JP2002078260A - Permanent magnet motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the peak value of counter electromotive voltage. SOLUTION: Two outer peripheral grooves 34 are provided in parallel with an electric motor shaft O on the outer peripheral surface of a rotor core 24 into which permanent magnets 26 are embedded. The angle θ formed by lines that are looking at the motor that O from the two outer peripheral grooves 34, is approximately equal to the angle χ that inside edges A, B of tip portion of two magnetic poles 14a, 14b, with one in between, form at the motor shaft O. Thereby, the upper limit for the motor rotational speed can be elevated. In addition, the output characteristic of the motor is maintained unchanged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a second iron core of a permanent magnet motor having a first iron core having a coil formed thereon and a second iron core having a permanent magnet disposed therein.

[0002]

2. Description of the Related Art There is known an electric motor in which a moving magnetic field is formed by a first iron core having a coil formed therein, and the two magnetic cores are relatively moved by an interaction between the moving magnetic field and a permanent magnet disposed on a second iron core. I have. In such an electric motor,
A so-called back electromotive voltage is generated in the coil of the first iron core by the relatively moving permanent magnet. Since the magnetic flux formed by the permanent magnet changes sharply at the edge of the permanent magnet, a harmonic component is also included in the back electromotive voltage. In particular, in a motor having a small short-term coefficient, which is the reciprocal of the ratio between the number of magnetic poles and the number of permanent magnets, the effect of the edges of the permanent magnets is remarkable, so that the harmonic component increases and the back electromotive force increases. The peak value increases.

[0003] Regarding a generator using a permanent magnet, the peak value of the electromotive force increases due to the harmonic component, and when the short-term coefficient is small, the peak value tends to increase as in the case of the motor. Become.

[0004] An example of an electric motor having a small short-term coefficient is disclosed in Japanese Unexamined Patent Publication No.
-126279. In the motor of this publication, the ratio of the number of magnetic poles of the stator to the number of permanent magnets is 3: 1, and thus the short-term coefficient is 1/3.

[0005]

As described above, the peak value of the electromotive force increases due to the harmonic components of the electromotive force including the back electromotive force. In particular, in a rotating electric machine having a small short-term coefficient, the peak value of the electromotive force increases. The elements that make up the motor and its controller must be able to withstand the peak values described above. For this reason, it is conceivable to increase the withstand voltage of the element.
This leads to an increase in the size of the device. Reduce the magnetic flux density of the permanent magnet,
Although it is conceivable to lower the speed of the motor, in the former case, the output is directly linked to a decrease in the output, and in the latter case, there is a problem concerning the performance of the motor that the operating speed range is limited.

The present invention has been made to solve the above-described problem, and has as its object to provide an electric motor in which an increase in a peak value due to a harmonic component included in an electromotive voltage is suppressed.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, a permanent magnet motor according to the present invention has a first core having a coil formed thereon and a second core having a permanent magnet disposed therein,
By devising the structure of the second core, particularly the structure that affects the magnetic permeability, the peak of the electromotive force due to harmonics is reduced. Specifically, a portion having a low magnetic permeability is formed at a predetermined position of the second iron core to adjust the shape of the magnetic flux, thereby reducing the peak of the electromotive voltage. The low magnetic permeability part is located on the first iron core side of the second iron core with respect to the permanent magnet, and is disposed at least two positions in the driving direction with respect to one permanent magnet. The distance between the centers of the low magnetic permeability portions in the driving direction is substantially equal to the distance between the end portions of the two magnetic poles at both ends of the continuous three magnetic poles of the first iron core on the side of the central magnetic pole.

The present invention can be applied to both a linear motor in which the two iron cores move relatively in a straight line and a rotary motor in which the two iron cores rotate relatively. When applied to a rotary motor, the spacing between the low magnetic permeability portions can be paraphrased as follows. That is, the angle at which the center of at least two low magnetic permeability parts arranged in the rotation direction looks at the rotation center of the electric motor is the center magnetic pole of the magnetic poles located at both ends of the three consecutive magnetic poles of the first iron core. The ends of the side surfaces are approximately equal to the angle at which the rotation center of the motor is viewed.

According to another aspect of the present invention, in a motor having a first iron core having a coil formed thereon and a second iron core having a permanent magnet disposed therein, the ratio of the number of coils to the number of permanent magnets is three. : 1 and a portion having a low magnetic permeability can be formed on the first iron core side of the permanent magnet in the second iron core.

[0010] Further, the low magnetic permeability portion may be a groove provided in the second iron core.

[0011]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a quarter of the motor 10 orthogonal to the motor shaft. The stator 12 has a stator core 16 having magnetic poles 14 arranged at predetermined intervals in a circumferential direction inside a substantially cylindrical portion, and a coil 18 formed by winding a conductive wire around the magnetic pole 14. The part where the coil 18 is stored,
That is, the portion between the magnetic poles 14 is the slot 20. The coil 18 is a so-called concentrated winding formed by winding a conductive wire around one magnetic pole 14. When a current is applied to each coil 18 with an appropriate phase, a rotating magnetic field is formed inside the stator 12.

Inside the stator 12, coaxially therewith,
A substantially cylindrical rotor 22 is arranged. Rotor 22
Has a substantially cylindrical rotor core 24 and a permanent magnet 26 embedded in the rotor core 24. The permanent magnets 26 are arranged near the outer periphery of the rotor core 24 at predetermined intervals in the circumferential direction. Further, the permanent magnet 26 is
4 is completely embedded in the rotor core 24
Is not exposed in the outer peripheral portion of. The portion between the permanent magnets 26 forms a so-called salient pole 28 from which the rotor core 24 protrudes by an amount corresponding to the absence of the permanent magnets 26. A gap 30 is provided in a portion of the permanent magnet 26 adjacent to the rotor in the circumferential direction, in other words, in a portion between the permanent magnet 26 and the salient pole 28.

As shown in the figure, the number of magnetic poles 14 of this electric motor 10 is 24 (6 per 1/4 turn), and the number of permanent magnets 26 is 8 (2 in the same manner). That is, the number ratio is 3: 1, and the short-term coefficient is as small as 1/3. A motor having a small short-term coefficient tends to have a large back electromotive force peak value as described above.
Particularly, the peak value is reduced by optimizing the shape of the outer peripheral surface.

An outer peripheral portion 32 of the rotor core 24 corresponding to the permanent magnet 26, that is, an outer peripheral surface of a portion covering the permanent magnet 26, has two outer peripheral grooves 3 extending parallel to the motor shaft.
4 are provided. The outer peripheral groove 34 has a substantially triangular cross section as shown in the figure. Further, in the present embodiment, the length is formed over the entirety of the rotor core 24 in the axial direction of the electric motor, but may be formed partially. However, all or part of the two outer circumferential grooves are adjacent to each other in the rotation direction. FIG. 2 shows an example of the arrangement of the outer peripheral groove 34. FIG. 2 (a)
(D) shows the outer peripheral surface of the rotor 22, and the arrow indicates the rotation direction of the rotor 22. In (a) to (c), the outer peripheral grooves 34 are arranged adjacent to each other in the rotation direction. In (d), a part in the axial direction (a section indicated by reference numeral L in the drawing) is a part arranged adjacent to the rotation direction.

The outer peripheral grooves 34 are arranged symmetrically with respect to the center of the width of the permanent magnet, and the interval between them is determined as follows. The angle at which the motor shaft O is viewed from the two outer circumferential grooves 34 is indicated by θ. The angle at which the motor shaft O is viewed from the circumferentially inner edges A and B of the distal ends of the magnetic poles such as the magnetic poles 14a and 14b shown in FIG. The interval between the outer peripheral grooves 34 is determined so that the angle θ and the angle χ become substantially equal.

FIG. 3 shows a change in the back electromotive voltage at the time of no load. The motor of the present embodiment, that is, the outer circumferential groove 34
The state of the change of the back electromotive voltage in the case where is provided is represented by a solid line in the figure. On the other hand, the case where the outer peripheral groove is not provided and the shape of the outer peripheral surface is a cylinder is shown by a broken line in the figure. As shown in the figure, when the outer peripheral groove 34 is provided, both the maximum value and the minimum value have a small absolute value.

FIG. 4 shows the back electromotive force when no load is applied when the pair of outer circumferential grooves 34 changes the angle θ at which the motor shaft is viewed. Further, data when the width and the depth of the outer peripheral groove 34 are changed without changing the angle θ are also shown.
Data indicated by “△” indicates the amplitude of the fundamental wave component,
It can be seen that it is not affected by the change in the angle θ. It can be seen that the peak value of the back electromotive voltage indicated by “○” varies depending on the width and depth of the outer peripheral groove, but is minimized in the vicinity where the angle θ coincides with the angle χ.

As described above, by providing the outer peripheral groove 34, the peak value of the back electromotive force can be reduced.
In particular, the angle θ at which the two outer circumferential grooves 34 see the motor shaft is
The peak value can be reduced more effectively when the inner edges of the two magnetic pole tips arranged at a distance from each other are substantially equal to the angle χ at which the motor shaft is viewed.

As is well known, the back electromotive voltage increases as the rotational speed of the motor increases, but if the peak value of the back electromotive voltage is reduced by the present embodiment, the motor can be driven without increasing the withstand voltage of control elements and the like. Can be increased. Further, it is not necessary to lower the magnetic flux density of the permanent magnet to reduce the back electromotive voltage, and the output of the motor is maintained.

In the above embodiment, a groove is provided on the outer periphery of the rotor core to make this portion a low magnetic permeability portion, but the form is not limited to the groove. For example, as shown in FIG.
A hole 40 may be provided at an inner position, and a material 42 having a lower magnetic permeability may be embedded in the core 22. Also,
A material 44 having a low magnetic permeability may be attached or painted on the surface of the core 22 corresponding to the groove 34.

The interval between the outer peripheral grooves 34 is shown in FIG.
As shown in the figure, the distance N between the outer ends of the two outer circumferential grooves 34
However, a predetermined effect can be obtained in a range larger than the interval M between the two side faces of the two magnetic poles 14 on the side of the central magnetic pole side.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a part of a cross section orthogonal to an axis of an electric motor according to an embodiment.

FIG. 2 is a diagram illustrating an example of an arrangement of an outer peripheral groove.

FIG. 3 is a view showing an effect of an outer peripheral groove.

FIG. 4 is a diagram showing a relationship between a position where an outer peripheral groove is provided and a peak value of a back electromotive voltage.

FIG. 5 is a diagram showing a relationship between an outer circumferential groove and the arrangement of magnetic poles.

FIG. 6 is a diagram showing a configuration that can be substituted for an outer peripheral groove.

[Explanation of symbols]

10 motor, 12 stator, 14 (14a, 14
b) Magnetic poles, 16 stator cores, 22 rotors, 24
Rotor core, 26 permanent magnet, 34 outer circumferential groove.

Claims (5)

[Claims] An electric motor comprising: a first core having a coil formed by winding a conductive wire around a magnetic pole; and a second core having a permanent magnet disposed therein, wherein the first core of the permanent magnet in the second core is provided. On the side, a plurality of low magnetic permeability parts are formed in the driving direction of the motor,
The interval between the centers of the low magnetic permeability portions adjacent to each other in the driving direction of the motor is the interval between the end portions of the side faces of the magnetic poles located at both ends of the three consecutive magnetic poles of the first iron core on the central magnetic pole side. An electric motor characterized by being substantially equal. 2. A motor comprising: a first iron core wound around a magnetic pole of a conductor to form a coil; and a second iron core having a permanent magnet disposed therein, wherein the first iron core of the permanent magnet in the second iron core is provided. On the side, a plurality of low magnetic permeability parts are formed in the rotation direction of the electric motor,
The angle at which the centers of the low magnetic permeability portions adjacent to each other in the direction of rotation of the motor look at the rotation center of the motor is determined by the side of the center pole side of the poles located at both ends of the three consecutive magnetic poles of the first iron core. An electric motor characterized in that the ends are substantially equal in angle to the rotation center of the electric motor. 3. An electric motor including a first core in which a coil is formed by winding a conductive wire around a magnetic pole and a second core in which a permanent magnet is disposed, wherein the ratio of the number of the coils to the number of the permanent magnets is three. : 1, wherein a low magnetic permeability portion is formed on the side of the first core of the permanent magnet in the second core. 4. The electric motor according to claim 1, wherein the ratio between the number of the coils and the number of the permanent magnets is 3: 1. 5. The electric motor according to claim 1, wherein the low magnetic permeability portion is a groove.