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GM Introduces More Hybrid Models
There’s a lot going on with hybrids these days. In January at the Detroit Auto show, Toyota announced their new third-generation Prius, and Honda re-introduced their hybrid, the 2010 Insight. But for a lot of drivers, these four-cylinder sedans just won’t cut it.
For people who need more room or power, GM is now building full-size hybrid SUVs and trucks and I’ve just driven three different full-size models; the blinged-out Cadillac Escalade SUV and two pickup trucks, the GMC Sierra, and the Chevy Silverado.
Now normally, if one mentions the model names Escalade or Sierra or Silverado, people automatically think “gas hog.” But these full-size trucks deliver better city mileage than a sub-compact Scion tC coupe with a four-cylinder engine.
These three new GMs all use the same hybrid powertrain that has come from years of development that first bore fruit in 2008 with the Chevrolet Tahoe and GMC Yukon hybrid SUVs. These were the first production vehicles to feature what GM calls an electrically-variable transmission (EVT). Within a case that looks like a traditional automatic gearbox, GM (along with partners Mercedes-Benz, BMW, and Chrysler) managed to package two motor/generators and four fixed gear ratios.
When acting as motors, the EVT helps propel the these hybrids. As the SUV coasts or slows, the EVT goes into generator mode, transforming kinetic energy into electricity via regenerative braking. Countless hours of seat time went toward blending the EVT’s regen braking with the physical braking systems, and the transitions between the two are indistinguishable. The recaptured energy goes from the EVT for chemical storage in a 300-pound, 300-Volt nickel-metal hydride battery pack that resides under the second row seats.
Ahead of the EVT and in place of the a standard non-hybrid engines (a 403-horsepower 6.2 liter V-8 in the Escalade and a range of V-6 and V-8 engines in the pickups), there is a lightweight 6.0-liter all-aluminum V-8. To enhance efficiency, the engine utilizes cylinder deactivation (so it can run in V-4 mode) and variable valve timing (that enables the late closing of the intake valves to reduce pumping losses). The 6.0-liter produces 332 horsepower and 367 lb-ft of torque. Acceleration remains strong thanks to the immediate torque of the electric motors (184 lb-ft each) and a high-performance axle ratio.
A control unit manages all of the above elements using software that is much improved over the initial batch of GMC and Chevrolet SUVs. The result is that the new 2009 hybrids run strongly and smoothly. About all that’s lost compared to the non-hybrid, and this is particular to the Escalade, is the intoxicating exhaust note of the 6.2-liter that comes standard in the Cadillac.
The sensation of driving the hybrids is a bit odd if one expects a traditional experience. In easy-going driving, the engine RPM and exhaust note don’t correspond linearly to accele...