拖拉机液压机械无级变速器加速换段过程动力学仿真

拖拉机加速行驶时,破坏了严格意义上的液压机械无级变速器等速换段条件,加之惯性负载的影响,需要对拖拉机加速过程中液压机械无级变速器的换段过程及其影响因素进行研究。首先,在Simulation X下构建了现有试验台架的传动系统模型,包括发动机、变速器、负载以及离合器控制油路,并对其进行了试验验证。考虑到拖拉机加速过程中惯性质量对换段过程的影响,在前述模型的基础上,进一步构建了包括后桥在内的完整拖拉机模型。而后,基于换段期间拖拉机的峰值加速度与离合器摩擦损耗2项指标,对5组可能对换段过程构成影响的拖拉机或变速器工作参数进行了仿真分析。结果表明,在变速器理论换段点之前开始换段（该研究取?0.65 s）,延迟待分离离合器的卸油时间（该研究取0.2 s）,提升待接合离合器的流量水平（该研究取6 L/min）,使用一体式泵控液压马达以及限制换段时的发动机最高转速,均可提升拖拉机在加速换段过程中的换段品质。此外,拖拉机的设计质量应当综合考虑速度冲击与动载冲击的影响。该研究可为拖拉机无级变速器及其控制系统的研究提供参考。

Dynamic simulation on shift process of tractor hydraulic power split continuously variable transmission during acceleration

The effect of the design parameters of the hydraulic power split continuously variable transmission on the shift process during tractor acceleration was investigated. First, the model of the power train was developed with the software of Simulation X, including the engine, the transmission, the load and the clutch control system, and 8 groups of the experiments were used to validate the correctness of the model. Considering the effect of the rotational inertia on the shift process during acceleration, a complete model of the tractor with the rear axle was built. Then, based on the evaluating index of the tractor peak acceleration and the clutch friction work, five groups of design parameters were simulated and analyzed. According to the simulation results, the trend of the shift process according to the different shift starting time is not monotonous, the shift impact could be reduced by shifting before the designed shift points (about?0.65 s in this study); the maximum slipping time is a function of the flow and pressure of oil, in order to shorten the period of the slipping time and improve the shift quality, long overlap time (0.2 s in this study) and large charge flow (6 L/min in this study) should be used; the large tractor weight can reduce the speed impact of tractor and the friction work of clutch but lead to bad impact on dynamic load, therefore the determination of the tractor weight should fully consider the impact of both the traveling speed and dynamic load of tractor. In addition, the shift impact could also be reduced by using Integrated Hydraulic Pump-Motor and reducing the engine speed during shift, but the effect of the swash plate axial piston units and engine on shift process was not so significant. This study can provide references for the study in continuously variable tractor transmissions and the control system.