Field Operations Program Toyota Prius Hybrid Electric Vehicle Performance Characterization Report

The U.S. Department of Energy’s Field Operations Program evaluates advanced technology vehicles in real-world applications and environments. Advanced technology vehicles include pure electric, hybrid electric, hydrogen, and other vehicles that use emerging technologies such as fuel cells. Information generated by the Program is targeted to fleet managers and others considering the deployment of advanced technology vehicles. As part of the above activities, the Field Operations Program has initiated the testing of the Toyota Prius hybrid electric vehicle (HEV), a technology increasingly being considered for use in fleet applications. This report describes the Pomona Loop testing of the Prius, providing not only initial operational and performance information, but also a better understanding of HEV testing issues. The Pomona Loop testing includes both Urban and Freeway drive cycles, each conducted at four operating scenarios that mix minimum and maximum payloads with different auxiliary (e.g., lights, air conditioning) load levels.

The five passenger Prius is powered by a 70-hp, 1.5-liter, 4-cylinder gasoline engine and a 44-hp electric motor. The Prius also has a 274-volt nickel metal-hydride battery comprising 228 1.2-volt cells. The Prius exhibited test results of 35.7 to 55.6 miles per gallon (mpg) during the four types of Urban Loop testing; the EPA estimate for city driving is 52 mpg. During the four types of Freeway Loop testing, the Prius got 40.0 to 45.4 mpg; the EPA estimate for highway driving is 45 mpg. Even though the EPA tests are conducted on a dynamometer and the Pomona Loop tests are conducted as on-road driving tests, when tested with a minimum payload and no auxiliary loads, the mpg test results are the same for the Freeway Loop testing and the EPA highway testing. Under the same operating scenario, the Urban Loop results are 3.6 mpg higher than the EPA estimate for city driving.

The Pomona Loop testing of the Prius demonstrated the difficulty of accurately measuring fuel economy without physically modifying a vehicle. Unlike electric vehicles, where a kilowatthour meter can accurately measure energy flows, the energy use of a Prius type of HEV (non-grid connected) is determined by measuring how much gasoline was used; so a void must now be accurately measured. One option is to apply a known amount of fuel to the vehicle and run it until it stops. However, rarely will a perfectly uniform amount of fuel remain and even more rarely will the vehicle run out of fuel where it started, so this method is not practical for on-road testing. Download free Field Operations Program Toyota Prius Hybrid Electric Vehicle Performance Characterization Report pdf here

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