NAME
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Jeff Peters |
PROJECT
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3B2: Active vibration control of variable displacement axial piston pumps to reduce structure borne noise |
ABSTRACT
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The noise in piston machines originates from many different sources which can be divided in two main categories – fluid borne noise and structure borne noise. The finite number of pistons in piston pumps generates kinematic flow ripple which is superimposed by compressibility effects of the fluid. The flow ripple represents the main source of fluid borne noise. Dependent on system load, the flow ripple results in pressure ripple which is transferred to the entire hydraulic system through hydraulic lines connected to the pump. The pressure in each displacement chamber rapidly rises and drops between discharge and suction pressure during each revolution. This varying pressure causes oscillating piston forces which are transferred to the swash plate, leading to swash plate vibrations. The vibrations of the swash plate are transmitted to pump casing and to the structure on which the pump is mounted. Swash plate vibration represents the main source of structure borne noise. The signature of the radiated noise is dominated by tonal harmonics of the rotational speed. The aim of this research project is to investigate the feasibility of using the electrohydraulic pump control system of variable axial piston pumps for active vibration control to reduce the structure borne noise. An experiment has been designed to measure pump case vibration and noise, and to dynamically control the pump swash plate angle in order to minimize the pump casing vibrations. A dynamic model of a pump operating at steady state conditions was first created to simulate the fluctuating moments acting on the swash plate. The frequency spectra of the pump acceleration from simulation results were compared with measured acceleration spectra. The transfer function between swash plate angle and casing vibration amplitude was measured using a swept sine method. The response function was identified for many operating conditions. Future work will attempt active reduction of swash plate moment fluctuations through the manipulation of the swash plate actuator input signal. This should lead to reduced pump noise output. Utilizing a feedback from accelerometers, an adaptive cancellation signal will be generated and applied to the swash plate control actuator. The counteracting movement of the control actuator reduces swash plate vibration levels for the low order harmonics, below around 400 Hz. The goal is to supplement this active control methodology with passive reduction methods in order to achieve quiet operation without adverse effects on performance. |