Transmission of roll, pitch and yaw vibration to the backrest of a seat supported on a non-rigid car floor

The transmission of roll, pitch and yaw vibration from the floor of a small car to the seat backrest has been investigated with three road conditions. At the seat base, there were distinctive differences between roll vibration at the front and rear of the seat base and between pitch vibration at the left- and right-hand side of the seat base. The yaw motion was generally small relative to the roll and pitch motion. At high frequencies, the yaw motion calculated from the difference between fore-aft vibration at the left- and right-hand side of the seat base was less than the yaw motion calculated from the differences between lateral vibration at the front and back of the seat base. Furthermore, yaw motion calculated from the difference in lateral vibration at the right-hand side of the seat was greater than that at the left-hand side, due to differences between the two lateral accelerations at the two right corners of the seat base. The measurements indicated that the seat base was not a rigid structure in either roll, pitch or yaw.The transmission of rotational vibration from the non-rigid seat base to fore-and-aft, lateral and vertical vibration at the seat backrest was investigated using single- and multi-input models. It was found that pitch and roll vibration, together with translational vibration at the seat base, made significant contributions to seat backrest vibration. For predicting seat transmissibility in the fore-aft and vertical directions, a translational model comprising all the least-correlated fore-aft and vertical inputs, and a combined rotational and translational model consisting of the pitch vibration input and part of the least-correlated fore-aft and vertical inputs appeared equally good. Low coherency in the transmission of vibration to the lateral direction of the seat backrest observed when considering only translational vibration at the seat base was resolved after taking into account the effect of the roll vibration at the seat base