Laminated core and method for manufacturing the same

Abstract

To suppress an increase in iron loss of a laminated core due to caulking.SOLUTION: In the present invention, in a laminated core (1) formed by caulking a plurality of laminated electromagnetic steel plates and a method for manufacturing the laminated core (1), a compressive stress in a direction in which a magnetic flux flows does not remain on a path around a caulked portion through which the magnetic flux flows during magnetization. Further, a tensile stress in a direction in which a magnetic flux flows remains on a path through which the magnetic flux flows during magnetization around the caulked portion. Further, a long side of a dowel (6) for caulking the electromagnetic steel plate is formed orthogonal to a direction in which a magnetic flux flows during magnetization.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated core formed by crimping a plurality of laminated electromagnetic steel sheets, and a method for manufacturing the laminated core. [Background technology]

[0002] BACKGROUND ART Conventionally, iron core parts such as motor cores used in electromagnetic devices such as motors are manufactured by crimping a plurality of laminated electromagnetic steel sheets in order to reduce iron loss.

[0003] This iron core part (laminated core) made of multiple stacked electromagnetic steel plates has dowels formed on each electromagnetic steel plate and the dowels formed on the stacked electromagnetic steel plates are crimped together so that they fit together vertically to form an integrated laminated core (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-192417 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-mentioned conventional laminated core, by forming dowels in each electromagnetic steel sheet during manufacturing and by crimping the dowels of multiple electromagnetic steel sheets together, there is a risk that compressive stress will remain inside the laminated core after manufacturing.

[0006] In a laminated core made of multiple stacked electromagnetic steel sheets, the electromagnetic steel sheets are very sensitive to stress, so if compressive stress remains inside, there is a risk that the iron loss of the laminated core will increase. [Means for solving the problem]

[0007] Therefore, in the present invention according to claim 1, in a laminated core formed by crimping multiple stacked electromagnetic steel sheets, no compressive stress remains in the direction of magnetic flux flow around the crimped portion and on the path along which magnetic flux flows during magnetization.

[0008] Furthermore, in the present invention according to claim 2, in the present invention according to claim 1, tensile stress remains in the direction of magnetic flux flow around the crimped portion and on the path along which magnetic flux flows during magnetization.

[0009] Furthermore, in the present invention according to claim 3, in the present invention according to claim 1 or claim 2, the long side of the dowel for clamping the electromagnetic steel sheet is formed perpendicular to the direction in which magnetic flux flows during magnetization.

[0010] Furthermore, in the present invention according to claim 4, in a method for manufacturing a laminated core in which a laminated core is manufactured by crimping a plurality of stacked electromagnetic steel sheets, the electromagnetic steel sheets are crimped so that compressive stress in the direction of magnetic flux flow does not remain around the crimped portion and on the path through which magnetic flux flows during magnetization.

[0011] Furthermore, in the present invention according to claim 5, in the present invention according to claim 4, the electromagnetic steel sheet is crimped so that tensile stress in the direction of magnetic flux flow remains around the crimped portion and on the path along which magnetic flux flows during magnetization. [Effects of the Invention]

[0012] The present invention provides the following effects.

[0013] That is, in the present invention, in a laminated core formed by crimping multiple stacked electromagnetic steel sheets and in a manufacturing method thereof, no compressive stress remains in the direction of magnetic flux flow around the crimped portion and on the path along which magnetic flux flows during magnetization. Therefore, it is possible to suppress an increase in iron loss in the laminated core without having to perform heat treatment such as strain relief annealing to remove stress that occurs when processing the electromagnetic steel sheets into core layers of a predetermined shape, when forming dowels in the core layers of the electromagnetic steel sheets, or when stacking and crimping multiple electromagnetic steel sheets.

[0014] In particular, if tensile stress in the direction of magnetic flux flow remains around the crimped portion on the path along which magnetic flux flows during magnetization, the iron loss of the laminated core can be reduced.

[0015] Furthermore, if the long sides of the dowels used to clamp the electromagnetic steel sheets are formed perpendicular to the direction in which magnetic flux flows during magnetization, it is possible to prevent compressive stress in the direction in which magnetic flux flows from remaining around the crimped portion on the path along which magnetic flux flows during magnetization, thereby suppressing an increase in iron loss in the laminated core. [Brief explanation of the drawings]

[0016] [Figure 1] 1A is a plan view illustrating a laminated core according to the present invention, and FIG. 1B is a front view illustrating the same. [Figure 2] FIG. [Figure 3] FIG. 2 is an explanatory diagram showing the magnetic properties (relationship between magnetic flux density and iron loss) of an electromagnetic steel sheet. [Figure 4] FIG. 10 is an explanatory diagram schematically showing the analysis results. [Figure 5] FIG. [Figure 6] FIG. 4 is an explanatory diagram showing the relationship between the rate of change of iron loss and magnetic flux density. [Figure 7] An explanatory diagram showing the analysis results (stress). [Figure 8] FIG. 10 is an explanatory diagram showing the analysis results (magnetic flux density, magnetic flux lines). [Figure 9] FIG. 10 is an explanatory diagram showing the analysis results (iron loss change rate). DETAILED DESCRIPTION OF THE INVENTION

[0017] The specific configuration of the laminated core and the manufacturing method of the laminated core according to the present invention will be described below with reference to the drawings. In the following description, the laminated core will be described as a motor core (stator core) around which a coil is wound, but the present invention can also be applied to an iron core part integrally formed by stacking and crimping a plurality of electromagnetic steel sheets.

[0018] As shown in Fig. 1, the laminated core 1 has teeth 3 that protrude radially inward and are formed at equal intervals in the circumferential direction on the inner periphery of the annular back yoke 2. In this example, the laminated core 1 is divided into a plurality of split cores 4.

[0019] As shown in Figure 2, this laminated core 1 is magnetized when current is passed through the wound coil during use, and magnetic flux flows from the teeth 3 of the split core 4 through the back yoke 2 to the teeth 3 of the circumferentially adjacent split core 4 (schematically shown by dotted arrows in Figure 2).

[0020] Each split core 4 is formed by processing a thin electromagnetic steel sheet into a predetermined shape to form one core layer 5, forming a dowel 6 that is rectangular in plan view at a predetermined position on the core layer 5, and then stacking multiple core layers 5 one above the other with the upper and lower dowels 6 aligned, and pressing the stacked multiple core layers 5 vertically to crimp the upper and lower dowels 6 into one another, thereby integrally forming the split core 4. Note that the crimping may involve crimping dowels 6 of the same shape (here, rectangular) into one another, or may involve crimping dowels 6 of different shapes (for example, a round dowel and a round hole) into one another.

[0021] In this way, during manufacturing of the laminated core 1, compressive stress remains when the electromagnetic steel sheets are processed into the core layer 5 of a predetermined shape, when dowels 6 are formed in the core layer 5 of the electromagnetic steel sheets, and when multiple electromagnetic steel sheets are stacked and crimped.

[0022] As shown in Figure 3, the magnetic properties of this electrical steel sheet are sensitive to internal stress, and the magnetic properties, which show the relationship between magnetic flux density and iron loss, show that the iron loss (indicated by an x ​​mark in Figure 3) is larger when there is compressive stress (-60 MPa in this case) than when there is no stress (indicated by a △ mark in Figure 3), and conversely, the iron loss (indicated by a ◯ mark in Figure 3) is smaller when there is tensile stress (+60 MPa in this case).

[0023] Therefore, in the laminated core 1 made by laminating and crimping multiple electromagnetic steel sheets, if compressive stress remains inside after manufacturing, iron loss increases. On the other hand, if tensile stress remains inside after manufacturing, iron loss can be reduced.

[0024] In particular, in the case of a laminated core 1 in which dowels 6 are formed on electromagnetic steel sheets and the dowels 6 are used for crimping, stress is thought to remain around the dowels 6.

[0025] Therefore, we analyzed the residual stress when multiple electromagnetic steel sheets with a certain width were crimped together using rectangular dowels 6 by changing the orientation of the dowels 6. Here, we performed the analysis with a force acting on a rectangular hole equivalent to the dowel 6 in a direction that widens the rectangular hole, which corresponds to a state where the sheets were crimped together using the dowels 6.

[0026] An example is shown in Figure 4. In Figure 4, we assume that analysis piece 7 is made by integrally crimping multiple electromagnetic steel sheets, each with a fixed width in the left-right direction, together using a rectangular dowel 6, and that magnetic flux flows in the front-to-back direction (vertical direction in Figure 4) on both the left and right sides of dowel 6 during magnetization. Since this magnetic flux is thought to be strongly affected by stress in the same direction as the magnetic flux flow (vertical direction in Figure 4), we analyzed the residual stress in the same direction as the magnetic flux flow. In Figures 4 to 6, the state in which a dowel 6 is formed on an analysis piece 7 having a certain width so that its short side faces the width direction and its long side faces the magnetic flux direction (the angle between the extension direction of the long side of the dowel 6 and the magnetic flux direction is 0°) is referred to as a "rectangular hole 0°", and the state in which a dowel 6 is formed on an analysis piece 7 having a certain width so that its long side faces the width direction (orients perpendicular to the magnetic flux direction) and its short side faces the magnetic flux direction (the angle between the extension direction of the long side of the dowel 6 and the magnetic flux direction is 90°) is referred to as a "rectangular hole 90°".

[0027] As shown in Figure 4(a), when a dowel 6 was formed on an analysis piece 7 having a certain width so that the short side of the dowel 6 faced the width direction and the long side of the dowel 6 faced the magnetic flux direction, it was found that areas where compressive stress 8,8 remained were formed on the left and right sides of the long side of the dowel 6.

[0028] In this way, in the analysis piece 7 which has a constant width on the left and right and extends front and back, compressive stresses 8,8 remain in the same direction as the magnetic flux flow around the dowel 6 which extends front and back (around the crimped portion) between the end of the analysis piece 7 and the dowel 6, i.e., on the path along which the magnetic flux flows during magnetization.

[0029] Therefore, in this case, magnetic flux flows in the region where the compressive stresses 8, 8 remain, and the iron loss of the analysis piece 7 increases.

[0030] On the other hand, as shown in Figure 4(b), when a dowel 6 was formed on an analysis piece 7 having a certain width so that the long side of the dowel 6 was oriented in the width direction (orthogonal to the magnetic flux direction) and the short side of the dowel 6 was oriented in the magnetic flux direction, it was found that an area in which compressive stress 9,9 remained was formed in front of and behind the long side of the dowel 6 (top and bottom in Figure 4).

[0031] Moreover, in this case, it was found that regions in which tensile stresses 10, 10 remain are formed on the left and right sides of the short sides of the dowel 6, as shown in FIG. 4(c).

[0032] In this way, in the analysis piece 7 which has a constant width on the left and right and extends back and forth, around the dowel 6 which extends left and right (around the crimped portion), between the end of the analysis piece 7 and the dowel 6, i.e., on the path along which the magnetic flux flows during magnetization, only tensile stresses 10,10 remain in the same direction as the magnetic flux flow, and no compressive stresses 9,9 remain.

[0033] Therefore, in this case, magnetic flux flows in the area where tensile stress 10, 10 remains, and since there is no area where compressive stress 9, 9 remains on the path along which magnetic flux flows during magnetization, iron loss in the analysis piece 7 is reduced.

[0034] From the above, it can be seen that the stress state inside the laminated core 1 after manufacture can be changed by controlling conditions such as the form (shape, size, etc.) of the core layer 5 made of electromagnetic steel sheets, the position and form (shape, size, etc.) of the dowels 6, and the pressing force used during processing and crimping, and therefore the magnetic properties of the laminated core 1 can be changed.

[0035] In the laminated core 1, the state of stress remaining inside after manufacturing varies depending on conditions such as the form (shape, size, etc.) of the core layer 5 made of electromagnetic steel plate, the position and form (shape, size, etc.) of the dowel 6, and the pressing force used during processing and crimping.Therefore, it is preferable to perform analysis based on these conditions and manufacture the laminated core 1 under conditions where no compressive stress remains on the path along which the magnetic flux flows during magnetization.Furthermore, it is even more preferable to find conditions under which tensile stress remains on the path along which the magnetic flux flows during magnetization and manufacture the laminated core 1 under those conditions.

[0036] In this way, in the method of manufacturing the laminated core 1 in which the laminated core 1 is manufactured by crimping a plurality of stacked electromagnetic steel sheets, it is preferable to manufacture the laminated core 1 by crimping the electromagnetic steel sheets so that no compressive stress in the direction of magnetic flux flow remains around the crimped portion and on the path along which the magnetic flux flows during magnetization, and it is even more preferable to manufacture the laminated core 1 by crimping the electromagnetic steel sheets so that tensile stress in the direction of magnetic flux flow remains around the crimped portion and on the path along which the magnetic flux flows during magnetization.

[0037] To verify the above analysis results, we measured the residual stress when an electrical steel sheet (test piece 7') with the same fixed width as the analysis piece 7 was crimped using a rectangular dowel 6, changing the orientation of the dowel 6. The results are shown in Figure 5. As shown in Figures 5(a) and 5(b), a copper chip was fitted into a rectangular hole equivalent to the dowel 6 to simulate a crimped condition, and the residual stress was measured for each section within the shaded area around the rectangular hole (dowel 6). The residual stress for each section is indicated by + for tensile stress and - for compressive stress.

[0038] The actual measurement results are shown in Figures 5(c) to 5(f). Figure 5(c) shows the measurement results for the 0° rectangular hole before the chip was inserted (without crimping), and Figure 5(d) shows the measurement results for the 0° rectangular hole after the chip was inserted (with crimping). Figure 5(e) shows the measurement results for the 90° rectangular hole before the chip was inserted (without crimping), and Figure 5(f) shows the measurement results for the 90° rectangular hole after the chip was inserted (with crimping).

[0039] For the rectangular hole of 0°, as can be seen by comparing Figures 5(c) and 5(d), the compressive stress increases in the area diagonally rearward from the corner of the dowel 6 due to the crimping (the area shown in gray in Figure 5(d)), which is consistent with the analysis results shown in Figure 4(a).

[0040] For the 90° rectangular hole, as can be seen by comparing Figure 5(e) and Figure 5(f), the compressive stress is reduced by crimping, and in particular in the lateral region of the dowel 6 (the region shown in gray in Figure 5(f)), the compressive stress is reduced and turns into tensile stress, which is the same as the analysis results shown in Figure 4(c).

[0041] Furthermore, a single sheet magnetic test was performed on the electromagnetic steel sheet (test piece 7') that had been measured above to measure its magnetic properties. Here, the magnetic properties were also measured for test piece 7' that did not have dowels 6 formed, and this was compared with the other test pieces 7' to calculate the rate of change in iron loss when dowels 6 were present compared to when no dowels 6 were present, and the relationship between the rate of change in magnetic flux density and iron loss was determined. The results are shown in Figure 6.

[0042] Before the chip is fitted into the dowel 6 (without crimping), as can be seen from the case of the rectangular hole 0° without crimping shown by the thin dotted line in Figure 6 and the case of the rectangular hole 90° without crimping shown by the thick dotted line, the test piece 7' with the rectangular hole 90°, which has a larger surface area blocking the magnetic flux, has higher iron loss.

[0043] Then, after the chip is fitted into the dowel 6 (with crimping), as can be seen from the case of the rectangular hole 0° without crimping shown by the thin dotted line in Fig. 6 and the case of the rectangular hole 0° with crimping shown by the thin solid line, iron loss increases in the rectangular hole 0° due to crimping, whereas as can be seen from the case of the rectangular hole 90° without crimping shown by the thick dotted line in Fig. 6 and the rectangular hole 90° with crimping shown by the thick solid line in Fig. 6, iron loss decreases in the rectangular hole 90° due to crimping at magnetic flux densities of 1 T or less. Moreover, as can be seen from the case of the rectangular hole 0° with crimping shown by the thin solid line in Fig. 6 and the rectangular hole 90° with crimping shown by the thick solid line, iron loss is lower in the rectangular hole 90° than in the rectangular hole 0° at magnetic flux densities of 1 T or less.

[0044] In this way, it was found that in the case of a 90° rectangular hole, by fitting the chip into the dowel 6 and creating a crimped state, the compressive stress on the path of the magnetic flux around the dowel 6 is reduced and even converted into tensile stress, thereby improving the magnetic properties.

[0045] Furthermore, a magnetic field analysis of iron loss was performed on a laminated core 1 (motor core) as shown in Figures 1 and 2. The motor model used here had a stator with an outer diameter of 112 mm and an inner diameter of 56 mm, a rotor with an outer diameter of 55 mm and an inner diameter (shaft diameter) of 16 mm, and a thickness of 60 mm. A 1 x 2.5 mm rectangular hole was formed in the stator between the teeth of the motor core, with the long side of the rectangular hole aligned circumferentially (rectangular hole 0°) or radially (rectangular hole 90°). The rectangular hole was set to be subjected to a fitting stress of 0 to 50 MPa (stress that expands the long side of the rectangular hole). Furthermore, assuming that the motor core would be shrink-fitted into the motor case, the analysis was performed with and without shrink fitting. Regarding shrink fitting, a uniform stress of 10 MPa was applied to the outer periphery of the motor core from the periphery toward the center. The following analysis results are shown for a quarter of the motor core.

[0046] When the fitting stress is 30 MPa, the analysis results of the stress distribution are shown in Fig. 7, and the analysis results of the magnetic flux lines and magnetic flux density are shown in Fig. 8.

[0047] As shown in Figure 7, without shrink fitting, stress caused by fitting generates tensile stress around the short sides of the rectangular hole. With shrink fitting, the compressive stress between the teeth caused by shrink fitting is alleviated by the tensile stress around the short sides of the rectangular hole at a 90° angle. The area where this compressive stress is alleviated is an area with high magnetic flux density, so a reduction in iron loss can be expected.

[0048] Furthermore, as shown in FIG. 8, there is a difference in magnetic flux density between the rectangular hole and the coil end between the rectangular hole 0° and the rectangular hole 90°.

[0049] Therefore, the magnetic properties were investigated for rectangular holes of 0° and 90°, with and without shrink fitting. Here, the rate of change in iron loss from the case without a rectangular hole was determined. For the fitting stress, the average iron loss across the entire range of 0 to 50 MPa was used. The results are shown in Figure 9.

[0050] As shown in Fig. 9, without shrink fitting, iron loss increases slightly for a rectangular hole of 0° compared to when there is no rectangular hole, but iron loss decreases for a rectangular hole of 90°. When shrink fitting is used, the effect of shrink fitting is more pronounced, with iron loss increasing for both a rectangular hole of 0° and a rectangular hole of 90° compared to when there is no rectangular hole, but the rate of increase is smaller for a rectangular hole of 90°. This is thought to be due to the stress state that acts on the magnetic flux path due to the fit. This suggests that it is possible to control iron loss in a motor core by using fit stress.

[0051] As described above, it is preferable that the laminated core 1 formed by crimping multiple stacked electromagnetic steel sheets is configured so that no compressive stress in the direction of magnetic flux flow remains around the crimped portion and on the path along which magnetic flux flows during magnetization.

[0052] As a result, in the laminated core 1 having the above configuration, the magnetic flux is no longer affected by compressive stress, and an increase in iron loss in the laminated core 1 can be suppressed without performing heat treatment such as strain relief annealing to remove stress that occurs when processing the electromagnetic steel sheet into a core layer 5 of a predetermined shape, when forming dowels 6 in the core layer 5 of the electromagnetic steel sheet, or when stacking and crimping multiple electromagnetic steel sheets.

[0053] Furthermore, it is more preferable that the laminated core 1 be configured so that tensile stress remains in the direction of magnetic flux flow around the crimped portion and on the path through which magnetic flux flows during magnetization.

[0054] As a result, in the laminated core 1 having the above configuration, the magnetic flux is affected by the tensile stress, and the iron loss of the laminated core 1 can be reduced.

[0055] Furthermore, when rectangular dowels 6 are formed in the laminated core 1 to fasten the electromagnetic steel sheets, it is preferable to form the long sides of the dowels 6 so that they are perpendicular to the direction in which magnetic flux flows during magnetization.

[0056] As a result, in the laminated core 1 having the above configuration, compressive stress in the direction of magnetic flux flow does not remain around the crimped portion on the path along which the magnetic flux flows during magnetization, so the magnetic flux is no longer affected by compressive stress, and an increase in iron loss in the laminated core 1 can be suppressed. [Explanation of symbols]

[0057] 1 Laminated core 2 Back yoke 3-tooth 4-split core 5 Core layer 6 Dowel 7 Analysis piece 8 Compressive stress 9 Compressive stress 10 Tensile stress

Claims

1. In a laminated core formed by crimping multiple laminated electromagnetic steel sheets, A laminated core characterized in that no compressive stress in the direction of magnetic flux flow remains around the crimped portion and on the path through which magnetic flux flows during magnetization.

2. 2. The laminated core according to claim 1, wherein tensile stress in the direction of magnetic flux flow remains around the crimped portion and on a path through which magnetic flux flows during magnetization.

3. 3. The laminated core according to claim 1, wherein the dowels for fastening the electromagnetic steel sheets are formed so that their long sides are perpendicular to the direction of magnetic flux flow during magnetization.

4. In a method for manufacturing a laminated core, a laminated core is manufactured by crimping a plurality of stacked electromagnetic steel sheets, A method for manufacturing a laminated core, characterized in that an electromagnetic steel sheet is crimped so that compressive stress in the direction of magnetic flux flow does not remain around the crimped portion and on the path along which magnetic flux flows during magnetization.

5. 5. The method for manufacturing a laminated core according to claim 4, wherein the electromagnetic steel sheets are crimped so that tensile stress in the direction of magnetic flux flow remains around the crimped portion and on a path through which magnetic flux flows during magnetization.

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