Recently increased requirements for dynamic characteristics of hydraulic servo-drives demanded the use of nonlinear models, in addition to the linearized mathematical ones. Such models have to take into consideration the physical process features occurring in the hydraulic drive. However, references sometimes mention a discrepancy between the values of real natural frequency of oscillations and the theoretical value of natural oscillation frequency defined by the mathematical model, which takes into account only the standard nonlinearities. To identify reasons of abovementioned divergence the experiments have been conducted to study influence of flow unsteadiness on the auto-oscillation frequency of a hydraulic drive. Modern electrohydraulic throttle-controlled drives are usually equipped with the actuation (control) devices, which have operating speed much higher than that of the power part of a hydraulic drive. This circumstance allows us to use a mechanically controlled hydraulic drive to study the non-stationary characteristics of a spool-type valve. As a result of experiments, it has been found that the fluid flow unsteadiness can be taken into consideration through introducing the auto-oscillations of delay time into calculations.

The pilot studied results have a scientific novelty because they for the first time define the influence of the fluid flow unsteadiness in the spool-type valve on dynamics of a hydraulic drive with throttle control.