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Machine Design

Hybrid Bus Steels the Show

A 40-ft-long city bus built with help from Oak Ridge National Laboratory, DoE, and two Michigan companies, has twice the mileage of conventional hybrid buses, say its developers.

The bus is powered solely by electrical motors. Its gas engine recharges the batteries. At the heart of the bus, however, is its use of Nitronic 30, a nitrogen-strengthened stainless steel that is stronger and stiffer than conventional steel. This means less material and weight for the bus chassis, and it should last significantly longer.

When the chassis does wear out, however, the steel is 100% recyclable. Although Nitronic costs more than ordinary steel, its strength and reduced weight translate into improvements Hybrid bus steels the show in other components such as smaller tires and lighter brakes, batteries, and motors. Overall, engineers halved the weight of the bus compared to traditional buses. The metal did pose a problem with laser welding, so one of the developers, Autokinetics, Rochester, Mich., is using resistance spot welding in most places and tungsten inert-gas welding for the rest. Production versions of the bus should be delivered next year.

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