Abstract
The nozzle-flapper valve has been widely used as a preamplifier in electro-hydraulic servovalves by virtue of the characteristics of high sensitivity, broad bandwidth and a relatively simple construction.
However, when we increase the supply pressure, we often experience very high frequency self-excited oscillation of the nozzle-flapper valves, and also observe hysteresis phenomena such that two stability limits exist according to the struting and stopping of the oscillation.
To the authors, knowledge, there have been very few published papers about the self-excited oscillation of the nozzleflapper valve, and no researches has been made on the hysteresis of stability limit.
Therefore, the purpose of this research is to clarify the causes of the self-excited oscillation and the hysteresis of stability limit.
From the results of the experiments carried out the following became clear: 1) the magnitude of the discharge coefficient was strongly dependent of the flow rate through the orifice or the nozzle: 2) consequently, the nonlinearity between the flapper displacement and the jet force acting on the flapper was saturation (soft) or anti-saturation (hard) owing to the choice of the operating (equilibrium) point of the valve decided by the nozzle-flapper distance and the supply pressure.
As the result of the above mentioned, it was shown theoretically as well as experimentally that the jet force strongly. contributes to the self-excited oscillation of the valve and that the anti-saturation characteristic of the jet force results in the hysteresis of stability limit.
