JP2015180188A - brushless DC motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for making fine cogging torque which may occur in a nine-slot eight-pole brushless DC motor, into stable fine cogging torque.SOLUTION: A polar tooth 10 around which a stator coil 3 is wound is provided in an outer circumferential part of a stator core 4, and a polar tooth surface 6 is provided at a position of the polar tooth 10 facing an inner circumferential surface of a rotor 2. On the polar tooth surface 6, a recess 5 is provided and width of the recess 5 in a circumference direction is settled within an angle range 1.5 to 2 times as large as an angle range in a circumference direction of a gap between neighboring polar teeth 10. A depth dimension D of the recess 5 in a diameter direction is 0.6% or more in an inner diameter of a permanent magnet 8, and an angle range watching the polar tooth 10 from a rotation shaft is 0.65 to 0.8 times as large as an angle obtained by dividing 360 degrees with the number of magnetic poles of the permanent magnet 8 of the rotor 2.

Description

  The present invention relates to a technique for making a cogging torque generated in a 9-slot 8-pole brushless DC motor into a stable minute cogging torque.

  The order of the cogging torque is generally determined by the least common multiple of the number of slots and the number of magnetic poles. It is known that the higher the order, the smaller the cogging torque. As a technique related to cogging torque, one described in Patent Document 1 is known. The content is a technique for reducing the cogging force by the auxiliary groove 15 provided in the auxiliary salient pole part 14 and the main salient pole parts 12a to 12b. In addition, as a technique for suppressing vibration, a permanent magnet described in Patent Document 2 in which the pure radial force between the rotor and the stator is reduced by maintaining the balance of the radial magnetoresistive force between the two. There is a type of salient pole DC motor technology. According to this technique, the balance of the radial magnetoresistive force is achieved by inserting a slot in the magnetic pole face of the magnetic pole end of the salient pole of the motor.

Japanese Examined Patent Publication No. 58-42708 JP-A-8-214525

  However, in patent document 1, since it has an auxiliary salient pole part and the auxiliary salient pole part is provided in a stator part, the space of a stator coil reduces. Therefore, it is impossible to adapt to a large number of slots.

  In Patent Document 2, it is assumed that the pure radial force between the rotor and the stator is reduced by maintaining the balance of the radial magnetoresistive force between the rotor and the stator. ing. Specifically, the circumferential width of the pole face slot is approximately equal to the circumferential dimension between adjacent pole ends, and the pole face slot depth is approximately equal to the radial dimension of the radial gap. . However, under this condition, vibrations caused by imbalance of magnetic force are generated in which the vibration in the frequency band consisting of the number of slots and the number of magnetic poles does not decrease. In general, it is said that the vibration does not decrease with 9 slots and 8 poles. It is not adopted.

  In addition, the cogging torque of a brushless DC motor with 9 slots and 8 poles is very small compared to the slot / magnetic pole ratios of 4: 3, 3: 4, 2: 3, and 3: 2, but the order is generally It appears in the 9th order, not the 72nd order, calculated from the least common multiple. That is, the cogging torque of the 9-slot 8-pole brushless DC motor is as shown in FIG. 6A due to the sum of the cogging torques in which the phases of the 9 slots are canceled. In the 9-slot 8-pole magnetic circuit, the cogging torque T generated by each magnetic pole is expressed by the following equation.

  From this equation, in the brushless DC motor having the structure shown in FIG. 5, the cogging torque generated from an arbitrary pole is symmetrical about the Y axis and the direction of the force is reversed, and the cogging torque is canceled. Torque becomes very small. However, in reality, errors such as a coaxial shift and a magnetized pitch shift occur, so that the gap between the permanent magnet of the rotor and the pole tooth surface of the stator becomes non-uniform and the magnetic force cannot be canceled. For this reason, a large cogging torque is generated as shown by the broken line in FIG.

  In such a background, an object of the present invention is to provide a technique for stably obtaining a minute cogging torque in a 9-slot 8-pole brushless DC motor.

  The invention described in claim 1 is a brushless DC motor including a 9-slot stator and an 8-pole rotor, and a stator core having pole teeth on an outer peripheral portion and a coil wound around the stator core; A rotor having a permanent magnet with an inner diameter of 20 mm or more, which is arranged on the outer periphery of the stator with a gap therebetween, and the portion of the pole teeth facing the inner periphery of the rotor has pole teeth A surface is provided, and the pole tooth surface is provided with a recess, and the angle range of the recess viewed from the rotation center of the rotor is an angle range viewed from the rotation center of the rotor between the adjacent pole teeth. 1.5 to 2 times, the depth dimension in the radial direction of the recess is 0.6% or more of the inner diameter of the permanent magnet, and has a depth that does not interfere with the coil, and the pole tooth width is , Angle seen from the rotation center of the rotor The brushless DC motor is characterized in that the degree range is 0.65 to 0.8 times the value obtained by dividing 360 degrees by the number of magnetic poles of the permanent magnet.

  According to the first aspect of the present invention, a concave portion is formed in the pole tooth surface opposite to the inner peripheral surface of the rotor, the size of the recess is within the above range, and the pole tooth width is further limited, so that stable minute cogging is achieved. A torque brushless DC motor is obtained.

  According to the present invention, there is provided a technique capable of stably obtaining a minute cogging torque in a 9-slot 8-pole brushless DC motor. In addition, a motor with lower noise is provided by reducing the cogging torque.

They are sectional drawing (a) of the brushless DC motor of embodiment, and the A section enlarged view of (a) (a permanent magnet and a rotor yoke are not shown) (b). It is a relationship figure which shows the relationship of the parameter to limit. It is sectional drawing which shows a modification. It is sectional drawing which shows a modification. It is sectional drawing of the brushless DC motor of the conventional structure. A graph (a) showing the cogging torque when there is no coaxial deviation and magnetic pole pitch deviation of the conventional brushless DC motor, and a graph (b) showing the fluctuation of the cogging torque between the brushless DC motor of the embodiment and the conventional brushless DC motor. ). It is a graph which shows the relationship between a cogging torque ratio and (angle range Y of a pole tooth surface recessed part / angle range X between pole teeth). It is a graph which shows the relationship between a cogging torque ratio and (the depth D of the concave part of a pole tooth surface / inner diameter d of a permanent magnet). It is a graph which shows the relationship between a cogging torque ratio and (angle range T of a pole tooth / angle range Z of a permanent magnet).

(Constitution)
Hereinafter, an example of a brushless DC motor using the invention will be described. Fig.1 (a) is sectional drawing which looked at the brushless DC motor of embodiment from the axial direction of the rotating shaft. FIG.1 (b) is an enlarged view of the A section shown in Fig.1 (a). FIG. 2 is a relationship diagram showing the relationship of parameters described later in FIG. FIGS. 1A and 1B show a 9-slot 8-pole brushless DC motor 100. The brushless DC motor 100 is an outer rotor type brushless DC motor having a stator 1 on the inner side and a rotor 2 rotating on the outer side.

  The brushless DC motor 100 includes a stator 1. The stator 1 includes a stator core 4 composed of a plurality of electromagnetic soft irons. The stator core 4 includes nine pole teeth 10 extending in the radial direction. A stator coil 3 is wound around each pole tooth 10. The tip portion of the pole tooth 10 has an umbrella-like structure and is a pole tooth surface 6. This pole tooth surface 6 has an outermost peripheral surface excluding a concave portion 5 described later along a circumferential surface centering on the rotation axis, and is opposed to the inner peripheral surface of the cylindrical permanent magnet 8 with a gap. ing. The permanent magnet 8 is composed of eight magnetic poles 111 to 118 that are magnetized so that the polarities are alternately reversed. The permanent magnet 8 constitutes the rotor yoke 9 and the rotor 2. A concave portion 5 is formed on the pole tooth surface 6 of the pole tooth 10. The bottom surfaces inside the nine recesses 5 are curved along the circumferential surface with the rotation axis as the center, and the distance between the bottom surface inside the recess 5 and the inner peripheral surface of the rotor 2 is a constant value. Has been. According to this structure, the outermost peripheral surface of the nine pole tooth surfaces 6 and the bottom surfaces inside the nine recesses 5 are located on the circumferential surface sharing the center.

  The recess 5 is recessed in the direction of the axial center and has a shape extending in the axial direction. The width of the recess when viewed from the axial direction is set to a value that satisfies the dimensional relationship described below. First, as shown in FIG. 2, a value (this is called an angle range) when the circumferential dimension of the concave portion 5 when viewed from the rotation center of the rotor 2 is regarded as an angle range is defined as Y. Also, let X be the angle range when the gap between the tips of adjacent pole teeth 10 is viewed in the same way as Y. Here, the Y is in a relationship that is in the range of 1.2 to 3 times X. Further, the depth D in the radial direction of the recess 5 is set to 0.5% or more with respect to the inner diameter d of the permanent magnet 8. In the structure using the present invention, a remarkable improvement in characteristics is observed when the inner diameter d of the permanent magnet 8 facing the outer diameter of the stator 1 is φ20 mm or more. Further, the size of the spread of the pole teeth 10 viewed from the axial center is defined as an angle range T viewed in the same manner as described above, and the value of T is an angle Z obtained by dividing 360 degrees by the number of magnetic poles of the permanent magnet 8. 0.58 to 0.8 times. If the depth of the recess 5 is such that it interferes with the stator coil 3, the effect of providing the recess tends to saturate, so the upper limit of D is about the size of interference with the stator coil 3.

  A rotor 2 is disposed on the outer periphery of the stator 1 with a gap therebetween. The rotor 2 includes a multi-pole magnetized permanent magnet 8 and a rotor yoke 9, and is fixed to a shaft (not shown). The shaft (not shown) is rotatably held by a bearing (not shown) of the brushless DC motor 100 by a bearing. On the other hand, the stator 1 is fixed to the housing (not shown). With this structure, a structure in which the rotor 2 rotates with respect to the stator 1 is realized.

  As described above, the brushless DC motor 100 is provided with the pole teeth 10 around which the stator coil 3 is wound around the outer periphery of the stator core 4, and the pole teeth 10 are positioned at positions facing the inner periphery of the rotor 2. 6 is provided. The pole tooth surface 6 is provided with a recess 5, and the circumferential width of the recess 5 is 1.2 to 3 times the angular range of the gap between adjacent pole teeth 10 in the circumferential direction. . The depth D in the radial direction of the concave portion 5 is 0.5% or more of the inner diameter d of the permanent magnet 8, and the angle range when the pole teeth 10 are viewed from the rotation axis is 360 degrees of the magnetic pole of the permanent magnet 8 of the rotor 2. 0.58 to 0.8 times the angle divided by the number.

(Comparative example)
FIG. 5 is a configuration diagram of a brushless DC motor 200 having a conventional 9-slot stator and an 8-pole rotor. The brushless DC motor 200 includes a stator 11. The stator 11 includes a stator core 43 having pole teeth 50 on the outer periphery. A coil 31 is wound around the stator core 43. A rotor 21 having a permanent magnet 81 and a rotor yoke 91 magnetized into eight poles indicated by magnetic poles 121 to 128 is disposed on the outer periphery of the stator 11 with a gap therebetween. The rotor 21 is fixed to a shaft (not shown) and is rotatable by a bearing (not shown). In the brushless DC motor 200, no concave portion is formed on the pole tooth surface 61, and the pole tooth surface 61 is a circumferential surface centered on the rotation axis corresponding to the shape of the inner surface of the rotor 21.

(Advantages of the embodiment)
The present invention can prevent an increase in cogging torque due to an error such as a coaxial shift. That is, as shown in FIG. 1, the recess 5 is provided in the stator core 4, and the recess 5 is provided with an appropriate dimension, so that the cogging torque symmetric with respect to the Y axis described in FIG. The cogging torque attenuation of the pole teeth 10 alone, and the cogging torques of the magnetic pole 112 and magnetic pole 114 and the magnetic pole 116 and magnetic pole 118 are reversed, and a triple force that attenuates the cogging torque can be obtained. Thereby, a minute cogging torque as shown by the solid line in FIG. 6B can be stably obtained. FIG. 6B shows a graph in which the horizontal axis represents the rotation angle and the vertical axis represents the cogging torque. In FIG. 6B, the solid line graph is the measured value of the brushless DC motor 100 of the present embodiment, and the broken line is not provided with the recess 5 in the embodiment, and the outer periphery of the pole tooth surface 6 of the stator 1 is the circumference. It is the measured value of the brushless DC motor 200 of the comparative example of FIG. 5 made into the shape along the surface. As is apparent from FIG. 6B, by providing the recess 5, it is possible to prevent the cogging torque from increasing significantly and to obtain stable motor characteristics.

  In FIG. 7, the spread of the gap between the pole teeth is defined as an angular range X in the circumferential direction when viewed from the rotation axis, and a similar angular range in the circumferential direction of the recess 5 in the pole tooth surface 6 is defined as Y ( Y / X) is a graph with the horizontal axis representing the value of cogging torque and the vertical axis representing the cogging torque ratio. FIG. 2 shows the relationship between X and Y. Here, the cogging torque ratio in FIG. 7 is a parameter defined by (cogging torque when there is a recess) / (cogging torque when there is no recess). According to this definition, when the horizontal axis is 0, the cogging torque ratio is 1. In this case, the smaller the cogging torque ratio is, the lower the cogging torque is. As apparent from FIG. 7, it can be seen that the cogging torque ratio shows a low value when the value of Y / X is around 1.2-3. That is, in FIG. 7, the angular range in the circumferential direction of the concave portion 5 in the pole tooth surface 6 of the pole tooth 10 facing the inner circumference of the rotor 2 of the stator 1 is shown as the angular range in the circumferential direction of the gap between the pole teeth. It has been shown that 1.2 to 3 times is important in obtaining a low cogging torque. FIG. 7 shows data for model A, model B, and model C, which differ in that the outer diameter size of the motor is different. In either case, the Y / X value is 1. There is a tendency that the cogging torque ratio tends to decrease around 2-3.

  In FIG. 8, the depth of the concave portion 5 of the pole tooth surface 6 is D (see FIG. 2), the horizontal axis is (D / d) where the inner diameter of the permanent magnet 8 is d, and the cogging torque ratio is vertical. A graph with axes is shown. The cogging torque ratio in FIG. 8 is defined as a value obtained by dividing the cogging torque of the sample in which the value of the target D is changed by the cogging torque when D / d = 0 (that is, when there is no recess). Also in this case, the smaller the cogging torque ratio is, the lower the cogging torque is, and when the horizontal axis is 0, the cogging torque ratio is 1. From FIG. 8, it can be seen that when the depth D of the recess 5 is 0.5% or more of the inner diameter d of the permanent magnet 8, the cogging torque ratio is remarkably reduced. From this, it can be seen that, in order to reduce the cogging torque, it is effective to set the depth of the recess 5 to a value of 0.5% or more of the inner diameter of the permanent magnet 8.

  In FIG. 9, the angle obtained by dividing 360 degrees by the number of magnetic poles of the permanent magnet 8 is Z, and the value of (T / Z) when the circumferential angle range of the pole teeth 10 is T is the horizontal axis. A graph with the cogging torque ratio on the vertical axis is shown. FIG. 2 shows the relationship between T and Z. The cogging torque ratio in FIG. 9 is (TR1 / TR2) where TR1 is the cogging torque of the sample with the target (T / Z) value changed and TR2 is the cogging torque of T / Z = 0.5. Defined. Also in this case, the smaller the cogging torque ratio is, the lower the cogging torque is, and the cogging torque ratio is 1 when the horizontal axis is 0.5. It can be seen from FIG. 9 that the value of (T / Z) is around 0.58 to 0.8 and the cogging torque ratio shows a low value. That is, in order to reduce the cogging torque, it is preferable that the angle range occupied by the pole teeth 10 is an angle range 0.58 to 0.8 times the angle Z obtained by dividing 360 degrees by the number of magnetic poles of the permanent magnet 8. .

(Modification)
FIG. 3 shows a first modified example of the present invention. FIG. 3 shows the stator core 41. In the stator core 41, the pole teeth 10 a include a flat portion 51. Here, the flat portion 51 has a shape in which the central portion of the flat portion 51 in the circumferential direction is the portion farthest from the inner peripheral surface of the rotor (not shown) and extends straight from the portion to both ends. In this case, the angular range Y in the circumferential direction of the flat portion 51 becomes the angular range of the concave portion of claim 1.

  FIG. 4 shows a second modified example of the present invention. FIG. 4 shows the stator core 42. The stator core 42 includes pole teeth 10b. The pole teeth 10b have a recess 52, and the recess 52 is divided into two portions and formed in pairs at two locations. In this case, the circumferential angle range Y of the concave portion 52 of the pole tooth surface 62 is grasped by the angle between the outer ends of the two pairs of concave portions.

(Other)
The aspect of the present invention is not limited to the individual embodiments described above, and includes various modifications that can be conceived by those skilled in the art, and the effects of the present invention are not limited to the contents described above. That is, various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof. For example, the present invention is also applicable to an inner rotor type motor.

  DESCRIPTION OF SYMBOLS 100 ... Brushless DC motor, 1, 11 ... Stator, 2, 21 ... Rotor, 3, 31 ... Stator coil, 4, 41, 42, 43 ... Stator core, 5, 52 ... Recess, 6, 61, 62 ... Polar tooth surface 8, 81 ... permanent magnets, 9, 91 ... rotor yoke, 10, 10a, 10b, 50 ... pole teeth, 51 ... flat part, 200 ... brushless DC motor of conventional structure, X ... circumferential direction of gaps between pole teeth Y: the angular range in the circumferential direction of the recess angle, Z: an angle obtained by dividing 360 degrees by the number of magnetic poles of the permanent magnet 8, T: the angular range in the circumferential direction of the pole teeth, D: of the concave portion 5 Radial depth, d ... inner diameter d of the magnet.

Claims (1)

A brushless DC motor having a 9-slot stator and an 8-pole rotor,
A stator core having pole teeth on the outer periphery, and a stator having a coil wound around the stator core;
A rotor having a permanent magnet having an inner diameter of 20 mm or more, which is arranged on the outer periphery of the stator with a gap and is multi-pole magnetized,
A portion of the pole teeth facing the inner periphery of the rotor is provided with a pole tooth surface,
The pole tooth surface is provided with a recess,
The angle range seen from the rotation center of the rotor of the recess is 1.5 to 2 times the angle range seen from the rotation center of the rotor between the adjacent pole teeth,
The depth dimension in the radial direction of the recess is 0.6% or more of the inner diameter of the permanent magnet, and has a depth that does not interfere with the coil,
The brushless DC motor is characterized in that the pole tooth width is 0.65 to 0.8 times the value obtained by dividing 360 degrees by the number of magnetic poles of the permanent magnet when viewed from the rotation center of the rotor. .

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