Method of manufacturing stator of rotary electric machine

Abstract

To prevent a void from being formed between lead wire segments 2 when immersing a coil end 2 of a stator 1 in a liquefied resin 4 poured into a mold 3, in a method of manufacturing the stator of a rotary electric machine.SOLUTION: A method of manufacturing a stator of a rotary electric machine, in which a coil is wound on a stator tooth protruding radially inward from a stator core and protrudes from an end surface in an axial direction of the stator, includes a step of immersing and curing a portion of the coil protruding from the end surface in the axial direction of the stator in a liquefied thermosetting resin poured into a concave mold. The liquefied thermosetting resin in the mold is prepared so that a viscosity of upper portions 5 and 4a is lower than a viscosity of a lower portion 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a stator for a rotating electric machine, and more specifically, to a method for a stator having coils wound around the teeth (stator teeth) of a stator core, the method including a step of forming a resin portion on the end face of the stator to cover the joints of the wire segments located on the axial end face of the stator. [Background technology]

[0002] One method for winding coils around the teeth (stator teeth) of a stator core of a rotating electric machine involves inserting multiple annularly curved conductor segments into slots between the stator teeth so as to surround the stator teeth, and then joining the ends of the conductor segments together by welding them one by one on the axial end face of the stator core, resulting in a single coil wound around the stator tooth. In this configuration, the conductor segments are covered with an insulating coating except for both ends, but the end (joint) that joins to the end of another conductor segment on one axial end face of the stator core is exposed as bare wire. Therefore, to insulate the joints between adjacent conductor segments, a configuration is sometimes adopted in which the end face of the stator core where the joints of the conductor segments are lined up is immersed in liquid resin and the resin is cured while the resin is being coated.

[0003] Regarding the process of forming the resin portion on the end face of the stator core as described above, for example, Patent Document 1 proposes curing the resin under a positive pressure environment to prevent voids from forming in the resin portion (molded portion) that hardens on the end face of the stator core. Patent Document 2 proposes that when the lower coil end, in which multiple segment coils in a stator are joined together, is immersed in uncured insulating resin placed in a mold insulating resin, hardens, and covered with resin, the bottom of the mold is formed into a shape that corresponds to the contour of the lower coil end, thereby making the thickness of the insulating resin adhered around the lower coil end as thin as possible and ensuring high heat dissipation at the lower coil end. Patent Document 3 proposes a configuration in which the tip side of the coil end protruding from the stator core is immersed in a fluid first thermosetting resin to form a layer of the first thermosetting resin, and then a second thermosetting resin is dripped from the core side of the coil end toward the tip side to form a layer of the second thermosetting resin on the first thermosetting resin, and the first and second thermosetting resins are cured, thereby allowing the resin to reach every corner of the coil end and ensuring a more reliable insulation state. Patent Document 4 proposes degassing the inside of a casting tank and a resin tank, and then injecting an impregnation resin into a molding die to impregnate the armature winding, in order to prevent voids from occurring in the resin layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-136787 [Patent Document 2] Patent Publication No. 2019-57986 [Patent Document 3] Patent Publication No. 2019-97234 [Patent Document 4] Patent Publication No. 2005-204413 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in the process of coating and fixing the end portions (coil ends) of multiple annular conductor segments surrounded by stator teeth on the axial end face of the stator with resin, as shown in Figure 3(A), the joint portions 2a of the coil ends 2 protruding from the axial end face of the stator 1 are typically lowered (or the mold 3 is raised) as indicated by the arrow toward the inside 3a of a concave mold 3 into which liquid thermosetting resin 4 has been poured, and are then completely immersed in the liquid thermosetting resin 4 as shown in Figure 3(B), where the resin 4 is thermally cured. In this configuration, the thermosetting resin 4 used to coat and fix the coil ends 2 is required to have insulating properties, heat resistance to the temperature of the stator during operation of the rotating electric machine, and low expansion properties to accommodate the low expansion of the coil ends 2 when the temperature of the stator changes. Therefore, the thermosetting resin 4 used to coat and secure the coil end 2 is made of a highly heat-resistant resin material, such as epoxy resin, blended with inorganic fillers, such as silica and titanium oxide, to meet the low-expansion requirement. However, blending inorganic fillers into the resin material increases the viscosity of the resin material in its liquid state. This high viscosity increases the surface tension between the conductor segments and the liquid resin, reducing wettability of the conductor segment surfaces. As shown in the schematic diagram of Figure 3(B), when the coil end 2 is immersed in the liquid resin 4, the liquid resin has difficulty penetrating between adjacent conductor segments. This can result in air not being able to escape completely between the conductor segments, leaving voids (air bubbles) v inside the cured resin. If such voids v form in the resin, the strength of the cured resin may decrease, or the resin may become deformed due to increased expansion, resulting in insufficient insulation between the conductor segments and insufficient stability of the coil end.

[0006] In view of the above circumstances, the main object of the present invention is to prevent voids from being formed between the conductor segments when the coil ends of the stator are immersed in liquid resin poured into a mold in a method for manufacturing a stator for a rotating electric machine.

[0007] In this regard, as mentioned above, voids form between the conductor segments when the coil ends are immersed in liquid resin due to the high viscosity of the liquid resin used. Therefore, reducing the viscosity of the liquid resin can prevent void formation. On the other hand, reducing the amount of inorganic filler added to lower the viscosity of the liquid resin would result in the resin not meeting the low expansion characteristics required. However, once the liquid resin is adsorbed and spreads on the surfaces of the conductor segments during immersion of the coil ends, air is expelled without remaining between the conductor segments. Therefore, it is not necessary to reduce the viscosity of the entire liquid resin used for immersion. If the viscosity of the upper portion of the liquid resin in the mold where the coil ends contact only at the beginning of immersion is low, the liquid resin will adsorb and spread on the surfaces of the conductor segments, allowing air to escape from between the conductor segments. Then, when the coil ends are immersed deeper, the spaces between the conductor segments can be filled with high-viscosity liquid resin without leaving voids. This finding is utilized in the present invention. [Means for solving the problem]

[0008] According to the present invention, the above-mentioned problem is solved by a method for manufacturing a stator for a rotary electric machine, in which a coil is wound on stator teeth protruding radially inward from a stator core so as to protrude from an axial end face of the stator, a step of immersing the coil portion protruding from the axial end surface of the stator in a liquid thermosetting resin poured into a recessed mold and hardening the thermosetting resin; Including, This is achieved by a method in which the liquid thermosetting resin in the mold is prepared so that the viscosity of the upper portion is lower than that of the lower portion.

[0009] In the above configuration, the "rotating electric machine" may be any type of rotating electric machine (generator, electric motor, motor-generator) that uses a stator wound with a coil. In the present invention, the "coil" is a wire made of a conductive material (such as copper or aluminum) formed into a single spiral, and as described above, the coil is wound so that a portion of the coil protrudes from the axial end face of the stator. More specifically, the coil may be a coil formed by connecting multiple annular conductor segments in a single line, and both ends of the multiple conductor segments may be joined to ends of adjacent conductor segments on the axial end face of the stator, with the joined ends of the multiple conductor segments aligned along the stator teeth. In such a coil configuration, each conductor segment is entirely coated with an insulating coating so that they do not conduct electricity even when they come into contact with each other, but the insulating coating is removed from the portions at both ends where they are joined to other conductor segments, and the joint portions at the ends of these conductor segments are immersed in liquid thermosetting resin in a mold to be insulated. The above-mentioned stator core may be wound with multiple coils, in which case each coil is formed by connecting multiple conductor segments in a single spiral (i.e., the stator of the present invention also includes a case where multiple coils are wound around a stator core).

[0010] In the present invention, the liquid thermosetting resin poured into a recessed mold into which the coil portions (coil ends) protruding from the axial end faces of the stator are immersed is prepared so that the viscosity of the upper portion is lower than that of the lower portion. With this configuration, even if the liquid thermosetting resin that will be applied to the axial end faces of the stator to enclose the coil ends has a high enough viscosity that it does not wet the surface of the conductor segments when the coil ends are immersed, leaving voids between the conductor segments, the coil ends are immersed in a lower-viscosity, and therefore more wettable, liquid resin above the higher-viscosity liquid resin before being immersed in the higher-viscosity liquid resin. This allows the liquid resin to adhere to the conductor segments, facilitating the removal of air from between the conductor segments. When the coil ends are subsequently immersed in the higher-viscosity liquid resin, the liquid resin also fills the spaces between the conductor segments, thereby preventing the formation of voids.

[0011] In the above-described configuration of the present invention, the higher-viscosity resin prepared in the lower portion of the mold may be any resin that satisfies the heat resistance, insulating properties, and low expansion required for a resin that will be fixed to enclose the coil end after curing. On the other hand, the lower-viscosity resin prepared in the upper portion of the mold may be a resin that has high wettability on the surface of the wire segment. In this regard, it is preferable that the low-viscosity liquid resin in the upper portion be of the same quality as the high-viscosity liquid resin in the lower portion, so that when the coil end is immersed in the upper portion of the mold and the low-viscosity liquid resin is adsorbed onto the surface of the wire segment, the high-viscosity liquid resin is continuously introduced onto the surface of the wire segment when the coil end is immersed in the lower portion of the mold. More specifically, the high-viscosity resin for the lower portion, which is fixed to enclose the coil end, may be a highly heat-resistant thermosetting resin such as epoxy resin, unsaturated polyester resin, or phenolic resin, in which fibrous, plate-like, amorphous, or spherical inorganic fillers, such as silica, titanium oxide, calcium carbonate, aluminum hydroxide, or talc, are dispersed to meet the required low expansion characteristics. Meanwhile, the resin for the upper portion in the mold may be a thermosetting resin such as those described above, with a reduced amount of inorganic filler dispersed or no inorganic filler at all, to ensure sufficient wettability with the surface of the conductor segment. In one embodiment, the viscosity of the liquid thermosetting resin for the lower portion may be 2000 mPa·s or more upon immersion, and the viscosity of the liquid thermosetting resin for the upper portion may be 1000 mPa·s or less upon immersion.

[0012] In the present invention, adjusting the viscosity of the liquid thermosetting resin in the mold so that the viscosity of the upper portion is lower than the viscosity of the lower portion may be achieved by any method. Specifically, for example, a liquid thermosetting resin with a higher viscosity may be poured into the mold, and then a liquid thermosetting resin with a lower viscosity may be poured on top of it, thereby adjusting the viscosity difference between the upper and lower thermosetting resins in the mold. Alternatively, the viscosity of the liquid thermosetting resin may be adjusted by the amount of inorganic filler dispersed therein, so that after the liquid thermosetting resin with the inorganic filler dispersed therein is poured into the mold, at least a portion of the inorganic filler settles downward, so that the amount of inorganic filler dispersed in the upper portion is lower than the amount of inorganic filler dispersed in the lower portion, thereby adjusting the viscosity difference between the upper and lower thermosetting resins in the mold. [Effects of the Invention]

[0013] According to the configuration of the present invention, when the coil ends of a stator of a rotating electric machine are immersed in a liquid thermosetting resin poured into a mold and cured to form a resin portion that is bonded to the coil ends and surrounds them, the viscosity of the liquid thermosetting resin in the mold is adjusted so that the viscosity of the upper portion is lower than that of the lower portion, thereby preventing the formation of voids between the conductor segments when the coil ends of the stator are immersed in the liquid resin poured into the mold. In this configuration, even if the resin that is bonded to the coil ends and that satisfies the heat resistance, insulation, and low expansion requirements is high and the resin alone is prone to forming voids between the conductor segments, immersing the coil ends in a resin with higher wettability before immersing them in the resin allows the resin with sufficient low expansion to fill the spaces between the conductor segments, making it easy to use a resin that satisfies the heat resistance, insulation, and low expansion requirements as the resin to be bonded to the coil ends.

[0014] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0015] [Figure 1] 1(A) and (B) are schematic diagrams showing a process of immersing the coil end of a stator to which this embodiment is applied into liquid resin stored in a mold, where (A) shows the state immediately before immersion and (B) shows the state after immersion. [Figure 2] 2(A) to 2(D) are schematic diagrams illustrating the process of immersing the coil ends of a stator to which this embodiment is applied in liquid resin stored in a mold. (A) shows the state after the liquid resin with inorganic filler dispersed therein has been poured into the mold, (B) shows the state after some of the inorganic filler has settled in the liquid resin in the mold, creating a difference in viscosity between the liquid resin above and below the mold, (C) shows the state immediately before the coil ends are immersed, and (D) shows the state after the coil ends have been immersed. [Figure 3] 3(A) and (B) are schematic diagrams of the process of immersing the coil end of a conventional stator in liquid resin stored in a mold. (A) shows the state immediately before immersion, and (B) shows the state after immersion. [Figure 4] Fig. 4(A) is a schematic perspective view of a stator for a rotating electric machine. Fig. 4(B) is a schematic diagram of a coil formed by sequentially connecting both ends of an annularly curved conductor segment to the end of another conductor segment. Figs. 4(C) to 4(E) are schematic diagrams of the process of forming a resin portion on the end face of the stator. [Explanation of symbols]

[0016] 1... stator core, 2, 21, 22... coil end, 23... conductor segment, 2a... conductor segment joint portion, 3... mold, 3a... inside of mold, 4... (high viscosity) liquid resin, 4a... (low viscosity) liquid resin, 5... (low viscosity) liquid resin, v... void BEST MODE FOR CARRYING OUT THE INVENTION

[0017] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0018] Overview of the coils wound around the stator teeth In a stator for a rotating electric machine manufactured by applying the method of this embodiment, as can be seen from the upper part of Fig. 1(A) or Fig. 4(A), coils are wound around a plurality of stator teeth that protrude radially inward from an annular stator core 1, and a portion of the coils, i.e., coil ends 2, protrude from an end face 1a in the axial direction Ax of the stator core 1. More specifically, as schematically illustrated in Fig. 4(B), such coils are typically formed by arranging a plurality of annularly curved conductor segments 23 made of a conductive material in alignment along the protruding direction Tx of the stator teeth so as to surround the stator teeth (not shown), and joining, by welding or the like, both ends 21, 22 of one conductor segment 23 to the ends 22, 21 of another conductor segment 23 adjacent to each other, in order, to form a single coil wound around the stator tooth (note that the coil may be wound around the stator tooth in any manner (concentrated winding, distributed winding, etc.)). Therefore, as shown in FIG. 1B, the joint portions 2a of the conductor segments 23 are aligned along the extending direction of the stator teeth on one end face in the axial direction Ax of the stator.

[0019] The conductor segment 23 is formed by appropriately bending or curving a wire made of a conductive material such as copper or aluminum into a ring shape, and its surface, except for the tip, is covered with an insulating coating. The cross section of the conductor segment may be, for example, a rectangle of 3 mm x 2 mm or 3 mm x 4 mm, and its length is, for example, 100 to 150 mm, but is not limited to this.

[0020] Forming the resin part that covers the coil end on the stator end surface As described above, in a configuration in which the coil surrounding the stator teeth is joined by sequentially welding the ends of multiple conductor segments, the insulating coating is removed from the joint portion 2a of the conductor segments and its vicinity, exposing the conductor. In order to ensure insulation at the joint portion 2a and its vicinity and to stably hold the coil, as already mentioned, the axial end surface 1a of the stator where the coil ends are lined up is covered with a resin portion 4 (see Figure 1(A)).

[0021] Generally speaking, the process of forming the resin portion 4 that covers the coil ends 2 on the axial end face 1a of the stator begins as follows: first, as shown in Fig. 4(C), an annular mold 3 having a concave container portion is placed with its opening facing upward, and liquid thermosetting resin 4(L) is poured into it. Then, the axial end face 1a of the stator 1 on which the coil ends 2 are aligned is lowered facing downward, and the coil ends 2 protruding from the stator end face 1a are placed in the container portion of the mold 3 and immersed in the liquid resin 4(L), as shown in Fig. 4(D). Once the resin 4(L) has hardened in this state, the stator 1 is lifted with a mold release pin or the like, and the mold 3 is released from the resin portion 4 formed on the axial end face 1a (Fig. 4(E)).

[0022] Regarding the resin portion 4 enclosing the coil end 2, since the temperature of the stator core and coils during operation of the rotating electric machine becomes as high as, for example, 200°C, the resin enclosing the coil end 2 must be heat-resistant and insulating enough to withstand the operating temperatures of the rotating electric machine, and must also have low expansion properties so that the difference in thermal expansion between the resin and the metal materials, such as copper and iron, used in the stator core and coils due to temperature changes during operation of the rotating electric machine is minimized. In this regard, thermosetting resins such as epoxy resin, unsaturated polyester resin, and phenolic resin, which have heat resistance and insulating properties, generally have a significantly higher thermal expansion coefficient than the metal materials used in the stator core and coils. Therefore, to reduce the thermal expansion coefficient to approach that of the metal materials, inorganic fillers such as silica, titanium oxide, calcium carbonate, aluminum hydroxide, and talc are added and dispersed in the liquid resin.

[0023] However, when inorganic fillers such as those described above are dispersed in liquid resin, the viscosity of the liquid resin increases as the amount of dispersed inorganic filler increases. If the coil end 2 is directly immersed in such a highly viscous liquid resin, as already mentioned in relation to Figure 3, the liquid resin has low wettability on the surface of the conductor segments and is difficult for the liquid resin to adsorb to the surface of the conductor segments. As a result, air remains between the conductor segments, and voids v are likely to form in the resin portion after the resin hardens.

[0024] Therefore, in this embodiment, as described in the "Summary of the Invention" section, the liquid thermosetting resin poured into the mold 3 is prepared so that, as shown in Fig. 1(A), a high-viscosity resin 4 that meets the heat resistance, insulation properties, and low expansion requirements of the resin enclosing the coil end 2 is present in the lower portion of the mold 3, and a lower-viscosity liquid resin 4a is present above that. With this configuration, as shown in Fig. 1(B), when the coil end 2 is immersed in the liquid resin in the mold 3, the low-viscosity liquid resin first comes into contact with the surfaces of the wire segments and is adsorbed onto and spreads on these surfaces, expelling all air from between the wire segments. Then, when the coil end 2 reaches the region of high-viscosity resin in the lower portion of the mold 3, the high-viscosity resin 4 is expected to fill the spaces between the wire segments without forming voids.

[0025] As described above, creating a difference in viscosity between the upper and lower liquid resins in the mold 3 into which the coil end 2 is immersed may be achieved by any method. In one embodiment, as shown in Figures 1(A) and 1(B), high-viscosity liquid resin 4 may be poured first into the lower portion of the mold 3, and then low-viscosity liquid resin 5 may be placed in the upper portion of the mold 3 above it. The high-viscosity liquid resin 4 and the low-viscosity liquid resin 5 may be prepared by adjusting the amount of inorganic filler dispersed in the same resin material, respectively. The amount of inorganic filler dispersed in each liquid resin may be determined experimentally.

[0026] In another embodiment, as shown in Figure 2(A), liquid resin 4 containing an inorganic filler that tends to settle in the liquid resin is poured into mold 3, and then allowed to stand, allowing some of the inorganic filler to settle in the lower part of mold 3. As shown in Figure 2(B), this reduces the amount of inorganic filler dispersed in the upper part of mold 3, thereby reducing the viscosity (4a), and thereby creating a difference in viscosity between the upper and lower parts of the liquid resin in mold 3. The amount of inorganic filler dispersed in the liquid resin may be determined experimentally. Then, as shown in Figures 2(C) and 2(D), the coil end 2 is immersed in mold 3.

[0027] As described above, once the coil end 2 is immersed in the liquid resin in the mold 3, it is heated and the resin hardens. In one embodiment, for example, the coil end is immersed in the liquid resin in the mold when the temperature of the liquid resin is approximately 70°C. The resin temperature is then raised to approximately 180°C to harden the resin. In this case, the liquid resin in the lower portion of the mold is prepared to have a viscosity sufficient to penetrate between the wire segments, i.e., to allow deformation, at approximately 70°C. As mentioned above, the greater the amount of inorganic filler dispersed in the liquid resin, the lower the expansibility and the higher the viscosity. However, experiments have shown that liquid resins with a viscosity of up to approximately 2000 mPa·s can penetrate between the wire segments. Therefore, to minimize expansibility, the liquid resin in the lower portion of the mold may be prepared to have a viscosity of 2000 mPa·s or greater at approximately 70°C when the coil end is immersed. On the other hand, with regard to the liquid resin in the upper part of the mold, if the viscosity of the liquid resin is 1000 mPa·s or less, air will not remain between the conductor segments when the coil ends are immersed, so the liquid resin in the upper part of the mold may be prepared so that its viscosity is 1000 mPa·s or less at approximately 70°C.

[0028] Thus, when the coil ends of the stator of a rotating electric machine are immersed in liquid resin poured into a mold, the liquid resin in the upper part of the mold can be made to have a lower viscosity than the liquid resin in the lower part, thereby preventing voids from forming between the wire segments.

[0029] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

1. A method for manufacturing a stator of a rotary electric machine, in which a coil is wound on a stator tooth protruding radially inward from a stator core so as to protrude from an axial end face of the stator, a step of immersing the coil portion protruding from the axial end surface of the stator in a liquid thermosetting resin poured into a recessed mold and hardening the thermosetting resin; Including, The liquid thermosetting resin in the mold is prepared so that the viscosity of the upper portion is lower than the viscosity of the lower portion.

2. 2. The method of claim 1, wherein the high viscosity liquid thermosetting resin is poured into the mold, and then the low viscosity liquid thermosetting resin is poured on top of it, so that the viscosity of the liquid thermosetting resin in the mold is adjusted to be lower in the upper portion than in the lower portion.

3. 2. The method of claim 1, wherein the viscosity of the liquid thermosetting resin is adjusted by the amount of inorganic filler dispersed therein, and after the liquid thermosetting resin having the inorganic filler dispersed therein is poured into the mold, at least a portion of the inorganic filler settles downward, so that the amount of inorganic filler dispersed in the upper portion is lower than the amount of inorganic filler dispersed in the lower portion, thereby preparing the liquid thermosetting resin in the mold so that the viscosity of the upper portion is lower than the viscosity of the lower portion.

4. 2. The method of claim 1, wherein the viscosity of the liquid thermosetting resin in the lower portion is 2000 mPa·s or more at the time of immersion, and the viscosity of the liquid thermosetting resin in the upper portion is 1000 mPa·s or less at the time of immersion.

5. 2. The method of claim 1, wherein the coil is formed by connecting a plurality of annular conductor segments together, both ends of the plurality of conductor segments are respectively joined to ends of adjacent ones of the conductor segments on an axial end face of the stator, joint portions of the ends of the plurality of conductor segments are aligned along the stator teeth, and the joint portions of the ends of the conductor segments are immersed in liquid thermosetting resin in the mold.

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