SAN DIEGO. Deciding whether or not to invest in a hybrid truck boils down to one critical element: the vehicle’s duty cycle. That’s the view of Kevin Snow, chief engineer & hybrid application development manager for Eaton Corp., which manufactures hybrid drive systems. “The core message with hybrid trucks is that the duty cycle is critical to the fuel savings you expect to gain, along with the complimentary amount of emission reductions,” he said while addressing the Integer Research’s Diesel Emissions Conference here this week.
According to Snow, here is the key scenario for making today’s hybrid drive systems a good fit with a truck: The truck is engaged in a lot of short- range, start-and-stop driving under low average speeds and/or it requires a high level of engine idle time, such as a bucket truck at a job site would.
“However, if the vehicle in question spends over 50% of its operating time at steady-state highway speed, then it’s not a good fit for a hybrid application,” Snow cautioned.
Other OEMs currently testing hybrid technology in Class 8 trucks echo Snow’s perspective. “While we certainly are experimenting with hybrids for Class 8 highway vehicles, we have a lot more success with the technology in medium-duty and vocation al vehicles,” said David Siler, gm--central region for Freightliner Trucks at the conference.
“We just don’t see quite the promise for hybrids in the over-the-road tractor,” he added. “We see it really benefitting more vocational and urban [truck] applications.”
That’s because the diesel engine in a hybrid truck must do all the “work” at highway speeds, noted Eaton’s Snow.
“You really save the most fuel when the hybrid is being powered solely by the electric motor and batteries,” Snow explained, “when it’s completely disengaged from the diesel engine. So the more time you operate at low speeds with a lot of stops per mile and the more you idle your engine, that’s when a hybrid makes the most sense.”