Brushed motor

Provided is a brushed motor in which noise in a high rotational speed range is effectively decreased. A bar-shaped flat attachment 28 of synthetic resin is inserted along an axial line L into an opening of a slot 16 formed in a core 14 of a rotor 7, and fixed with respect to the core 14 and/or windings 17 using adhesive agent. The flat attachment 28 has side surfaces 28b and an inner peripheral surface 28c. The side surfaces 28b are engaged from an inner peripheral side with inclined surfaces 15a of teeth 15 adjacent to each other across the opening of the slot 16. The inner peripheral surface 28c of the flat attachment 28 has two ridges 28d protruding therefrom which are abutted against the windings 17. The flat attachment 28 closes the opening of the slot 16 and shapes an outer peripheral surface 14a of the core 14 into a flat cross sectional shape suitable for suppression of wind noise.

BACKGROUND

1. Technical Field

The present invention relates to a brushed motor in which an armature including a core with windings wound thereon is disposed on a rotary shaft, the armature being electrically fed by means of brushes slidably engaged with a commutator on the rotary shaft.

2. Description of the Related Art

A brushed motor of this type includes a stator and a rotor which are disposed in a housing. The stator includes a field magnet fixed on an inner peripheral surface of the housing. The rotor includes an armature disposed on a rotary shaft rotatably supported in the housing. The armature has a core with windings for respective poles wound thereon. The windings for the poles are electrically connected to a commutator. The commutator has an outer peripheral surface with which brushes are slidably engaged to supply power to the armature. The direction of electric current flowing through the windings is successively reversed to vary the magnetic fields between the windings and the field magnet, thereby rotating the rotor.

Small, inexpensive, and high-efficiency brushed permanent magnet motors are being widely used for various applications. However, the structure in which the brushes are slidably engaged with the outer peripheral surface of the commutator, and in which the rotor having the windings disposed in the grooves between salient poles of the core is rotated leaves room for improvement in terms of quietness during operation. Accordingly, various proposals have been made.

For example, JP-A-2001-309615 discloses a brushed motor in which a brush holder made of sheet metal for holding the brushes is formed with reinforcement ribs and has a two-fold double structure for increased stiffness. In this way, vibrations at the distal end of the brushes when slidably engaged with the commutator are suppressed to reduce noise.

JP-A-2006-211758 discloses a brushed motor in which a vibrator is configured by fixing, via an elastic body, a substantially dice-shaped weight to the distal end of a brush holder for holding a brush. Vibrations caused in the brush holder are transmitted to the weight and dissipated in the form of vibration energy, thereby reducing the vibration of the brush holder and hence noise.

SUMMARY

As a means for expanding the application of brushed motors, high rotation types have been developed. These motors have overcome various obstacles to achieving higher speed rotation, and their practical rotational speed ranges are becoming gradually higher.

However, as shown inFIG. 6indicating the results of a noise test, compared with a normal rotational speed range (such as less than 20,000 rpm), an increase in noise in a high rotational speed range achieved by an increase in rotational speed is unavoidable. Even when the countermeasures described in JP-A-2001-309615 and JP-A-2006-211758 are adopted during the development of high rotation motors, the decrease in noise achieved in the high rotational speed range has been insufficient.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a brushed motor in which the noise in a high rotational speed range is effectively decreased.

In order to achieve the purpose, a brushed motor of the present invention includes: a housing; a field magnet disposed on an inner peripheral surface of the housing; a rotor including a core, a rotary shaft rotatably supported in the housing, and a commutator disposed on the rotary shaft, the core having a plurality of teeth circumferentially arranged about an axial line of the rotary shaft, and a slot formed between the teeth, the slot having an opening on an outer peripheral side of the core and extending in an axial line direction of the core, the rotor further including a winding wound on each of the teeth in the slot; a brush slidably engaged with an outer peripheral surface of the commutator to supply power to the winding; and a shape complementing member molded from an insulating material, the shape complementing member being inserted and fixed into the opening in the slot of the core from the axial line direction of the core.

In the brushed motor thus configured, the slot opening onto the outer peripheral surface of the core has a cross sectional shape recessed from the outer peripheral surface of the core even after the windings are wound. In addition, the opening extends throughout in the axial line direction of the core. These provide a potential cause of significant wind noise. In the present invention, the shape complementing member molded from insulating material is inserted and fixed into the opening of the slot. Because the opening in the slot is closed by the shape complementing member, the outer peripheral surface of the core is shaped into a cross sectional shape with increased flatness. Thus, the wind noise due to the slot during motor operation, and further the noise of the motor are reduced.

In a preferred embodiment, the shape complementing member may have an outer peripheral surface which is recessed with respect to an outer peripheral surface of the core in a radius direction of the core about the rotary shaft, the recess having a depth set in a range of from 0 to 1.5 mm.

In the brushed motor thus configured, as indicated by the test results shown inFIG. 8, while a satisfactory noise reduction effect is obtained at the depth of 1.5 mm, the noise sharply increases at 3.0 mm. This indicates that the upper limit of an optimum range of the depth is 1.5 mm. Meanwhile, protrusion of the outer peripheral surface of the shape complementing member beyond the outer peripheral surface of the core should be avoided. Accordingly, the optimum range of the depth is identified to be from 0 to 1.5 mm.

In a preferred embodiment, the slot and the shape complementing member may each have a length in the axial line direction of the core along the rotary shaft, and a ratio of the length of the shape complementing member to the length of the slot is set in a range of from 50 to 100%.

In the brushed motor thus configured, as indicated by the test results shown inFIG. 7, the noise hardly increases when the ratio is decreased from 75% to 50%. Thus, the lower limit of the optimum range of the ratio may be considered 50%. Meanwhile, lengths of the shape complementing member exceeding the length of the core are meaningless. Accordingly, the optimum range of the ratio is identified to be from 50 to 100%.

In a preferred embodiment, in the slot, the shape complementing member may be engaged with the windings wound on the teeth so as to be biased in an outer peripheral direction, and may be engaged with inner surfaces of the teeth extending on both sides of the opening of the slot.

In the brushed motor thus configured, the shape complementing member is engaged with the windings wound on the teeth and is thereby biased in the outer peripheral direction. The shape complementing member is also engaged with the inner surfaces of the teeth extending on both sides of the opening of the slot. Thus, the shape complementing member is held in a predetermined position in the opening of the slot. As a result, the outer peripheral surface of the core and the outer peripheral surface of the shape complementing member are maintained in a predetermined positional relationship, making it possible to perform even more reliable reduction of noise.

In a preferred embodiment, the brushed motor may further include a cooling fan having an annular shape about the rotary shaft and disposed at an end in the axial line direction of the core. The cooling fan may be connected with one end of the shape complementing member and integrally formed with the shape complementing member, the cooling fan being supported from the core via the shape complementing member.

In the brushed motor thus configured, during the assembly of the motor, as the shape complementing member is inserted and fixed into the opening of the slot along the axial line direction, the cooling fan is necessarily disposed in a regular position with respect to the core, and is supported from the core via the shape complementing member. Thus, a plurality of shape complementing members can be inserted and fixed into a plurality of slots at once, while the cooling fan is also supported in the regular position. Accordingly, the assembly operation is simplified.

In a preferred embodiment, the cooling fan may include: an annular base member and a plurality of fins circumferentially arranged on an anti-core side of the base member; and the one end of the shape complementing member may be connected to the base member at a position circumferentially aligned with any of the fins of the cooling fan.

In the brushed motor thus configured, one end of the shape complementing member is circumferentially aligned with any of the fins of the cooling fan, so that the shape complementing member and the fin are directly connected across the base member. As a result, the shape complementing member, the base member, and the fin together function as a single stiff body continuous in the axial line direction. Thus, the rotation of the rotor can be reliably transmitted to the cooling fan without damage.

According to the brushed motor of the present invention, the noise in a high rotational speed range can be effectively decreased.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

In the following, a first embodiment of a brushed motor of the present invention will be described.

FIG. 1is a cross sectional view of the brushed motor of the present embodiment.FIG. 2is a perspective view of a rotor and a cooling fan of the brushed motor.FIG. 3is a view along arrow A of the rotor and the cooling fan of the brushed motor ofFIG. 2. InFIG. 1, the right side corresponds to the front side of the motor, and the left side corresponds to the rear side of the motor.

The motor1has a housing2which includes a metal case3, a brush holder29made from synthetic resin, and an end bell4made from metal. The metal case3has a cylindrical cup shape with an opening toward the rear side. The end bell4is attached to close the opening. The end bell4is mated with a step formed at the opening of the metal case3, and is fixed in place by swaging as the end bell4is sandwiched between the step and a part of the metal case3that has been cut and bent.

On the inner peripheral surface of the metal case3, two-pole field magnets5are fixed by means of a metal spring and adhesive agent, which are not illustrated. The field magnets5and the metal case3, which functions as a yoke, constitute a stator6. Inside the field magnets5, a rotor7is disposed. The rotor7includes a rotary shaft8, an armature9, and a commutator10.

The front side of the rotary shaft8of the rotor7is rotatably supported by a bearing12in the metal case3. The rear side of the rotary shaft8is rotatably supported by a bearing13in the end bell4. The rotary shaft8includes an extension protruding out of the metal case3on the front side, the extension functioning as an output shaft of the motor1.

The armature9includes a core14made of a stack of a plurality of laminated silicon steel sheets. As illustrated inFIG. 3in particular, the core has three rows of teeth15circumferentially arranged side by side about an axial line L of the rotary shaft8, forming a substantially cylindrical shape. The teeth15are connected at the center, with both sides at the outer peripheral end of each tooth extending circumferentially, forming a T-shaped cross section. Between the teeth15, slots16are formed extending along the axial line L of the core14, each of the slots16having one side opening to an outer peripheral surface14a(as illustrated inFIG. 3) of the opening core14.

Due to the extensions at the outer peripheral ends of adjacent teeth15, each of the slots16has a sac-like cross section with a narrowed opening at the outer peripheral surface14aof the core14. After the core14is entirely provided with insulating coating, the teeth15are wound with windings17in the respective slots16, forming a plurality of coils and the armature9.

As illustrated inFIG. 1, a predetermined clearance is formed between the outer peripheral surface14aof the core14and the inner peripheral surface of the field magnets5. The commutator10is disposed on the rotary shaft8and positioned within the end bell4. The commutator10is circumferentially divided into three poles and electrically connected, not illustrated, to the respective poles of the windings17.

In the end bell4, a brush holder device18is disposed so as to internally hold the commutator10. The configuration of the brush holder device18is similar to that of well-known brush holders, and its detailed description will be omitted.

At 180° opposed positions about the center of the commutator10, a pair of brushes20(of which only one is illustrated) supported at the distal ends of brush arms19is disposed. The brushes20are engaged with the outer peripheral surface of the commutator10due to elasticity of the brush arms19. At the proximal ends of the brush arms19, terminals21are integrally formed. The terminals21protrude out of the end bell4and are configured for connection with power supply cables, which are not illustrated.

As power is supplied to the terminals21via the power supply cables, electric current flows via the brush arms19, the brushes20, and the commutator10to the windings17forming the plurality of coils of the armature9, whereby magnetic fields are generated in the core14. As a result, the rotor7rotates, and each of the brushes20is successively slidably engaged with one or two of the divided sections of the outer peripheral surface of the commutator10. Accordingly, the coils of the armature9that are energized and the direction of the electric current flowing through each of the coil are successively switched, whereby the magnetic fields between the core14and the field magnets5are varied, causing the rotor7to keep rotating.

FIG. 4is a view along arrow A ofFIG. 2, illustrating a cooling fan and a flat attachment of the brushed motor1.

As illustrated inFIGS. 1, 2, and 4, the cooling fan23is disposed at the rear-side end in the direction of the axial line L of the core14. The cooling fan23as a whole has an annular shape with the rotary shaft8at the center. The cooling fan23includes an annular base member24with a number of lightening holes24aformed in an outer peripheral surface thereof. The cooling fan23also includes a number of fins25arranged on a rear side surface (anti-core side) of the base member24. The members24and25are integrally formed from synthetic resin material.

The central sides of the fins25are connected with each other and form a circular hole26through which the rotary shaft8is passed. The outer peripheral sides of the fins25are connected to the base member24and integrated with each other. The gaps between the fins25are continuous with the spaces in the direction of the axial line L.

The cooling fan23configured as described above is adhered to the rear-side end face of the core14with adhesive agent, and is rotated integrally with the rotor7. During rotation of the cooling fan23, air is ejected by the fins25from the central side toward the outer peripheral side. The air then passes through outlet holes4aformed in the end bell4and is discharged externally. Accordingly, the rotor7and the windings17are cooled by air that flows into the housing2via inlet holes3aformed in the metal case3. Also, the commutator10and the brushes20are cooled by air that flows into the housing2via inlet holes, not illustrated, in the end bell4.

According to the present embodiment, the motor1is adapted for high-speed rotation where the practical rotational speed range has an upper limit of 40,000 rpm. Accordingly, the amount of heat generated due to the energization of the windings17and the brushes20, and the amount of heat generated due to electric resistance and slide friction where the brushes are slidably engaged with the commutator10are both large. However, due to the cooling effect provided by the cooling fan23, temperature increases in the core14and the windings17are suppressed, and the slidably engaged portions including the brushes20are also cooled and their temperature increases are suppressed. Thus, wearing of the brushes20due to their sliding engagement is also effectively suppressed.

As discussed above with reference toFIG. 6illustrating the results of noise tests, an increase in the practical rotational speed range of the brushed motor1leads to an increase in noise in the high rotation rotational speed range. With the countermeasure techniques proposed in JP-A-2001-309615 and JP-A-2006-211758, it has been unable to obtain sufficient noise reduction effect.

In view of the above problem, the present inventors have discovered that the increase in the noise in a high rotational speed range is mainly due to the wind noise generated by the slots16formed in the outer peripheral surface14aof the core14, and devised a countermeasure. The process of analysis leading to the conclusion will be discussed below.

It can be considered that the countermeasure described in JP-A-2001-309615 for increasing the brush holder stiffness by means of reinforcement ribs, and the countermeasure described in JP-A-2006-211758 for dissipating the vibration of the brush holder by means of a vibrator both act to suppress the vibrations of the brushes. Accordingly, the noise due to the sliding engagement of the brushes should be reduced. However, there is still an increase in noise in the high rotational speed range. This indicated the possibility that there are causes other than the sliding engagement of the brushes.

As one major source of noise for the increase in the high rotational speed range of the motor1, the wind noise of the rotor7rotating in the housing2was considered. As a result of an analysis of the shape of various parts of the rotor7, it was concluded that the slots16in the outer peripheral surface14aof the core14were the parts with a shape that most easily caused wind noise.

In the first place, the slots16have the sac-like cross section with one side opening onto the outer peripheral surface14aof the core14. Even after the windings17are wound on the teeth15, the slots16still have a cross sectional shape which is significantly recessed from the outer peripheral surface14aof the core14, the openings extending throughout in the direction of the axial line L of the core14. Thus, the slots16provide a cause for significant wind noise. However, the slots16are an indispensable requirement in the brushed motor1to allow for the windings17to be wound on the teeth15of the core14. The slots16in the outer peripheral surface14aof the core14, therefore, are unavoidable.

In addition, the wind noise due to the slots16is also generated in a normal rotational speed range in a less pronounced manner than in the high rotational speed range. And there was the conventional knowledge that the brushed motor1having the winding slots generated greater noise than a brushless motor provided with a rotor having, e.g., a ring magnet without outer peripheral irregularities, the knowledge being suggestive of the fact that the noise was due not only to the sliding engagement of the brushes20but also to the wind noise generated by the slots16. Accordingly, it was contemplated that the suppression of the wind noise due to the slots16would provide a significant effect for reducing noise not only in the high rotational speed brushed motor1of the present embodiment but also in brushed motors having normal rotational speed ranges.

Based on the above knowledge, in the present embodiment, the wind noise due to the slots16is countered by means of a flat attachment (shape complementing member) disposed in each of the slots16of the rotor7, as described in detail below.

FIG. 5is a perspective view of a flat attachment28being inserted into a slot16.

In simple terms, the flat attachment28, by being disposed in the opening of each of the slots16, provides the function of closing the opening and shaping the outer peripheral surface14aof the core14into a cross sectional shape with increased flatness.

The flat attachment28is made by injection molding an insulating and non-magnetic material, such as synthetic resin material, into a generally bar shape corresponding to the opening of the slots16. As indicated by an arrow inFIG. 5, the flat attachment28is inserted into the opening in the slot16from the rear side in the direction of the axial line L, and is fixed with respect to the core14and/or the windings17using adhesive agent.

The inside of the slot16formed of the core14that is a silicon steel sheet laminated body has a succession of minute depths in the direction of the axial line L. Accordingly, to enable smooth insertion of the flat attachment28, the distal end in the insertion direction of the outer peripheral surface28ais tapered. As illustrated inFIG. 2, in the direction of the axial line L of the core14, the flat attachment28has a length Lf which is slightly shorter than a length Lc of the core14, and the ratio Lf/Lc is set to 96.6% in the present embodiment.

The cross sectional shape of the flat attachment28will be described. As illustrated inFIG. 3, the flat attachment28has a generally trapezoidal cross section. The flat attachment28has an outer peripheral surface28awhich, corresponding to the upper base of the trapezoid, has an arc shape with the same curvature as that of the outer peripheral surface14aof the core14. The flat attachment28has a width slightly wider than the width (interval at the extending portions of the teeth15) of the slots16. The shape of the outer peripheral surface28ais not limited to the illustrated example, and may be planar, for example.

At the ends of the extending portions of the adjacent teeth15across the opening of the slot16, inclined surfaces15a(inner surfaces) facing each other and also facing the inner peripheral side of the core14are formed. Specifically, the inclined surfaces15aare inclined so as to be increasingly spaced apart from each other toward the inner peripheral side of the core14. The inclined surfaces15aare set with a preferable shape for winding the windings17and generating the magnetic field. The flat attachment28has side surfaces28b, corresponding to the legs of the trapezoid. The side surfaces28bare inclined so as to respectively correspond to the inclined surfaces15a. The side surfaces28bare engaged with the inclined surfaces15afrom the inner peripheral side of the core14.

The flat attachment28has a flat inner peripheral surface28c, corresponding to the lower base of the trapezoid. On the inner peripheral surface28c, two ridges28dare formed at a circumferential interval from each other and extending throughout the core14in the direction of the axial line L. The ridges28drespectively abut the windings17wound on the adjacent teeth15in the slots16. Accordingly, the flat attachment28is biased in an outer peripheral direction, whereby the inclined side surfaces28bare abutted against the inclined surfaces15aat the extending portions of the teeth15, as described above.

As a result, the flat attachment28is sandwiched between the windings17and the inclined surfaces15aof the teeth15in the opening of the slot16. The ridges28dare slightly elastically deformed to regulate the positional displacement of the flat attachment28in the direction of the axial line L, the radius direction, and the circumferential direction. The engagement of the side surfaces28bwith the inclined surfaces15aof the teeth15enables the flat attachment28to sufficiently resist large centrifugal force in the high rotational speed range.

Thus, the opening of the slot16is closed by the flat attachment28. In this case, the width of the outer peripheral surface28aof the flat attachment28is slightly larger than the width of the slot16. Accordingly, the outer peripheral surface28aof the flat attachment28is slightly recessed with respect to the outer peripheral surface14aof the core14in the radius direction of the core14, and a depth D of the recess is set to 0.4 mm in the present embodiment.

The present inventors conducted a noise test on the brushed motor1configured as described above according to the present embodiment.

During the noise test, as illustrated inFIG. 1, a measurement device M was disposed at a distance of 30 cm from the front side of the motor1, and the noise (JIS C1502-A characteristics; overall value) generated from the motor1during operation at various rotational speeds was measured.FIG. 6is a chart illustrating the results of the noise test performed on the brushed motor1of the embodiment and a brushed motor according to conventional technology (adapted for high speed rotation but not including the flat attachment28).

As shown in the chart, in the present embodiment, the noise, while increasing as the rotational speed increases, is sufficiently reduced compared with the conventional technology. The noise reduction effect is more pronounced in higher rotational speed ranges. For example, at 40,000 rpm, the noise is greatly reduced from the approximately 89 dB of the conventional technology down to approximately 78 dB. It can also be estimated from the test results that a sufficient noise reduction effect can be obtained when the flat attachment28of the present embodiment is applied in a conventional brushed motor in a normal rotational speed range (such as less than 20,000 rpm).

As described above, the only difference in motor specifications between the present embodiment and the conventional technology is the presence or absence of the flat attachment28. Accordingly, the fact that the noise reduction effect was obtained by means of the flat attachment28can be considered to prove that the main cause of an increase in the noise in the high rotational speed range is the wind noise generated by the slots16in the outer peripheral surface14aof the core14. Thus, in the brushed motor1of the present embodiment, by suppressing the wind noise due to the slots16, the noise in all of the rotational speed ranges including high rotational speed range can be effectively decreased.

Meanwhile, the present inventors, with a view to identifying the optimum range of the rate Lf/Lc of the length Lf of the flat attachment28to the length Lc of the core14, and the optimum range of the depth D between the outer peripheral surface14aof the core14and the outer peripheral surface28aof the flat attachment28, conducted a noise test in which the ratio Lf/Lc and the depth D were gradually varied by using different specifications of the flat attachment28.

The noise test for the ratio Lf/Lc was conducted with respect to four ratios of Lf/Lc of 100%, 75%, 50%, and 0% with the depth D fixed at 0.4 mm.

As indicated by the test results shown inFIG. 7, the overall tendency was that while the noise increased as the ratio Lf/Lc was decreased (i.e., the length Lf of the flat attachment28was decreased), the noise hardly increased when the ratio Lf/Lc was decreased from 75% to 50%. Thus, it can be considered that the lower limit of the optimum range of the ratio Lf/Lc is 50%. Since the length Lf of the flat attachment28in excess of the length Lc of the core14is meaningless, the optimum range of the ratio Lf/Lc can be identified as being 50 to 100%.

The noise test for the depth D was conducted with respect to three depths D of 1.5 mm, 3.0 mm, and 5.0 mm with the ratio Lf/Lc fixed at 100%.

As indicated by the test results shown inFIG. 8, the overall tendency was that as the depth D was increased, the noise increased, and that while a satisfactory noise reduction effect was obtained at 1.5 mm, the noise sharply increased at 3.0 mm Thus, it can be considered that the upper limit of the optimum range of the depth D is 1.5 mm Since any protrusion of the outer peripheral surface28aof the flat attachment28from the outer peripheral surface14aof the core14should be avoided to prevent interference with the field magnet, the optimum range of the depth D can be identified as being 0 (flush) to 1.5 mm.

In the brushed motor1of the present embodiment, the ratio Lf/Lc is set at 98% and the depth D is set at 0.4 mm, thus satisfying both optimum range conditions. Accordingly, the above-described noise reduction effect can be obtained.

In the brushed motor1of the present embodiment, the flat attachment28separately fabricated from the core14is inserted and fixed into the slots16for the following reasons.

In a conventional brushed motor, the slots16opening onto the outer peripheral surface14aof the core14may be filled with adhesive agent. In this case, the outer peripheral surface14aof the core14may be more or less close to being flat in cross sectional shape. However, the filling with adhesive agent is not intended to suppress the wind noise due to the slots16, but to prevent the windings17from sticking out of the slots16due to centrifugal force.

Accordingly, the adhesive agent is filled into the central portion of the slots16in the direction of the axial line L where the windings17tend to stick out. In addition, shrinkage may occur during curing, causing the surface after curing to be greatly recessed from the outer peripheral surface14aof the core14. The former may create a cause for failing to meet the condition for the optimum range of the ratio Lf/Lc, and the latter may create a cause for failing to meet the condition for the optimum range of the depth D. As a result, the adhesive agent filled into the slots16may fail to contribute to the suppression of the wind noise, thereby failing to obtain the noise reduction effect of the embodiment described with reference toFIG. 6.

In the case of adhesive agent, it may be possible to satisfy the conditions for the optimum ranges of the ratio Lf/Lc and the depth D by repeating the filling and curing. However, this would be very cumbersome and time-consuming, and can hardly be considered practical in terms of yield or manufacturing cost.

In the brushed motor1of the present embodiment, the flat attachment28separately fabricated from the core14is inserted and fixed into the slots16, making it possible to satisfy the conditions for the optimum ranges of both the ratio Lf/Lc and the depth D. In other words, the outer peripheral surface14aof the core14can be shaped into a flat cross sectional shape suitable for suppression of wind noise, thus making it possible to obtain the noise reduction effect as described above.

In addition, similarly to the adhesive agent, the flat attachment28with which the opening of the slots16is closed also provides the function of preventing the windings17from sticking out of the slots16. Furthermore, the flat attachment28extends substantially throughout the slots16in the direction of the axial line L, rather than disposed only at the central portion in the direction of the axial line L as in the case of the adhesive agent. Accordingly, the flat attachment28provides the additional effect of more reliably preventing the sticking-out of the windings17.

The optimum ranges of the ratio Lf/Lc and the depth D are not limited to the above settings. Because the wind noise due to the slots16may vary depending on the circumferential velocity of the rotor7or the width of the slots16, for example, the optimum ranges of the ratio Lf/Lc and the depth D may be modified in accordance with such requirements.

In the brushed motor1of the present embodiment, the ridges28dformed on the inner peripheral surface28cof the flat attachment28are abutted against the windings17so that the inclined side surfaces28bcan be engaged with the inclined surfaces15aof the extending portions of the teeth15. Thus, positional displacement of the flat attachment28is regulated by the elasticity of the ridges28d, and the flat attachment28is held in a predetermined position in the opening of the slots16. As a result, the outer peripheral surface14aof the core14and the outer peripheral surface28aof the flat attachment28are maintained in a predetermined positional relationship, contributing to even more reliable reduction of noise.

Second Embodiment

A second embodiment of a brushed motor1of the present invention will be described.

FIG. 9is a perspective view of a rotor7and a cooling fan23of the brushed motor1of the present embodiment.FIGS. 3 and 4, with reference to which the first embodiment has been described, also illustrate the brushed motor1of the present embodiment.

The second embodiment differs from the first embodiment in that flat attachments28are formed integrally with the cooling fan23, and that the cooling fan23is supported from the core14via the flat attachments28. Accordingly, parts having common configurations are designated with similar reference signs and their descriptions will be omitted, the following descriptions focusing on the differences.

To the base member24of the cooling fan23, the end (one end) of each flat attachment28is connected from the front side. The cooling fan23and the flat attachments28are integrally formed from synthetic resin material. The positional relationship between the base member24and the flat attachments28is set such that, with the flat attachments28being inserted and fixed into the slots16of the core14illustrated inFIG. 9, the cooling fan23is supported in a regular position as in the first embodiment.

As illustrated inFIG. 4, the rear-side ends of the flat attachments28are connected to the base member24at positions which are circumferentially aligned with any of the fins25of the cooling fan23.

When the motor1is assembled, after the windings17are wound on the teeth15of the core14, the flat attachments28having adhesive agent applied thereto are inserted into the openings of the respective slots16from the rear side along the direction of the axial line L, and are fixedly mounted therein. Consequently, the cooling fan23is necessarily disposed in the regular position on the rear side of the core14, and is supported from the core14via the flat attachments28.

In the first embodiment, it is necessary to insert the flat attachments28separately into the slots16. It is also necessary in the first embodiment to hold the cooling fan23in a regular position with respect to the core14using a jig and the like, until the adhesive agent for the cooling fan23cures. Thus, the assembly operation in the first embodiment may be cumbersome. On the other hand, in the present embodiment, it is possible to insert and fix the flat attachments28integrated by means of the cooling fan23into the slots16at once, while the cooling fan23is supported in the regular position. Thus, the assembly operation is greatly simplified and the manufacturing cost is decreased.

In the configuration of the present embodiment, rotation of the rotor7is transmitted to the cooling fan23via the flat attachments28. Accordingly, if the rotation of the rotor7is sharply changed, the connecting portions between the flat attachments28and the cooling fan23may experience a large force. In the present embodiment, the ends of the flat attachments28are circumferentially aligned with any of the fins25of the cooling fan23, so that the flat attachments28and the fins25are directly connected across the base member24.

As a result, the flat attachments28, the base member24, and the fins25together function as a single stiff body continuous in the direction of the axial line L, making it possible to reliably transmit the rotation of the rotor7to the cooling fan23without damage. Thus, the durability and reliability of the motor1are greatly improved.

While the embodiments have been described, the present invention is not limited to the embodiments. In the foregoing embodiments, the stator6have two poles, the armature9have three poles, and the brushed motor1is provided with the cooling fan23. However, the specifications of the brushed motor are not limited to the embodiments, and the number of the poles and the like of the stator6or the armature9may be modified as appropriate. When the flat attachments28of the first embodiment are implemented, the cooling fan23may be omitted unless any temperatures problems are encountered.

In the foregoing embodiments, the flat attachments28are inserted into the openings in the slots16and fixed to the core14and/or the windings17using adhesive agent. However, the method for vising the flat attachments28is not limited to the above.FIG. 10is a view along arrow C ofFIG. 9, illustrating another example based on the configuration of the second embodiment. As illustrated, hooks31may be formed at the distal end of the flat attachment28, and the hooks31are formed with a longitudinal groove32for elasticity.

When the flat attachment28is inserted into the slot16, the hooks31are bent toward each other. As the insertion is completed, the hooks31elastically recover and become hooked on the end face of the core14. Because the core14is sandwiched between the hooks31and the cooling fan23, it is possible to fix both the cooling fan23and the flat attachments28in regular positions with respect to the core14. The need for applying adhesive agent or the like to the flat attachments28as in the second embodiment is eliminated, and it is not necessary to wait until the adhesive agent cures. Accordingly, the assembly operation can be even more simplified.