High Torque Density Propulsion Motors

The size and weight of electric drive components are primary considerations in their successful integration into various Naval platforms. Direct drive propulsion motors are of particular importance due to their requirement of developing full power at low shaft speed. As such, their torque density (ft‐lbs of motor torque developed per lb of motor mass) is the key defining metric. Torque density projections of existing and future technology machines require thorough understanding of the constituent mass elements that comprise an electrical machine and their specific scaling relationships. Such models can be used to compare machine performance across a wide range of objective torques and technologies. Liquid‐cooled permanent magnet motors typify current state of the art propulsion motors. The torque density of such motors at ∼ 2Mftlbs is roughly 8 ft‐lbs/lb which represents a twofold increase over the prior generation of air‐cooled induction motors at ∼ 4 ft‐lbs/lb. The next generation of propulsion motors technology, advanced PM motors and high temperature superconductivity motors, are targeting >16 ft‐lbs/lb as achievable goals.