- New exterior color – Mocha Steel Metallic
- OnStar Gen 9.0 offers more robust voice recognition
- Revised second-row head restraints
2011 CHEVROLET TAHOE HYBRID: 33-PERCENT GREATER CITY FUEL ECONOMY AND 100-PERCENT CAPABILITY
Chevrolet Tahoe Hybrid delivers a dramatic improvement in fuel economy over non-hybrid models – a 33-percent improvement in city driving – with all of the comfort and capability customers expect in a full-size SUV, including eight-passenger seating and a towing capacity of up to 6,200 pounds (2,812 kg) on 2WD models.
The Tahoe Hybrid’s improved fuel economy over gasoline-only models is due largely to GM’s state-of-the-art two-mode hybrid system, which helps 2WD Tahoe Hybrid models, for example, deliver an estimated 20 mpg in the city. That’s comparable to the city fuel economy of much-smaller cars.
Changes for 2011 include a new exterior color, Mocha Steel Metallic as well as OnStar Generation 9.0 hardware for more improved compatibility with cell phones and improved voice recognition; and revised second-row head restraints to provide enhanced protection in rear-impact crashes.
Hybrid system details
GM’s advanced Electrically Variable Transmission (EVT) and 300-volt nickel-metal hydride Energy Storage System (ESS) work in concert with the standard 6.0L V-8 gasoline engine with Active Fuel Management (AFM) and late intake valve closing (LIVC) technology to enable the Tahoe Hybrid’s efficient performance. This hybrid system not only enables the Tahoe to launch and drive up to 30 mph on electricity alone, it also allows the 6.0L V-8 engine to operate in its more economical V-4 mode for longer periods.
GM designed the EVT to provide the best combination of city and highway fuel economy. Used with the Vortec 6.0L V-8 engine with Active Fuel Management, it is an all-purpose system well-suited to providing excellent economy and full-size SUV passenger-carrying, cargo-hauling and trailer-towing capabilities.
The EVT is designed to bolt directly to the standard four-wheel-drive transfer case found on the gasoline-only models for true four-wheel-drive capability. The following major components comprise the Tahoe Hybrid’s unique powertrain system:
Electrically variable transmission (EVT): The key to GM’s EVT is its unique assemblage of two 60 kW electric motors, three planetary gearsets and four traditional hydraulic wet clutches. This arrangement allows continuously variable operation, and provides four fixed gear ratios (with operation comparable to that of a standard electronically controlled automatic transmission).
A sophisticated Hybrid Optimizing System constantly receives torque-based data from the powertrain and other vehicle systems, and then determines the most efficient means of propelling the vehicle — either via electric power, gasoline engine power or a combination of the two. The EVT is like having two transmissions in one — continuously variable drive for light-load conditions and fixed-ratio drive for high-load situations.
Energy storage system (ESS): A 300-volt nickel-metal hydride Energy Storage System (ESS) provides power to the EVT’s two electric motors. This battery pack is located under the second-row seat, where it takes up virtually no additional space and does not interfere with second- or third-row ingress/egress. The fold-and-tumble capability of the second-row seat remains, and flipping the seat forward provides a flat load floor from the liftgate forward to the front seats.
In addition to supplying power to the EVT, the ESS also provides power to the air conditioning compressor and the Accessory Power Module (APM), which converts the high-voltage supply to 42 volts for the electric power steering system, and 12 volts for the vehicle battery and other 12-volt electrical accessories.
Battery pack durability and reliability are maintained via optimized charge and discharge cycles, as well as a dedicated cooling system that draws air from the passenger compartment. As part of the vehicle’s emission control system, the ESS is warranted for eight years/100,000 miles.
Vortec 6.0L V-8 engine: Engineers chose the Vortec 6.0L V-8 gasoline engine for the Tahoe Hybrid because of its favorable torque characteristics. This is especially important because GM engineers adapted the 6.0L V-8 to operate with late intake valve closing (Atkinson-cycle combustion process) for reduced pumping losses and better overall fuel economy.
Using flat-top pistons, cylinder heads borrowed from GM’s 5.3L high-output V-8 and a 10.8:1 compression ratio, the Vortec 6.0L V-8 produces 332 horsepower (248 kW) at 5100 rpm and 367 lb.-ft. of torque (498 Nm) at 4100 rpm, yet requires only regular unleaded fuel.
The Vortec 6.0L also features variable valve timing to control late intake closing, as well as Active Fuel Management, which allows four of the eight cylinders to be shut off during periods of light load. With the benefit of electric boost, the engine is able to stay in V-4 mode for longer periods in the Tahoe Hybrid.
Auto Stop mode and regenerative braking
A key contributor to fuel economy is the gasoline engine’s Auto Stop mode. At vehicle speeds between 0 and 30 mph, the gasoline engine may be automatically shut down. By leaving the engine off and allowing the vehicle to move only under electric power up to 30 mph, such as during heavy stop-and-go traffic, fuel consumption is greatly reduced.
The regenerative braking system works in concert with the hydraulic braking system. The system uses a brake pedal emulator, which provides progressive resistance as the pedal is depressed. This consistent pedal feel is very much like that of a standard hydraulic braking system in operation.
Peace and quiet
The superior passenger comfort of both these SUVs has been maintained throughout, with a quiet cabin environment at the very top of the list. Tahoe Hybrid models match their gasoline-only siblings in comfort and convenience, but attention to acoustic details makes these SUVs even more enjoyable.
Some of the significant accomplishments in noise reduction include the following:
Hybrid interior features
A unique hybrid gauge cluster includes a special tachometer incorporating an Auto Stop position just above the 0 rpm mark that indicates when the gasoline engine is in shut-down mode. An analog economy gauge, to the left of the tachometer, helps the driver maintain the most efficient driving style.
Located midway down the center stack, the standard navigation system’s 6.5-inch full-color VGA display doubles as a monitor that shows a graphic representation of the hybrid drivetrain’s power flow. This display continuously informs the occupants how the system is sending power to the wheels from the ESS/electric motors, the gasoline engine or both. The screen also displays reverse electrical flow during regenerative braking and whether the vehicle is in two- or four-wheel-drive mode.
While the Tahoe Hybrid bears a close resemblance to other models, styling revisions are made for aesthetic and functional purposes. In addition to setting these models apart from other SUVs, the following exterior styling changes contribute to improved fuel economy:
Mass reduction inside and out
Mass is an important factor in overall vehicle efficiency. Because of the slight increase in curb weight resulting from the various hybrid components, engineers reduced the mass of numerous vehicle components, keeping the Tahoe Hybrid in the same test weight class as its gasoline-only counterparts.
On the outside, an aluminum hood and liftgate (with fixed glass) replace the standard steel units. Substituting an aluminum front bumper beam saved additional weight, as well as using low-mass, aero-efficient 18-inch cast aluminum wheels.
On the inside, special thin-profile, lighter-weight front seats provide all the function and comfort of those found in the gasoline-only Tahoe. Another advantage of these new seats is the additional 1.5 inches (38 mm) of second-row passenger knee room.
Additional mass was eliminated by adapting a tire inflator kit that takes the place of the spare wheel and tire, hoist mechanism, jack and tools found on gasoline-only models. Easy to use, the tire inflator kit is conveniently located behind the left-rear quarter trim panel in the cargo area.