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2008 Chevy Tahoe Two-Mode Hybrid Preview

GM Looks to Hybrid Technology to Reinvigorate Big SUV Sales 

Patience will be required, but soon enough Chevy will deliver a full-size SUV capable of pint-size SUV fuel economy; and isnt that a contradiction in terms? Perhaps so, but definitely a most welcome contradiction thanks to the bowtie brands claim of a 25 percent boost in the composite fuel efficiency of a V8-powered Tahoe when GMs two-mode full hybrid technology and its advanced Active Fuel Management technology are both applied.

GMs Active Fuel Management (AFM) technology, known previously as Displacement on Demand (DoD), deactivates four of the engines eight cylinders when the need for output is low, resulting in less fuel burned,
Chevys Tahoe Hybrid, rolling onto GMs stage at the North American International Auto Show in Detroit. (Photo: Justin Couture, American Auto Press)
money saved and emissions reduced. Theres nothing particularly new or groundbreaking about this technology, which, in various forms, is currently in use by GM, Chrysler and Honda. Marrying AFM with a two-mode, full hybrid system is, however, the latest in fuel conservation science. Hondas new Accord Hybrid incorporates a mild-hybrid system with its cylinder-deactivated
The two-mode full hybrid system in question is currently being developed by GM, along with partners BMW and DaimlerChrysler. (Photo: Justin Couture, American Auto Press)
V6, mind you, so working the two technologies in tandem isnt an entirely new concept. And while GMs two-mode full hybrid system has been in-use in transit buses, it has not been applied to their car and light truck divisions as of yet.

The two-mode full hybrid system in question is currently being developed by GM, along with partners BMW and DaimlerChrysler, with the intent
GMs two-mode hybrid system is intended to optimize both highway and city fuel efficiency. (Photo: General Motors)
on making it capable of running on gasoline or diesel, for use in private vehicles in both North America and fuel-starved Europe. Reduced fuel consumption equals fewer hydrocarbons and less exhaust emissions, which will also help auto manufacturers meet tightening emissions regulations for diesel-powered vehicles.

The two-mode hybrid system under development is intended to optimize both highway and city fuel efficiency, with the first mode engineered to address slow moving traffic patterns.
While Chevy sells a hybrid Silverado and GMC a Sierra with a hybrid drivetrain, the all-new two-mode hybrid in the Tahoe is a much more sophisticated system. (Photo: Justin Couture, American Auto Press)
It enables the vehicle to operate in any one of three ways: electric power only, engine power only or any combination of the two power sources. Maximum benefit is naturally derived from electric power propulsion operating alone, allowing fossil-fuel-free movement in stop and go bumper-to-bumper traffic, until the engine cuts-in to recharge the 300-volt battery pack or hustle the Tahoe away with greater urgency.

It should be noted that even the first Toyota Prius featured a full hybrid
The second of the two modes incorporates sophisticated electronic controls, such as active fuel management, cam phasing, and late intake valve closure. (Photo: Justin Couture, American Auto Press)
powertrain, a setup that continues forward with every new Toyota and Lexus hybrid the automaker builds. Ford also has engineered its Escape Hybrid with a full-hybrid system, while Hondas have always been less expensive engine-assisted mild hybrids, that is, until the most recent 2006 Civic Hybrid was introduced this fall. Hondas change from mild- to full-hybrid systems is a significant move, now supported by GMs move from its Chevy Silverado and GMC Sierra hybrids, currently available, which are engine-assisted mild hybrids, to this new, more sophisticated powertrain introduced
Unlike more typical continuously variable transmissions, GMs example uses no mechanical belts or bands to continuously feed torque to the wheels. (Photo: Justin Couture, American Auto Press)
in the upcoming Chevy Tahoe Hybrid on Friday, January 8, at the North American International Auto Show in Detroit.
The second of the two modes incorporates sophisticated electronic controls, such as active fuel management, cam phasing, and late intake valve closure to increase the engines efficiency when its working in partnership with the electrical power source or operating independent of it. GM states that the shifts between the two hybrid modes are synchronous, which means no engine speed changes are necessary for the mode shift to occur, resulting in ultra smooth acceleration.

An interesting design aspect of
GMs Active Fuel Management technology, previously known as Displacement on Demand, helps its 5.3L V8, the gasoline-powered portion of this hybrid system, to optimize fuel economy even more. (Photo: General Motors)
GMs two-mode hybrid system is the integration of powerful compact electric motors engineered to fit within the space allotted a conventional automatic transmission. Both the engine and the electric motors transfer torque to a series of gears inside the Tahoes sophisticated transmission, which multiplies the incoming torque to propel the heavy vehicle. But unlike more typical continuously variable transmissions, GMs example uses no mechanical belts or bands to continuously feed torque to the wheels.

Although GM has yet to provide specifications and performance data for the upcoming two-mode full hybrid Tahoe, Mark Cieslak, assistant vehicle chief engineer for the hybrid project had this
By the time the Tahoe Hybrid is available for sale, there will be many full-size hybrid-electric competitors vying for green-minded consumers attention. (Photo: Justin Couture, American Auto Press)
to say about the vehicle: "We took the brand-new, next-generation full-size truck platform, which already had segment-leading fuel economy and world-class aerodynamics, and took it to the next level. This was in addition to maintaining important performance attributes of full-size trucks, such as off-road capability, towing at 6,000 pounds, great 0-60 times and much more."

I recently joined General Motors in Arizona for the launch of the all-new 2007 conventionally-powered Tahoe, featuring the brands 5.3-liter (327 cu-in), 4th generation small-block V8, which will also be used in the upcoming hybrid edition. Chevy placed much emphasis on the efficiency of this mill, which EPA ratings confirm will return 15 mpg in the city and 21 mpg on the highway respectively. Such
The new Tahoe is such a refined package, thats it is a perfect fit for a hybrid drivetrain. (Photo: Justin Couture, American Auto Press)
class-leading fuel economy is in part attributable to GMs Active Fuel Management technology. Adding the proposed two-mode full hybrid system to this already stingy Vortec V8 is bound to launch it into uncharted fuel-efficiency territory, at least among full-size sport utilities.

Of course, it should be noted that Chrysler Group, which shares in the dual-mode fully hybrid technology used by GM in this Tahoe, will be incorporating it into its large SUV lineup, which we have just learned will increase in size thanks to the Durango-based Aspen SUV expected in production trim later this year. Most likely, the Aspen hybrid, and other hybrid versions of Dodge and Jeep models, will arrive around the same time as the fuel efficient Tahoe Hybrid, and also take advantage of cylinder-deactivation technology. Trumping both GM and DaimlerChrysler will most likely
Inside, the new Tahoe awaits a beautifully constructed cabin, full of space, opulence and high quality materials and surfaces (regular Tahoe interior shown). (Photo: Rob Rothwell, American Auto Press)
be Ford and Toyota, which are expected to develop versions of their full hybrid systems for their larger, V8-powered SUVs. Neither rival currently offers cylinder-deactivation, mind you, but the technology is likely in the works.
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