JPH0216106B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is a rotational frequency detection means (hereinafter referred to as FG) that outputs a frequency signal according to the rotational speed of a rotor.
It relates to a brushless motor having
It is particularly effective when used as a drive source for audio/visual equipment.

Conventional configurations and their problems Brushless motors are widely used in audio/visual equipment, etc., but are often required to have high-precision rotational performance. frequency detection means according to the rotation of the child;
In other words, FG becomes necessary. Various types of FG structures have been proposed, including electromagnetic induction and optical methods, but the electromagnetic induction method is often used because of its ease of construction and low cost.

FIG. 1 shows a side sectional view of an example of a conventional brushless motor having such an electromagnetic induction type FG structure, and FIG. 2 shows a cutaway perspective view of the rotor of the brushless motor. In those drawings, this brushless motor 1 has a first flat part 2
An annular permanent magnet rotor 3 magnetized to a plurality of predetermined poles is arranged on a stator flat plate 4 made of a magnetic material and facing the first plane portion 2 with a predetermined gap therebetween. The permanent magnet rotor 3 is provided with a rotational position detecting section 6 for detecting the rotational position of the plural-phase stator winding 5 and the permanent magnet rotor 3. The permanent magnet rotor 3
The second flat part 8 of the permanent magnet rotor 3 is fixed to a back yoke 7 made of a magnetic material by contacting the second flat part 8 of the permanent magnet rotor 3, and rotates integrally with the motor shaft 9. The motor shaft 9 has a bearing portion 1 attached to a motor board 10.
1, and is thrust supported by a thrust receiver 12 mounted on the stator 4.

The back yoke 7 is constructed so as to wrap around the permanent magnet rotor 3, as shown in FIG. Rotational frequency detection means (FG) 13 that generates a signal with a frequency corresponding to the number of rotations of the permanent magnet rotor 3
is attached to the outer periphery of the back yoke 7,
An annular magnet 14 magnetized on the circumferential surface, and an annular magnet 14 provided on a fixed portion near the circumferential surface.
It includes a magnetic detection element 15 that detects changes in magnetic flux generated by the magnetic flux. The magnetic detection element 15 includes a magnetic head, a Hall element, a magnetoresistive element, and the like.

In the conventional brushless motor configured as described above, the annular magnet 14 is attached to the outer periphery of the back yoke 7 by means such as press-fitting or gluing. There was a drawback that the annular magnet 14 fell off from the back yoke 7. Further, when the annular magnet 14 is made of a resin magnet in which a magnetic material is mixed into a resin material, the coefficient of thermal expansion is larger than that of the back yoke 7 made of a magnetic material, so that it can be easily used even when subjected to temperature changes. It had the drawback of falling out.

Purpose of the Invention The present invention provides a brushless motor that prevents the FG annular magnet from unnecessarily separating from the back yoke even if an external shock is applied or there is a significant temperature change, and that maintains the rotational accuracy of the motor. The purpose is to provide motors.

Composition of the Invention The present invention comprises an annular main permanent magnet whose first plane part is magnetized with a required number of poles, and a main permanent magnet arranged on a second plane part side of the main permanent magnet. A rotor including a back yoke made of a magnetic material configured to wrap around the outer periphery of a permanent magnet, and a stator winding provided on a stator flat plate facing a first flat portion of the main permanent magnet. a stator, an annular magnet whose outer peripheral surface is magnetized with a plurality of poles and rotates integrally with the rotor, and at least one magnetic detection element provided near the peripheral surface of the annular magnet. The annular magnet is made of a resin magnet and has a U-shaped cross section with a recess formed in the inner peripheral part, and the outer peripheral surface of the back yoke is fitted into the recess. It has a built-in structure.

DESCRIPTION OF EMBODIMENTS The present invention will be described below based on illustrated embodiments. FIG. 3 is a side sectional view of one embodiment of the brushless motor of the present invention, and FIG. 4 is a cutaway perspective view of a rotor in the same embodiment. Since the operation of the brushless motor of this embodiment is essentially the same as the operation of the conventional brushless motor shown in FIG. 1 described above, the explanation here will be omitted. The most characteristic feature of the brushless motor of the present invention is that the annular magnet 16 corresponding to 14 in FIG. The recess 17
The outer circumferential surface of the back yoke 7 is fitted into the inner part of the back yoke 7. The annular magnet 16 made of a resin magnet for the FG uses mainly polyamide, which has excellent moldability, as the resin material, and barium ferrite, strontium ferrite, etc. as the magnet material. The resin magnet is manufactured by melting and kneading a resin material and magnet material powder, then pulverizing the mixture, and then using injection molding or other means. Although the resin magnets have inferior magnetic properties compared to sintered magnets, they have very high dimensional accuracy after molding. Therefore, unlike sintered magnets, which have a high shrinkage rate during sintering and have low dimensional accuracy, which requires machining such as grinding after sintering, we have the excellent advantage of not necessarily requiring machining after forming. have. In addition, when manufacturing a magnet with a very thin wall thickness in the radial direction using a sintered magnet, such as an annular magnet for FG, cracks are likely to occur and manufacturing is difficult. Annular magnet 16
Since it is made of resin magnet, a thin annular magnet can be easily manufactured.

This annular magnet 16 can be easily molded integrally with the back yoke 7 by a well-known molding method (outsert molding, etc.) so that the outer peripheral surface of the back yoke 7 is held in the recess 17 on the inner peripheral surface. . In addition, there is no need for any means such as gluing or press-fitting.
It is possible to provide an inexpensive FG magnet with excellent mass productivity. When the FG magnet is a sintered magnet, the degree of freedom in the shape of the magnet is very small due to its manufacturing method, and it is very difficult to configure it as described above.

Furthermore, when the motor is subjected to a significant temperature change, the outer circumferential surface of the back yoke 7 and the inner circumferential surface of the annular magnet 16 are not chemically bonded to each other by adhesive means, so that the annular magnet 17 moves in the radial direction of the motor. can be expanded uniformly. Therefore, while the rotor of the motor rotates once, the air gap distance between the magnetic sensing element 15 and the magnetic sensing element 15 is kept constant.
Since the FG output is not subjected to AM modulation and the FG accuracy does not deteriorate, it is possible to obtain the excellent effect of not causing uneven rotation of the motor.

Further, the annular magnet 16 has a U-shaped cross section in the radial direction, with a recess 17 formed in the inner circumference.
Since the annular magnet 16 for FG fits the back yoke 7 by fitting the concavity and convexity between the concave portion 17 and the outer peripheral surface of the back yoke 7, even if the brushless motor is subjected to an external shock or Annular magnet 16 for FG due to significant temperature changes
Even if it is thermally deformed, it will not unnecessarily separate from the back yoke 7.

Effects of the Invention With the structure described above, since the annular magnet for FG is made of a resin magnet, the annular magnet for FG can be easily integrated into the back yoke so as to sandwich the outer peripheral surface of the back yoke. It can be molded, and there is no need for any means such as adhesion or press-fitting, making it possible to provide an inexpensive annular magnet for FG that is excellent in mass production. Furthermore, even if the present brushless motor is subjected to significant temperature changes, the annular magnet for FG can expand uniformly, so the excellent effect of maintaining the rotational accuracy of the motor can be obtained. In addition, even if the brushless motor is subjected to external shocks as well as temperature changes, it will not fall off from the back yoke due to the fit between the concave part of the annular magnet and the concavity and convexity of the outer peripheral surface of the back yoke. be.

[Brief explanation of drawings]

Figure 1 is a side sectional view of a conventional brushless motor.
Fig. 2 is a cutaway perspective view of the rotor of the conventional brushless motor, Fig. 3 is a side sectional view of the brushless motor according to an embodiment of the present invention, and Fig. 4 is a cutaway perspective view of the rotor of the same embodiment. be. 2...First plane part, 3...Main permanent magnet, 4...
... Stator flat plate, 5 ... Stator winding, 7 ... Back yoke, 8 ... Second plane part, 13 ... Rotational frequency detection means (FG), 15 ... Magnetic detection element, 16
...Annular magnet, 17...Concavity.

Claims (1)

[Claims] 1. An annular main permanent magnet whose first plane part is magnetized with the required number of poles, and which is arranged on the second plane part side of the main permanent magnet and wraps around the outer periphery of the main permanent magnet. a rotor including a back yoke made of a magnetic material configured as follows; a stator having stator windings disposed on a stator flat plate facing the first plane portion of the main permanent magnet; A rotation frequency comprising a circular ring magnet whose surface is magnetized with multiple poles and rotates integrally with the rotor, and at least one magnetic detection element provided near the periphery of the circular magnet. The magnet is equipped with a detection means, and the annular magnet is made of a resin magnet, and has a U-shaped cross section with a recess formed in the inner circumference, and the outer circumference of the back yoke is fitted into the recess. brushless motor.