An outer rotor motor with self-wind cooling discrete sheath and a rotor size determination method

Abstract

The application discloses an outer rotor motor with self-air cooling discrete sheaths, which comprises a stator and an outer rotor. The outer rotor comprises a rotor iron core which is in a cylindrical shape and is provided with a plurality of discrete sheaths protruding from the inner wall of the rotor iron core. The discrete sheaths are made of magnetically conductive material and are uniformly and spacedly arranged along the circumference of the rotor iron core. Cooling medium channels are formed between adjacent discrete sheaths. The axis of the cooling medium channels forms an inclination angle with the axial direction of the rotor iron core. The middle part of the discrete sheaths is provided with a magnet cavity. Axial or circumferential laminated permanent magnets are fixedly arranged in the cavity. The laminated permanent magnets form rotor magnetic poles. The stator comprises a stator iron core. The outer circumferential surface of the stator iron core is provided with stator teeth. Coils are arranged on single stator teeth. Coils belonging to the same phase are connected in series to form phase windings. The application further discloses a rotor size determination method of the outer rotor motor. The application can inhibit the circulation path of rotor eddy current, reduce the eddy current loss and optimize heat dissipation.

Description

TECHNICAL FIELD

[0001] The application relates to an outer rotor motor, in particular to an outer rotor motor with a self-air-cooled split sheath and a rotor size determination method thereof, and belongs to the technical field of generators. BACKGROUND

[0002] As a core component of the next generation of new energy vehicle electric drive system, the wheel hub motor has the attributes of high torque density, low torque fluctuation, simple topology structure and high efficiency. Benefiting from the excellent magnetic properties of rare earth magnets, permanent magnet motors are widely used in wheel hub electric drive systems. In order to simplify the drive architecture, the wheel hub motor often adopts an outer rotor topology, and the motor rotor is designed integrally with the wheel hub, which is beneficial to improve the torque density of the system. In addition, due to the low speed of the wheel hub motor, in order to reduce the size of the winding end and the stator and rotor yoke, the stator side often adopts a tooth-wound winding.

[0003] Due to the existence of tooth harmonics, armature magnetic potential space harmonics and stator current time harmonics, the magnetic field in the rotor is no longer a constant magnetic field, and there are many harmonic components, which induce eddy currents in the conductive parts and produce large losses. Due to the small number of slots per pole per phase, the tooth-wound winding armature magnetic potential harmonic content is much higher than that of the conventional integer slot distributed winding motor, and the rotor eddy current loss problem caused by the space harmonics is more prominent. The rotor eddy current loss and the temperature rise caused by it offset the advantages of using a tooth-wound winding, limiting the operating frequency and the upper limit of the electromagnetic load of the wheel hub motor.

[0004] Due to the compact structure, the wheel hub motor has high loss density, and the winding copper loss and magnetic material iron loss can be well conducted when using conventional stator water cooling, but the rotor eddy current loss and its temperature rise problem still exist. In addition, due to the limitations of installation size and rotation, it is difficult for the wheel hub motor to arrange an active cooling system on the rotor, and at present it still relies on natural convection and forced convection cooling during operation, which limits the overload capacity and the upper limit of the thermal design of this type of motor, and becomes one of the core bottlenecks of the wheel electric drive system. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the application provides an outer rotor motor with a self-air-cooled split sheath to reduce the rotor loss of the motor and improve the heat dissipation capacity of the rotor. The application also provides a rotor size determination method for an outer rotor motor with a self-air-cooled split sheath.

[0006] The technical solution of this invention is as follows: An external rotor motor with a self-cooled discrete sheath includes a stator and an external rotor. The external rotor includes a rotor core, which is cylindrical. Several discrete sheaths protruding from the inner wall of the rotor core are fixedly provided. The discrete sheaths are made of magnetically conductive material and are evenly spaced along the circumference of the rotor core. Adjacent discrete sheaths form a cooling medium channel. The axis of the cooling medium channel forms an angle with the axial direction of the rotor core. A magnet cavity is provided in the middle of the discrete sheath. Stacked permanent magnets are fixedly provided in the magnet cavity, either axially or circumferentially. The stacked permanent magnets form rotor poles. The stator includes a stator core. Several stator teeth are provided on the outer circumferential surface of the stator core. Coils are wound around a single stator tooth. Coils belonging to the same phase are connected in series to form a phase winding.

[0007] Furthermore, the discrete sheath is provided with guide fluids at both ends to direct airflow into the cooling medium channel. This enhances the cooling effect.

[0008] Furthermore, the guide fluid at the head end of the discrete sheath has a first surface extending forward from the first side of the discrete sheath and a second surface connecting the front end of the first surface and the front end of the second side of the discrete sheath; the guide fluid at the tail end of the discrete sheath has a third surface extending backward from the second side of the discrete sheath and a fourth surface connecting the tail end of the third surface and the tail end of the first side of the discrete sheath.

[0009] Furthermore, the outlines of the second and fourth surfaces are Archimedean spirals.

[0010] Furthermore, the discrete sheath is integrally formed with the rotor core.

[0011] Furthermore, each of the discrete sheaths is divided into several segments in the axial direction, with adjacent segments insulated from each other, to suppress the axial flow of eddy currents within the sheath and reduce eddy current losses.

[0012] Another technical solution of the present invention is a method for determining the rotor size of an external rotor motor, wherein the external rotor motor is the aforementioned external rotor motor with a self-cooled discrete sheath, and the rotor size determination method includes the following steps:

[0013] Step 1: Calculate the armature magnetomotive force harmonic spectrum when the phase winding is excited by a sinusoidal current using the winding function method. Based on the relationship between the harmonics and the fundamental wave, determine the harmonic with the largest amplitude and the harmonic with the lowest relative frequency to the fundamental wave in the armature magnetomotive force.

[0014] Step 2: Determine the tilt angle θ as half of the pole moment angle corresponding to the relative frequency of the harmonic with the largest amplitude and the fundamental wave;

[0015] Step 3: Determine that the thickness h1 of the laminated permanent magnet along the circumferential or axial direction is 1 / e of the skin depth of the lowest relative frequency harmonic in the permanent magnet, where e is the natural logarithm.

[0016] The advantages of the technical solution provided by this invention are as follows:

[0017] This invention features a discrete sheath machined inside the rotor core, enabling effective fixation of the laminated permanent magnets. The sheath and stator core are an integral structure, eliminating the need for additional magnet fixing clips and significantly simplifying the manufacturing and assembly process. Compared to an integral sheath, the discrete structure suppresses eddy current flow paths in the rotor, reducing eddy current losses, offering significant advantages during high-frequency operation. Furthermore, the discrete sheath of this invention significantly enhances the rotor's structural strength and rigidity, reduces vibration and noise in thin-walled rotors, and facilitates integration with hub systems.

[0018] Furthermore, the discrete sheaths proposed in this invention, arranged axially at an angle, effectively reduce motor torque fluctuations. On the other hand, during rotor rotation, the angled discrete sheaths drive the cooling medium to flow through the channels formed between the sheaths, simultaneously cooling the motor's stator and rotor, thus improving the upper limit of thermal load and the magnet's anti-demagnetization reliability. The thermal management system eliminates the need for a separate forced cooling structure for the rotor, simplifying rotor heat dissipation design and resulting in a more compact drive motor structure. Attached Figure Description

[0019] Figure 1 This is an overall structural diagram of the external rotor motor with a self-cooled discrete sheath according to the present invention.

[0020] Figure 2 yes Figure 1 A schematic diagram of an outer rotor containing a self-cooled discrete sheath.

[0021] Figure 3 yes Figure 1 Schematic diagram of a self-cooled, discrete sheath.

[0022] Figure 4 yes Figure 1 Schematic diagram of the stator structure of the electric motor.

[0023] Figure 5 This is a schematic diagram of a stacked permanent magnet in a circumferential arrangement.

[0024] Figure 6 This is a waveform diagram of the armature magnetomotive force of a three-phase winding.

[0025] Figure 7 It is the harmonic spectrum of the armature magnetomotive force of the three-phase winding. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments, but these are not intended to limit the scope of the invention.

[0027] Please combine Figures 1 to 4 As shown, this embodiment relates to an external rotor motor with self-cooled discrete sheaths, comprising an external rotor 100 and a stator 200, the stator 200 being located inside the external rotor 100 and coaxially arranged with the external rotor 100. The external rotor motor has a rated power of 50kW and a speed of 1230r / min. The external rotor 100 includes a cylindrical rotor core 101, and 26 discrete sheaths 102, evenly distributed along the circumference and with certain gaps, are machined on the inner wall of the rotor core 101, thus forming an integral structure with the rotor core 101. Alternatively, the discrete sheaths 102 can be machined separately from the rotor core 101, using the same magnetically conductive material as the rotor core 101, and then fixedly connected to the rotor core 101 as a whole.

[0028] like Figure 2 , Figure 3 As shown, discrete sheaths 102 are evenly spaced along the circumference of the rotor core 101, and adjacent discrete sheaths 102 form an inclined cooling medium channel 103. The inclined cooling medium channel 103 means that the axis of the cooling medium channel 103 forms an angle with the axial direction of the rotor core 101. In other words, the side of the discrete sheath 102 adjacent to other discrete sheaths 102 forms an angle with the axial direction of the rotor core 101, rather than being parallel to the axial direction of the rotor core 101. A magnet cavity is provided in the middle of the discrete sheath 102, and the magnet cavity is filled with axially stacked samarium cobalt laminated permanent magnets 104. The magnet cavity has the same outline as the samarium cobalt laminated permanent magnet 104, meaning that the samarium cobalt laminated permanent magnet 104 is surrounded by walls formed by discrete sheaths 102. The samarium cobalt laminated permanent magnet 104 is bonded and fixed inside the discrete sheaths 102 with epoxy adhesive. Each discrete sheath 102 houses a set of samarium cobalt laminated permanent magnets 104, thus forming 26 rotor poles, each pole also inclined to the axial direction of the rotor core 101. It should be noted that in some embodiments, the samarium cobalt laminated permanent magnets 104 can also be stacked in a circumferential direction, such as... Figure 5As shown. Furthermore, in these embodiments, the discrete sheath 102 is divided into several segments axially, with adjacent segments insulated from each other. Each segment of the discrete sheath 102 has a separate magnet cavity, within which a samarium cobalt laminated permanent magnet 104 is disposed. The samarium cobalt laminated permanent magnet 104 can be stacked axially or circumferentially. The axial segmentation of the discrete sheath 102 suppresses the axial flow of eddy currents, reducing eddy current losses within the sheath. During operation of the external rotor motor, the rotation of the external rotor causes airflow to continuously pass through the cooling medium channel 103, thereby enhancing the cooling effect on the rotor.

[0029] To further enhance the cooling effect and optimize airflow, in a preferred embodiment, at the cooling medium inlet and outlet of the cooling medium channel 103, i.e., at the axial head and tail ends of the discrete sheath 102, guide fluids 105 are respectively provided on the discrete sheath 102 to guide the flow. The guide fluid 105 at the head end of the discrete sheath 102 has a first surface 105a extending forward from the first side surface 102a of the discrete sheath 102, and a second surface 105b connecting the front end of the first surface 105a and the front end of the second side surface 102b of the discrete sheath 102. The guide fluid 105 at the tail end of the discrete sheath 102 has a third surface 105c extending backward from the second side surface 102b of the discrete sheath 102, and a fourth surface 105d connecting the tail end of the third surface 105c and the tail end of the first side surface 102a of the discrete sheath 102. Thus, the guide fluids 105 at the head and tail ends of the discrete sheath 102 are arranged symmetrically at the center, and one side of the guide fluid 105 is an inclined surface, forming a funnel shape at the inlet and outlet of the cooling medium. In another preferred embodiment, the contour lines of the inclined surfaces of the guide fluid 105, namely the second surface 105b and the fourth surface 105d, are Archimedean spirals.

[0030] like Figure 4 As shown, the stator 200 structure of the external rotor motor with a self-cooled discrete sheath 102 mainly includes a stator core 201 and coils 202. In this embodiment, the outer circumferential surface of the stator core 201 is provided with 36 radially arranged stator teeth 203, and each stator tooth 203 is individually wound with a coil 202, for a total of 36 coils 202. The coils 202 belonging to the same phase are connected in series to form a phase winding. When current is passed through the phase winding, a rotating armature magnetomotive force is generated, such as... Figure 6 As shown.

[0031] The rotor dimensions of the external rotor motor with a self-cooled discrete sheath 102, as described above, specifically the axial tilt angle θ of the discrete sheath 102 and the thickness h1 of the samarium cobalt laminated permanent magnet 104, are determined according to the following steps:

[0032] Step 1: Calculate the armature magnetomotive force waveform and its harmonic spectrum when the three-phase windings of the motor are simultaneously sinusoidally excited using the winding function method, such as... Figure 6 and Figure 7 As shown, the relationship between each harmonic and the fundamental frequency is determined;

[0033] Step 2, the angle θ at which the discrete sheath 102 and the samarium cobalt laminated permanent magnet 104 are tilted along the axial direction is half the pole pitch angle corresponding to the relative frequency of the harmonic with the largest amplitude in the armature magnetomotive force spectrum and the fundamental wave. For example... Figure 5 As shown, for the 26-pole, 36-slot motor in this embodiment, the amplitude of the 23rd / 13th harmonic is the largest, and the pole pitch angle relative to the fundamental component is 10 degrees. Therefore, the axial tilt angle θ is 5 degrees.

[0034] Step 3: The lamination thickness h1 of the samarium cobalt laminated permanent magnet 104 is 1 / e of the skin depth of the armature magnetomotive force harmonic with the lowest relative frequency in the permanent magnet. For the 26-pole 36-slot motor in this embodiment, the 7 / 13 and 19 / 13th harmonics have the lowest relative frequencies with the fundamental wave, and the skin depth of these two harmonics in the magnet is 4.28 mm. Therefore, the lamination thickness h1 is 1.58 mm. After determining the rotor size using the above method, the rotor eddy current loss is reduced from 315.41 W to 101.73 W.

Claims

1. A method for determining the rotor dimensions of an external rotor motor, characterized in that, The external rotor motor includes a stator and an external rotor. The external rotor includes a rotor core, which is cylindrical. Several discrete sheaths protruding from the inner wall of the rotor core are fixedly provided. These discrete sheaths are made of magnetically conductive material and are evenly spaced along the circumference of the rotor core. Adjacent discrete sheaths form a cooling medium channel, the axis of which forms an angle with the axial direction of the rotor core. A magnet cavity is provided in the middle of each discrete sheath, and stacked lamellar permanent magnets, arranged axially or circumferentially, are fixedly provided within the magnet cavity. These stacked permanent magnets form rotor poles. The stator includes a stator core, and several stator teeth are provided on the outer circumferential surface of the stator core. Coils are wound around a single stator tooth, and coils belonging to the same phase are connected in series to form a phase winding. The rotor size determination method includes the following steps: Step 1: Calculate the armature magnetomotive force harmonic spectrum when the phase winding is excited by a sinusoidal current using the winding function method. Based on the relationship between the harmonics and the fundamental wave, determine the harmonic with the largest amplitude and the harmonic with the lowest relative frequency to the fundamental wave in the armature magnetomotive force. Step 2: Determine the tilt angle θ as half of the pole moment angle corresponding to the relative frequency of the harmonic with the largest amplitude and the fundamental wave; Step 3: Determine that the thickness h1 of the laminated permanent magnet along the circumferential or axial direction is 1 / e of the skin depth of the lowest relative frequency harmonic in the permanent magnet, where e is the natural logarithm.

2. The method for determining the rotor size of an external rotor motor according to claim 1, characterized in that, The discrete sheath has guide fluids at both ends to guide airflow into the cooling medium channel.

3. The method for determining the rotor size of an external rotor motor according to claim 2, characterized in that, The fluid guide located at the head end of the discrete sheath has a first surface extending forward from the first side of the discrete sheath and a second surface connecting the front end of the first surface and the front end of the second side of the discrete sheath. The fluid guide located at the tail end of the discrete sheath has a third surface extending backward from the second side of the discrete sheath and a fourth surface connecting the tail end of the third surface and the tail end of the first side of the discrete sheath.

4. The method for determining the rotor size of an external rotor motor according to claim 3, characterized in that, The outlines of the second and fourth surfaces are Archimedean spirals.

5. The method for determining the rotor size of an external rotor motor according to claim 1, characterized in that, The discrete sheath is integrally formed with the rotor core.

6. The method for determining the rotor size of an external rotor motor according to claim 1, characterized in that, Each of the discrete sheaths is divided into several segments in the axial direction, and adjacent segments are insulated from each other.

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