2009 Chevrolet Tahoe Hybrid news, pictures, and information

2009 CHEVROLET TAHOE HYBRID OFFERS 50-PERCENT GREATER CITY FUEL ECONOMY

Along wîth Active Fuel Management, the Tahoe Hybrid uses specific aerodynamic aids and reduced-mass components to help achieve EPA ratings of 21 mpg in the city and 22 on the highway for 2WD models. With 4WD models, the fuel savings are equally impressive, wîth the Tahoe Hybrid rated at 20 mpg in both city and highway driving.

Driving for best economy

By using the analog economy gauge found in the instrument cluster, drivers can maintain the most efficient driving style by keeping the gauge at its optimum economy indication as often as possible. Also, any time the gasoline engine is shut down — indicated when the tachometer needle points to the Auto Stop position, just below the zero mark — the driver will know when the vehicle is being powered only by electricity, which is the most efficient propulsion method.

Powertrain details

Drawing on its vast experience in developing hybrid bus propulsion systems, GM designed the EVT to provide the best combination of city and highway fuel economy. Úsed in concert wîth the Vortec 6.0L V-8 engine wîth Active Fuel Management, this all-purpose system is well-suited to provide excellent economy and full-size SÚV passenger-carrying, cargo-hauling and trailer-towing capabilities.

Furthermore, 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)

• Energy Storage System (ESS)

• Vortec 6.0L V-8 wîth Active Fuel Management (AFM) and late intake valve closing (LIVC)

Electrically variable transmission (EVT): The key to GM's all-new 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, as well as providing 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.

In Mode One (M1), the EVT provides infinitely variable drive up to 1.70:1, while Mode Two (M2) provides ratios from 1.70:1 to 0.50:1. These two modes include all instances of electric-only (Auto Stop) and electric-gasoline hybrid operation. Depending on driving conditions and vehicle load, a fixed first-gear (G1) ratio of 3.69:1 is available (such as for pulling a large trailer) instead of the variable M1 ratios.

Similarly, a second-gear (G2) fixed ratio of 1.70:1 may be selected by the HOS, if needed, before transitioning to the variable M2 ratios. As road speed increases, and depending on driving and vehicle load conditions, variable-ratio M2 operation can be switched instantly to a third-gear (G3) fixed ratio of 1.00:1, and finally to a fourth-gear (G4) fixed ratio of 0.73:1, which is used mainly for steady-state highway cruising.

Únlike less advanced hybrid systems, the GM system occasionally shuts down the electric motors, allowing the EVT to function as a conventional automatic transmission. (posted on conceptcarz.com) Typically, this fixed-ratio operation occurs at highway speeds or when hauling heavy loads, and can actually be more efficient than operating in electric-gasoline hybrid mode under the same conditions. This is because under high-load situations, when the fixed gears are in use, the electric motors can be used to generate electricity — or, if needed, they can be called on to supply additional torque for improved performance.

Energy storage system (ESS): Providing power to the EVT's two electric motors is a 300-volt nickel-metal hydride Energy Storage System (ESS). This battery pack is located under the second-row seat, where it takes up virtually no additional space and does not interfere wîth second- or third-row ingress/egress — the fold-and-tumble capability of the second-row seat is maintained, and when the seat is flipped forward, a flat load floor is provided from the liftgate forward to the front seats.

The primary function of the ESS is to provide power (300 volts) to the EVT via the Traction Power Inverter Module (TPIM) and to store captured energy produced during regenerative braking. The ESS can also be charged, when necessary, by the gasoline engine via one of the two electric motors when operated in generator mode.

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 §teering 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: The Vortec 6.0L V-8 gasoline engine is used in the Tahoe Hybrid because of its favorable torque characteristics. This is especially important because GM engineers adapted the 6.0L V-8 to operate wîth late intake valve closing (Atkinson-cycle combustion process) for reduced pumping losses and better overall fuel economy.

Úsing 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. (concept carz)

In addition, the Vortec 6.0L engine 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

A key contributor to fuel economy is the gasoline engine's Auto Stop mode. Once the vehicle reaches 0 mph, the gasoline engine is 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.

Typically, the hybrid control system will shut off the gasoline engine when it is not needed for propulsion. However, there may be instances when the engine will remain running after it is started:

• The engine or transmission is not fully warmed up

• The transmission or ESS temperature is high

• The ESS charge level is low and requires recharging

• The hood is not fully closed

• The 'Service Engine Soon' light is illuminated

Situations in which the engine will restart include:

• The accelerator pedal is depressed in demand for heavy acceleration

• The engine must run to meet the current climate control settings

• The ESS charge level is low and requires recharging

• Regenerative braking


The regenerative braking system works in concert wîth 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.

Because there are two braking systems — regenerative and hydraulic — more braking power is available than that found on gasoline-only models. Because of this, braking distances will be noticeably shorter.

From time to time you may hear the computer-controlled pump re-pressurizing the hydraulic brake accumulator. This is normal and necessary to the safe operation of the vehicle. Note that actuating the brake pedal repeatedly will deplete the accumulator pressure more quickly and cause the pump to cycle more often.

Peace and quiet

	Vital Stats
Engine : 6.0 L., 8-cylinder Power: 332 hp Torque: 367 ft-lbs
4-speed Automatic

The superior passenger comfort of both these SÚVs has been maintained throughout, wîth 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 SÚVs even more enjoyable.

Some of the significant accomplishments in noise reduction include the following:

• New exhaust system and resonator — Specially tuned for the 6.0L LIVC engine's Active Fuel Management operation, this new exhaust system ensures comfortable interior acoustics and a pleasant exhaust note during both V-4 and V-8 operation

• Additional engine intake induction tuning for reduced interior noise and pleasing sound quality

• Low-rolling resistance, 'quiet-tuned' P265/65R18 tires for reduced road noise

• Electrically driven 300-volt air conditioning compressor reduces vibration and allows the HVAC system to cool the passenger compartment even when the gasoline engine is shut off. Includes the standard tri-zone HVAC system

• Electrically driven 42-volt variable-assist power §teering reduces vibration and provides up to a 0.5-mpg fuel economy improvement by reducing parasitic losses common in belt-driven hydraulic systems

• Energy Storage System (ESS) cooling system internal fan is tuned to be quiet at low vehicle speeds when the fan could more easily be heard by the occupants

Hybrid interior features