JP2001251830A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce rated current of a brushless motor, quickly change the speed of the motor, reduce dimensions of the motor and attach resin-made gears with high accuracy. SOLUTION: At least a pair of resin-made sleeve bearings 30 and 31 are attached to the inner circumferential surface of a cylindrical bearing holder 38 of a bracket 37. A shaft 32, to whose one end a rotor 10 is fixed is supported rotatably by the bearing holder 38 via the resin-made sleeve bearings 39 and 31. A stator 12 is attached to the bearing holder 38, and faces a rotor magnet 11. The bearing holder 38 supports the stator 12 with a plurality of bushes 39, protruding radially outwardly from the outer circumferential surface of the bearing holder 38 integrally, and placed at a relative position to the stator 12 with a space 41.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor mainly used for a drive source of a paper feed mechanism in a laser beam printer, a copying machine, or the like.

[0002]

2. Description of the Related Art As a brushless motor used for the above-mentioned applications, there is known a brushless motor having a structure as shown in a vertical sectional view of FIG. This brushless motor is
A cylindrical bracket 3 that partially penetrates through a mounting hole 2 of a mounting member 1 serving as a base for mounting at a required location in an application device such as the laser beam printer or the copier described above and is fixed with a screw (not shown). A shaft 9 is rotatably supported on the inner surface side of the bearing holder 4 of the bracket 3 via a pair of upper and lower oil-impregnated metal sleeve bearings 7 and 8.

A cup-shaped rotor 10 is fixed to the upper end of the shaft 9 extending from the upper end of the bracket 3 by press-fitting or the like, and the rotor 10 rotates integrally with the shaft 9. An annular rotor magnet 11 is internally fixed to the inner peripheral surface of the outer peripheral wall of the rotor 10. On the other hand, on the outer peripheral surface of the bearing holder 4 of the bracket 3, a stator 12 in which a stator coil 14 is wound around a stator core 13 is externally fitted and fixed to the rotor magnet 11 with a small gap therebetween.
7. A rotor bush 18 fixed to the rotor 10 is interposed between the rotor 10 and the upper surface of the upper sleeve bearing 7.
Holds the rotating rotor 10 while slidingly contacting the upper end surface of the upper sleeve bearing 7 at its lower surface. A circuit board 20 on which required electronic components are mounted and on which a rotation drive circuit for the rotor 10 and a coil current control circuit for the stator 12 are formed is fixed to the flange 19 of the bracket 3.

[0004] A screw tooth 21 is formed integrally with a lower end portion of the shaft 9 derived from the bracket 3. When the brushless motor is attached to an electronic device or the like, a transmission gear (not shown) such as a speed reduction mechanism of the electronic device is meshed and connected to the screw teeth 21. The brushless motor is driven by an external drive power supply via a control circuit of the circuit board 20 to form the stator 12.
A drive current (excitation current) is supplied to the stator coil 14 of the stator 12 and the rotor magnet 11.
A rotational force is generated in the rotor 10 by the attraction force and the repulsive force due to the magnetic action generated therebetween, and the rotational force of the rotor 10 is transmitted to the rotational drive load of the applied electronic device through the screw teeth 21 of the shaft 9 and the transmission gear.

[0005]

However, in the above-mentioned brushless motor used for the above-mentioned applications, generally, an oil-impregnated metal sleeve bearing 7, which is an inexpensive sliding bearing as compared with a ball bearing or a fluid dynamic bearing, is used. Although the shaft 9 is rotatably supported by the shaft 8, the oil-impregnated metal sleeve bearings 7, 8 have a relatively large friction coefficient, so that the rated current of the motor needs to be set large and the speed is switched. The disadvantage is that it takes too long. Moreover, in order to ensure a long life, the oil-impregnated metal sleeve bearings 7 and 8 need to be increased in volume in order to increase the amount of oil contained, which is one factor that hinders downsizing of the motor. . Furthermore, in particular, the lower sleeve bearing 8 is supported on the shaft 9 via a sliding ring 22, a washer 23 and a stopper ring 24,
The number of parts for supporting the lower sleeve bearing 8 increases.

On the other hand, the cost of the shaft 9 is high because the screw teeth 21 for transmitting the rotational force are integrally formed at the lower end. In order to solve this problem, a configuration in which a resin gear 29 is fixed to the shaft 9 without forming the screw teeth 21 on the shaft 9 as shown in FIG. That is, the shaft 9 is provided with a small-diameter shaft portion 27 integrally at the lower end thereof, and the small-diameter shaft portion 27 is formed with knurls 28 extending along the axial direction. The resin gear 29 having a substantially cylindrical shape having a through hole 29a therein is prevented from rotating by the small diameter shaft portion 27 being press-fitted into the peripheral surface of the through hole 29a. In this state, it is fixed to the shaft 9.

However, in the above configuration, the resin gear 29
When the resin gear 29 is press-fitted into the small-diameter shaft portion 27, the inner diameter of the resin gear 29 is deformed by the press-fitting and the knurling 28, which deteriorates the accuracy. The end gear end surface is pressed. When the resin gear 29 is pressed, deformation occurs in the vicinity of the gear end surface, and the inner diameter of the cylindrical resin gear 29 changes, thereby lowering the engagement accuracy of the resin gear 29 with the transmission gear and the like. A new problem has arisen.

In view of the above, the present invention has been made in view of the above-mentioned conventional problems, and can reduce the rated current, can perform speed switching quickly, can further reduce the size of the motor, and can reduce the size of the resin. It is an object of the present invention to provide a brushless motor having a configuration in which gears can be accurately mounted.

[0009]

In order to achieve the above object, a brushless motor according to the present invention comprises a bracket having a cylindrical bearing holder and at least a pair of resin attached to an inner peripheral surface of the bearing holder. Sleeve bearings,
A shaft rotatably supported by the bearing holder via the resin sleeve bearing, a rotor having a rotor magnet and fixed to one end of the shaft, and a bearing opposed to the rotor magnet; And a plurality of bushes that are integrally provided to project radially outward from an outer peripheral surface of the bearing holder and support the stator.
It is characterized by being arranged at a relative position with a space between the stator and the outer peripheral surface of the bearing holder.

In this brushless motor, a resin sleeve bearing having a smaller coefficient of friction than an oil-impregnated metal sleeve bearing conventionally used in motors is used, so that the rated current of the motor can be set small. Speed switching can be performed quickly. Moreover, since the resin sleeve bearing has a structure that does not contain lubricating oil unlike the oil-impregnated metal sleeve bearing, the bearing function does not decrease even when the volume is reduced. The service life can be ensured, and the size of the motor, particularly in the radial direction, can be reduced by that much, and downsizing can be achieved. Furthermore, since the resin sleeve bearing can be manufactured at a lower cost than the oil-impregnated metal sleeve bearing, there is an advantage that the material cost is reduced.

Further, in this brushless motor, the stator is supported by a plurality of bushes integrally projecting radially outward from the outer peripheral surface of the bearing holder in the bracket, so that the outer peripheral surface of the bearing holder in the bracket can be formed. Since the space is provided between the stator and the stator, the heat generated by the stator can be discharged to the outside of the motor through the space, and the occurrence of thermal contraction of the resin sleeve bearing can be suppressed. Therefore, the resin sleeve bearing can be used without any trouble by preventing inconvenience.

In the above invention, the resin sleeve bearing has a large amount of thermal contraction and thermal expansion as compared with the oil-impregnated metal sleeve bearing, but the resin sleeve bearing contacts the opening end face of the cylindrical bearing holder. It is preferable that a flange portion to be in contact is provided integrally. As a result, when all of the heat generated by the stator cannot be completely exhausted through the space between the bearing holder and the stator, even a small amount of heat shrinks in the resin sleeve bearing, and the mounting position with respect to the bearing holder is reduced. Although slightly changed, the resin sleeve bearing is held at the mounting position by the flange portion abutting on the end face of the bearing holder, so that axial displacement along the shaft is prevented.

Further, in the above invention, a small-diameter shaft portion is formed integrally with the other end of the shaft having the rotor fixed to one end thereof, and a root portion of the small-diameter shaft portion is engaged with the shaft along the axial direction. A cylindrical resin gear integrally formed with a joint portion and integrally provided with a flange portion at one end engages an engagement groove formed on an inner peripheral surface of the flange portion with a press fit into the engagement stripe portion. It is preferable to adopt a configuration in which they are fixed to the small-diameter shaft portion by being combined.

Thus, when attaching the resin gear to the small-diameter shaft, the small-diameter shaft is simply inserted into the through-hole of the cylindrical resin gear to form the engagement formed on the inner peripheral surface of the flange. The resin gear can be pressed into the small-diameter shaft portion by pressing the flange portion of the resin gear from the time when the mating groove comes into contact with the tip of the engagement ridge at the root of the small-diameter shaft portion. Therefore, the gear portion of the resin gear is not deformed because no pressing force is applied, and can be meshed with the transmission gear of the applied electric device with high accuracy.

In the above invention, the resin sleeve bearing opposed to the resin gear may be slidably supported on a flange portion of the resin gear via a metal washer. it can. Thus, the flange portion integrally formed with the resin gear can also be used as a support member of the resin sleeve bearing, so that members for supporting the bearing such as a sliding ring and a stopper ring in the conventional motor can be reduced. In addition, the metal gear washer is interposed between the flange and the resin sleeve bearing in order to prevent the resin gear from sliding directly against the resin sleeve bearing to prevent the coefficient of friction from increasing. , Can be smoothly rotated by sliding on a metal washer.

[0016]

Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing a brushless motor according to an embodiment of the present invention.
The same or equivalent components as those described above are denoted by the same reference numerals, description thereof will be omitted, and a configuration different from FIG. 5 will be described below. The main difference between this brush motor and the conventional motor of FIG. 5 is that instead of the oil-impregnated metal sleeve bearings 7 and 8, resin sleeve bearings 30 and 31 are used, and the lower end of the shaft 32 has a small diameter. The shaft portion 33 is provided integrally, and a substantially cylindrical resin gear 34 having a through hole therein is press-fitted and fixed to the small-diameter shaft portion 33.

By the way, the above-mentioned resin sleeve bearing 3
In the case where 0, 31 is used, the resin sleeve bearings 30, 31 can be prevented from being thermally shrunk due to the thermal influence of the heat generated by the stator 12, and the resin sleeve bearings 30, 31 can be thermally shrunk. A new problem arises in that it is necessary to provide a configuration capable of preventing the pressing force against the shaft 32 from being reduced due to the occurrence and preventing the axial displacement along the shaft 32. In this embodiment, the above-mentioned problem is solved, and the resin sleeve bearings 30, 31 are used without any trouble.

First, as means for preventing thermal contraction of the resin sleeve bearings 30, 31, as shown in FIG. 2, which is a sectional view taken along the line AA of FIG. 38 is set smaller than that of the conventional motor, and three bushes 3
9 are arranged at equal intervals (120 ° intervals) so as to protrude outward in the radial direction and to support the stator 12 by the supporting step portions 40 of the bushes 39 shown in FIG. Therefore, the bearing holder 38 of the bracket 37
Since the outer diameter is set smaller than that of the conventional motor, three locations between two adjacent bushes 39 are provided between the outer peripheral surface of the bearing holder 38 and the inner peripheral surface of the stator 12. Is formed in the space 41. Thereby, the heat generated by the stator 12 can be discharged to the outside of the motor through the three spaces 41, so that the thermal contraction of the resin sleeve bearings 10, 31 can be suppressed.

However, it is difficult to completely discharge all the heat generated by the stator 12 through the space 41. Therefore, the resin sleeve bearings 30 and 31 undergo a slight heat shrinkage and are pressed against the shaft 32. Power drops. On the other hand, the resin sleeve bearings 30, 31 include:
Flange portions 42 and 43 extending radially outward from the respective upper end portions or lower end portions are integrally formed. The resin sleeve bearings 30 and 31 are formed such that the flange portions 42 and 43 are formed on the upper end surface or the lower end surface of the bearing holder 38. , The mounting position is held by sliding each other, so that even when the pressing force on the shaft 32 is reduced, the displacement in the axial direction along the shaft 32 is prevented.

On the other hand, the resin gear 34 is integrally formed with a flange portion 44 on the tip side in the press-fitting direction with respect to the small-diameter shaft portion 33. In contrast, the small-diameter shaft portion 33 has
As shown in FIG. 3, the knurls 28 are formed along the axial direction only at the base where the flange portion 44 is press-fitted. The resin gear 34 has a substantially cylindrical shape with a through hole 47 concentric.

Therefore, when attaching the resin gear 34 to the small diameter shaft portion 33, the small diameter shaft portion 33 is simply inserted into the through hole 47 of the resin gear 34 as a guide, and the inner peripheral surface of the flange portion 44 is formed. The resin gear 34 is pressed into the small-diameter shaft portion 33 from the point when the engagement groove of the knurl 28 comes into contact with the tip of the knurled eye 28. At this time, the resin gear 34
As shown by the two-dot chain line arrow in FIG. 3, the flange 44 is pressed into the small diameter shaft 33 by pressing it. Therefore, the gear portion of the resin gear 34 is not deformed because no pressing force is applied, and can be meshed with the transmission gear of the applied electric device with high accuracy.

The flange portion 44 formed integrally with the resin gear 34 can also be used as a support member for the lower resin sleeve bearing 43. Therefore, the sliding ring 22 and the stopper ring 24 in the conventional motor shown in FIG. The number of bearing support members can be reduced. However, in this case, when the sleeve bearing 31 and the gear 34, both of which are made of resin, are slid, the friction coefficient becomes large.
1 flange portion 43 and flange portion 44 of resin gear 34
And a metal washer 48 interposed therebetween. As a result, the flange portion 44 of the resin gear 34 slides on the metal washer 48 to rotate smoothly.

As described above, in the brushless motor of this embodiment, since the resin sleeve bearings 30 and 31 can be used without any trouble, the resin sleeve bearing 3 having a smaller friction coefficient than the oil-impregnated metal sleeve bearing.
By adopting 0 and 31, the rated current of the motor can be set small, and the speed can be switched quickly.

Moreover, the resin sleeve bearings 30, 31
Unlike oil-impregnated metal sleeve bearings, they have a structure that does not contain lubricating oil, so that the bearing function does not deteriorate even when the volume is reduced. Therefore, as is clear from the comparison between FIG. 1 and FIG. 5, the resin sleeve bearings 30 and 31 can secure a long life while reducing the volume thereof, and the motor especially in the radial direction can be secured accordingly. It is possible to reduce the size and downsize. Further, the resin sleeve bearings 30 and 31 can be manufactured at a lower cost than the oil-impregnated metal sleeve bearings, and thus have the advantage of reducing material costs.

[0026]

As described above, according to the brushless motor of the present invention, the shaft is rotatably supported via at least one pair of resin sleeve bearings attached to the inner peripheral surface of the cylindrical bearing holder of the bracket. So,
By adopting a resin sleeve bearing with a smaller coefficient of friction than the oil-impregnated metal sleeve bearing used in conventional motors, it is possible to set the rated current of the motor small and to switch speeds quickly. be able to. Moreover, unlike the oil-impregnated metal sleeve bearing, the resin sleeve bearing has a structure that does not need to contain lubricating oil, so even if the volume is reduced, the bearing function does not deteriorate and the Therefore, a long life can be ensured while reducing the size of the motor, so that the size of the motor, particularly in the radial direction, can be reduced by that much, and the size can be reduced. Furthermore, since the resin sleeve bearing can be manufactured at a lower cost than the oil-impregnated metal sleeve bearing, there is an advantage that the material cost is reduced.

Further, in this brushless motor, the bearing holder of the bracket has a plurality of bushes for projecting radially outward from the outer peripheral surface of the bracket and supporting the stator. In this configuration, the heat generated by the stator is exhausted to the outside of the motor through the space, so that the thermal contraction of the resin sleeve bearing can be suppressed. Therefore, the resin sleeve bearing can be used without any trouble by preventing inconvenience.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a brushless motor according to one embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an exploded front view showing a process of attaching a resin gear in the brushless motor.

FIG. 4 is an exploded front view showing a process of attaching a resin gear in a conventional brushless motor.

FIG. 5 is a longitudinal sectional view showing a conventional brushless motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Rotor 11 Rotor magnet 12 Stator 28 Knurl eyes (engaging strip part) 30, 31 Resin sleeve bearing 32 Shaft 33 Small diameter shaft part 34 Resin gear 37 Bracket 38 Bearing holder 39 Bush 41 Space 42, 43 Resin sleeve bearing Flange part 44 Flange part of resin gear 48 Metal washer

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) GA01 GA04 JK08 JK11 JK15 JK19

Claims (4)

[Claims] 1. A bracket having a cylindrical bearing holder, at least a pair of resin sleeve bearings attached to an inner peripheral surface of the bearing holder, and a rotatable bearing mounted on the bearing holder via the resin sleeve bearing. A supported shaft, a rotor having a rotor magnet and fixed to one end of the shaft, and a stator mounted on the bearing holder so as to face the rotor magnet; It has a plurality of bushes that are integrally protruded radially outward from the outer peripheral surface of the bearing holder to support the stator, and at a relative position where there is a space between the stator and the outer peripheral surface of the bearing holder. A brushless motor characterized by being arranged. 2. The brushless motor according to claim 1, wherein the resin sleeve bearing is integrally provided with a flange portion abutting on an opening end face of the cylindrical bearing holder. 3. A small-diameter shaft portion is integrally formed on the other end of a shaft having a rotor fixed to one end portion, and an engagement strip along an axial direction is formed at a root portion of the small-diameter shaft portion. A cylindrical resin gear integrally formed and integrally provided with a flange portion at one end engages an engagement groove formed on an inner peripheral surface of the flange portion with the engagement ridge portion by press-fitting. The brushless motor according to claim 1, wherein the brushless motor is fixed to the small-diameter shaft portion. 4. The brushless motor according to claim 3, wherein the resin sleeve bearing opposed to the resin gear is slidably supported on a flange portion of the resin gear via a metal washer.