JPH07298526A - Rotor for motor - Google Patents

Abstract

PURPOSE:To provide a motor employing a ring magnet in the rotor thereof wherein a sine wave voltage is induced even if the stator is not skewed nor the short-pitch winding is employed in the stator winding and torque ripple of the motor is suppressed while reducing the cost. CONSTITUTION:The cavity part 2 of a rotary yoke 3 is enlarged in the radial direction at the pole branch point of a ring magnet 1 and constricted toward the center of the pole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotor structure for an electric motor in which a ring-shaped permanent magnet is bonded to the outer circumference of a rotor yoke.

[0002]

2. Description of the Related Art As a rotor of an electric motor in which permanent magnets are adhered to the outer peripheral surface of a rotor yoke, a plurality of segment type permanent magnets are generally attached directly to the outer peripheral surface of the rotor yoke. However, since many working steps and working times are required, the number of those in which a ring-shaped permanent magnet is bonded to the outer peripheral surface of the rotor yoke has recently increased. Among them, rare earth magnets made of neodymium-iron-boron have been widely used as magnet materials because of their high magnetic flux density. FIG. 8 shows a cross-sectional view of a rotor of a conventional electric motor perpendicular to the axis. A rotor yoke 13 made by laminating a plurality of steel plates made of magnetic material is integrally attached to the motor shaft 4 by press fitting or the like. A ring magnet 1 made of neodymium-iron-boron and magnetized with four poles is fixed to the outer periphery of the rotor yoke 13 by adhesion or the like.

The magnetic field orientation of the ring-shaped permanent magnet is a radial orientation due to manufacturing reasons. Considering the magnetic circuit of the rotor manufactured in this way, the magnetic resistance is small near the magnetic pole branch point, and increases from the magnetic pole branch point toward the magnetic pole center. Therefore, the induced voltage waveform of this motor is 11 in FIG.
As shown in, it becomes a trapezoidal wave including harmonics. Considering the output torque of the synchronous motor, the torque T
Is represented by the following formula.

[0004]

[Equation 1] BU = B0 cos θ

[Formula 2] BV = B0 cos (θ + 2 / 3π)

[Equation 3] BW = B0 cos (θ + 4 / 3π)

## EQU4 ## T = F.R = B.I.L.R = L.R {I0 cos .theta..times.B0 cos .theta. + I0 cos
(Θ + 2 / 3π) × B0 cos (θ + 2 / 3π) + I0
cos (θ + 4 / 3π) × B0 cos (θ + 4/3)
π)} = 3/2 · B0 · I0 · L · R (B0 = magnetic flux density, IO = current, L = effective length, R = average radius of armature winding) {BU = orthogonal to U-phase winding Magnetic flux, (induction voltage of U-phase winding)} {BV = magnetic flux orthogonal to V-phase winding, (V-phase winding induced voltage)} {BW = magnetic flux orthogonal to W-phase winding, ( W-phase winding induced voltage)}

As can be seen from this equation, when the induced voltage waveform (BU, BV, BW) of each phase is a sine waveform, the torque T
Is proportional to the current Io and has a constant value regardless of the rotational angle position. However, when the induced voltage waveform contains harmonics, the torque T does not have a constant value and so-called torque ripple occurs. Therefore, in general, the stator core is skewed or the winding method of the stator winding is set to the short pitch winding so that the induced voltage waveform becomes close to a sine wave to reduce the torque ripple. The torque ripple cannot be sufficiently reduced only by these measures.

[0006]

In the above-described conventional rotor, the torque ripple is not sufficiently eliminated even if the stator core is skewed or the stator winding is wound in a short pitch. When used on the feed shaft, problems such as abnormal noise and vibration could occur.
Further, since the stator core is skewed and the stator winding is wound in short pitches, the man-hours for manufacturing the stator core and the stator winding are increased and the cost of the motor is increased.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to significantly increase the torque ripple of an electric motor without skewing the stator core or making the stator windings shorter. An object of the present invention is to provide a rotor of an electric motor that can be reduced in cost and cost.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a rotor of an electric motor in which a ring-shaped permanent magnet is adhered to the outer circumference of a rotor yoke. The above object of the present invention is to provide a cavity in the rotor yoke. , By making the induced voltage waveform a sine wave.

[0009]

In the present invention, the amount of magnetic flux on the outer circumference of the ring magnet is adjusted by the influence of the cavity provided in the rotor yoke.
By making the electromotive voltage waveform a sine wave, the torque ripple of the electric motor can be reduced.

[0010]

1 is a sectional view of a rotor of an electric motor of the present invention perpendicular to the axis. A rotor yoke 3 manufactured by punching a steel plate by a press or the like is provided near the magnetic pole branch point so as to penetrate the cavity 2 in the axial longitudinal direction. The magnetic circuit of the magnetic flux is shown by 5, but in the magnetic circuit, the width in the radial direction is widened so as to increase the magnetic resistance in the vicinity of the magnetic pole branch point, and the magnetic resistance decreases toward the magnetic pole center. Is narrowed. In the rotor manufactured as described above, the magnetic flux amount increases at the center of the magnetic pole, and the magnetic flux amount decreases toward the magnetic pole branch point.
It becomes a sine wave as shown in 2. Here, the cavity 2
The dimension of is determined by the characteristics of the magnet used so that the induced voltage waveform becomes a sine wave.

2 to 6 show another embodiment, in which the hollow portions 6 to 10 have the same effect as the hollow portion 2. Figure 2
~ The shape of the cavity of Fig. 6 will be described. The cavity portion of FIGS. 2 to 6 is illustrated at one magnetic pole branch point. The shape of the cavity portion 6 in FIG. 2 is such that a cavity is provided between the outer circumference of the rotor yoke 3 and the inner circumference of the magnet. It is made smaller toward the center. FIG. 3 shows an arcuate slit shape, in which the outer peripheral side of the rotor yoke 3 has a larger angular width and the inner peripheral side has a smaller angular width. Figure 4
Is the shape of the hollow portion 8 in the shape of an inverted triangle. In FIG. 5, the shape of the cavity 9 is a linear slit shape,
The slit near the magnetic pole branch point is longer, and the slit is shortened toward the magnetic pole center. In FIG. 6, the cavity 10 is provided only on the N pole side, and the radial dimension is increased so that the magnetic resistance increases near the magnetic pole branch point.
It is made smaller toward the center of the magnetic pole. The cavity 10 may be provided only on the S pole side. The induced voltage waveform is further improved by skewing the hollow portion of the rotor yoke 3. Further, although the description has been given on the case of magnetizing four poles, the same effect can be obtained even if the number of poles is other than this.

[0012]

As described above, according to the rotor of the electric motor of the present invention, it is not necessary to skew the stator core or make the winding method into the short pitch winding, and the torque ripple of the electric motor can be significantly reduced. Therefore, it is possible to reduce the cost of the electric motor and provide a high-performance and highly reliable electric motor.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a rotor of an electric motor according to the present invention, which is perpendicular to a first axis.

FIG. 2 is a sectional view perpendicular to a second axis of the rotor of the electric motor according to the present invention.

FIG. 3 is a sectional view of a rotor of an electric motor according to the present invention, taken along a third axis perpendicular to the rotor.

FIG. 4 is a cross-sectional view of the rotor of the electric motor according to the present invention, which is perpendicular to the fourth axis.

FIG. 5 is a sectional view of a rotor of an electric motor according to the present invention, taken along a plane perpendicular to a fifth axis.

FIG. 6 is a cross-sectional view of a rotor of the electric motor according to the present invention, taken along a sixth axis.

FIG. 7 is a diagram showing an induced voltage waveform according to the present invention and an induced voltage waveform obtained by a conventional electric motor.

FIG. 8 is a cross-sectional view of a rotor of a conventional electric motor perpendicular to the axis.

[Explanation of symbols]

 1 ring magnet 2, 6, 7, 8, 9, 10 cavity part 3, 13 yoke 4 axis 5 magnetic circuit 11 induced voltage waveform including harmonics 12 sinusoidal induced voltage waveform

Claims (2)

[Claims] 1. In a rotor of a synchronous motor in which a ring-shaped permanent magnet is adhered to the outer periphery of a rotor yoke, a hollow portion is provided in a magnetic circuit in the rotor yoke, and the hollow portion has an induced voltage waveform of the electric motor. A rotor for an electric motor, which is shaped so as to have a sine wave. 2. The rotor for an electric motor according to claim 1, wherein the hollow portion is skewed in a longitudinal direction of the rotor yoke.