NEAR FIELD NOISE ATTENUATOR

Abstract: The invention is concerned with a near field noise attenuator (1) having the function of attenuating noise originating from rotating of a rotor within the air gap between rotor and stator (6) of the electric motors, especially of those having salient-poles (3). Perforations (2) in number more than one lined up in parallel with each other positioned in vertical or normal rows over a set (1) which forms an obstacle between rotor and stator (6) in the periphery of the former and inserted between the ends of salient poles (3) of a stator (6), attenuate noise which occurs as a result of pressure fluctuations due to irregular surface profiles of rotor and stator, by attenuating such pressure fluctuations.

Description: NEAR FIELD NOISE ATTENUATOR TECHNICAL FIELD Hereby invention is concerned with a near field noise attenuator having the function of attenuating air noise which, as a result of rotor rotating in the air gap between stator and rotor, is brought about in electric motors, especially in those having salient poles. PRIOR ART As known, the "acoustical near field" is the hydrodynamic field where propagation of sound waves does not manifest itself in any discernible sound motion and where sound pressure continuously displays fluctuations. Such a variability of sound pressure may within this hydrodynamic field be patterned both in space and time interval by setting down Helmholtz equations. Motors with salient poles are electric motors with poles approaching towards armatures. Among motors to be included into such a class, there may be listed switch reluctance motors and shaded-pole motors. In salient pole motors, any asymmetric propagation that occurs in the air gap between stator and rotor causes noise and pressure fluctuations to a large extent within that air gap. In the applications heretofore undertaken, it is aimed to correct flow characteristics. Ways of reducing pressure fluctuations and reducing noise therefrom using various arrangements so as to form a symmetric structure along flow paths have been studied. Noise originating from pressure fluctuations formed in the air gap of salient-pole electric motors due to rotor and stator irregular surface profiles has caused designers to seek solutions. Some applications are known directed to reducing the effects of the irregularities on rotor surfaces. Among applications current in the art, there may be listed the folio wrapping of rotor surface, wrapping the rotor with complete injection, or squeezing of rotor ducts with plastic bars or pressurized paper and closing with an appropriate flat plate complying with air gap profile the space between stator poles. Such practices have as object the making of rotor and stator surfaces regular and smooth, to ensure smooth flow and to reduce to a minimum pressure fluctuations. OBJECT OF THE INVENTION The object of the present invention is to bring about a near field noise attenuator which attenuates noise originated by pressure fluctuations due to irregular stator and rotor surface profiles in the air gap in electric motors with salient poles by attenuating_such pressure fluctuations. BRIEF EXPLANATIONS OF FIGURES A preferred configuration of the near field noise attenuator brought about for the attainment of the invention object has been given as annex in attached drawings, where Figure la is the top view of the larger piece of the noise attenuator Figure lb is the front view of the larger piece of the noise attenuator Figure lc is the side view of the larger piece of the noise attenuator Figure 2 is the three - dimensional top view of the larger piece of the noise attenuator Figure 3, is the three-dimensional top view showing the stator mounted with the noise attenuator Figure 4, is the front view with stator mounted with noise attenuator Figure 5, is a sectional view taken along line AA of the figure 4. Names assigned to parts numbered in figures are as shown under; 1. Attenuator 2. Perforation 3. Salient pole 4. Attenuator small piece 5. Attenuator larger piece 6. Stator DESCRIPTION OF THE INVENTION While in the current applications , it is aimed to have continuous and smooth rotor and stator surfaces, to ensure regular flow and maintaining the same and by these ways attenuating pressure fluctuations to a minimum, in the present invention it is aimed on to attenuate pressure fluctuations formed in due to the fluid dynamic characteristics. The operational principle of the noise attenuator (1) is based upon attenuating before propagation and in the near field of hydrodynamics of sound waves and therefrom upon attenuating sound pressure fluctuations. What is recommended in the invention is into a correction over flow paths, but rather an improvement brought at the source of a physical formation. The noise attenuator (1), by being located between edges of salient poles at stators of salient-pole motors, provides attenuating air-borne noise formed as a result of rotor's rotating. The subject noise attenuator of the invention is formed of a perforated structure constituting an obstacle between stator (6) and rotor, around the latter (Figures 4 and 5). The noise attenuator (1) is characterized by its having perforations on it arranged in lines in number more than one which are located parallel to each other. On the figures attached, there is shown a noise attenuator (1) located in stator of a salient-pole motor used in washing machines. In the preferred above configuration of the attenuator, the perforations are located (2) at a distance equal to each other and there exist in total twenty eight perforations if the gap between salient poles (3) is considered as being a rectangle, of these perforations seven is placed along the long edge of the rectangle, and four along the shorter edge. Tests performed verifies that noise attenuation efficiency is the best if perforations are circular. However, such perforations may be in variety of any geometrical form as desired. In parallel with sizes of salient-pole motors, manufactured for different aims, number of perforations as well as sizes of noise attenuator may vary. Variation also may be considered in locating perforations in lines. The function of the subject invention is independent of materials used in its manufacturing. Various metals, sheets or plastic may be used for the purpose. In order to join opposite ends of salient poles (3) situated symmetrically on stator (6), two noise attenuators (1) are used. These are mounted by close fitting. In the preferred embodiment of the invention, in order to make connection of the terminals easier in the course of mounting of salient-pole motor, the noise attenuator has been formed of two separate pieces fitting each other, (4 and 5) one of which being smaller than the other one. Perforations on the smaller piece (4) fitted to the larger one (5) during the mounting operation, are placed in rows in conformity with the attenuator's shape. The efficiency of the noise near field attenuator varies in relation with the attenuator's geometry, type of positioning and number of perforations. In accordance with source of aerodynamic formations and characteristics, the noise attenuator can be tuned to the desired frequencies and bands. Tuning or adjustment of the system according to frequencies where noise is suppressed may be ascertained by perforations geometry (2), sizes and numbers of perforations thus opened. The efficiency of attenuating noise of the perforations noise attenuator is directly proportional to attenuator's peripheral length, number of perforations the same contains and depth of perforations and inversely proportional to wave lengths and perforations cross-sectional area. Thus by using the formula (1), Where P is the number of perforations 1 Peripheral length of acoustical attenuator A perforations' sectional area LI Efficiency of attenuating noise of the noise attenuator h perforations' depth λ sound wave length Δi, - ^ ( ! ) A χ it is possible to estimate efficiency of attenuating noise of the subject attenuator. Moreover, it is also of importance angles of reflection and transmission from perforations' structure of sound waves. If it is considered iωt+K t P. = P.e 2] P., =P τ e' ω,+κ " ' 4! P τ =Pι+P R If θ 0 = is incoming wave angle : angle of reflected wave. θ i = is incident wave angle than sin#, a sin6> n Here, according to the equations below, z 0 = p 0 c V, there will be noticed that angles of positioning are critically important on the angles of incidence, reflection and transmission. Due to these reasons, the efficiency of the noise attenuator will vary in relation with; • Diameters, sectional areas and bore depths of perforations • Number of perforations and their positioning • Peripheral length of noise attenuator and its distance from noise source • Angles of positioning of attenuator and perforations Another characteristic of the near-field noise attenuator, that it is applied more easily compared against alternative systems and its lower cost.

Claims: CLAIMS 1. A near field noise attenuator inserted between the salient poles (3) of a stator to attenuate air noise formed as a result of rotor rotating in the air gap between stator and rotor of electric motors, especially of salient-pole electric motors, characterized in that perforations in number more than one on a set (1) constituting an obstacle between rotor and stator in the periphery of this former. 2. A noise attenuator as specified in claim 1, characterized in that the perforations in circular shape. 3. A near field noise attenuator as specified in claims 1 and 2, characterized in that perforations are lined up in parallel with each other, with rows, either vertical or normal in number more than one. 4. A near field noise attenuator as specified in claim 3, characterized in that perforations are positioned (2) of equal distance to each other.

Inventors: ERGUEN MITHAT, OEZTUERK CUENEYT, ERGUEN, MITHAT, OEZTUERK, CUENEYT
Applicants: ERGUEN MITHAT, OEZTUERK CUENEYT, TUERK ELEK K ENDUESTRISI A & S, ERGUEN, MITHAT, OEZTUERK, CUENEYT, TUERK ELEKTRIK ENDUESTRISI A.&SCEDIL
Application year: 2000
Main classification: H03H
IPC codes: H02K1, H02K5