1 IMPLEMENTATION OF SINGLE FEEDBACK CONTROL LOOP FOR CONSTANT POWER REGULATED SWASH PLATE AXIAL PISTON PUMPS

Variable displacement pumps are often used in both industrial applications and mobile hydraulic machinery. In such pumps, flow rate is dictated by the system requirements. Mathematical model has been previously developed to simulate the dynamic performance of the electrically controlled constant power regulated swash plate axial piston pumps with conical cylinder blocks. The pump is currently equipped with a double negative feedback control loop with an inner control loop to control the position of proportional valve using PID controller. Consequently, the proportional valve distributes the control pressure across the two sides of a control piston that is mechanically attached to the pump swash plate in order to change the pump flow rate. The outer control loop is used to control the pump flow rate in accordance with the system pressure change in order to keep the constant power operation using PD controller. For the convenience of pump constant power operation, PD controller is tuned to keep limited power shocks on the pump drive motor during the transient periods. The selected PD parameters results in relatively reduced settling time. Consequently swash plate steady state vibration appears. Purpose of this paper is to investigate features of the pump performance in view of an alternative control scheme. Counting on the relatively good open loop static characteristics of the proportional valve, a control scheme with a single control feedback loop is proposed to simplify the currently used control scheme. Using such singl