CONTROL MODES OF A HYDRAULIC DRIVE WITH INDEPENDENT CONTROL OF FLOWS UNDER DIFFERENT LOAD CONDITIONS

A hydraulic drive of a mobile machine under a passive load is considered, based on proportional metering elements that independently control the inlet and outlet flows of the hydraulic cylinder and on controlled check valves. The influence of the load mass, the load force direction and the required rod velocity on the choice of the control mode is studied. Four modes are analysed: meter-in control, meter-out control with pump unloading, combined control and control by the pump flow rate. A quasi-static model with constraints on cavitation, pressure, flow rate and controllability is compiled; the comparison criterion is the total pressure drop across the metering elements. A mode map in the coordinates “load mass – required velocity” is built and the energy consumed from the pump over a loader cycle is analysed.