The Case for Induction Motors with Die-cast Copper Rotors for High Efficiency Traction Motors

This paper considers the application of die-cast copper rotor induction motors in the drive system of parallel gas/electric hybrid vehicles and compares performance in a realistic driving scenario to that of a permanent magnet motor where efficiency is substantially reduced by PM drag loss. It is concluded from this analysis that the induction machine has a substantial advantage because it can be de-excited when it is not producing torque, eliminating no-load rotational magnetic and electrical loss.

Application of die-cast copper rotor traction motors in the hybrid drive system of the latest generation of large U.S. Army severe-duty trucks is then considered. Results of two different electric motor designs are presented, one with a cast aluminum rotor cage and one with a die-cast copper rotor cage. The copper die-cast rotor motor is shown to be 23% lighter and 30% smaller than the aluminum rotor machine.