Autoblog

Official Press Release:

CHEVROLET TAHOE WITH TWO-MODE FULL HYBRID EXPLOITS FUEL SAVINGS, SUV DRIVING PLEASURE AND PERFORMANCE

DETROIT ­ The Chevrolet Tahoe full-size SUV has earned its outstanding reputation with independent consumer studies recognizing its sales and quality leadership.
With the addition of the world's first two-mode full hybrid propulsion system, the Chevrolet Tahoe takes its outstanding reputation even further with a 25-percent improvement in fuel economy and a superior driving experience that SUV customers know and love. "The Chevrolet Tahoe Two-mode Hybrid combines the functionality and comfort of a full-size SUV with a two-mode full hybrid system that optimizes fuel efficiency in both city and highway driving, the way most Americans use their vehicles," said Tom Stephens, group vice president, GM Powertrain. "The Tahoe Two-mode Hybrid delivers on GM's commitment to apply advanced technologies where we will realize the most fuel savings."

The Vortec V-8 powered Tahoe Two-mode Hybrid is expected to deliver a composite fuel efficiency improvement of 25 percent when combined with Active Fuel Management™ cylinder deactivation technology.

The Tahoe Hybrid will go on sale next year as a 2008 model, along with the GMC Yukon Two-mode Hybrid. Pricing and production volumes have not been announced.

Design Manager David Smith and his team gave Chevy Tahoe Two-mode Hybrid a distinctive look befitting its unique powertrain, while ensuring a design reflecting that it is still unmistakably a Chevy. The Tahoe Two-mode Hybrid is 10 mm lower in the front and touts additional aerodynamic features compared to the non-hybrid Tahoe.

Special features, including prominent hybrid badges and a Glacier Gold exterior finish, complete the look. "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," said Mark Cieslak, assistant vehicle chief engineer for the Chevy Tahoe Two-mode Hybrid. "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. It was understood from the start that we would deliver the goods on fuel economy, with typical full-size truck performance, and provide the integration detail that results in a flawless vehicle. And we have, with confidence."

GM, BMW and DaimlerChrysler are co-developing the two-mode full hybrid system that will leverage automatic transmission technology and electronic controls in an integrated, powerful and compact system that can be used with both gas and diesel engines.

The Tahoe, the industry's best-selling SUV, was completely redesigned for 2007 with dramatically increased attention to detail on nearly every aspect of the vehicle. The development team focused on improving ride and handling, quietness, efficiency, and safety and security. They refined the interior and gave it a distinctive, sporty exterior. "Tahoe is known for delivering what its customers want, whenever they want to do it," said Ed Peper, Chevrolet general manager. "The Tahoe Two-mode Hybrid offers great performance, 25-percent better fuel economy and all of the kind of utility that our current SUV has."

The two-mode hybrid system
GM's two-mode full hybrid system in transit buses has been established as the starting point for the GM-BMW-DaimlerChrysler collaboration. The design integrates proven automatic transmission technology with a patented hybrid-electric drive system to deliver the world's first two-mode full hybrid.

The two-mode is patented hybrid technology with two modes optimized for city and highway driving. In the first mode, at low speed and light loads, the vehicle can operate in three ways: electric power only, engine power only or in any combination of engine and electric power. When operating with electric power only, it provides all the fuel savings benefits of a full hybrid system. Leaving the engine shut off for extended periods of time and moving under electric power at low speed is key to reducing fuel consumption in heavy stop and go traffic. The second mode is used primarily at highway speeds. In addition to electric assist, the second mode provides full eight-cylinder engine power when conditions demand it, such as when passing, pulling a trailer or climbing a steep grade. The second mode integrates sophisticated electronic controls, such as Active Fuel Management, cam phasing, and late-intake valve closure, allowing even more efficient engine operation.

Two-mode system innovations allow for more compact packaging because its compact and powerful electric motors are designed to fit within the approximate space of a conventional automatic transmission ­, an efficiency advantage compared with today's typical single-mode systems that rely on much larger electric motors.

A sophisticated controller determines when the vehicle should operate in either mode of the two-mode drive system. Input from the controller determines the necessary torque for the driving conditions and sends a corresponding command to the engine and electric motors. The engine and electric motors transfer torque to a series of gears in the transmission, which multiply torque similar to a conventional automatic transmission to propel the vehicle. But unlike conventional continuously variable transmissions, the two-mode full hybrid's electrically controlled system uses no mechanical belts or bands. Shifts between the two modes are synchronous, which means no engine speed changes are necessary for the mode shift to occur, resulting in ultra smooth accelerations.

The 300-volt battery pack provides electric power for the system, and while it is larger than a typical automotive battery, it is designed to fit in the vehicle without compromising passenger space. Special converters located under the vehicle's hood convert the motors' AC output to DC current and power conventional 12-volt accessories, such as interior lighting, climate control and the radio. The vehicle's internal combustion engine provides power to charge the battery pack, so the vehicle doesn't have to be plugged in to keep the battery pack maintained.

Because the architecture can be scaled to fit multiple vehicles and adapted to gasoline or diesel engines, the two-mode full hybrid can be applied globally. In Europe, for example, where diesel engines are common in passenger vehicles, it can provide a significant reduction in fuel consumption, which would help automakers meet the region's ever-stringent carbon dioxide emissions standard. "We have several additional proprietary innovations that will make the two-mode system even more capable in high power-to-weight ratio vehicles, such as in SUVs and full-size pickups … innovations that combine our two-mode full hybrid with our extensive capability in automatic transmissions and electronic control systems," said Stephens. "We believe it is the most efficient full hybrid design for a broad variety of vehicle configurations."

Designed for efficiency
When it comes to saving fuel, even the most discreet design features can add up to significant fuel savings. Design Manager David Smith's team used the existing, newly redesigned Chevrolet Tahoe, which already features segment-leading fuel economy and world-class aerodynamics, as a basis for additional aerodynamic refinements aimed at achieving even further fuel savings.

Testing was conducted in GM's aerodynamics laboratory in Warren, Mich. The front of the Chevrolet Tahoe Two-mode Hybrid has been lowered 10 mm compared to the conventional Tahoe, which provides additional aerodynamic benefits as well as a smoother and sleeker appearance. The hood and liftgate are made of aluminum to trim weight, and the leading edges of the hood have been streamlined. The Tahoe Two-mode Hybrid retains Chevy's trademark dual-port grille with Chevy bowtie, but with a larger intake to accommodate the hybrid powertrain's higher airflow requirement for cooling. The fascias are tuned at the corners and air dam, and the running boards are flared in front in an effort to guide airflow around the wheel openings. "This truly looks like a special vehicle," said Smith. "It is packed with details, and every one of them serves a function."

There's no mistaking this truck for anything other than a hybrid: Badging appears on the C-pillar, on the rear liftgate and on the hitch cover. Other aerodynamic refinements include sharpening of the D-pillar rearward, including the taillamps, a CHMSL appliqué detail spoiler over the rear hatch and a closeout panel under the back of the vehicle to facilitate airflow. Lightweight, aero-efficient wheels with the lowest rolling-resistance tires available for full-size trucks further trim fuel use, and are complemented with a tuned ride to provide the ride and handling performance and attention to detail that customers expect from a totally integrated vehicle.