Renault Introduces Two B30 Light Commercial Vehicles
UK Approves Construction of 1.3GW of Offshore Wind Power Capacity

Oshkosh ProPulse Hybrid Drive System Uses Copper Motor Rotor Technology

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).




This reminds me of the way AC Propulsion designed their induction motors. They used solid copper bars instead of windings.


The standard induction motor has used a squirrel cage for quite some time.  Copper vs. aluminum is really the only change here.

I suppose the next advance will be when carbon nanotube conductors start to get cheap; they conduct better than copper. ;-)

Harvey D.

Quadrangular copper conductors can be shaped to reduce blank (waste) spaces and maximize conductivity with very little extra cost. Large power generators make use of that approach.

Coating optimized conductors with carbon nanotube material would further increase conductivity. Does anybody know what would be the extra cost?

How close to 100% efficiency can you get from an electric motor/generator?


An external rotor motor, made with standard materials can get about 92%. It would be interesting to hear if anyone is attempting to make them with this approach.

My idea for all-wheel drives uses the external rotor.

Things have been quiet about this lately. Don't know if Mitsubishi and Seimens have given it up or come to realize that it's a giant leap forward for electric drive.


These guys had some interesting motors.



AC motors with rotor bars have been around for many, many years. Including the copper rotor bars. The induction motor has been superior to the ICE ever since it was first invented in the 1900's. Its was batteries that were inferior to gasoline that held back the EV, but now that battery technology has progressed significantly you are starting to hear more about these motors. If you want to see some induction motors then have a look around your house and if you work in an industrial plant then about 90% of the motors are all induction.


The cast copper rotor actually reduces peak output significantly by reducing pullout torque when compared to a more conventional semi-enclosed rotor slot design using copper bars. This becomes significant at high speeds when trying to achieve a specified power output. This made the design of the Oshkosh motor that much more of a challenge for a certain consultant hired to figure out how to actually design the motor.

Copper rotors were successfully cast in the mid 70's by Reliance Electric, but never went into production until someone outside the company developed the process and used it to cast rotors for Reliance (Rockwell) 30 years later. You have to be in the motor business to understand this type of thing.

The comments to this entry are closed.