Effects of gear selection of an agricultural tractor on transmission and PTO load during rotary tillage

•Torque on the transmission increased significantly with increase of both ground and PTO speeds.•Torque on the PTO increased significantly with the increase of PTO rotational speed.•Rotary tillage exerted significantly greater loads on PTO than on transmission. For better performance and durability of a tractor during field operations, it is necessary to select the optimal gear setting for the operation. The purpose of this study was to analyze effects of the gear selection on load acting on the transmission and PTO shafts of a 75kW agricultural tractor during rotary tillage with a 20-cm tillage depth. In order to measure the loads acting on the transmission and PTO input shafts, a load measurement system was installed on the tractor. The system consisted of strain-gauge sensors to measure the torque on the transmission and PTO input shafts, a radio telemetry I/O interface to acquire the sensor signals, and embedded software to acquire the data. Rotary tillage was conducted at three ground speeds and three PTO rotational speeds under upland field sites with the same soil conditions. The load data was converted to a load spectrum using the rain-flow counting and SWT (Smith Watson Topper) equations. Sum of damage due to the load was calculated using the Modified Miner's rule for each gear selection, and then the load severeness was calculated as the relative magnitude of the damage sum. The average torque on the transmission input shaft increased significantly as the ground speed increased from L1 (1.87kmh−1) to L3 (3.77kmh−1) at the same PTO rotational speed. Also, the average torque on the PTO input shaft increased as the PTO rotational speed increased at the same ground speed. Rotary tillage exerted significantly greater loads on the PTO input shaft than on the transmission input shaft. The severeness of the load on the transmission and PTO shafts increased, indicating possible decreased fatigue life, as both the ground and PTO rotational speeds increased. Results of the study might provide information useful for optimum gear selection for rotary tillage, considering not only field efficiency, but load severeness on the transmission and PTO input shafts.