Electric motor and method of manufacturing the same

Abstract

An electric motor includes an annular housing and an annular stator core having the inner periphery the shape of which differs from a perfect circle. The stator core is supported by the housing in such a manner that the outer periphery of the stator core and the inner periphery of the housing are partially in contact with each other. The inner periphery of the stator core is deformed to become close to the shape of the perfect circle when the stator core is securely fitted in the housing by shrink fitting.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a longitudinal cross-sectional view of a compressor according to a first preferred embodiment of the present invention;

FIG. 2A is a cross-sectional view of a motor housing and a stator core according to the first preferred embodiment;

FIG. 2B is a schematic view showing a relation between the shapes of the outer periphery of the stator core before and after shrink fitting and a relation between the shapes of the inner periphery of the stator core before and after the shrink fitting according to the first preferred embodiment;

FIG. 2C is a schematic view showing a relation between the shapes of the outer periphery of a conventional stator core before and after the shrink fitting and a relation between the shapes of the inner periphery of the conventional stator core before and after the shrink fitting;

FIG. 3A is a graph showing a relation among the rotational speed of an electric motor having the conventional stator core, the acceleration of the electric motor and vibrations of the motor housing;

FIG. 3B is a graph showing a relation among the rotational speed of an electric motor having the stator core, the acceleration of the electric motor and vibrations of the motor housing according to the first preferred embodiment;

FIG. 4A is a cross-sectional view of a motor housing and a stator core according to a second preferred embodiment of the present invention;

FIG. 4B is a schematic view showing a relation between the shapes of the outer periphery of the stator core before and after the shrink fitting and a relation between the shapes of the inner periphery of the stator core before and after the shrink fitting according to the second preferred embodiment;

FIG. 5A is a cross-sectional view of a motor housing and a stator core according to a third preferred embodiment of the present invention;

FIG. 5B is a schematic view showing a relation between the shapes of the outer periphery of the stator core before and after the shrink fitting and a relation between the shapes of the inner periphery of the stator core before and after the shrink fitting according to the third preferred embodiment;

FIG. 6A is a cross-sectional view of a motor housing and a stator core according to a fourth preferred embodiment of the present invention;

FIG. 6B is a schematic view showing a relation between the shapes of the outer periphery of the stator core before and after the shrink fitting and a relation between the shapes of the inner periphery of the stator core before and after the shrink fitting according to the fourth preferred embodiment;

FIG. 7A is a cross-sectional view of a motor housing and a stator core according to a fifth preferred embodiment of the present invention;

FIG. 7B is a schematic view showing a relation between the shapes of the outer periphery of the stator core before and after the shrink fitting and a relation between the shapes of the inner periphery of the stator core before and after the shrink fitting according to the fifth preferred embodiment;

FIG. 8A is a cross-sectional view of a motor housing and a stator core according to a sixth preferred embodiment of the present invention; and

FIG. 8B is a schematic view showing a relation between the shapes of the outer periphery of the stator core before and after the shrink fitting and a relation between the shapes of the inner periphery of the stator core before and after the shrink fitting according to the sixth preferred embodiment.

Claims

1. An electric motor comprising: an annular housing; andan annular stator core having the inner periphery the shape of which differs from a perfect circle, the stator core being supported by the housing in such a manner that the outer periphery of the stator core and the inner periphery of the housing are partially in contact with each other;wherein the inner periphery of the stator core is deformed to become close to the shape of the perfect circle when the stator core is securely fitted in the housing by shrink fitting.

2. The electric motor according to claim 1, wherein a shape of the stator core before the shrink fitting is determined by factoring degree of deformation of the stator core by the shrink fitting so that the shape of the inner periphery of the stator core after the shrink fitting becomes close to the perfect circle.

3. The electric motor according to claim 1 wherein the housing has a plurality of projections which are provided on the inner peripheral surface of the housing and circumferentially spaced at intervals, the projections being in contact with the outer peripheral surface of the stator core.

4. The electric motor according to claim 3, wherein the shape of the stator core before the shrink fitting is an elliptic cylindrical shape, the projections being four projections which include a first pair of adjacent projections and a second pair of adjacent projections, intervals between the first pair and between the second pair being smaller than those between one of the first pair and one of the second pair adjacent to each other and between the other of the first pair and the other of the second pair adjacent to each other, the elliptic cylindrical shape having a major axis which extends between the first pair of adjacent projections and between the second pair of adjacent projections.

5. The electric motor according to claim 3, wherein the shape of the stator core before the shrink fitting is an elliptic cylindrical shape having a major axis, the projections being two projections which are spaced at even angular intervals, the major axis passing through the centers of the projections.

6. The electric motor according to claim 3, wherein the shape of the stator core before the shrink fitting has a plurality of large radius portions in cross-section, the projections being spaced at even angular intervals and corresponding to the large radius portions after the shrink fitting, respectively.

7. The electric motor according to claim 6, wherein a number of the projections is three, a number of the large radius portions being three.

8. The electric motor according to claim 1, wherein the stator core has a plurality of projections which are provided on the outer peripheral surface of the stator core and circumferentially spaced at intervals, the projections being in contact with the inner peripheral surface of the housing.

9. The electric motor according to claim 8, wherein the shape of the stator core before the shrink fitting is an elliptic cylindrical shape, the projections being four projections which include a first pair of adjacent projections and a second pair of adjacent projections, intervals between the first pair and between the second pair being smaller than those between one of the first pair and one of the second pair adjacent to each other and between the other of the first pair and the other of the second pair adjacent to each other, the elliptic cylindrical shape having a major axis which extends between the first pair of adjacent projections and between the second pair of adjacent projections.

10. The electric motor according to claim 8, wherein the shape of the stator core before the shrink fitting is an elliptic cylindrical shape having a major axis, the projections being two projections which are spaced at even angular intervals, the major axis passing through the centers of the projections.

11. The electric motor according to claim 8, wherein the shape of the stator core before the shrink fitting has a plurality of large radius portions in cross-section, the projections being spaced at even angular intervals and corresponding to the large radius portions after the shrink fitting, respectively.

12. The electric motor according to claim 11, wherein a number of the projections is three, a number of the large radius portions being three.

13. The electric motor according to claim 1, the electric motor being used for a motor-driven compressor, the motor-driven compressor comprising; a rotary shaft driven to rotate by the electric motor;a rotor provided on the rotary shaft in the housing and facing the stator core; anda compression motion body driven by the rotation of the rotary shaft for compressing a gas in a compression chamber and discharging the gas therefrom.

14. A method of manufacturing an electric motor having an annular stator core and an annular housing, the method comprising the steps of: forming the stator core having the inner periphery the shape of which differs from a perfect circle; andsecuring the stator core to the housing in such a manner that the inner periphery of the stator core is deformed to become close to the shape of the perfect circle by shrink fitting.

15. The method according to claim 14, wherein the forming step includes determining a shape of the stator core before the shrink fitting by factoring degree of deformation of the stator core by the shrink fitting so that the shape of the inner periphery of the stator core after the shrink fitting becomes close to the perfect circle.

16. The method according to claim 14, further comprising the step of providing, after the step of forming the stator core, a plurality of projections circumferentially spaced at intervals on one of the inner peripheral surface of the housing and the outer peripheral surface of the stator core

17. The method according to claim 16, wherein the providing step includes providing the projections circumferentially spaced at even intervals.

18. The method according to claim 16, wherein the forming step includes forming the stator core in a shape of an elliptic cylindrical shape.

19. The method according to claim 18, wherein the providing step including providing four projections which include a first pair of adjacent projections and a second pair of adjacent projections so that intervals between the first pair and between the second pair are smaller than those between one of the first pair and one of the second pair adjacent to each other and between the other of the first pair and the other of the second pair adjacent to each other, the elliptic cylindrical shape having a major axis which extends between the first pair of adjacent projections and between the second pair of adjacent projections.