rotor

Abstract

A rotor includes a rotor core (21) having a magnet accommodating hole (24), and a permanent magnet (22) embedded into the magnet accommodating hole of the rotor core and having a fold-back shape projecting toward a radially inner side. The rotor is configured to obtain a magnet torque generated by the permanent magnet and a reluctance torque generated by an outer core portion (25) in the rotor core at a radially outer side portion than the permanent magnet. A radially outer end portion (24a) of the magnet accommodating hole has a curved shape in which a distance between the radially outer end portion of the magnet accommodating hole and an outer periphery of the rotor core is close at a center in a circumferential direction of the rotor.

Description

[0001] Citation of relevant applications

[0002] This application is based on Japanese Patent Application No. 2020-024208, filed on February 17, 2020, the contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to a rotor with an embedded magnet. Background Technology

[0004] Conventionally, rotary electric machines using rotors with embedded magnets are well known. An embedded magnet rotor includes: a rotor core having a magnet receiving hole; and a permanent magnet embedded in the magnet receiving hole of the rotor core and having a folded-back shape protruding radially inward. The rotor obtains a magnetic torque generated by the permanent magnet and a reluctance torque from an outer core portion of the rotor core that is radially outward from the permanent magnet (for example, see Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-41530 Summary of the Invention

[0008] In a rotor like the one described above, the radially outer end of the magnet receiving hole has a roughly circumferentially straight shape. During rotation, due to centrifugal force, the stress at the circumferential end of the radially outer end of the magnet receiving hole is the greatest. At this stress concentration point, the bridge portion of the rotor core may break. Alternatively, the position of the radially outer end of the magnet receiving hole could be moved entirely away from the outer periphery of the rotor core in a way that would not cause rotor core breakage. However, in this case, the cross-sectional area of ​​the magnetic circuit at the bridge portion, which is further radially outer than the radially outer end of the magnet receiving hole, becomes larger, resulting in increased leakage flux through this magnetic circuit and a decrease in the performance of the rotating motor.

[0009] The purpose of this disclosure is to provide a rotor that can suppress leakage flux to a small extent and suppress rotor core damage caused by stress concentration.

[0010] To achieve the above objectives, the rotor according to a first aspect of this disclosure includes: a rotor core having a magnet receiving hole; and a permanent magnet embedded in the magnet receiving hole of the rotor core, having a radially inwardly protruding, folded-back shape. The rotor is configured to obtain a magnetic torque generated by the permanent magnet and a reluctance torque generated by an outer core portion of the rotor core that is radially outer than the permanent magnet. The radially outer end of the magnet receiving hole has a curved shape such that the distance between the radially outer end of the magnet receiving hole and the outer periphery of the rotor core is approximately at the center of the rotor's circumference. The magnet receiving hole has an axial portion with a different shape from other portions. The axial portion is located at the center of the axial direction of the magnet receiving hole. The permanent magnet is a bonded magnet filling the magnet receiving hole. The permanent magnet and the axial portion engage with each other in the axial direction.

[0011] According to this structure, the radially outer end of the magnet receiving hole has a curved shape in which the distance between the radially outer end of the magnet receiving hole and the outer periphery of the rotor core is close to that at the center of the rotor's circumference. Therefore, leakage flux can be minimized, and damage to the rotor core caused by stress concentration at the circumferential end of the radially outer end of the magnet receiving hole can be suppressed. That is, the stress is greatest at the circumferential end of the radially outer end of the magnet receiving hole, but by increasing the distance from the outer periphery of the rotor core, the bridge portion of the rotor core becomes thicker, thereby suppressing damage. In addition, at the circumferential center of the radially outer end of the magnet receiving hole, since the distance from the outer periphery of the rotor core becomes closer, the cross-sectional area of ​​the magnetic circuit of the bridge portion 51 becomes smaller, thereby minimizing leakage flux through the magnetic circuit. Furthermore, since the magnet receiving hole has an irregularly shaped portion in the axial direction that differs from other parts, the permanent magnet can be engaged axially by the irregularly shaped portion, preventing the permanent magnet from falling out of the magnet receiving hole. In addition, since the irregular part is located at the axial center of the magnet receiving hole, the permanent magnet can be prevented from falling out of the magnet receiving hole with high balance in both axial directions. Attached Figure Description

[0012] The above-mentioned objects, as well as other objects, features, and advantages of this disclosure, will become clearer with reference to the accompanying drawings and the following detailed description.

[0013] Figure 1 This is a cross-sectional view of a rotary electric motor according to one embodiment.

[0014] Figure 2 This is an exploded perspective view used to illustrate a rotor according to one embodiment.

[0015] Figure 3 This is a top view used to illustrate a rotor according to one embodiment.

[0016] Figure 4 This is a partially enlarged top view used to illustrate a rotor according to one embodiment.

[0017] Figure 5 This is a partially enlarged top view used to illustrate a rotor core of one embodiment.

[0018] Figure 6 This is a partially enlarged perspective view used to illustrate a rotor core according to one embodiment.

[0019] Figure 7 This is a partially enlarged top view used to illustrate another example of a rotor core.

[0020] Figure 8 This is a partially enlarged perspective view used to illustrate another example of a rotor core.

[0021] Figure 9 This is a partially enlarged perspective view used to illustrate another example of a rotor core. Detailed Implementation

[0022] The following is based on Figures 1-6 An embodiment of a rotary electric motor will be described.

[0023] like Figure 1 As shown, the rotary motor M in this embodiment is a brushless motor with embedded magnets, and is a motor for a position control device configured in the engine compartment of a vehicle, specifically a motor for a variable valve timing device connected to the engine.

[0024] The rotary electric machine M has an electric motor housing 1. The electric motor housing 1 has a cylindrical front outer shell 2 and an end frame 3. The cylindrical front outer shell 2 is made of a magnetic material that is formed into a covered cylindrical shape. The end frame 3 closes the opening of the cylindrical front outer shell 2 and is made of aluminum (a non-magnetic material).

[0025] The rotary electric motor M includes a stator 5 and a rotor 7 with embedded magnets. The stator 5 is fixed to the inner circumferential surface of the cylindrical front housing 2, and the rotor 7 has a rotating shaft 6 disposed inside the stator 5. The rotating shaft 6 is supported by bearings 8 and 9 in a manner that allows it to rotate relative to the motor housing 1. The bearings 8 are housed and fixed in a bearing retaining portion 2a formed in the cylindrical front housing 2, and the bearings 9 are housed and fixed in a bearing retaining portion 3a formed in the end frame 3. A magnetic sensor 10, such as a Hall effect IC, is fixed to the axial inner surface 3b of the end frame 3.

[0026] The front end of the rotating shaft 6 protrudes from the cylindrical front housing 2. Furthermore, the rotation of the rotating shaft 6 drives the valve timing, which corresponds to the operating state, to be appropriately changed, i.e., the relative rotational phase of the camshaft relative to the crankshaft of the engine.

[0027] [Stator 5]

[0028] A stator 5 is fixed to the inner circumferential surface of the cylindrical front housing 2. The stator 5 has a cylindrical stator core 11, the outer circumferential surface of which is fixed to the inner surface of the cylindrical front housing 2. Inside the stator core 11, a plurality of pole teeth 12 are formed along the axial direction and are arranged at equal intervals in the circumferential direction. The plurality of pole teeth 12 extend radially inward.

[0029] In each pole tooth 12, three-phase windings 15 are wound around an insulator 13. Furthermore, when three-phase drive current is supplied to the windings 15, a rotating magnetic field is generated in the stator 5, and the rotor 7 is rotated in both directions.

[0030] [Rotor 7]

[0031] The rotor 7 includes: the aforementioned rotating shaft 6; a generally cylindrical rotor core 21 in which the rotating shaft 6 is inserted at the center; and a plurality of permanent magnets 22 (eight in this embodiment) embedded inside the rotor core 21.

[0032] like Figure 2 As shown, the rotor core 21 is composed of multiple electromagnetic steel plates 23 made of magnetic metal material stacked along the axial direction.

[0033] like Figures 1-3 As shown, the rotor core 21 has magnet receiving holes 24 for accommodating permanent magnets 22. Multiple magnet receiving holes 24 are provided at equal intervals along the circumference of the rotor core 21 (eight in this embodiment). Each magnet receiving hole 24 has a continuous, approximately U-shaped, folded-back shape protruding radially inward, and all holes have the same shape as each other.

[0034] The permanent magnet 22 is composed of bonded magnets, which are formed by molding and hardening a magnetic material after mixing magnetic powder with resin. Specifically, the permanent magnet 22 is formed by using the magnet receiving hole 24 of the rotor core 21 as a molding die, allowing the unhardened magnetic material to be injection molded into the magnet receiving hole 24 without gaps, and then hardening it within the magnet receiving hole 24 after filling. Therefore, the shape of the magnet receiving hole 24 is consistent with the external shape of the permanent magnet 22.

[0035] Incidentally, although the magnet powder used as the permanent magnet 22 in this embodiment is, for example, a samarium iron nitride (SmFeN) type magnet, other rare earth magnets can also be used. Furthermore, the permanent magnet 22, hardened within the magnet receiving hole 24 of the rotor core 21, is magnetized from the outside of the rotor core 21 using a magnetizing device (not shown) to function as a magnet. The permanent magnet 22 is magnetized such that its polarity alternates along the circumferential direction of the rotor core 21. Additionally, the permanent magnet 22 is energized in its thickness direction.

[0036] The portion of the rotor core 21 that is radially outer than the permanent magnets 22, i.e., the portion opposite to the stator 5, functions as the outer core portion 25 for obtaining reluctance torque. Furthermore, the rotor 7 has an eight-pole rotor pole portion 26, which is configured to include eight permanent magnets 22 and an outer core portion 25 surrounded by the permanent magnets 22. Each rotor pole portion 26 functions as the N pole and S pole, respectively. The rotor 7 is configured to obtain both magnetic torque and reluctance torque through the aforementioned rotor pole portions 26.

[0037] Next, the detailed shape of the permanent magnet 22 will be described. Furthermore, the shape of the permanent magnet 22 is consistent with the shape of the magnet receiving hole 24.

[0038] like Figure 3 and Figure 4 As shown, when viewed from the axial direction, the permanent magnet 22 has a roughly U-shaped, continuous folded shape that bulges radially inward. The permanent magnet 22 is linearly symmetrical with respect to the circumferential center line L passing through the axial center Z of the rotor 7 and the circumferential center of the permanent magnet 22 itself.

[0039] The permanent magnet 22 has: a first straight portion 31 as a straight portion on one circumferential side (e.g., counterclockwise side); a second straight portion 32 as a straight portion on the other circumferential side (e.g., clockwise side); and a curved portion 33 that connects the radially inner ends of the first straight portion 31 and the second straight portion 32 to each other and is in a curved shape. The first straight portion 31 and the second straight portion 32 extend radially along the rotor 7. Specifically, the first straight portion 31 and the second straight portion 32 extend parallel to a straight line passing through the axis center Z of the rotor 7. Furthermore, in circumferentially adjacent permanent magnets 22, adjacent first straight portions 31 and second straight portions 32 are parallel to each other.

[0040] Here, the rotor 7 of this embodiment includes an annular end face magnet 41 with magnetic poles arranged in a manner that repels the outer iron core portion 25 at a position opposite to the axial end face of the outer iron core portion 25.

[0041] In detail, firstly, the end face magnet 41 is fixed to the axial end face of the rotor core 21 and the permanent magnet 22 by an adhesive.

[0042] Furthermore, the outer diameter of the end face magnet 41 is set to be above the outermost diameter of the permanent magnet 22 and below the outermost diameter of the rotor core 21. In other words, viewed axially, the outer periphery of the end face magnet 41 is positioned between the outermost radially outer position of the permanent magnet 22 and the outermost radially outer position of the rotor core 21. Additionally, the inner diameter of the end face magnet 41 is set to be the innermost diameter of the outer core portion 25. In other words, viewed axially, the inner periphery of the end face magnet 41 is positioned at the innermost radially inner position of the outer core portion 25.

[0043] Furthermore, the end-face magnets 41 are energized axially and are magnetized with alternating polarities in the circumferential direction. The end-face magnets 41 are magnetized in the same number as the permanent magnets 22 and the outer core portion 25, i.e., eight, with alternating polarities in the circumferential direction. Moreover, the end-face magnets 41 are arranged such that their own magnetic poles repel the outer core portion 25; in other words, their own magnetic poles align with the magnetic poles of the opposing outer core portion 25. This configuration reduces leakage flux that passes over the axial end face of the permanent magnet 22 and leaks from or toward the axial end face of the outer core portion 25.

[0044] In addition, such as Figure 1 As shown, the end face magnet 41 is arranged opposite to the magnetic sensor 10 with a gap, and constitutes a sensor magnet capable of detecting the rotation angle of the rotor 7 using the magnetic sensor 10. That is, the end face magnet 41 also serves as a sensor magnet.

[0045] Here, as Figure 4 As shown, the radially outer end 24a of the magnet receiving hole 24 has a curved shape in which the distance between the radially outer end of the magnet receiving hole 24 and the outer periphery of the rotor core 21 changes continuously in the circumferential direction of the rotor 7 and approaches the center in the circumferential direction. In detail, viewed from the axial direction, the radially outer end 24a of the magnet receiving hole 24 in this embodiment has a semi-circular shape with the center X of the width of the magnet receiving hole 24 as the axis. That is, the magnet receiving hole 24 has a shape in which a pair of inner walls that receive the first straight portion 31 and the second straight portion 32 in the permanent magnet 22 are connected radially outward by a semi-circular shape. As a result, for the bridge portion 51 formed in the rotor core 21 at a position further outward than the radially outer end 24a of the magnet receiving hole 24, it is thinner towards the center in the circumferential direction and thicker towards the end in the circumferential direction.

[0046] In addition, such as Figure 5 and Figure 6 As shown, the magnet receiving hole 24 has an irregularly shaped portion 24b that differs in shape from the other parts along its axial direction. Additionally, Figure 5 and Figure 6The rotor core 21 without the permanent magnet 22 is shown. More specifically, as... Figure 6 As shown, the irregularly shaped portion 24b is disposed at the axial center of the magnet receiving hole 24. Furthermore, the irregularly shaped portion 24b is disposed at the radially outer end 24a of the magnet receiving hole 24, and protrudes inward relative to other parts. That is, viewed axially, the irregularly shaped portion 24b of this embodiment protrudes inward from the semi-circular radially outer end 24a to form a semi-circular shape. Additionally, the irregularly shaped portion 24b of this embodiment is provided by stacking multiple electromagnetic steel plates 23. That is, the rotor core 21 of this embodiment is formed by stacking multiple electromagnetic steel plates 23, but the electromagnetic steel plates 23 include a first electromagnetic steel plate 23a with a shape corresponding to the irregularly shaped portion 24b and a second electromagnetic steel plate 23b corresponding to other parts, and the rotor core 21 of this embodiment is formed by stacking them.

[0047] Next, the function of the rotary motor M configured as described above will be explained.

[0048] For example, at a timing point based on the rotation angle of the rotor 7 detected by the magnetic sensor 10, if a three-phase drive current is supplied to the winding 15 from an external power supply, a rotating magnetic field is generated in the stator 5, and the rotor 7 is driven to rotate. This rotational drive changes the valve timing corresponding to the operating state, that is, the relative rotational phase of the camshaft relative to the engine crankshaft.

[0049] Next, the effects of the above-described embodiments will be described.

[0050] (1) Since the radially outer end 24a of the magnet receiving hole 24 has a curved shape in which the distance between the radially outer end of the magnet receiving hole and the outer periphery of the rotor core 21 is close to the center of the circumference of the rotor, leakage flux can be reduced, and damage to the rotor core 21 caused by stress concentration at the circumferential end of the radially outer end 24a of the magnet receiving hole 24 can be suppressed. That is, the stress is greatest at the circumferential end of the radially outer end 24a of the magnet receiving hole 24, but by increasing the distance from the outer periphery of the rotor core 21, the bridge portion 51 of the rotor core 21 becomes thicker, thereby suppressing damage. In addition, at the circumferential center of the radially outer end 24a of the magnet receiving hole 24, since the distance from the outer periphery of the rotor core 21 is closer, the cross-sectional area of ​​the magnetic circuit of the bridge portion 51 becomes smaller, thereby reducing the leakage flux through the magnetic circuit.

[0051] (2) Since the radially outer end 24a of the magnet receiving hole 24 has a semi-circular shape with the center X of the width of the magnet receiving hole 24 as the axis when viewed from the axial direction, the bridge portion 51 becomes equally thick at both ends of the radially outer end 24a of the magnet receiving hole 24, and the breakage is suppressed in a high balance.

[0052] (3) Since the magnet receiving hole 24 has an irregularly shaped portion 24b that is different in shape from other parts in the axial direction, the permanent magnet 22 can be engaged in the axial direction by the irregularly shaped portion 24b, thus preventing the permanent magnet 22 from falling out of the magnet receiving hole 24. In addition, in this embodiment, even if an end face magnet 41 is provided on the axial end face of the permanent magnet 22, it is still possible to prevent the permanent magnet 22 from falling out of the magnet receiving hole 24.

[0053] (4) Since the irregular part 24b is provided at the axial center of the magnet receiving hole 24, the permanent magnet 22 can be prevented from falling out of the magnet receiving hole 24 with high balance in both axial directions.

[0054] (5) The irregular part 24b is provided at the radially outer end 24a of the magnet receiving hole 24 and protrudes inward relative to other parts. Therefore, it can prevent the permanent magnet 22 from falling out of the magnet receiving hole 24 and improve the strength of the bridge part 51 of the rotor core 21 which is further outward than the magnet receiving hole 24.

[0055] The above-described embodiments can be modified in the following ways. Furthermore, this embodiment and the following variations can be combined and implemented within the scope of technical inconsistencies.

[0056] In the above embodiment, an example was described in which the irregular part 24b is provided at the radially outer end 24a of the magnet receiving hole 24 and protrudes relative to other parts, but it is not limited to this and may be provided in other shapes at other locations.

[0057] For example, such as Figure 7 and Figure 8 As shown, the irregularly shaped portion 52 can also be provided around the entire circumference of the magnet receiving hole 24 and protrude inward relative to other parts. In this way, it is possible to further prevent the permanent magnet 22 from falling out of the magnet receiving hole 24.

[0058] Additionally, for example, such as Figure 9 As shown, the irregularly shaped portion 53 can also be provided in a part of the magnet receiving hole 24 and recessed relative to other parts. In this way, the manufacture of the rotor core 21 becomes easier.

[0059] In the above embodiment, an example was described where the radially outer end portion 24a of the magnet receiving hole 24 is formed into a semi-circular shape with the center X of the width of the magnet receiving hole 24 as the axis. However, the radially outer end portion 24a of the magnet receiving hole 24 can be any curved shape as long as the distance from the outer periphery of the rotor core 21 is close to the center in the circumferential direction. For example, the radially outer end portion 24a of the magnet receiving hole 24 can also be formed into an elliptical shape or other curved shapes.

[0060] In the above embodiment, an example of the irregular portion 24b being provided at the axial center of the magnet receiving hole 24 has been described, but it is not limited to this and may also be provided at a position off the axial center. In addition, multiple irregular portions may be provided along the axial direction.

[0061] In the above embodiment, an example of a magnet receiving hole 24 having an irregularly shaped portion 24b with a portion of its axial direction that is different from the other portions has been described. However, it is not limited to this, and the magnet receiving hole 24 may not have an irregularly shaped portion.

[0062] In the above embodiment, the rotor 7 is described as including an end face magnet 41 fixed to the axial end face of the rotor core 21 and the permanent magnet 22, but the structure may also not include the end face magnet 41.

[0063] In the above embodiment, the permanent magnet 22 is described as having a first straight portion 31, a second straight portion 32 and a curved portion 33, but it is not limited to this. For example, it may also be formed into a shape that is curved as a whole when viewed from the axial direction.

[0064] In the above embodiment, the permanent magnet 22 was described as being composed of a bonded magnet formed using the magnet receiving hole 24 as a molding die. However, this is not the only possibility; for example, it could be a bonded magnet inserted into the magnet receiving hole 24 after molding, or a sintered magnet inserted into the magnet receiving hole 24 after sintering. Furthermore, in order to provide a permanent magnet 22 with a shape corresponding to the irregular part 24b as described in the above embodiment, it is ideal to provide a bonded magnet formed using the magnet receiving hole 24 as a molding die.

[0065] In the above embodiment, an example of the rotor core 21 being formed by stacking multiple electromagnetic steel plates 23 along the axial direction has been described, but it is not limited to this. For example, it may have other structures such as a structure formed by sintering magnetic powder.

[0066] While this disclosure has been described based on embodiments, it should be understood that this disclosure is not limited to the above embodiments and structures. This disclosure also includes various modifications and equivalent variations. Furthermore, various combinations and arrangements, including combinations and arrangements with only one element, or more than one or fewer elements, also fall within the scope and spirit of this disclosure.

Claims

1. A rotor, The rotor comprises: a rotor core having a magnet accommodating hole; and a permanent magnet embedded into the magnet accommodating hole of the rotor core and having a fold-back shape projecting toward a radially inner side, the rotor is configured to obtain a magnet torque generated by the permanent magnet and a reluctance torque generated by an outer core portion of the rotor core at a radially outer side portion than the permanent magnet, a radially outer end portion of the magnet accommodating hole has a curved shape in which a distance between the radially outer end portion of the magnet accommodating hole and an outer periphery of the rotor core is close at a center in a circumferential direction of the rotor, the magnet accommodating hole has a shaped portion in which a portion in an axial direction is different in shape from other portions, the shaped portion is provided at a center in the axial direction of the magnet accommodating hole, the permanent magnet is a bonded magnet filled into the magnet accommodating hole, the permanent magnet and the shaped portion are engaged with each other in the axial direction, an end surface magnet having magnetic poles arranged in repulsion with the outer core portion is included at a position opposite to an axial end surface of the outer core portion, the end surface magnet is annular, an outer diameter of the end surface magnet is set to be equal to or greater than an outermost diameter of the permanent magnet and less than an outermost diameter of the rotor core, and an inner diameter of the end surface magnet is set to be equal to or greater than an innermost diameter of the outer core portion.

2. The rotor according to claim 1, wherein a radially outer end portion of the magnet accommodating hole has a semicircular shape having a center of a width of the magnet accommodating hole as an axis.

3. The rotor according to claim 1, wherein the shaped portion is provided at a radially outer end portion of the magnet accommodating hole and is projected with respect to other portions.

4. The rotor according to claim 1, wherein the end surface magnet is fixed to axial end surfaces of the rotor core and the permanent magnet.

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