拖拉机液压机械无级变速器的速比控制

Speed ratio control of tractor hydraulic mechanical CVT

为了实现无级调速拖拉机工作时的速比调节与动力换段,该文对其液压机械无级变速器的速比控制进行了研究。根据变速器的速比特性和液压系统辨识试验,确定了变量泵励磁电流、泵-马达速比与变速器速比三者之间的稳态和动态数学模型。基于该模型,设计了基于单神经元网络的神经PID控制器,在Matlab/Simulink下研究了其参数整定规律,得到了一组可行参数并通过了试验验证;在此基础上提出了开环与闭环相结合的继电控制模式,使神经PID控制器工作于特定的区间和条件之下,有效避免了频繁的换段和马达换向问题;并通过台架试验证实了该算法的正确性及可行性。试验中,每个偏向的开环调节时间为5~6s,调速过程平稳、无静差,变速器能在包含换段点在内的任意速比条件下可靠运行。该研究可为变速器的后续设计及动力匹配提供参考。

This paper studied the speed ratio control problem of the hydraulic mechanical continuously variable transmission. First, based on the speed ratio characteristics of the transmission and the experiment on the identification of the hydraulic system, the steady-state and dynamic mathematical model among the excitation current of the variable displacement pump, the speed ratio of the pump-motor system and the speed ratio of the transmission were built. It showed that the speed ratio of the transmission is a segmented function of the speed ratio of pump-motor system. The relationship between the excitation current of the variable displacement pump and the speed ratio of pump-motor can be considered as a third-order system. According to this model, a neural PID controller based on single neuron network was developed. A set of feasible parameters, i.e. the inertia coeffecient k and the learning coeffecient ηP, ηI, ηD of the PID controller can be determined according to the tuning law which have been studied based on the simulation and experiment. From that, it showed that an appropriate k,ηP, a largerηI and a smallerηD can meet a satisfactory internal-stage control quality. Secondly, the open-loop and closed-loop control mode defined by a relay logic was proposed in this paper, so as to make the neural PID controller work at specific intervals and conditions and effectively avoid the frequently power-shift and direction-changed of motor rotation. The controller calculates the target stage and direction of motor rotation according to the target speed ratio of transmission. Once the current stage and direction of motor rotation are different from the target, the power-shift logic and the displacement adjustment logic of the pump can be actived by the open-loop controller to reach the target states following the stepless speed changing rule, otherwise, the closed-loop controller would adjust the speed ratio of the transmission to the target without power-shift and direction-changed of motor rotation based on the neural PID technology. Finally, an experiment of speed ratio control was conducted. During the experiment, it took 5-6 s to hold one direction of motor rotation when the open-loop controller worked, the process under the speed ratio control was smooth and steady and no steady-state error was there at the end of the experiment, the results proved the algorithm to be correct and feasible.