parallel hybrid petrol-electric powertrain for medium-size cars, developed by
engineers at Southwest Research Institute (SwRI), achieved combined highway and
urban average fuel economy of 79 miles per U.S. gallon.

Dynamometer tests of the Parallel Hybrid Electric Combination of Speeds (PECOS)
powertrain were conducted to determine full acceleration performance and fuel
economy over the urban and highway driving profiles.

The PECOS powertrain accelerates a vehicle with a mass of 1,265 kilograms,
aerodynamic drag coefficient of 0.34, and frontal area of 2m2 from zero to 60
miles per hour in 14.9 seconds.

The powertrain achieved fuel economy of 77 miles per U.S. gallon for city driving
and 82 miles per gallon for highway driving, resulting in a combined fuel economy
of 79 miles per gallon.

SwRI engineers recently completed prototyping and testing of the patented hybrid
powertrain. Its simple design consists of off-the-shelf components, including
a 40 kW (peak), one-litre spark ignition engine, a 53 kW (peak) and 32 kW (continuous)
permanent magnet brushless DC motor, a power splitting planetary gear box, and
a lead acid battery pack (312 volt bus).

The planetary gearbox contains one sprag (one-way) clutch and one wet clutch.
The sprag clutch and wet clutch transition the PECOS powertrain from one mode
of operation to another. Four operating modes are possible: pure electric, a
battery pack charge mode, motor assisted engine, and regenerative braking.

The engine can either be coupled to the road or decoupled from the vehicle’s
speed. The controller automatically switches the powertrain from one mode of
operation to another using a fuzzy logic rule-based strategy based on road conditions.
This control strategy minimises mode transition instabilities.

The PECOS system has several advantages over conventional powertrains. It does
not require a clutch to launch the vehicle. The engine does not require a starter,
since the electric motor starts the engine. Finally, no transmission is required
except for a differential.

To view related research reports, please follow the links

Vehicles – prospects for battery, fuel cell and hybrid powered vehicles

Electric Vehicles to 2002