JP2649403B2 - AC motor - Google Patents

Description

The present invention relates to an AC motor having a stator having a large number of magnetic poles and a rotor having a large number of permanent magnets.

[Related Art] In the AC motor, the output torque fluctuates irrespective of the coil current due to the positional relationship between the magnetic pole and the permanent magnet during rotation, and so-called cogging torque is generated. Conventionally,
Various proposals have been made to reduce the cogging torque and make the rotation of the AC motor smooth. The simplest way is to increase the distance (gap) between the magnetic poles and the magnets. However, this reduces the output torque of the motor and lowers the efficiency. In contrast, for example,
JP-A-144348 states that the cogging torque can be theoretically reduced to zero by changing the thickness of the multipole magnet in the circumferential direction. However, in this case, the magnet is one annular continuous body. Japanese Patent Application Laid-Open No. Sho 62-104459 attempts to reduce the cogging torque by cutting off the corners of a rectangular magnet to make it octagonal.

Conventionally, ferrite magnets are generally used as permanent magnets, but in recent years, rare-earth magnets having more excellent magnetic properties than ferrite, that is, having higher residual magnetic flux density and coercive force, have been used.

[Problems to be Solved by the Invention] When the cogging torque is reduced by the shape of the magnet, it is necessary to process the magnet into such a shape. However, ferrite magnets and the above rare earth magnets are often difficult to process, which increases the cost of forming. Even if machining is possible, the optimal magnet shape depends on the size of the magnet pitch, gap between magnetic poles, gap between magnetic pole and magnet, etc. There is also the hassle of having to redesign. Further, means for cutting off the corners of the magnet, for example, only partially increases the distance between the magnet and the magnetic pole, and inevitably reduces the output torque to some extent.

Both of the above two prior arts attempt to reduce the cogging torque by changing the gap between the magnetic pole and the magnet, and therefore have the problems of increasing the cost associated with molding and lowering the output torque.

The present invention adopts a simple shape to make the gap between the magnetic pole and the magnet uniform, thereby preventing a reduction in output torque, selecting an optimal size after facilitating formation and reducing processing cost. This enables the cogging torque to be significantly reduced (to zero). That is, the present invention increases the output torque of the motor as much as possible to improve the efficiency of the motor, eliminates the hassle of designing and manufacturing the magnet shape for that purpose, and provides various magnet pitches, gaps between the magnetic poles, and magnetic poles. To provide an AC motor that generally has a cogging torque of approximately zero with respect to the size of the gap between the magnets.

[Means for Solving the Problems] In the present invention for solving the above problems, the length gp between the adjacent magnetic poles is set.
A stator having a plurality of magnetic poles arranged at a constant pitch Pp on the circumference by providing a gap (gap), and a gap having a length g in the radial direction opposed to the magnetic poles to provide a circumference In an AC motor having a rotor having a large number of permanent magnets arranged above, a circumferential length L of each permanent magnet is determined by L = n ・ Pp + ag ・ b ・ gp + c ・ Pp (1). Where n is an arbitrary integer, a is 0.4 to 0.6,
b is set to 0.3 to 0.5 and c is set to -0.06 to 0.04.

[Operation] A description will be given with reference to the schematic diagram of FIG. 1 in which the stator 12 and the rotor 14 of the motor, which are originally circular, are developed linearly.
A large number of magnetic poles 16 are arranged at equal pitch Pp on the stator 12, and a coil is wound around the column portion 16a of each magnetic pole 16, and the tip portion 16b is wider than the column portion 16a. The length of the gap between the adjacent magnetic pole tip portions 16b is gp. The rotor 14 has a large number of long magnets 20 arranged at equal pitches. FIG. 1 shows only one of them. The length of the gap between the pole tip portion 16b and the magnet 20 is gp.

Here, assuming that the length L of the magnet 20 is simply an integral multiple of the magnetic pole pitch Pp (L = n · Pp), the total length of the gap (gp) between the magnetic poles facing the magnet 20 is Regardless of the position, it is always constant. For this reason, if the flow of the magnetic flux between the magnetic pole tip 16b and the magnet 20 is strictly only in the radial direction of the motor (the vertical direction in FIG. 1), this state (that is, L =
n · Pp), no cogging torque is generated. However, in actuality, as shown in the computer simulation results of FIG. 2, the magnetic flux deviates from the radial direction at the corner portion of the magnetic pole tip 16b and the corner portion of the magnet 20, and the rotation direction (in FIGS. 1 and 2). (Horizontal direction). In such a case, the length L of the magnet 20 that minimizes the cogging torque
Deviates from the integral multiple of the magnetic pole pitch Pp, and the additional length L
The value is obtained by adding α.

The present invention determines this additional length as a function of Lα = agg + bgp + cpp (2), the gap length g between the magnetic pole and the magnet, the length gp of the gap between the magnets, and the magnetic pole pitch Pp, The parameters a, b, and c of the respective parameters are set within the above ranges. The reason for this determination is as follows.

Under the arrangement shown in FIG. 1, the length L of the magnet 20 is variously changed, and for each length, the magnetic field is broken as shown in FIG. 2 (in FIG. 2, many curves represent magnetic fluxes). ) Was performed to calculate what the cogging torque (here, the maximum thrust of the rotor 14) would be. As a result, as shown in FIG.
The maximum value of the cogging torque periodically changes (positive or negative) with respect to the magnet length L, and the magnet lengths L1 and L2 when the maximum value of the cogging torque becomes zero are the magnetic pole pitch Pp.
Is slightly longer than the integer multiple of. Where (L1
−Pp) or (L2-2 · Pp) is the additional length Lα.

FIG. 3 is a graph of a result of calculation in which the gap gp between the magnetic poles and the gap length g of the magnetic pole-magnet are fixed to fixed values. FIG. 4 shows the obtained graph. In FIG. 4, all parameters are generalized by dividing by the magnetic pole pitch Pp, but the horizontal axis represents the gap length g / Pp between the magnetic pole and the magnet, and the vertical axis represents the additional length Lα / Pp. The straight line in the figure is drawn using the length gp / Pp of the gap between the magnetic poles as a parameter. In addition,
For the visibility of the figure, only two values of the gap length gp / Pp between the magnetic poles are shown. From Fig. 4, the additional length Lα / P
It can be seen that p is approximately represented by a linear expression of the other two parameters g / Pp and gp / Pp. That is, Lα / Pp = a · (g / Pp) + b · (gp / Pp) + c or Lα = a · g + b · gp + c · Pp. Based on a number of calculations, the coefficients a, b, c
Is found, a = 0.5, b = 0.4, and c = −0.05. Furthermore, as a result of analyzing the effect of the fluctuation of the values of these coefficients on the magnitude of the cogging torque,
In the range of 0.4 ≦ a ≦ 0.6, 0.3 ≦ b ≦ 0.5, −0.06 ≦ c ≦ −0.04, the cogging torque can be suppressed to about 20% or less of the maximum value (the peak height Fm in FIG. 3). It was found that there was no practical problem.

Embodiment An example in which the present invention is applied to a three-phase AC motor 30 having an output of 700 W as shown in FIG. 5 will be described below. In this embodiment, the outer cylinder is a stator 34 having 18 magnetic poles 32 arranged on its inner surface, and the inner cylinder is a rotor having 6 magnets 36 arranged on its outer periphery.
It becomes 38. The tip 32b of the magnetic pole 32 of the stator 34 is at a distance of a radius of 20 mm from the center of rotation O, the magnetic pole pitch on the circumference thereof is Pp = 2 × 20 × π / 18 = 6.98 mm, and the length of the gap between the magnetic poles is gp. = 2.0mm, and the gap length between the magnetic pole and the magnet is g = 0.9mm. By substituting these values into the above equation (2), Lα = 0.5 × 0.9 + 0.4 × 2.0−0.05 × 6.98 = 0.90 Therefore, assuming that n in equation (1) is 2, L = 2 × 6.98 + 0.90 = 14.8mm.

The rotation of the AC motor 30 that determines the circumferential length of the magnet 36 in this manner is smooth, and the cogging torque is substantially zero.

In addition, in the above example, even if n = 1, the cogging torque becomes almost zero as apparent from FIG. 3, but n = 2.
In this case, the distance between the magnets 36 becomes smaller, and a larger output torque can be obtained.

[Effects of the Invention] When the specifications of the magnetic pole pitch, the gap between the magnets, and the gap between the magnetic poles and the magnet are determined when designing the AC motor, the length L of the magnet with respect to the magnetic pole is determined according to the present invention. The cogging torque of the motor can be reduced to almost zero. As a result, the gap between the magnetic pole and the magnet can be reduced while suppressing the generation of cogging torque, so that a highly efficient motor can be obtained. Further, since the shape of the magnet may be simple, machining is facilitated, and a decrease in output torque (a decrease in motor efficiency) due to a change in the shape of the magnet can be avoided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a positional relationship between a magnetic pole and a magnet, FIG. 2 is a magnetic flux diagram as a result of computer simulation, FIG. 3 is a graph showing a change in cogging torque with respect to a length L of the magnet, and FIG. FIG. 5 is a graph showing the relationship between the gap length g between the magnetic pole and the magnet and the additional length Lα of the magnet where the cogging torque becomes zero with respect to the gap length gp between the magnets in a dimensionless manner by the magnetic pole pitch Pp. FIG. 3 is a cross-sectional view of a three-phase AC motor in which the operation of FIG. 16, 32: magnetic pole, 20, 36: magnet

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yukio Inakuma 41 Toyoda Central Research Laboratories, Toyota Chuo R & D Laboratories Co., Ltd. 41, Yokomichi, Toyota Central Research Laboratory Co., Ltd. (72) Inventor, Toshifumi Arakawa 41, Yoji, Chukuji, Nagakute-cho, Aichi-gun, Aichi Prefecture 1 Toyota Motor Central Research Institute, Inc. (56) References (JP, A) JP-A-61-58455 (JP, A)

Claims (1)

(57) [Claims] 1. A stator having a plurality of magnetic poles arranged at a constant pitch Pp on a circumference by providing a gap of a length gp between adjacent magnetic poles, and a stator having a length g in a radial direction opposed to the magnetic poles. In an AC motor including a rotor having a large number of permanent magnets arranged on the circumference with a gap, a circumferential length L of each permanent magnet is represented by L = nｎPp + a ・ g + b ・ gp + c ・ Pp. Where n is an arbitrary integer, a is 0.4 to 0.6,
An AC motor, wherein b is 0.3 to 0.5 and c is -0.06 to 0.04.