Cooling jacket with coolant mass balancing for electric motors

A permanent magnet electric motor, comprising:

• a shaft extending along a longitudinal axis;
• a rotor mounted on the shaft, wherein the rotor is rotatable concomitantly with the shaft about the longitudinal axis, the rotor defines an innermost rotor edge, and the innermost rotor edge is sized to receive the shaft;
• a stator electromagnetically coupled to the rotor, wherein stator is disposed around the rotor and remains stationary relative to the rotor;
• wherein the shaft defines a jacket configured to receive a coolant, the jacket is disposed about the longitudinal axis, the jacket is elongated in a first direction, and the first direction is parallel to the longitudinal axis;
• and
• wherein the rotor defines a plurality of longitudinal channels, each of the plurality of longitudinal channel is elongated along the first direction, and each of the plurality of longitudinal channels is in fluid communication with the jacket to allow fluid flow between the jacket and the plurality of the longitudinal channels;
• and
• wherein the rotor defines a plurality of interconnection channels, each of the plurality of interconnection channels directly interconnects an adjacent pair of the plurality of longitudinal channels to direct the coolant from one of the plurality of longitudinal channels to another one of the plurality of the longitudinal channels, the jacket is entirely disposed inside the shaft, each of the plurality of longitudinal channels is entirely disposed inside the rotor, and each of the plurality of interconnection channels is entirely disposed inside the rotor;
• and
• wherein the permanent magnet electric motor includes a plurality of pole pieces, each of the plurality of longitudinal channels has a first lateral end and a second lateral end opposite the first lateral end, each of the plurality of longitudinal channels is shaped as an arc extending from the first lateral end to the second lateral end, each of the plurality of longitudinal channels has a central angle, the central angle of each of the plurality of longitudinal channels is subtended by the arc extending from the first lateral end to the second lateral end, and the central angle of each of the plurality of longitudinal channels is less than
• 360
• ⁢
• °
• M
• ×
• 0.95
• degrees, and M is a number of polar pieces.