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By John Voelcker

http://www.spectrum.ieee.org/images/...carf3small.jpg
2008 GMC Yukon Two-Mode Hybrid
A hybrid heavy hauler
GMC’s Yukon is a strapping 2500 kilograms unloaded. In other words, it ain’t no Prius.
And yet, Yukons fitted with GM’s new two‑mode hybrid system use essentially the same principle to reduce energy consumption as Toyota’s celebrity-friendly it-car. An electric drive can power the vehicle, by itself or together with the combustion engine. The battery that powers the motor is charged by the engine and also through regenerative braking.
Being as big as it is, though, the Yukon outdoes other hybrids by having two electric drive motors, each capable of 40 kilowatts sustained. A single motor with enough torque to move such a mass couldn’t be accommodated inside the truck. So GM’s engineers, who led a design effort that later included engineers from DaimlerChrysler and BMW as well, used a pair of electric motors—a system GM had previously put into production for its hybrid transit buses. As in the Prius, the Yukon’s motors are actually motor/generators that can produce torque when fed with electricity—or vice versa.
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