2008 Chevrolet Tahoe 2-Mode Hybrid

The 2008 Chevrolet Tahoe already boasts best-in-class fuel economy. Now, Chevy takes another leap forward with the Tahoe 2-Mode Hybrid. It features the world's first production 2-Mode full hybrid propulsion system, which on the 2WD model offers 50-percent better EPA city fuel economy than its gasoline-only sibling and 30-percent better combined city-highway fuel economy. Better still, the fuel-saving advantages of the Tahoe Hybrid are balanced with a superior driving experience and uncompromised capability.

"The Chevrolet Tahoe Hybrid combines the functionality and comfort of a full-size SUV with a Vortec V-8-based full-hybrid system that provides city fuel economy comparable to that of a four-cylinder midsize car," said Ed Peper, Chevrolet general manager. "The Tahoe Hybrid is an example of Chevrolet's commitment to offer fuel solutions in all of our segments with technologies that add value without subtracting capability or capacity."

The 2WD Tahoe Hybrid delivers 21 mpg in the city, a 50-percent improvement over its 5.3L non-hybrid sibling. It matches the city fuel economy of the much-smaller 2008 2.4L-equipped Toyota Camry midsize sedan, according to figures obtained from www.fueleconomy.gov. The fuel savings are equally impressive on the 4WD Tahoe Hybrid, rated at 20 mpg in both city and highway driving.

Along with exceptional fuel economy, the Tahoe Hybrid delivers full-size SUV capability - up to 6,200 pounds (2,812 kg) of usable towing capacity (2WD) and 6,000 pounds (2,722 kg) on 4WD models; 12,000 pounds (5,443 kg) GCWR and standard eight-passenger seating capacity.

All Tahoe models are built on GM's full-size SUV platform, which incorporates features such as a fully boxed frame, coil-over-shock front suspension, rack-and-pinion steering and a premium interior that bolsters the vehicle's comfort, quality and capability. Wide front and rear tracks enhance handling and lower the center of gravity for a more confident road feel.

The Tahoe Hybrid was designed with safety in mind. It delivers a 360-degree safety system of occupant protection and crash-avoidance technology, with features such as standard StabiliTrak stability control system with rollover mitigation technology. For 2008, the long list of standard safety features is enhanced with the addition of head-curtain side impact air bags on all models.

Tahoe Hybrid powertrain
The Tahoe Hybrid features 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 the vehicle is operated with electric power only, the engine is shut off for extended periods of time. Moving under electric power at low speeds 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. It extends the AFM bandwidth to allow longer and more consistent periods of AFM use.

The 2-Mode system innovations allow for more efficient 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 hybrid 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.

Unlike conventional continuously variable transmissions, however, the 2-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 Energy Storage System (ESS) 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 and regenerative braking system provide power to charge the Energy Storage System so the vehicle doesn't have to be plugged in to keep the system charged.

Because the architecture can be scaled to fit multiple vehicles and adapted to gasoline or diesel engines, the 2-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.

Aerodynamic enhancements
The Tahoe Hybrid has a look that is as distinctive as its unique powertrain; it is 10 mm lower in the front and has additional aerodynamic features compared to gasoline-only models. The hood and liftgate are made of aluminum to trim weight, and the leading edges of the hood have been streamlined.

The Tahoe Hybrid retains Chevy's trademark 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. There's no overlooking the fact that this SUV is a hybrid, with badging on the C-pillars and rear liftgate. Additionally, Hybrid decals are located on both the upper portions of the front windshield as well as the rear liftgate glass.

Other aerodynamic refinements include sharpening of the D-pillar rearward, including the taillamps, a CHMSL appliqu detail spoiler over the rear hatch and a closeout panel under the back of the vehicle to facilitate airflow and reduce drag.

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.

Source: General Motor Corp.