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[FONT="]GM Gives First Look at 2-Mode Hybrid SUVs [/FONT]
[FONT="]By Mike Sutton[/FONT]
[FONT="]WardsAuto.com, [/FONT][FONT="]May 3, 2007[/FONT]
[FONT="]MILFORD[/FONT][FONT="], [/FONT][FONT="]MI[/FONT][FONT="] General Motors Corp. super-sizes its hybrid-electric vehicle push as it gives an introductory look behind the wheel of the upcoming 08 Chevrolet Tahoe and GMC Yukon hybrids the industrys first ambassadors of HEV technology to feature 8-passenger seating and fullsize utility.[/FONT]
[FONT="]Part of the auto makers recent effort to show its progress on alternative powertrain development, the new hybrids offer up much of the same form, function and feel of conventional SUVs, accompanied by the eerie silence of all-electric acceleration that portends fuel savings of up to 25%.[/FONT]
[FONT="]Considerable fine-tuning remains before the trucks are ready for their November Job One date, but preliminary drives around GMs proving grounds here reveal the highly capable vehicles feature much more than simply one of the most advanced transmissions currently on the market.[/FONT]
[FONT="]We took a complete vehicle perspective, Mark Cieslak, vehicle chief engineer-Chevrolet Tahoe Hybrid, says, noting GMs efforts to dial in the handling and feel of the new SUVs to differentiate them from the volume models.[/FONT]
[FONT="]We had to strike a balance between hybrid and truck (features), he says.[/FONT]
[FONT="]Most of the specifics and ratings for the trucks, which will be the first vehicles to feature the 2-mode hybrid transmission GM developed in conjunction with DaimlerChrysler AG and BMW AG, still are being finalized, GM officials say.[/FONT]
[FONT="]However, they assert both vehicles easily will achieve the promised fuel economy improvement without sacrificing utility.[/FONT]
[FONT="]Offered in both rear- and 4-wheel-drive layouts, the Tahoe and [/FONT][FONT="]Yukon[/FONT][FONT="] hybrids will be powered mainly by a 6.0L OHV V-8 featuring start/stop capability, late-intake-valve closing technology (for improved efficiency) and 300-plus hp, says Cieslak.[/FONT]
[FONT="]GMs Active Fuel Management (AFM) cylinder deactivation system is featured, as well, and has been tuned to switch the engine to 4-cyl. mode more frequently and for longer durations than the standard models 5.3L V-8.[/FONT]
[FONT="]A pair of electric motors in the 2-mode transmission add 221 lb.-ft. (300 Nm) of low-end torque and can propel the hybrid SUVs to about 25 mph (40 km/h) on electric power alone. A 300-volt nickel-metal hydride battery (packaged neatly beneath the second row of seats), along with the requisite electronic controls and hybrid computers under the hood, complete the drivetrain.[/FONT]
[FONT="]The first mode of the 2-mode system is for low speed and light loads, where the electric motors, the engine, or any combination of the two, can provide propulsion, the auto maker says.[/FONT]
[FONT="]The second mode works primarily at higher speeds, reducing fuel consumption with AFM while providing the V-8 with an electric boost for improved passing and towing performance. The transmission also can lock out the electric motors at high speeds, giving the engine a direct mechanical link to the wheels and improving efficiency, says Scott Miller, lead development engineer-fullsize hybrid trucks.[/FONT]
[FONT="]Although limited drive time prohibited a full evaluation, the Tahoe hybrid proves to be a smooth-runner, with nearly seamless transitions between hybrid modes and 4- and 8-cyl. Operation.[/FONT]
[FONT="]Acceleration is brisk (accompanied by an un-hybrid-like V-8 growl), with driving dynamics close to those of the standard Tahoe and Yukon, albeit slightly unique due to the hybrids 42-volt electric power steering, low-rolling-resistance tires and special suspension tuning required by the lower center of gravity of the 2-mode transmission and battery.[/FONT]
[FONT="]Stopping performance from the regenerative braking system, which can recapture the vehicles kinetic energy from up to 100 mph (161 km/h), feels more than adequate without the heightened pedal sensitivity found on other HEVs.[/FONT]
[FONT="]Transparency is further aided by the hybrid SUVs still-cavernous cargo capacities and 6,200-lb. (2,812-kg) maximum tow ratings (6,000 lbs. [2,722 kg] for 4WD models), the most of any hybrid and about 2,000 lbs. (907 kg) less than that of conventional 4WD Tahoes and Yukons.[/FONT]
[FONT="]Cieslak says the NiMH battery pack is designed to last the life of the vehicle, with its state-of-charge kept between 40%-75% for optimum performance and longevity.[/FONT]
[FONT="]([/FONT][FONT="]Battery[/FONT][FONT="]) safety is first and foremost, he adds, noting GM spent considerable time conferring with emergency responders about safety features, emergency shut-off protocols and the location of high-voltage electrical components.[/FONT]
[FONT="]Other mechanical features unique to the new hybrids include an electric air-conditioning compressor and a lower 3.08:1 axle ratio for better highway cruising.[/FONT]
[FONT="]Despite GMs efforts in developing the 2-mode system, the powertrain encompasses only one leg of the auto makers 3-pillar strategy for the Tahoe and Yukon Hybrids.[/FONT]
[FONT="]Improved aerodynamics and reduced mass (to compensate for the greater weight of the hybrid components) were key to optimizing efficiency and are evident in each vehicles revised appearance.[/FONT]
[FONT="]Aluminum components (hood, liftgate, bumper and prop shafts) replace steel to keep curb weights in check with the standard vehicles. Unique 18-in. alloy wheels further reduce weight and rolling resistance, while also serving to reduce aerodynamic drag, GM says.[/FONT]
[FONT="]Also helping to achieve the new models lower 0.34-drag coefficient vs. the standard vehicles 0.36 Cd are new front and rear fascias, running boards, wheel-arch fairings, lower front air dam and revised rear air deflector, spoiler and D-pillars.[/FONT]
[FONT="]Special badging further signifies the vehicles HEV status.[/FONT]
[FONT="]Inside is standard Tahoe and Yukon fare, with the exception of thinner, low-mass front seats (which significantly improve rear-seat legroom), a 110-volt power outlet in the rear cargo bay and slightly less cargo room due to the battery pack under the second row of seats.[/FONT]
[FONT="]To inform the driver of the hybrid systems efficiency, the auto maker fitted a simple power gauge in the upper-left corner of the instrument cluster. The meter resembles the top half of a clock face and shows when the system is operating at its greatest efficiency.[/FONT]
[FONT="](Keeping the needle) between [/FONT][FONT="]10 oclock[/FONT][FONT="] and [/FONT][FONT="]2 oclock[/FONT][FONT="] is optimal (for efficiency), with straight up and down at [/FONT][FONT="]12 oclock[/FONT][FONT="] being ideal, Miller says of the meters ability to display efficiency in real time.[/FONT]
[FONT="]A power-flow diagram also is integrated into one of the navigation screen menus and shows how, and in which direction, energy is being transferred between the engine, batteries, transmission and wheels much like the system Toyota Motor Corp. pioneered on its Prius hybrid sedan.[/FONT]
[FONT="]With the formal launch of vehicle assembly in [/FONT][FONT="]Arlington[/FONT][FONT="], [/FONT][FONT="]TX[/FONT][FONT="], and 2-mode transmission production in [/FONT][FONT="]Baltimore[/FONT][FONT="], [/FONT][FONT="]MD[/FONT][FONT="], still more than six months away, GM declines to give details about output and rollout of the new hybrids.[/FONT]
[FONT="]However, Mark Clawson, marketing manager-Chevrolet Tahoe/Suburban/Avalanche, says the auto maker will build as many as it can sell.[/FONT]
[FONT="]We have not missed one mark since this program started, Cieslak adds, noting he and his team intend to fulfill Chairman and CEO Rick Wagoners recent promise that 2-mode hybrid SUVs will be on dealer lots by the end of the year.[/FONT]