A multi-shaft, multi-layer motor has a stator coaxially disposed between inner
and outer rotors which are driven independently by a compound current. For cooling
stator coils, first through last branch coolant passages are arranged around the
axis. The upstream ends of the first through last branch passages are arranged
in sequence circumferentially along a distributing circumferential passage in a
direction away from a common introduction port for introducing the coolant into
the distributing circumferential passage, and the downstream ends of the first
through last branch passages are distributed in sequence circumferentially along
a collecting circumferential passage in a direction toward a common discharge port
for discharging the coolant from the collecting circumferential passage.
