Case History: Noise Source Identification of an Automobile Alternator by RPM Dependent Noise and Vibration Spectrum Analysis

Abstract

The noise of an automobile alternator generally increases with rotating speed. However, at some low rotating speeds, the alternator generates tonal noise in the frequency range of 1 to 3 kHz, which is the most irritating to the human ear. These tonal noises annoy the driver as well as passengers, especially at low speeds where background noise is relatively insignificant. Experiments were conducted to identify these noise sources by analyzing the noise and vibration signals. Modal tests were also performed using impact testing to study the modal vibrations of the stator. The source of tonal noises was identified as the magnetic noise which was caused by the strong alternating magnetic force on the stator. The magnetic noise increased abnormally at some specific rotating speeds when its frequency coincided with one of the modal frequencies of the stator.Volume 37/Number 1 31

Noise of Automobile Alternator

“…kHz in good awordance with equation(1). Overall sound powerlevels are shown in Figure4, It is seen that in this revolution range there are two maxima coneded with resonace of the stator.…”

Noise Generation by Vacuum Cleaner Suction Units

“…The excited forces are caused by the non-uniform steady flow fields, by turbulence and interaction of the turbulent flow with the rigid structure along with the flow through the blower and the electric motor, with accompanying vortices, which are caused by widening or narrowing and banding in the flow passages, by asymmetries of the flow in the blower intake opening, by flow hitting and declination on the flow obstruction such as rotor blades, diffuser vanes, return passages, etc. The turbulent noise depends on the flow velocity, design, dimensions and roughness of the passages within the blower and the electric motor [12].…”

“…The ball bearings generate noise with discrete frequencies corresponding to the rotating frequency of the elements within the bearings, such as the shaft, outer or inner race, balls (usually 7 balls) and cage. The magnitude of the ball bearing noise depends on the speed of rotation and their manufacturing perfections, alignment, wear and damage [12,[14][15][16][17]. Shahan and Kamperman [18] have identified seven discrete frequencies (and their harmonics) that are related to bearing geometry and rotational speed.…”

“…Tonal noise of electromagnetic origin is characteristically with a great number of discrete frequency tones; the most important are at the frequency fEM = zp • n (where zp is the number of the poles, and n is the rotating speed) and its higher harmonics [12,23].…”

Numerical research on aerodynamic radiation noises of alternators in vehicles

“…As one of key parts of vehicles, the alternator has a great impact on the noise of vehicle assembly, especially single orders [1]. At the section of high rotational speed more than 6000 r/min, aerodynamic noises become a main part of alternator noises and are the most difficult to control [2][3][4]. Noise control becomes difficult due to the complexity of aerodynamic noise sources and the inseparable noise sources of alternators and uncertain contribution amount of main orders to total noise, which has a direct influence on the improvement of performance and noise characteristics of alternators.…”