Boat U.S. - May 2008 - (Page 36) HHH Hitching to Photos by Michel Istaphanous For nearly two decades, boaters, campers and other outdoor enthusiasts have looked to full-sized SUVs as multi-purpose vehicles that could transport their entire family during the week and also tow their boat or camper on the weekends. Their popularity has waned in recent years as higher gas prices have made them less appealing. But now, the availability of gas-electric hybrid versions of full-sized SUVs such as the Chevy Tahoe Hybrid could once again make the SUV a practical choice for families whose weekends include trips into the great outdoors. “We call this the ‘No excuse hybrid’”, says Mark Cieslak, the chief engineer for fullsized trucks at General Motors Corp. and a BoatU.S. member. “It was very important for us to keep full-size truck performance and capabilities. I’m a boater and I know how important it is to be able to tow a boat.” GM spent five years developing and testing their new, “two-mode” hybrid system for the Chevy Tahoe and GMC Yukon. The resulting vehicles are packed with innovations that go beyond the drive train and include changes to many systems as well as both the interior and exterior of the SUVs. 36 BoatU.S. Magazine May 2008 The hybrid versions of these SUVs get 50% better fuel economy during city driving compared with their gas-only siblings. The eight-passenger Tahoe Hybrid mates a 300-volt battery system to two electric motors and a six-liter V8 specially tuned for increased fuel efficiency. The Tahoe Hybrid is rated to tow 6,200 pounds for the 2WD version. The 4WD version tows 6,000 pounds. We drove the hybrid Tahoe for nearly two weeks, making daily commutes to BoatU.S. national headquarters in Alexandria, VA, and took it out to the shores of the Chesapeake Bay for towing tests. The differences and refinements made to the hybrid version of the Tahoe, as compared to the gasonly models, stand out in daily driving. First, the hybrid Tahoe accelerates so smoothly, particularly with gentle pressure on the accelerator, that you can scarcely feel the Electronic Variable Transmission (EVT) shifting. This new transmission incorporates two 60-kW electric motors into the drive train along with three planetary gear systems and four hydraulic clutches. The addition of the electric motors gives the transmission an infinite selection of gear ratios to comple- ment a more traditional four-speed automatic. The transmission can act like a normal automatic when conditions warrant, such as at high speeds on the highway, or it can use electric power only in low-speed, high-torque demands. A computer-controlled Hybrid Optimization System automatically selects the most efficient way to use the power coming from either the electric motors or the V8, or a combination of both. The second mode of the hybrid system incorporates GM’s existing “displacement on demand technology,” now called Active Fuel Management. This allows the V8 engine to “turn off” four cylinders during periods of low power demand, such as when cruising at a steady speed or coasting downhill. With the electric motors supplying additional power to the wheels, the system can keep the gas engine in four-cylinder mode longer than is possible in a gas-only version. From a stop, the electric motors do all the work, unless you really mash the gas pedal. Typically the V8 doesn’t turn over until around 20 mph, but you can hit 30 mph on electric power alone. Driving on electric power only makes it seem like you H H H H H H H H H H H
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