Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-09-08
2001-07-24
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S216055, C310S193000, C310S043000
Reexamination Certificate
active
06265804
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric motor provided with a split stator core including a plurality of circumferentially disposed unit cores and a method of making such a motor.
2. Description of the Prior Art
For the purpose of effective utilization of steel material, the prior art has provided an annular split stator core formed by disposing a plurality of circumferentially split unit cores into a generally circularly or squarely annular configuration. More specifically, when annular steel sheets which are to be stacked into a stator core are punched out of steel sheets, portions of each steel sheet outside and inside the annular configuration are left unused. The above-mentioned annular split stator core provided by the prior art is directed to a reduction in such unused portions of the steel sheets.
However, a location of portions of the unit cores adjacent to each other is selected at random. This results in unbalance in magnetic attractive forces acting between the unit cores, whereupon vibration and noise are produced.
Each of a number of steel sheets stacked together into a unit core is formed by punching a silicon steel sheet having a surface treated for electrical insulation by a press. The punching sometimes results in warpage and/or burrs in ends of the silicon steel sheet. In a stator core formed by annularly disposing a plurality of unit cores, when the unit cores adjacent to each other are displaced in the direction of stack of the steel sheets or when one or more steel sheets have the warpage and/or burrs, the steel sheets of each unit core are electrically short-circuited by the ends of the steel sheets of the other unit core. This results in eddy currents flowing in the direction of stack of steel sheets in the unit core, so that an iron loss is increased.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an electric motor in which the unbalance in the magnetic attractive forces acting between the unit cores can be restrained so that the vibration and noise are prevented, and a method of making the motor.
Another object is to provide an electric motor which is provided with a stator core including a plurality of unit cores and in which the iron loss can be reduced.
The present invention provides an electric motor comprising a rotor and a stator including a plurality of unit cores each of which has two ends. The unit cores are disposed so that the ends of each unit core are adjacent to the ends of the neighboring unit cores respectively. Each unit core includes a yoke section and a plurality of salient poles which are integral with the yoke section and on which concentrated windings are wound. In this construction, each unit core is disposed so that the yoke section thereof is adjacent to the yoke sections of the neighboring unit cores and so that the salient poles thereof are separate from the salient poles of the neighboring unit cores. Further, the salient poles are arranged circumferentially with a regular pitch. Further, a number of the salient poles of each unit core is equal to a number of phases of the windings multiplied by any integer. Additionally, each of the portions of the unit cores adjacent to each other is set so as to assume an angular position where a multiple obtained by multiplying a pitch angle of the salient poles agrees with a multiple obtained by multiplying a pitch angle of magnetic poles of the rotor.
Upon excitation of the windings of the above-described motor, a rotating magnetic field is generated so that the rotor is rotated. An amount of magnetic flux passing through each yoke section changes momentarily as the rotor is rotated. However, when a plurality of salient poles are provided so as to correspond to each of the phases, the yoke sections of the stator core have at an interval of a predetermined angle portions where amounts of magnetic flux passing therethrough become the same. In the present invention, the number of salient poles of each unit core is determined so that the interval of the predetermined angle coincides with the adjacent portions of the unit cores. Accordingly, the amounts of magnetic flux passing through the respective adjacent portions of the unit cores become approximately the same although changing momentarily. Consequently, when the adjacent portions of the unit cores are located so as to correspond to positions where the magnetic fluxes passing the respective yoke sections are substantially the same, the magnetic attractive forces acting between the unit cores can be balanced to be canceled, whereupon occurrence of the vibration and noise due to the magnetic attractive forces can be prevented.
Each unit core preferably includes the salient poles the number of which is represented as CM(Nt/CD(Nt, Np), Nf) where CM(A, B) is a common multiple of integers A and B, CD(A, B) is a common divisor of integers A and B, Nt is a total number of salient poles of a stator, which is equal to or larger than 2, Np is a total number of magnetic poles of a rotor, which is equal to or larger than 2, and Nf is the number of winding phases.
In a case where the positions where the magnetic fluxes passing through the yoke sections are substantially the same are obtained when a rotor used With the above-described stator has a plurality of magnetic poles, a total number of magnetic poles of the rotor is preferably equal to the number of unit cores multiplied by any positive number, in addition to the condition that the number of salient poles of each unit core is equal to the number of winding phases multiplied by any positive integer.
The number of unit cores is obtained when a divisor common to the above-mentioned total numbers Nt and Np is found. Accordingly, when the total number Np is divided by the number of unit cores, the least number of salient poles that can be provided on a single unit core is obtained. Accordingly, the number of salient poles of each unit core can be obtained from a multiple common to the least number of salient poles and the total number Nf of winding phases.
The salient poles preferably have different shapes of distal ends and arranged in a pattern in which said salient poles having the different shapes of distal ends adjoin each other, the pattern being repeated circumferentially. The number of the salient poles of each unit core is equal to a common multiple to a number of the distal end shapes of the salient poles and the number of winding phases.
In the above-described arrangement pattern of the salient poles, the arrangement pattern of salient poles of each unit core needs to correspond to those in the adjacent unit cores in addition to the condition that the number of salient poles of each unit core is equal to the number of winding phases multiplied by any positive integer. This is met when the number of salient poles is a common multiple to the number of types of distal ends of the salient poles and the number of winding phases. In this case, the multiple is preferably a least common multiple.
The invention also provides an electric motor comprising a rotor and a stator core including a plurality of unit cores each of which has two ends. The unit cores are disposed so that the ends of each unit core are adjacent to the ends of the neighboring unit cores with electrically insulating clearance maintaining members being interposed therebetween, respectively. Each unit core is formed by stacking a number of steel sheets each of which has a surface to which a treatment for electrical insulation is applied. Since the ends of the adjacently disposed unit cores are separated from each other by the clearance maintaining members, the ends can be insulated from each other such that eddy current loss is reduced.
In a preferred form, the clearance between the ends of each unit core and the neighboring unit cores is set to be in a range between 0.01 and 0.15 mm.
REFERENCES:
patent: 4015154 (1977-03-01), Tanaka et al.
patent: 4365180 (1982-12-01), Licata et al.
patent: 4665329 (1987-05-01), Raschbichler
patent: 46
Hayashi Kinya
Nitta Isamu
Dinh Le Dang
Enad Elvin
Kabushiki Kaisha Toshiba
Pillsbury & Winthrop LLP
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