JP3845241B2 - Brushless motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a brushless motor used mainly for applications such as a drive source of a paper feed mechanism in a laser beam printer or a copying machine.
[0002]
[Prior art]
As a brushless motor used for the above-mentioned purposes, a brushless motor having a configuration as shown in a longitudinal sectional view of FIG. 5 is known. This brushless motor is a cylinder that passes through a part of the mounting hole 2 of the mounting member 1 serving as a base for mounting at a required location in the above-described application apparatus such as a laser beam printer or a copying machine 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.
[0003]
A cup-shaped rotor 10 is fixed to the upper end portion of the shaft 9 derived from the upper end of the bracket 3 by press-fitting or the like, and the rotor 10 rotates integrally around the shaft 9. An annular rotor magnet 11 is fitted and 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 fitted and fixed so as to face the rotor magnet 11 with a slight gap, and a screw 17. It is fixed by. 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. The rotor bush 18 rotates while sliding on the upper surface of the upper sleeve bearing 7 on the lower surface. The inner rotor 10 is held. In addition, a circuit board 20 on which required electronic components are mounted and 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 portion 19 of the bracket 3.
[0004]
Screw teeth 21 are integrally formed at the lower end portion of the shaft 9 led out 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 with and connected to the screw teeth 21. The brushless motor is generated between the stator 12 and the rotor magnet 11 by supplying a drive current (excitation current) from an external drive power source to the stator coil 14 of the stator 12 via the control circuit of the circuit board 20. A rotational force is generated in the rotor 10 by the attractive force and repulsive force due to the magnetic action, 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 and the transmission gear of the shaft 9.
[0005]
[Problems to be solved by the invention]
However, in the brushless motor used for the above-described applications, the shaft 9 is generally rotatably supported by oil-impregnated metal sleeve bearings 7 and 8 which are low-cost sliding bearings compared to ball bearings and fluid dynamic bearings. However, since the oil-impregnated metal sleeve bearings 7 and 8 have a relatively large coefficient of friction, it is necessary to set the rated current of the motor to be large, and there is a disadvantage that it takes too much time to switch the speed. . In addition, the oil-impregnated metal sleeve bearings 7 and 8 need to be increased in volume in order to increase the amount of oil contained when it is desired to ensure a long life, which is one factor that hinders downsizing of the motor. . In particular, the lower sleeve bearing 8 is supported by the shaft 9 via the sliding ring 22, the washer 23, and the stopper ring 24, and the number of parts for supporting the lower sleeve bearing 8 is increased.
[0006]
On the other hand, the shaft 9 is costly because the screw teeth 21 for transmitting the rotational force are integrally formed at the lower end. In order to solve this problem, conventionally, as shown in FIG. 4, a structure in which the resin gear 29 is fixed to the shaft 9 without forming the screw teeth 21 on the shaft 9 is also employed. That is, the shaft 9 is integrally provided with a small-diameter shaft portion 27 at the lower end thereof, and a knurled eye 28 is formed in the small-diameter shaft portion 27 along the axial direction. The resin gear 29 having a through hole 29a therein and having a substantially cylindrical shape is prevented from rotating by the engagement of the knurled eyes 28 by press-fitting the small diameter shaft portion 27 into the peripheral surface of the through hole 29a. In this state, it is fixed to the shaft 9.
[0007]
However, in the above configuration, 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 eyes 28, and the accuracy is deteriorated. Further, the gear end surface of the resin gear 29 at the rear end in the press-fitting direction 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, and the meshing accuracy of the resin gear 29 with respect to the transmission gear and the like deteriorates. New problems have arisen.
[0008]
Therefore, the present invention has been made in view of the above-described conventional problems. The rated current can be reduced, the speed can be switched quickly, the motor can be miniaturized, and the resin gear can be reduced. It is an object of the present invention to provide a brushless motor having a configuration that can be attached with high accuracy.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a brushless motor according to the present invention includes 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 the resin sleeve. A shaft rotatably supported by the bearing holder via a bearing, a rotor having a rotor magnet fixed to one end of the shaft, and a stator mounted on the bearing holder so as to face the rotor magnet A plurality of bushes that are integrally protruded radially outward from the outer peripheral surface of the bearing holder so as to face the rotor magnet, and that support the stator and are spaced apart in the circumferential direction. And a relative position with a space between the inner peripheral surface of the stator and the outer peripheral surface between the bushes adjacent to the bearing holder. It is characterized in that.
[0010]
This brushless motor employs a resin sleeve bearing with a smaller coefficient of friction than the oil-impregnated metal sleeve bearings used in conventional motors, so the motor's rated current can be set low and the speed can be switched. Can be done quickly. In addition, unlike the oil-impregnated metal sleeve bearing, the resin sleeve bearing has a structure that does not contain lubricating oil. Therefore, the bearing function does not deteriorate even when the volume is reduced. The service life can be ensured, and the motor can be reduced in size by reducing the dimension in the radial direction of the motor. Further, 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.
[0011]
Further, in this brushless motor, the stator is supported by a plurality of bushes that are integrally protruded radially outward from the outer peripheral surface of the bearing holder in the bracket and are installed at intervals in the circumferential direction . Since a space is provided between the outer peripheral surface of the bearing holder in the bracket and the stator, the generated heat of the stator can be discharged to the outside of the motor through this space, and the occurrence of heat shrinkage of the resin sleeve bearing can be suppressed. Is possible. Therefore, the resin sleeve bearing can be used without any trouble by preventing occurrence of inconvenience.
[0012]
In the above invention, the resin sleeve bearing has a larger amount of thermal shrinkage and thermal expansion than the oil-impregnated metal sleeve bearing, but the flange portion abuts on the opening end surface of the cylindrical bearing holder on the resin sleeve bearing. Are preferably provided integrally. As a result, if all of the heat generated by the stator cannot be completely exhausted through the space between the bearing holder and the stator, even if the resin sleeve bearing is small, heat shrinkage occurs, and the mounting position with respect to the bearing holder is reduced. Although slightly changed, the resin sleeve bearing is prevented from being displaced in the axial direction along the shaft because the flange portion is held at the mounting position by contacting the end face of the bearing holder.
[0013]
In the above invention, a small-diameter shaft portion is integrally formed with the other end portion of the shaft having the rotor fixed to one end portion, and the engagement strip portion along the axial direction is formed at the root portion of the small-diameter shaft portion. Is formed integrally, and a cylindrical resin gear integrally provided with a flange portion radially extending from the gear portion at one end has an engagement groove formed on an inner peripheral surface of the flange portion. It is preferable that the portion is fixed to the small-diameter shaft portion by being engaged with the portion in a press-fitted state.
[0014]
Thus, when attaching the resin gear to the small diameter shaft portion, the small diameter shaft portion is simply inserted into the through hole of the cylindrical resin gear, and the engagement groove formed on the inner peripheral surface of the flange portion is formed. The resin gear can be press-fitted into the small-diameter shaft portion by pressing the flange portion of the resin gear from the point of contact with the tip of the engaging strip at the base of the small-diameter shaft portion. Therefore, the gear portion of the resin gear is not deformed because no pressing force is applied thereto, and can be meshed with the transmission gear of the applied electric device with high accuracy.
[0015]
In the above invention, the resin sleeve bearing facing the resin gear may be slidably supported by the flange portion of the resin gear via a metal washer. As a result, the flange portion formed integrally with the resin gear can also be used as a support member for the resin sleeve bearing, so that it is possible to reduce bearing support members such as a sliding ring and a stopper ring in a conventional motor. Moreover, since the resin gear is slid directly with respect to the resin sleeve bearing to prevent the friction coefficient from increasing, a metal washer is interposed between the flange portion and the resin sleeve bearing. It can slide on a metal washer and rotate smoothly.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is a longitudinal sectional view showing a brushless motor according to an embodiment of the present invention. In FIG. 1, the same or equivalent parts as those in FIG. Hereinafter, a configuration different from FIG. 5 will be described. The brush Les Sumota the conventional motor and differences to main points of Figure 5, instead of the oil retaining metal sleeve bearings 7,8, and the resin sleeve bearings 30 and 31 is used, the lower end portion of the shaft 32 The small-diameter shaft portion 33 is integrally provided, and the small-diameter shaft portion 33 is press-fitted and fixed with a resin gear 34 having a through-hole inside and having a substantially cylindrical shape.
[0018]
By the way, when the resin sleeve bearings 30 and 31 are used, a structure that can prevent the resin sleeve bearings 30 and 31 from being thermally contracted due to the heat effect of the heat generated by the stator 12 and a resin sleeve are provided. There arises a new problem that the bearings 30 and 31 must be provided with a configuration that can prevent the bearings 30 and 31 from being displaced in the axial direction along the shaft 32 due to a decrease in the pressure-bonding force applied to the shaft 32. In this embodiment, the above-described problems are solved and the resin sleeve bearings 30 and 31 are used without any trouble.
[0019]
First, as a means for preventing thermal shrinkage of the resin sleeve bearings 30 and 31, as shown in FIG. 2 which is a cross-sectional view taken along the line AA of FIG. The diameter is set smaller than that of the conventional motor, and three bushes 39 project from the outer surface of the bearing holder 37 integrally at an equal interval (120 ° interval) outward in the radial direction. The structure which supports the stator 12 by the support step part 40 of each bush 39 shown is provided. Therefore, since the bearing holder 38 of the bracket 37 is set to have a smaller outer diameter compared to the conventional motor, there are two adjacent ones between the outer peripheral surface of the bearing holder 38 and the inner peripheral surface of the stator 12. Spaces 41 are formed at three locations between the bushes 39. As a result, the heat generated by the stator 12 can be discharged to the outside of the motor through the three spaces 41, so that thermal contraction of the resin sleeve bearings 10 and 31 can be suppressed.
[0020]
However, since it is difficult to completely exhaust all the heat generated by the stator 12 through the space 41, the resin sleeve bearings 30 and 31 are slightly shrunk, and the pressure applied to the shaft 32 is reduced. To do. On the other hand, the resin sleeve bearings 30 and 31 are integrally formed with flange portions 42 and 43 extending radially outward from the upper end portion or the lower end portion of the resin sleeve bearings 30 and 31, respectively. Since the mounting positions are maintained by sliding the portions 42 and 43 respectively on the upper end surface or the lower end surface of the bearing holder 38, the axial displacement is performed along the shaft 32 even when the crimping force to the shaft 32 is reduced. Is prevented.
[0021]
On the other hand, the resin gear 34 is integrally formed with a flange portion 44 on the distal end side in the press-fitting direction with respect to the small diameter shaft portion 33. On the other hand, as shown in FIG. 3, the knurled eye 28 is formed in the small diameter shaft portion 33 along the axial direction only at the root portion into which the flange portion 44 is press-fitted. The resin gear 34 is substantially cylindrical with the through holes 47 concentrically.
[0022]
Therefore, when the resin gear 34 is attached to the small diameter shaft portion 33, the small diameter shaft portion 33 is simply inserted as a guide into the through hole 47 of the resin gear 34, and the inner peripheral surface of the flange portion 44 is engaged. The resin gear 34 is press-fitted into the small-diameter shaft portion 33 from the time when the groove contacts the tip of the knurled eye 28. At this time, the resin gear 34 is press-fitted into the small diameter shaft portion 33 by pressing the flange portion 44 as indicated by a two-dot chain line arrow in FIG. Therefore, the gear portion of the resin gear 34 is not deformed because no pressing force is applied thereto, and can be meshed with a transmission gear of an applied electric device with high accuracy.
[0023]
Further, since 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, it supports bearings such as the sliding ring 22 and the stopper ring 24 in the conventional motor of FIG. The number of members can be reduced However, in this case, if the sleeve bearing 31 and the gear 34, both of which are made of resin, are slid, the coefficient of friction increases. Therefore, the flange portion 43 of the resin sleeve bearing 31 and the flange portion 44 of the resin gear 34 are used. A metal washer 48 is interposed therebetween. As a result, the flange portion 44 of the resin gear 34 slides on the metal washer 48 and rotates smoothly.
[0024]
As described above, in the brushless motor of this embodiment, since the resin sleeve bearings 30 and 31 can be used without hindrance, the resin sleeve bearings 30 and 31 having a smaller coefficient of friction than the oil-impregnated metal sleeve bearings. By adopting it, the rated current of the motor can be set small, and the speed can be switched quickly.
[0025]
Moreover, unlike the oil-impregnated metal sleeve bearings, the resin sleeve bearings 30 and 31 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 a comparison between FIG. 1 and FIG. 5, the resin sleeve bearings 30 and 31 can ensure a long life while reducing the volume thereof, and the motor sleeve bearings 31 and 31 can be secured by that much in the radial direction. The size can be reduced by reducing the size. Further, since the resin sleeve bearings 30 and 31 can be manufactured at a lower cost than the oil-impregnated metal sleeve bearing, there is an advantage that the material cost is reduced.
[0026]
【The invention's effect】
As described above, according to the brushless motor of the present invention, the shaft is rotatably supported via at least a pair of resin sleeve bearings attached to the inner peripheral surface of the cylindrical bearing holder in the bracket. By adopting a resin sleeve bearing with a smaller coefficient of friction than the oil-impregnated metal sleeve bearing used in the motor, it is possible to set the motor's rated current to a smaller value and to quickly change the speed. Can do. In addition, unlike the oil-impregnated metal sleeve bearing, the resin sleeve bearing has a structure that does not need to contain lubricating oil. Therefore, even when the volume is reduced, the bearing function is not deteriorated. Since a long service life can be ensured while reducing the size of the motor, it is possible to reduce the size of the motor by reducing the size in the radial direction. Further, 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.
[0027]
In this brushless motor, the bearing holder of the bracket has a plurality of bushes which are integrally projected radially outward from the outer peripheral surface thereof to support the stator, and between the outer peripheral surface of the bracket and the stator itself. Since the space is disposed at a relative position, the generated heat of the stator is discharged to the outside of the motor through the space, so that the heat shrinkage of the resin sleeve bearing can be suppressed. Therefore, the resin sleeve bearing can be used without any trouble by preventing occurrence of inconvenience.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a brushless motor according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is an exploded front view showing a process of attaching a resin gear in the brushless motor same as above.
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]
10 Rotor 11 Rotor magnet 12 Stator 28 Knurled eyes (engaging strip)
30, 31 Resin sleeve bearing 32 Shaft 33 Small diameter shaft portion 34 Resin gear 37 Bracket 38 Bearing holder 39 Bush 41 Space 42, 43 Flange portion of resin sleeve bearing 44 Flange portion of resin gear 48 Metal washer

Claims (4)

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 shaft rotatably supported by the bearing holder via the resin sleeve bearing; A rotor having a rotor magnet fixed to one end of the shaft, and a stator mounted on the bearing holder facing the rotor magnet,
The bracket includes a plurality of bushes that are integrally protruded radially outward from the outer peripheral surface of the bearing holder, support the stator , and are installed at intervals in the circumferential direction. A brushless motor, wherein the brushless motor is disposed at a relative position with a space between a surface and an outer peripheral surface between the bushes adjacent to the bearing holder.   The brushless motor according to claim 1, wherein the resin sleeve bearing is integrally provided with a flange portion that comes into contact with an opening end surface of the cylindrical bearing holder.   A small-diameter shaft portion is integrally formed with the other end portion of the shaft having the rotor fixed to one end portion, and an engagement strip portion along the axial direction is integrally formed at the root portion of the small-diameter shaft portion. A cylindrical resin gear that is integrally provided with a flange portion that is larger than the gear portion in the radial direction is engaged with an engagement groove formed on the inner peripheral surface of the flange portion in a press-fitted state in the engagement strip portion. The brushless motor according to claim 1 or 2, wherein the brushless motor is fixed to the small-diameter shaft portion by combining them.   The brushless motor according to claim 3, wherein the resin sleeve bearing facing the resin gear is slidably supported by a flange portion of the resin gear via a metal washer.

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