JP2013247815A - Electric motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric motor enabling reduction in core loss of a stator core.SOLUTION: An annular core loss reduction groove of which depth gradually increases from an intermediate portion in the axial direction of a frame toward both ends is formed throughout the entire area in the peripheral direction of the frame in a region opposing to an outer peripheral face of a stator core out of an inner peripheral face of the frame. Thus, an interfere gradually decreases from the intermediate portion to both ends, so as to gradually reduce compressive stress applied to a surface contact region of the stator core with the frame from the intermediate portion toward both ends. Therefore, compared to conventional cases, compressive stress of outer peripheral portions of both ends of the stator core is eased, and compressive stress of an inner face part of an intermediate portion of each tooth is also reduced. As a result, core loss of the stator core can be reduced.

Description

  The present invention relates to an electric motor, and more particularly to an electric motor in which a cylindrical frame is held on an outer peripheral surface of a stator core by a clamping force of the frame and a rotor rotates in an internal space of the stator core.

  An inner rotor type electric motor (electric rotating machine) includes a cylindrical frame, a stator core that is inserted into the inner space of the frame, and is held by the tightening force of the frame by bringing the outer peripheral surface into surface contact with the inner peripheral surface of the frame. And a rotor that rotates in the internal space of the stator core. There are various methods for fixing the stator core to the frame. However, in the case of a small electric motor, a “shrink fit” in which the stator core is fitted to the frame with a crimping margin is generally used. For shrinking, use a frame whose inner diameter is smaller than the outer diameter of the stator core, heat the frame just before fitting, expand the diameter by thermal expansion, insert the stator core into the inner space of the frame in this state, Cool down. Tensile stress acts on the surface contact area with the stator core in the frame thus reduced in diameter, compressive stress from the frame is generated in the stator core, and both members are in a tightened state.

  However, the compressive stress generated in the stator core due to this shrinkage deteriorates the characteristics of the stator core, increases the iron loss, and decreases the efficiency of the electric motor. In particular, the compressive stress generated at both end portions in the axial direction of the stator core (hereinafter sometimes simply referred to as both end portions) in the portion that fits the frame on the outer peripheral surface of the stator core is not only large in the radial direction of the stator core. Not only that, but also a bending stress is generated from the outer peripheral surface side of both ends of the stator core toward the center of the stator core. This is because the contraction force of the frame generates a force toward the center of the stator core at both ends of the stator core.

  Therefore, as a conventional technique for solving this problem, for example, “Rotating machine” of Patent Document 1 is known. Specifically, in Patent Document 1, in the surface contact area between the inner peripheral surface of the frame and the stator core, notch portions along the circumferential direction of the frame are provided at both ends of the frame, respectively, and compressive stress generated in the stator core To reduce the iron loss of the stator core. This notch is a groove having a constant depth over the entire area in the axial direction (length direction).

JP 2010-119157 A

  As described above, in the rotating machine of Patent Document 1, in order to relieve the compressive stress generated at both ends of the stator core, in the surface contact area between the inner peripheral surface of the frame and the stator core, An annular cutout portion was formed along each. This makes it look as if the purpose has been achieved. However, since the notch is a groove having a constant depth over the entire area in the axial direction, in actuality, the area of the contact surface of each of the stator cores is reduced, and the part of the surface contact with the frame on the outer peripheral surface of the stator core. The same compressive stress was concentrated at both ends of the stator core, causing high iron loss and reducing the efficiency of the rotating machine.

  Further, in the case of the rotating machine of Patent Document 1, due to the stress concentration acting on the surface contact area with the frame at both ends of the stator core described above, each tooth portion also pushes from the outer peripheral surface side of both ends of the stator core. A bending force was applied, and compressive stress was increased at the inner surface portion of the intermediate portion in the length direction (axial direction of the stator core) of each tooth portion. As a result, the iron loss of the stator core was further increased.

  Therefore, as a result of intensive studies, the inventors have determined that, in the inner peripheral surface of the frame, at least the region facing the outer peripheral surface of the stator core, at both ends in the axial direction of the frame, over the entire region in the circumferential direction of the frame. It has been conceived that an annular iron loss reducing groove whose depth gradually increases from an intermediate portion in the axial direction (of the iron loss reducing groove) toward a corresponding end portion in the axial direction may be formed. That is, if this configuration is adopted, the interference between the frame and the stator core is gradually reduced at both end portions as compared with the intermediate portion in the axial direction. As a result, it was found that the stress concentration at both ends of the stator core in the axial direction was alleviated, and as a result, all the problems described above were solved, and the present invention was completed.

  The present invention relates to compressive stress acting on the outer peripheral portion of both ends in the axial direction of the stator core due to the fit between the frame and the stator core, and the inner surface portion of the intermediate portion in the length direction of each tooth portion. An object of the present invention is to provide an electric motor that can alleviate the generated compressive stress and thereby reduce the iron loss in the axial direction and the circumferential direction of the stator core.

  The invention according to claim 1 is a cylindrical frame, and a stator core that is inserted into the inner space of the frame and that is held by the clamping force of the frame by bringing the outer peripheral surface into surface contact with the inner peripheral surface of the frame. In the electric motor including a rotor that rotates in the inner space of the stator core, an annular region is formed in the region facing the outer peripheral surface of the stator core in the inner peripheral surface of the frame over the entire circumferential direction of the frame. An iron loss reducing groove is formed, and the iron loss reducing groove has a depth that gradually increases from an axially intermediate portion of the iron loss reducing groove toward both ends of the iron loss reducing groove. It is a motor.

  In the case of a conventional electric motor, the area facing the stator core on the inner peripheral surface of the frame is a plane (complete cylindrical surface) over the entire length in the axial direction, so when the frame and the stator core are fitted (when tightening) In this case, stress concentration occurs at the contact portions with the frames at both ends of the stator core, and as a result of this, the compressive stress at the contact portions increases, and each tooth portion also has a stress from the outer peripheral surface side of both ends of the stator core. A compressive stress was increased at the inner surface portion of the intermediate portion in the length direction of each tooth portion due to the pressing and bending force.

In order to solve this problem, in the present invention, the axial direction of the iron loss reducing groove (hereinafter referred to as the groove axial direction) is formed in the region facing the outer peripheral surface of the stator core in the inner peripheral surface of the frame over the entire circumferential direction of the frame. An annular iron loss reducing groove having a depth that gradually increases from the middle part to the both end parts in the groove axis direction is formed.
Thereby, at the time of fitting, the interference margin of a flame | frame and a stator core becomes small gradually toward the both ends from the intermediate part of the axial direction of a stator core. As a result, the compressive stress acting on the surface contact region of the stator core with the frame due to the fitting gradually decreases from the intermediate portion in the axial direction of the stator core toward both ends, and acts on the outer peripheral portions of both ends of the stator core. Compressive stress is relieved compared to the conventional case. Along with this, also in each tooth portion, the pushing and bending force from the outer peripheral surface side of both ends of the stator core is reduced, and the compressive stress acting on the inner surface portion of the intermediate portion in the length direction of each tooth portion is also conventionally increased. Compared to As a result, the iron loss in the axial direction of the stator core and in the circumferential direction thereof can be reduced.

The electric motor is of an inner rotor type. The electric motor is configured such that at least an intermediate portion in the axial direction of the stator core in the region facing the inner peripheral surface of the frame on the outer peripheral surface of the stator core is in surface contact with the frame throughout the entire circumferential direction of the stator core.
As used herein, “at least an intermediate portion in the axial direction of the stator core in the region facing the inner peripheral surface of the frame on the outer peripheral surface of the stator core” means that the surface contact region with the frame is, for example, the inner surface of the frame on the outer peripheral surface of the stator core. It means that only the intermediate portion in the axial direction of the stator core in the region facing the peripheral surface may be used, or the entire region facing the inner peripheral surface of the frame on the outer peripheral surface of the stator core may be used. From another viewpoint, the depth (maximum depth) at both ends in the axial direction of the frame of the iron loss reducing groove may be larger or smaller than the interference allowance.
In addition, when only the intermediate portion in the axial direction of the stator core is in surface contact (surface contact region) with the frame over the entire circumferential direction of the stator core, the role of fixing the stator core to the frame is sufficient even with only the intermediate portion. I can do it. Therefore, as long as the iron loss reducing groove is machined on the inner peripheral surface of the frame as in the present invention, the purpose of fixing the stator core and the effect of reducing the iron loss by reducing the compressive stress from the frame to the stator core are achieved. can get.

As the frame material, for example, various aluminum alloys can be employed.
The inner diameter of the frame is smaller than the outer diameter of the stator core by the amount of the interference for tightening. This is done by fitting the frame to the stator core by heating the frame to a high temperature and fitting it into the stator core, cooling the stator core to cool it and assembling it into the frame, and press fitting to fix the stator core to the frame with a slight amount of interference. This is for holding with a predetermined tightening force. The thickness of the frame varies depending on the size of the electric motor.
As a material for the stator core, a laminate of electromagnetic steel sheets can be employed.
As the type of the stator core, for example, a laminated electrical steel sheet type in which a large number of thin electrical steel sheets are superposed can be adopted. On the inner peripheral portion of the stator core, a large number of teeth portions around which coils are wound are arranged at a predetermined pitch in the circumferential direction of the stator core and aligned in the length direction in the axial direction of the stator core.

The length relationship (in the axial direction) between the stator core and the frame is longer in the frame than in the stator core. Even when the lengths of the frame and the stator core are the same, the effect of the present invention is exhibited.
“Iron loss reduction groove” means that the frame is divided into two sections (vertically) along the vertical plane including the axis (each of which is parallel to the axis of the frame and opposed to each other at 180 ° intervals) (In the cross-section divided in half), a convex arc groove in which the middle part in the groove axis direction on the back (back, bottom, width) protrudes outward, or the middle in the groove axis direction on the back It is possible to employ a chevron groove that has a (mountain peak) and has slope portions on both sides in the groove axial direction on the back surface. Of these, when the iron loss reducing groove has a circular arc cross section on the back surface, the stress distribution in the axial direction of the stator core is gradually relaxed toward both ends, and the contact portion changes stepwise. There is no stress concentration.

The radius of curvature of the cross-sectional arc on the back surface is 5 to 35 times the inner diameter of the frame. If it is less than 5 times, the frame and the stator core cannot be fixed sufficiently. Further, if it exceeds 35 times, the interference of the frame is almost the same as that of the conventional stator core, and the iron loss increases at both ends of the stator core. A preferable radius of curvature of the back surface of the iron loss reducing groove is 7 to 15 times. Within this range, it is sufficient to fix the stator core at both end portions and teeth portions of the back yoke of the stator core, and the stress distribution is uniform and small, and iron loss is reduced.
When the back surface of the iron loss reducing groove has a mountain-shaped cross section, a flat portion having a constant inner diameter is formed in the axial direction intermediate portion of the iron loss reducing groove on the back surface in the axial direction. May be. At that time, the cross-sectional shape of the back surface is a trapezoid.
Further, the iron loss reducing groove has the shortest distance from the axial line of the frame and the stator core that coincide with each other to the intermediate point in the axial direction of the back surface of the iron loss reducing groove (the innermost peripheral edge of the iron loss reducing groove). The distance may be the same as or shorter than the shortest distance from the axis to the inner peripheral surface of the frame (excluding the iron loss reducing groove).
As the rotor, for example, a general inner rotor can be adopted.

  According to a second aspect of the present invention, in the electric motor according to the first aspect, the maximum depth of the iron loss reducing groove is 0.1 to 1 times the maximum value of the interference between the frame and the stator core. It is.

According to the second aspect of the present invention, since the maximum depth of the iron loss reducing groove is set to be equal to or less than the maximum value of the interference margin between the frame and the stator core before fitting, at the shaft end portion of the stator core, compressive stress and The stress toward the center of the stator core is reduced, and the iron loss is reduced as a whole.
The maximum depth of the iron loss reduction groove (the depth of both ends in the axial direction of the frame of the iron loss reduction groove) is the same as the maximum value of the interference allowance between the frame and the stator core (1 time). It is up to 0.1 times smaller. If it is this range, a compressive stress and the stress which goes to the center part of a stator core will become small in the axial end part of a stator core, and an iron loss will be reduced. Also, if the maximum depth of the iron loss reducing groove is the same as the maximum value of the interference allowance, the outer diameter of the stator core and the inner diameter of the frame are the same at the shaft end portion of the stator core during fitting (the intermediate State), compressive stress and stress toward the center of the stator core are not generated, and the iron loss is reduced as a whole.
Here, the maximum amount of interference between the frame and the stator core corresponds to an intermediate portion in the axial direction of the iron loss reducing groove, which is an opposing portion of the frame and the stator core (an intermediate portion in the axial direction of the stator core). is there.

  According to the first aspect of the present invention, in the region of the inner peripheral surface of the frame facing the outer peripheral surface of the stator core, from the intermediate portion in the axial direction of the iron loss reducing groove across the entire circumferential direction of the frame The structure which forms the groove | channel for annular | circular shaped iron loss reduction which depth increases gradually toward both ends was employ | adopted. As a result, when the stator core and the frame are fitted together, the interference between the frame and the stator core gradually decreases from the intermediate portion in the axial direction of the stator core toward both ends thereof. As a result, the compressive stress acting on the surface contact area of the stator core with the frame gradually decreases from the intermediate portion in the axial direction of the stator core toward both ends, and acts on the outer peripheral portions at both ends of the stator core as compared with the conventional case. Compressive stress is relieved. In addition, along with this, in each tooth portion, the pushing and bending force from the outer peripheral surface side of both end portions of the stator core is reduced, and the compressive stress in the inner surface portion of the intermediate portion of each tooth portion is reduced as compared with the related art. From the above, the iron loss in the axial direction of the stator core and in the circumferential direction thereof can be reduced.

  According to the second aspect of the present invention, the maximum depth of the iron loss reducing groove is 0.1 to 1 times the maximum value of the interference between the frame and the stator core. If it is this range, in the axial end part of a stator core, the compressive stress and the stress which goes to the center part of a stator core will become smaller than before, and an iron loss will reduce as a whole.

It is a principal part expanded vertical sectional view which shows the fitting state of the flame | frame which comprises some electric motors which concern on Example 1 of this invention, and a stator core. It is a longitudinal cross-sectional view which shows the fitting state of the frame before cooling which comprises some electric motors which concern on Example 1 of this invention, and a stator core. The principal part expansion longitudinal cross-sectional view which shows the stress distribution of the formation wall of the iron core reduction groove | channel of a stator core in the fitting state of the frame which comprises a part of electric motor which concerns on Example 1 of this invention, and a stator core, and a teeth part It is. In the stator core that forms part of the electric motor according to Embodiment 1 of the present invention and the stator core that forms part of the conventional electric motor, after lamination of the electromagnetic steel sheets, after shrinking according to the present invention, and conventional shrinking It is a graph which shows the transition of the iron loss in the axial direction of the stator core after and after. (A) is a principal part perspective sectional view which shows stress distribution in the fitting state of the upper half of the frame which comprises a part of electric motor which concerns on the conventional means, and the upper half of a stator core. (B) is a principal part perspective sectional view which shows stress distribution in the fitting state of the upper half of the frame which comprises a part of electric motor which concerns on Example 1 of this invention, and the upper half of a stator core.

  Examples of the present invention will be specifically described below. Here, an electric motor in which the frame and the stator core are fitted together by a shrinking shrinkage method is taken as an example.

  1 and 2, reference numeral 10 denotes an electric motor (hereinafter referred to as a rotating machine) according to Embodiment 1 of the present invention. The rotating machine 10 includes a cylindrical frame 11 and a stator core that is inserted into the inner space of the frame 11 and that is held by the tightening force of the frame 11 by shrinking the frame 11 with the outer peripheral surface being in surface contact with the inner peripheral surface of the frame 11. 12 and a rotor (not shown) that rotates in the internal space of the stator core 12.

Hereinafter, these components will be specifically described.
The rotating machine 10 has an output of about several kW.
The frame 11 is made of an aluminum alloy (A2027), and is a cylindrical body having an inner diameter Ra, an outer diameter Rb (thickness t), and an axial length Lf.
The stator core 12 is a laminated cylindrical body in which a large number of thin and annular electromagnetic steel plates are stacked in the axial direction. A large number of teeth 13 projecting radially toward the axis of the stator core 12 are arranged at a predetermined pitch in the circumferential direction of the stator core 12 over the entire inner peripheral portion of the stator core 12. The inner diameter of the main body portion excluding the tooth portion 13 of the stator core 12 is Rc, the outer diameter of the main body portion is Ra + 0.6 mm, the thickness T of the main body portion, and the axial length of the main body portion is Ls. As a result, the interference margin “a” (before shrinking) of the frame 11 and the stator core 12 has an intermediate position in the axial direction of the stator core 12 due to the influence of the shape of the back surface 14 a of the iron loss reducing groove 14 described later. In addition to the maximum (for example, 0.6 mm), the interference margin a of the shaft end portion of the stator core 12 is appropriately reduced according to shrinkage conditions, such as 0.1 mm and 0.2 mm.
A rotor (not shown) is housed in the internal space of the stator core 12 so as to be rotatable about its axis. A general-purpose inner rotor is used as the rotor.

Next, the frame 11 will be described in detail with reference to FIG.
In the frame 11, the inner surface of the frame 11 is opposed to the outer surface of the stator core 12, and is gradually extended from the intermediate portion in the axial direction of the frame 11 toward both ends of the frame 11 over the entire circumferential direction of the frame 11. An annular iron loss reducing groove 14 having an increased depth is formed. The “region facing the outer peripheral surface of the stator core 12” here is a portion of the inner peripheral surface of the frame 11 excluding both ends in the axial direction of the frame 11. At the time of fitting (shrinking), the frame 11 and the stator core 12 are overlapped at the midpoints of the lengths in the axial direction on the mutually matching axes.

The iron loss reducing groove 14 has a convex arcuate back surface 14a in which a middle portion in the groove axis direction protrudes outward in a cross section obtained by dividing the frame 11 into two perpendicular planes including the axis thereof ( State before shrinking). An intermediate point in the axial direction of the back surface 14 a is arranged concentrically with the inner peripheral surface of the frame 11 in a cross section orthogonal to the axis of the frame 11. The iron loss reducing groove 14 has a length in the axial direction that is 0.2 mm longer than the axial length of the stator core 12 (up and down by 0.1 mm), and before the shrinkage, The depth at both ends in the axial direction is the maximum depth b of the iron loss reducing groove 14. The maximum groove depth b is 0.5 mm, which is 0.5 times the maximum value of the interference allowance a, and the maximum depth c after shrinking is 0.6 mm.
For example, the maximum depth b of the iron loss reducing groove 14 may be set to 0.6 mm, which is the same as the maximum value of the interference allowance a. In this case, the radius of curvature of the cross-sectional arc of the back surface 14 a of the iron loss reducing groove 14 is 5.6 times the inner diameter of the frame 11. At this time, there is no interference margin at the shaft end of the stator core 12.

  At the time of manufacturing the rotating machine 10 configured as described above, the frame 11 and the stator core 12 are fitted together by shrinkage shrinkage. At this time, a core loss reducing groove 14 is formed in the inner peripheral surface of the frame 11 in a region facing the outer peripheral surface of the stator core 12 and a region 0.1 mm above and below it. As described above, the depth of the groove 14 gradually increases from the intermediate portion in the axial direction toward both ends over the entire circumferential direction of the frame 11, and the maximum depth b is 0.3 mm. For this reason, during shrinkage, among the regions of the outer peripheral surface of the stator core 12 facing the inner peripheral surface of the frame 11, the intermediate portion in the axial direction of the stator core 12 has the largest interference allowance a (the maximum value of the interference allowance a). As the stator core 12 moves to the upper and lower ends, the interference margin a gradually decreases. Further, the interference c between the frame 11 and the stator core 12 after shrinking is 0.6 mm over the entire area of the opposed area between the inner peripheral surface of the frame 11 and the outer peripheral surface of the stator core 12 (FIG. 1). At this time, the surface contact region between the inner peripheral surface of the frame 11 and the outer peripheral surface of the stator core 12 is the same as this facing region.

In this way, the interference allowance a gradually decreases from the intermediate portion in the axial direction of the stator core 12 toward both end portions thereof, so that the compressive stress acting on the surface contact region with the frame 11 of the stator core 12 is reduced in the surface contact region. Including the upper and lower ends of the nearby stator core 12, the stator core 12 gradually decreases from the middle in the axial direction toward both ends (FIG. 3). Therefore, the compressive stress acting on the outer peripheral portions of both end portions of the stator core 12 when shrinking the frame 11 and the stator core 12 is reduced as compared with the conventional rotating machine (graph in FIG. 4). In addition, along with this, in each tooth portion 13, the pushing and bending force from the outer peripheral surface side of both end portions of the stator core 12 is reduced, and compressive stress is also conventionally applied to the inner surface portion of the intermediate portion in the length direction of each tooth portion 13. It becomes smaller (FIG. 3).
For example, when the maximum depth b of the iron loss reducing groove 14 is set to 0.6 mm, which is the same as the maximum value of the interference allowance a, the shaft end portion of the stator core 12 is in an intermediate swallow state having no interference allowance. As a result, no compressive stress or stress toward the central portion of the stator core 12 is generated at the shaft end portion of the stator core 12, and the iron loss is reduced as a whole. If the maximum depth b of the iron loss reducing groove 14 is made larger than the maximum value of the interference allowance a, a gap appears between the shaft end of the stator core 12 and the inner peripheral surface of the frame 11, A surface contact region between the inner peripheral surface of the frame 11 and the outer peripheral surface of the stator core 12 is smaller than the facing region. Even in this case, since the interference allowance a gradually decreases from the intermediate portion in the axial direction of the stator core 12 toward both ends thereof, the iron loss at the shaft end portion of the stator core 12 can be reduced.

Here, with reference to FIG. 5, the result of actually performing the stress analysis of the fitting part of a flame | frame and a stator core in the electric motor of this invention (Example 1) and the conventional electric motor is reported. The only structural difference between the electric motor of the present invention and the conventional electric motor is whether or not the inner peripheral surface of the frame has a core loss reducing groove.
As shown in FIG. 5 (a), in the case of the conventional electric motor, the compressive stress that acts on the outer peripheral portion of both ends of the stator core that occurs during shrinkage, and the intermediate portion in the length direction of each tooth portion. The compressive stress acting on the inner surface part was large.
On the other hand, as shown in FIG. 5B, in the present invention, the interference allowance a between the frame 11 and the stator core 12 gradually decreases from the intermediate portion in the axial direction of the stator core 12 toward both ends thereof. It was. As a result, the compressive stress acting on the outer peripheral portions of both end portions of the stator core 12 generated during shrinkage was relaxed. In connection with this, the compressive stress which acts on the inner surface part of the intermediate part in the length direction of each teeth part 13 was also relieved. Therefore, the iron loss in the axial direction and the circumferential direction of the stator core 12 could be reduced as compared with the case of the conventional machine.

  The present invention is a technique useful for reducing iron loss of a stator core of an electric motor.

10 Electric motor,
11 frames,
12 stator core,
14 Iron loss reduction groove,
a Crushing cost.

Claims (2)

A cylindrical frame;
A stator core that is inserted into the inner space of the frame and that is held by the clamping force of the frame by bringing the outer peripheral surface into surface contact with the inner peripheral surface of the frame;
In an electric motor comprising a rotor that rotates in the internal space of the stator core,
Of the inner peripheral surface of the frame, in the region facing the outer peripheral surface of the stator core, an annular iron loss reducing groove is formed over the entire circumferential direction of the frame,
The iron loss reducing groove is an electric motor that gradually increases in depth from an intermediate portion in the axial direction of the iron loss reducing groove toward both ends of the iron loss reducing groove.   2. The electric motor according to claim 1, wherein a maximum depth of the iron loss reducing groove is 0.1 to 1 times a maximum value of a fastening margin between the frame and the stator core.

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