拖拉机液压功率分流无级变速器换段规律研究

Shift Performance of Tractor Hydraulic Power-split Continuously Variable Transmission

为了改善拖拉机液压功率分流无级变速器的换段品质,基于仿真与试验相结合的方法,对其影响因素及其参数匹配关系进行了深入研究。首先,基于油压试验与回位弹簧位移补偿试验建立了离合器轴向力模型以及传动系整机模型,并对该仿真计算模型进行了不同工况下的试验验证;而后,将液压功率分流无级变速器换段品质的影响因素划分为3大类,即工况因素、设计因素与可控因素,并分别对其中的8个子类因素进行了仿真研究,从理论上阐述了其变化规律;最后,研究了换段品质各影响因素之间的交互性及其作用规律的稳健性,据此得到换段参数之间的最佳匹配关系。研究结果表明:轴向柱塞单元油液工作容积对换段品质无显著影响;发动机转速对换段品质的影响是相对的,受到换段点泵排量的制约;在等速换段条件下,离合器充油流量和换段时序的提高均对换段品质具有改善作用;离合器充油压力、负载转矩、负载惯量3因素对换段品质的影响则受到多种因素制约,其规律自身不具备稳健性。

In order to improve the shift performance of the tractor hydraulic power-split CVT,the influence factors and the parameters matching were studied based on the method of both simulation and experiments. First of all,the model of clutch axial force and the model of transmission system were built based on the experiments on shift pressure and piston displacement. The model was proved to be correct and effective with eight groups of experimental verification under different test conditions. Then,the influence factors were divided into three groups,i. e.,the external factors,the designing factors and the controllable factors,and each influence factor on shift performance was simulated and analyzed. Finally,the interactive effects among these factors on shift performance were studied and the optimal parameters were acquired. The research results showed that there was no significant effect of the pipeline volume of swash plate axial piston units on shift performance. The effect of engine speed on shift performance was influenced by the displacement of variable displacement pump. The shift performance would be improved with the increase of clutch oil charge flow and shift timing under the prerequisite of constant output speedcondition. The effects of clutch oil charge pressure,load torque and inertia on shift performance were not robustness. The research is helpful to improve the dynamic characteristics of the hydraulic power-split CVT and it is useful to develop the control unit.