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Allison Transmission Unveils 'Home-Grown' Hybrid Vehicle Technology

February 25, 2002

The Allison Transmission Division of General Motors showcased its “home-grown” hybrid technology in a new bus. Allison’s hybrid technology, called Allison Electric Drives EP System, uses a parallel hybrid system to power a 40-passenger city bus. According to Allison, the system is viable for use in buses and medium- to heavy-duty trucks. Distantly related in design to that used in a diesel-electric locomotive, the system uses electric motors to drive the vehicle. Battery power is used to accelerate from rest, and the system switches to a diesel generator to provide electric power while cruising. The generator also charges the batteries. Electric motors provide maximum torque from zero rpm, so with its electric motors, the bus accelerates faster than a traditional diesel-powered bus. Diesel engines burn fuel most efficiently when they run at steady rpm, so the diesel engine operates when the vehicle is cruising at a steady speed. The result is a bus that delivers about 60 percent better fuel economy than a conventional vehicle, and has a 90 percent lower particulate output and 50 percent lower nitrogen oxide (NOx) emissions. In addition, the electric motors deliver 50 percent greater acceleration than a conventional diesel powertrain.
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