Permanent magnet external rotor for electric machine and such electric machine

Abstract

The utility model discloses a permanent magnet external rotor (1) for a motor (10), comprising: a cup-shaped body (2) having a bottom (20) and a side wall (21); the arc-shaped magnetic wedges (3) are arranged next to one another to form an annular structure, and the arc-shaped magnetic wedges are fixed in the cup-shaped body (2); the metal insert (4) is arranged between the side wall (21) and the arc-shaped magnetic wedges (3) so as to limit closing of a magnetic circuit of the motor (10); each of the plurality of arcuate magnetic wedges (3) comprises at least two tapered portions (3B) at opposite ends, wherein the cross-section of the tapered portions (3B) tapers from a maximum cross-section (S1) to a tip cross-section (S2). The utility model also provides a corresponding motor. The permanent magnet external rotor provided by the utility model can ensure that the polarity conversion is relatively stable, thereby reducing the vibration and noise of a motor.

Description

Technical Field

[0001] According to its more general aspects, the present invention relates to a permanent magnet external rotor, in particular for a synchronous motor, and to a motor comprising such a component.

[0002] The technical field of the present invention therefore relates to electric motors. Electric motors with permanent magnet external rotors can find useful applications in various industrial fields; more specifically, the present invention is preferably applied to the industrial field of large household appliances, such as motors for operating the drum and / or fan in washing machines or dryers. Background Art

[0003] Electric motors with permanent magnet rotors are well known in the technical field and are currently used in a wide range of applications, including components in household appliances and the operation of pumps.

[0004] Like other electric motors, these motors are traditionally constructed with an inner rotor rotating within a stationary stator; however, in some cases, a cup-shaped outer rotor surrounding a central stator is preferred. This solution has proven particularly advantageous, for example, as it allows for significant size reductions in the motor assembly used to operate the fan and drum of a drying washing machine.

[0005] The outer rotor of these motors, particularly in industries like home appliances where small size and cost-effective production are key, can be made from multiple ferrite wedges arranged adjacent to each other to form a ring. This ring is inserted into the aforementioned cup-like structure, which can be a plastic cover. Obviously, a metal ring is necessary to close the magnetic circuit and enable the motor to operate.

[0006] Although the choice of multiple wedge rings presents some manufacturing challenges, it is more cost-effective than using a continuous plastic ferrite ring, which requires precise and expensive mechanical grinding of the cylindrical inner surface.

[0007] However, multiple wedges still have the drawback of having a sharp transition from one magnetic pole to the next, which can cause the motor to vibrate.

[0008] Therefore, the technical problem to be solved by the present invention is to design an improved external rotor which can reduce vibration. Utility Model Content

[0009] In order to solve the above technical problems, the present invention provides a permanent magnet external rotor for an electric motor, which includes: a cup-shaped body with a bottom and a side wall; a plurality of arc-shaped magnetic wedges, which are arranged closely to each other to form an annular structure and are fixed inside the cup-shaped body; and a metal insert (preferably ferromagnetic), which is located between the side wall and the at least one magnet to limit the closure of the motor magnetic circuit.

[0010] Each of the plurality of arcuate magnetic wedges includes at least two tapered portions located at opposite ends, wherein a cross section of the tapered portion gradually decreases from a maximum cross section to a tip cross section.

[0011] This solution ensures that the polarity changeover is relatively smooth and less abrupt, which can reduce vibration in the motor.

[0012] In other words, this shape of the wedge makes the change in magnetic field more gradual, without a sharp discontinuity when switching from one magnetic pole to the next, thereby reducing vibration and noise in the motor as mentioned above.

[0013] Preferably, the cross section decreases along the entire arc length of the tapered portion, and the arc length of each tapered portion is at least 1 / 8 of the total arc length of the arc-shaped magnetic wedge, preferably at least 1 / 4.

[0014] The largest cross section is preferably the cross section at the midpoint of the arc defined by the arc-shaped magnetic wedge.

[0015] The tip cross-section is preferably zero, ie the tapered portion tapers to an acute angle defining the apex of the wedge.

[0016] Specifically, the free end of the tapered portion defines a tip having an acute angle.

[0017] Preferably, the plurality of arc-shaped magnetic wedges are symmetrical around a radial plane.

[0018] Preferably, the tapered portion has an inner arc surface which is convex at least along a majority of its arc length. This obviously means that the inner diameter of the tapered portion deviates from the usual cylindrical shape of the wedge, so that the thickness of the wedge decreases gradually towards its free end.

[0019] Preferably, the arc-shaped magnetic wedge has an outer arc surface which is cylindrical along most of the arc length of the magnetic wedge.

[0020] As can be seen from the above, the shapes of the inner and outer arc surfaces are different: the inner arc surface mostly deviates from the cylindrical shape, while the outer arc surface mostly maintains the cylindrical shape so as to form an outer ring in the metal insert.

[0021] In other words, the gradual reduction in the thickness of the magnetic wedge is due to the change in the shape of the inner arc surface, while the outer arc surface is substantially consistent with the shape of the prior art device.

[0022] The arcuate wedge may or may not include a central portion of constant cross-section between tapered portions.

[0023] The metal insert is preferably formed of a coil spring mounted around an annular structure defined by the plurality of arcuate magnetic wedges.

[0024] The helical spring, i.e. a helically wound metal body, adapts elastically to the annular structure of the multiple arc-shaped magnetic wedges mounted on it, but on the other hand ensures the continuity of the material over the entire circumference and the resulting closure of the magnetic circuit.

[0025] The metal insert is preferably a helical spring, which ensures that the magnet, consisting of a plurality of arc-shaped wedges, and the ferromagnetic insert are perfectly connected together while minimizing the difficulties associated with the manufacture of the assembly.

[0026] The use of a coil spring is particularly advantageous when using multiple magnetic wedges instead of a single ring-shaped magnet. In this case, the spring can clamp the ring structure defined by adjacent magnets and help maintain their position during the overmolding process of the outer cover. This ensures that the outer surfaces of successive wedges are aligned, making the construction process simpler and more efficient.

[0027] Preferably, at least the sidewalls of the cup are made of plastic and are overmolded over the plurality of arcuate wedges and the metal insert. Obviously, for manufacturing economy reasons, it is preferable to make the entire cup as a single overmolded component; alternatively, it is also possible to make only the sidewalls of plastic and then connect them to the other components of the separately manufactured cup.

[0028] Preferably, the cup-shaped body comprises a flange and an inner shoulder, which axially constrain the metal insert at opposite ends, producing a fixing effect on the spring.

[0029] Preferably, the flange and the inner shoulder also fully or partially cover the opposite axial ends of the annular structure defined by the plurality of arc-shaped magnetic wedges.

[0030] It is also preferred that at least one magnet has no contact with the encapsulating plastic along its inner surface, so that it faces the air gap in the finished electric machine.

[0031] The inner diameter of the coil spring defining the metal insert is preferably smaller in the rest state than the outer diameter of the annular structure defined by the at least one magnet, so that the coil spring is elastically deformed when mounted on the at least one magnet.

[0032] It should also be noted that when the coil spring is in a stationary state, the windings are arranged together, and the length is substantially equal to the axial length of the ring magnet, so that an armature is obtained that substantially completely surrounds the bottom permanent magnet.

[0033] The windings of the helical springs are preferably of square or rectangular cross-section to ensure that the thickness of the magnetic path surrounding the rotor poles is as uniform as possible.

[0034] It should be noted that the side wall of the cup-shaped body is preferably cylindrical.

[0035] On the other hand, the bottom may comprise a central hub connected to the sidewalls by a continuous cover or a plurality of radial arms. In the case of a continuous cover, the continuous cover may have a concave surface facing the sidewalls, on which convex radial ribs may be provided.

[0036] In order to solve the above technical problems, the present invention also provides a motor, which includes an internal stator provided with multiple magnetic poles and the external rotor provided above which is rotatably mounted on the top of the internal stator, wherein the annular structure of the multiple magnetic wedges surrounds the magnetic poles, and an air gap is arranged between the two.

[0037] In the case of multiple magnetic wedges during the injection molding process, the wedges can be clamped and held in an annular configuration, for example, by means of helical springs, to counteract the thrust of the injection molding material, which would otherwise cause the magnetic wedges to shift.

[0038] The injection mold is preferably capable of keeping the two axial ends of the coil spring in place, otherwise the coil spring will be deformed by the flow of the injection material during the injection molding process.

[0039] Two preferred embodiments of the present invention will be described below in a non-limiting example manner with reference to the accompanying drawings to further illustrate the features and advantages of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A side view of a motor device for a clothes dryer is shown, the device including a motor designed according to the present invention;

[0041] Figure 2 It is a three-dimensional diagram of the external rotor of the utility model;

[0042] Figure 3 yes Figure 2 Perspective views of the external rotor from different angles;

[0043] Figure 4 Shows Figure 2 a front view of the outer rotor shown;

[0044] Figure 5 The external rotor of the utility model Figure 4 A side view of a section taken along plane DD is shown;

[0045] Figure 5a Shows Figure 5 The detail marked by D in the middle can be magnified to see the structural details more clearly;

[0046] Figure 6 A cross-sectional view of an outer rotor designed according to the present invention is shown. DETAILED DESCRIPTION

[0047] With reference to the drawings, reference numeral 1 indicates a first embodiment of a permanent magnet external rotor for an electric machine, in particular a synchronous machine.

[0048] exist Figure 1 In the figure, the motor of the present invention is indicated by 10 and is used in the context of driving a drum and a fan of a washing and drying machine.

[0049] In a manner known per se, the electric motor 10 is a synchronous motor designed to rotate and drive a drive shaft 32, to which, in the embodiment shown here, a fan and a pulley for operating the drum of the clothes dryer are fixed. The motor has an inner stator 30 comprising a plurality of magnetic poles (not shown in the figures), and an outer rotor 1 integral with the drive shaft 32, which is rotatably mounted on the stator 30. The outer rotor 1 surrounds the magnetic poles of the inner stator 30 with an air gap located therebetween.

[0050] According to the present invention, the outer rotor 1 uses a plurality of arc-shaped magnetic wedges 3 , which are arranged adjacent to each other to form an annular structure.

[0051] In other words, each magnetic wedge 3 is in the shape of an arc, and its axial thickness is proportional to the thickness of its side wall. A plurality of arc-shaped magnetic wedges 3 are arranged side by side to form a cylindrical body.

[0052] The number of the plurality of arc-shaped magnetic wedges 3 used to form the outer rotor 1 is eight, and this number can obviously be modified according to specific design requirements.

[0053] Each of the plurality of arcuate wedges 3 includes a central portion 3A having a maximum cross section S1 and two opposite tapered portions 3B, the cross sections of the tapered portions 3B gradually decreasing from the maximum cross section S1 to a tip cross section S2 , which in this example is zero.

[0054] The cross-section of the tapered portions 3B gradually decreases because their inner arcs are convex, unlike the generally concave and cylindrical inner arcs of the central portion 3A. In contrast, the outer surface of the tapered portions 3B is substantially cylindrical.

[0055] The arc lengths A2 of the two opposite side portions 3B are both greater than 1 / 8, preferably about 1 / 4, of the total arc length A of the opposite arc-shaped magnetic wedge 3. Therefore, the arc length A1 of the central portion 3A is about 1 / 2 of the total arc length.

[0056] The "arc length" is the distance between two points along the "total arc length" A, measured on the circumference of a circle passing through the middle longitudinal section from tip to tip of each wedge 3.

[0057] This solution makes the polarity change less abrupt, thus reducing vibrations in the motor.

[0058] In other words, the wedge shape design can make the change of the magnetic field more gradual, without sudden interruptions, thereby reducing the vibration and noise of the motor.

[0059] Furthermore, each wedge 3 is in particular formed as a plastic ferrite ring on which is mounted a metal insert 4, preferably but not necessarily a helical spring made of ferromagnetic material. A plastic cover is applied to the top of the assembly consisting of the plurality of magnetic wedges 3 and the helical springs, defining the cup 2 of the rotor.

[0060] The coil spring has windings 40 of square cross-section. These windings, when in the static state, are arranged together, forming a ferromagnetic covering of substantially uniform thickness atop the plurality of magnetic wedges 3, thereby properly closing the magnetic circuit on the rotor. In the preferred embodiment shown here, there are five windings 40. It should also be noted that the inner diameter d of the coil spring in the static state is slightly smaller than the outer diameter D of the annular structure of the plurality of magnetic wedges 3; this allows the coil spring to elastically deform in the radial direction when mounted atop the magnets.

[0061] The cup-shaped body 2 overmolded with plastic material has a bottom 20 for laterally covering the motor 10 and is connected to a substantially cylindrical side wall 21 , which protrudes along the opening direction of the cup-shaped body 2 .

[0062] The bottom 20 includes a hub 25 . In the embodiment shown in the figure, the hub 25 has a through hole for keying with the drive shaft 32 . The bottom also includes a continuous cover 24 , which is preferably recessed toward the inside of the cup-shaped body 2 and connected to the side wall 21 .

[0063] The concave inner surface of the continuous cover 24 has a plurality of radial ribs 26 extending towards the peripheral edge; the outer surface of the base 20 also has similar ribs, but only involving the hub portion 25.

[0064] The continuous cover 24 defines a shoulder 23, opposite which lies the front flange 22 of the side wall 21. The flange 22 and shoulder 23 axially surround the assembly consisting of the plurality of curved wedges 3 and the coil spring mounted on top of them. Furthermore, the coil spring is radially constrained by the side wall 21 and is therefore completely embedded within the plastic sheath. The free inner sides of the plurality of curved wedges 3, on the other hand, are designed to face the air gap of the motor 10.

[0065] The assembly consisting of the arc-shaped magnetic wedge 3 and the superimposed metal spring is overmolded with the plastic cup 2 , thereby defining the final structure of the outer rotor 1 .

[0066] It should be noted that the overmolding mold used in production is designed to keep the two axial ends of the coil spring in place, otherwise the flow of the injection material during the injection molding process will cause the two axial ends to deform.

[0067] Obviously, a person skilled in the art may make numerous modifications and variations to the motor described above in order to meet any specific requirements that may arise, and all of these are included within the scope of protection of the present invention, as defined in the claims.

Claims

1. A permanent magnet external rotor (1) for an electric motor (10), comprising: A cup-shaped body (2) is provided with a bottom (20) and a side wall (21); a plurality of arc-shaped magnetic wedges (3) are arranged closely together to define an annular structure, and the plurality of arc-shaped magnetic wedges are fixed in the cup-shaped body (2); and a metal insert (4) is arranged between the side wall (21) and the plurality of arc-shaped magnetic wedges (3) to define the closure of the magnetic circuit of the motor (10); characterized in that each of the plurality of arc-shaped magnetic wedges (3) includes at least two tapered portions (3B) located at opposite ends, wherein the cross section of the tapered portion (3B) gradually decreases from a maximum cross section (S1) to a tip cross section (S2).

2. The permanent magnet external rotor (1) for an electric machine (10) according to claim 1, characterized in that The cross section of the tapered portion (3B) decreases along the entire arc length of the tapered portion (3B), and the arc length of each tapered portion (3B) is at least 1 / 8 of the total arc length of the arc-shaped magnetic wedge (3).

3. The permanent magnet external rotor (1) for an electric machine (10) according to claim 1, characterized in that The arc length of each tapered portion (3B) is at least 1 / 4 of the total arc length of the arc-shaped magnetic wedge (3).

4. The permanent magnet external rotor (1) for an electric machine (10) according to claim 1, characterized in that The maximum cross section (S1) is a cross section at the midpoint of an arc defined by the arc-shaped magnetic wedge.

5. The permanent magnet external rotor (1) for an electric machine (10) according to claim 1, characterized in that The tip cross section (S2) is zero.

6. The permanent magnet external rotor (1) for an electric machine (10) according to claim 5, characterized in that The free end of the tapered portion (3B) defines a tip having an acute angle.

7. The permanent magnet external rotor (1) for an electric machine (10) according to claim 1, characterized in that The plurality of arc-shaped magnetic wedges (3) are symmetrical around a radial plane.

8. The permanent magnet external rotor (1) for an electric machine (10) according to claim 1, characterized in that The tapered portion (3B) has an inner arc surface that is convex at least along most of its arc length.

9. The permanent magnet external rotor (1) for an electric machine (10) according to claim 1, characterized in that The outer arc surface of the arc-shaped magnetic wedge (3) is cylindrical along most of the arc length of the magnetic wedge (3).

10. A permanent magnet external rotor (1) for an electric machine (10) according to any one of claims 1 to 9, characterized in that The arc-shaped magnetic wedge (3) further comprises a central portion (3A) of constant cross-section located between the tapered portions (3B).

11. The motor (10) is characterized in that include: An inner stator (30) having a plurality of magnetic poles is provided, and a permanent magnetic outer rotor (1) for an electric machine (10) according to any one of claims 1 to 10, wherein the permanent magnetic outer rotor (1) is rotatably mounted on top of the inner stator (30), wherein the plurality of arc-shaped magnetic wedges (3) surround the magnetic poles with an air gap arranged between the two.

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