Abstract: Two-stage directional valves usually employ proportional pilot control technology, which has the disadvantages of dead zones, leakage, and the large moving mass of the pilot valve. It is difficult, therefore, to achieve fast-response performance of the main valve. In order to overcome this problem, a switching pilot technology that employs two independent high-speed on/off valves (HSVs) is proposed to replace the traditional pilot proportional valve. Due to the rapid switching characteristics of HSVs, the dead zone of the pilot stage is avoided, and the dynamic response performance of the main valve is improved. The experiments indicate that the switching frequency of the pilot HSVs and supply pressure of the pilot stage have a very large effect on the dynamic performance and control accuracy of the main valve. Increasing the switching frequency of the pilot HSVs is helpful for improving main-valve control accuracy. The larger supply pressure of the pilot stage can achieve a faster dynamic performance of the main valve while causing larger static errors. The results show that the switching pilot technology can clearly improve the static and dynamic performances of the main valve. With the increase of pilot supply pressure, the step rise time is reduced from 21.4 ms to 16.8 ms, and the dynamic performance of the main valve is improved by 21.5%. With the increase of pilot switching frequency, the steady-state error decreases from 24 μm to 20 μm, and the control accuracy of the main valve is improved by 16.7%.

Key words: Pilot-operated proportional valve; Switching pilot stage; High-speed on/off valve (HSV); Dynamic performance; Control accuracy

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