Development Research of Variable Resonance-Mode Type of Side-Branch Resonators.

Abstract

The variable resonance-mode type of side-branch resonators which can be adjusted freely at the desired resonance modes (i.e., desired resonance frequencies and mode shapes) with a single closed-end tube configuration, unlike a conventional side branch, are newly developed and their attenuation characteristics are investigated theoretically and experimentally. The mechanism of variable-mode is based on the principle that the resonance mode of fluid wave motion in a side-branch tube can be changed arbitrarily with the adjustment of reflection factors at the choke orifices which are inserted in it. The present variable resonance-mode type of side-branch resonators are devised in order to reduce the several harmonics of the fixed discrete-frequency pressure pulsation such as those generated by a fixed speed hydraulic pump. A successful mathematical means (optimum design method) of sizing the desired lengths and diameters of n number of choke orifices and lengths of divided n+1 number of side-branch tube parts so as to coincide resonance frequencies with the desired one is outlined. It has been confirmed in the bench tests that the proposed side-branch resonators yield the satisfactory insertion loss characteristics so far as they are used in a hydraulic circuit with very short length of outlet pipe in which the influence of standing wave is negligible. Further, the present side-branch designed so as to reduce the 1st and 2nd harmonics of pressure pulsation has proven to be very successful also in application to a real hydraulic excavator for reduction of air-borne noise as well as pressure pulsation of these harmonics.