Development of Bogie for UserFriendly, Extra Low Floor, LightR a i l Ve h i cl e ( L RV ) U s i n g
Independent Wheel Systemand Next Generation LRVMITSUAKI HOSHI* 1

YOSHIKI OOKUBO* 1

NOBUYUKI MURAKAMI* 1

TOKUHIRO ARAI* 1

HIROYUKI KONO* 2

HIROYASU ARUGA* 2

The next generation, extra low floor, light rail vehicle (LRV) is increasingly drawing attention as a user friendly
and comfortable urban traffic system. Mitsubishi Heavy Industries, Ltd. (MHI) has developed a bogie for the LRV bybuilding the first domestic independent wheel system, and an extra low floor LRV, called the Green Mover Max,equipped with this bogie is now operating without trouble for Hiroshima Electric Railway Co., Ltd. In the course of
the development of the bogie, both the electric powered bogie and the motor-less bogie were the subject of exhaustive
design discussions and a thorough technical verification was carried out so that differentiation from the vehicles offoreign manufacturers and customer needs were attained. As a result, a vehicle with a high percentage of completion was able to be realized. Further, we have already started work on the development of the next generation LRV
which is equipped with secondary batteries and does not use overhead lines and on the development of a vehicle
suitable for urban service operation, aiming to further expand the market for the 100% extra low floor LRV.

The Green Mover Max was developed as a joint projectof three companies, Mitsubishi Heavy Industries, Ltd.
(MHI), Kinki Sharyo Co., Ltd., and Toyo Denki Seizo K.K.
with Hiroshima Electric Railway Co., Ltd. acting as anadvisor in the field of operation service. The four companies mustered their efforts in the development andmanufacture of the LRV (light rail vehicle) in harmony
with the Japanese landscape and Japanese society using Japanese technology.
Three points were listed in the development concept:(1) ultimate, (2) user friendly, and (3) urban. The initial letters of these points were used to name the project
the U3 Project. In the U3 project, MHI took the bogie,
brakes and inner and outer riggings, Kinki Sharyo fo-

cused on design, car body, articulation and the driver'scabin, and Toyo Denki Seizo took responsibility for electrical parts and control and drive units.
The new generation urban traffic system LRT (lightrail transit) is drawing attention as a symbolic city transport system that is comfortable and friendly not only tothe environment but also to people. In particular, thehigh performance, stylish, barrier-free, and extra low
floor tram, well beyond existing tram concepts, has already been introduced in Europe and North America, andits effectiveness has been highly evaluated.
However, European manufacturers are ahead of Japanese ones in terms of the technology for independent
wheel bogies, so that the 100% extra low floor LRV introduced to Japan was limited to vehicles manufactured
by foreign manufacturers or partially manufactured bydomestic makers by adopting foreign technology.
This gave rise to operability and maintenance problems, and the development of a domestic vehicle for use
in Japan was an immediate need and was long awaited.
The first 100% extra low floor LRV developed with Japanese technology is 30 m long and has a 5 car, 3 bogie
configuration. MHI was involved in the project for thedevelopment, design, manufacturing and verification of
the bogies based on the achievement of "Technical Research Institute for Extra-Low-Floor Bogie" establishedby the Land, Infrastructure, and Transportation Minist r y, a n d h a s r e a l i z e d a w i d e r a n g e o f t r a v e l i n g
performance such as barrier-free charter, low noise, lowvibration, low speed, and high speed.

*1 Plant and Transportation Systems Engineering & Construction Center*2 Hiroshima Research & Development Center, Technical Headquarters

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 44 No. 2 (Jul. 2007)

1. Introduction
The first domestically-made independent wheel type
100% extra low floor LRV started service operation on
the streets of Hiroshima on March 30, 2005. The vehicle, called the Green Mover Max, became a reality five
years after it was conceived, after overcoming many problems over that time. T h i s p a p e r d e s c r i b e s t h edevelopment of its key component, the independent
wheel type bogie and also an outline of the vehicle. It
also describes the development of the next generation
LRV which is expected to show increasing growth infuture.

2. Concept of development

1Elastic wheels were adopted to reduce noise and vibration. As for brakes, three types (electric, hydraulic,and rail) are used to allow speed changes with fewer
shocks to bring the car to a safe stop under all conditions.
As the bogie is one of the most important parts of thevehicle, the bogie frame, its most crucial part, was subject to strength testing on a step-by-step basis including
Figs. 3 and 4 ), fatigue
FEM analysis, static load testing (Figs.
testing, and actual load stress measurement, in that order. In particular, the static load testing and the fatigue
testing were conducted by using the prototype bogie
frame, whose results were reflected in the mass production design. In the static load testing, from stressmeasurement at about 280 points on the motorized bogie
frame and about 250 points on the motor-less bogie, noproblem was identified regarding strength. In the fatigue testing, each bogie frame was repeatedly loaded
continuously for about one month and 3 million times intotal, and it was confirmed from magnetic particle testing that there were no cracks or permanent deformations.
Following the fatigue tests, the bogie frame was cut andexamined, and no problem was identified.

3. Development of technology for independent wheelbogie
The key to the development of the 100% extra lowfloor LRV was the bogie with an independent wheel system. Normally, the left and right wheels are connectedwith a shaft, which determines the floor height. Therefore, an independent wheel system without shafts wasFig
adopted for our bogie. The electric-powered bogie (FigFig.. 1 )has its motor and drive unit installed outside of thewheels. The adoption of the new bogie system allowed afloor height of 330 mm (passage section 360 mm), enabling step-less boarding into the car. In addition, thebogie structure was made compact to allow an 880 mm
wide aisle (located immediately above the bogie) of 50
mm wider than the LRV manufactured by foreign manuFig. 2
facturers. Moreover, the motor-less bogie (Fig.
2) withno motor installed was specially designed to drasticallyincrease the width of the aisle to 1,120 mm thus contributing to the smooth movement of passengers boarding
and alighting while ensuring a wider and unobstructed
view from the passenger compartment.

Fig. 3 Static load test of motorized bogie frameFig. 1 View of motorized bogie

Fig. 4 Static load test of motor-less bogie frameFig. 2 View of motor-less bogie

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 44 No. 2 (Jul. 2007)

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When testing the vehicle, MHI built a special 900 mlong test rail track at the Plant and Transportation System Engineering & Construction Center in the company'sWada-Oki Plant. A thorough verification of the technology was carried out at this test track to realize a vehicleFig. 5
with outstanding performance (Fig.
5).
We verified the acceleration and deceleration performance and safe running performance on the test rail
track by measuring the car body behavior and thestrength of the bogie and car body parts. We also measured the ride quality and the noise inside and outside
the car to verify the ride comfort. The independent wheelbogie behavior was observed by a camera to verify running stability and measure the wheel load and lateralforce to verify that it would not derail, and confirmed
there were no problems. We established a method of
measuring the wheel load and lateral load and have applied for a patent.

The car body is made of steel for its safety, stiffness
and maintainability which are required for vehicles traveling on the road. Thanks to the thorough measurestaken to reduce weight, a car with a strong and lightbody has been realized. In the 5 car, 3 bogie configuration, the central cars are floating, and the articulations
connecting each car body ensure high reliability, while
being light in weight, compact in size and needing littlemaintenance.
The vehicle was designed to have a soft, roundish,front end to provide a fresh feeling and friendly flavor tothe passengers as the new domestic extra-low-floor vehicle.
The interior design was based on the concept of a comfortable space, and maple motifs, the symbol of
Hiroshima, were used on the inside and outside of thecar body to give the local tone required of a tram car.

5. Development of next generation LRV

4. General specifications for vehicle

An outline of the Green Mover Max and the development of the bogie have been described above. In March
2007 the Green Mover Max with a train formation ofseven vehicles was introduced in the city of Hiroshima
and the tram car became widely recognized and loved byits citizens.
We believe that the domestic manufacture of the100% extra low floor LRV has triggered the diffusion ofthe LRV to various cities in Japan and we have alreadystarted the development of the next generation LRV,
aiming to further expand sales of the 100% extra low
floor LRV.

Table 1 shows the general specifications of the Green
Mover Max. The vehicle main body is equipped with aTrain Information System (TIS), and the monitor is fitted to the driver's control platform. Thus the control
platform was made compact, with centralized switches,
due to the use of a monitor. Driving and maintenancesupport is possible by using maintenance and problem
indicators to reduce the workload of the driver who isresponsible for both operating the vehicle and processing passengers.
The vehicle control system employs an individual
motor control system using a VVVF inverter unit withhigh energy performance, where the difference in rotational speed of the left and right wheels due to the
100 kW motor installed outside the driving bogie (4units per 1 train) and the unbalanced torque due tothe wheel radius are absorbed to ensure outstanding
running performance.

Table 1 General specifications of vehicle
Configuration

5 car, 3 bogie, extra-low-floor vehicle

Number of passengers
Weight(t)33.9Size(mm)

L 30 000 x W 2 450 x H 3 450

Floor level, low floor rate(mm)

360 (doors 330),
extra-low-floor rate 100%

Electric mode(mm)DC 600Track gauge

(mm)

1 435

Maximum speed(km/h)

60(km/h/s)

3.5

Normal deceleration(km/h/s)
Emergency deceleration (km/h/s)

4.8
6.0

AccelerationFig. 5 Traveling test on test rail track

149 (56 seated)

Main control unit

2 level IGBT-VVVF inverter,
Regenerative and generation
blending brake system

Brake unit

Mechanical (hydraulic) brake system,
regenerative and generation brake,safety brake (track brake),deadman's handle

Main motor

Three phase squirrel cage induction
motor 100kW x 4 units

Bogie

Shaftless, independent right and left
wheel rotation type bogie

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 44 No. 2 (Jul. 2007)

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Fig. 6 Test vehicle not using overhead line

Fig. 7 Car interiorThe first development is a hybrid LRV which does notuse overhead lines and employs lithium ion secondarybatteries. Due to its merits including a better cityscapealong the route by eliminating the overhead lines andan increase in energy recovery rate attained by preventing energy regeneration loss, it is already being studied
by various research institutes and vehicle manufacturers. In Europe, the commercial operation of a tramequipped with secondary batteries and not using overhead lines has already started in limited sections.
MHI has conducted various running tests on its inhouse test tracks utilizing used vehicles supplied byFig. 6
Hiroshima Electric Railway (Fig.
6) to study systems,
running performance, and battery life.
The second development is a system with a smaller
number of cars per train than the Green Mover Max.
While the Green Mover Max is 30 m long and has a 5car, 3 bogie configuration, a new system having 18 mlong with a 3 car, 2 bogie configuration is now developed, aiming at a vehicle suitable for urban service
operation.
Thirdly, aggressive efforts are under way for technological development and next generation concept designfocusing on the design of the inside and outside vehicles.
As trams have a role as a symbol of a city, stylish design
is desired. MHI is making the most of our company de-signers in discussing designs suitable for the next generation LRV.
Figure 7 is an illustration of the new concept vehicle
for the next generation LRV.

Mitsuaki Hoshi

Yoshiki Ookubo

6. Conclusion
The development of the bogie for the first domestic a l l y m a d e , 1 0 0 % e x t r a l o w f l o o r L RV a n d t h edevelopment of the next generation LRV have been described above. The development involved a number of
new elements such as the independent wheel type bogie
not used in conventional vehicles, therefore technicalverification in various fields was required. As a resultof these efforts, a domestically manufactured model wasrealized and MHI has been able to contribute to the development of the LRV market in Japan. MHI willcontinuously upgrade our technology and promote thenext generation LRV, while hoping for the increased introduction of domestically manufactured low floor
vehicles in various areas.
Finally, we would like to extend our gratitude toHiroshima Electric Railway Co., Ltd., the Technical Research Institute for Low Floor LRV Bogie, Kinki SharyoCo., Ltd., and Toyo Denki Seizo K.K. for their valuable
cooperation and guidance in the development of the first
domestically made, low floor LRV.

Nobuyuki Murakami

Tokuhiro Arai

Hiroyuki Kono

Hiroyasu Aruga

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 44 No. 2 (Jul. 2007)4