JPH10243621A - Permanent magnetic field type brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a winding factor, and reduce magnitude of cogging torque by specifying the relation between the number of the permanent magnetic poles of a permanent magnetic field and the number of salient magnetic poles of a stator. SOLUTION: The relation between the number of a permanent magnetic poles P and the number of salient magnetic poles M of a stator is given by the following expressions: (2/3)M<P<(4/3)M, M=6n and P<6n-2 or P>6n+2 (where, n is an integer which is 2 or more). A stator 1 is formed with twelve salient magnetic poles 3 at its outer circumference, and is wound around intensively by an armature winding 2. A permanent magnetic rotor 6 is formed with fourteen permanent magnet poles 4 which are magnetized alternately to N and S, and disposed at the inside of a yoke 5 so as to face the salient magnetic poles 3. The number of cogging torque pulsation per turn becomes 84 which is the least common multiple of 14, the number of the permanent magnet poles 4 and 12, the number of the salient magnetic poles, thus it is possible to reduce the cogging torque. For a winding factor, a fractional pitch winding factor becomes COS30/2=0.966, and a factor due to the distribution of the salient magnetic poles also becomes 0.966, therefore, it becomes 0.966×0.966=0.933 in total. It is thus to improve it more than a conventional type.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a permanent magnet field type brushless motor.

[0002]

2. Description of the Related Art It is desired that a small motor for audio equipment such as a capstan motor for a VTR has a large output and a small cogging torque. In general, many motors of this type have a coreless type without salient magnetic poles, but a coreless type motor has no cogging torque, but has a problem that it is difficult to obtain a motor having a large output. On the other hand, the core-attached type easily obtains a large output, but has a disadvantage that the cogging torque is increased due to the saliency. JP-B-49-8568 discloses that the number of permanent magnet poles is made larger than the number of salient pole magnets in order to improve cogging torque in a cored motor.

The cogging torque is a pulsating torque of the least common multiple of the number M of salient poles and the number P of permanent magnet poles per rotation, and the magnitude of the cogging torque is inversely proportional to the number of pulsations.

A conventional permanent magnet rotor type brushless motor of this type will be described with reference to FIG.
The stator 1 includes salient magnetic poles 3 around which an armature winding 29 is concentratedly wound. On the outer circumference of the stator 1, a rotor 6 having a permanent magnet 4 magnetized to N and S at equal intervals and a yoke 5 for passing a magnetic flux is rotatably supported via a gap. In the example of Japanese Patent Publication No. 49-8568, the number of pulsations of the cogging torque is increased by setting the relationship between the number P of permanent magnet magnetic poles and the number M of salient magnetic poles in an m-phase configuration to P: M = m + 2: m + 1.
It is proposed to reduce the magnitude of the cogging torque. Further, the winding workability is improved by intensively winding the armature winding number 2 around the salient pole 3.

[0005]

[Table 1]

Table 1 summarizes the number of pulsations of the cogging torque and the utilization factor of the winding when the ratio of the number P of the permanent magnet magnetic poles to the number M of the salient magnetic poles is P: M = 4: 3 in three phases. And the number P of the permanent magnet magnetic poles is 16 and the number M of the salient magnetic poles
In the example of FIG. 12, the number of pulsations of the cogging torque reaches 48, and a small cogging torque can be obtained. Further, since the salient poles 3 having a phase of 90 degrees are electrically in phase with each other, the utilization ratio of the armature winding 2 is good, and the pulsation of the induced voltage which is a factor of the pulsation torque is reduced. Has the advantage of being able to

[0007]

However, in this type of motor, it is desired to further reduce the cogging torque and improve the utilization efficiency of the armature winding. Although the cogging torque can be reduced by increasing the number of phases m, in a brushless motor, the structure is increased by increasing the number of magnetic pole position detection elements and the number of switching elements of the rotor used for controlling the armature winding current. It becomes complicated and expensive. And
To improve the utilization rate of the armature winding 2, there is a method of providing an auxiliary salient pole having no armature winding between the salient poles 3 to make the utilization rate of the armature winding unity. If a large number of poles are provided, the winding workability is reduced, and the number of grooves between the auxiliary magnetic poles is increased, which causes an increase in cogging torque.

An object of the present invention is to provide a permanent magnet field type brushless motor which has a simple structure, a small cogging torque, and a relatively large output.

[0009]

According to the present invention, the relationship between the number of permanent magnet magnetic poles P of the permanent magnet field and the number of salient magnetic poles M of the stator is expressed as follows.
By setting (2/3) M <P <(4/3) M, and M = 6n, and P <6n-2 or P> 6n + 2 (where n is an integer of 2 or more), the cogging torque is obtained. And the winding coefficient is improved, that is, the magnitude of the cogging torque is reduced while the winding coefficient is improved (output is improved), and mechanically 180 degrees with respect to the center of the motor. Since the armature windings wound around the salient magnetic poles near each other can be selected to have the same phase, the influence of the irregularity of the air gap is reduced, and the vibration of the motor is reduced.

In the relationship between the number of permanent magnet magnetic poles P of the permanent magnet field and the number of salient magnetic poles M of the stator, in particular, P
In the case of <6n−2, the smaller the number P of the permanent magnet magnetic poles, the smaller the mounting error in the electrical angle of the position detecting element of the permanent magnet magnetic pole provided every 120 degrees in electrical angle. The torque ripple where it occurs can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described with reference to FIGS.

The stator 1 has twelve salient poles 3 on the outer periphery, and the armature windings 2 are intensively wound around the salient poles 3. 1 The number of corresponding Ri salient poles 3 4 a is salient _{3 U1, 3 U2, 3 U3} , 3 U4 wound on the armature winding 2 is connected to the same phase constituting the U-phase. In other words, this U-phase is based on the center salient pole 3 _U1 (which can be set arbitrarily), and the armature wound around the salient pole 3 having an electrical angle in the range of 180K (K is an integer) to less than 180K + 60 degrees. It is composed of a winding 2. The V and W phases are mechanically 120 degrees and 24 degrees from the U-phase magnetic poles.
1 around salient poles 3 _V1 , 3 _W1 separated by 0 degrees (-120 degrees)
It is constituted by an armature winding (not shown) wound around the salient pole 3 in a range of 80K to less than 180 + 60 degrees.

The permanent magnet rotor 6 includes fourteen permanent magnet magnetic poles 4 which are alternately magnetized to N and S and are arranged inside the yoke 5 and face the salient poles 3.

According to the permanent magnet field type brushless motor as described above, the number of cogging torque pulsations per rotation is:
The cogging torque is reduced to 84, which is the least common multiple of the number of permanent magnet poles 14 and the number of salient poles 12.

On the other hand, regarding the winding utilization rate (winding coefficient),
Since the short section winding coefficient is cos 30/2 = 0.966, and the coefficient based on the distribution of salient magnetic poles is also cos 30/2 = 0.966, the whole becomes 0.966 × 0.966 = 0.933. Better. Similar results can be obtained by setting the number P of permanent magnet magnetic poles to 10 and the number M of salient magnetic poles to 12.

Further, salient poles 3 of the same phase, for example, 3 _U1 ,
3 _U2 , 3 _U3 , and 3 _U4 are arranged in a distributed manner, and the induced voltage of the armature winding 2 wound therewith is close to a sine wave. By performing the current control, there is an effect that the torque pulsation due to the induced voltage harmonic component is corrected.

In the above description, the case where M is 12 and P = M ± 2 is taken as an example, and it is described that the cogging torque and the winding coefficient are not inferior. However, when P is smaller than M,
A description will be given below of how the above-described effects unique to the brushless motor can be obtained as compared with the case where P is larger than M.

In a brushless motor, a current is distributed to a three-phase winding based on a signal from a position detecting element of a permanent magnet magnetic pole provided at every 120 electrical degrees, and the current flows through the three-phase winding. Regarding the influence on the control accuracy due to the mounting error (every 120 degrees), the smaller the number P of permanent magnet magnetic poles, the smaller the error in the electrical angle. Therefore, the torque ripple caused by this error can be reduced.

[0019]

[Table 2]

Table 2 shows the number of pulsations and the number of turns of the cogging torque for a combination of the permanent magnet magnetic pole number P in the vertical direction and the salient magnetic pole number M in the horizontal direction. The winding factor is the product of the short winding factor and the distributed winding factor. The short winding factor is sin (90
P / M), and the distributed winding coefficient is calculated from the distribution of salient magnetic poles of the same phase. In the case of this type of conventional motor,
At M = (3/4) P or M = (3/2) P, the distributed winding coefficient is 1, but the short-pitch winding coefficient is 0.866.

From Table 2, if the number of permanent magnet magnetic poles P and the number of salient magnetic poles M are (2/3) M <P <(4/3) M, both cogging torque and winding coefficient can be improved. It is clear that. However, when M = P, MＰP is necessary because three-phase connection cannot be performed.

In the example shown in Table 2, when P = M ± 1, M = 3 m (where m is an odd number larger than 2), the number of pulsations of the cogging torque is the largest and the pulsation of the torque is the smallest.

FIG. 3 shows an example in which the number P of the permanent magnet magnetic poles is 16 and the number M of the salient magnetic poles is 15. This combination is shown in Table 2.
As can be seen, both the cogging torque pulsation number and the winding coefficient are better than any of the combinations. However, it can be seen that the tendency for the winding coefficient to decrease particularly increases as P increases. In addition, in the same figure, a winding method different from the previous FIGS. 1 and 2 is described as the armature winding method regardless of the combination of P and M. In the case of FIG. Since the salient magnetic poles 3 around which the armature windings 2 of the same phase are wound are unevenly distributed in one place, a voltage imbalance is likely to occur between the phases unless the gap length is made uniform.

On the other hand, in the example shown in Table 2, the relationship between the number P of the permanent magnet magnetic poles and the number M of the salient magnetic poles is set to 6n ± 2: 6n (where n is an integer of 2 or more), whereby the pulsation of the cogging torque is obtained. While increasing the number, the armature windings 2 wound around the salient poles 3 mechanically differing by nearly 180 degrees can be selected to have the same phase, so that it is possible to obtain a motor with less influence of air gap unbalance.

The winding coefficient is 180K + 0 in electrical angle.
The maximum value is obtained when the armature windings 2 wound around the salient poles 3 located in a range of less than ６０660 degrees (K is an integer) are connected in phase, and Table 2 shows the best windings based on this concept. The coefficient is shown.

Although the above embodiment has been described on the premise that the armature winding 2 is wound around all of the salient poles 3, a part of the salient pole 3 is replaced with auxiliary salient poles (armature windings). (Not wound).

The present invention is also applicable to a linear motor.
In this case, the width of the permanent magnet 1 / P and the width of the salient pole 1 / P
M will be 2/3 <P / M <4/3.

[0028]

As described above, according to the present invention, by appropriately selecting the relationship between the number P of the permanent magnet magnetic poles and the number M of the salient magnetic poles, it is possible to improve the winding coefficient (improve the output) while cogging. A permanent magnet field type brushless motor with small torque can be provided. Furthermore, by selecting the armature winding wound around the salient pole at a position mechanically different from the center of the motor by nearly 180 degrees (symmetric position) in the same phase, the influence of the air gap unbalance is reduced, and the vibration is reduced. Can provide a small motor.

In the case of P <6n-2, the smaller the number P of the permanent magnet magnetic poles, the smaller the mounting error in the electrical angle of the position detecting element of the permanent magnet magnetic pole provided every 120 degrees in electrical angle. Therefore, the torque ripple generated by this error can be reduced.

[Brief description of the drawings]

FIG. 1 is a side view of a motor showing each embodiment of the present invention.

FIG. 2 is a development view of the motor shown in FIG.

FIG. 3 is a side view of a motor showing each embodiment of the present invention.

FIG. 4 is a side view of a conventional motor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... stator, 2 ... armature winding, 3 ... salient pole magnetic pole, 4 ... permanent magnet magnetic pole, 6 ... rotor.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takeo Konno 1-1-1 Higashitaga-cho, Hitachi City, Ibaraki Prefecture Inside the Taga Plant of Hitachi, Ltd.

Claims (5)

[Claims] 1. A permanent magnet field having P permanent magnet magnetic poles arranged at equal intervals over the entire circumference, M salient poles arranged at equal intervals over the entire circumference, and concentrated on the salient poles Armature having an armature winding wound three-phase and connected in three phases, and controlling the armature winding current according to the moving position of the permanent magnet field to control the permanent magnet field. In the permanent magnet field type brushless motor that generates torque, the relationship between the number P of the permanent magnet magnetic poles and the number M of the salient magnetic poles is expressed as: (2/3) M <P <(4/3) M and M = 6n and P <6n-2 or P> 6n + 2 (where n is an integer of 2 or more). 2. The permanent magnet field type brushless motor according to claim 1, wherein (2/3) M <P <6n-2 and M = 6n (where n is an integer of 2 or more). Permanent magnet field type brushless motor. 3. The permanent magnet field type brushless motor according to claim 2, wherein P: M = 10: 12. 4. The permanent magnet field type brushless motor according to claim 1, wherein 6n + 2 <P <(4/3) M and M = 6n (where n is an integer of 2 or more). Permanent magnet field type brushless motor. 5. A permanent magnet field type brushless motor according to claim 4, wherein P: M = 14: 12.