The NREL team evaluated fuel economy during equal 5-month periods from different years. During the second period, the route assignments originally assigned to the conventional and hybrid van groups were swapped so that the conventional vehicles were assigned to the original hybrid van routes and vice versa.

During the on-road portion of our study, the hybrid vans demonstrated a 13 to 20 percent higher fuel economy than the conventional vans. During dynamometer testing, three standard drive cycles were chosen to represent the range of delivery routes. The hybrids showed a 13 to 36 percent improvement in fuel economy and up to a 45 percent improvement in ton-miles-per-gallon. This wide range in fuel economy is largely dependent on drive cycle.

—NREL Project Engineer Michael Lammert

The team found that the fuel economy of the hybrid group on the original conventional route assignments over 5 months was 10.4 mpg, 13% greater than the 9.2 mpg of the conventional group on those routes a year earlier.

They also found that the fuel economy of the hybrid group on the original hybrid route assignments over 5 months was 9.4 mpg, 20% greater than the 7.9 mpg of the conventional group on those routes a year later.

The difference in hybrid advantage in fuel economy is as expected. The hybrids demonstrated a greater advantage on the initial hybrid route assignments, which were more “urban” (low speed, high stops-per-mile routes) and lower advantage on initial conventional route assignments with a longer highway leg and less dense delivery zones.

—“Eighteen-Month Final Evaluation of UPS Second Generation Diesel Hybrid-Electric Delivery Vans”

The reliability of the hybrids was slightly lower, 92.5% compared to 99.7%, in part due to troubleshooting and recalibration issues related to prototype components, Lammert said. The differences in per-mile maintenance and operating costs were not statistically significant.

Primary hybrid components arranged in the undercarriage of a UPS delivery van. Source: NREL. Click to enlarge.

The hybrids studied represented a second-generation,an evolution from UPS’ original 50 Eaton hybrids that NREL documented in earlier studies. The new hybrids have more advanced control algorithms and an integrated “engine off at idle” feature that automatically stops and restarts the engine at stoplights and other short stops when certain conditions are met.

The revised Eaton hybrid system consists of a Fuller medium-duty automated manual 6-speed transmission; a synchronous brushless, permanent magnet motor delivering continuous power of 26 kW and peak power of 44 kW; a 340 VDC Li-ion battery pack with 1.8 kWh capacity; and power electronics.

NREL has been working in partnership with UPS for five years to track and evaluate the performance of its hybrid vehicles. The first study, performed in 2008, focused on first-generation hybrid vans operated by UPS in Phoenix. (Earlier post.) In 2010, UPS deployed 200 second-generation hybrid vans to eight US cities, including the 11 under study in Minneapolis.

Resources

• M. Lammert and K. Walkowicz (2012) Eighteen-Month Final Evaluation of UPS Second Generation Diesel Hybrid-Electric Delivery Vans. NREL/TP-5400-55658