Eaton Displays Heavy Duty Hybrid
A diesel-electric hybrid-drive system for heavy-duty road tractors is being developed by Eaton Corp., which says it could save considerable fuel and reduce exhaust emissions. The ProLaunch system captures braking energy and reuses it to help propel the vehicle, and later to power "hotel" accessories in the tractor's sleeper.
Now installed in a Peterbilt 386 test tractor, the system shares some of the components used in Eaton's medium-duty hybrid product now being purchased by package-delivery and electric utility companies. The heavy-duty system combines an automatic clutch and UltraShift automated mechanical transmission with an electric traction motor that doubles as a generator to produce electric power during braking.
Electric energy is stored in three lithium-ion batteries, which are also charged by the engine's high-output alternator. The system operates at 340 volts DC, while the chassis runs on 12 volts. Direct current is inverted to 120-volt alternating current to run other house-type accessories.
An electric heating, ventilation and air conditioning pack keeps the sleeper warm or cool during rest stops, during which the truck's engine remains shut down most of the time. The engine restarts to charge the batteries when necessary, then shuts down in a "smooth" fashion to avoid disturbing the sleeping driver. Stationary recharging might take four to five minutes per hour, which is within restrictions imposed by anti-idling laws in many locations.
The 60-horsepower electric motor produces torque that can be blended with that of the engine to increase performance, reduce the engine's work or in some cases move the vehicle on its own. The motor can help launch the truck or help keep it moving at highway speeds. Undulating terrain, where the truck continuously descends and climbs grades, would allow repeated regenerative braking and powering through the motor, engineers said.
Dyno tests have shown that the launch-assist function would improve fuel economy by 5 to 7 percent while driving, and the electric HVAC saves a gallon of fuel per hour compared to constantly idling the tractor's engine. For a tractor running 125,000 miles a year, this would save about $9,500 a year if the engine otherwise idled 1,825 hours a year burning fuel costing $2.90 a gallon, Eaton engineers said. It would save about $7,600 in a tractor running 70,000 miles a year.
The tractor's brakes would see less wear because the electric motor would assist in slowing the vehicle while generating electricity for the special batteries. But brake-wear savings have not been calculated.
Engineers continue to develop the heavy-duty ProLaunch system while talking with fleets and truck builders to begin an operational test program. Eaton hopes to have the system in limited production by sometime in 2009.
—Tom Berg
Senior Equipment Editor
