rotor

Abstract

To provide a technology related to rotor configuration to ensure magnetic force while suppressing leakage of magnetic flux.SOLUTION: A rotor includes a shaft having a rotating axis, a rotor core that covers the circumference of the shaft, and in which the cross section perpendicular to the rotation axis has a substantially polygonal shape having at least a first pair of parallel sides and a second pair of parallel sides perpendicular to the first pair of sides, a magnet having a plate shape and arranged on each of the outer surfaces of the first pair of sides and the second pair of sides, and a covering member that covers the rotor core and the magnet. When viewed in the cross section, the outer periphery of the rotor core in the range connecting adjacent magnets in the circumferential direction of the shaft is located within a closed area defined by the extension of the first pair of sides and the second pair of sides, and when the shortest distance between adjacent magnets in the circumferential direction of the shaft is Wa, and the width of the magnet along the outer surface is Wm, the relationship of Wm / Wa≤1.72 is satisfied.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a rotor. [Background technology]

[0002] Patent Document 1 discloses a rotor for use in an electric motor. The rotor includes a shaft, a rotor core that surrounds the shaft and has a substantially rectangular cross section, and four magnets that are arranged on the outer surface of the rotor core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-81776 Summary of the Invention [Problem to be solved by the invention]

[0004] When using a polygonal rotor core, a shorter distance between adjacent magnets in the circumferential direction of the shaft reduces magnetic flux leakage and improves motor performance. Meanwhile, the magnetic force of a magnet correlates with its volume; the larger the volume, the greater the magnetic force. Therefore, if the width of a magnet is increased to shorten the distance between adjacent magnets in the circumferential direction of the shaft, the thickness of the magnet must be reduced. Reducing the thickness of a magnet reduces its magnetic force due to self-demagnetization. Therefore, a rotor design that can ensure magnetic force while suppressing magnetic flux leakage is required. This specification provides technology related to a rotor configuration that ensures the magnetic force of magnets while suppressing magnetic flux leakage. [Means for solving the problem]

[0005] The rotor disclosed in this specification includes a shaft having a rotation axis, a rotor core surrounding the shaft and having a generally polygonal cross section perpendicular to the rotation axis, the cross section having at least a first pair of parallel sides and a second pair of parallel sides perpendicular to the first pair of sides, plate-shaped magnets arranged on the outer surfaces of the first pair of sides and the second pair of sides, and a covering member covering the rotor core and the magnets. When viewed in cross section, the outer peripheral edge of the rotor core in a range connecting adjacent magnets in the circumferential direction of the shaft is located within a closed area defined by extensions of the first pair of sides and the second pair of sides, and the relationship Wm / Wa≦1.72 is satisfied, where Wa is the shortest distance between adjacent magnets in the circumferential direction of the shaft and Wm is the width of the magnet along the outer surface.

[0006] In this specification, the term "substantially polygonal" is not limited to a shape in which the connecting portion of two sides forms a corner, but also includes a shape in which two sides are connected by a curved surface (i.e., a polygon with rounded corners). Furthermore, the term "polygonal" is not limited to a shape in which the connecting portion of two sides has a convex shape, but also includes a so-called concave polygon.

[0007] In a motor using a rotor with a rotor core, a phenomenon can occur in which magnetic flux from a magnet returns to itself without passing through other components (e.g., a stator). Such magnetic flux leaks without contributing to the operation of the motor. In the rotor described above, the outer periphery of the rotor core is located within a closed area defined by the extension lines of a first pair of sides and a second pair of sides in cross section. After extensive research, the inventors have found that the above-mentioned phenomenon can be suppressed by configuring the rotor core in this way. In other words, the above configuration reduces magnetic flux leakage.

[0008] On the other hand, in the above rotor, the ratio of the magnet width Wm to the shortest distance Wa between adjacent magnets is relatively small. In other words, the shortest distance Wa between the magnets is relatively large, making the structure prone to magnetic flux leakage. However, as described above, in the above rotor, the rotor core has a shape that makes it difficult for magnetic flux to leak. Therefore, this shape can compensate for the magnetic flux leakage caused by the small ratio of the width Wm to the shortest distance Wa. In other words, in the above rotor, an increase in magnetic flux leakage is suppressed overall.

[0009] Furthermore, in the rotor described above, the width Wm of the magnet is relatively small. In other words, the thickness of the magnet can be increased without changing the volume of the magnet compared to conventional rotors. This suppresses self-demagnetization and reduces the reduction in magnetic force. As described above, the rotor described above can ensure the magnetic force of the magnet while suppressing magnetic flux leakage.

[0010] When the thickness of the rotor core in the radial direction of the shaft in the range connecting adjacent magnets in the circumferential direction of the shaft is defined as h, the relationship h≧Wm / 2 may be satisfied. The rotor core functions as a magnetic path through which magnetic flux passes. If the rotor core is thin, the area of ​​the magnetic path becomes small, resulting in high magnetic resistance. As described above, by making the thickness h of the rotor core at least half the width Wm of the magnet, a sufficient magnetic path is ensured, and an increase in magnetic resistance can be suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a vertical cross-sectional view showing the schematic configuration of a fuel pump. [Figure 2] 2 is a cross-sectional view showing the rotor and the stator taken along line II-II in FIG. 1; [Figure 3] FIG. 3 is an exploded perspective view showing a configuration of a part of the rotor. [Figure 4] FIG. 3 is an enlarged cross-sectional view of a portion of FIG. 2. [Figure 5] 10A to 10C are diagrams showing various changes in the shape of the rotor core; [Figure 6]10 is a graph showing the no-load rotation speed of motors using rotor cores with various shapes. [Figure 7] 10A and 10B are diagrams showing various variations in the shape and arrangement of magnets in a rotor core having a predetermined shape. [Figure 8] 10 is a graph showing the rate of change in magnetic flux leakage when the shape of the rotor core is changed for a given magnet shape and arrangement. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Fuel pump configuration) 1, a fuel pump 10 will be described. The fuel pump 10 is disposed in a fuel tank mounted on a vehicle such as an automobile. The fuel pump 10 includes a motor unit 20 and a pump unit 40.

[0013] The pump section 40 is disposed at the lower end of the fuel pump 10. The pump section 40 includes a casing 42 and an impeller 46. The casing 42 includes a space that houses the impeller 46 and an intake port 44 that communicates with the space. The impeller 46 is housed in the space within the casing 42 so as to be able to rotate freely.

[0014] The motor section 20 is disposed above the pump section 40. The motor section 20 is a three-phase (U-phase, V-phase, W-phase) motor. The motor section 20 is a brushless motor. The motor section 20 includes a stator 30 and a rotor 50. The stator 30 includes a stator core 32, six coils 38, a resin layer 39, and terminals 37. As shown in FIG. 2, the stator core 32 includes a yoke 34 and six teeth 36. The yoke 34 has a cylindrical shape that forms the outer circumferential surface of the stator 30. Each tooth 36 protrudes from the inner circumferential surface of the yoke 34 toward the central axis CL of the cylindrical shape of the yoke 34. The tip of each tooth 36 (i.e., the end opposite the yoke 34) extends in the rotational direction of the rotor 50.

[0015] As shown in Fig. 1, six coils 38 are arranged on the stator core 32 via a resin bobbin 33. Each coil 38 is wound around a corresponding tooth 36. The coils 38 are connected to an external power supply via terminals 37. The stator 30 is covered with a resin layer 39 except for the outer peripheral surface of the stator core 32. The resin layer 39 has an outlet port 12 for discharging fuel.

[0016] (Rotor configuration) A rotor 50 is disposed inside the stator 30. As shown in FIG. 2, the rotor 50 includes a shaft 52, a rotor core 54, a magnet 56, and a covering member 58.

[0017] The shaft 52 is made of martensitic stainless steel. The shaft 52 may be made of other magnetic or non-magnetic materials. The shaft 52 has a rotation axis CL that coincides with the central axis CL, and has a cylindrical shape extending along the rotation axis CL. Since the rotation axis CL and the central axis CL coincide, both terms may be used hereinafter. The shaft 52 rotates around the rotation axis CL. As shown in FIG. 1 , the impeller 46 is fitted to the lower end of the shaft 52. The shaft 52 is rotatably supported above the impeller 46 in the casing 42 via a bearing. This allows the shaft 52 to be rotatable relative to the stator 30.

[0018] As shown in Fig. 2, a rotor core 54 is disposed around the shaft 52. When viewed in cross section as shown in Fig. 2, the rotor core 54 has a substantially square shape. That is, the cross section of the rotor core 54 is defined by a pair of parallel sides 54a and a pair of parallel sides 54b that are perpendicular to the pair of sides 54a. More specifically, the sides 54a and 54b are connected by a curved surface, and the cross section of the rotor core 54 has a rounded square shape.

[0019] A magnet 56 is disposed on each of the outer surfaces of the pair of sides 54a and the pair of sides 54b. That is, four magnets 56 are disposed on the outer surface of the rotor core 54. The magnets 56 are disposed at intervals in the circumferential direction of the shaft 52. As shown in FIG. 3, each magnet 56 has a plate shape (a rectangular parallelepiped shape). Each magnet 56 is disposed so as to extend parallel to the rotation axis CL. Each magnet 56 has a length in the direction of the rotation axis CL that is equal to that of the rotor core 54. The magnets 56 have substantially the same shape, and are disposed rotationally symmetrical with respect to the rotation axis CL.

[0020] The rotor core 54 and each magnet 56 are covered by a covering member 58. The covering member 58 has a cylindrical shape. The shaft 52 passes through the center of the covering member 58. The covering member 58 is fixed to the outer surface of the rotor core 54 and the outer surface of each magnet 56. The central axis of the covering member 58 coincides with the rotation axis CL. The covering member 58 does not have to cover at least one of the upper and lower ends of the magnet 56. In this case, at least one of the upper and lower ends of the magnet 56 may be exposed from the covering member 58. The covering member 58 is made of, for example, resin. The rotor 50 is produced by molding the covering member 58 by placing the shaft 52, rotor core 54, and magnets 56 in a molding die, a process known as molding.

[0021] As shown in Figure 4, when the shortest distance between adjacent magnets 56 in the circumferential direction of shaft 52 is Wa and the width of magnet 56 along the outer surface of side 54a or side 54b is Wm, magnets 56 are designed and arranged so as to satisfy the relationship Wm / Wa≦1.72.

[0022] Furthermore, the outer peripheral edge of rotor core 54 is located within a closed region R1 defined by extension lines 55a of a pair of sides 54a and extension lines 55b of a pair of sides 54b. More specifically, in this embodiment, the outer peripheral edge of rotor core 54 in the range connecting adjacent magnets 56 is located within region R1 and region R2 (within the region indicated by dotted hatching in FIG. 4). Region R2 is a region in which the thickness h of rotor core 54 in the radial direction of shaft 52 between adjacent magnets 56 (in this embodiment, the thickness h of rotor core 54 on line A1 connecting intersection P of extension lines 55a and 55b with rotation axis CL) satisfies the relationship h≧Wm / 2.

[0023] Next, with reference to FIGS. 5 and 6, the magnitude of magnetic flux leakage depending on the shape of the rotor core 54 will be described. FIG. 5 shows various variations in the shape of the rotor core 54 in the rotor 50. In FIG. 5, the cross-sectional area of ​​the rotor core 54 decreases from (a) to (f). Specifically, in FIGS. 5(c) to (f), the thickness h (see FIG. 4) of the rotor core 54 decreases from (c) to (f). The rotor core 54 shown in FIG. 5(c) has a shape corresponding to FIG. 2, etc. The rotor core 54 shown in FIG. 5(f) has a shape that satisfies the relationship h = Wm / 2. Furthermore, the rotor core 54 shown in FIGS. 5(a) and (b) shows a comparative example in which the outer peripheral edge of the rotor core 54 in the area connecting adjacent magnets 56 is located more radially outward than the contact surface of the magnet 56 with the rotor core 54. That is, in (a) and (b) of FIG. 5, the outer peripheral edge of the rotor core 54 in this range extends further outward than the region R1 in FIG.

[0024] FIG. 6 shows the no-load rotation speed of a motor using the rotor core 54 of each shape shown in FIGS. 5(a) to 5(f). The no-load rotation speed of the motor correlates with the magnitude of magnetic flux leakage. Specifically, the higher the no-load rotation speed of the motor, the greater the magnetic flux leakage. As shown in FIG. 6, it can be seen that the slope of the graph changes significantly at the boundary of the shape of the rotor core 54 shown in FIG. 5(c). That is, in the configurations to the right of FIG. 6 (i.e., where the thickness h of the rotor core 54 in the area connecting adjacent magnets 56 is smaller), the magnitude of magnetic flux leakage does not change significantly, and it can be said that the magnetic flux leakage is small. On the other hand, in the configurations shown in FIGS. 5(a) and 5(b), the no-load rotation speed of the motor increases. That is, it can be said that the magnetic flux leakage is large. As described above, with the shapes of the rotor core 54 of this embodiment (i.e., the shapes shown in FIGS. 5(c) to 5(f)), magnetic flux leakage is small and can be suppressed.

[0025] Next, with reference to Figures 7 and 8, the magnitude of magnetic flux leakage in relation to the relationship between the shortest distance Wa between adjacent magnets 56 and the width Wm of the magnets 56 for a given shape of the rotor core 54 will be described. The rotor core 54 shown in Figure 7 (c1) to (c4) corresponds to the shape shown in Figure 5 (c), and the rotor core 54 shown in Figure 7 (e1) to (e4) corresponds to the shape shown in Figure 5 (e). In Figure 7, the width Wm of the magnets 56 increases and the shortest distance Wa decreases from the state shown on the left to the state shown on the right. Specifically, in the embodiment shown in (c1), Wa = 7.198 and Wm = 3.5 (Wm / Wa = 0.49), in the embodiment shown in (c2), Wa = 5.784 and Wm = 5.5 (Wm / Wa = 0.95), in the embodiment shown in (c3), Wa = 4.37 and Wm = 7.5 (Wm / Wa = 1.72), and in the embodiment shown in (c4), Wa = 2.956 and Wm = 9.5 (Wm / Wa = 3.21). The shortest distance Wa and width Wm in (e1) to (e4) of Figure 7 correspond to (c1) to (c4), respectively.

[0026] Figure 8 shows the rate of change in magnetic flux leakage when the shape of the rotor core 54 is changed for a given shape and arrangement of the magnets 56. For example, (1) in Figure 8 represents the rate of increase in magnetic flux leakage for the embodiment shown in (c1) relative to the embodiment shown in (e1) in Figure 7, and (2) represents the rate of increase in magnetic flux leakage for the embodiment shown in (c2) relative to the embodiment shown in (e2) in Figure 7. The same applies to (3) and (4). The rate of increase in magnetic flux leakage is calculated as the rate of increase in the no-load rotation speed of a motor using a rotor of the embodiment shown in (c) relative to the no-load rotation speed of a motor using a rotor of the embodiment shown in (e) in Figure 7.

[0027] As described above, when the rotor core 54 shown in (c) and (e) of FIG. 5 is used, there is not much change in the amount of magnetic flux leakage. In other words, when the rate of increase in magnetic flux leakage is large in the graph shown in FIG. 8, it can be said that changes in the shape and arrangement of the magnets 56 (i.e., the relationship between Wm and Wa) contribute greatly to the magnetic flux leakage. In (3) and (4) of FIG. 8, the rate of increase is small, and there is not much change in the amount of magnetic flux leakage with changes in the shape of the rotor core 54. In other words, it can be said that changes in the shape and arrangement of the magnets 56 contribute little to the magnetic flux leakage. On the other hand, in (1) and (2) of FIG. 8, the rate of increase is large, and a relatively large amount of magnetic flux leaks with changes in the shape of the rotor core 54. In other words, it can be said that changes in the shape and arrangement of the magnets 56 contribute greatly to the magnetic flux leakage. As described above, it can be seen that magnetic flux is more likely to leak when the ratio of width Wm to shortest distance Wa is smaller (i.e., Wm / Wa≦1.72) than in the state shown in Figure 8 (3) (i.e., Wm / Wa=1.72).

[0028] As described above, in this embodiment, the relationship Wm / Wa≦1.72 is satisfied, and therefore the magnetic flux leakage due to the shape and arrangement of the magnets 56 is relatively large. However, in this embodiment, as described above, the rotor core 54 has a shape that makes it difficult for magnetic flux leakage to occur. In other words, the magnetic flux leakage due to the shape of the rotor core 54 is small. In this way, in this embodiment, magnetic flux leakage is suppressed by the shape of the rotor core 54 (i.e., the outer peripheral edge of the rotor core 54 is located within region R1 and region R2), so the magnetic flux leakage due to the shape and arrangement of the magnets 56 can be compensated for, and an increase in magnetic flux leakage is suppressed overall.

[0029] Furthermore, in the embodiments shown in FIGS. 8(1) and 8(2), the width Wm of the magnets 56 is relatively small. That is, the thickness of the magnets 56 can be increased without changing the volume of the magnets 56 compared to conventional embodiments. Therefore, the self-demagnetization effect of the magnets 56 is suppressed, and a reduction in magnetic force is suppressed. As described above, in this embodiment, the rotor core 54 is shaped to reduce magnetic flux leakage, and the shortest distance Wa between the magnets 56 is increased and the width Wm of the magnets 56 is reduced. Therefore, the thickness of the magnets 56 can be increased while compensating for magnetic flux leakage due to the shape and arrangement of the magnets 56. This makes it possible to ensure the magnetic force of the magnets 56 while suppressing overall magnetic flux leakage.

[0030] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. Modifications of the above-described embodiments are listed below.

[0031] In the embodiment described above, the outer peripheral edge of rotor core 54 in the range connecting magnets 56 is located within region R1 and region R2. However, the outer peripheral edge may be located within region R1.

[0032] The technical elements described in this specification or drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of those objectives is itself technically useful. [Explanation of symbols]

[0033] 30: Stator 50:Rotor 52: Shaft 54: Rotor core 56: Magnet

Claims

1. a shaft having a rotation axis; a rotor core that covers the periphery of the shaft and has a substantially polygonal cross section perpendicular to the rotation axis, the cross section having at least a first pair of parallel sides and a second pair of parallel sides perpendicular to the first pair of sides; a plate-shaped magnet disposed on each of the outer surfaces of the first pair of sides and the second pair of sides; a covering member that covers the rotor core and the magnet; Equipped with an outer peripheral edge of the rotor core in a range connecting adjacent magnets in the circumferential direction of the shaft is located within a closed area defined by extension lines of the first pair of sides and the second pair of sides when viewed in the cross section, When the shortest distance between adjacent magnets in the circumferential direction of the shaft is Wa and the width of the magnet along the outer surface is Wm, the relationship Wm / Wa≦1.72 is satisfied. Rotor.

2. 2. The rotor of claim 1, A rotor that satisfies the relationship h≧Wm / 2, where h is the thickness of the rotor core in the radial direction of the shaft in a range connecting adjacent magnets in the circumferential direction of the shaft.

Images