A low-speed, high-torque permanent magnet motor with an axial outer rotor

Abstract

An axial outer rotor low-speed high-torque permanent magnet motor belongs to the technical field of permanent magnet motors. The purpose of the present application is to provide a permanent magnet synchronous motor with a large torque output and a small torque fluctuation. The present invention includes a hollow casing, in which an outer rotor coaxially arranged with the hollow casing is arranged, an inner stator part is installed in the outer rotor, and a plurality of surface-mounted permanent magnets are installed on the inner wall of the outer rotor. The permanent magnets are evenly arranged axially and circumferentially along the inner side of the outer rotor, and the permanent magnets are divided into a first magnet and a second magnet by an air gap groove. The improved motor structure of the present application reduces the torque fluctuation when the motor is running smoothly, making the motor more stable and reliable in actual operation.

Description

Technical Field

[0001] The motor structure described in the present application belongs to the technical field of permanent magnet motors, and in particular, relates to an axial outer rotor low-speed high-torque permanent magnet motor. Background Art

[0002] Low-speed, high-torque drive systems generally refer to drive systems with a speed lower than 500r / min and a transmission torque greater than 500N·m. They are widely used in machine tools, mines, oil fields, electric power, chemicals, lifting and elevators. For a long time, people have used reducers to reduce speed, increase torque, and increase torque / inertia ratio. Reducers rely on the reduction ratio of large and small gears to work, so they have the disadvantages of low reliability and drive system efficiency, noise and large size, which brings environmental pollution problems caused by lubricating oil and increases manufacturing difficulty and process cost. Permanent magnet motors use permanent magnet excitation, which makes it easier to achieve multi-pole. There are good efficiency and power factor characteristics within a very wide load rate range. Compared with asynchronous motors, permanent magnet motors have relatively higher efficiency and power factor. When the asynchronous motor has a large number of poles, the proportion of the motor excitation current is large, which provides the possibility of achieving low-speed and high-torque direct drive; but the key to the design of low-speed and high-torque permanent magnet synchronous motors is to ensure high torque output while ensuring low-speed operation, and in this process, the torque pulsation caused by various harmonics must be eliminated. The low-speed and high-torque motors in the prior art usually sacrifice the efficiency of the motor in order to maintain high torque output, and the torque fluctuation is too large, and the motor performance cannot be guaranteed. Summary of the invention

[0003] The embodiments of the present invention can provide a permanent magnet motor structure, which reduces the torque fluctuation when the motor is running smoothly. The torque fluctuation when the motor is running smoothly is greatly reduced, the efficiency of the motor is improved, and the motor is more stable and reliable in actual operation.

[0004] The present invention discloses an axial outer rotor low-speed high-torque permanent magnet motor, comprising a hollow casing, an outer rotor coaxially arranged with the hollow casing is arranged in the hollow casing, an inner stator part is installed in the outer rotor, a plurality of surface-mounted permanent magnets are installed on the inner wall of the outer rotor, the permanent magnets are uniformly arranged axially and circumferentially along the inner side of the outer rotor, and the permanent magnets are divided into a first magnet and a second magnet by an air gap groove.

[0005] Furthermore, the outer rotor is a hollow cup-shaped cylindrical structure, and the inner stator part is coaxially installed inside the outer rotor.

[0006] Furthermore, the stator part includes a stator bracket and a stator sleeved outside the stator bracket, and a stator slot extending along the axial direction of the stator is opened on the outer wall of the stator.

[0007] Furthermore, the cross section of the stator slot is a pear-shaped flat-bottom slot structure.

[0008] Furthermore, the stator bracket includes a fixed shaft, and a plurality of fixed blades arranged in a uniform circumferential array are installed on the circumferential side wall of the fixed shaft, and the outer edges of the fixed blades are fixedly connected to the inner wall of the stator.

[0009] Furthermore, the two sides of the hollow casing include a front cover and a rear cover, and the rear cover is fixedly connected to the stator bracket.

[0010] Furthermore, the rear end cover is provided with ventilation holes, which are evenly arranged in a circumferential array around the center of the end cover.

[0011] Furthermore, the outer rotor and the stator are both formed by stacking silicon steel sheets, and the thickness of the silicon steel sheets is 0.35 mm.

[0012] The present invention has the following beneficial effects. The present invention replaces the traditional induction motor external mechanical reduction device to achieve low-speed and high-torque output method, and provides an axial outer rotor horizontal low-speed and high-torque permanent magnet synchronous motor. The motor rotor permanent magnet provided by the present invention adopts a segmented surface-mounted structure, the purpose of which is to reduce the harmonic content of the motor's no-load air gap magnetic flux and back electromotive force and the cogging torque, thereby reducing the torque fluctuation when the motor is running smoothly. The torque fluctuation under the smooth operation of the motor is greatly reduced, making the motor more stable and reliable in actual operation; the structure of the end cover and the inner stator is improved, so that the motor dissipates heat evenly, and the heat dissipation speed is increased by more than 3 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A partial main cross-sectional view of an axial outer rotor low-speed high-torque permanent magnet motor according to an embodiment of the present invention;

[0014] Figure 2 is a schematic diagram of the overall structure of the outer rotor;

[0015] Figure 3 for Figure 2 The structural diagram of the middle A end face;

[0016] FIG4 is a schematic diagram of the permanent magnet structure of an embodiment of the present invention, Figure 4a for Figure 3 The structural diagram of part B in the figure is as follows: Figure 4b This is a schematic diagram of specific structural parameters of the permanent magnet of an embodiment of the present application;

[0017] Figure 5 It is a structural schematic diagram of the inner stator part;

[0018] Figure 6 is a schematic diagram of the stator slot structure. Figure 6a is a cross-sectional diagram of the stator slot. Figure 6b This is the schematic diagram of the structure after the stator slot is filled. Figure 6c Schematic diagram of the structural dimensions of the stator slot;

[0019] Figure 7 is a three-dimensional schematic diagram of the stator bracket;

[0020] Figure 8 It is a structural schematic diagram of the rear end cover of the motor;

[0021] Fig. 9 is a three-dimensional schematic diagram of the motor housing;

[0022] Fig.10 This is a waveform diagram comparing the torque waveform of the motor in this application with the torque waveform of a traditional motor. The torque waveform of the induction motor without a permanent magnet segmented structure and an external reduction device is shown. The motor torque waveform of this embodiment is shown, where the horizontal axis represents time and the vertical axis represents torque.

[0023] In the figure, 1, stator, 1-1, first slot body, 1-2, second slot body, 1-3, slot mouth, 1-4, slot bottom, 1-5, stator winding, 2, permanent magnet, 2-1, first magnet, 2-2, second magnet, 2-3, air gap groove, 3, outer rotor, 4, casing, 5, rear end cover, 5-1, fixing screw hole, 5-2, ventilation hole, 6, front end cover, 7, transmission shaft, 8, stator bracket, 8-1, fixed blade, 8-2, fixing ring. DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the specific technical solution of the present application, the present application is described below in conjunction with the accompanying drawings.

[0025] like Figure 1 As shown, this embodiment provides a low-speed, high-torque permanent magnet motor with an axial outer rotor 3 having a rated speed of 60 r / min and a rated torque of 3183 N / m, which is mainly used in occasions such as cranes and oil pumping units that require low-speed, high-torque output. Since the motor of this embodiment is relatively large in size, a horizontal structure is required, specifically including a hollow housing 4. The horizontal motor hollow housing 4 is as shown in FIG. Fig. 9 As shown, the outer rotor 3, the stator 1 and the stator bracket 8 are coaxially installed in the hollow casing 4 from the outside to the inside, and the two sides of the hollow casing 4 are connected by the front cover 6 and the rear cover 5 respectively;

[0026] This embodiment belongs to the category of speed-regulating permanent magnet synchronous motor. The main dimensions of the speed-regulating permanent magnet synchronous motor can be determined by the required maximum torque and dynamic response performance index. When the maximum electromagnetic torque index of the speed-regulating permanent magnet synchronous motor is T emmax (N·m), the maximum torque, electromagnetic load and main dimensions of the motor can be determined as follows:

[0027]

[0028] Among them: Bδ1 —Air gap magnetic density fundamental wave amplitude (T);

[0029] A—effective value of stator electrical load (A / cm);

[0030] L ef —Effective length of core;

[0031] like Figure 2 As shown, the outer rotor 3 of this embodiment is a hollow cup-shaped cylindrical structure, the inner wall of the outer rotor 3 is recessed to form a plurality of magnetic pole slots, and surface-mounted permanent magnets 2 are installed in the magnetic pole slots. The plurality of permanent magnets 2 are evenly arranged along the inner side of the outer rotor 3 in the axial direction and circumferential direction. The permanent magnets 2 of this embodiment are radially magnetized and adopt a surface-mounted structure, and are evenly distributed and attached to the magnetic pole slots of the inner circle of the rotor;

[0032] In order to reduce the torque fluctuation and harmonic components of the air gap flux density when the motor is running stably and to improve the sinusoidality of the no-load waveform, the permanent magnet 2 of this embodiment is structured as follows: Figure 3 As shown in FIG4 , the middle part of the permanent magnet 2 is sunken downward to form an air gap groove 2-3, and the air gap groove 2-3 divides the permanent magnet 2 into a first magnet 2-1 and a second magnet 2-2. The structure, shape and size of the first magnet 2-1 and the second magnet 2-2 are completely equal. Because the permanent magnet 2 is fragile, and the motor will have a higher temperature rise when it is running, if the magnetic poles are divided into multiple pieces in the actual transfer process, the permanent magnet 2 will be demagnetized if the permanent magnet 2 is segmented too much. In this embodiment, the torque fluctuation at 1mm is the smallest through parameterized simulation with 1mm-2mm as the interval and 0.2mm as the variable. Therefore, the distance L4 between the first permanent magnet 2 and the second permanent magnet 2 is 1mm, and the distance between the two adjacent permanent magnets 2 is 1 / 40 (the circumference of the inner circle of the rotor - 40*the width of each large permanent magnet 2), and the number of magnetic pole slots on the rotor is the same as the number of permanent magnets 2;

[0033] The size of the permanent magnet, together with the rotor magnetic circuit of the motor, determines the magnetic load of the motor, and the magnetic load determines the power density and loss of the motor. For a speed-regulating permanent magnet synchronous motor with a surface-mounted rotor magnetic circuit structure, the size of the permanent magnet can be determined by the following method:

[0034] (Thickness of permanent magnet)

[0035] b M =α p τ2 (permanent magnet width); δ i —Calculated breath length of the motor; B r / B δGenerally, it is between 1.1 and 1.35; τ2 motor rotor pole moment; This embodiment is different from the segmented structure of the permanent magnet type of the splicing structure in the prior art. In this embodiment, an air gap groove is opened in the middle of a permanent magnet, and the extension direction of the air gap groove is collinear with the central axis of the rotor, and the outer edge and the inner edge of the permanent magnet are eccentric structures, which reduces the Fourier decomposition coefficient of the air gap magnetic flux that affects the cogging torque, thereby weakening the cogging torque. Specifically, Figure 4b As shown, the width L1 of the outer side of the permanent magnet 2 is 35.26mm, the width L2 of the inner side of the permanent magnet 2 is 33.66mm, the air gap width L4 of the permanent magnet is 1mm, the depth of the air gap is 3mm, the outer edge and the inner edge of the permanent magnet are arc-shaped structures, the center of the arc where the outer edge is located is O1, the center of the arc where the inner edge is located is O2, and the distance L3 between the two centers is 0.5mm. Different from the traditional unequal thickness permanent magnet structure, the eccentric angle α between the two centers of the permanent magnet of this embodiment is 3.5°, which can reduce the torque fluctuation during the stable operation of the motor and the waveform of the no-load back electromotive force to make it more sinusoidal, and can also reduce the amplitude of the cogging torque of the permanent magnet motor. The reduction of the cogging torque can reduce the vibration effect of the motor and also slow down the torque fluctuation of the motor. At the same time, the starting process of the motor is also more stable. Considering the processing and versatility of the magnetic pole, the shape of the permanent magnet in this embodiment is tile-shaped, and the material is neodymium iron boron NDF30.

[0036] As shown in FIG6 , the stator part of the present embodiment includes a stator bracket 8 and a stator 1 sleeved outside the stator bracket 8. The outer wall of the stator 1 is provided with a stator slot extending along the axial direction of the stator 1. In order to reduce magnetic leakage and make the magnetic lines of force take the simplest path and improve the material utilization rate of the silicon steel sheet, the cross section of the stator slot of the present embodiment is a pear-shaped flat bottom slot structure, such as Figure 5 As shown, the slot opening 1-3 to the slot bottom 1-4 of the stator slot of this embodiment is composed of a first slot body 1-1 and a second slot body 1-2 connected to each other. The width of the first slot body 1-1 increases from the slot opening 1-3 to the second slot opening 1-3, and the width of the second slot body 1-2 decreases from the upper end opening to the slot bottom 1-4. The width of the slot opening 1-3 is smaller than the width of the slot bottom 1-4. The stator 1 winding 1-5 is filled in the second slot body 1-2, and the magnetic pole slot wedge 1-6 is in the first slot body 1-1. Figure 6b As shown;

[0037] The motor of this embodiment adopts an inner stator structure to make the path of the motor magnetic lines of force simple, and also considers improving the utilization rate of the stator slots and the slot full rate to 73%. Therefore, the stator 1 adopts a pear-shaped flat-bottomed slot. The stator slots in the prior art usually adopt pear-shaped slots, trapezoidal slots, etc., and their shapes are usually selected differently according to different motor application occasions. During the operation of the motor, the tooth slot torque is closely related to the shape of the stator. The slot shape parameters of the stator slots of this embodiment are as follows: Figure 6c As shown, in this embodiment, the width of the slot opening 1-3 of the stator slot is D1, the bottom width of the first slot body 1-1 is D2, the width of the slot bottom 1-4 is D3, the height of the slot opening 1-3 is H1, and the height of the second slot body 1-2 is H2. Figure 6c As shown, the specific parameters of the stator slot of the present embodiment are: D1:D2=1:6, D2:D3=5:3, the height ratio of the first slot body 1-1 to the second slot body 1-2 is between 10-12, D1 of the present embodiment is 2.5mm, D2 is 15mm, D3 is 9mm, H1 is 2mm, and H2 is 46.1mm. It can be seen that compared with the traditional stator slot, the height of the second slot body of the stator slot of the present embodiment is larger than the height of the first slot body, which increases the motor slot area when the motor allows, and also makes the number of winding turns and the wire diameter of the wire placed in the slot, which is beneficial to reduce the same and improve the efficiency of the motor; and the opening of the slot is small. This structure is applied to the permanent magnet synchronous motor with large torque of the present embodiment, which is not only conducive to embedding the winding, but also conducive to weakening the cogging torque, reducing the torque fluctuation of the motor, and improving the efficiency of the motor.

[0038] like Figure 7 As shown, the stator bracket 8 includes a fixed shaft and a fixed ring 8-2. Eight fixed blades 8-1 arranged in a uniform circumferential array are installed on the circumferential side wall of the fixed shaft. The fixed blade 8-1 is rectangular. One short side of the fixed blade 8-1 is inserted and connected with the fixed ring 8-2. A plurality of grooves are opened on the inner wall of the stator 1. The position and size of the grooves match and correspond to the fixed blades 8-1. The long side edges of the fixed blades 8-1 are inserted and connected in the grooves of the inner wall of the stator 1, so that the stator bracket 8 is fixedly connected to the stator 1. When the stator 1 is connected through the grooves to form a stable whole, it not only plays a role in fixing the stator 1, but also can make the overall structure of the motor stable, thereby improving the mechanical strength of the motor.

[0039] Furthermore, the stator winding in the present application adopts a 48-slot 40-pole fractional slot concentrated winding structure, which can weaken the high-order harmonic potential generated by the non-sinusoidal distribution of the magnetic pole magnetic field, effectively weaken the amplitude of the tooth harmonic potential, and improve the waveform of the electromotive force; reduce the pulse amplitude of the magnetic flux per pole caused by the change of the air gap magnetic permeability, and reduce the pulse loss on the surface of the magnetic pole; and the use of the fractional slot concentrated winding structure can shorten the end of the motor stator winding to save the space of the motor, reduce the amount of wire used, reduce the resistance of the winding coil, reduce the copper loss, and increase the efficiency of the motor, and the motor efficiency reaches 92.66%.

[0040] In order to reduce the eddy current and hysteresis losses generated by the rotating magnetic field in the iron core, the outer rotor 3 and the stator 1 of this embodiment are both made of stacked silicon steel sheets with a thickness of 0.35 mm, so that the eddy current loss of the silicon steel sheets will be very low.

[0041] The air gap is the gap between the stationary magnetic poles and the rotating armature, i.e., δ i =D i2 -D1,D i2 The inner diameter of the outer rotor (including the thickness of the permanent magnet) D1 is the outer diameter of the inner stator; the air gap determines the size of the magnetic flux through the size of the air gap. If the air gap is large, the leakage magnetic flux will be large, and the efficiency of the motor will be reduced. If the air gap is too small, it is easy to sweep the stator bore. Therefore, it is necessary to control the air gap to a reasonable value to achieve the best effect. The air gap of this embodiment is 2mm, so that the motor can run stably under the premise of high efficiency.

[0042] The assembly process of the present invention is as follows: the stator bracket 8 is extended into the stator 1 along the groove to assemble to form an inner stator part, the inner stator part is extended into the outer rotor 3, and shaft bearings are provided on both sides of the outer rotor 3. The two ends of the transmission shaft 7 of the stator bracket 8 are respectively connected to the outer rotor 3 through the shaft bearings, so that an air gap is left between the outer edge of the inner stator part and the permanent magnet 2 of the outer rotor 3; the assembled stator part and the outer rotor 3 are installed in the casing 4, and the front and rear sides are respectively buckled by the front cover 6 and the rear cover 5, and the front and rear ends of the transmission shaft 7 of the stator bracket 8 extend out of the front cover 6 and the rear cover 5 respectively.

[0043] Ordinary outer rotor 3 motors use flanges to fix the motor stator 1, which cannot effectively meet the cooling requirements of the motor. Therefore, the rear end cover 5 of this embodiment is fixedly connected to the stator bracket 8 by screws passing through the fixing screw holes 5-1, and ventilation holes 5-2 are opened on the rear end cover 5. The ventilation holes 5-2 are evenly arranged in a circumferential array around the center of the end cover. The ventilation holes 5-2 and the gaps between the eight fixed blades 8-1 form a heat dissipation channel. During the operation of the motor, the motor is cooled by air cooling, the heat dissipation effect is uniform, and the heat dissipation speed is increased by more than three times.

[0044] The speed of the low-speed, high-torque permanent magnet synchronous motor in the prior art is usually greater than 60r / min, and the rated torque is usually much smaller than the rated torque value of 3183N / m of this embodiment. Therefore, in order to meet the parameter requirements of this embodiment, it is necessary to use a reduction gear in conjunction with an induction motor transmission system to achieve this. The motor of this embodiment is compared with the transmission system composed of an induction motor with an external reduction device in the prior art that does not have a permanent magnet 2-segment structure. The torque fluctuation effect is as follows: Fig.10 As shown, it can be seen that the torque ripple of the motor of this embodiment is reduced by about 50%.

[0045] The permanent magnet motor of this embodiment is compared with a 15kw inner rotor low-speed and high-torque motor, which has a power of 15kw, a speed of 50r / min, a torque of 2877.87N / m, and an efficiency of 88.2%. Compared with this motor, the motor torque (3183N / m) of this embodiment is larger and the efficiency of the motor (92.66%) is also higher, and the overall performance of the motor is better than that of this motor.

[0046] The above description of the embodiments of the present invention is given for the purpose of example and illustration. They are not exhaustive, nor are they intended to limit the present invention to the contents of these precise descriptions. Under the guidance of the above teachings, there can also be many changes and variations. These embodiments are selected and described only to best explain the principles of the present invention and their practical application, so that those skilled in the art can better apply the present invention in various embodiments and using various changes suitable for the intended specific use. Therefore, it should be understood that the present invention is intended to cover all changes and equivalents within the scope of the following claims.

Claims

1. An axial outer rotor low speed high torque permanent magnet motor, comprising a hollow casing, an outer rotor coaxially arranged with the hollow casing is arranged in the hollow casing, an inner stator part is installed in the outer rotor, characterized in that: A plurality of surface-mounted permanent magnets are mounted on the inner wall of the outer rotor. The permanent magnets are evenly arranged axially and circumferentially along the inner side of the outer rotor. The permanent magnets are divided into a first magnet and a second magnet by an air gap groove. The first magnet and the second magnet are completely equal in structure, shape and size. The stator part includes a stator bracket and a stator sleeved on the outside of the stator bracket, and a stator slot extending along the axial direction of the stator is opened on the outer wall of the stator; the stator bracket includes a fixed shaft, and a plurality of fixed blades arranged in a uniform circumferential array are installed on the circumferential side wall of the fixed shaft, and the outer edges of the fixed blades are fixedly connected to the inner wall of the stator; the two sides of the hollow casing include a front cover and a rear cover, and the rear cover is fixedly connected to the stator bracket; the rear cover is provided with ventilation holes, and the ventilation holes are arranged in a uniform circumferential array around the center of the end cover.

2. According to claim 1, an axial outer rotor low speed high torque permanent magnet motor is characterized in that: The outer rotor is a hollow cup-shaped cylindrical structure, and the inner stator part is coaxially installed inside the outer rotor.

3. According to claim 1, the axial outer rotor low speed high torque permanent magnet motor is characterized in that: The cross section of the stator slot is a pear-shaped flat-bottom slot structure.

4. According to claim 2, an axial outer rotor low speed high torque permanent magnet motor is characterized in that: The outer rotor and the stator are both formed by stacking silicon steel sheets, and the thickness of the silicon steel sheets is 0.35 mm.

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