In the solution of the motor damage problems of excavating chain hydraulic system of a certain type of domestic ballast cleaning machine, based on the closed hydraulic system structure and considering the pressure changes of low pressure side, characteristic qualitative analysis model of the closed hydraulic system output characteristics was established and the load changes of the motor were analyzed. The analysis was verified by simulation and tests. The results show that the low pressure of closed hydraulic system changes with the load of the motor, while the low pressure fluctuations can amplify the high pressure and flow turbulence, which makes the motor cavity piston rings under the load of high frequency and high amplitude and makes them break in very short time. According to the variable mechanism requirements of the pump and motor, the low pressure should at least meet the requirements for the maximum variable of the pump or motor. For load fluctuation condition, the short of flow and pressure of the low pressure side should be considered when load is at its maximum, and the flow match of oil supply pump, flushing valve and the system should be determined reasonably. For the closed hydraulic system with higher requirements, independent constant voltage source should be used to provide control oil to the variable mechanism. The setting pressure of the overflow valve by the oil supply pump should be no less than 2 Mpa, and the low pressure can be maintained a constant by connecting a 10 mL ? R-1 oil supply pump to the low pressure side.%在解决国产某型清筛机使用时挖掘链闭式液压系统马达损坏问题的过程中,基于闭式液压系统的结构,在考虑低压侧压力变化的前提下建立闭式液压系统输出特性定性分析模型,分析马达负载的变化,并通过仿真和试验加以验证.结果表明:闭式液压系统低压侧压力随着马达上外负载的变化而波动,而低压侧压力的波动会放大高压侧压力和流量的震荡,使马达高压腔活塞环受到高频高幅交变负载的作用,并在短时间内断裂；根据泵和马达的变量机构工作需要,低压侧压力的设置至少应满足泵或马达的最大变量要求；对于负载波动的工况,应考虑负载处于最大幅值时可能出现低压侧流量和压力不足的情况,合理确定补油泵、冲洗阀流量与系统油路流量的匹配；对于要求较高的闭式液压系统,应采用独立的恒压源向变量机构提供控制油；补油泵旁接的溢流阀的设定压力应不低于2 MPa,并且在低压侧外接一排量为10 mL·r-1的补油泵即可维持低压侧压力的恒定.
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