with

A function to generate a driving load that corresponds to impact torque and a continuous uphill driving condition

Each motor's voltage, amperage, wattage, motor speed, torque, and motor temperature (of coil, case, etc.)

In addition to the above, the battery charge/discharge amount (voltage, amperage, wattage)

A function to simultaneously sample the above data and the internal processing data of the HEV motor control CPU

Same as above

Engine equivalent

motor Sensor (~

Driving Generator Drive S/T motor S/T I pad motor

I Inv ~ Control

I I wattage data ] S/T Inv Bat Watt

Measurement & control computer

:Speed & torque :Inverter :Batteries :Wattmeter

Fig. 4. Test system configuration.

4.1. Mechanical portion

The mechanical portion of the test system consists of a motor (which creates a drive force equivalent to that of an engine) that is paired on a shared axis with a generator and a drive motor that shares an axis with a driving load motor. This configuration has been designed to minimize

any causes of measurement error, such as mechanical friction loss.

4.2. Motor control portion

Figure 5 is a block diagram of the motor control portion. The HEV control software to be evaluated is

396 E. Yamada, E Kawabata / JSAE Review 18 (1997) 393-399

Speed pattern sett ing

Vehicle Drive speed torque I

]oomandl Drive I co~and I torque ~1 I ca cu at on

HEV control

Accelerator command _ Engine equivalent

v motor control

Generator comand Generator

control

Drive motor

command Drive motor

control

P

Driving load motor

control

Fig. 5. Motor control block diagram.

z

03

O E

.>

g

kv3

I I I

Engine equivalent motor speed (rpm)

Fig. 6. Engine-equivalent motor control map.

Accelerator command

Engine equivalent motor torque command /

/

Time

Fig. 7. Engine torque rise approximation.

incorporated in the measurement control computer. Changes to the control program and adjustments of control parameters can be made easily from a terminal.

The torque of the engine-equivalent motor is con- trolled in accordance with the accelerator command that has been determined in the HEV control process. In order to simulate the engine behavior as faithfully as possible, an engine torque data map, which corres- ponds to the speed and throttle opening as shown in Fig. 6, is provided in advance and torque is generated in accordance with this map. As shown in Fig. 7, we simulated the engine torque rise-up characteristic according to the throttle opening angle at the first- order lag.

The speed control of the driving load motor is per- formed based on the acceleration pattern that is cal- culated from the driving conditions (such as the vehicle weight, air resistance, and slope angle) and from the torque of the driving motor.

Because all the motor control processing tasks are performed at 2 ms intervals at an identical timing, control delays are negligible. Thus, a high precision of synchronous control was achieved.

4.3. Data measurement portion

As described in Section 3, in order to precisely measure the efficiency of the motor units during a mode driving pattern, the problem is how the momentary efficiency in a transient state, such as during acceleration or deceler- ation, can be measured precisely. To solve this problem, a data measurement performance that is faster than the motor's transient response time is required. Figure 8 shows the items that are measured by the tester, with the relevant data being sampled at 2 ms intervals. Further- more, to check these data against control conditions, a data storage function is provided to simultaneously store sensor data and motor control CPU data as shown in Fig. 9.

E. Yarnada, Y. Kawabata /JSAE Review 18 (1997) 393-399 397

Unit efficiency ~

Measurement] item J

Engine equivalent --Engine equivalent -~--~ m°t°r torque

Generator / motor o u t p u t motorEnginespeedequivalent

--efficiency ~ r --Generator voltage

--Generator wattage l~|Generator current

Drive motor efficiency

Battery charge s B a t t e r y voltage /discharge wattage - LBattery current

Drive motor ~[---Drive motor voltage

--consumed wattage [-~Drive motor current

[---Drive motor torque ~ B r i v e motor output-- 1

L--Drive motor speed

Fig. 8. Measurement items required for efficiency evaluation.

[Control processing [ S [ Communication processing

I/0 processing Motor unit control processing ...........

Drive motor control ] processing

I [ Accelerator sensor input, I ........

IRe.solver dataj input I ............ ."

IGenerator & drive motor speed[ . . . . . . . .

[Data storage memory I

Clock data [i] ,- .......................... Accelerator sensor data

......................... Resolver data .......... Generator speed data

Drive motor speed data .................. Generator temperature data

Driving motor temperature da .......... Inverter temperature data

Motor torque command Current command value Current detection value Switching pulse data

Clock data [2] [ Accelerator sensor data Generator & drive motor [ ........ I----l----I ............

temperature detection ] [ [ [ Resolver data Generator speed data

I J-----l---J- Drive motor speed data Ilnverter temperature detection I . . . . . . . . . . . . . . . . . . . . . Generator temperature data

l Y / Driving motor temperature data [Dr ive mot.or torque I ~ " Inverter temperature data ]

Fig. 9. Data storage function.

Also , b e c a u s e the re a re m a n y cases in wh ich d e t a i l e d C P U d a t a will be r equ i red , the s a m p l e of d a t a a t the m o t o r c u r r e n t c o n t r o l cycle of 100 o r 500 ~ts i n t e rva l s has been m a d e poss ib le . T h e func t i ons d e s c r i b e d a b o v e have m a d e it p o s s i b l e to a n a l y z e m i n u t e l y the m e a s u r e m e n t d a t e of t r a n s i e n t s t a t es a l o n g wi th c o n t r o l c o m m a n d s .

5. Man-machine interface

The eva lua t ion of H E V m o t o r units forces a heavy load on the o p e r a t o r because of the n u m e r o u s types of da t a tha t are involved. This sect ion discusses the m a n - m a c h i n e inter- face function in which the ease of visibil i ty and the ease of ope ra t ion of the eva lua t ion sys tem are t aken in to account .

398 E. Yamada, Y. Kawabata / JSAE Review 18 (1997) 393 399

f " E]l- l l-IOperation monitor l IE]E]

Operation mode : Auto Operating status : Running Program No. : 123

00010 SPO 1000,100, 20 00020 TRQ 500, 200, 30

• "*00030 TIME 500 00040 SPO 1100,100, 20

0pe. mode Torque cnt. HEV Command val **8*. * ***8. *

SpeedIrDm] ****. * ****. *

Current[A] * , 8 , . * **88.*

Torque[Nml * , 8 , . * 8 , 8 8 . *

Power [Wl ****. * **88. *

cn t . sDd cnt .

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( a ) R e a l - t i m e mon i to r ( b ) S t o r e d d a t a m o n i t o r

Fig. 10. Measurement control monitor.

5.1. Real-time measurement and control condition display function

Figure 10(a) shows the display of the measurement and control conditions on the real-time monitor, in which the operating modes of the motors, command values, and detected values are easily monitored.

5.2. Control parameter setting function

Because this function makes it possible to easily set or modify control parameters (such as a motor's control gain, which is adjusted while actually running the motor) from a terminal, it can dramatically shorten the adjust- ment time.

5.3. Graphic measurement and control data display function

As shown in Fig. 10(b), the system is equipped with a function to graphically display the data that have been stored in the data storage memory upon completion of the operation, enabling the operator to easily analyze phenomena. Furthermore, because the measurement data uses a universal file management operating system (OS) format, it is also possible to directly utilize commer- cially available calculation software for editing the data or drawing various graphs.

5.4. Automatic operation program creation and editing function

The user program commands shown in Table 2 have been provided to enable the system to automatically operate and measure complex driving patterns such "as those of the city street driving mode. By giving the

Table 2 User program commands

Command Parameter Function

TRQ SPD REV ACC

TIME MES

(torque) (time constant) Torque comand setting (speed) (acceleration) Speed command setting (rev) (time constant) Engine rev comand setting (throttle angle) Throttle angle command

setting (time) Wait timer None Measurement timing setting

operation commands individually to each of the motors, and by recording data at the desired timings this function makes it possible to accurately carry out highly complex operations. In addition, because an editing software for ordinary computers can be used to create an automatic operation program, it is easy to create, for example an operation pattern that lasts a long time, provided that a vehicle speed pattern file is available. Furthermore, this function makes it possible be obtain data measurements that can be replicated with the least variations.

5.5 Abnormal measurement control data detection and display function

During an unmanned automatic operation, such as a lengthy durability test, the components could overheat

.or malfunction due to overloads. In such cases, this function records the location of the problem and related data. This is an effective function for identifying the causes of problems such as in the initial stages of proto- type development. In addition to sensor signals such as that of a temperature sensor, this function makes it

E. Yamada, Y. Kawabata / JSAE Review 18 (1997) 393-399 399

200C Motor speed IOOC (rpm)

Motor 101 torque (Nm)

Battery wattage (kW)

[20000 g6000 72000 48000 24000 0 T i me [msec]

Fig. l 1. Measurement results for LA4 mode driving.

possible to detect abnormal data conditions in the motor control CPU.

conditions given above. The energy of the engine output was calculated from the generator's speed and torque that are shown in the same figure, and the output energy of the drive motor was calculated in the same way. The efficiency of the HEV unit in the LA 4 mode can be calculated from these input/output ratios. Fur- thermore, because it is possible to simultaneously measure the batteries charging/discharging wattage data, by accumulating this data, it becomes possible to estimate the residual power of the batteries. Re- petitive charging/discharging cycles affect the useful life of the batteries. Because this measurement result enables the operator to easily understand how much current flows at any given moment, it is particularly useful for forecasting the life of the batteries.

6. Examples of HEV motor evaluations

6.1. Evaluation conditions

Operation and data measurements were carried out in the LA 4 mode, which is a representative city driving mode. This mode, which lasts approximately 26 min, covers a driving distance of 12 km. Using the user com- mands described earlier, this speed pattern was conver- ted into commands issued at l s intervals to create the program.

6.2 Measurement data

Figure 11 shows the measurement results for the initial 120s of data when the system is driven under the

7. Summary

The testing system we developed produced the follow- ing results: (1) It was possible to measure and analyze the energy

transmission conditions of motors for HEV use with a high degree of precision.

(2) It was possible to execute various driving patterns using simple programs and to collect data that can be simulated at a high level.

(3) It was possible to display the energy flow through the substantiality of monitoring functions.

Considering that environmental problems are be- coming more important, as discussed in the introduction, we would like to be able to contribute to the early development of a highly efficient hybrid electrical vehicle system.