1995-02-01

The Design of a Vehicle Inertia Measurement Facility 950309

This paper describes the design of a vehicle inertia measurement facility (VIMF): a facility used to measure vehicle center of gravity position; vehicle roll, pitch, and yaw mass moments of inertia; and vehicle roll/yaw mass product of inertia. The rationale for general design decisions and the methods used to arrive at the decisions are discussed.The design is inspired by the desire to have minimal measurement error and short test time. The design was guided by analytical error analyses of the contributions of individual system errors to the overall measurement error. A National Highway Traffic Safety Administration (NHTSA) database of center of gravity position and mass moment of inertia data for over 300 vehicles was used in conjunction with the error analyses to design various VIMF components, such as the roll and yaw spring sizes. This provides for a design that yields good experimental repeatability for the full range of vehicles that can be tested on the VIMF, basically all currently produced light vehicles.The paper also discusses aspects of the VIMF software, for example: the analytical curve fitting, used to determine periods of oscillation to improve system accuracy and repeatability; and the error checking of results, developed to increase system reliability.Lastly, results from the VIMF for two calibration fixtures are presented and compared to the computed center of gravity position and inertia values.

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