Patent Application
20130342068
The present invention relates to a structure of a stator in a motor.
A motor of conventional type comprises a cylindrical casing, a cylindrical stator fixed to an inside of the casing by shrinkage of the casing, and a rotor accommodated rotatably in an inner periphery of the stator. The stator has a plurality of protruding portions provided around an outer periphery thereof at predetermined intervals along a circumferential direction, and each of the protruding portions has a predetermined width in the circumferential direction and through-holes provided at both ends thereof in the circumferential direction (refer to patent literature 1, for example).
The motor of this kind has hitherto had a problem that an iron loss increases due to degradation in magnetic property of the magnetic body that composes the stator, because of a compressive stress built up in the stator due to heat shrinkage of the cylindrical casing when the stator disposed inside the casing is fixed by means of shrink fitting or the like method.
For this reason, a structure of the motor described in patent literature 1 is provided with through-holes 107 at both ends of protruding portion 108 formed along the outer periphery of stator 102, and the compressive stress built up in the inner periphery of stator 102 is reduced by making through-holes 107 deform to absorb a pressing force to stator 102 attributed to the heat shrinkage of casing 101.
In the structure discussed above, however, the pressing force to stator 102 attributed to the heat shrinkage of casing 101 cannot be absorbed in a center area of protruding portion 108, although the compressive stress built up in the inner periphery of stator 102 can be reduced by through-holes 107 at both the ends of protruding portion 108. It thus has the problem that an iron loss occurs due to the compressive stress built up in the inner periphery of stator 102.
PTL 1: Unexamined Japanese Patent Publication No. 2009-261058
NPL 1: The Institute of Electrical Engineers of Japan, IEEJ Transactions on Industry Applications (D) Vol. 127, No.1, P60-P68
A motor of the present invention comprises a cylindrical casing, a cylindrical stator fixed to an inside of the casing by shrinkage of the casing, and a rotor accommodated rotatably in an inner periphery of the stator. The stator has a plurality of protruding portions provided around an outer periphery thereof at predetermined intervals along a circumferential direction, and each of the protruding portions has a predetermined width in the circumferential direction, and through-holes provided at both ends thereof in the circumferential direction. A total length of the widths of the protruding portions in the circumferential direction is equal to or less than 25% of an outer circumference of the stator.
As a result, this structure can reduce a compressive stress built up in the inner periphery of the stator by making the through-holes deform at both the ends of the protruding portions to absorb a pressing force to the stator. In addition, the structure also helps reduce the compressive stress built up in the inner periphery of the stator by distributing the compressive stress in center areas of the protruding portions toward the outer periphery of the stator by virtue of positional arrangement of the through-holes.
According to the present invention, the compressive stress produced in the inner periphery of the stator can be reduced by distributing the compressive stress produced in the stator due to shrink fitting and the like to the outer periphery of the stator, thereby reducing an iron loss and achieving the motor of high efficiency.
Description will be provided hereinafter of an exemplary embodiment of the present invention with reference to the accompanying drawings. However, the embodiment described herein is not intended to limit the scope of the present invention.
The motor constructed as above operates and functions in a manner which is described hereinafter.
The motor of this kind is subjected to shrink fitting for fixing the stator to the casing, which mainly uses heat shrinkage of the cylindrical casing to fix the stator. During this process, magnetic property of a magnetic body composing the stator degrades because of a compressive stress built up in the stator due to the heat shrinkage of the casing, thereby giving rise to an increase in iron loss. The structure hitherto adopted is to reduce the compressive stress built up in the inner periphery of the stator by providing through-holes at both ends of protruding portions formed along the outer periphery of the stator and making the through-holes deform and absorb a pressing force to the stator at both the ends of the protruding portions. In the case of the stator having such a structure, however, the compressive stress remains to exist in the inner periphery of the stator since the pressing force to the stator due to the heat shrinkage of the casing cannot be absorbed in a center area of the protruding portion.
The motor of this exemplary embodiment is so configured that a total length of the widths of protruding portions 8 in the circumferential direction becomes equal to or less than 25% of the outer circumference of stator 2. With this structure, the pressing force to stator 2 is absorbed by deformation of through-holes 7 at both the ends of protruding portions 8. As a result, the compressive stress built up in stator 2 can be reduced. In addition, the structure can distribute the compressive stress in the center areas of protruding portions 8 toward the outer periphery of stator 2 by virtue of positional arrangement of the through-holes. It thus becomes possible to reduce the compressive stress acting on the inner periphery of stator 2, suppress degradation of the magnetic property of stator 2, and prevent an increase in the iron loss.
Described next is a result of the study conducted for verification of the effectiveness of this exemplary embodiment. Compressive stresses built up in the inner periphery of teeth 3 are calculated by analyzing the compressive stresses while making changes in the ratio of total length of the widths of protruding portions 8 in the circumferential direction to the outer circumference of stator 2.
For the purpose of comparison, a reference value set at this time is a compressive stress built up in stator 2 when the total length of the widths of protruding portions 8 in the circumferential direction is 27% in the ratio to the outer circumference of stator 2, and variations in value of the compressive stress are shown when the total length of the widths of protruding portions 8 in the circumferential direction to the outer circumference of stator 2 is changed with respect to the reference value. It can be verified that the compressive stress that acts on the inner periphery of stator 2 decreases by 2% when the ratio of the total length of the widths of protruding portions 8 in the circumferential direction to the outer circumference of stator 2 is set to 25% or less according to this embodiment.
Further study is made of the effectiveness of reducing the stress upon suppression of the iron loss, according to the relationship between stress built up in magnetic body and iron loss, which is shown in non-patent literature 1.
According to this exemplary embodiment, as discussed above, stator 2 is provided with the plurality of protruding portions 8 respectively having the predetermined width in the circumferential direction, and disposed at a predetermined interval along the outer periphery thereof, and that each of protruding portions 8 is provided with through-holes at both ends thereof in the circumferential direction. The total length of the widths, which the plurality of protruding portions 8 respectively have, in the circumferential direction is set equal to or less than 25% of the outer circumference of stator 2. As a result, this reduces the compressive stress built up in stator 2 by making through-holes 7 deform at both the ends of protruding portions 8 and absorb the pressing force to stator 2. In addition, the positional arrangement of through-holes 7 also can distribute the compressive stress in the center areas of individual protruding portions 8 toward the outer periphery of stator 2. The structure can hence reduce the compressive stress built up in the inner periphery of stator 2, suppress degradation of the magnetic property of the magnetic body that constitutes stator 2, and prevent an increase in the iron loss.
In this exemplary embodiment, the protruding portions may be so provided that their centers in the circumferential direction are aligned individually with centers in the circumferential direction of the corresponding slots, and that the protruding portions are formed respectively on the outer peripheral side of the slots. This structure can divert the compressive stress distributed at the centers of the protruding portions toward peripheral side of teeth that do not constitute the main magnetic circuit.
Furthermore, the pressing force imposed on each of protruding portions 8 of stator 2 can be reduced by having the number of protruding portions 8 in this embodiment equal to or larger than the number of the slots. Accordingly, degradation of the magnetic property of the magnetic body can be suppressed around the inner periphery of stator 2 by distributing the compressive stress built up in stator 2, thereby suppressing any increase in the iron loss.
Description provided next is an example in which the motor of this exemplary embodiment is used in a compressor to be mounted to an apparatus such as an air conditioner.
The motor of this embodiment, when used as shown in a compressor mounted to an air conditioner and the like equipment, for instance, is capable of contributing to an improvement of the efficiency of the equipment.
As illustrated above, the motor of the present invention comprises a cylindrical casing, a cylindrical stator fixed to the inside of the casing by shrinkage of the casing, teeth formed to protrude on an inner peripheral side of the stator and respectively arranged at a predetermined interval along a circumferential direction, a winding disposed to a slot formed between adjoining two of the teeth, and a rotor accommodated rotatably in a place facing the teeth at an inner peripheral side of the teeth. The stator has a plurality of protruding portions having a predetermined width in the circumferential direction, and respectively disposed at a predetermined interval along an outer periphery of the stator. Each of the protruding portions is provided with through-holes at both ends thereof in the circumferential direction. A total length of the widths of the protruding portions in the circumferential direction is set equal to or less than 25% of an outer circumference of the stator.
The above structure can distribute a compressive stress built up in center areas of the protruding portions due to a pressing force to the stator by shrinkage of the casing toward the outer periphery of the stator, by virtue of the through-holes provided at both the ends of the protruding portions. The structure is thus capable of reducing the compressive stress built up in the inner periphery of the stator, and preventing increase in the iron loss.
The motor of the present invention has the protruding portions so provided that their centers in the circumferential direction are aligned individually with centers in the circumferential direction of the corresponding slots, and that the protruding portions are formed on the outer peripheral side of the slots. This structure can divert the compressive stress distributed at the centers of the protruding portions toward the peripheral side of the teeth. Since the peripheral side of the teeth has an insignificant influence to the main magnetic circuit, the structure can suppress the increase in iron loss even if degradation occurs in the magnetic property as a result of the compressive stress.
Furthermore, the motor of the present invention reduces the pressing force of the casing imposed upon each of the protruding portions by making the number of the protruding portions equal to or larger than the number of the slots and increasing locations where the casing is in contact with the stator. This structure can also suppress the increase in the iron loss since it can distribute the compressive stress built up in the stator.
In addition, the electric equipment of the present invention has an advantage of suppressing an iron loss attributable to the compressive stress when the above motor of the present invention is used for a compressor mounted to an air-conditioner, for instance, thereby helping to compose a highly efficient motor.
The motor according to the present invention is useful for such an apparatus as a compressor for air-conditioning equipment, in which the stator is fixed to the casing by shrink fitting, since it is capable of reducing a compressive stress of the casing that acts on an inner periphery of the stator during the shrink fitting and the like process.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-020347 | Feb 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/000667 | 2/1/2012 | WO | 00 | 9/16/2013 |
