Title page for ETD etd-11092011-115101


Type of Document Master's Thesis
Author Meyer, Mark J.
Author's Email Address mjmeyer@vt.edu
URN etd-11092011-115101
Title Understanding the challenges in HEV 5-cycle fuel economy calculations based on dynamometer test data
Degree Master of Science
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Nelson, Douglas J. Committee Chair
Anderl, Reiner Committee Member
Lohse-Busch, Henning Committee Member
Winner, Hermann Committee Member
Keywords
  • fuel consumption
  • hybrid electric vehicles
  • fuel economy
  • dynamometer testing
Date of Defense 2011-11-16
Availability unrestricted
Abstract
EPA testing methods for calculation of fuel economy label ratings, which were revised beginning in 2008, use equations that weight the contributions of fuel consumption results from multiple dynamometer tests to synthesize city and highway estimates that reflect average U.S. driving patterns. The equations incorporate effects with varying weightings into the final fuel consumption, which are explained in this thesis paper, including illustrations from testing. Some of the test results used in the computation come from individual phases within the certification driving cycles. This methodology causes additional complexities for hybrid electric vehicles, because although they are required to have charge-balanced batteries over the course of a full drive cycle, they may have net charge or discharge within the individual phases. The fundamentals of studying battery charge-balance are discussed in this paper, followed by a detailed investigation of the implications of per-phase charge correction that was undertaken through testing of a 2010 Toyota Prius at Argonne National Laboratory’s vehicle dynamometer test facility. Using the charge-correction curves obtained through testing shows that phase fuel economy can be significantly skewed by natural charge imbalance, although the end effect on the fuel economy label is not as large. Finally, the characteristics of the current 5-cycle fuel economy testing method are compared to previous methods through a vehicle simulation study which shows that the magnitude of impact from mass and aerodynamic parameters vary between labeling methods and vehicle types.
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