03-01-2013, 04:46 PM
Examination of an Interior Permanent Magnet Type Axial Gap Motor
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INTRODUCTION
RECENTLY, public concern about environmental issues
such as global climate change has grown and various
technologies have been considered. Within this context, improving
the energy use efficiency of automobiles is required in
order to limit emissions of carbon dioxide gas. Hybrid electric
vehicle (HEV) technologies, which contribute to reducing
global warming, have thus attracted increased attention, and
HEV market penetration has been increasing rapidly. For
further advancement of HEV dissemination, electric traction
motors with sophisticated performance, such as small size, high
power density, and high efficiency, are necessary.
References [1]–[4] examined axial gap motors with feasibility
for high torque density performance. Our research group
therefore focuses on axial gap motors. However, it is difficult
for general axial gap motors, such as surface permanent magnet
(SPM)-type or inset-type motors, to realize a wide speed range
of constant output [5], a requirement for HEV driving systems.
The IPM-type axial gap motor was therefore proposed as an
axial flux interior permanent magnet (AFIPM) motor in [6]
and [7]. This motor can realize a wide speed range of constant
output, but it is difficult for this motor to generate reluctance
torque effectively. Additionally, no previous studies have attempted
to apply this motor to the actual motor size of an HEV
motor, for example, a 60 kW motor.
STRUCTURE OF THE PROPOSED IPM-TYPE AXIAL GAP MOTOR
Table I shows comparison and target values for the proposed
motor. Comparison values are based on the newest radial gaptype
60 kW motor mounted in the third-generation Toyota Prius,
a commercialized HEV [8]. The size of the comparison motor
was measured in our laboratory. The target values of the proposed
motor were set with a goal of 400 Nm output, about twice
the torque of the same-sized comparison motor. The maximum
output power of the proposed motor was the same as that of the
60 kW motor. With an increase in torque, the torque density
increased and the rated speed decreased. In this study, the maximum
current density was set to 20 Arms/mm .
CONCLUSION
This paper proposed an axial gap motor with a novel IPMtype
rotor structure. The proposed motor has leakage poles that
pierce the rotor in the axial direction. Since -axis flux can easily
Fig. 8. Relationship between unbalanced electromagnetic force and rotor eccentricity.
pass through the leakage poles in the axial direction, the proposed
motor can make effective use of reluctance torque.
As a target for comparison, we selected the newest radial
gap-type 60 kW motor mounted in the Toyota Prius, a commercialized
HEV. The target values of the proposed motor were set
with a goal of outputting 400 Nm, about twice the torque of the
same-sized comparison motor.
Analysis results indicated that the proposed motor had a maximum
average torque of 403.8 Nm. Compared with the comparison
motor, the proposed motor could achieve a torque density
of more than 1.95 times higher while retaining the same size.
Moreover, we confirmed that the proposed motor had sufficient
durability against irreversible demagnetization of the permanent
magnets and the stress caused by rotating the rotor.We conclude
that the proposed motor has sufficient performance for practical
use.