tionary coil windings wrapped around iron cores and
arranged around the armature, Figure 38-7B. The motor-
generator housing holds the stator assembly in place
around the armature. It also fastens the motor-generator
to the rear of the engine, inside the transmission/
transaxle, or in the rear drive axle assembly, Figure 38-7C.
When the motor-generator is assembled, Figure 38-7D,
the armature spins in close proximity to the stator
assembly.
Motor-Generator as a Motor
A hybrid motor-generator is usually a synchronous,
ac permanent magnet, brushless motor-generator design.
There are no electrical windings in the armature and no
electrical connections to it. The permanent magnet
design improves reliability over dc motors that have
armature windings, which can fail.
The term synchronous means the rotation of the
armature is synchronized, or timed, with the 3-phase
alternating current entering the stator windings. The
3-phase ac sets up a 3-wave magnetic field that moves
around the stator, pushing and pulling the armature
around with it. The 3-phase ac is delivered to the
motor-generator through three cables. Each of the
cables carries a single phase, or waveform, of alter-
nating current. Each phase is staggered in time from the
others.
Modern hybrids use 3-phase ac power for the same
reason that industrial applications and factories have used
this form of electrical energy for decades. A 3-phase ac
motor can produce more horsepower and torque than an
equal-size dc motor while consuming less electrical
energy. When the 3-phase ac motor-generator is func-
tioning as a generator, it can produce more electricity
than a comparable dc generator.
The motor-generator in Figure 38-8 uses 18 coil
windings (electromagnets) and iron cores organized
around the armature. Since the outer surface of the arma-
ture is close to the stator windings, the permanent mag-
netic fields and the electromagnetic fields can repel or
attract each other with great force.
As the ac voltage cycles from positive to negative in
the stator coils, it generates alternating north and south
magnetic poles in the motor-generator electromagnets.
Current is passed through each set of coil windings in a
circular pattern so that the armature is rotated with the
movement of the magnetic fields.
Each armature pole is “pushed” around by magnetic
repulsion. The adjacent armature pole is “pulled” by
magnetic attraction. With multiple poles (permanent
magnets) on the armature and multiple electromagnets in
the stator, the motor-generator can generate high torque
to propel the vehicle. Refer to Figure 38-9.
Basically, motor-generator torque is controlled by
current flow, while speed is controlled by the frequency
and phase shift of the alternating current waves.
Motor-Generator as a Generator
The motor-generator acts as a generator during
regenerative braking and when being driven by the
internal combustion engine to recharge the HV battery
pack. When the motor-generator is functioning as a
generator, the internal combustion engine or drive train
components spin the motor-generator’s permanent
magnet armature. The magnetic field produced by the
permanent magnets cuts across and through the stationary
Chapter 38 Hybrid Drive System Operation and Repair 701
Figure 38-8. This motor-generator is for a parallel hybrid drive
system. Note the segmented steel armature, which is located
inside the stator. (Honda)
High-voltage,
high-current
connector
Segmented
armature with
permanent
magnets