Control of hydraulic systems

Abstract

The precise and smooth control of the hydraulic fluid supplied to a hydraulic system, such as the lifting cylinders of a turret stockpicker, under varying operating conditions includes an optical encoder on the operator's control handle connected to an electronic control of a hydraulic pump motor, which s initially operated at a predetermined minimum speed, and a hydraulic valve which provides the initial control of hydraulic fluid under the control of an operator's handle. Because the pump is initially at a low speed, greater efficiency of the system is realized, an important feature in a battery operated vehicle. As the operator moves the handle from the off or neutral towards the fully open position, the hydraulic valve will open and reach its fully open position as the handle passes approximately the one-third on position. Pump motor speed is maintained at a minimum speed until the hydraulic valve is almost opened, and then the pump motor speed will be increased at a predetermined rate until its maximum speed has been obtained with the handle being almost fully on. The last few degrees of movement of the handle will not cause any further increase in hydraulic pressure or motor pump speed, but it will by-pass an SCR pump motor control circuit, thus further increasing efficiency.