GM first debuted its two-mode hybrid system on transit buses in 2003 and today, there are more than 550 buses powered by this technology running in 42 cities in the U.S. and Canada.

Buses powered by the hybrid system typically experience fuel economy improvements greater than 20 percent and as much as 55 percent on some routes. It's estimated that a bus powered by GM's two-mode hybrid system saves an estimated 1,460 gallons of fuel per year. For the current fleet on the road today, it is estimated that more than 730,500 gallons of fuel are saved annually. Other benefits the system provides include reductions of certain emissions by up to 90 percent; superior torque; better acceleration than conventional diesel buses; and operation sound levels equal to passenger cars.

How it Works

Two sources of power to move the bus: an internal combustion engine and a hybrid transmission consisting of two 100 kW motors and a 600-volt, nickel metal hydride battery pack. The engine is coupled to an electronically variable transmission that provides an infinite range of gear ratios to drive the wheels. The Control Module and Power Electronics DPIM (Dual Power Inverter Module) provide precise controls for the system and its electric motors.

When the bus accelerates from a stop, the battery-powered electric motors assist the diesel engine for powerful acceleration. As the vehicle comes up to speed, a diesel engine provides the power to maintain the speed once the vehicle is under way. At the same time, the engine-driven generator charges the batteries, giving the vehicle self-sustaining mobility. In addition, the vehicle's regenerative braking captures energy normally lost as brake heat and returns it to the vehicle's energy storage system (the battery) for reuse.

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