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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。
When the tractor accelerates, the condition of equal speed changing section of hydraulic mechanical continuously variable transmission in the strict sense is destroyed, and the influence of inertia load is needed to study the changing process and the influencing factors of hydraulic mechanical continuously variable transmission in the process of accelerating tractor. First, the drive system model of the existing test rig, including the engine, transmission, load, and clutch control circuit, was built under Simulation X and tested. Considering the influence of inertial mass on the course of changing section during the accelerating process of tractor, a complete tractor model including the rear axle is further constructed on the basis of the foregoing model. Then, based on two indexes of tractor peak acceleration and clutch frictional loss, the five groups of tractor or transmission operating parameters that may affect the course-changing process are simulated and analyzed. The results show that the section change is started before the theoretical change point of the transmission (-0.65 s in this study), the unloading time of the clutch to be separated is delayed (0.2 s in this study), and the flow of the clutch to be engaged is increased L / min), the use of integrated pump control hydraulic motor and limit the maximum engine speed when the section change, can improve the tractor section change process in the acceleration section quality. In addition, the design quality of the tractor should consider the impact of speed impact and dynamic impact. The research can provide reference for the research of tractor CVT and its control system.