A segmented skewed pole surface-mount permanent magnet brushless DC motor rotor and its application

Abstract

This invention relates to a segmented skewed-pole surface-mount permanent magnet brushless DC motor rotor and its application, belonging to the field of permanent magnet motor technology. The rotor includes a permanent magnet, an iron core, and a main shaft. The main shaft has at least two axially parallel keyways, with the center lines of adjacent keyways deflected by a preset angle θ along the circumferential direction. A flat key is provided within each keyway. A second groove is provided within the annular iron core, and the iron core is fitted onto the main shaft via the second groove and the flat key. A first groove is provided on the outer surface of the iron core. A rib is provided within the annular permanent magnet, and the annular permanent magnet is fitted onto the iron core via the rib and the first groove. A positioning snap ring is provided on the main shaft outside the annular permanent magnet. This invention can easily achieve segmented skewed poles, reduce cogging torque, facilitate assembly, and provide precise positioning. Furthermore, by introducing delayed commutation, it optimizes the commutation method, compensates for the performance degradation problem of segmented skewed-pole motors, and improves the utilization rate of the permanent magnet.

Description

Technical Field

[0001] This invention relates to a segmented skewed pole surface-mounted permanent magnet brushless DC motor rotor and its application, belonging to the field of permanent magnet motor technology. Background Technology

[0002] Permanent magnet brushless DC motors have advantages such as high power density, high efficiency, low cost, and simple control, and are currently widely used in new energy vehicles, smart homes, wind power generation, and other fields. Based on the position of the magnets in the rotor core, permanent magnet motors can be divided into surface-mounted and embedded types. Among them, surface-mounted magnetic ring structures are easier to process and assemble, have a high yield rate, and have broad application prospects in the field of micro-motors.

[0003] Cogging torque is a problem unique to permanent magnet motors, caused by the tangential component of the interaction force between the stator core and the rotor permanent magnets. During motor operation, cogging torque causes fluctuations in the motor's output torque, affecting control accuracy and smoothness, and leading to vibration and noise issues. Therefore, cogging torque is a problem that must be considered in the design and manufacturing of high-performance permanent magnet motors. To reduce the cogging torque of permanent magnet motors, rotor skew can be used, mainly including continuous skew and segmented skew. For ease of manufacturing, segmented skew is commonly used in the industrial field. Segmented skew divides the permanent magnet into several segments along the axial direction, with the center lines of each segment offset by a certain angle in the circumferential direction. It is necessary to ensure the accuracy of the offset angle; overly complex tooling will affect assembly efficiency and delay production progress.

[0004] Most existing rotor skew pole structures are quite complex. For example, the built-in segmented equivalent rotor skew pole structure disclosed in Chinese patent document CN113507177A requires the use of various rotor laminations of different shapes to ensure that the threaded hole positions of each segment of the iron core are the same during its assembly process. Therefore, multiple sets of molds need to be customized, and the molds need to be changed many times when stamping the rotor, resulting in low production efficiency and high cost.

[0005] When a skewed rotor structure is applied to a permanent magnet motor, the inconsistent magnetomotive force directions of the permanent magnet segments after segmentation lead to a decrease in motor output performance. The control strategy for permanent magnet brushless DC motors generally employs a six-step commutation method, which requires the rotor to commutate six times per electrical cycle. Properly controlling the commutation position can effectively improve the motor's output torque and power density. The commutation timing depends on the rotor position information. Hall effect sensors determine the permanent magnet position by detecting the magnetic flux direction; their small size contributes to a compact motor structure.

[0006] Furthermore, the current rotor skewed pole structure of surface-mount magnetic rings lacks effective positioning and assembly methods, and the skewed pole structure also leads to a reduction in output torque. Therefore, this invention is proposed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a segmented skewed-pole surface-mount permanent magnet brushless DC motor rotor and its application. The centerlines of adjacent keyways are offset at a certain angle in the circumferential direction. A flat key is inserted into the keyway to circumferentially position the rotor core. The core is then bonded to a ring-shaped permanent magnet, causing it to deflect by a preset angle in the same rotational direction around the axis. This structure achieves segmented skewed poles. The permanent magnet motor employs a six-step commutation control, ensuring commutation occurs at the optimal commutation position by setting a delay time. This invention facilitates segmented skewed poles, reduces cogging torque, is easy to assemble, and provides precise positioning. Furthermore, the introduction of delayed commutation optimizes the commutation method, compensates for the performance degradation of segmented skewed-pole motors, and improves the utilization rate of the permanent magnet.

[0008] The technical solution of the present invention is as follows:

[0009] A segmented, skewed-pole surface-mount permanent magnet brushless DC motor rotor includes a permanent magnet, an iron core, and a main shaft. The main shaft has at least two axially parallel keyways, with the center lines of adjacent keyways deflected by a preset angle θ in the circumferential direction. A flat key is provided within each keyway. A second groove is provided within the annular iron core, which is fitted onto the main shaft via the second groove and the flat key. A first groove is provided on the outer surface of the iron core. A rib is provided within the annular permanent magnet, which is fitted onto the iron core via the rib and the first groove. A positioning snap ring is provided on the main shaft outside the annular permanent magnet. The positioning mechanism, consisting of the flat key, groove, and rib, circumferentially positions the annular permanent magnet, causing at least two segments of the annular permanent magnet, arranged axially, to deflect sequentially by a preset angle θ in the same rotational direction around the axis.

[0010] According to a preferred embodiment of the present invention, a magnetic shielding ring is fitted on the main shaft between adjacent permanent magnets. Both sides of the magnetic shielding ring are in contact with the iron core and the permanent magnet. The magnetic shielding ring can effectively reduce magnetic leakage and avoid the problem of excessive repulsive force between two adjacent permanent magnets, which leads to installation difficulties.

[0011] According to a preferred embodiment of the present invention, when the segmented slant angle is equal to the period of the cogging torque, the cogging torque can be effectively reduced. Therefore, the preset angle θ satisfies the following formula:

[0012]

[0013] Where z is the number of stator slots; p is the number of pole pairs; n is the number of permanent magnet segments; LCM(z,2p) is the least common multiple of the number of stator slots and the number of poles;

[0014] According to a preferred embodiment of the present invention, the retaining ring is an E-type retaining ring, which is fitted to the permanent magnet. The E-type retaining ring is interference-fitted with the main shaft, the keyway is interference-fitted with the flat key, the magnetic shielding ring is interference-fitted with the main shaft, the permanent magnet is clearance-fitted with the iron core and is bonded with an adhesive, and the iron core is clearance-fitted with the flat key and is bonded with an adhesive.

[0015] The application of the segmented skewed pole surface-mounted permanent magnet brushless DC motor rotor in permanent magnet brushless DC motors follows these steps:

[0016] (1) A stator is installed on the outside of the rotor of a surface-mounted permanent magnet brushless DC motor. A winding is installed inside the stator. An inverter bridge is connected to the winding. Three Hall sensors are installed at the edge of the stator. The Hall sensor output signal shows a high and low level change, which is used to detect the rotor position and speed. The inverter bridge and Hall sensors are both connected to a controller. The permanent magnet brushless DC motor is assembled.

[0017] (2) The permanent magnet brushless DC motor adopts a six-step commutation control. In the control process, a DC power supply provides a constant voltage to the inverter bridge, which converts the DC power into three-phase power and controls the conduction of different coils. Hall sensors monitor rotor position information, and registers and counters are used to delay the output signal. The inverter bridge switching mode is adjusted according to the commutation logic to complete the commutation of the motor at the optimal position. The process adopts closed-loop control. Hall sensors monitor the actual speed of the motor. When there is a difference between the actual speed and the ideal speed, the controller will adjust the voltage to make the motor speed closer to the desired value.

[0018] According to a preferred embodiment of the present invention, in step (1), three Hall sensors are respectively installed at the 30° electrical angle position of the back electromotive force waveform of the stator A, B, and C phase windings, so that the adjacent two Hall sensors are spaced 120° electrical angle apart.

[0019] According to a preferred embodiment of the present invention, the calculation steps for the delay time of the delayed output signal in step (2) are as follows:

[0020] ① The rotor magnetomotive force F is obtained by vector synthesis of the magnetomotive force generated by each permanent magnet segment. r Vector synthesis employs the parallelogram rule. When synthesizing multiple magnetomotive forces, first, two magnetomotive forces are randomly selected to obtain the combined magnetomotive force. The obtained combined magnetomotive force is then combined with the third magnetomotive force, and so on, until all magnetomotive forces are synthesized to obtain the rotor magnetomotive force F. r The Hall sensor detects the rotational position of the permanent magnet at the edge, and the magnetomotive force F of the permanent magnet closer to the Hall sensor. r1 Rotor magnetomotive force F synthesized by vector r The difference in mechanical angle θ1 can be derived as follows:

[0021]

[0022] Where z is the number of stator slots; p is the number of pole pairs; n is the number of permanent magnet segments; LCM(z,2p) is the least common multiple of the number of stator slots and the number of poles;

[0023] ② The Hall sensor detects the current rotor speed as n. After reaching the commutation position, commutation occurs with a mechanical delay of θ1. The formula for the delay time t can be calculated as follows:

[0024]

[0025] Where θ1 is the magnetomotive force F of the permanent magnet at the edge of the Hall sensor. r1 Rotor magnetomotive force F synthesized by vector r The difference in mechanical angles; n is the actual rotational speed of the motor;

[0026] The delay time t is calculated based on the real-time rotational speed and loaded into the register. The counter starts counting down. After the set delay time t is reached, a commutation signal is output, and the motor commutates and enters the next working state, completing the commutation at the optimal commutation phase, i.e., the stator magnetomotive force F. a Leading rotor magnetomotive force F r 120° electrical angle.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. The segmented skewed rotor structure provided by the present invention has at least two keyways on its main shaft. The center lines of two adjacent keyways are deflected by a preset angle θ in the circumferential direction. A flat key is provided in the keyway, which cooperates with the groove on the iron core for circumferential positioning. A positioning structure is provided on the iron core for circumferential positioning of the annular permanent magnet, so that at least two annular permanent magnets arranged along the axial direction are deflected by a preset angle θ in the same rotation direction around the axis. This facilitates the segmented skewed pole structure, reduces the cogging torque of the motor, reduces the vibration and noise of the motor during operation, and effectively solves the problems of difficult assembly and low positioning accuracy of the current segmented skewed pole structure.

[0029] 2. The segmented skewed-pole rotor provided by this invention is applied to a permanent magnet brushless DC motor. It adopts a six-step commutation control and ensures that the motor commutates at the optimal position by setting a delay time t, which effectively improves the output torque and power density of the motor and makes up for the problem of motor performance degradation caused by the segmented skewed-pole structure. Attached Figure Description

[0030] Figure 1 This is a structural cross-sectional view of the present invention;

[0031] Figure 2 This is an assembly structure diagram of the present invention;

[0032] Figure 3 This is an exploded view of the structure of the present invention;

[0033] Figure 4 This is a schematic diagram of the positioning mechanism of the present invention;

[0034] Figure 5This is a two-dimensional schematic diagram of the application structure of the present invention;

[0035] Figure 6 This is a three-dimensional schematic diagram of the application structure of the present invention;

[0036] Figure 7 This is a schematic diagram of rotor magnetomotive force vector synthesis according to the present invention;

[0037] Figure 8 This is a flowchart of the six-step commutation control of the present invention;

[0038] Figure 9 This is a comparison diagram of the cogging torque waveforms of the permanent magnet brushless DC motor of the present invention with those of the two-segment skewed pole and the unsegmented skewed pole.

[0039] Figure 10 This is a comparison diagram of the output torque waveforms of the permanent magnet brushless DC motor of the present invention with those of the optimal commutation position and ordinary commutation position.

[0040] In the diagram, 1. Snap ring; 2. Permanent magnet; 3. Iron core; 4. Magnetic shielding ring; 5. Flat key; 6. Main shaft; 7. Hall sensor; 8. Stator; 9. Winding;

[0041] 21. Convex ribs;

[0042] 31. First groove; 32. Second groove. Detailed Implementation

[0043] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0044] Example 1:

[0045] A segmented, skewed-pole surface-mount permanent magnet brushless DC motor rotor includes a permanent magnet 2, an iron core 3, and a main shaft 6. The main shaft 6 has two parallel keyways along the axial direction. The center lines of adjacent keyways are deflected by a preset angle θ in the circumferential direction. A flat key 5 is provided within the keyways. A second groove 32 is provided within the annular iron core 3. The iron core 3 is fitted onto the main shaft 6 via the second groove 32 and the flat key 5. A first groove 31 is provided on the outer surface of the iron core 3. A rib 21 is provided within the annular permanent magnet 2. The annular permanent magnet 2 is fitted onto the iron core 3 via the rib 21 and the first groove 31. A positioning snap ring 1 is provided on the main shaft 6 outside the annular permanent magnet 2. The positioning mechanism, consisting of the flat key, groove, and rib, provides circumferential positioning of the annular permanent magnet, causing at least two segments of the annular permanent magnet arranged axially to deflect sequentially by a preset angle θ in the same rotational direction around the axis. The permanent magnet 2 uses neodymium iron boron material and is manufactured using integrated injection molding technology, with radial magnetization.

[0046] A magnetic shielding ring 4 is fitted on the main shaft 6 between adjacent permanent magnets 2. Both sides of the magnetic shielding ring 4 are in contact with the iron core 3 and the permanent magnet 2. The magnetic shielding ring 4 can effectively reduce magnetic leakage and avoid the problem of excessive repulsion between two adjacent permanent magnets 2, which leads to installation difficulties.

[0047] When the segmented slant angle equals the period of the cogging torque, the cogging torque can be effectively reduced. Therefore, the preset angle θ satisfies the following formula:

[0048]

[0049] Where z is the number of stator slots; p is the number of pole pairs; n is the number of permanent magnet segments; LCM(z,2p) is the least common multiple of the number of stator slots and the number of poles;

[0050] The retaining ring 1 is an E-type retaining ring, which is fitted to the permanent magnet 2. The E-type retaining ring is interference-fitted with the main shaft, the keyway is interference-fitted with the flat key, the magnetic shielding ring is interference-fitted with the main shaft, the permanent magnet is clearance-fitted with the iron core and is bonded with adhesive, and the iron core is clearance-fitted with the flat key and is bonded with adhesive.

[0051] The application of the segmented skewed pole surface-mounted permanent magnet brushless DC motor rotor in permanent magnet brushless DC motors follows these steps:

[0052] (1) A stator 8 is installed on the outside of the rotor of a surface-mount permanent magnet brushless DC motor. A winding 9 is installed inside the stator 8. The winding 9 is connected to an inverter bridge. Three Hall sensors 7 are installed at the edge of the stator 8. The three Hall sensors 7 are respectively installed at the 30° electrical angle position of the back electromotive force waveform of the A, B, and C phase windings of the stator, so that the adjacent two Hall sensors are spaced 120° electrical angle apart. The Hall sensor output signal shows high and low level changes, which are used to detect the rotor position and speed. The inverter bridge and Hall sensors are all connected to a controller. The controller adopts a PID control system. The permanent magnet brushless DC motor is assembled.

[0053] (2) The permanent magnet brushless DC motor adopts a six-step commutation control. In the control process, a DC power supply provides a constant voltage to the inverter bridge, which converts the DC power into three-phase power and controls the conduction of different coils. Hall sensors monitor rotor position information, and registers and counters are used to delay the output signal. The inverter bridge switching mode is adjusted according to the commutation logic to complete the commutation of the motor at the optimal position. The process adopts closed-loop control. Hall sensors monitor the actual speed of the motor. When there is a difference between the actual speed and the ideal speed, the controller will adjust the voltage to make the motor speed closer to the desired value.

[0054] The steps for calculating the delay time of the delayed output signal are as follows:

[0055] ① The rotor magnetomotive force F is obtained by vector synthesis of the magnetomotive force generated by each permanent magnet segment. rVector synthesis employs the parallelogram rule. When synthesizing multiple magnetomotive forces, first, two magnetomotive forces are randomly selected to obtain the combined magnetomotive force. The obtained combined magnetomotive force is then combined with the third magnetomotive force, and so on, until all magnetomotive forces are synthesized to obtain the rotor magnetomotive force F. r The Hall sensor detects the rotational position of the permanent magnet at the edge, and the magnetomotive force F of the permanent magnet closer to the Hall sensor. r1 Rotor magnetomotive force F synthesized by vector r The difference in mechanical angle θ1 can be derived as follows:

[0056]

[0057] Where z is the number of stator slots; p is the number of pole pairs; n is the number of permanent magnet segments; LCM(z,2p) is the least common multiple of the number of stator slots and the number of poles;

[0058] ② The Hall sensor detects the current rotor speed as n. After reaching the commutation position, commutation occurs with a mechanical delay of θ1. The formula for the delay time t can be calculated as follows:

[0059]

[0060] Where θ1 is the magnetomotive force F of the permanent magnet at the edge of the Hall sensor. r1 Rotor magnetomotive force F synthesized by vector r The difference in mechanical angles; n is the actual rotational speed of the motor;

[0061] The delay time t is calculated based on the real-time rotational speed and loaded into the register. The counter starts counting down. After the set delay time t is reached, a commutation signal is output, and the motor commutates and enters the next working state, completing the commutation at the optimal commutation phase, i.e., the stator magnetomotive force F. a Leading rotor magnetomotive force F r 120° electrical angle.

[0062] Finite element simulations of cogging torque were performed on the permanent magnet motor of this embodiment and the permanent magnet motor without segmented skewed pole structure. The finite element simulation results are as follows: Figure 9 As shown, the peak cogging torque of the permanent magnet motor without the segmented skewed pole structure is 18.75 mN·m, while the peak cogging torque of the permanent magnet motor with the two-segment skewed pole structure in this embodiment is 7.87 mN·m, with a reduction of about 58% in cogging torque, demonstrating a significant optimization effect.

[0063] The commutation output finite element simulation of the permanent magnet motor in this embodiment and the permanent magnet motor without segmented skewed pole structure were performed. The finite element simulation results are as follows: Figure 10As shown, the motor output torque is 173.91 mN·m under the ordinary commutation method without delayed commutation, while the average output torque of the motor under the commutation method used in this embodiment is 180.91 mN·m, which is an increase of about 4% in output torque.

Claims

1. The use of a segmented skew-pole surface-mounted permanent magnet brushless DC motor rotor in a permanent magnet brushless DC motor, characterized in that, The rotor comprises a permanent magnet, an iron core and a main shaft, the main shaft is provided with at least two key grooves parallel to the axial direction, the center lines of adjacent key grooves are deflected by a preset angle θ in the circumferential direction, a flat key is arranged in the key groove, the iron core is sleeved on the main shaft through the flat key, a first groove is arranged on the outer surface of the iron core, a protruding rib is arranged in the annular permanent magnet, the annular permanent magnet is matched and sleeved on the iron core through the protruding rib and the first groove, and a snap spring for positioning is arranged on the main shaft outside the annular permanent magnet. The preset angle θ satisfies the following formula: Wherein, z is the number of stator slots; p is the number of pole pairs; n is the number of permanent magnet segments; LCM(z, 2p) is the least common multiple of the number of stator slots and the number of poles; The application of the above segmented inclined pole surface-mounted permanent magnet brushless DC motor rotor in a permanent magnet brushless DC motor is as follows: (1) A stator is installed outside the surface-mounted permanent magnet brushless DC motor rotor, the stator is provided with a winding, the winding is connected with an inverter bridge, three Hall sensors are arranged at the edge position of the stator, the Hall sensor output signal presents high and low level changes, and is used for detecting the rotor position and speed, the inverter bridge and the Hall sensor are both connected with a controller, and the permanent magnet brushless DC motor is assembled; (2) The permanent magnet brushless DC motor adopts six-step commutation control, a direct current power supply is used for providing a constant voltage for the inverter bridge in the control process, the inverter bridge converts the direct current into three-phase current, controls the conduction of different coils, the Hall sensor monitors the rotor position information, a register and a counter are used for delaying the output signal, the inverter bridge switch mode is adjusted according to the commutation logic, and the motor is commutated at the best position; The delay time calculation steps of the delayed output signal are as follows: ① The calculation formula of the mechanical angle θ1 is as follows: Wherein, z is the number of stator slots; p is the number of pole pairs; n is the number of permanent magnet segments; LCM(z, 2p) is the least common multiple of the number of stator slots and the number of poles; ② The Hall sensor detects the current rotor speed n, and commutates after delaying the mechanical angle θ1 when reaching the commutation position, and the formula of the delay time t is as follows: Wherein, θ1 is the magnetic potential F of the permanent magnet at the edge of the Hall sensor r1 The rotor magnetic potential F synthesized with the vector r The mechanical angle of phase difference; n is the actual rotating speed of the motor According to the real-time rotation speed, the delay time t is calculated and loaded into a register, and a counter starts timing. After the set delay time t is reached, a commutation signal is outputted, and the motor commutates to the next working state, thereby completing commutation at the optimal commutation position, i.e. the stator magnetic potential F a The leading rotor magnetic potential F r 120° electrical angle.

2. The use of the segmented skew-pole surface-mounted permanent magnet brushless DC motor rotor of claim 1 in a permanent magnet brushless DC motor, characterized in that, A magnetic separation ring is sleeved on the main shaft between adjacent permanent magnets, and the two side surfaces of the magnetic separation ring are attached to the iron core and the permanent magnet.

3. The use of the segmented skew-pole surface-mounted permanent magnet brushless DC motor rotor of claim 1 in a permanent magnet brushless DC motor, characterized in that, The snap spring is selected as an E-shaped snap spring, the E-shaped snap spring is attached to the permanent magnet, the permanent magnet is in clearance fit with the iron core, the iron core is in clearance fit with the flat key, and the iron core and the flat key are bonded through an adhesive.

4. The use of the segmented skew-pole surface-mounted permanent magnet brushless DC motor rotor of claim 1 in a permanent magnet brushless DC motor, characterized in that, In step (1), the three Hall sensors are respectively installed at the 30° electric angle position of the counter electromotive force waveforms of the stator A, B and C phase windings, so that the interval between the two adjacent Hall sensors is 120° electric angle.

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