METHOD FOR PRODUCING A CORE OF A ROTATING ELECTRIC MACHINE

Abstract

Method for manufacturing a core of a rotating electric machine, wherein the core has a plurality of receiving slots and a plurality of permanent magnets, wherein each permanent magnet is received in one of the receiving slots, the method comprising the following steps: Injecting a liquid crystal polymer, which is a fixing agent, into a space between an inner surface of each receiving slot and an outer surface of the associated permanent magnet, wherein the injection of the liquid crystal polymer comprises a flow of the liquid crystal polymer through a heating section, and Maintaining a core temperature between 40 and 80 degrees Celsius when the fixer is injected into the space by flowing a refrigerant through a refrigerant passage located above the core, wherein the liquid crystal polymer is injected into the room at a temperature between 300 and 350 degrees Celsius, The liquid crystal polymer has a melting viscosity of 1.2 to 8.0 Pascal seconds at 300 to 350 degrees Celsius and at a shear rate of 1000 s -1 has, and The heating section is located above the refrigerant section.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method for manufacturing a core of a rotating electrical machine.

[0002] For example, Fig. 5 shows an example of the configuration of a known conventional rotor core 31 of a motor. According to this conventional configuration, the rotor core 31 has a plurality of receiving slots 32 arranged along the outer circumference. A permanent magnet 33 is received in each receiving slot 32. The space between the inner surface of each receiving slot 32 and the corresponding permanent magnet 33 is filled with a fixing agent 34 for fixing the permanent magnet 33 in the received state. Epoxy resin, which is a thermosetting resin, is generally used as the fixing agent 34.

[0003] The rotor core 31 is typically manufactured according to the processes described below, as in Fig. 6. In a first step 35, core plates are formed by pressing and laminated to form a rotor core 31. In the next step 36, a permanent magnet 33 is inserted into and received in each receiving slot 32. In the subsequent step 37, the rotor core 31 receiving the permanent magnets 33 is heated to approximately 150°C using, for example, a heating furnace. This is because, since the epoxy resin, which is a thermosetting resin, is used as the fixing agent 34 for fixing the permanent magnets 33 in the received state, the rotor core 31 and the permanent magnets 33 must be preheated before injecting the fixing agent 34.

[0004] In the next step 38, with the rotor core 31 and the permanent magnets 33 heated, the space between the inner surface of each receiving slot 32 and the corresponding permanent magnets 33 is filled with the fixing agent 34 made of epoxy resin using, for example, a molding machine. When the fixing agent 34 hardens, the permanent magnets 33 are fixed in the receiving slots 32 in the received state. In the subsequent step 39, the rotor core 31, in which the permanent magnets 33 are received and fixed, is cooled to an ordinary temperature using, for example, a cooling furnace.

[0005] After the rotor core 31 has been processed through the steps described above, the rotor core 31 is subjected to further steps, including installing a rotor shaft.

[0006] Furthermore, JP 2010-141989 A discloses a conventional rotor core used in this type of motor. In this conventional design, the permanent magnet housed in each receiving slot of the rotor core is divided into two or more pieces, and a foamed plastic plate is provided between the magnet pieces. After the permanent magnets are inserted into the receiving slots, the foamed plastic plates are heated, increasing their thickness due to thermal expansion. This presses the divided magnet pieces against the inner surface of the receiving slot, thus fixing the magnet pieces in a received state.

[0007] The conventional designs described above have the following disadvantages.

[0008] In the conventional design, which is Fig. 5 and Fig. As shown in Fig. 6, an epoxy resin, which is a thermosetting resin, is used as the fixing agent 34 for fixing the permanent magnets 33. The design requires the heating step 37, which is performed before injecting a fixing agent 34 to preheat the rotor core 31 and the permanent magnet 33, and the cooling step 39, which is performed after injecting the fixing agent 34 to cool the rotor core 31 and the permanent magnet 33. Thus, a relatively large number of steps are required for manufacturing the rotor core 31, and the equipment for performing the steps accordingly tends to be large in size.

[0009] In the manufacturing process of the rotor core 31, the magnetic steel constituting the permanent magnets 33 has a property of expanding in the width direction as shown by arrows in Fig. 5 when the rotor core 31 and the permanent magnets 33 are cooled to an ordinary temperature. Due to this characteristic, stress may concentrate on the permanent magnets 33 or narrow parts 311 in the outer periphery of the rotor core 31, which may deform these parts.

[0010] Furthermore, the conventional design disclosed in JP 2010-141989 A has foamed plastic plates that function as a fixing means for fixing permanent magnets in the receiving slots. Thus, the design has an increased number of components of the rotor core 31. Furthermore, during manufacturing, a foamed plastic plate must be placed between the permanent magnet pieces, and the rotor core and the permanent magnets must be heated with the foamed plastic plates inserted into the receiving slots so that the foamed plastic plates are thermally expanded in the thickness direction. Thus, this conventional design not only has a complicated manufacturing process but also requires a heating step and a cooling step, as in the case of the previous conventional design disclosed in Fig. 5 and Fig. 6. This means that a relatively large number of steps are required to manufacture a rotor core.

[0011] JP 2007-306726 A discloses a method for manufacturing a core of a rotating electrical machine, the core having a plurality of receiving slots and a plurality of permanent magnets, each permanent magnet being received in one of the receiving slots. The method includes the step of injecting a liquid crystal polymer, which is a fixing agent, into a space between an inner surface of each receiving slot and an outer surface of the associated permanent magnet.

[0012] Further methods for producing a core of a rotating electrical machine are known from CN 1 159 371 C and JP H07 - 304 866 A. SUMMARY OF THE INVENTION

[0013] Accordingly, it is an object of the present invention to provide a method for manufacturing a core of a rotating electrical machine, which can simplify the process for manufacturing the core and reduce a stress generated during the core manufacturing process.

[0014] The object of the invention is achieved by a method according to claim 1. Advantageous developments of the invention are the subject of the dependent claims.

[0015] According to the manufacturing method of the present invention, a liquid crystal polymer that cures at ordinary temperature is used as a fixing agent for fixing the permanent magnets in the receiving slots in a received state. Therefore, it is not necessary to heat the core and the permanent magnets before injecting the fixing agent or to cool the core and the permanent magnets after injecting the fixing agent. Therefore, unlike the conventional designs, the manufacturing method of the present invention eliminates the need for the heating step and the cooling step, thereby simplifying the core manufacturing process. Furthermore, since the permanent magnets are not heated or cooled in the core manufacturing process, no expansion of the permanent magnets in the width direction due to temperature changes is caused.Therefore, the manufacturing process can reduce stress generated in the thin parts of the core, thereby reducing a possibility of deformation of the core.

[0016] The manufacturing process can simplify the manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view illustrating a rotor core of a motor according to an embodiment; Fig. 2 is a cross-sectional view taken along a line 2-2 of Fig. 1; Fig. 3 is a block diagram showing in sequence steps of a method for manufacturing the rotor core of Fig. 1 and Fig. 2 shows; Fig. 4 is a cross-sectional view showing the injection step of a fixing agent in the manufacturing process of Fig. 3 shows; Fig. 5 is a partial plan view showing a rotor core of a conventional motor; Fig. 6 is a block diagram showing in sequence steps of a method for manufacturing the rotor core of Fig. 5 shows; and Fig. 7 is a cross-sectional view illustrating a modification of the embodiment which is not subject to the claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A rotor core 11 of a motor according to an embodiment will now be described with reference to Fig. 1 and Fig. 2 described.

[0018] As in Fig. 1 and Fig. As shown in Figure 2, the rotor core 11 of the present embodiment is formed by laminating core plates 111. The rotor core 11 has a shaft hole 12 at its center, which has a circular cross-sectional shape and accommodates a rotor shaft (not shown). The rotor core 11 also has accommodation slots 13 with a rectangular cross-sectional shape in its outer periphery. Each accommodation slot 13 is formed close to an adjacent accommodation slot 13 to form a pair. Each accommodation slot 13 accommodates a plate-shaped permanent magnet 14 extending in the lamination direction of the core plates 111.

[0019] As in Fig. 1 and Fig. As shown in Fig. 2, the space between the inner surface of each receiving slot 13 and the outer surface of the corresponding permanent magnet 14 is filled with a fixing agent 15. A liquid crystal polymer (LCP), which is a thermoplastic resin and cures at an ordinary temperature, is used as the fixing agent 15. Specifically, a liquid crystal polyester is used. The liquid crystal polyester is a known aromatic polyester resin that is linearly ester-bonded with various known elements. For example, the liquid crystal polyester is a wholly aromatic polyester belonging to a thermotropic liquid crystal. Injecting and curing the fixing agent 15 integrally fixes each permanent magnet 14 in the corresponding receiving slot 13 in a received state.

[0020] A method of manufacturing the rotor core 11 having the configuration described above will now be described.

[0021] When the rotor core 11 is manufactured, three steps are carried out in the order shown in Fig. 3. In a first step 17, core plates 111 are formed by pressing a magnetic material, such as magnetic steel plates, and the core plates 111 are laminated to form a rotor core 11. In the next step 18, a permanent magnet 14 is inserted into and received in each receiving slot 13 of the rotor core 11. In the subsequent step 19, the space between the inner surface of each receiving slot 13 and the outer surface of the permanent magnet 14 is filled with the fixing agent 15 made of liquid crystal polyester, for example, by means of a molding machine 20 provided in Fig. 4. The fixing agent 15 hardens at an ordinary temperature, so that the permanent magnet 14 is fixed in the receiving slot 13 in a received state.

[0022] As in Fig. As shown in Fig. 4, the molding machine 20 includes a base 21 for supporting the rotor core 11, an annular outer frame 22 surrounding the outer periphery of the rotor core 11, and an upper frame 23 placed on the upper surface of the rotor core 11. The upper frame 23 has a heating section 235. While the rotor core 11 is inserted into the molding machine 20, an injector 30 injects the fixing agent 15 into an injection passage 232 via an injection port 231 of the upper frame 23. When the fixing agent 15 passes through the injection passage 232, it is maintained at 300 to 350 degrees Celsius and a low viscosity by the heating section 235, thus ensuring favorable fluidity of the fixing agent 15.In this state, the injector 30 injects the fixing agent 15 in a molten state into the space between the inner surface of each receiving slot 13 of the rotor core 11 and the outer surface of the corresponding permanent magnet 14 via nozzles 236 of the upper frame 23. In this case, the temperature of the rotor core 11 may be an ordinary temperature (10 to 30 degrees Celsius), but it is preferably maintained at 40 to 80 degrees Celsius. The upper frame 23 has a refrigerant passage 237 that prevents the rotor core 11 from overheating and maintains the temperature of the rotor core 11 at a substantially ordinary temperature (10 to 30 degrees Celsius) or at 40 to 80 degrees Celsius.

[0023] In injecting the fixing agent 15, the melt viscosity of the fixing agent 15 made of liquid crystal polyester is set to 1.2 to 8.0 Pascal seconds (hereinafter referred to simply as Pa s), and is preferably set to 1.2 to 3.5 Pa s at a shear rate of 1000 s -1The viscosity of the fixing agent 15 is preferably as low as possible. In other words, the viscosity is preferably as close to 0 Pa·s as possible. However, since such a liquid crystal polymer has not yet been discovered, the lower limit of the viscosity of the fixing agent 15 is set to 1.2 Pa·s. By using the fixing agent 15 described above, the injection speed (flow rate) of the fixing agent 15 is set to 100 to 300 mm per second, and preferably 150 to 300 mm per second. In this case, since the liquid crystal polymer used as the fixing agent 15 cures at an ordinary temperature, it is not necessary to heat the rotor core 11 and the permanent magnets 14 to high temperatures before injecting the fixing agent 15 or to cool the rotor core 11 and the permanent magnets 14 after injecting the fixing agent 15.As a result, the manufacturing process of the rotor core 11 is simplified. In some cases, the rotor core 11 is heated to a temperature slightly higher than the usual temperature to ensure sufficient fluidity of the liquid crystal polymer. However, in such a case, the required temperature increase is small. Thus, even if cooling is necessary, the time for cooling the rotor core 11 is short, and the manufacturing process of the rotor core 11 is still simplified.

[0024] During the manufacturing process of the rotor core 11, since the permanent magnets 14 are neither heated nor cooled, the permanent magnets 14 are essentially not expanded in the width direction due to temperature changes. Therefore, during the manufacturing process of the rotor core 11, no large stress is generated in the thin parts 112 of the rotor core 11, unlike conventional designs. This means that the thin parts 112 are less likely to be damaged.

[0025] The present embodiment therefore has the following advantages.

[0026] (1) A permanent magnet 14 is housed in each housing slot 13 formed in the core 11, and the space between the inner surface of the housing slot 13 and the outer surface of the permanent magnet 14 is filled with the fixing agent 15. A liquid crystal polymer that can cure at an ordinary temperature is used as the fixing agent 15. Specifically, a liquid crystal polyester is used.

[0027] Therefore, during the manufacturing of the core 11, it is not necessary to heat the core 11 and the permanent magnets 14 before injecting the fixing agent 15 or to cool the core 11 and the permanent magnets 14 after injecting the fixing agent 15. Therefore, the above-described manufacturing process of the core 11 eliminates the need for the heating and cooling steps, unlike conventional designs, thereby simplifying the manufacturing process. In the manufacturing process of the core 11, since the permanent magnets 14 are neither heated nor cooled, the permanent magnets 14 are not expanded in the width direction due to temperature changes. Thus, no large stress is generated in the thin parts 112 of the rotor core 11. Therefore, the core 11 is prevented from being deformed.

[0028] (2) In the core manufacturing method according to the present embodiment, after the permanent magnets 14 are housed in the housing slots 13 of the core 11, the space between the inner surface of each housing slot 13 and the outer surface of the corresponding permanent magnet 14 is filled with the fixing agent 15 made of a liquid crystal polymer having a melt viscosity of 1.2 to 8.0 Pa·s. Thus, the fixing agent 15 is allowed to efficiently fill the space between the inner surface of each housing slot 13 and the outer surface of the corresponding permanent magnet 14 with a favorable low viscosity.

[0029] (3) In the core manufacturing method according to the present embodiment, the fixing agent 15 is injected at a flow rate of 100 to 300 mm per second, and preferably at a flow rate of 150 to 300 mm per second. Therefore, the fixing agent 15 can be efficiently injected at a favorable flow rate while maintaining a predetermined melt viscosity. The liquid crystal polymer used as the fixing agent 15 has a property that the melt viscosity increases as the flow rate decreases. Modifications

[0030] The above embodiment may be modified as described below.

[0031] As in Fig.7, which is a modification not claimed, the heating section 235 and the nozzles 236 in the upper frame 23 of the molding machine 20 may be omitted. If the molding machine 20 has such a structure, the temperature of the liquid crystal polymer is slightly lower than that in the above-described embodiment. However, sufficient fluidity is ensured due to the low viscosity.

[0032] As the liquid crystal polymer of the fixing agent 15, a material other than liquid crystal polyester may be used.

[0033] The above-described embodiment may be applied to a method for manufacturing a stator core instead of a method for manufacturing a rotor core.

Claims

[1] A method of manufacturing a core of a rotating electrical machine, the core having a plurality of receiving slots and a plurality of permanent magnets, each permanent magnet being received in one of the receiving slots, the method comprising the steps of: Injecting a liquid crystal polymer, which is a fixing agent, into a space between an inner surface of each receiving slot and an outer surface of the associated permanent magnet, wherein the injection of the liquid crystal polymer comprises flowing the liquid crystal polymer through a heating section, and Maintaining a temperature of the core at one of a substantially ordinary temperature and a temperature between 40 and 80 degrees Celsius when the fixing agent is injected into the space by flowing a refrigerant through a refrigerant passage arranged above the core, wherein the liquid crystal polymer is injected into the room at a temperature between 300 and 350 degrees Celsius, the liquid crystal polymer has a melt viscosity of 1.2 to 8.0 Pascal seconds at 300 to 350 degrees Celsius and at a shear rate of 1000 s -1 has, and the heating section is arranged above the refrigerant section. [2] A method for manufacturing a core of a rotating electrical machine according to claim 1, wherein the liquid crystal polymer is a liquid crystal polyester. [3] A method of manufacturing a core of a rotating electrical machine according to claim 1 or 2, further comprising the steps of: Receiving each of the plurality of permanent magnets in one of the receiving slots; and After the permanent magnets are accommodated in the receiving slots of the core, injecting the liquid crystal polymer into the space between the inner surface of each receiving slot and the outer surface of the corresponding permanent magnet. [4] A method for manufacturing a core of a rotating electrical machine according to claim 3, wherein the melt viscosity of the injected liquid crystal polymer is 1.2 to 3.5 Pascal seconds at 300 to 350 degrees Celsius at a shear rate of 1000 s -1 is. [5] A method for manufacturing a core of a rotating electrical machine according to claim 1 or 4, wherein the liquid crystal polymer is injected at a speed of 100 to 300 mm per second. [6] A method for manufacturing a core of a rotating electrical machine according to claim 1 or 4, wherein the liquid crystal polymer is injected at a speed of 150 to 300 mm per second.

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