Subjective and Objective Quantification of Steady-State Idle Vibration Felt Through the Seat

This research is the result of an effort to objectively quantify idle vibration felt at the seat during steady-state idle conditions. A previously used seat vibration metric using the root-sum-square (RSS) of vertical, lateral and longitudinal degrees-of-freedom (DOFs) measured at the seat base was found to not adequately describe the human perception of 34 test subjects (R²=0.63). Using the Ford vehicle vibration simulator, a new metric was developed. Thirty-four test subjects participated in a paired comparison study in which six-DOF (vertical, lateral, longitudinal, pitch, roll and yaw) simulations were reproduced from eight different vehicles. The stimuli used in the study spanned a wide range of vehicles, engine types and configurations. The paired comparison subjective results were used in a correlation of objective metrics. The resulting metric takes vibration measured at various locations of the seat base and projects these vibrations to the seat top. The seat top vibrations are then frequency weighted according to previously measured seat transmissibilities for vertical, lateral and longitudinal DOFs. Using non-linear regression, it was then determined that the RSS of the frequency-weighted and projected DOFs could adequately describe the impressions of the subjects if the vertical DOF is weighted more heavily as either lateral or longitudinal DOFs. This new metric better represents the actual vibration felt by customers and, as a result, produced a fit of R²=0.94 to the subjective data. A follow-on subjective experiment was then conducted to validate the new metric using five new data samples. The combined data set of 13 vehicles produced a linear fit of R²=0.84.