Hybrid Power Swap

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Taking the electric motors out of the drivetrain delivers two benefits. When moving heavy loads at a steady clip, the electric motors are inefficient because they actually represent a drag on the engine. Taking the electric motors completely offline in such scenarios makes the car's overall operation more efficient. The more significant benefit, says Grewe, comes in packaging the transmission. By swapping out the motors under high-power operation, the alliance partners get by with smaller motors. The result is a hybrid transmission that is no bigger than a conventional transmission. "We took clutches out and we put electric motors in, and with that we were able to get it to package in a similar volume," says Grewe. That should simplify the design and assembly changes required to offer hybrid as an option on existing vehicles.

Rich Schaum, former chief engineer at Chrysler and the incoming president of the Warrendale, PA-based Society of Automotive Engineers, says GM has a "very robust" patent position for the two-mode transmission and that is allowing the alliance partners to go their own way with a better technology. "The architecture of the dual-mode technology being pursued by GM, DaimlerChrysler, and BMW is superior to what's currently on the streets from other manufacturers," says Schaum.

Of course, warns Schaum, one should not assume that Toyota will stand still. Toyota hybrid engineer Hermance won't commit on whether Toyota would consider a two-mode system. For one thing, says Hermance, it's not clear whether drivers actually cruise enough to deliver a significant benefit. "The question becomes, what fraction of the total drive is in that steady-state regime? Until we see actual cycle test data for their system, it's hard to evaluate what kind of an improvement they may or may not have made," says Hermance.

Nevertheless, Hermance calls the two-mode concept a "good idea" in principle, especially in full-size trucks--a market segment where Toyota has yet to apply its hybrid technology.

GM will debut the two-mode late next year in the full-size Chevy Tahoe SUV, and DaimlerChrysler will follow in early 2008 with a hybrid version of the equally beefy Dodge Durango. Both manufacturers claim the two-mode system and more-efficient engines will make their SUVs as much as 25 percent less fuel-thirsty than their nonhybrid counterparts--performance that could be worth big bucks if it can reverse the recent sharp decline in high-profit margin SUVs brought on by high prices at the pumps.