JP2017212762A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brushless motor which attains reduction of torque ripple or cogging torque by making a rotor of SPM rotatable in a bidirectional manner and making a magnetization direction of a magnet watching a stator from a rotation center of the rotor into a different polarity in an inverse direction.SOLUTION: A brushless motor comprises a stator and a rotor which is accommodated in the stator and in which separated permanent magnets are mounted at a front side. There are at least two or more electrode pairs in each of permanent magnets, intervals of permanent magnets are not equal, an interval of permanent magnets with adjacent numbers of electrode pairs is made closer to the equal interval just at an in-plane skew angle θon one hand and adjacent permanent magnets which face each other are separated just at the in-plane skew angle θ.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a brushless motor having a different polarity in which a permanent magnet is disposed on a rotor, and more particularly, to a brushless motor having a structure in which cogging torque and torque ripple are reduced by making the arrangement interval of permanent magnets nonuniform with an in-plane skew angle. .

  In recent years, brushless motors in which magnetic poles formed by permanent magnets are provided on the rotor side have been adopted and attracted attention in a wide range of fields. In this type of brushless motor, for example, as shown in FIGS. 1 and 2, a rotor 120 is accommodated in a stator 110, a coil is wound around a slot 111 of the stator 110, and a permanent magnet 121 is formed on the surface of the rotor 120. ~ 128 are arranged. The permanent magnets 121 to 128 are spaced apart from the adjacent permanent magnets by an angle θ0 and are equally spaced. The same applies to a rotor having an SPM (Surface Permanent Magnet) structure in which a permanent magnet is fixed to the outer peripheral surface of a rotor core, and an IPM (Interior Permanent Magnet) structure rotor having a permanent magnet embedded in the rotor core. is there.

  In such a brushless motor, further downsizing and higher output are required, and cogging torque and torque ripple are also required to be suppressed.

  As a motor for solving such a problem, there is a brushless motor disclosed in Japanese Patent Application Laid-Open No. 2011-83047 (Patent Document 1). The brushless motor disclosed in Patent Document 1 provides an asymmetric air gap by arranging the first permanent magnet M1 to the fourth permanent magnet M4 arranged in the rotor core so as to be at unequal angular intervals as seen from the central axis. It is intended to reduce torque ripple and cogging torque while maintaining the torque characteristics of a brushless motor having an equiangular arrangement.

JP 2011-83047 A

  However, the brushless motor of Patent Document 1 is a continuous type rotor, and the magnetizing direction of the magnet viewed from the rotation center of the rotor is the same polarity. Since it is a continuous type rotor, there is a problem that the manufacturing cost increases. In addition, the configuration of the brushless motor of Patent Document 1 assumes a specific rotational direction, and there is a problem that the theoretical basis for the calculation of angles with unequal intervals is unknown.

  The present invention has been made under the circumstances as described above, and an object of the present invention is an SPM rotor that can be rotated in both directions, and the magnetizing direction of the magnet viewed from the rotor rotation center when the stator is viewed. It is an object of the present invention to provide a brushless motor that has a reverse polarity and that reduces torque ripple and cogging torque without skewing the rotor and stator.

The present invention relates to a brushless motor comprising a stator and a rotor housed in the stator and having a separated permanent magnet mounted on the surface side. The object of the present invention is to provide at least two pole pairs of the permanent magnet. The interval between the permanent magnets is not equal, but the interval between the adjacent permanent magnets of the number of pole pairs is close to the equal interval by an in-plane skew angle θ _s , and the adjacent permanent This is achieved by a structure in which magnets are separated by the in-plane skew angle θ _s .

Further, the object of the present invention is that the magnetization direction of the permanent magnet when the stator is viewed from the rotation center of the rotor has opposite polarities between the adjacent permanent magnets, or The in-plane skew angle θ _s is a half cycle of the mechanical angle, which is achieved more effectively.

The brushless motor of the present invention is an SPM rotor, the magnetizing direction of the magnet viewed from the rotation center of the rotor is opposite to the opposite polarity, and the distance between adjacent permanent magnets in the number of pole pairs of the permanent magnet is In this case, the in-plane skew angle θ _{s is} approached with respect to the equal interval, and the adjacent permanent magnets facing each other are separated by the in-plane skew angle θ _s , and the in-plane skew angle θ _s is set as a half cycle of the mechanical angle. Therefore, manufacturing is easy, and it is possible to reduce torque ripple and cogging torque with an inexpensive configuration.

  By mounting the brushless motor on the electric power steering device, it is possible to provide a high-performance electric power steering device in which torque ripple and cogging torque are suppressed and steering feeling is improved.

It is sectional drawing which shows the structural example of a general brushless motor. It is sectional drawing which shows the rotor structural example of a general brushless motor. It is sectional drawing which shows the basic structure of the brushless motor which concerns on this invention. It is sectional drawing which shows the rotor structural example of the brushless motor which concerns on this invention. It is a chart which shows the influence which in-plane skew has on average torque of the brushless motor concerning the present invention. It is a chart which shows the influence which in-plane skew has on torque ripple of the brushless motor concerning the present invention.

The rotor of the brushless motor of the present invention is of the SPM type, the number of pole pairs of the permanent magnet is at least 2 (number of poles is 4 or more), and the interval between the permanent magnets is not equal, but the number of pole pairs adjacent to each other. On the other hand, the interval is made closer to the equal interval by the in-plane skew angle θ _s , and the adjacent adjacent permanent magnets are separated by the in-plane skew angle θ _s , and the stator is rotated from the rotation center of the rotor. The magnetizing direction of the permanent magnets seen in FIG. 3 has opposite polarities between adjacent permanent magnets. As a result, the brushless motor of the present invention can cope with bidirectional rotation, and the in-plane skew angle θ _s which is the optimal unequal interval is theoretically clear. Shown and explained.

FIG. 3 is a sectional view of the brushless motor 100 according to the present invention, and FIG. 4 is a sectional view showing details of the rotor 120. In the present invention, the magnetizing direction of the magnet viewed from the rotation center of the rotor has a so-called different polarity, which is the reverse direction between adjacent magnets. That is, for the permanent magnets 121 to 128 in FIG. 4, for example, the permanent magnets 121, 123, 125, and 127 have the same polarity, and the 122, 124, 126, and 128 have different polarities. In the case of the 8-pole 12-slot brushless motor 100 as shown in FIG. 3, the optimal in-plane skew angle θ _s is 15 ° obtained by dividing 360 ° by the greatest common divisor 24 of “8” and “12”. It can be calculated as half, ie 7.5 °.

A specific calculation process of the optimum in-plane skew angle θ _s will be described below. When the number of pole pairs of the brushless motor is P, consider reducing the sixth component of the electrical angle, which is the main component of torque ripple. Since the mechanical angle is one cycle θ _mp = 360 [deg], one electrical angle cycle θ _ep is expressed by the following formula 1.
(Equation 1)
θ _ep = 360 / P [deg]
Therefore, the mechanical angle θ _t for one cycle of torque ripple is given by
(Equation 2)
θ _t = (360 / P) / 6 = 60 / P [deg]
By setting the in-plane skew angle θ _s to be a half cycle of the mechanical angle θ _t , torque ripple peaks and troughs cancel each other. Therefore, the in-plane skew angle θ _s is obtained by the following formula 3.
(Equation 3)
θ _s = θ _t / 2 = 60 / P / 2 = 30 / P [deg]
From Equation 3, for example, in the case of a motor with 8 poles, that is, the number of pole pairs P = 4, the in-plane skew angle θ _s can be calculated as θ _s = 30/4 = 7.5 [deg].

By adopting such a structure in which the permanent magnets are non-uniformly arranged, the motor of the present invention has an effect equivalent to the skew configuration of the stator and the rotor, and is effective in reducing cogging torque and torque ripple. In other words, when the existing skew and the magnet position of the present invention are moved closer to and away from each other by the in-plane skew angle θ _s , the rotor magnetic pole is displaced in a direction to advance or delay with respect to the rotating magnetic field formed by the stator winding. In common.

3 and 4, the adjacent permanent magnet 121 and the permanent magnet 128 are brought close to each other by the in-plane skew angle θ _s and are opposed to each other, and the adjacent permanent magnet 124 and the permanent magnet 125 are made in-plane skew angle θ. _Move close by _s . Further, the adjacent permanent magnet 122 and the permanent magnet 123 are separated from each other by the in-plane skew angle θ _s , and are opposed to each other, and the adjacent permanent magnet 126 and the permanent magnet 127 are separated from each other by the in-plane skew angle θ _s . By setting the in-plane skew angle θ _s based on the above equation 3, the peaks and valleys of the torque ripple cancel each other.

  Thus, the torque ripple is reduced by offsetting the torque generated at the position where the rotor magnetic pole is advanced and the torque ripple generated at the position where the magnetic pole is delayed with respect to the rotating magnetic field of the stator.

Figure 5 is a plane skew angle theta _s is shows the effect on the average torque, and the average torque plane skew angle theta _s = 0 and 100% reference. Also, FIG. 6, plane skew angle theta _s is shows the effect on the torque ripple, and the torque ripple of the plane skew angle theta _s = 0 and 100% reference. These are summarized in Table 1 below.

なお、上述ではロータコアの表面に永久磁石が配置されているが、表面全面をモールド加工しても良い。

In the above description, the permanent magnet is disposed on the surface of the rotor core, but the entire surface may be molded.

100, 100A Brushless motor 110 Stator 111 Slot 120 Rotor 121-128 Permanent magnet

Claims (3)

In a brushless motor consisting of a stator and a rotor housed in the stator and separated from the permanent magnet mounted on the surface side,
The number of pole pairs of the permanent magnet is at least 2 and the interval between the permanent magnets is not equal, but the interval between the adjacent permanent magnets of the number of pole pairs is set to the in-plane skew angle θ _{s with} respect to the equal interval. And a brushless motor having a structure in which the adjacent permanent magnets facing each other are spaced apart by the in-plane skew angle θ _s . 2. The brushless motor according to claim 1, wherein a magnetization direction of the permanent magnet as viewed from the rotation center of the rotor has opposite polarities between the adjacent permanent magnets. The brushless motor according to claim 1, wherein the in-plane skew angle θ _s is a half cycle of a mechanical angle.

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