Cooling pipes and motors having cooling pipes

Abstract

The present invention provides a cooling pipe and a motor having a cooling pipe that reduce eddy current losses in the cooling pipe while having a cooling pipe inside the motor for cooling the windings, thereby reducing the overall loss of the motor. [Solution] The cooling pipe according to the present invention is a cooling pipe provided inside a motor having a stator on which windings are provided and a rotor on which permanent magnets are arranged, and comprises a pipe through which a cooling medium flows, and a soft magnetic material provided on the outer surface of the pipe, and is arranged in a slot provided in the stator.

Description

Technical Field

[0001] The present invention relates to a cooling pipe and a motor having the cooling pipe.

Background Art

[0002] In recent years, as measures to solve the global warming problem, the promotion of decarbonization, carbon neutrality, etc. has been progressing. Under such circumstances, the electrification of aircraft engines is also being considered. The aircraft mobility motor adopted in this electrification can suppress the carbon dioxide emissions compared to jet engines, so the environmental performance can be improved.

[0003] The aircraft mobility motor has a high rotational speed exceeding 10,000 (rpm) and requires a high torque density. There are concerns about the large heat generation of the motor itself and the decrease in efficiency due to the increase in heat loss.

[0004] In conventional motors, a technique of cooling by providing a pipe through which cooling water called a water jacket flows outside a stator core made of electromagnetic steel sheets is common. Although this can cool the stator core, it cannot directly cool the windings with large heat generation, so the heat generation of the motor itself increases due to the heat generation of the windings. When the heat generation of the motor increases, it not only causes a decrease in output density and efficiency, but in the worst case, there is a risk of motor burnout.

[0005] In addition to the water-cooling method such as the above-described water jacket, there are also air-cooling and oil-cooling methods. However, the air-cooling method has problems such as low cooling performance, and the oil-cooling method has a risk of oil leakage, so the adoption of the water-cooling method is desirable.

[0006] In order to suppress the heat generation of the above-described windings, a method of cooling the windings by water-cooling is also considered. This is a method of providing a copper pipe in a space between adjacent windings inside the motor and flowing cooling water through this pipe (Non-Patent Document 1).

Prior Art Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-23035 [Non-patent literature]

[0008] [Non-Patent Document 1] Markus Schiefer, Martin Doppelbauer, "Indirect Slot Cooling for High-Power-Density Machines with Concentrated Winding", 2015 IEEE International Electric Machines & Drives Conference (IEMDC), 10-13 May 2015 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, using the cooling method described in Non-Patent Document 1, while motor heat generation is suppressed by cooling, eddy current losses occur in the copper piping. This is due to the magnetic flux from the permanent magnets inside the motor, and there are concerns that this magnetic flux also affects the windings, increasing AC copper losses due to the windings. These heat losses, such as eddy current losses and AC copper losses, contribute to motor heat generation and, of course, lead to a decrease in motor efficiency. Therefore, it is desirable to minimize heat losses caused by eddy current losses and AC copper losses as much as possible.

[0010] Therefore, the present invention aims to provide a cooling pipe for cooling windings located inside the motor, while reducing eddy current losses in the cooling pipe and thereby reducing the overall loss of the motor, as well as a motor having a cooling pipe. [Means for solving the problem]

[0011] The cooling pipe according to the present invention is a cooling pipe provided inside a motor having a stator on which windings formed by winding conductive wires around a plurality of teeth are provided, and a rotor on which permanent magnets are arranged facing the stator, and comprises a pipe through which a cooling medium flows and a soft magnetic material arranged on the outer surface of the pipe, and is arranged in a slot provided in the stator. A motor having a cooling pipe according to the present invention comprises a stator having windings formed by winding conductors around a plurality of teeth, a rotor having permanent magnets arranged opposite to the stator, a cooling pipe arranged in a slot provided in the stator and through which a cooling medium flows, and a soft magnetic material arranged on the outer surface of the pipe. [Brief explanation of the drawing]

[0012] [Figure 1] Cross-sectional view of a motor with copper cooling pipes installed inside. [Figure 2] Detailed view of section A in Figure 1 [Figure 3] Motor Loss Comparison Graph [Figure 4] Magnetic flux density contour diagram of section A in Figure 1 [Figure 5] Joule loss density contour diagram of section A in Figure 1 [Figure 6] Cross-sectional view of the cooling pipe 20 according to the first embodiment. [Figure 7] Magnetic properties of the magnetic composite material Sendust 69 (vol. / %) [Figure 8] Joule loss density contour diagram of the cooling pipe 20 according to the first embodiment [Figure 9] Cross-sectional view of the cooling pipe 30 according to the second embodiment. [Figure 10] Joule loss density contour diagram of the cooling pipe 30 according to the second embodiment [Figure 11] Cross-sectional view of the cooling pipe 40 according to the third embodiment. [Figure 12] Joule loss density contour diagram of the cooling pipe 40 according to the third embodiment [Modes for carrying out the invention]

[0013] (First Embodiment) Hereinafter, the cooling pipe according to the first embodiment will be described in detail with reference to the drawings. First, FIG. 1 shows a cross-sectional view of a motor in the prior art in which a copper cooling pipe is provided inside the motor to cool the winding in the motor. The motor 1 in FIG. 1 includes a stator 2 made of electromagnetic steel sheets which is a stator, a plurality of teeth 3 provided on the stator 2, a winding 4 formed by winding a conductor around each tooth 3, a slot 10 which is a groove provided on the stator 2, a rotor 11, and a permanent magnet 12 provided inside the rotor 11 and arranged to face the stator 2.

[0014] The stator 2 which is a stator is installed on the outer peripheral portion of the motor 1. In the prior art, it is made of electromagnetic steel sheets. Electromagnetic steel sheets are materials in which iron and trace amounts of alloy elements (such as silicon) are combined to improve magnetic properties, and are coated with a coating called an insulating film. They are inexpensive steel materials and are the most widely used as stator materials.

[0015] The teeth 3 serve as a so-called iron core around which the conductors constituting the winding 4 are wound. A plurality of teeth 3 are formed, for example, at equal intervals in the circumferential direction on the inner peripheral surface side of the stator 2. The teeth 3 form a slot 10 which is a groove provided on the stator 2 described later.

[0016] The winding 4 is formed by winding a conductor multiple times with the teeth 3 as the iron core. In the prior art, the material of the conductor is a flat copper wire with a rectangular cross-section, but a copper wire with a circular cross-section may also be used. The material of the winding 4 is not limited to copper and may be other materials such as enameled wire or aluminum wire.

[0017] As described above, slot 10 is a groove provided in the stator 2, and is a groove-shaped space formed between adjacent teeth 3. When the number of slots 10 increases, that is, when the number of teeth 3 which are the iron core increases, the number of windings 4 increases accordingly, and such a motor can generally obtain high torque. In the prior art, the number of slots 10 is 12, but this is just an example, and other numbers of slots are also acceptable.

[0018] The rotor 11 is the rotating part of the motor, located in the center of the motor. For example, the rotor 11 is connected to a shaft (not shown), which is the axis of rotation, and the shaft is rotatably supported by bearings, thereby allowing it to rotate freely within the stator 2. In the prior art, the rotor 11 is made of electrical steel sheet, similar to the stator 2. The rotor 11 rotates due to the repulsion between the permanent magnets 12 located inside the rotor 11 and the magnetic field generated by the current flowing through the windings 4 of the stator 2.

[0019] Multiple permanent magnets 12 are provided inside the rotor 11. In the prior art, adjacent permanent magnets 12 are magnetized so that their N and S poles alternate, as shown in Figure 1. Alternatively, the permanent magnets 12 may be magnetized so that their magnetic flux has a sinusoidal distribution.

[0020] Next, the configuration within slot 10 will be explained using Figure 2, which is a detailed view of section A in Figure 1. As shown in Figure 2, a tooth edge 5 is provided at the tip of the tooth 3. A copper pipe 7 is provided in the gap 6, which is the space formed between the tooth edge 5 and the winding 4. In addition, a winding-side copper pipe 9 is provided in the winding gap 8, which is the space formed by adjacent windings 4.

[0021] The tooth edge 5 is a flange that protrudes from the rotor-side end of the tooth 3 to reduce the opening area of ​​the slot 10. By providing the tooth edge 5, the opening area of ​​the slot 10 is reduced, and the eddy current loss due to the permanent magnet 12 is reduced.

[0022] The copper pipe 7 and the winding-side copper pipe 9 are made of copper. The copper pipe 7 is placed in the gap between the winding 4 and the teeth edge 5 to cool the winding 4, and is a pipe through which a cooling medium flows. The cooling medium is, for example, cooling water. Since a material with good thermal conductivity is desirable for the pipe material, copper is used in conventional technology. However, the material of the pipe is not limited to copper; it may be made of other materials such as iron, stainless steel, or resin. In addition, the cross-sectional shape of the copper pipe 7 in conventional technology is rhomboid, and the cross-sectional shape of the winding-side copper pipe 9 is triangular, but the cross-sectional shape is not limited to these. Any cross-sectional shape that fits within the gap 6 is acceptable, such as an ellipse or rectangle. Furthermore, multiple pipes may be integrated into a single pipe, for example, by overlapping two pipes with a triangular cross-sectional shape to form a rhomboid.

[0023] Here, we compare the loss analysis results for each part when driving the conventional motor 1 described above with the loss analysis results for each part when driving a motor without cooling piping (copper pipe 7 and winding-side copper pipe 9). By comparing these, we will explain the loss increase due to the cooling piping. First, the motor specifications used in the analysis are shown in Table 1, and the analysis conditions are shown in Table 2.

[0024] [Table 1] [Table 2]

[0025] Table 3 shows the analysis results under the conditions described above, and Figure 3 shows a graph comparing the losses of each part of the motor. [Table 3]

[0026] Table 3 and Figure 3 show that the overall motor loss is greater when copper pipe 7 and winding-side copper pipe 9 are installed. In other words, when copper pipe 7 and winding-side copper pipe 9 are placed in slot 10 to directly cool winding 4, the eddy current losses generated in these pipes increase the overall motor loss.

[0027] Furthermore, Figure 4 shows the magnetic flux density contour map of section A in Figure 1. Figure 4 shows that the magnetic flux that flows through the copper tube 7 flows directly into the winding 4. It can also be seen that the magnetic flux density around the teeth edge 5 is high, causing the magnetic flux to saturate and increasing the eddy current losses in the copper tube 7 and winding 4.

[0028] Furthermore, Figure 5 shows a Joule loss density contour map of section A in Figure 1. Figure 5 shows that the Joule loss occurring in the winding 4 is concentrated at one point on the tooth edge 5 side, and the Joule loss occurring in the copper pipe 7 is also concentrated at one point at the end of the copper pipe 7.

[0029] As explained above, in the conventional cooling method, eddy current losses generated in the copper pipe 7 and the winding-side copper pipe 9 increase the overall loss of the motor. The cooling piping according to the first embodiment, which prevents this increase in loss, will be described below.

[0030] Figure 6 shows a cross-sectional view of the cooling pipe 20 according to the first embodiment. As shown in Figure 6, the cooling pipe 20 according to this embodiment is constructed by placing a soft magnetic material 21 on the outer surface of the copper pipe 7. The soft magnetic material 21 is placed in close contact only with the outer surface of the copper pipe 7 on the tooth edge 5 side, and is in contact with the teeth 3 and tooth edge 5 that form the slot 10. This is because it is expected that the magnetic flux generated from the permanent magnet 12 will be guided towards the stator 2 side so as to bypass the copper pipe 7, thereby preventing an increase in magnetic flux density at one end of the winding 4 or copper pipe 7, as in the example in Figure 1 where the soft magnetic material 21 is not placed.

[0031] In this embodiment, the thickness of the soft magnetic material 21 is 0.5 mm, but this thickness is not limited to this. A thickness of approximately 0.2 mm to 0.7 mm is desirable, as long as both the copper pipe 7 and the soft magnetic material 21 fit within the gap 6. Furthermore, in this embodiment, the circumferential width of the soft magnetic material 21 is such that it is in contact with the teeth 3, but this is not limited to this, and it may be such that there is a gap between the soft magnetic material 21 and the teeth 3.

[0032] The soft magnetic material 21 may be, for example, an electrical steel sheet, ferrite (MnZn ferrite or NiZn ferrite), a nanocrystalline plate, or a magnetic composite material. In terms of relative permeability, electrical steel sheets and ferrite are suitable as materials for the soft magnetic material 21, but magnetic composite materials are superior in terms of high resistivity, low eddy current loss, high thermal conductivity, and ease of molding. In this embodiment, the soft magnetic material 21 is made of the magnetic composite material Sendust 69 (vol. / %). The magnetic composite material is made by mixing, stirring, and casting spherical magnetic powder with a resin such as acrylic, fluororesin, or rubber and a diluent, and then heat-curing it. The magnetic composite material Sendust 69 (vol. / %) uses Sendust as the magnetic powder and mixes this magnetic powder in a ratio of 69 (vol. / %).

[0033] Here, the magnetic properties of the magnetic composite material Sendust 69 (vol. / %) are shown in Figure 7. The magnetic composite material Sendust 69 (vol. / %) has the relative permeability characteristics shown in Figure 7, which is relatively lower than that of electrical steel sheet. The relative permeability of the magnetic composite material Sendust 69 (vol. / %) in Figure 7 is approximately 20, but any soft magnetic material with a relative permeability of 5 to 200 may be used.

[0034] Furthermore, while this embodiment employs the magnetic composite material Sendust 69 (vol. / %), other magnetic powders such as Fe-based amorphous material, pure iron, Fe-Si, and nanocrystals can also be used.

[0035] Next, we will explain the loss analysis results for each part of the motor 1 when using the cooling pipe 20 according to this embodiment. Table 4 shows the breakdown of losses for each part of the motor 1, and Figure 8 shows the Joule loss density contour map of the cooling pipe 20 according to the first embodiment.

[0036] [Table 4]

[0037] According to the results in Table 4, compared to the case without the soft magnetic material 21, Sendust 69 (vol. / %), the eddy current loss in the copper pipe 7 was reduced from 1509.3 (W) to 1273.6 (W). In the case of the copper pipe 7, the loss was improved by 235.7 (W), and a loss reduction rate of approximately 16% was confirmed.

[0038] Figure 8 also clearly shows that the Joule loss in the copper tube 7 is significantly reduced, confirming that the magnetic flux is controlled by the soft magnetic material 21, and the influence of the magnetic flux on the copper tube 7 is reduced.

[0039] The AC copper loss in winding 4 increased from 329.4(W) to 364.8(W), a difference of 35.4(W). However, there was no significant difference in other losses. Overall losses were reduced from 4507.3(W) to 4253.4(W), representing an improvement of 253.9(W) in losses, and a loss reduction rate of approximately 6% was confirmed.

[0040] As described above, when the soft magnetic material 21 is placed in close contact only with the outer surface of the copper pipe 7 on the tooth edge 5 side, the magnetic flux from the permanent magnet 12 is controlled by the soft magnetic material 21, reducing the eddy current loss in the copper pipe 7 and improving the overall loss.

[0041] (Second embodiment) The cooling pipe 30 according to the second embodiment will now be described in detail with reference to the drawings. A cross-sectional view of the cooling pipe 30 according to the second embodiment is shown in Figure 9.

[0042] The cooling pipe 30 according to the second embodiment is the cooling pipe 20 according to the first embodiment with a non-magnetic insulator 31 added. Since the other components are the same as in the first embodiment, the same reference numerals are used for the same components, and parts that overlap in description are omitted.

[0043] In the cooling piping 30 according to the second embodiment, as shown in Figure 9, a non-magnetic insulator 31 is provided between the copper pipe 7 and the soft magnetic material 21. This is to increase the distance between the soft magnetic material 21 and the copper pipe 7, preventing magnetic flux from linking between the copper pipe 7 and the end of the winding 4, thereby reducing eddy current losses in the copper pipe 7 and AC copper losses in the winding 4.

[0044] In this embodiment, the thickness of the soft magnetic material 21 is reduced to 0.3 mm compared to the first embodiment by the thickness of the non-magnetic insulator 31. However, the thickness of the soft magnetic material 21 is not limited to this, nor is the thickness of the non-magnetic insulator 31.

[0045] Furthermore, although the non-magnetic insulator 31 in this embodiment is an air layer, it is not limited to an air layer; any material with excellent heat resistance and high thermal conductivity, such as silicone tape, high thermal conductivity plastic, or silica, may be used.

[0046] Next, we will explain the loss analysis results for each part of the motor 1 when using the cooling pipe 30 according to this embodiment.

[0047] Table 5 shows the breakdown of losses in each part of the motor 1, and Figure 10 shows the Joule loss density contour diagram of the cooling pipe 30 according to the second embodiment.

[0048] [Table 5]

[0049] According to the results in Table 5, compared to the first embodiment, a further reduction of 26.2 W was confirmed in the eddy current loss of the copper tube 7, from 1273.6 W to 1247.4 W.

[0050] Furthermore, a reduction of 20.2W was confirmed in the AC copper loss of winding 4, from 364.8(W) to 344.6(W). This confirms that the AC copper loss of winding 4, which did not show any reduction effect in the first embodiment, is improved in the second embodiment.

[0051] Compared to the first embodiment, there were no significant differences in other losses, and the overall loss was further reduced from 4253.4(W) to 4217.2(W), resulting in an overall loss improvement of 36.2(W). Of course, this represents a significant loss improvement compared to the case without the soft magnetic material 21.

[0052] (Third embodiment) The cooling pipe 40 according to the third embodiment will now be described in detail with reference to the drawings. A cross-sectional view of the cooling pipe 40 according to the third embodiment is shown in Figure 11.

[0053] In the third embodiment, the cooling pipe 40 is provided with a soft magnetic material 41 that has a narrower circumferential width than the soft magnetic material 21 in the second embodiment. Since the other components are the same as in the second embodiment, the same reference numerals are used for the same components, and parts that overlap in description are omitted.

[0054] In the third embodiment, the cooling pipe 40 has a shape in which the circumferential width of the soft magnetic material 41 is narrower than the circumferential width of the copper pipe 7, as shown in Figure 11. Both ends of the soft magnetic material 41 in the circumferential direction have a gap between them and the teeth 3 that form the slot 10 in which the cooling pipe 40 is arranged.

[0055] This is to prevent magnetic flux from linking at the end of winding 4, and aims to reduce AC copper loss in winding 4 compared to the second embodiment.

[0056] In this embodiment, the circumferential width of the soft magnetic material 41 is not specified as the width shown in Figure 11, but should be narrower than the circumferential width of the copper pipe 7. The width may be 50-90% of the circumferential width of the copper pipe 7, but it is preferable that the circumferential width of the soft magnetic material 41 be wider than the opening of the slot 10.

[0057] Next, we will explain the loss analysis results for each part of the motor 1 when using the cooling pipe 40 according to this embodiment.

[0058] Table 6 shows the breakdown of losses in each part of the motor 1, and Figure 12 shows the Joule loss density contour diagram of the cooling pipe 40 according to the third embodiment.

[0059] [Table 6]

[0060] According to the results in Table 6, compared to the second embodiment, an increase of 35.7 W was observed in the eddy current loss of the copper tube 7, from 1247.4 W to 1283.1 W.

[0061] On the other hand, the AC copper loss of winding 4 was reduced from 344.6(W) to 326.9(W), a reduction of 17.7(W), which was confirmed to be an improvement over the AC copper loss of winding 4 in the second embodiment.

[0062] Compared to the second embodiment, there was no significant difference in other losses, and although the overall loss increased from 4217.2(W) to 4250.4(W), it can be seen that the overall loss reduction effect was greater than that of the first embodiment. Of course, a significant improvement in losses is observed compared to the case without the soft magnetic material 21.

[0063] According to any of the embodiments described above, it is possible to provide a cooling pipe and a motor having a cooling pipe that reduces eddy current losses in the copper pipe 7 and the winding-side copper pipe 9, thereby reducing the overall loss of the motor 1, even while having the copper pipe 7 and the winding-side copper pipe 9, which are cooling pipes for cooling the winding 4, inside the motor 1.

[0064] In other words, preferably, losses are reduced by providing the soft magnetic material 21 only on the outer surface of the cooling pipe (copper pipe 7) on the teeth side. It has also been confirmed that sufficient effect cannot be obtained when the soft magnetic material 21 is provided on the entire outer surface of the copper pipe 7. Thus, the fact that losses can be reduced by not providing the soft magnetic material 21 on the cooling pipe (winding-side copper pipe 9) on the winding side, rather than on the entire outer surface of the copper pipe 7, has advantages such as being able to achieve the effect with minimal space in the limited space inside the motor 1 and reducing material costs.

[0065] As a variation, it is desirable to provide cooling pipes 20, 30, and 40 in all slots 10, but the configuration is not limited to providing them in all slots 10. For example, they may be provided in every other slot.

[0066] Although several embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0067] 1...Motor, 2...Stator, 3...Teeth, 4...Winding, 5...Teeth edge, 6...Gap, 7...Copper tube, 8...Winding gap, 9...Winding-side copper tube, 10...Slot, 11...Rotor, 12...Permanent magnet, 20...Cooling pipe according to the first embodiment, 21...Soft magnetic material, 30...Cooling pipe according to the second embodiment, 31...Non-magnetic insulator, 40...Cooling pipe according to the third embodiment, 41...Soft magnetic material

Claims

1. A cooling pipe provided inside a motor having a stator with windings formed by winding conductors around multiple teeth, and a rotor with permanent magnets arranged opposite the stator, It comprises a pipe through which a cooling medium flows, and a soft magnetic material placed on the outer surface of the pipe, and is positioned in a slot provided in the stator, Cooling pipes.

2. The teeth are provided with a tooth edge that protrudes from the rotor-side end to reduce the area of ​​the slot opening, Displaced in the gap between the winding and the tooth edge provided within the slot, Cooling piping according to claim 1.

3. The soft magnetic material is arranged only on the outer surface of the tooth edge side of the piping. Cooling piping according to claim 2.

4. A non-magnetic insulator is provided between the soft magnetic material and the outer surface of the tooth edge side of the piping. Cooling pipe according to claim 3.

5. The circumferential width of the soft magnetic material is narrower than the circumferential width of the pipe. Cooling piping according to claim 3 or claim 4.

6. The soft magnetic material is a magnetic composite material. Cooling piping according to any one of claims 1 to 4.

7. A stator is provided with windings formed by winding conductors around multiple teeth, A rotor having permanent magnets arranged opposite to the stator, A cooling pipe comprising a pipe arranged in a slot provided in the stator and through which a cooling medium flows, and a soft magnetic material arranged on the outer surface of the pipe, A motor having cooling piping equipped with a motor.

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