Electric motor having fluid circulation system and methods for cooling an electric motor

An electric motor comprising:

• a housing;
• a stator mounted in the housing;
• a rotor mounted in the housing for rotation relative to the stator about a central axis, the rotor having first and second opposite ends and a plurality of fluid flow passages extending through the rotor between the first and second ends;
• an electro-magnetic drive system operatively connected to the rotor for driving rotation of the rotor relative to the stator;
• and
• a fluid circulation system in fluid communication with the fluid flow passages for providing fluid flow from the first end of the rotor to the second end of the rotor through at least one of the fluid flow passages and fluid flow from the second end of the rotor to the first end of the rotor through at least one other of the fluid flow passages, wherein the fluid circulation system comprises at least one impeller mounted in the housing for rotation relative to the stator, the impeller having a peripheral edge margin, an inlet positioned radially inward from the peripheral edge margin and in alignment with an opening at the end of at least one of the fluid flow passages so the impeller inlet is positioned to receive fluid as it exits the opening, and an outlet positioned radially outward from the inlet, the impeller being adapted to produce at least some of said fluid flow by propelling said fluid radially outward from the inlet to the outlet when the impeller is rotated relative to the stator.