Performance analysis of a high-frequency two-stage proportional valve piloted by two high-speed on/off valve arrays

Two-stage proportional valves (TSPV) have been used extensively for electro-hydraulic control systems with large-flow applications. Due to the inherent characteristics of the pilot spool, such as hysteresis, motion quality, and dead zone, the dynamic performance of the traditional TSPV cannot be further improved. To solve this issue, this paper proposes a high-frequency two-stage proportional valve (HFTSPV) piloted by two high-speed on/off valve arrays, which integrates the advantages of dual nozzle flapper mechanism and parallel-connected valve technology. First, an entire mathematical model is established, in which some key parameters are estimated by experiments, such as the actual diameters and flow coefficients of orifices, and flow coefficient of pilot valve. Then, the influences of fixed orifices with different diameters on the dynamic characteristics of main spool are explored. Subsequently, the optimal diameter of fixed orifice is calculated theoretically by using the maximum pressure sensitivity and flow linearity, aiming to realize the high dynamic and small displacement fluctuation. Finally, step and sinusoidal tracking experiments show that the delay time of the HFTSPV is close to 3.3 ms, and the displacement fluctuation decreases with the increase of tracking frequency. Amplitude-frequency results indicate that -3 dB frequency of the HFTSPV reaches 16 Hz under +/- 50% full scale and 30 Hz under 0%-50% full scale.