Analysis of the Driving Seat Vibrations in High Forward Speed Tractors

The transition towards increased forward speeds in agriculture introduces new technical problems related to dynamic behaviour and the exposure of tractor drivers to high levels of whole-body vibration during on-road and off-road transportation and during field operations. In this study, vibrations transmitted from the ground to the driver's seat have been analysed using methods that meet International Organisation for Standardisation (ISO) standards using a four-wheel-drive tractor, equipped with a front suspension axle and a suspended cab, operating at 11.1 and 13.9 m s?1. The test runs simulating the transportation of agricultural implements were conducted on a rectilinear plane tract of a conglomerate bituminous closed track. Two different tyre types, coded ‘A’ and ‘B’, were tested at different forward speeds. Values for the root-mean-square (RMS) accelerations for each measurement axis and the corresponding vector sum av measured on the tractor rear axle were not proportional to the forward speeds 11.1 and 13.9 m s?1 for tyre A. For tyre B, the vector sum av decreased by 18%. No significant difference was found in the acceleration values on the driver's seat. A 1/3 octave band analysis was performed at the frequency range 1–1000 Hz. Accelerations of the tractor rear axle, beyond the forward speed range of 11.1–13.9 m s?1, increased by 48% along the vertical Z-axis in the frequency range 400–1000 Hz for tyre A and decreased by 66% in the frequency range 1–2 Hz along the horizontal X-axis and by 28% along the Y-axis for tyre B. Comparing the two tyres at 11.1 m s?1 forward speed, the average acceleration values for tyre B compared with tyre A were lower along the X-axis (84%) and greater along the Z (74%) and Y (51%) axes. Comparing the two tyres at 13.9 m s?1 forward speed, the acceleration values for tyre B compared with tyre A were lower along the X-axis (78%) and greater (53%) along the Z-axis. The same analysis was also applied to driving seat accelerations at frequencies of 1–80 Hz. Accelerations for tyre A appeared to have similar trends at the two forward speeds except along the vertical Z-axis, for which acceleration decreased by 22% when forward speed increased. For tyre B, the average acceleration along the X-axis increased by 50% in the frequency range 1–2.5 Hz when forward speed increased. On the other hand, accelerations along the Y and Z axes decreased by 27% and 44%, respectively, when forward speed increased. Comparing the two tyres at 11.1 m s?1, average accelerations for tyre B were found. They were lower by 36% along the X-axis in the frequency range 1–2.5 Hz and greater by 14% along the Z-axis compared with tyre A. At 13.9 m s?1 forward speed, the average acceleration for tyre B compared with tyre A was lower by 17% along the Y-axis. Despite the differences in behaviour of the two tyres with respect to forward speed, the performances were the same in the values of limit fatigue that were bounded within the limit of 4 h for all treatments.