Dynamics of Hydraulic Drive Equipped with Discrete Return Flow Controller

This paper dwells upon the research into the dynamics of a hydraulic drive equipped with a flow controller for the return line of its hydraulic cylinder. This circuit is different from the existing discrete control solutions we know in the sense that its discrete controller is at the return line, making such circuit usable in hydraulic drives that carry co-directional or alternating loads. To assess the dynamic properties of this type of hydraulic drive, the authors built a mathematical model. The simulations in SimInTech produced the curves of speed change and piston rod positioning, pressures, and flow from the cylinder cavities; curves of pressures as the functions of the controller parameters (frequency and duty cycle of PWM). The findings are as follows: the amplitude of pressure fluctuations in the hydraulic cylinder cavities depends on the PWM frequency, as at under 15 Hz (which is close to the self-oscillation frequency of a hydraulic system), this amplitude can reach 100% of the static pressure; at 15–30 Hz, 50%; at ≥50 Hz, it is below 10%; the time it takes the rod to change its speed depends on the PWM frequency. Approaching 50 Hz, the transient becomes ever longer; at >50 Hz, it becomes virtually constant; for a discrete flow controller placed at the outlet, the optimal parameters are PWM frequency of 25–50 Hz and PWM duty cycle of 0–0.5.