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NREL Evaluates Performance of Hydraulic Hybrid Refuse Vehicles

October 1, 2015

NREL is evaluating the performance of hydraulic hybrid vehicles (HHVs) and comparable conven­tional diesel vehicles operated by Miami-Dade County's Public Works and Waste Management Department in Florida. Launched earlier this year, the study aims to improve understanding of the overall usage and effectiveness of HHVs in refuse operation. Initial results indicate that the HHVs under study offer significant fuel-saving opportunities compared to similar conventional vehicles.

The study was designed to help Miami-Dade County determine the ideal routes for maximizing the fuel-saving potential of its HHVs, and the results could also help other fleet managers around the country as they explore the fuel-saving technology options available today.

The fuel economy of heavy-duty vehicles, such as refuse trucks, largely depends on the load carried and the drive cycles on which they operate. In the right applications, HHVs can offer a substantial fuel-cost advantage over similar conventional vehicles. The extent of this advantage is contingent on driving behavior and drive cycles with high kinetic intensity (such as with stop-and-go traffic) that take advantage of regenerative braking.

The HHVs under study -- Autocar E3 refuse trucks equipped with Parker Hannifin's RunWise Advanced Series Hybrid Drive systems -- reportedly recover as much as 70% of the energy typically lost during braking and reuse that energy to power the vehicle. The system features a two-speed hydrostatic drive combined with a mechanical direct drive, which optimizes vehicle performance at both low and high speeds. 

The on-road portion of NREL's evaluation focuses on validating the technology benefits by collecting and analyzing vehicle performance data -- fuel economy, maintenance costs, and drive cycles -- from the HHVs and the conventional diesel vehicles. Based on the field data, NREL will develop a validated vehicle model using the Future Automotive Systems Technology Simulator, or FASTSim, to study the impact of route selection and other vehicle parameters. NREL is also analyzing fueling and maintenance data to support total-cost-of-ownership estimations and forecasts. 

In addition to the on-road testing, NREL will conduct chassis dynamometer testing of the HHVs and baseline conventional vehicles to determine the fuel economy and emissions impact of the hydraulic hybrid technology in a controlled laboratory setting.

—Wayne Hicks