拖拉机液压机械无级变速箱换段控制优化与试验

为了提高无级变速拖拉机的换段质量，该文对所开发的一种新型液压机械无级变速箱的换段过程进行了试验研究。离合器充油特性试验中，通过改变离合器控制油路参数，获得主油路压力与充油流量对换段时间的影响规律；单因素加载试验中，通过单独改变发动机转速、主油路压力、充油流量、负载转矩，获得各因素单独作用时对换段质量的影响规律；多因素组合加载试验中，设计了3水平4因素组合试验方案，对多个因素综合作用时的变速箱换段质量问题进行了研究；时序优化试验中，通过控制器改变离合器动作时机，获得最佳的换段时序。试验结果表明：离合器主油路压力、充油流量可通过影响换段时间而间接影响到换段质量；重叠时序换段会引起油压陷阱，证明了重叠换段的安全性和可行性；单因素作用时，换段质量与离合器压力、流量正相关，与负载转矩负相关，与发动机转速无关；多因素共同作用时，换段质量的主次影响因素依次为充油流量、负载转矩、主油路压力、发动机转速；此外，采用重叠时序换段可显著改善换段质量。根据试验结果得出，为使该变速箱获得最佳的换段质量，其离合器主油路压力应取值4MPa，充油流量取值5L/min，重叠时序取值120ms。该结论为换段控制策略的制定提供了重要参考。

Experimental optimization on shift control of hydraulic mechanical continuously variable transmission for tractor

Abstract: In order to improve the power shift quality of agricultural tractors with continuously variable transmission, the power shift process of a new kind of tractor hydraulic mechanical CVT was studied. Based on bench tests of the power-shift of the CVT and a homemade control system, we conducted a suite of experiments on the oil charge of the clutches, transmission load with single and multiple factors, and shift timing optimization. During the experiments on the oil charge of the clutches, the engine was turned off, and the relationships between the shift time and the oil pressure of the hydraulic system and the flow rate of the clutch were revealed. During the load experiments with single and multiple factors, the relationship between the shift quality and the rotation speed of the engine, the oil pressure of the hydraulic system, the flow rate of the clutch, and the load torque were revealed. During the experiments on shift timing optimization, the optimized connection time of the clutch was studied. The results show that the shift quality is influenced by the oil pressure of the hydraulic system and the flow rate of the clutch, which would change the shift time. The pressure changing rule of the clutches during the shift process was revealed and proved the overlapping shift to be safe and feasible. The shift experiments with a single factor show that the shift quality is positively related to the flow rate of the clutch and the oil pressure of the hydraulic system, but inversely related to the load torque. There is no significant relation between the shift quality and the engine speed. The shift experiments with multiple factors show that the significance of the factors affecting speed drop and speed impact are the flow rate of the clutch, the load torque, the oil pressure of the hydraulic system, and the engine speed. The significance of the factors affecting the dynamic load are the load torque, the flow rate of the clutch (which is in parallel with the oil pressure of the hydraulic system), and the engine speed. In addition, the overlapping shift would evidently improve the shift quality. According to the experiment results, the optimal flow rate of the clutch is 5 L per minute, the optimal oil pressure of the hydraulic system is 4 Mpa, and the optimal shift timing is 120 ms, i.e. one clutch should be energized 120 ms ahead of the other. The conclusion provides an important reference for the design of transmission control units.