Motor stator and rotor structure with low cogging torque and low torque ripple
By optimizing the design of the motor stator and rotor structure, and using stator slots and permanent magnets with specific shapes and layouts, the problems of reduced motor power density and vibration and noise caused by axial electromagnetic force were solved, and a motor stator and rotor structure with low cogging torque and low torque pulsation performance was achieved.
Patent Information
- Application Number
- CN202422990690.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-05
- Publication Date
- 2025-12-09
- Estimated Expiration
- 2034-12-05
AI Technical Summary
In existing electric power steering systems, conventional rotor segmented skew pole, rotor skew pole and stator skew slot schemes lead to reduced motor power density, increased cost, and NVH problems caused by the introduction of axial electromagnetic force.
A motor stator and rotor structure with low cogging torque and low torque ripple is designed. Specific geometries and layouts of the stator core and rotor permanent magnets are adopted, including optimized designs of the stator slots, tooth shoes, and permanent magnets. This ensures good no-load and load performance when the rotor is in direct polarity, and avoids vibration and noise caused by axial electromagnetic forces.
It achieves low cogging torque and low torque ripple performance, simplifies motor structure and manufacturing, reduces costs, and avoids vibration and noise problems caused by axial electromagnetic force, thereby improving the overall performance of the motor.
Smart Images
Figure CN223652020U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of steering system technology, specifically to a motor stator and rotor structure with low cogging torque and low torque pulsation. Background Technology
[0002] In electric power steering (EPS) systems, the motor is required to have extremely low cogging torque and to maintain extremely low torque ripple under different load conditions. Common solutions for reducing motor cogging torque and torque ripple include rotor skew, rotor skew, and stator skew. Currently, mainstream EPS motor suppliers typically adopt a rotor skew design to meet system technical requirements and address manufacturing challenges. However, rotor skew, rotor skew, and stator skew solutions also have some drawbacks: 1. Slightly reduced motor power density and slightly increased motor cost; 2. Complex rotor assembly, increased production line design and manufacturing costs; 3. Rotor skew introduces axial electromagnetic force, which can introduce additional NVH (noise, vibration, and harshness) issues in certain scenarios. Summary of the Invention
[0003] To overcome the shortcomings of the prior art, this utility model provides a motor stator and rotor structure with low cogging torque and low torque pulsation. It optimizes the stator and rotor structure of permanent magnet motors. Permanent magnet motors using this stator and rotor design have good no-load cogging torque and load torque pulsation performance even with direct rotor poles, avoiding the related problems introduced by conventional rotor segmented skew pole, rotor skew pole, and stator skew slot schemes.
[0004] To achieve the above objectives, a motor stator-rotor structure with low cogging torque and low torque pulsation is designed, including a motor stator and a motor rotor. The motor rotor is housed within the motor stator, and the center lines of the motor stator and the motor rotor are the rotation center lines of the motor. The motor stator includes a stator core, and the motor rotor consists of a rotor core and 2p permanent magnets disposed on the outer periphery of the rotor core. Its characteristics are:
[0005] The stator core has N stator slots evenly distributed on the inner circumference of the stator core yoke. A stator shoe is located between two adjacent stator slots, and the distance between two adjacent stator shoes is B. S0 The rotation center point of the stator core is O1, and the minimum distance between two stator teeth with a gap of one stator tooth shoe is L. S1 The minimum width of the stator tooth shoe is L S2The stator toothed shoe includes a stator toothed shoe head and a stator toothed shoe root. The end face of the stator toothed shoe head is an arc surface. The left and right sides of the stator toothed shoe head protrude outwards respectively, forming a left protrusion and a right protrusion of the stator toothed shoe. The center of the stator toothed shoe head is O1, the radius of the arc of the stator toothed shoe head is R1, the central angle of the stator toothed shoe head is θ1, and the chord length corresponding to the stator toothed shoe head is W1.
[0006] The permanent magnet is composed of a permanent magnet arc body, a left permanent magnet arc body, and a right permanent magnet arc body. The permanent magnet arc body has a cylindrical structure, with its center line coinciding with the center line of the permanent magnet. The center of the permanent magnet arc body is O1, the radius of the arc body is R2, the central angle is θ2, and the chord length corresponding to the arc body is W2. The width of the permanent magnet is W. pm1 The angle between the two ends of the permanent magnet and O1 is θ3;
[0007] The left and right sides of the arc of the permanent magnet are respectively connected to the left arc of the permanent magnet and the right arc of the permanent magnet. The centers of the left arc of the permanent magnet and the right arc of the permanent magnet are on the center line of the permanent magnet. The radius of the arc of the left arc of the permanent magnet and the right arc of the permanent magnet is R3, and R2>R3.
[0008] Define angle θ r =360° / 2p; therefore: 0.8≤θ³ / θ r ≤0.95; 0.1≤θ² / θ r ≤0.2; 0.35≤R3 / R2≤0.55; 0.85≤W1 / W2≤1.15; 0.9≤R3 / L S2 ≤1.1; 0.95 <L S1 / W pm1 ≤1.15.
[0009] The stator core yoke of the stator core is a circular ring structure.
[0010] The stator core has N=12 stator slots.
[0011] The number of permanent magnets is 2p = 8.
[0012] The left and right protrusions of the stator tooth shoe are symmetrical about the center line of the stator tooth shoe, and the surfaces of the left and right protrusions of the stator tooth shoe that are close to the permanent magnet are flat or arc surfaces.
[0013] Compared with the prior art, this utility model provides a motor stator and rotor structure with low cogging torque and low torque pulsation, and optimizes the stator and rotor structure of permanent magnet motors. Permanent magnet motors using this stator and rotor design have good no-load cogging torque and load torque pulsation performance even with direct rotor poles, avoiding the related problems introduced by conventional rotor segmented skew pole, rotor skew pole and stator skew slot schemes. Attached Figure Description
[0014] Figure 1 This is an exploded view of the structure of this utility model.
[0015] Figure 2 This is a cross-sectional view of the structure of this utility model.
[0016] Figure 3 This is a cross-sectional view of the stator in this utility model.
[0017] Figure 4 This is a cross-sectional view of the rotor in this utility model.
[0018] Figure 5 The image shows the no-load back EMF waveform of a rotor direct-pole motor using the structure of this utility model.
[0019] Figure 6 The image shows the cogging torque waveform of a rotor direct-pole motor using the structure of this utility model.
[0020] Figure 7 This is a diagram showing the order of the cogging torque of a rotor direct-pole motor using the structure of this utility model.
[0021] Figure 8 The diagram shows the 24th-order torque pulsation of a rotor direct-pole motor using the structure of this utility model under different loads.
[0022] Figure 9 This is a diagram showing the 48th-order torque pulsation of a rotor direct-pole motor using the structure of this utility model under different loads.
[0023] Figure 10 The waveforms of the axial electromagnetic force of a rotor direct-pole motor using the structure of this utility model and the axial electromagnetic force of a rotor segmented skew-pole motor are shown. Detailed Implementation
[0024] The present invention will be further described below with reference to the accompanying drawings.
[0025] To meet the application requirements of low cogging torque and low torque ripple, some existing permanent magnet motors employ solutions such as segmented skewed rotor poles, skewed rotor poles, and skewed stator slots. According to motor theory, permanent magnet motors with segmented skewed rotor poles, skewed rotor poles, and skewed stator slots will have axial electromagnetic forces, the direction of which is related to the motor's rotation direction. These axial electromagnetic forces can cause axial vibration in the motor, and in extreme cases, this axial vibration can lead to serious noise problems.
[0026] To address the aforementioned problems, a motor stator and rotor structure with low cogging torque and low torque ripple is designed, such as... Figures 1 to 4 As shown, a motor stator and rotor structure with low cogging torque and low torque pulsation includes a motor stator and a motor rotor. The motor rotor is housed inside the motor stator, and the center line of the motor stator and the motor rotor is the motor rotation center line 4. The motor stator includes a stator core 1, and the motor rotor is composed of a rotor core 3 and 2p permanent magnets 2 disposed on the outer periphery of the rotor core 3.
[0027] The stator core 1 has N stator slots evenly distributed on the inner circumference of the stator core yoke 11. A stator tooth shoe 12 is located between two adjacent stator slots, and the distance between two adjacent stator tooth shoes 12 is B. S0 The rotation center point of stator core 1 is O1, and the minimum distance between two stator teeth 12 with a spacing of one stator tooth shoe 12 is L. S1 The minimum width of stator toothed shoe 12 is L S2 The stator toothed shoe 12 includes a stator toothed shoe head 121 and a stator toothed shoe root 13. The end face of the stator toothed shoe head 121 is an arc surface. The left and right sides of the stator toothed shoe head 121 protrude outwards respectively, forming a left protrusion 123 and a right protrusion 122. The center of the stator toothed shoe head 121 is O1, the radius of the arc of the stator toothed shoe head 121 is R1, the central angle of the stator toothed shoe head 121 is θ1, and the chord length corresponding to the stator toothed shoe head 121 is W1.
[0028] The permanent magnet 2 is composed of a permanent magnet arc 21, a left-side arc 22, and a right-side arc 23. The permanent magnet arc 21 is a cylindrical arc structure. The centerline of the permanent magnet arc 21 coincides with the centerline of the permanent magnet 2. The center of the permanent magnet arc 21 is O1, the radius of the arc is R2, the central angle is θ2, and the chord length is W2. The width of the permanent magnet 2 is W. pm1 The angle between the two ends of the permanent magnet 2 and O1 is θ3.
[0029] The left and right sides of the arc of the permanent magnet 21 are connected to the left arc 22 and the right arc 23 of the permanent magnet, respectively. The centers of the left arc 22 and the right arc 23 of the permanent magnet are on the center line of the permanent magnet 2. The radius of the arc of the left arc 22 and the right arc 23 of the permanent magnet is R3, and R2>R3.
[0030] Define angle θ r =360° / 2p; therefore: 0.8≤θ³ / θ r ≤0.95; 0.1≤θ² / θ r≤0.2; 0.35≤R3 / R2≤0.55; 0.85≤W1 / W2≤1.15; 0.9≤R3 / L S2 ≤1.1; 0.95 <L S1 / W pm1 ≤1.15.
[0031] The stator core yoke 11 of the stator core 1 has a circular ring structure.
[0032] The stator slots of stator core 1 are N=12.
[0033] The number of permanent magnets 2 is 2p = 8.
[0034] The left protrusion 123 and the right protrusion 122 of the stator tooth shoe are symmetrical about the center line of the stator tooth shoe 12. The surfaces of the left protrusion 123 and the right protrusion 122 of the stator tooth shoe that are close to the permanent magnet 2 are flat or arc surfaces.
[0035] The stator core 1 consists of a stator core yoke 11 and 12 stator tooth shoes 12, each with teeth evenly distributed along the circumference. Each stator tooth shoe 12 consists of a stator tooth shoe head 121 and a stator tooth shoe root 13. The stator tooth shoe 12 is composed of the stator tooth shoe head 121 and a left protrusion 123 and a right protrusion 122 on both sides. The centerline of the stator tooth shoe head 121 coincides with the centerline of the stator tooth shoe 12, and the other stator tooth shoes are symmetrical about the centerline of the stator tooth shoe 12.
[0036] The motor rotor consists of a rotor core 3 and permanent magnets 2, wherein the permanent magnet arcs 21 of the permanent magnets 2 are uniformly distributed along the circumference. On the side of the permanent magnets 2 closest to the stator core 1, the radius and center of the arcs 21 of the permanent magnets 2 are not exactly the same. The centerline of the arc 21 coincides with the centerline of the corresponding permanent magnet 2, and the other arc surfaces of the permanent magnets coincide with the centerlines of their respective permanent magnets 2.
[0037] like Figure 3 The figure shown is a cross-sectional view of the stator core 1 of this invention. The center of the stator core 1 is perpendicular to the rotation center line 4 of the motor, and the intersection point is O1. The minimum distance between two adjacent stator tooth shoes 12 is B. S0 The minimum distance between two stator teeth 12 spaced apart is L. S1 The minimum width of stator toothed shoe 12 is L S2 The head of the stator gear shoe 121 is an arc with center O1, radius R1, central angle θ1, and corresponding chord length W1.
[0038] like Figure 4The diagram shows a cross-sectional view of the permanent magnet 2 of this invention. The permanent magnet arc 21 of the permanent magnet 2 has a circular arc shape. The centerline of the permanent magnet arc 21 coincides with the centerline of the permanent magnet 2, with its center at O1, radius at R2, central angle at θ2, and corresponding chord length at W2. The left and right sides of the permanent magnet arc 21 are the left arc 22 and the right arc 23, respectively. The left arc 22 and the right arc 23 are symmetrical to the centerline of the permanent magnet 2, with their center at O2 and on the centerline of the permanent magnet 2, corresponding to a radius of R3, where R2 > R3. The width of the permanent magnet is W. pm1 The angle between the two endpoints C and D of the permanent magnet arc 21 and O1 is θ3.
[0039] According to calculations, when the stator and rotor of a motor meet certain conditions, the motor rotor adopts a direct-pole scheme, and the motor also has good no-load performance, load performance and minimal axial electromagnetic force.
[0040] Assume the motor rotor has 2p permanent magnets, and define the angle θr = 360° / 2p. Then, 0.8 ≤ θ³ / θ r ≤0.95; 0.1≤θ² / θ r ≤0.2; 0.35≤R3 / R2≤0.55; 0.85≤W1 / W2≤1.15; 0.9≤R3 / L S2 ≤1.1; 0.95 <L S1 / W pm1 ≤1.15.
[0041] like Figure 5 The diagram shows a stator-rotor core motor using the structure of this invention. The rotor is a straight pole motor, and the stator has straight slots. The stator has N = 12 slots, and the rotor has 2p = 8 permanent magnets. The no-load back EMF, cogging torque and its order, and the 24th and 48th order torque ripples of the motor under different loads are shown below. Figures 5-9 As shown. The rotor direct-pole motor using this stator-rotor design has good no-load performance (low back EMF harmonics, low cogging torque) and load performance (low torque pulsation). Figure 10 The waveforms of the axial electromagnetic force of this direct-pole motor and a conventional rotor-segmented skew-pole motor are shown. The conventional rotor-segmented skew-pole motor has a larger axial force (average 6.3N, peak-to-peak 1.55N), while the axial electromagnetic force of this direct-pole motor is smaller (average 0.02N, peak-to-peak 0.29N).
[0042] Through the above design, the newly designed motor stator and rotor core scheme can achieve good no-load and load performance even with a straight rotor pole, meeting the application requirements of low cogging torque and low torque pulsation. However, the motor using this novel stator and rotor core design eliminates the need for rotor segmentation and skewed pole configurations that would lead to electromagnetic axial forces, thus effectively solving the vibration and noise problems caused by internal axial electromagnetic forces. Furthermore, the motor's structural design is simpler, and its manufacturing process is simpler and less expensive than designs with segmented rotor poles, contributing to lower overall costs.
Claims
1. A motor stator and rotor structure with low cogging torque and low torque pulsation, comprising a motor stator and a motor rotor, wherein the motor stator contains the motor rotor, and the center line of the motor stator and the motor rotor is the rotation center line of the motor (4); the motor stator includes a stator core (1), and the motor rotor is composed of a rotor core (3) and 2p permanent magnets (2) disposed on the outer periphery of the rotor core (3), characterized in that: The stator core (1) has N stator slots evenly distributed on the inner circumference of the stator core yoke (11), and stator tooth shoes (12) are located between two adjacent stator slots. The distance between two adjacent stator tooth shoes (12) is B. S0 The rotation center point of the stator core (1) is O1, and the minimum distance between two stator teeth (12) separated by one stator tooth shoe is L. S1 The minimum width of the stator toothed shoe (12) is L S2 The stator toothed shoe (12) includes a stator toothed shoe head (121) and a stator toothed shoe root (13). The end face of the stator toothed shoe head (121) is an arc surface. The left and right sides of the stator toothed shoe head (121) protrude outwards respectively to form a left protrusion (123) and a right protrusion (122) of the stator toothed shoe. The center of the stator toothed shoe head (121) is O1, the radius of the arc of the stator toothed shoe head (121) is R1, the central angle of the stator toothed shoe head (121) is θ1, and the chord length corresponding to the stator toothed shoe head (121) is W1. The permanent magnet (2) is composed of a permanent magnet arc body (21), a left permanent magnet arc body (22), and a right permanent magnet arc body (23). The permanent magnet arc body (21) is a cylindrical arc structure. The center line of the permanent magnet arc body (21) coincides with the center line of the permanent magnet (2). The center of the permanent magnet arc body (21) is O1, the radius of the arc of the permanent magnet arc body (21) is R2, the central angle of the permanent magnet arc body (21) is θ2, and the chord length corresponding to the permanent magnet arc body (21) is W2. The width of the permanent magnet (2) is W. pm1 The angle between the two ends of the permanent magnet (2) and O1 is θ3; The left and right sides of the arc of the permanent magnet arc body (21) are respectively connected to the left arc body (22) and the right arc body (23) of the permanent magnet. The center of the left arc body (22) and the right arc body (23) of the permanent magnet is on the center line of the permanent magnet (2). The radius of the arc of the left arc body (22) and the right arc body (23) of the permanent magnet is R3, and R2>R3; Define angle θ r =360° / 2p; We conclude that: 0.8 ≤ θ³ / θ r ≤0.95; 0.1≤θ² / θ r ≤0.2; 0.35≤R3 / R2≤0.55;0.85≤W1 / W2≤1.15;0.9≤R3 / L S2 ≤1.1;0.95<L S1 / W pm1 ≤1.15。 2. The motor stator and rotor structure with low cogging torque and low torque pulsation according to claim 1, characterized in that: The stator core (1) has a circular ring structure in its stator core yoke (11).
3. The motor stator and rotor structure with low cogging torque and low torque pulsation according to claim 1, characterized in that: The stator core (1) has N=12 stator slots.
4. The motor stator and rotor structure with low cogging torque and low torque pulsation according to claim 1, characterized in that: The number of permanent magnets (2) is 2p = 8.
5. A motor stator and rotor structure with low cogging torque and low torque pulsation according to claim 1 or 2, characterized in that: The left protrusion (123) and the right protrusion (122) of the stator tooth shoe are symmetrical about the center line of the stator tooth shoe (12). The surfaces of the left protrusion (123) and the right protrusion (122) of the stator tooth shoe that are close to the permanent magnet (2) are either flat or arc-shaped.