为了满足挖掘机液压马达在复杂工况下变速驱动控制的要求，设计了采用变速阀控制的液压马达的变转速调节系统，建立了带变速阀的液压马达系统模型，分析了变速阀先导油腔阻尼孔直径、主阀初始开口量、阻尼孔直径以及弹簧刚度等参数对马达转速切换稳定性的影响．理论与试验结果表明: 先导油腔设置阻尼孔有利于提高变速阀的换向性能，缩短马达转速切换响应时间; 主阀初始开口量、阻尼孔直径、弹簧刚度对马达转速切换稳定性均有显著影响; 所建立的带变速阀的液压马达系统模型的计算结果与试验结果相吻合．

In order to meet the variable speed drive requirements of the hydraulic motor of excavators under com-plex operation conditions,a variable speed control system with a shift valve was designed for the hydraulic motor.Then,the system model of the hydraulic motor was established,and the effects of some main parameters,such asthe diameter of the damper orifice at the pilot pressure port,the initial displacement of the valve spool,the diame-ter of the damper orifice at the valve pool and the spring stiffness,on the speed- switching stability,were analyzed.Theoretical and experimental results show that (1) setting a damper orifice at the pilot pressure port helps to im-prove the commutation performance of the shift valve and shorten the speed- switching time of the motor; (2) the ini-tial displacement of the valve spool,the diameter of the damper orifice and the spring stiffness all remarkably influ-ence the speed- switching stability of the hydraulic motor; and (3) the calculated results obtained by the theoreticalmodel accord well with the experimental ones.