Two-Mode Hybrid Technology Delivers Up to 50-Percent City Fuel Improvement

Freescale Semiconductor, the leading supplier of semiconductors to the automotive industry, is providing advanced microcontroller (MCU) technology for the complete hybrid drive train used in General Motors’ Chevy Tahoe Hybrid and GMC Yukon Hybrid, the world’s only hybrid full-size SUVs.

The Tahoe Hybrid and Yukon Hybrid models are entering the market as hybrid vehicles sales in the U.S. have reached an all time high. According to J.D. Power & Associates, U.S. hybrid sales surged a record 40 percent in 2007. The research firm also estimates that hybrid vehicles may account for 2.4 percent of new vehicle sales in the U.S.

GM’s two-mode hybrid transmission is an innovative, highly efficient powertrain design that boosts the fuel economy of the SUVs and large luxury vehicles by up to 50 percent in city driving compared to traditional gasoline engines. Based on the GM-Allison hybrid system for city buses, this patented hybrid technology is equally optimized for city and highway driving, unlike current production hybrid systems, which generally are optimized for city driving. In addition, the 2008 Tahoe/Yukon models are the first hybrids with a 6,000-pound towing capacity, making these two-mode hybrid transmissions similar in power to traditional SUVs.

“With the introduction of the world’s first full-size hybrid SUVs, GM is pioneering a niche in the automotive market that’s in step with today’s growing concerns about the environment and global warming,” said Paul Grimme, senior vice president and general manager of Freescale’s Microcontroller Solutions Group. “We’re proud that Freescale technology is helping make these innovative, fuel-efficient SUVs a reality in the market.”

The power inverter module used in GM’s two-mode hybrid powertrain is controlled by Freescale 32-bit Power Architecture™ MCUs – the “brains” of the system. The smooth, uninterrupted blending of power between the electric motor and gasoline or diesel engine requires powerful computer controls to calculate and conduct complex functions. All of the switching is controlled by the powertrain control units and the software, which monitor driving and select the proper transmission mode.

GM’s patented hybrid technology features 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 operating with electric power only, the two-mode powerplant provides the fuel savings benefits of a full hybrid system. Leaving the engine shut off for extended periods of time while moving under electric power at low speed 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 other vehicles, pulling a trailer or climbing a steep grade. A sophisticated control unit determines when the vehicle should operate in either mode of the two-mode drive system.

GM, Chrysler, Mercedes and BMW Group co-developed the two-mode full hybrid system, which leverages automatic transmission technology and electronic controls in an integrated, powerful and compact system used with both gasoline and diesel engines.

The 2008 Tahoe Hybrid and Yukon Hybrid are currently available. Pricing and production volumes have not been announced. The Cadillac Escalade Hybrid will be available later this year with the two-mode hybrid transmission.

GM electronic control systems have incorporated Freescale technology since 1979, when a Freescale automotive MCU was first used in GM’s closed-loop carburetor controller. In 2004, GM announced a landmark agreement to use 32-bit Power Architecture™ MCUs from Freescale in its powertrain engine control systems around the world. Freescale currently leads the market in powertrain MCUs, with nearly 50 percent market share.

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