The Car and Truck Fleet and Leasing Management Magazine

GM Offers Fuel-Saving Technology in Several 'Flavors'

May 2008, by Paul Dexler - Also by this author

General Motors has been exploring ways for drivers to remain mobile while reducing or eliminating petroleum consumption. The result is technologies such as active fuel management and electric propulsion with an onboard generator to charge the batteries.

Active Fuel Management

Active Fuel Management has been incorporated into many GM engines already on the market and will  be added to more soon. Active Fuel Management enables the engine to automatically operate on half its cylinders under light load conditions, thereby improving fuel efficiency in some vehicles by up to 12 percent. When loads are light, the control system automatically closes both intake and exhaust valves of half the cylinders, cutting off air and fuel supply. Then, when needed for quick acceleration or hauling heavy loads, the fuel supply resumes and the valves are reopened to provide all-cylinder operation.

A sophisticated electronic engine controller determines when to deactivate cylinders, allowing the engine to maintain vehicle speed in lighter-load conditions such as highway cruising. The process is virtually imperceptible to the driver. Active Fuel Management technology is offered on several 5.3L V-8 engines and 6.0L V-8 engines. For the 2008 model-year, it’s been added to the 3.9L V-6 engine in some applications.

Hybrid Technology

For many years, GM has offered hybrid vehicles, starting with mild hybrid systems. Their most recent hybrid models feature GM’s two-mode hybrid system, the result of a consortium between GM, BMW, Chrysler, and Daimler.

In the earlier mild hybrid systems, the gasoline engine did most of the work and was assisted by a small electric motor that added torque boost on acceleration. The gasoline engine could be shut down at traffic lights and other stops, so fuel was not consumed during idling. On deceleration, the electric motor helped recharge the battery, a process called regenerative braking. In slow traffic conditions, regenerative braking was all that was needed to decrease vehicle speed. Mild hybrid systems relied on engine power, such as power steering and air conditioning to help generate electric power, and continued to operate even if the gasoline engine was not running.

By the end of 2008, GM is expected to offer nine hybrid models in the United States, more than any other automaker. They include the Saturn VUE  V-6 Two-Mode Hybrid, Saturn VUE four-cylinder Hybrid, Saturn AURA Hybrid, and Chevrolet Malibu Hybrid. GM’s two-mode hybrid technology is currently available in the Chevrolet Tahoe Two-Mode Hybrid and GMC Yukon Two-Mode Hybrid, and will be added later this year to the Cadillac Escalade Two-Mode Hybrid, Chevrolet Silverado Two-Mode Hybrid, and GMC Sierra Two-Mode Hybrid.

The two-mode hybrid system delivers highly efficient performance and full functionality. With the two-mode system, the vehicle can operate on electric power alone at speeds up to 30 mph. The gasoline engine is supplemented by two 55Kw electric motors that fit inside the transmission case.

Under light-duty operation, the transmission operates in a continuously variable transmission (CVT) mode. When more power is needed for climbing hills or towing a trailer, the transmission switches to the second mode which features four fixed-gear ratios.

So far, the SUVs GM has equipped with the two-mode hybrid system can benefit most from hybrid technology. These larger, heavier vehicles can offer the fuel economy of a smaller, lighter vehicle while maintaining both carrying or towing capacity.

Later this year, production of the front-wheel-drive Saturn VUE Two-Mode Hybrid will begin. It’s expected to deliver up to 50-percent greater combined city and highway fuel economy compared with the current non-hybrid VUE XR, based on current federal test procedures. It’s also the first V-6 powered vehicle, and the first front-wheel-drive vehicle to use the two-mode system. The driving range is more than 500 miles.

In addition, the VUE Two-Mode’s 3.6L VVT V-6 engine with direct injection technology means no trade-offs in performance or fuel economy. Acceleration time from 0-60 mph is expected to be around 7.3 seconds, and the maximum towing load will be 3,500 lbs.



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