Abstract:The compilation of the load spectrum of tractor power output components is the main method to study the relationship between tractor working load and fatigue life. Based on the peak over threshold (POT) model, the time-domain extrapolation method of the tractor power take-off (PTO) operation load spectrum was studied. Aiming at the problems of complex calculation and low accuracy of the commonly used threshold selection methods for timedomain extrapolation, an automatic threshold selection method based on false discovery rate (FDR) was proposed. Based on this method, extrapolation of the tractor PTO torque load spectrum was realized. Firstly, a tractor PTO torque wireless acquisition system was developed to collect tractor PTO operating load data and perform data preprocessing;then, the FDR automatic threshold selection method was used to select the optimal threshold, and the upper threshold of the time-domain extrapolation data was determined to be 342N·m and the lower threshold was 100N·m. The maximum likelihood estimation was used to fit the scale parameters and shape parameters of the generalized Pareto distribution of excess threshold data, and the peak over threshold (POT) model of PTO torque load was built and compared with the fitting results of traditional image methods: the determination coefficients between the fitting results of the two methods and the load samples were greater than 0.995;from the perspective of goodness of fit, for the upper threshold, the goodness of fit of the automatic threshold selection method was 8.7% smaller than that of the image method, and for the lower threshold, the goodness of fit of the automatic threshold selection method was 31.21% smaller than that of the image method. Finally, the PTO load data was extrapolated based on the POT model, and 1 time extrapolated load data was compared with the original load time history;when the time domain extrapolation factor was 131 and the cumulative frequency of PTO torque reached 106 times, the PTO torque load spectrum was obtained. The extrapolated load spectrum was verified based on statistical characteristics and rainflow counting method. The results showed that the extrapolated load spectrum had the same distribution law as the original load spectrum, which can realize the twoway extrapolation of the average amplitude on the basis of retaining the load characteristics, providing a theoretical basis for the compilation of the tractor PTO torque load spectrum.
