Constant pressure control of a swash plate type axial piston pump by varying both volumetric displacement and shaft speed

In this paper both the volumetric displacement and the shaft speed of a variable displacement swash-plate type piston pump were varied in order to minimize power consumption in supplying constant-pressure oil to a valve-controlled hydraulic cylinder, particularly during idle modes. At operating modes which were launched by position command inputs, the pump speed was varied by a pressure control algorithm to maintain a constant system pressure, with the swash plate angle fixed at the maximum. At idle, with no position controller input signal and the system pressure greater than or equal to the reference value, the swash plate angle and pump speed were lowered to their minimum limits. Computer simulation and experimental results showed that the idling power could be reduced by up to 83% by reducing the pump speed from 1800 rpm to 300 rpm and the swash plate angle to 3°, compared to a conventional system consisting of a pressure-compensated variable displacement type pump driven at a constant speed of 1800 rpm.