Copper rotors boost hybrid truck efficiency by 40%

The US Army has begun testing tough 15.9-tonne trucks powered by a hybrid diesel-electric system which uses 105kW copper-rotor motors to drive each of four axles. The drive system is said to decrease emissions and increase fuel efficiency by up to 40%, as well as reducing noise levels and reducing lifecycle costs.

The trucks, built by Oshkosh, are powered by 400hp (300kW) diesel engines driving generators which, in turn, power the wheel motors directly, eliminating the need for torque converters, drive shafts and gearboxes. Braking energy is recovered regeneratively and stored in ultracapacitors.

As well as providing propulsion, the 335kW generators can produce electricity for field hospitals, command centres or airstrips. The hybrid technology could also be applied to civilian application such as rubbish trucks.

The 520V induction motors were built by Reliance Electric, which Rockwell Automation has sold recently to Baldor. "Using die-cast copper rotor technology was the only way we could meet the rigorous military requirements for, weight, size and performance," says Rich Schiferl, Reliance`s director of advanced technology.

Because copper is a better conductor than aluminium, copper rotors are more efficient than traditional aluminium rotors, allowing motors to be smaller and run cooler. "The result," says Schiferl, "is an induction motor with the highest power density possible today".

The technology for diecasting the copper rotors was developed by the Copper Development Association, in a programme sponsored by the US Army Research Laboratory.