The Oshkosh ProPulse series hybrid drive system (earlier post)—as applied in the military’s next-generation Heavy Expanded Mobility Tactical Truck HEMTT-A3 and in commercial vehicles—is using motors with die-cast copper rotors.
The rotors in the 140hp (104kW) electric motors represent a breakthrough in motor technology developed by the Copper Development Association (CDA) and delivered under the Copper-Based Casting Technology (C-BCT) program.
In the HEMTT-A3, the 480V motors are powered by a 400hp (298kW) diesel engine, making a series-hybrid drive system that can move the 35,000-pound vehicles and run a 335kW generator to operate field hospitals, command centers or airstrips.
Oshkosh says the new drives will lower life-cycle costs as well as lower interior and exterior noise profiles.
Reliance Electric Company, a division of Rockwell Automation, produced the electric drives. According to Richard Shiferl, director of advanced technology, using the die-cast copper rotor technology was the only way Reliance could meet the military requirements for weight, size and performance. Shiferl says the CDA-developed process for die-casting the rotor now enables cost-effective production of such rotors on a large scale for smaller motors (1- to 400-hp).
A copper rotor is more efficient than a traditional aluminum rotor, because copper is a better conductor of electricity and has lower resistance. Motors with copper rotors can be smaller and run cooler.
The result, Shiferl says, “is an induction motor with the highest power density possible today.”
The C-BCT research program is sponsored by the Army Research Laboratory and is tasked to develop, demonstrate and deploy applications of copper-based alloys to make significantly lighter, more efficient AC induction motors for use in defense and industrial systems.
CBC-T is a partnership comprising government, industry, and academic team members. The team includes motor manufactures Reliance Electric and Ramco Rotors; Vforge—an advanced casting and manufacturing facility; SatCon, a leader in analysis and testing for power electronic and electromechanical systems; and Worcester Polytechnic Institute (WPI) and Massachusetts Institute of Technology (MIT).