HONDA Insight - Manual (Page 58)

58
Design
The IMA motor is a permanent-magnet type, brushless DC motor.
The only moving part in this type of motor, the rotor, consists of nothing
but permanent magnets. The electromagnets are located around the perimeter
of the stator. There are several key attributes of this type of motor:
• Because the electromagnets are located around the perimeter,
the electromagnets can be cooled by conduction to the motor
casing, requiring no airflow inside the motor for cooling. This in
turn means that the motor's internals can be entirely enclosed
and protected from dirt or other foreign matter.
• With no windings on the rotor, they are not subjected to
centrifugal forces.
• Commutation (switching current between different sets of electromagnets to produce rotation)
is not accomplished by any sort of physical switching, such as brushes that wear out. Instead,
this switching is accomplished by an electronic controller - the Motor Drive Module. This
allows electronic control over torque and magnet field slip angle, which makes it easy to
operate the motor as a generator.
• Inefficiencies caused by brush material resistance, and brush drag friction are eliminated.
The IMA motor's disc shaped design allows it to fit into the same space that would otherwise have been
occupied by a fourth cylinder. The thin, relatively large diameter shape means that it produces a great deal
or torque.