JP2000350393A - Permanent magnet motor - Google Patents

Abstract

(57) [Problem] To provide a high-output high-precision control permanent magnet motor having a magnet embedded type rotor with reduced cogging torque. SOLUTION: In a permanent magnet motor in which a rotor in which a plurality of permanent magnets are embedded in a rotor yoke in a radial direction and a stator in which a winding is wound around an iron core having a plurality of slots are arranged via a gap. A petal-shaped rotor having an eccentric center of the outer diameter such that an outer diameter passing through an outer contour of the permanent magnet is smaller than an outer diameter passing through a vertex of an adjacent permanent magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo motor,
The present invention relates to a synchronous permanent magnet motor such as a C brushless motor.

[0002]

2. Description of the Related Art Permanent magnet motors are used for servomotors and other control motors because of their high efficiency and good controllability. For example, a radial air gap type permanent magnet motor as shown in FIG. 2 is used for the AC servo motor. The permanent magnet motor shown in FIG.
A rotor 12 having a C-shaped permanent magnet 10 adhered to the surface of the rotor yoke 11 in the radial direction;
And a stator yoke 13 having a plurality of slots 15 and a coil 17 wound around the teeth 14. In the case of the permanent magnet motor shown in FIG. 2, the number of poles of the permanent magnet is 6, and the number of teeth is 18, and the arrow in the permanent magnet indicates the direction of magnetization of the permanent magnet. Further, as shown in FIG. 3, the coil has a three-phase Y connection with distributed winding, and the number of turns of the coil is 30 turns per slot.

By the way, torque of an AC servomotor or the like that requires high-precision torque control must have a small pulsation. Therefore, the cogging torque (torque when no current flows through the coil) and the induced voltage due to the change in the magnetic flux distribution in the air gap due to the positional relationship between the slot of the stator and the permanent magnet when the permanent magnet rotates. It is not preferable that the torque ripple is generated by the pulsation of the torque. Torque ripple not only causes poor controllability but also causes noise.

As a method of reducing the cogging torque, as shown in FIG. 4, a permanent magnet in which the center of the outer diameter of a C-shaped or D-shaped permanent magnet is eccentric so that the end shape of the permanent magnet 20 becomes thinner. Is used. In this way,
The magnetic flux distribution at the end of the permanent magnet, which is the switching portion of the magnetic pole where the change in the magnetic flux distribution is large, becomes smooth, and the cogging torque can be reduced. In FIG. 4, reference numeral 21 denotes a rotor yoke.

Other methods for reducing cogging torque include skewing the armature (stator) yoke and skewing the permanent magnet of the rotor. Skew refers to a state in which rotation is applied in the circumferential direction according to the position in the axial direction. When skew is applied to the armature (stator) yoke, the laminated steel plates must be skewed and stacked, or the windings must be accommodated in the skewed stator slots, which makes the process cumbersome. Then, a method of skewing and fixing the permanent magnet 30 of the rotor is adopted. The skew angle (AOB) 33 at this time is selected to be 1/2 or 1 times the slot pitch of the normal stator. In FIG. 5, 31 is a rotor yoke, 32 is a shaft, and A
Is the center point of the upper permanent magnet end face, B is the center point of the lower permanent magnet end face, and O is the axis center.

However, in a permanent magnet motor in which a permanent magnet is attached to the surface of a rotor yoke with an adhesive or the like as shown in FIG. 2, the centrifugal force applied to the permanent magnet during rotation causes the permanent magnet to rotate.
There is a risk that the permanent magnet will come off the rotor and scatter. As a result, the permanent magnet is caught in the gap, and the permanent magnet motor stops suddenly. For example, if this type of motor is used for electric power steering of an automobile, in the worst case, the steering locks, and the steering becomes impossible, which is fatal. Therefore, in order to prevent the permanent magnet from coming off the rotor, as shown in FIG. 2, a nonmagnetic sleeve 16 made of aluminum or the like is put on the surface of the permanent magnet, or glass fiber is impregnated with epoxy resin. The tape is wrapped and heat cured. However, if the sleeve or tape is too thick, the output of the motor is reduced. Therefore, the thickness is selected from about 0.1 mm to 0.3 mm, but the strength for holding down the permanent magnet is not sufficient. A strong and thin sleeve or tape is expensive to manufacture and leads to an increase in the cost of the permanent magnet motor.

As a rotor structure in which a permanent magnet is not scattered, there is a magnet embedded type rotor in which a permanent magnet 40 is embedded in a rotor yoke 41 as shown in FIG. The magnet-embedded rotor yoke is manufactured by punching out a silicon steel plate with an electromagnetic steel plate of about 0.5 mm and laminating them. Due to recent improvements in punching technology, the manufacturing cost of this magnet embedded rotor yoke is not high. However, since this type of rotor has a permanent magnet embedded inside, the influence of the shape of the permanent magnet on the magnetic flux distribution on the rotor surface is smaller than that of the surface magnet type shown in FIG. Therefore, the magnet-embedded rotor cannot sufficiently reduce the cogging torque by changing the shape of the permanent magnet, and thus generally has a problem that the cogging torque is larger than that of the surface magnet rotor.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-power, high-precision control permanent magnet motor having a magnet embedded type rotor with reduced cogging torque.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and have made the following improvements to a permanent magnet motor having a magnet-embedded rotor that does not cause the permanent magnet to scatter. In addition, smooth rotation without torque unevenness was realized. That is, the present invention provides a permanent magnet in which a rotor in which a plurality of permanent magnets are embedded in a rotor yoke in the radial direction and a stator in which a winding is wound around an iron core having a plurality of slots are arranged via a gap. In the motor,
A petal-shaped rotor having an eccentric center of the outer diameter such that an outer diameter passing through an outer contour of the permanent magnet is smaller than an outer diameter passing through a vertex of an adjacent permanent magnet. It is a permanent magnet motor.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. As described above, in the permanent magnet motor having the magnet-embedded rotor, the outer diameter passing through the outer contour of the permanent magnet is smaller than the outer diameter passing through the top of the contour of the adjacent permanent magnet. Thus, the present invention has a petal-shaped rotor in which the center of the outer diameter of the rotor is eccentric. Specifically, the center of the outer diameter is eccentric so that the outer diameter passing through the outer contour of the permanent magnet is smaller than the outer diameter passing through the top of the contour of the adjacent permanent magnet, and the amount of eccentricity is equal to or greater than the thickness of the magnet. And a petal-shaped rotor. As a result, smooth rotation without unevenness in torque is achieved, and cogging torque is reduced. As shown in FIG. 1, the permanent magnet motor of the present invention has a structure in which a rotor 3 has permanent magnets 1 magnetized with N and S poles alternately arranged in a radial direction inside a rotor yoke 2. ing.
The shape of the permanent magnet 1 is a D-shaped cross section in FIG. 1, but may be a C shape or a rectangle as shown in FIGS. 7 (b) and 7 (c). As other configurations of the permanent magnet motor,
Stator yoke 4 having a plurality of slots 6 and teeth 5
The stator composed of the coil 7 wound on the rotor 3 is arranged with the rotor 3 via a gap as in the conventional example of FIG. Note that the permanent magnet motor illustrated in FIG. 1 has six permanent magnet poles and eighteen teeth.

As shown in FIG. 1, the surface shape of the rotor 3 is a petal shape in which the outer diameter passing through the outer contour of the permanent magnet is smaller than the outer diameter passing through the vertex of the contour of the adjacent permanent magnet. Specifically, as shown in FIG. 7A, the center of the outer diameter of the rotor yoke is eccentric at each magnetic pole.
Also, the thinnest part of the rotor yoke outside the permanent magnet, if too thick, the magnetic flux of the permanent magnet is short-circuited in the rotor yoke, and the utilization efficiency of the permanent magnet is reduced. Minimum wall thickness 0.5 required to prevent scattering
mm is selected. Further, as described above, the cogging torque is caused by the fact that the magnetic flux distribution in the air gap changes due to the positional relationship with the slot of the stator when the permanent magnet rotates, so that the adjacent portion which is the switching portion of the magnetic pole is used. By increasing the length between the magnetic poles, the change in the air gap magnetic flux distribution is reduced, and the cogging torque can be reduced. In a preferred embodiment of the present invention, the rotor has a plurality of axial directions, and the cogging torque can be further reduced by disposing the permanent magnets in the circumferential direction with respect to each axial direction.

[0012]

The present invention will be described in detail below with reference to embodiments. Note that N
Although a d-Fe-B-based permanent magnet will be described, the present invention is not limited to an Nd-Fe-B-based magnet. The permanent magnet was manufactured by the following steps. Ingots were prepared by melting and casting in a vacuum melting furnace using Nd, Fe, Co, M (M is Al, Si, Cu) having a purity of 99.7% by weight and B having a purity of 99.5% by weight, respectively. The ingot was coarsely pulverized with a jaw crusher and further jet mill pulverized in a nitrogen stream to obtain a fine powder having an average particle size of 3.5 μm. This fine powder is subjected to a vertical magnetic field press in a magnetic field of 12 kG,
Molding was performed at a molding pressure of 1.0 t / cm ² . This compact was sintered at 1090 ° C. for 1 hour in Ar gas,
Heat treatment was performed at 80 ° C. for 1 hour. Thereafter, grinding was performed with a grindstone to obtain a C-shaped permanent magnet. The characteristics of this permanent magnet are as follows: Br: 13.0 kG, iHc: 15 kOe, (B
H) max: 40 MGOe.

Comparative Example As a comparative example, the cogging torque of a surface magnet type permanent magnet motor having the dimensions shown in FIG. 6 where the depth of the rotor and the stator is 30 mm, and the permanent magnet motor without turning on the power, are shown. When the motor is rotated at a constant speed (a permanent magnet motor is used as a generator), an induced voltage (Electric Motive F) generated between the three-phase windings is generated.
orce) was measured. In FIG. 6, arrows in the permanent magnet 40 indicate the direction of magnetization of the permanent magnet, and the coil 46 has a three-phase Y connection with distributed winding as shown in FIG. Is 3 turns per slot
0 turns. The cogging torque was measured by fixing a shaft of a permanent magnet motor to a torque detector and rotating one of the shafts at a slow speed of 10 rpm or less by another permanent magnet motor. The induced voltage EMF is the amount of magnetic flux linked to the coil per unit time, and is a value proportional to the drive torque when compared with a fixed rotation speed. In this case, the rotation speed was measured at 1000 rpm. The outer diameter of the permanent magnet of the permanent magnet motor shown in FIG. 6 was eccentric to reduce cogging torque. Further, as shown in FIG. 4, skew was performed by dividing the permanent magnet into two in the axial direction. The skew angle was set to 20 ° for one slot of the stator. There is a point where the cogging torque decreases as the amount of eccentricity increases, and the amount of eccentricity in this case was 4 mm. Table 1 shows the values of the cogging torque and the induced voltage. The cogging torque is a difference between the maximum value and the minimum value of the pulsating waveform, and the induced voltage is an effective value. In the high-precision control permanent magnet motor, the target value of the cogging torque is 1% or less of the rated torque, and the rated value of the comparative example is 0.63 Nm / 3000 rpm. Therefore, the target value is 0.006 Nm. Was 0.041 Nm and did not clear the target value. Note that the conventional permanent magnet motor shown in FIG. 2 was not compared because the measures to prevent the scattering of magnets could not be sufficiently performed.

EXAMPLE As an example, as shown in FIG. 1, the cogging torque and the induced voltage of a permanent magnet motor having a petal-shaped rotor were evaluated. The dimensions and skew angle of the permanent magnet are the same as in the conventional example, and the shape of the rotor yoke is shown in FIG.
(A) As shown, the amount of eccentricity of the center of the outer diameter of the rotor yoke in each magnetic pole was 4 mm. The cogging torque of the example was 0.003 Nm, which cleared the target value. Furthermore, since the thickness of the yoke outside the permanent magnet was thinner than that of the comparative example, short-circuit of magnetic flux was small and EMF was improved.

[0015]

[Table 1]

[0016]

As described above, according to the present invention, it is possible to prevent the scattering of the permanent magnet from the rotor and reduce the cogging torque, and to improve the performance of AC servo permanent magnet motors, DC brushless permanent magnet motors and the like. It is useful for improving reliability, and its industrial value is extremely high.

[Brief description of the drawings]

FIG. 1 is a sectional view of a permanent magnet motor of the present invention.

FIG. 2 is a sectional view of a conventional permanent magnet motor.

FIG. 3 is an explanatory diagram showing a stator winding.

FIG. 4 is a diagram in which the center of the outer diameter of a permanent magnet is eccentric to reduce cogging torque.

5A and 5B are explanatory diagrams of skew performed for reducing cogging torque, wherein FIG. 5A is a cross-sectional view and FIG. 5B is a front view.

FIG. 6 is a cross-sectional view of a magnet embedded rotor of a comparative example.

7A and 7B are cross-sectional views of a magnet-embedded rotor having different magnet shapes according to the present invention, wherein FIG. 7A is a D-shape, FIG.
(C) shows the case of a rectangular permanent magnet.

[Explanation of symbols]

 1, 10, 20, 30, 40 Permanent magnet 2, 11, 21, 31, 41 Rotor yoke 3, 12, 42 Rotor 4, 13, 43 Stator yoke 5, 14, 44 Teeth 6, 15, 45 Slot 7, 17, 46 Coil 16 Sleeve 32 Shaft 33 Skew angle

Claims (3)

[Claims] 1. A permanent magnet motor in which a rotor in which a plurality of permanent magnets are embedded in a rotor yoke in a radial direction and a stator in which a winding is wound around an iron core having a plurality of slots are arranged via a gap. , A petal-shaped rotor having an eccentric center of the outer diameter such that an outer diameter passing through an outer contour of the permanent magnet is smaller than an outer diameter passing through a vertex of an adjacent permanent magnet. And a permanent magnet motor. 2. The eccentric center of claim 1, wherein the outer diameter passing through the outer contour of the permanent magnet is smaller than the outer diameter passing through a vertex of the contour of the adjacent permanent magnet.
A permanent magnet motor having a petal-shaped rotor having an eccentric amount equal to or greater than the thickness of the magnet. 3. The permanent magnet motor according to claim 1, wherein the rotor has a plurality of axial directions, and permanent magnets are gradually shifted in the circumferential direction with respect to each axial direction.