Synchronous acceleration method of load spectrum for tractor rotary tillage operation based on wavelet transform

Advancing indoor reliability tests based on load spectrum is an important means to improve the efficiency and accuracy of tractor product quality verification. However, due to the large amount of time occupied by small load cycles in the load spectrum of tractor tillage operations, indoor reliability tests are long, costly, and inefficient. This paper addresses the limited capability of conventional load spectrum acceleration methods to simultaneously accelerate multiple load types and proposes a synchronized acceleration method for rotary tillage load spectrum based on wavelet transform, along with loading application experiments. First, a tractor tillage operation load collection experiment was conducted, and based on the peak over threshold model, a 1-time extrapolated tillage load spectrum was obtained for acceleration method research. Subsequently, by combining wavelet transform with Hilbert envelope analysis, a process for synchronizing the acceleration of tillage load spectra was proposed. The Daubechies wavelet basis function (DbN) was used to decompose the load signal, and by reconstructing the detail wavelet coefficients, detail wavelet components at different scales were obtained. The cumulative sum of squares of detail wavelet components across all scales was computed to represent the load damage contribution. By setting a threshold, the segments with significant damage were identified, and based on Hilbert envelope analysis, the extraction of high-damage segments was realized. Finally, synchronization acceleration was achieved based on the time-domain synchronicity of the tillage load spectrum. In addition, to measure the acceleration efficiency of load spectrum and find the optimal acceleration parameters suitable for tractor tillage load spectra, a pseudo-damage acceleration efficiency (PDAE) index was proposed to evaluate the acceleration effect. Ultimately, through data comparison, the optimal acceleration parameters suitable for tractor tillage operation load spectra were determined. For the power take-off (PTO) torque load spectrum, the Db1 wavelet should be used at a threshold step size of 16 for acceleration; for the suspension load spectrum, the Db7 wavelet should be used at a threshold step size of 18 for acceleration. Based on these parameters, synchronization acceleration of the 1-time extrapolated tillage load spectrum was achieved, with a time retention ratio of 81.32% for the accelerated load spectrum, a pseudo-damage retention ratio of 98.99% for the PTO torque load spectrum, and a pseudo-damage retention ratio of 97.56% for the suspension load spectrum. This was compared with and validated against traditional damage-retention-based acceleration methods. The comparative results of statistical characteristic parameters show that the proposed acceleration method can accelerate the testing time by 10.07% while retaining the load damage characteristics, demonstrating higher acceleration efficiency. Through rainflow counting, the mean-frequency and amplitude-frequency histograms of the accelerated load spectrum were obtained. On the basis of verifying the accuracy of the acceleration effect, the reasons for the high acceleration efficiency of the wavelet method were analyzed. Finally, a bench test method for tillage load spectrum was proposed, and a loading bench was developed. A fuzzy PID controller-based loading control algorithm for tillage load spectrum was also proposed. Bench loading application tests based on the accelerated tillage load spectrum were conducted. The test results indicate that the loading bench has a response error of -7.53% for the PTO torque load spectrum and a response error of -2.48% for the suspension load spectrum, showing that the overall error of the loading bench for the rotary tillage load spectrum meets the actual loading application requirements, and dynamic loading of the tillage working conditions can be achieved. This research can provide theoretical references and platform support for tractor load testing and accelerated fatigue reliability test applications.