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In-vehicle subjective evaluations of a mid-sized SUV exhibited an objectionable vibration character when driven over smooth road surfaces with minor rolling irregularities. As a result, a project was initiated to systematically identify problem frequency components and degrees-of-freedom that contribute to the phenomenon sometimes referred to as “nervousness.” The Ford Vehicle Vibration Simulator (VVS) was used to simulate the vibrations felt on the road. Eleven degree-of-freedom (DOF) simulations were produced. The seat simulation contained three translational (vertical, lateral and longitudinal) and three rotational (pitch, yaw and roll) DOFs. The steering wheel consisted of all three translational components in addition to the DOF associated with wheel rotation. The floorpan was excited in the vertical direction only. By systematically eliminating various DOFs, it was determined that the seat contributed the most to the objectionable vibration.

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.