［ FL Driving System ］

Development of New Motor andController Models for Battery
Forklift Trucks
Keywords

Takeo Kuwabara,
Hitoshi Fujihara,
Ryuichi Nakano

High efﬁciency, Compact design and lightening, Environment-friendly, Developing country support

Abstract

For more than half a century, we have supplied motors and controllers thatare the motor drive units for battery forklift trucks. These machines are key devices for the forklift trucks industry.
Until now, most of the world forklift truck market consisted of Japan, North
America, and European countries. Asian markets in China and other Asian countries are rapidly growing. In order to supply high-performance and inexpensive
motor drive products to these new markets and establish a solid market position
there, we are promoting the development of motors and controllers.

1 Preface
After the worldwide recession caused by theglobal ﬁnancial crisis in 2008, the market sales offorklift trucks drastically declined. Afterward, there
was a sharp market recovery mainly driven by markets in China and other newly developing countries.
According to a record of worldwide unit sales
achievements in 2015, the number of forklift trucksales reached 1,064,000 units; this is the highest
achievement since the start of worldwide statistics.
Fig. 1 shows the worldwide transition of sales in theforklift trucks sector. In 2015, there was recession ofbusiness transactions in China and also shrinkage
of market in newly developing countries. Despite
this, the requirements of mechanization in logistic
systems are anticipated to expand in developing
countries due to possible rises of labor costs inChina. Steady growth of markets is expected inrising nations.
Regarding worldwide vehicle model sales from2011 to 2015, business in total sales volume ofengine type forklift trucks. It became evident thatbattery type forklift trucks became an overall market
driver. The reasons for such business trends werethat there was a rise in environmental consciousness and that the reduction of lifecycle cost issought after through market penetration of motorized forklift trucks. Generally speaking, the initialcost is high for a battery forklift truck, but runningcost is low. Overall lifecycle cost can consequently
be low.

Million units
1201101,063,029 1,064,224 units
988,781
941,808 943,724

100
90
80

740,690
438,127 427,788

70

60 565,748

475,231454,084

344,23450
233,84840

259,986 261,792

30

310,852
281,141

341,674 units

174,296

61,45291,424 100,252 98,801

100,379 110,838 units

71,315

154,755
176,56796.152 117,241 152,271 153,892009

10Engine counter
type
Battery walkie
type207,900

2010430,231 units

111213

14

181,481 units

Battery narrowisle type
Battery countertype

15(Cited from worldwide survey)

Source: “Industrial Vehicles” (March 2016) [Japan Industrial Vehicles Association]

Fig. 1Worldwide Transition of Sales in the Forklift
Trucks Sector

Worldwide transition of sales in the forklift trucks sector is shown,with graphs classiﬁed for each model.

For classiﬁcation by world region, the rate ofelectric forklift in leading countries is alreadyexceeding 50%: 55% in Japan, 64% in North
America, and 82% in EU countries. On the one
hand, the rate of electric forklift is 30% in China,
which is a comparatively low ﬁgure. In the past ﬁve
years, however, the rate rose from 20% to 30%. In
MEIDEN REVIEW Series No.172 2018 No.131

the future, even in developing countries including
China, the rate of electric forklift is estimated torise rapidly.
We are developing a motor drive unit applicable to battery forklift trucks because the market forthese machines is expected to expand substantially.
The new models are developed to assure high quality and satisfactory functions that can be acceptedin leading countries and be inexpensively priced indeveloping countries. This paper introduces therecently released frameless motors and the AC450
Series that is under development.

2 Motor for a Forklift Truck
For electric vehicles, PM motors are generally
used for its compact design, light weight, and highefﬁciency. Even for the same application to vehicles, induction motors tend to be adopted for forklift
trucks because of the low price. This is because
there is a large difference in characteristics between
two types of vehicles. Since the forklift truck isequipped with a counterweight for the purpose of
the prevention of falling down during cargo handlingof heavy articles, the light weight of the driving
motor is not signiﬁcantly noticed. In addition, unlike
the case of motors for electric vehicles, restrictions
for the motor mounting space are not very rigorous.
As such, requests for compact design are rare.
Even a motor in a sufﬁciently large size can be
adopted and performance of high efﬁciency can beattained even by an induction motor.
For comparison of motors for forklift trucks withthose for electric vehicles, there is a great difference in speciﬁcations of the protection construction.
Compared with electric vehicles, battery voltage is
low for forklift trucks. Accordingly, it is constructedto prevent contact with the live part. It is, therefore,
unnecessary to establish a completely waterproofstructure. An enclosure structure called the “opentype” is generally adopted. The enclosure may nothave an opening greater than 12 mm in diameter.

promoted an optimal design according to the application.

2.2 Optimal Design Specialized for Application to Forklift Trucks
The forklift truck is equipped with two types ofmotors, one for traveling and the other for cargohandling. There are also two types of vehicles,
counter type and reach type. The performancerequired for the motor is respectively different
among the traveling, cargo handling, counter type,and reach types. Drawing on our track records andexperiences for more than 50 years, we designed
the most suitable motors applicable to forklift trucksof traveling, cargo handling, counter, and reachtypes. We supply such vehicles ranging from 1t to 3t
classes. Fig. 2 shows the minimum and maximum
models of our frameless motors. We realized theuse of common parts by changing the stator length
to realize a wide range of characteristics and uniﬁed
the stator diameter.
The most important factor needed in designing
the motors for forklift trucks is to secure a wide
range of operations from low to high motor speed
and light to heavy cargo handling, and assure ahigh efﬁciency in a regular operational range where
the forklift truck is operated most frequently. Such a
motor design approach results in the reduction ofvehicle battery consumption and the extension of
per-charge traveling distance (traveling distancepossible by one-time charging). For a framelessinduction motor where construction is simple, andthe number of parts is small, the rate of stator cost
occupying the overall motor cost is extremely high.

Stator

2.1 Frameless Motor

The “open type” motor to be applied to a forklift
truck is designed so that the stator coils are chilled
by direct wind through vanes on both sides of therotor. Due to the structure, it is unnecessary to dispel motor heat generation through the motor frame.
To achieve further cost competitiveness with forklift
truck motors, we adopted a frameless structure and32

MEIDEN REVIEW Series No.172 2018 No.1(a) Minimum modelFig. 2(b) Maximum model

Minimum and Maximum Models of FramelessMotors

Minimum and maximum models of frameless motors are shown.
Applicable models: 1t class counter/reach type, 2t class counter/reach type, 3t class counter/reach type
Application: Traveling and cargo handlingMagnetic flux density

Thin yokes part

HighThick yokes partDC drive
Output density (kW/L)Low

8

AC drive

DC100

6Result of Stator Magnetic Flux Density
Distribution Analysis

Compared with a part of the stator where yokes are thick, themagnetic ﬂux density is high in the part where yokes are thin. We
determined the most optimal thickness without causing magneticsaturation.

For this reason, reduction of the required stator
materials is the most important challenge for motor
designing.
To ﬁnd a suitable solution for the aforementioned, we researched the most optimal stator androtor shapes making full use of electromagnetic
ﬁeld analysis. As a result, high-efﬁciency motors
suitable for application to forklift trucks have beendeveloped. Fig. 3 shows the result of stator magnetic ﬂux density distribution analysis.

Fig. 4AC300
6.8kW/L

0.8kW/L
2000

Fig. 3

AC100
AC200

42AC450
New
model

AC400
Presentproduct4.1kW/L
1.4kW/L

2.6kW/L

200520102015year

Transition of Controller Output Density

Transition of improvement of output density is shown for controllers produced formerly.

Fig. 5AC450S

An image of controller AC450S is shown.

3 Controller for Forklift Trucks
Regarding the controller for battery type forklift
trucks, high efﬁciencies and a high level of compact
design are essential. Fig. 4 shows the transition ofcontroller output density for the controller for battery
type forklift trucks. The initial AC drive available
around Y2000 offered an output density of 0.8kW/L.
In the case of a recent AC450 machine, the densityvalue has been raised to 6.8kW/L and efﬁciency
has also been improved.
Regarding essential the model conﬁguration ofthe AC450 Series that has been developed newly,
there are two types like the present AC400 Series:
Type S for a small capacity (“AC450S” hereafter)
and Type L for a large capacity (“AC450L” hereafter). For the respective capacities, battery voltagesof 48V system and 72V system are available. Fig. 5shows an external appearance of the AC450S andFig. 6 shows that of the AC450L.

Fig. 6AC450L

An image of controller AC450L is shown.

semiconductor. In addition, the switching system
has been reviewed to reduce further switchinglosses. By taking such actions, inverter efﬁciencies
have been improved, from a maximum of 96% for
the AC400L to a maximum of 97.5% (calculatedvalue) for the AC450L.

3.1 High Efﬁciency

3.2 High Output Density

Since a new type of Metal-Oxide-Semiconductor
Field Effect Transistor (MOSFET) is adopted, it ispossible to reduce the ON-resistance of the power

Due to the adoption of new large-capacity
MOSFETs and reduction of losses by reviewing theswitching system, we reduced the number of power
MEIDEN REVIEW Series No.172 2018 No.133

semiconductors used. In addition, we also reduced
the number of control connectors used by optimizing the number of I/O points in digital I/O andanalog input circuits. As a result, areas of the powerand control circuit boards were greatly reduced for
the AC450 Series, and the controller mounting
space was decreased to about 70% compared withthe previous model.

3.3 Protection Degree
The protection degree for the AC400 is Level
IP54. In consideration of use under more rigorous
conditions, however, the protection construction
was reviewed. The resin cover and the connector
housing are joined into an integral body to eliminate
any joint parts. To prevent possible intrusion ofwater due to hydraulic pressure through a clearance
between the resin cover and the base, formerlyadopted use of gaskets was modiﬁed for hermetic
sealing by using an adhesive agent. By taking theabove measures, we realized the protection degreeof IP65.

34

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4 Postscript
By switching to electric forklift trucks, we expect
a reduction of CO2 emission. As a top supplier ofmotors and controllers of forklift trucks in Japan, weare promoting the development of products withimproved performance characteristics for battery
type forklift trucks based on more than half a century of our track record and experience.
Compared with our conventional products, theframeless motors developed for this time and theAC450 Series under development are our latest
products that demonstrate a remarkable compact
design and high efﬁciencies. We intend to contribute to the reduction of environmental impact throughthe supply of these products.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.