Copper Motor Rotors Boost Performance of Army Trucks

January 4, 2007


Four 140-hp electric motors power the latest generation of U.S. Army severe-duty trucks. The AC induction motors use die-cast copper rotors on each of four axles. The new rotors are a major breakthrough in motor technology developed by the Copper Development Association (CDA) and delivered under the Copper-Based Casting Technology (C-BCT) program. The 520-V motors are powered by a 400-hp diesel engine, making a hybrid drive system that can move the 35,000-pound vehicles and run a 335-kW generator to operate field hospitals, command centers or airstrips.

Called ProPulse® by Oshkosh Truck Corporation, the innovative hybrid electric drive system is said to decrease emissions and increase fuel economy by as much as 40 percent. Aside from several configurations for the military's 8x8 HEMTT-A3 (Heavy Expanded Mobility Tactical Truck) series, the drive system is also configured for commercial use with refuse vehicles. Oshkosh says the new drives will lower life-cycle costs as well as lower interior and exterior noise profiles.

The electric motors were manufactured by Reliance Electric. Rich Schiferl, Reliance's director of advanced technology, said, "Using the die-cast copper rotor technology was the only way we could meet the rigorous military requirements for weight, size and performance." He says the CDA-developed process for die-casting the rotor now enables cost-effective production of such rotors on a large scale for motors for this type of application.

Schiferl explains it's always been known that a copper rotor is more efficient than a traditional aluminum rotor, because copper is a better conductor of electricity and has lower resistance. Because of that, motors with copper rotors can be smaller and run cooler." The result, Schiferl 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. Chuck Stark, C-BCT program manager said, "These copper-rotor motors improve the efficiency of the vehicle drive system and result in a more fault tolerant vehicle, better equipped for mission completion."