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Contribution to the Special Issue on Advanced Technologies for New Modern Automobile Lifestyle
In the global auto industry today, major developed markets such as Japan, the U.S. and Europe are unlikely to
grow significantly, whereas sales volumes are rising, albeit not steadily, in the emerging markets of Brazil, Russia,
India, and China (BRICs). Automobiles are facing difficult times with challenges such as global warming, higher
crude oil prices, and traffic accidents. Against this backdrop, technological developments for better fuel consumption
and conservation of natural resources, as well as safety and security, are becoming increasingly important for the
whole auto industry. Mitsubishi Electric is working hard to develop and use state-of-the-art technologies and new
products.
Automobiles in the 21st century must be in harmony with the environment, people-friendly, and enjoyable.
Future development efforts must encompass diverse, sophisticated research and development based on not only
downsizing and light-weight design techniques and advanced electronics control techniques, but also
communications and information technologies. Mitsubishi Electric will use and integrate these to successfully develop
“advanced technologies for a new modern automobile lifestyle,” and thus, we will continue to contribute to the
development of society through creating a new automobile culture in the 21st century.
1. Introduction
To meet the demands of major automobile manufacturers
for high-performance products, we have developed
a new generation (9G) alternator with higher
output and efficiency without sacrificing quietness, by
using state-of-the-art manufacturing technologies for
improving the fill factor of the stator coil for which conventional
methods had reached their limit, This report
introduces technological aspects of the stator used for
the new generation (9G) alternator.
2. Trends of Alternators
Alternators for automobiles in general are driven
via belt by engines for AC generation, and the current
thus generated is converted into DC by built-in rectifiers
to provide electric power to the various electric loads on
the vehicle and also to recharge its battery. Recently,
electric loads on automobiles have increased further as
the number of electronics-based systems have increased
to meet demands related to the environment,
safety and security, and information and entertainment.
As for environmental needs, after the Kyoto Protocol,
which was adopted at the Third Session of the
Conference of the Parties to the United Nations
Framework Convention on Climate Change (COP3) in
1997, announced legally binding reduction targets for
greenhouse gas emissions for respective advanced
nations, controls on automobile fuel consumption have
been tightened worldwide in order to reduce CO2 emissions.
(1) In order to satisfy these regulations on improving
fuel economy, the electrical loads on automobiles,
directly or indirectly have rapidly increased. As a
result, technological requirements for alternators have
become much more complicated.
3. Challenges for Alternators
The recent technological challenges for alternators
are described below. The development themes listed
below are trade-offs to each other yet must be solved
simultaneously.
(1) High outputs for increased electrical loads
As mechanical engine accessories are increasingly
motorized to improve fuel economy, the output of alternators
will need to be increased by 30 amperes by the
year 2015.
(2) High power generation efficiency
Even if mechanical engine accessories are motorized,
its merits would be offset if alternator power generation efficiency were low, because driving torque will
increase for higher output.
(3) Compact and light-weight
The high outputs of alternators must be attained
without increasing the size of alternators, due to vehicle
requirement for weight reduction and limited underhood
space.
(4) Quietness
Quietness of each engine part is strongly required
in order to increase product value of the vehicle.
Therefore, power generation noise, which tends to
increase when alternator output is enhanced, must be
lowered.
4. Technological Features of New Generation
(9G) Alternator
4.1 Outline of new generation (9G) alternator
We have solved the above problems and completed
the development of the new generation (9G)
alternator (Fig. 1) by simultaneously improving the fill
factor of the stator coils and increasing both the cooling
performance and noise suppression required for increased
output levels. The technological features are
described below.
(1) Output current: Increased by 54% (against the
conventional model 6GA)
(2) Power generation efficiency: Increased by 12%
(against the conventional model 6GA)
(3) Electromagnetic noise: Reduced by 10 dB (against
the conventional model 6GA)
4.2 Improvement of stator fill factor
The factor that most influences the power genera-tion efficiency of an alternator is the copper loss of the
stator. With the conventional model 6GA series, the
copper loss accounts for approximately 67% of the total
loss under full load and temperature saturated condition.
One effective way to reduce the copper loss of a stator
is to increase the cross section area of the coil by making
the most of the available stator coil winding space,
that is to say, increasing coil fill factor (∑ copper wire
cross-section/stator coil winding space). For example,
Mitsubishi developed and commercially produced the
8GM alternator with higher fill factor by applying coil
forming only to the portion to be inside the slots of the
stator core, whereas no coil forming was conducted on
6GA stator.
However, the scope for improving the fill factor by
this method is limited since the copper wires in the
conventional models must be inserted axially into the
stator core in the manufacturing process.
Meanwhile in 1993, we developed a stator structure
called “Poki-Poki motor”, and this structure has
since been employed in various information devices,
factory automation equipment, electric home appliances,
automobile devices, and elevators. This original technology
of Mitsubishi can improve the fill factor without
sacrificing productivity. (2)
Under these circumstances, we have developed a
new stator manufacturing method that combines the
conventional 8GM technology (partial coil forming for
copper lines in the slot) with the Poki-Poki motor technology.
The stator cores, which are ring-shaped in
conventional models, are now flat bands. Furthermore,
band shaped strands of continuous copper wires, to
which coil forming is conducted, are inserted into the
opening of the slot (see Figs. 2 and 3). This method has dramatically improved the fill factor of the stator coil
(Fig. 4) and reduced the coil resistance remarkably by
reducing the height of the coil end.