Abstract
Since introduction of the Prius to the Japanese automotive market in 1997, Toyota has sold more than 1 million of these hybrid electric vehicles in the USA and 3 million in the worldwide market up to 2013. The market penetration of the vehicle has been successful because it provides outstanding fuel economy. However, the reduction in the vehicle’s efficiency under severe weather conditions, especially when the weather is very cold, has not been carefully investigated. The engine’s fuel efficiency decreases when the engine is cooled during use in the electric drive mode, or the battery’s efficiency is also degraded under cold weather conditions. Whereas the impacts of the thermal conditions on the fuel economies of vehicles are being increasingly emphasized, an analysis of these impacts has not been conducted widely because this type of analysis needs to be based on test results obtained from a well-designed environmental chamber that can simulate different thermal conditions. The Advanced Powertrain Research Facility at Argonne National Laboratory has equipped its environmental thermal chamber appropriately and has tested the 2010 Toyota Prius at different ambient room temperatures (−7 ºC, 22 ºC, and 35 ºC). On the basis of the test results, the findings include the fact that the control behavior changes significantly according to the thermal conditions. For instance, the controller forces the engine to be turned on if the engine coolant temperature is below 53 ºC. In addition to the thermal impacts on the controller, performance degradation of the powertrain components and the fuel efficiency levels of the vehicle are also analyzed using the test results. Although this study does not advance a novel idea, the information provided herein should be very useful to researchers seeking to understand controller behavior in the real world under different thermal conditions.
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