不等ピッチシリンダによるアキシャルピストンポンプの静音化

Abstract

The main source of noise in hydraulic system is usually the positive displacement pump, which produces structure- and fluid-borne noise. Hence, to reduce noise in any hydraulic component, both structural and fluid vibrations must be reduced. For noise control, however, reducing noise is all very well, but improving noise into a desirable tone quality is also advisable.This paper presents the development of an axial piston pump utilizing the irregular pitch cylinders to drastically improve the tone quality of noise generated by a pump. Irregular pitch angles of cylinders were determined within the range of 40±3° by a trial and error method so as to distribute the spectra of vibromotive force and moment as widely and uniformly as possible throughout the harmonics of pump rotational frequency (not of a piston frequency). The effectiveness of devised technique was examined mainly by the degree of dispersion and amplitude ratio of the harmonic spectrum of the sound intensity and sound pressure, and by sensory evaluation by means of hearing experiments.It could be seen from a comparison test with a regular pitch pump that, in the case of an irregular pitch pump, the spectra of sound intensity and sound pressure as well as the vibration acceleration of the pump casing abundantly contained harmonics of small amplitude of pump rotational frequency, and that the pump noise was greatly improved from violent and harsh tone quality of standard (i.e., regular pitch) pump into a rather silent and mild tone quality. Consequently, it was confirmed that arranging cylinders irregularly in circumferential direction was extremely effective measures for quieting the noise from an axial piston pump.