BIG BLUE; Mercedes ML450 hybrid aims to be large and in charge.(NEWS)

Byline: ROGER HART

Call it a case of going big or going home. This fall, Mercedes-Benz aims to launch a two-mode gasoline-electric hybrid sport-ute that its engineers say will top fuel-economy charts for large SUVs.

That's a big claim, but Mercedes has a history of backing up big claims.

The ML450 BlueHybrid has a 3.5-liter Atkinson-cycle V6 gasoline engine that makes 279 hp and 249 lb-ft of torque, plus two electric motors rated at 61 hp each. The result is a combined output of 321 hp and 354 lb-ft.

EPA numbers aren't final, but Neil Armstrong, director of the Mercedes Hybrid Develop-ment Center in Troy, Mich., said he believes fuel savings will be 25 to 30 percent over a standard 3.5-liter ML. That ute gets 15 mpg city and 20 mpg highway, so we figure this hybrid will rate about 20 mpg city and 26 mpg highway.

Developed in conjunction with General Motors, Chrysler and BMW, the heart of the ML's hybrid system is a transmission with four fixed gears and a pair of electric motors. Together, they provide the advantages of a conventional automatic transmission with the effect of a CVT. The driver can switch modes via a dash-mounted button. At higher speeds, the fixed-gear modewhich simulates an eight-speed transmissiondrops engine speed over the CVT, although there is a slight fuel-mileage penalty.

"We don't want to tell our customers what they should be driving, Armstrong said. "In CVT mode, you get a 3 to 4 percent ...