Generation mechanism of high-frequency oscillation in proportional valve with a high-speed on/off valves bridge as the pilot stage

A digital proportional valve has a main spool that operates with a high-speed on/off valves bridge as the pilot stage. However, this can cause the spool to undergo high-frequency oscillation during movement, leading to a slower valve response, lower control accuracy, and even control failure. Therefore, it is important to study the oscillation mechanism of the valve. To address this issue, we establish a detailed dynamic model of the digital proportional valve, and analyze the factors affecting the response performance of the proportional valve spool. A method of half-bridge control based on duty cycle is proposed to eliminate the oscillation. The influence regularity of each factor on the response performance of the valve is explored. It is proved that the control method of the high-speed on/off valves bridge and the Pulse-width modulation (PWM) signal-switching frequency of the high-speed on/off valves are the main reasons for the oscillation of the main spool. The proposed half-bridge control method based on duty cycle can eliminate the oscillation in a lower frequency range. In addition, the results show that the pilot oil pressure is an important contributor to the oscillation; the higher the pilot oil pressure, the easier the main spool oscillation occurs. However, the spool mass, oil temperature, and coil temperature of the high-speed on/off valve do not affect the stability of the digital proportional valve.