Optimal Control Method for Tractor Power-shifting Process Using Time-varying Disturbance Observer
Abstract
Due to the complex working conditions of tractors, which are influenced by the working environment, soil conditions, and traction loads, random time-varying disturbances during power shifting process could easily cause shifting jerk and even damage the transmission. Therefore, an optimal control method for tractor power shifting process considering time-varying disturbance observer was proposed. Firstly, the dynamic characteristics of the tractor shift process were analyzed to establish the shifting process dynamics model. The shift time, sliding friction work, and shock degree were taken as the shifting quality indicators, and a quadratic index function of the shifting control system was constructed. Then a high-order disturbance observer (HDO) was introduced to estimate the time-varying disturbances and their derivatives during the shifting process, and the linear quadratic regulator (LQR) was derived and solved for the optimal control law of the shifting process based on the Hamiltonian function. Finally, a hardware-in-the-loop simulation platform for tractors was built based on dSPACE and Matlab/Simulink to verify the shifting process performance under different operating conditions. The results showed that taking the shift from 1LL gear to 1L gear as an example, the shifting times under the transportation and plowing working conditions were 0.72s and 0.85s respectively, which were reduced by 22.58% and 38.4% compared with that of LQR. After compensation by HDO, the maximum shifting jerks were 16.11m/s3 and 8.51m/s3, respectively, which were 5.29% and 2.04% higher than that of LQR, the shifting jerk difference was not obvious, but the sliding friction work control effect was significant, being only 4.61kJ and 8.82kJ, which were reduced by 38.04% and 59.17% compared with that of LQR. The method could effectively observe and suppress the time-varying disturbances during the shifting process, and improve the shifting comfort.
Keywords: power shift transmission;shifting process control;high-order disturbance observer;linear quadratic regulator;shifting quality
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