A Modified Secondary Source Method for Characterizing Pump Acoustic Source Impedance in Hydraulic Systems

Abstract

Abstract Hydraulic pumps generate flow ripples which interact with the hydraulic circuit and cause pressure pulsations (fluid-borne noise). This kind of noise is a major source of structural vibration and airborne noise. In order to study the noise and vibration in hydraulic systems, the pump source impedance must be characterized. In general, the pump source impedance is independent of the interaction between the pump and circuits connected to it. Former researchers [1,2,3,4] measured acoustic pressures along the transmission line at different locations and used plane-wave propagation theory to find the source impedance. However, the acoustic pressures used in previous research are dependent on the dynamic response of the circuits as well as the pump. Edge and Johnston [5,6] developed the ‘secondary source’ method to evaluate the source characteristics of hydraulic pumps. They used a secondary source to excite the pump at two different frequencies. The pump source impedance (termination impedance for the second source) could then be estimated. Since the impedance obtained from their method is for different frequencies than the harmonic frequencies of the pump, they used a suitable model along with the experimental results to find the impedance of the pump at the desired harmonic frequencies. In this paper, a new method is proposed using a ‘modified secondary source’ method which is achieved by use of two experimental configurations. By using the principle of superposition for a linear system, the pump impedance can be found from addition of the impedances obtained from the two setups. The proposed method will be able to cover the whole frequency range without using a mathematical model for the pump.