SAN ANTONIO--A parallel hybrid gasoline-electric powertrain for medium-size cars achieved an average fuel economy of 79 mpg.

Developed by engineers at the Southwest Research Institute, the Parallel Hybrid Electric Combination of Speeds (PECOS) powertrain was tested using federal procedures to emulate highway and city driving. PECOS achieved a fuel economy of 77 mpg for city driving and 82 mpg for highway driving.

The powertrain can accelerate a vehicle with a mass of 1,265 kilograms, an aerodynamic drag coefficient of 0.34, and a frontal area of 2 square meters from 0 to 60 mph in 14.9 seconds.

PECOS conists of 40-kilowatt, 1-liter spark ignitition engine; a 53-kilowatt, permanent-magnet brushless DC motor; a power-splitting planetary gearbox, and a 312-volt lead-acid battery pack.

The gearbox contains one sprag clutch and one wet clutch. The two clutches transition the powertrain from one mode of operation to another, using a fuzzy logic strategy based on road conditions. Four operating modes are possible: a pure electric mode, a battery pack charge mode, a motor-assisted engine mode, and a regenerative braking mode.

PECOS has several advantages over conventional powertrains. It does not require a clutch to launch the vehicle--the motor can spin backward until the drive wheels are engaged. The engine does not require a starter, and no transmission is required except for a differential.

For more information, call 210-522-3965 or visit