Investigation on the output characteristics of a bidirectional pulse width modulation rotary valve variable mechanism for hydraulic motor

Pump control system is widely used for flow control in hydraulic system. However, variable mechanism structure in variable displacement pump system is very complicated, and the dynamic response speed of variable speed pump system is low under frequent regulation. Therefore, a new bidirectional variable mechanism based on the principle of fluid pulse width modulation is proposed. Through the design of two shoulders, the oil flow direction is changed. The nonlinear system mathematical model of bidirectional variable mechanism is established, and the dynamic and static characteristics are simulated and analyzed. Research shows that the bidirectional variable mechanism can generate fluid pulse width modulation waveform. The bidirectional adjustment of the hydraulic motor speed can be realized by the axial displacement of the valve core. Within 0.15 s, the motor speed can output stably and reach 28.6 rad/s. The experimental platform of bidirectional variable mechanism is built. The output waveform of the valve port pressure produced by the bidirectional variable mechanism conforms to the pulse width modulation law. At a frequency of 200 Hz, the opening and closing time of the valve port is only 1.5 ms, showing good dynamic response characteristics. The flow output of both load ports can reach 25 l/min. The average flow curve has good linearity between 10% and 90% duty cycle. It provides a new flow control method for the quantitative pump to meet the requirements of frequent positive and negative rotation and variable speed.