对称负重合型气动伺服阀零位流动状态分析

针对负重合型气动伺服阀(PSV)零位特性设计缺少理论依据问题,根据单个节流口的气体质量流量公式建立起气动伺服阀滑阀级的数学模型,采用假设求证法分析了零位时气体流经上、下游节流口的流动状态与影响因素之间的关系。结果表明在不同供、排气压力比下,负重合量不均等系数小于0.5283的气动伺服阀有3种可能的零位流动状态,即上、下游节流口均为亚声速流动,或者均为声速流动,或者上游节流口为声速时下游节流口为亚声速流动;负重合量不均等系数不小于0.5283的气动伺服阀有两种可能的零位流动状态,即上、下游节流口均为亚声速流动,以及上游节流口为亚声速时下游节流口为声速流动。可知气动伺服阀的零位流动状态由负重合量不均等系数与供、排气压力比共同决定。以负重合量不均等系数分别为0.5、1、2的气动伺服阀为例进行了计算和实验验证,实验结果与理论分析相吻合。

Neutral flow state analysis of pneumatic servovalves with symmetric underlaps

In view of lacking a theoretical basis for null characteristics design of pneumatic servovalves (PSV) with symmetric underlaps, their slide valve stage mathematical model is established according to gas mass flow formula of single orifice. Influencing factors of the neutral flow states of the upstream and downstream orifices are analyzed adopting hypothesis verification method. It shows that at different ratios of supply and exhaust pressure, PSVs of uneven coefficient less than 0.5283 have three combinations of neutral flow state, which are both upstream and downstream orifices in subsonic state, in sonic state, and the upstream orifice in sonic flow while the downstream one in subsonic flow; and PSVs of uneven coefficient no less than 0.5283 have two combinations of neutral flow state, respectively, both the upstream and downstream orifices in subsonic flow, and the upstream orifice in subsonic state while the downstream one in sonic state. So the uneven coefficient of underlaps and the ratio of supply and exhaust pressure jointly determine the neutral gas flow state. Three valves with uneven coefficient of 0.5,1,2 are verified by calculations and experiments. The theoretical analysis is in good agreement with experimental results.