JP2006320168A - Permanent magnet type brushless motor, and electric power steering apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a permanent magnet type brushless motor which suppresses the cogging torque to reduce vibration and noise, and an electric power steering apparatus having good handle-operating feeling using the brushless motor. <P>SOLUTION: The permanent magnet type brushless motor is provided with a rotor having a plurality of permanent magnets which form a plurality of magnetic poles arranged around a rotary shaft or annular permanent magnets which are maltipole-magnetized, and a stator iron core which is provided facing the rotor and wherein a plurality of teeth are projectively provided in the center shaft direction and which is formed as a closed slot having a connecting part which connects between the teeth where the teeth tip ends near the rotor side are adjacent to each other. The inner peripheral surface shape of the rotor iron core which is formed of the tip end part of the teeth facing the periphery of the rotor and of the connecting part is symmetrical with respect to each center line of the teeth, other than a circle. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a permanent magnet type brushless motor, and more particularly to a permanent magnet type brushless motor with low cogging and less vibration and noise. The present invention also relates to an electric power steering device using a permanent magnet type brushless motor.

  An electric power steering device that energizes a steering device of an automobile or a vehicle with the rotational force of a motor applies an auxiliary force to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It has come to force. Since the motor used in such an electric power steering device may be installed in the passenger compartment on the side of the steering wheel, when the motor rotates to urge the steering assist force, vibration and noise are generated. This can give the driver an unpleasant sensation or vibration. In addition, even when steering assistance is not required when driving at high speeds on highways, the cogging torque of the motor is amplified by the reduction ratio of the reducer and transmitted to the steering wheel, causing unpleasant pulsation Is transmitted to. In addition, a motor with a large cogging torque has large vibration and noise during rotation.

  From such a viewpoint, the motor is required to be a motor that does not generate vibration and noise and has a small cogging torque. Conventionally, a motor with a brush has been used as the motor, but a permanent magnet type brushless motor free from problems due to brushes is desired due to recent demands for small size, large output and low frictional force. It is becoming.

  As described above, in Japanese Utility Model Laid-Open No. 5-4738 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-142391 (Patent Document 2), the stator has a closed slot structure, and the magnetic flux flows through the gap between the rotor and each tooth tip. By smoothing the distribution, the change in the magnetic attractive force in the rotational direction is smoothed to reduce the cogging torque. In particular, in Patent Document 2, it is possible to increase the amplitude in synchronism with the magnetic attractive force in the rotational direction generated in each tooth by making the connecting portions that connect adjacent teeth non-uniformly in the circumferential direction. By preventing this, the cogging torque is further reduced.

  In any example, the inner peripheral surface of the stator has an annular shape with a single diameter. When such a closed slot structure is used, the thickness of the connecting portion is increased in order to reduce cogging torque. There is only a way. However, when the thickness of the connecting portion is increased, the magnetic flux passing through the connecting portion increases, and as a result, the amount of interlinkage magnetic flux decreases, resulting in a motor with a small torque.

  Moreover, as an example of trying to reduce the cogging torque by another method, for example, there is JP-A-2003-250254 (Patent Document 3). Since the cogging torque is generated in principle by the least common multiple of the number of poles P and the number of slots S of the motor, Patent Document 3 uses that the larger the cogging torque pulsation number, the smaller the amplitude. The example of Patent Document 3 is an example of 10 poles and 12 slots, and the configuration of the motor is shown in FIG. In the case of a motor with 10 poles and 12 slots, the least common multiple of the number of poles and the number of slots is “60”, so the number of cogging torque pulsations is 60 per revolution. However, such a motor whose ratio of the number of poles to the number of slots is not a ratio of 1: 3 or 2: 3 is very sensitive to mechanical errors and magnetic errors. Alternatively, a cogging torque pulsation number based on the number of slots is generated, and the cogging torque pulsation number is often not the least common multiple of the number of poles and the number of slots. Therefore, 10 or 12 cogging torque pulsations occur in a 10 pole 12 slot motor, and the cogging torque is not reduced as expected.

Further, in the case of such a combination of the number of poles and the number of slots, since the greatest common divisor is “2”, the rotor and the stator have a mechanical angle of 180 °, and the amount of magnetic flux in the stator The part with many is distributed in two places on the diagonal. For this reason, the outer peripheral portion of the stator is strongly attracted to the rotor only at two locations on the diagonal line through the teeth, and as a result, is deformed into an elliptical shape. Since the annular structure is most deformed when a force is applied to two points on such a diagonal line, there is a problem that it becomes a motor with large vibration and noise.
Japanese Utility Model Publication No. 5-4738 JP 2002-142391 A JP 2003-250254 A

  As described above, even if a permanent-magnet brushless motor having a closed slot structure or a permanent-magnet brushless motor focusing on the relationship between the number of poles and the number of slots is used, the cogging torque cannot be reliably reduced in any case. There is a problem. Therefore, when such a permanent magnet type brushless motor is used in an electric power steering apparatus, noise and vibration are transmitted to the driver, which causes anxiety and discomfort.

  The present invention has been made for the above-mentioned circumstances, and an object of the present invention is suitable for a permanent magnet type brushless motor, particularly an electric power steering device, which has high output but low cogging and low noise and vibration. The object is to provide a permanent magnet type brushless motor.

  The present invention relates to a rotor having a plurality of permanent magnets or a multi-pole magnetized annular permanent magnet that forms a plurality of magnetic poles provided around a rotation axis, and a central axis that faces the rotor. A permanent magnet type brushless motor provided with a stator core formed as a closed slot having a plurality of teeth projecting in a direction and having a connecting portion for connecting between the adjacent teeth of the tooth tip portion close to the rotor side The object of the present invention is that the shape of the inner peripheral surface of the stator core formed by the tip portion and the connecting portion of the teeth that are circumferentially opposed to the rotor is a shape other than a circle, and each of the teeth This is achieved by making the shape symmetrical with respect to the center line.

  Further, the object of the present invention is to provide a linear shape portion of each adjacent tooth, wherein the symmetrical shape includes a linear shape orthogonal to the center line, and the shape of the inner peripheral surface of the connecting portion is adjacent to each other. It is a polygonal shape having sides of S (S is the number of teeth) formed by connecting the extended straight lines, or the symmetrical shape is a linear shape orthogonal to the center line. And the inner peripheral surface shape is a polygon having sides of S (S is the number of teeth) × m (integer), or the symmetrical shape is orthogonal to the center line. This is achieved more effectively by including a linear shape and the shape of the inner peripheral surface of the connecting portion being a curved shape, or by the connecting portions being non-equally spaced in the circumferential direction.

  Furthermore, the present invention provides a rotor having a plurality of permanent magnets or a multi-pole magnetized annular permanent magnet that forms a plurality of magnetic poles provided around a rotation axis, and is opposed to the rotor. A stator core formed as a closed slot having a plurality of teeth projecting in the central axis direction and having a connecting portion for connecting the adjacent teeth to the tip end portion of the teeth close to the rotor side, and distributed winding A permanent magnet type brushless motor including the stator having a line, and the object of the present invention is to set the number of poles P of the rotor to P = 2n (n is an integer), and the number of slots S of the rotor. Is achieved by setting S = 6n.

  The electric power steering apparatus of the present invention uses the permanent magnet type brushless motor, and can achieve the object of the present invention.

  According to the present invention, the shape of the inner peripheral surface of the stator core formed by the tip portion and the coupling portion of the teeth that are circumferentially opposed to the rotor (opposed in the circumferential direction) is a shape other than a circle, and each center line of the teeth By making the shape symmetric with respect to the permanent magnet, it is possible to prevent a steep change in the magnetic attractive force in the rotational direction generated between the teeth on the rotor and stator side, so that a permanent magnet with reduced cogging torque Type brushless motor can be provided.

  Further, since the rotor pole number P is P = 2n (n is an integer) and the rotor slot number S is S = 6n, the outer periphery of the stator is strongly attracted to the rotor through the teeth. Therefore, the permanent magnet brushless motor can be provided in which the deformation of the outer periphery of the stator due to the electromagnetic force of the normal direction component is small and vibration and noise are reduced.

  Furthermore, by using a permanent magnet type brushless motor with reduced cogging torque, vibration and noise in the electric power steering device, it is possible to provide an electric power steering device with good handle operation feeling and quiet operation even though the assist force is large. Therefore, it is possible to improve the performance of the electric power steering device.

  First, a description will be given of a first embodiment of the present invention in which cogging torque can be reduced by the shape of the inner peripheral surface of the tip of the tooth being flat.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an example of a sectional structure of a stator 10 and a rotor 20 of a motor, and FIG. 2 shows the stator 10 in more detail.

  As shown in FIG. 1 and FIG. 2, a rotor 20 is coaxially installed inside the stator 10, and the rotor 20 has eight rotating shafts 21 and eight surfaces disposed at equal intervals on the surface of the rotating shaft 21. Permanent magnets 22-1 (S pole), 22-2 (N pole), ..., 22-8 (N pole). The yoke portion 12 of the stator core 11 of the stator 10 has an annular shape, and a plurality (12 in this example) of teeth 1-1, 1-2, ..., 1-12 are provided radially inside the yoke portion 12. A plurality of (in this example, 12) slots 3-1, 3-2,..., 3-12 are formed between the teeth 1-1 to 1-12. The teeth 1-1, 1-2,..., 1-12 are connected by connecting portions 5-1, 5-2,. In addition, the coil | winding 4 is wound by each slot 3 (31--3-12).

  The present embodiment is a stator 10 of a type in which each tip portion (inner peripheral side) of the teeth 1-1 to 1-12 is divided, but a stator of a type in which a tooth root portion (outer peripheral side) is divided. Will be described later.

  3, 4, and 5 are partially enlarged views in which the portion A of FIG. 2 is enlarged, and each feature of the present invention will be described with reference to these drawings.

  In the example of FIG. 3, the shapes of the inner peripheral surfaces of the tips of the teeth 1-1, 1-2, 1-3 that are circumferentially opposed to the rotor 20 are made flat, and the inner peripheral surface of the stator 10 is made overall. It is formed into a polygon. Although not shown in figure, the shape of the inner peripheral surface of the front-end | tip part of teeth 1-4, ..., 1-12 is also flat. In the embodiment of FIG. 2, the shape of the connecting portion C between the teeth 1-2 and the teeth 1-3 connects the straight lines obtained by extending the flat portions B of the adjacent teeth 1-2 and 1-3. This is an embodiment of the shape formed by doing. Although not shown, the shape of the connecting portion C of the teeth 1-3 and 1-4, the shape of the connecting portion C of the teeth 1-4 and 1-5, ..., the shape of the connecting portion C of the teeth 1-11 and 1-12 Is a shape formed by connecting straight lines obtained by extending the flat portions B of adjacent teeth. The flat part B is symmetric with respect to the center line of each of the teeth 1-1 to 1-12. Therefore, the inner peripheral surface of the stator 10 is a regular polygon as a whole.

  In the example of FIG. 4, the shape of the connecting portion C between the teeth 1-2 and the teeth 1-3 is deformed with a relatively short flat portion D obtained by further straightening (flattening) the intersecting portion of the flat portion B. is there. Although not shown, the shape of the connecting portion C between the teeth 1-3 and 1-4, the shape of the connecting portion C between the teeth 1-4 and 1-5, ..., the connecting portion C between the teeth 1-11 and 1-12. Each of the shapes is also formed by a flat portion D. The flat portion D is symmetric with respect to the center line of the connecting portion C. Therefore, the inner peripheral surface of the stator 10 is a polygon (for example, a 24-gon) having more corners than the regular polygon (for example, a regular dodecagon) formed by the flat portion B.

  In the example of FIG. 5, the shape of the connecting portion C between the teeth 1-2 and the teeth 1-3 is deformed with a curved portion E obtained by curving the intersecting portion of the flat portion B with a short portion. Although not shown, the shape of the connecting portion C between the teeth 1-3 and 1-4, the shape of the connecting portion C between the teeth 1-4 and 1-5, ..., the connecting portion C between the teeth 1-11 and 1-12. Similarly, the shape is a curve E. The curved portion E is symmetric with respect to the center line of the connecting portion C. Accordingly, the inner peripheral surface of the stator 10 is a polygon (for example, a 24-gon) having more corners than a regular polygon (for example, a regular dodecagon) formed by the flat portion B, but each flat portion B is curved. Since it is connected by the part E, it becomes a shape close to a circle.

  In any of the shapes described above, the distribution of magnetic flux flowing through the gaps between the rotor 20 and the tips of the teeth 1-1 to 1-12, particularly the distance between the poles of the rotor 20 (between permanent magnets) is different. There is an effect that the steep change in magnetic flux amount applied to the teeth 1-1 to 1-12 is alleviated and smoothed. Therefore, it is possible to prevent the magnetic attractive force in the rotation direction generated in the rotor 20 and each of the teeth 1-1 to 1-12 from changing sharply, thereby reducing the cogging torque. Which shape is optimal depends on the shape of the permanent magnets 22-1 to 22-8, the magnetic path shape of the stator 10, and the like, and may be appropriately selected.

  FIG. 6 shows a conventional motor having a stator configured with an open slot, a conventional motor configured with a closed slot, and a shape of the inner peripheral surface of the tip of the tooth is a circle, and a closed motor. Each cogging torque generated by the motor of the present invention in which the shape of the inner peripheral surface of the tip end portion of the tooth is flat (polygonal) and (the example of 8 poles and 12 slots) is compared. It is shown. The vertical axis represents the cogging torque, and the smaller the better. The horizontal axis indicates the motor angle, and in FIG. 6, it indicates from 0 degrees to 135 degrees.

  The cogging torque generated by a conventional open slot motor is the largest and most undesirable. It can be seen from FIG. 6 that the cogging torque generated by the motor having the closed slot of the present invention and the motor having a flat inner peripheral surface at the tip of the tooth is the smallest and most preferable. . That is, the example of FIG. 3 is most preferable, and then a conventional motor having a closed slot and a circular inner peripheral surface is preferable, and the conventional open slot has a considerably large cogging torque.

  FIG. 7 shows a modification of the present invention. In the stator 10A of the type in which the tooth root portion is divided, the shape of each tip portion of the teeth 1-1 to 1-12 becomes flat, and the inner peripheral surface This is an example in which a regular polygon is formed as a whole. Even in the case of the stator 10A of the type in which the teeth root portion is divided in this way, the generation of cogging torque can be suppressed by the flat shape of each tip portion of the teeth 1-1 to 1-12. . Further, if the connecting portions C are equally spaced in the circumferential direction as in the F portion and F ′ portion of FIG. 5, the portions with strong cogging torque overlap each other if the back surface shape is configured at non-uniform intervals. Less. In other words, since the cogging torque does not occur so as to resonate, the cogging torque can be further suppressed.

  Next, a second embodiment of the present invention for reducing the cogging torque based on the relationship between the number of poles of the motor and the number of slots will be described.

  FIG. 8 shows a 6 pole 18 slot motor as an example satisfying the relationship that the number of poles P of the rotor 20B is P = 2n (n is an integer) and the number of slots S of the rotor 20B is S = 6n. Show. The rotor 20B is composed of a rotating shaft 21B and six permanent magnets arranged on the surface thereof, that is, a permanent magnet 22-1B (S pole), a permanent magnet 22-2B (N pole), and a permanent magnet. 22-3B (S pole),... And permanent magnet 22-6B (N pole).

  On the other hand, the stator 10B includes a stator core 11B, 18 teeth 1-1B to 1-18B, and 18 slots 3-1B to 3-18B. And the relationship of the structure is that the yoke portion 12B of the stator core 11B has an annular shape, and a plurality of teeth 1-1B to 1-18B are provided inside the yoke portion 12B. Eighteen teeth 1-1B,..., 1-18B are arranged radially, and 18 slots 3-1B, 3-2B,..., 3-18B are formed between the teeth. Each of the teeth 1-1B, 1-2B,..., 1-18B has a closed slot structure. In addition, although not shown in figure in each slot 3-1B-3-18B, the coil | winding is wound by distributed winding.

  Such a 6-pole 18-slot configuration can suppress vibration and noise, and the reason will be described below with reference to FIGS.

  FIG. 9 shows an example of characteristics when a current is applied to a motor having a 6-pole 18-slot configuration according to the present invention. FIG. 9 (A) shows a magnetic flux distribution, as well as measurement points, normal directions, and circumferential directions. FIG. 9B shows the relationship between the electromagnetic force acting on the measurement point with respect to the rotation angle (mechanical angle) with respect to the normal direction component and the circumferential direction component. Indicates the displacement of the measurement point with respect to the rotation angle (mechanical angle) with respect to the normal direction component and the circumferential direction component.

  On the other hand, FIG. 10 shows an example of characteristics when a current is applied to a conventional motor configured with 10 poles and 12 slots, and FIG. 10A shows the magnetic flux distribution, as well as measurement points and normal directions. 10A shows the relationship of the electromagnetic force with respect to the rotation angle (mechanical angle) in the normal direction and the circumferential direction, and FIG. 10C shows the amount of displacement with respect to the rotation angle. Are shown for the normal direction component and the circumferential direction component.

  In the motor of the present invention shown in FIG. 9A, the greatest common divisor of the number of poles and the number of slots is “6”, and the stator 10B and the rotor 20B have a magnetic similarity that repeats at an angular interval of 60 degrees. Have. That is, six portions with a large amount of magnetic flux are distributed in the outer peripheral portion of the stator 10B as shown in FIG. This part with a large amount of magnetic flux is where the electromagnetic force of the normal component between the rotor 20B and the stator 10B is strong. Since there are many parts with a larger amount of magnetic flux than a conventional 10-pole 12-slot motor which will be described later, the outer periphery of the stator 10B is deformed to a hexagon, but the span that supports the electromagnetic force of the normal direction component Is as short as 1/6 of the outer peripheral length. Therefore, the displacement of the normal direction component shown in FIG. 9C is relatively small, about 0.2 μm.

  On the other hand, in the conventional 10-pole 12-slot motor shown in FIG. 10 (A), the greatest common divisor of the number of poles and the number of slots is “2”, and the stator and the rotor are magnetic angles that repeat at 180 degrees in mechanical angle. Have similarities. That is, in the outer peripheral portion of the stator, as shown in FIG. 10 (A), locations where the amount of magnetic flux is large are distributed only at two locations on the diagonal line. Therefore, although the electromagnetic force has a normal component equivalent to that in FIG. 9, the stator is largely displaced in an elliptical shape, and the displacement is about 3 μm as shown in FIG. Compared with the motor of, it deforms very greatly. 9 and 10 are comparisons in a state where the same level of torque is output.

  As described above, when the relationship between the number of poles P and the number of slots S is P = 2n (n is an integer) and S = 6n, the outer periphery of the stator is strongly attracted to the rotor through the teeth. Are distributed to locations equal to the number of poles, and the span of the stator outer peripheral length that supports the electromagnetic force of the normal direction component is shortened. As a result, deformation of the outer periphery of the stator is small, and vibration and noise during motor rotation can be suppressed as compared with the conventional case.

  In addition, in either the permanent magnet type brushless motor of the first embodiment or the permanent magnet type brushless motor of the second embodiment, the closed slot structure allows the winding to protrude from the stator and the rotor is locked. Can be prevented. In the above-described embodiment, the rotor is composed of a plurality of permanent magnets that form a plurality of magnetic poles. However, the rotor may be composed of a multi-pole magnetized annular permanent magnet.

  Furthermore, if the permanent magnet type brushless motor of the present invention is used in an electric power steering device, cogging torque is suppressed and vibration and noise from the motor are reduced, so that the handle operation feeling is good and the assist force is large. However, quiet operation can be expected.

It is a sectional structure figure showing an example of a structure of a stator and a rotor of a motor concerning the present invention. FIG. 3 is a cross-sectional structure diagram illustrating a structural example of a stator (a type in which a tooth tip portion is divided) of a motor according to the present invention. It is the elements on larger scale of a connection part. It is the elements on larger scale of the connection part of a straight line. It is the elements on larger scale of the connection part of a curve. It is a characteristic view which compares and shows the cogging torque of the conventional motor and the motor which concerns on this invention. FIG. 4 is a structural diagram showing a structural example of a stator (a teeth base portion is a divided type) of a motor according to the present invention. It is a structural diagram which shows another Example of this invention. It is a figure which shows the example of a characteristic of the motor which concerns on this invention. It is a figure which shows the example of a characteristic of the conventional motor.

Explanation of symbols

10, 10A, 10B Stator 11, 11A, 11B Stator core 12, 12B Yoke part 20, 20B Rotor 21, 21B Rotating shaft 22-1 to 22-8 Permanent magnet 22-1B to 22-8B Permanent magnet 1 1-112 Teeth 3-1 to 3-12 Slot 1-1B to 1-12B Teeth 3-1B to 3-12B Slot 4 Winding 5-1 to 5-12 Connecting portion

Claims (7)

A rotor having a plurality of permanent magnets forming a plurality of magnetic poles provided around the rotation axis or a multi-pole magnetized annular permanent magnet; and a plurality of rotors provided opposite to the rotor in a central axis direction A permanent magnet type brushless motor provided with a stator core formed as a closed slot having a connecting portion for connecting teeth between teeth adjacent to each other, the teeth tip portion close to the rotor side protruding from the teeth, The shape of the inner peripheral surface of the stator core formed by the tip portion and the connecting portion of the teeth that are circumferentially opposed to the rotor is a shape other than a circle, and is symmetrical with respect to each center line of the teeth. A permanent magnet type brushless motor characterized by that. The symmetric shape includes a linear shape orthogonal to the center line, and the shape of the inner peripheral surface of the connecting portion connects straight lines extending from the linear shape portions of adjacent teeth. The permanent magnet type brushless motor according to claim 1, wherein the permanent magnet type brushless motor has a polygonal shape having sides of S (where S is the number of teeth). The left-right symmetric shape includes a linear shape orthogonal to the center line, and the inner peripheral surface shape is a polygon having sides of S (S is the number of teeth) × m (integer). Item 10. The permanent magnet type brushless motor according to Item 1. The permanent magnet brushless motor according to claim 1, wherein the symmetrical shape includes a linear shape orthogonal to the center line, and a shape of an inner peripheral surface of the connecting portion is a curved shape. The permanent magnet type brushless motor according to any one of claims 1 to 4, wherein the connecting portions are non-equally spaced in the circumferential direction. A rotor having a plurality of permanent magnets forming a plurality of magnetic poles provided around the rotation axis or a multi-pole magnetized annular permanent magnet; and a plurality of rotors provided opposite to the rotor in a central axis direction The stator having a stator core formed as a closed slot having a connecting portion for connecting teeth between teeth adjacent to each other, and the tip end portion of the teeth close to the rotor side, and the stator having distributed windings And the number of poles P of the rotor is P = 2n (n is an integer), and the number of slots S of the rotor is S = 6n. Permanent magnet type brushless motor. An electric power steering apparatus using the permanent magnet type brushless motor according to any one of claims 1 to 6.

Images