Tahoe, Yukon debut hybrid versions

Electric motors and gas engine power SUVs, with computer deciding which option is most efficient.

Scott Burgess / The Detroit News

MILFORD -- General Motors Corp. unveiled working versions of its large SUV hybrid Tuesday.

The Chevrolet Tahoe and GMC Yukon will offer the gas-electric hybrid by the end of the year, improving the vehicles' gas mileage by 25 percent, GM officials said.

"We're still in the development stages, but we're on track to have these vehicles ready by the fourth quarter of this year," said Larry Nitz, GM's executive director of hybrid technology.

The hybrid system powers the SUVs using electric motors (mounted inside the transmission), the gas engine alone or a combination, said Tim Grewe, GM's chief engineer for rear-wheel drive powertrain hybrids. Additionally, the electric motors can be locked out of the drive train during times the engine's power is needed, such as in towing up to 6,000 pounds.

Both models include a valve shutoff system that allows the 6-liter V-8 to operate on half of its cylinders to help conserve fuel when at cruising speed.

A computer monitors the entire system and determines every 1/100th of a second what method is the most efficient means to propel the vehicle, Grewe said.

When moving in slow traffic, the electric motors drive the car -- with the engine turning on only when needed or to help recharge the batteries. When the vehicle brakes, some of that energy is captured and returned to the 300-volt battery packs that are stored under the floor of the second row seats.

GM used a number of tools to improve the vehicle's gas mileage. Besides the hybrid system, it lightened the SUVs by more than 300 pounds. It replaced the hood and front tailgates with aluminum and changed the front fascia, side rails and back of the vehicle. It also redesigned the vehicle grille and made other improvements to make it more streamlined, said Mary Sipes, vehicle line director for full-size SUVs.

The insides of the Tahoe and Yukon closely resemble their gas-only namesakes.

In a short test drive, the Tahoe transitioned from electric to gas power during acceleration. Its handling was driven by its new electric power steering. In slow driving, the Tahoe could reach 25 mph without starting the gas engine.

A small gauge in the dash helps drivers know if they're saving energy or losing it through heavy acceleration or heavy braking.

Scott Burgess can be reached at (313) 223-3217 or sburgess@detnews.com.