Two-Mode Hybrid (p. 2)

September 28, 2010

The transmission is ultra smooth. I couldn't feel it shifting, and judging by the tach, it seemed to go to the highest ratio possible in any situation. The engine seldom got above 2,000 rpm and often loafed along at 1,200 to 1,400.

The tach needle drops as vehicle speed slows and soon the needle rests on Auto Stop, indicating the engine has shut down because it's not needed. That label on the tach is useful to someone not familiar with the truck's hybrid operation because the engine simply stopping might otherwise be disconcerting. (“Hey! It's not running! What'd I do?!”) The engine shuts off when the truck is coming to a stop or coasting slowly; when it does you can faintly feel it, but you can't always hear it, and probably never would if you're playing the radio or yakking on a cell phone.

Electric-only operation is even quieter, but you can hear a descending whine as the truck slows and the system regenerates while you brake, capturing energy, converting it to volts and amps that it sends to the batteries. And there's an ascending whine from the electric motors as you move away from a stop. Pedestrians, especially the blind who protect themselves by listening for engines, might not hear this, so toot the horn if they make a move toward the truck's nose.

And don't poke around blindly under the hood or you might penetrate an orange-clad cable that's carrying 300 volts. That's what the motors run on and so does the air conditioning compressor, so you stay comfy at red lights while the engine naps. Rescuers and tow-truck drivers are being trained to watch for bright-orange cables and connectors in hybrids so they don't fry themselves.

Electric propulsion is what sets the 2-Mode Hybrid apart from GM's “mild” hybrid system used in several cars and in the now-discontinued Silverado-Sierra Hybrid pickups. The mild system's generator does not help to move those vehicles; it only captures braking energy that's then used to run accessories while the engine shuts off during stops and at low speeds. Otherwise the engines in those vehicles do all the work, and the mild hybrid system at best saves only about 10 percent in fuel.

The 2-Mode Hybrid operates like other “parallel” hybrids in that it'll go on electric or gasoline power or both. Incorporating the motors inside the transmission sets it apart from the Eaton electric hybrid systems now available in several medium-duty trucks and vans (but not from GM or Dodge), where a single motor-generator is placed outside the transmission.

Like them, the 2-Mode Hybrid is expensive to buy, even though federal tax credits might mitigate the financial sting. Sticker prices on fancy Tahoe and Yukon Hybrid SUVs are above $50,000 per, and the recently announced Cadillac Escalade is even higher. But a Chevy or GMC Hybrid pickup truck should cost somewhat less, as the system will be available as a stand-alone option on base-trim pickups as well as better-trimmed versions.

One has to wonder how much it will cost to repair or rebuild the complex Electronically Variable Transmission, and who'll be able to do it; buying an extended warranty might be a good idea. But for now the 2-Mode Hybrid is a technological marvel that saves some serious gasoline money. That's hard to ignore, even if the hybrid's hard to hear.