GM's Hybrid SUVs Have 'Street Smarts'

Freescale Semiconductor's technology provides brains behind powertrain system.

General Motors' Chevy Tahoe Hybrid and GMC Yukon Hybrid are seeing a 50% increase in fuel efficiency over their conventional counterparts thanks to chips produced by Freescale Semiconductor, according to the companies. Freescale is providing advanced microcontroller (MCU) technology for the complete hybrid drive train.

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.

The 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.

The 2008 Tahoe Hybrid and Yukon Hybrid are currently available. The Cadillac Escalade Hybrid will be available later this year with the two-mode hybrid transmission.

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.

According to J.D. Power & Associates, U.S. hybrid sales surged a record 40% in 2007. The research firm also estimates that hybrid vehicles may account for 2.4% of new vehicle sales in the U.S.

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