JPH0731121A - Stepping motor - Google Patents

Abstract

PURPOSE:To provide a high torque, low cost stepping motor for wide application by extending the axial length of a pectinated tooth pole without increasing the leakage flux. CONSTITUTION:The poles of a stator comprises an inner stator 6, i.e., a hollow tubular inductor pectinated on the opposite sides, and two cup-like outer stators 4, 11, i.e. inductors pectinated on side, disposed on the opposite sides of the inner stator 6. The pectinated tooth poles of the inner stator 6 and the outer stators 4, 11 have tips opposing each other. Since the adjacent tooth poles do not oppose each other over the entire length thereof, leakage flux 21 is reduced. Leakage flux 21 does not occur at the root of tooth pole where the flux density is high, because the tooth poles are not arranged contiguously thereat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized, high-torque step motor used in a vehicle actuator.

[0002]

2. Description of the Related Art A conventional stepping motor having improved torque characteristics is disclosed in Japanese Patent Laid-Open No. 61-128762. According to this, the comb-teeth pole of the stator core is formed by bending a plate material whose developed shape is a star shape and is formed into a cup-shaped comb-shape, and has a tooth pole structure that is long in the axial direction. This long comb tooth pole expands the facing area of the rotor with the permanent magnet, and secures the required amount of magnetic flux. Then, the magnetic poles of one phase of the stator core are made up of a pair of cups in which the bottoms of the cups are overlapped, the tooth tips are aligned in the same direction, and the tooth poles are arranged in parallel on the same circumference. Are formed from comb-shaped tooth poles. Therefore, for one stepper motor, the cup-shaped comb tooth poles are
There are four magnetic poles, two for each.

[0003]

A conventional step motor generates a large torque in a region where the pulse rate, that is, the self-starting frequency is low, but has a low torque in a region where the self-starting frequency is high. That is, the motor had a low maximum self-starting frequency. This is because there is a large amount of leakage magnetic flux from the side surfaces of adjacent tooth poles, since the area of the side surfaces facing each other is large. Moreover, since the distance between the tooth poles adjacent to each other is the shortest at the root of the tooth pole where the magnetic flux density is high, the bad condition that the magnetic flux further leaks overlaps. The fact that there is a large amount of leakage magnetic flux means an increase in leakage inductance, and this increase in inductance causes a decrease in motor current in a high frequency region, that is, a decrease in motor torque. Unlike the rotary solenoid, the purpose of using the step motor is to perform position control even at high frequencies, and therefore it is important to secure torque in the high frequency range. Here, there is one of the problems of reducing the leakage magnetic flux and obtaining a high torque motor.

Although there is an axial type motor in which exciting coils are arranged in the axial direction, a radial type motor in which exciting coils are arranged in the radial direction has not been produced. This is because a normal magnetic circuit cannot be obtained if the exciting coils are arranged in the radial direction. When the exciting coils are arranged in the radial direction in the configuration of the conventional technique, an air gap is required between the tip side of the cup-shaped tooth pole and the yoke in addition to the air gap between the stator and the rotor. This increases the magnetic resistance and reduces the magnetic flux. If this air gap is eliminated, a magnetic circuit will be formed only by the tooth pole and the yoke, and the magnetic flux linked to the coil will be greatly reduced. If this is solved and a radial type motor is also obtained, it is effective from the viewpoint of the application range of the step motor.

As for the number of parts, the cup-shaped tooth poles are A phase and B phase.
There are two in each phase, a total of four, and this also has the problem of obtaining a motor with a small number of parts.

[0006]

SUMMARY OF THE INVENTION The above object is to provide a step motor having a stator core composed of a plurality of inductor teeth arranged in the circumferential direction, with a hollow cylindrical double-toothed comb-shaped inductor tooth inside. It is achieved by sandwiching two cup-shaped one-sided comb-shaped inductor teeth from the left and right to form the stator core.

Further, the comb-shaped inductor tooth for achieving the above-mentioned object has a trumpet shape in which the circumference of the tip of the comb tooth is larger than the circumference of the root of the comb tooth.

[0008]

[Operation] The magnetic circuit of the step motor is centered on the exciting coil and passes from the comb-teeth pole of the stator to the permanent magnet of the rotor,
A magnetic circuit that goes from another adjacent tooth pole to the yoke, and the magnetic flux that links the exciting coil generates the torque of the motor.

When the torque is increased, the tooth pole length is generally increased. However, even if the tooth pole is made larger than a certain length, magnetic saturation occurs at the root of the tooth pole, so that there is a limit length. When exceeding the limit length, the amount of magnetic flux does not increase, but iron loss increases, and the torque warps and decreases. Even if the tooth pole length can be set to an ideal length which is slightly shorter than the permanent magnet of the rotor, the next problem is the existence of leakage magnetic flux that does not interlink with the exciting coil. This is a magnetic flux that leaks out from the side surfaces of adjacent comb tooth poles, that is, shorts.

As a method of reducing the leakage flux in the configuration of the prior art, there is a method of shortening the tooth poles or reducing the plate thickness of the tooth poles to reduce the side surface area of the adjacent tooth poles facing each other. However, in the former method, the facing area between the tooth pole and the permanent magnet also decreases, so the amount of magnetic flux in the core decreases and the torque decreases. According to the latter method, the magnetic flux density at the root of the tooth pole becomes too high and the magnetic saturation occurs, and the torque also decreases. Further, even if these methods are adopted, the distance between adjacent tooth poles at the root of the tooth pole where the magnetic flux density becomes high does not change, so that the bad condition in which the magnetic flux easily leaks cannot be removed.

In conclusion, in order to obtain a large torque, the diameter of the tooth pole should be increased and the width of the tooth pole should be increased to increase the facing area with the permanent magnet, or to increase the distance between adjacent tooth poles. It is to be. In other words, in the prior art, it cannot be said that a large torque cannot be obtained unless the outer dimensions of the motor are increased.

According to the structure of the present invention, even if the tooth pole length is set to an ideal length slightly shorter than that of the permanent magnet of the rotor, adjacent teeth can be secured while ensuring a necessary facing area between the tooth pole and the permanent magnet. The length dimension of the poles facing each other is shortened, and the side surface area of the tooth poles facing each other is reduced. Further, since the tooth poles are not adjacent to each other at the root of the tooth pole where the magnetic flux density is high, the bad condition that the magnetic flux is likely to leak is eliminated. Therefore, the leakage magnetic flux can be reduced without increasing the outer size of the motor, and the torque can be secured even in a high frequency range.

Also, regardless of whether the exciting coils are arranged in the axial direction or the radial direction, the air gap can be constituted only between the stator and the rotor, so that both types of motors can be manufactured.

Further, since the integrally formed tooth pole provided in the center shares the A-phase and B-phase tooth poles, the number of parts of the tooth pole is reduced by one and can be constituted by three points.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a step motor showing an embodiment of the present invention. The figure shows a radial type step motor. The step motor includes a rotor 3 including a rotating shaft 1 that transmits torque, a permanent magnet 2 that is fixed around the shaft and is magnetized in multiple poles, a bearing 30 that supports the rotor 3, and the rotor 3. An outer stator 4 having a plurality of comb-teeth poles arranged at equal intervals in parallel with the axis of the rotor 3 facing the permanent magnet 2 through a gap in the outer diameter direction of the rotor 3 is fixed. Side plate 5
An inner stator 6 having a plurality of comb tooth poles arranged on the same circumference as the outer stator 4 and alternately assembled in the middle of the comb tooth poles of the outer stator 4, and a center plate for fixing the inner stator 6 7, a yoke 8 connecting the side plate 5 and the center plate 7, an exciting coil 10 wound around a bobbin 9 installed in a space formed between the outer stator 4, the inner stator 6 and the yoke 8. And an A-phase stator composed of a lead wire 31 extending from the coil, an outer stator 11 having a structure similar to the above and arranged symmetrically with the A-phase stator, a side plate 12, and a bobbin 13. , B consisting of the excitation coil 14
And the stator of the phase. At this time, Phase A and B
The phase of the phase is the electrical angle
It is offset by 90 degrees.

2 and 3 show one phase magnetic pole configuration of the stator of a conventional motor. The cup-shaped one-sided comb-teeth poles 15 and 16 form a pair of magnetic poles in one phase. The excitation coil 17 is sandwiched between the bottoms of the two cups, the tooth tips of the tooth poles are aligned in the same direction, and the two are superposed. The rotor 3 is inserted inside the comb teeth poles 15 and 16. With this configuration, the amount of magnetic flux is secured,
As shown in FIG. 3, since the adjacent tooth poles 15 and 16 face each other over the entire length of the tooth poles, the leakage magnetic flux 21 that adversely affects the torque characteristics is large. Furthermore, since the distance between adjacent tooth poles is the shortest at the root of the tooth pole where the magnetic flux density is high, the magnetic flux easily leaks. This is the reason why the conventional motor has a low maximum self-starting frequency.

FIG. 4 shows the relationship between the tooth pole length and the amount of magnetic flux. From this, it is understood that there is a limit point where the magnetic flux amount hardly increases even if the tooth pole length is increased, that is, there is a limit point. Therefore, it can be understood that the amount of magnetic flux does not increase, but conversely only the iron loss increases and the torque decreases. In general,
It has been found that it is ideal and effective to set the tooth pole length to a length slightly shorter than the length of the permanent magnet due to the magnetism collecting effect of the tooth pole.

FIG. 5 shows the outer stator 4 according to an embodiment of the present invention before and after bending. The outer stator 4 is formed by bending a plate material having a star shape as shown in FIG. 5A into a cup-shaped one-sided comb-shaped inductor tooth pole as shown in FIG. 5B. , With a structure having long tooth poles in the axial direction.

FIG. 6 shows that the outer stator 4 is fixed to the side plate 5 which is a separate body.

7 and 8 show an inner stator 6 according to one embodiment of the present invention. The inner stator 6 is
As shown in FIG. 7 (a), a plate material punched out in a comb shape with two teeth as shown in FIG. 7 (a) is rolled into a hollow cylindrical two-tooth comb-shaped inductor tooth pole as shown in FIG. 7 (b). It is a thing.
Then, as shown in FIG. 8, a separate center plate 7
It is welded to and has a tooth pole shape that shares the A and B phases. It should be noted that the single-tooth comb-shaped plate materials punched separately may be joined back to back.

FIG. 9 shows the arrangement structure of the comb-teeth poles of one embodiment according to the present invention. The magnetic poles of the stator are sandwiched by two cup-shaped, single-sided comb-shaped inductor teeth, the outer stators 4 and 11, with the inner stator 6, which is a hollow-cylindrical, double-sided comb-shaped inductor tooth, inside. ,It is configured.
At this time, for example, if the left side is the A-phase magnetic pole, the right side is B
It becomes the magnetic pole of the phase. The tips of the comb teeth of the outer stators 4 and 11 and the tips of the comb teeth of the inner stator 6 face each other. In the case of the present invention, at first glance, the tooth pole length, that is, the tooth pole area is smaller than that of the conventional example, so it seems that the amount of magnetic flux that produces torque is also reduced.
Certainly, the required magnetomotive force of the magnetic circuit decreases in proportion to the tooth pole area. However, there is a point that the magnetic flux density inversely proportional to the required magnetomotive force increases. As a result, due to the relationship of magnetic flux amount = tooth pole area × magnetic flux density, the tooth pole area and the magnetic flux density cancel each other, and the magnetic flux amount of the present invention hardly decreases as compared with the conventional example. This has been confirmed by experiments.

Further, in this way, as is clear from the figure, since the facing portions of the adjacent tooth poles do not extend over the entire length of the tooth pole, the leakage magnetic flux 21 is reduced.
Further, since the tooth poles are not adjacent to each other at the root of the tooth pole where the magnetic flux density is high, the magnetic pole density is further reduced. Therefore, although the amount of magnetic flux is almost the same, the leakage magnetic flux decreases, that is, the leakage inductance decreases,
Even in the region where the pulse rate, that is, the self-starting frequency is high, the motor current does not decrease much and torque is secured. This means that a step motor having a high maximum self-starting frequency can be obtained.

FIG. 10 shows the relationship between the pulse rate and the torque by comparing the present invention with a conventional example. Compared with the conventional example, the torque of the motor according to the present invention is obtained up to a high pulse rate region. The motor according to the present invention exhibits a wide range of torque characteristics.

FIG. 11 shows the relationship of the torque characteristic with respect to the tooth pole length of one embodiment according to the present invention. When the torque characteristics in the high pulse rate region are emphasized, the tooth pole length is shortened for the purpose of reducing leakage flux and iron loss. That is, as shown in FIG. 9A to FIG. 9B, the facing portions of the adjacent tooth poles of the outer stator 4 and the inner stator 6 are further reduced. In this case, since the tooth pole area also decreases, the total magnetic flux amount decreases, and the holding torque and the torque in the low pulse rate region slightly decrease, but due to the decrease in the leakage magnetic flux and the iron loss,
Torque can be secured even in a region where the pulse rate is high. In the related art, even if the tooth pole is structurally shortened, the leakage magnetic flux does not decrease, only the amount of magnetic flux decreases, and it is difficult to increase the maximum self-starting frequency. The arrangement structure of the tooth pole according to the present invention can reduce the leakage magnetic flux while securing the required magnetic flux amount even if the tooth pole length is shortened. In this respect, the motor according to the present invention has a major feature.

FIG. 12 shows the phase shift relationship between the tooth pole and the permanent magnet. In the embodiment described above, A
The phase of B phase and B phase are shifted by 90 ° in terms of electrical angle by devising the method of magnetizing the permanent magnet, but when forming the tooth poles of the inner stator 6, the tooth poles of A phase and B phase are shifted. A method of shifting the phase can be considered. That is, as shown in FIG. 12A, the arrangement of the tooth arrangement of the left comb and the tooth arrangement of the right comb with respect to the center plate 7 of the inner stator 6 is shifted to shift the phase.

When the arrangement of the teeth of the comb is not displaced, as shown in FIG. 12 (b), the permanent magnet of the rotor is divided into right and left halves, and the mounting position on the shaft is shifted to change the phase. A shift method can be considered.

FIG. 13 shows the built-in structure of the inner stator 6 according to one embodiment of the present invention. The next problem is the accuracy of the gap size between the inner diameter of the tooth pole and the outer diameter of the permanent magnet 2 which is caused by lengthening each comb tooth pole. If the gap becomes too narrow, the tooth poles will contact the permanent magnets. If it becomes too wide, the torque will decrease.
Further, if the tooth poles are vertically swung by the electromagnetic force as it rotates, noise is also generated. Therefore, in the present embodiment, as shown in FIG. 13, the comb tooth teeth of the outer stators 4 and 11 and the inner stator 6 are preliminarily opened in a trumpet shape toward the tip of the tooth pole by a predetermined amount. The bobbin 9 holds the tip of the tooth pole when the bobbin 9 of the outer cylinder is inserted. By doing so, the springback force that tries to open to the outside of the tooth pole tip and the force that is held by the inner diameter portion of the bobbin 9 are appropriately balanced, so that the accuracy of the gap dimension is secured over the entire length of the long tooth pole. It Further, the vertical deflection of the tooth pole due to the electromagnetic force can be suppressed.

On the other hand, as shown in FIG. 13, the axial and circumferential runouts of the tooth poles are aligned so that the tooth pole tips are fitted into the portions of the inner diameter of the bobbin 9 where the tooth pole tips hit. There is a method of providing and pressing 23. Protrusion 23
Instead, it may be a groove. Also, if there is alignment, assembly becomes easy.

FIG. 14 shows an axial type step motor according to an embodiment of the present invention. Like the motors of the prior art, the excitation coils 24 and 25 are arranged axially. FIG. 1 shows a radial type step motor. In either of the axial direction and the radial direction, the magnetic circuit forms a circuit that interlinks with the coil from the yoke through one tooth pole to the other tooth pole without any problem. Therefore, both radial and axial types can be manufactured. With this, the radial type or the axial type can be selected according to the mounting space of the step motor, so that the application range is wide.

Further, the number of parts of the tooth pole is four in total, two in the conventional cup-shaped tooth pole for each of the A-phase and the B-phase. Since it is a single component that shares both phase and phase B, there are three.

[0032]

According to the present invention, since the amount of magnetic flux can be secured and the leakage magnetic flux can be reduced without changing the outer diameter of the motor, a step motor that generates torque up to a high self-starting frequency range can be obtained. can get. Also, since two types of motors, axial type and radial type, can be obtained, the application range is wide. Further, the number of parts of the stator magnetic pole is reduced from 4 to 3, and the assembling property is improved, so that the cost is reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a step motor showing an embodiment according to the present invention.

FIG. 2 is a perspective exploded view showing magnetic poles of a conventional step motor.

FIG. 3 is an arrangement structure diagram of a comb tooth pole of a conventional example.

FIG. 4 is a diagram showing a relationship between the length of a comb tooth pole and the amount of magnetic flux.

5A and 5B are views of an outer stator before and after bending according to an embodiment of the present invention.

FIG. 6 is a sectional view of an outer stator and a side plate showing an embodiment according to the present invention.

7A and 7B are views of an inner stator according to an embodiment of the present invention before and after rounding.

FIG. 8 is a perspective structural view showing an inner stator according to an embodiment of the present invention.

FIG. 9 is an arrangement structure diagram of a comb-shaped tooth pole according to an embodiment of the present invention.

FIG. 10 is a diagram showing a comparison of torque characteristics between the present invention and a conventional example.

FIG. 11 is a diagram showing a torque characteristic with respect to a tooth pole length according to an embodiment of the present invention.

FIG. 12 is an explanatory diagram showing a phase shift relationship between a tooth pole and a permanent magnet in the present invention.

FIG. 13 is a sectional view showing a built-in structure of an inner stator according to an embodiment of the present invention.

FIG. 14 is a sectional view of a step motor according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Rotation shaft, 2 ... Permanent magnet, 3 ... Rotor, 4, 11 ... Outer stator, 5, 12 ... Side plate, 6 ... Inner stator, 7 ... Center plate, 8 ... Yoke, 9, 13 ... Bobbin, 10 , 14 ... Excitation coil

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Kenji Sato 2520 Takaba, Katsuta City, Ibaraki Prefecture Hitachi Ltd. Automotive Equipment Division

Claims (4)

[Claims] 1. A step motor having a stator core composed of a plurality of inductor teeth arranged in a circumferential direction, wherein two hollow comb-shaped inductor teeth are placed inside and two cup-shaped inductors are provided from the left and right sides. A stepping motor comprising the stator core, which is sandwiched by one-sided comb-shaped inductor teeth. 2. The step motor according to claim 1, wherein the two-tooth comb-shaped inductor teeth are formed by shifting one tooth arrangement and the other tooth arrangement of a comb of both teeth from each other. 3. A step motor having a stator core composed of a plurality of comb-shaped inductor teeth arranged circumferentially,
A stepper motor, wherein the stator core is constituted by the trumpet-shaped comb-shaped inductor teeth whose circumference at the tip of the comb teeth is larger than that at the root of the comb teeth. 4. The comb-shaped inductor tooth according to claim 1 or 3, wherein the comb-shaped inductor tooth is fitted with an alignment portion such as a groove or a protrusion provided in the circumferential direction of the exciting coil bobbin. A step motor characterized in that