Road Vibration Investigation Using the Ford Vehicle Vibration Simulator 2001-01-1572

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. The steering wheel was the next important contributor followed by the floorpan. Various simulations were created in which certain spectral components were either partially or completely eliminated using FIR zero-phase filters. Whether or not a component was filtered depended on its spectral prominence for the particular degree-of-freedom being addressed. At the seat track, the nervous character was most affected by 10.5, 11, 15, 17 and 17.5 Hz components At the steering wheel, components in the 30-32 Hz range and the 36 Hz component attenuated together resulted in a perceivable difference. In general, a 6 dB reduction of the components was necessary to significantly improve the ride and place the vehicle among the leaders for this phenomenon. Finally, operational deflection shapes taken from on-road data were used to uncover potential sources of these spectral components. These sources, and measures to reduce their contributions, are discussed.