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In recent years the fuel efficiency of modern hybrid electric vehicle (HEV) powertrains has progressed to a point where low voltage auxiliary electrical system loads have a pronounced impact on fuel economy (FE). While improving the energy consumption of an individual component may result in minor improvements, the collective optimization of such loads across a complete vehicle system can result in meaningful FE gains. Traditional methods using chassis dynamometer testing alone to quantify the impact of a specific auxiliary load can lead to issues where signal state changes are too small for accurate detection. This presents difficulties in accurately predicting the influence of such loads on FE of next-generation electrified vehicles under development. This paper describes a newly developed method where dynamometer test results are combined with computer simulation analyses to create a practical technique for assessing the impact of small changes in auxiliary load energy consumption.

The automotive industry is rapidly expanding its Hybrid, Plug-in Hybrid and Battery Electric Vehicle product offerings in response to meet customer wants and regulatory requirements. One way for electrified vehicles to have an increasing impact on fleet-level CO2 emissions is for their sales volumes to go up. This means that electrified vehicles need to deliver a complete set of vehicle level attributes like performance, Fuel Economy and range that is attractive to a wide customer base at an affordable cost of ownership. As part of “democratizing” the Hybrid and plug-In Hybrid technology, automotive manufacturers aim to deliver these vehicle level attributes with a powertrain architecture at lowest cost and complexity, recognizing that customer wants may vary considerably between different classes of vehicles. For example, a medium duty truck application may have to support good trailer tow whereas a C-sized sedan customer may prefer superior city Fuel Economy.