Brush holding structure for motor

Abstract: A brush holding structure is provided for guiding a brush to a commutator which is supported in a motor case. The structure includes an insulator plate which is attached to the motor case. The insulator plate is provided with guide means for guiding the brush in a direction which is inclined to a radial direction of the commutator within a plane including the axis of the commutator. The structure further includes a plate-­ like spring which has, at its both ends, coil portions for winding up. An intermediate part of the plate-like spring presses the brush against the commutator to hold the brush without any play into contact with the commutator.

Description: Field of the Invention The present invention relates to a brush holding structure for a motor disposed in a motor case comprising: a brush to be pressed against a commutator to make contact therewith; a spring for pressing the brush against the commutator, the spring comprising coiled end portions, a flat pressing portion provided at an intermediate portion thereof to contact and press the brush toward the commutator, and a pair of holding portions respectively, provided between each of the coiled end portions and the flat pressing portion; and guide means for holding and guiding the brush in a direction in which the brush comes into contact with the commutator. Brush holding structures of said type are known from US-A-4 371 803 or US-A-4 800 313. In these motors, however, because pressing forces for the respective brushes vary as the brushes wear, it is impossible to always give the respective brushes uniform pressing forces. Moreover, in these motors, consideration is given only to the play of the respective brushes occurring in the radial directions of the commutators, and the play of the respective brushes occurring in the axial directions of the commutators has not been considered. Hitherto, therefore, in order to eliminate the play of each brush which occurs in the axial directions of a commutator, a structure for inclining the brush within a plane along the axial direction of the commutator has been proposed in JP-A-58-112075. However, even with this motor, a biasing force for pressing the brush varies as the brush wears, and it is therefore impossible to ensure elimination of the play of the brush. Generally, brushes of a direct current motor are so arranged as to be pressed against a commutator in radial directions thereof, or in directions perpendicular with respect to the axis of the commutator. In these holding structures there is play which allows fine movements due to a clearance between the brush holder and the brush to cause the occurrence of noise at the time when the motor rotates. Therefore, a structure for biasing each brush in a tangential direction of a commutator by means of a resilient body to press the brush against the interior of a holder has been proposed in JP-A- 61-62547. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a structure for holding a brush, which is capable of eliminating the play of a brush in the plane including the rotary shaft of a commutator while being capable of always obtaining a uniform pressing force for the brush even when the brush wears. The technical solution offered by the present invention is characterized features which are indicated in the characterising portion of claim 1. According to the invention, the brush is inclined by the guide means within the plane which includes the rotary shaft of the commutator, and receives a pressing force due to the bias by the spring. Accordingly, the brush is always pressed in one of the axial directions of the commutator at the time when the commutator rotates, and the play of the brush in the axial directions of the commutator can be prevented. Further, because the brush is pressed against the commutator by the intermediate part of the leaf spring which has both ends formed into coiled portions, the coiled portions enable the spring to give the brush a substantially uniform pressing force even when the brush has worn. In addition, as the holding portions formed on the both sides of the brush pressing portion hold the brush in the tangential direction of the commutator, the play of the brush within the plane which is perpendicular to the axis of the commutator can also be prevented. Further, receiving portions which receive the respective coiled portions of the spring may be so formed that they do not support the coiled portions at axes thereof by means of support shafts but support the same correspondingly with the circumferences of the coiled portions. With these receiving portions, any unnecessary external force is not caused even when the spring is drawn out from or wound up into said coiled portions, so that a uniform biasing force can be provided for the commutator pressing portion. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view showing an essential part of the structure according to an embodiment of the present invention; Fig. 2 is a sectional view taken along the axis of the motor showing a motor to which the invention is applied. Fig. 3 is a front view showing the state in which brushes are installed on an insulator plate. The view is equivalent to a plan view of the motor shown in Fig. 2; Fig. 4 is a sectional view taken along line IV - IV in Fig. 3; Fig. 5 is a front view of the insulator plate; Fig. 6 is a sectional view taken along line VI - VI in Fig. 5; Fig. 7 is a side view of the plate shown in Fig. 5; Fig. 8 is a rear view of the plate shown in Fig. 7; Fig. 9 is a sectional view showing the relationship between the brush and a coil spring. The view corresponds to a section taken along line IX - IX in Fig. 10A; Fig. 10A is a front view of a brush holder, Fig. 10B is a sectional view taken along line XB - XB in Fig. 10A; Fig. 10C is a plane view of the brush; and Fig. 10D is a sectional view of leg portions in their caulked state. The view corresponds to a section taken along line XD - XD in Fig. 10C. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 2, a motor 10 to which the present invention is applied is shown. This motor 10 has a rotary shaft 14 which is coaxially inserted into a cylindrical shaped motor case 12 and supported by a bearing 16 and a bearing 22. The bearing 16 is provided in a bottom portion of the motor case 12, while the bearing 22 is secured to a bracket 18 which is fitted into an inlet opening of the motor case 12. The rotary shaft 14 is provided with a coil 24 which is wound around a core and which corresponds to magnets 26 fixed on the inner periphery of the motor case 12. An insulator plate 28 is fixedly installed to the bracket 18 in the inlet opening of the motor case 12. This insulator plate 28 is formed of a thin synthetic resin as shown in Figs. 1 and 5 through 8, and has a through hole 32 perforated in a central portion thereof. As shown in Fig. 8, on the rear side of the insulator plate, three fixing legs 34 are formed to protrude so that they surround the through hole 32. The insulator plate 28 is secured to the bracket 18 via these fixing legs 34 and spacers 36 as shown in Fig. 4. A commutator 38 is fixedly installed on the rotary shaft 14 to rotate under the condition that it is inserted into the through hole 32. On the insulator plate 28, raised portions 42 are formed integrally therewith at opposite positions with the through hole 32 lying therebetween. The top face of each of these raised portions 42 is heightened at its remoter end from the through hole 32 in such a manner that it is inclined within the plane including an axis S of the rotary shaft 14, which serves as a rotary shaft of the commutator 38, at an angle ϑ with respect to a radial direction of the rotary shaft 14 so as to form an inclined surface 42A. Brush holders 44 are securely installed on these inclined surfaces 42A, respectively. Each holder 44 is made of a thin plate material by bending the same as shown in Figs. 1 and 10, and is in the shape of an inverted letter U in cross section in which a pair of leg portions 44B are respectively bent at right angles to a top portion 44A of the brush holder on both sides thereof. Each leg portion 44B has a fixing piece 44c which projects therefrom to be inserted into a fixing hole 46 formed in the corresponding raised portion 42. The bush holders 44 are fixedly attached onto the respective inclined surfaces 42A by bending the ends of the fixing pieces at the rear of the insulator plate 28. In this state, each brush holder 44 holds a brush 48 between the holder and the corresponding inclined surface 42A to guide the same along the inclined surface 42A of the raised portion in a direction, as indicated by an arrow A , for contact of the brush with the commutator 38 in the through hole 32. This direction is inclined within the plane including the axis S of the rotary shaft 14 at the angle ϑ with respect to the radial direction of the rotary shaft 14. Each brush 48 is in the shape of a substantially rectangular block, and its bottom face 48A serves as a sliding face on the inclined surface 42A. A top face 48B of the brush is parallel to a bottom face 48A thereof, and a rear face 48C of the brush is perpendicular to the bottom face 48A. However, a face 48D of the brush for contact with the commutator 38 is inclined at angle ϑ to the rear face 48C so as to come into contact with an outer periphery of the commutator 38 over a wide area. The commutator is formed in a cylindrical shape around the axis of the rotary shaft 14. The leg portions 44B of each brush holder 44 are made identical in their heights from the inclined surface 42A of the raised portion, and the top portion 44A of the holder is parallel to the top face 48B of the brush 48. Further, an elongated slit 52 is formed in the top portion 44A of the brush holder 44 to longitudinally extend from a front end thereof (the end closer to the commutator 38) and serves as a slit for allowing the passage of a connection pig tail 54 which leads to the bottom face 48A of the brush 48. Moreover, in each of the front ends of the leg portions 44B of the brush holder 44, a piece 56 cut and bent outwardly, is formed at its front end to thereby form a substantially U shaped rectangular cut-out portion 58. Opposite edges 58A and 58B of the cut-out portion 58 are parallel to the inclined surface 42A to serve as guide faces for a leaf spring 62. More particularly, the leaf spring 62 has coil portions 62A formed at both ends thereof, and an intermediate part of the leaf spring constitutes a pressing portion 62B which is to come into abutment with the rear face 48C of the brush 48 so as to press the brush 48 against the commutator 38 by a biasing force of the coil portions 62A. The width of this leaf spring 62 is so sized as to be slightly smaller than the distance between the opposite edges 58A and 58B, so that the leaf spring 62 is positioned widthwise by the cut-out portions 58 when being drawn out or wound up. Further, the leaf spring 62 is so arranged as to rest at one of its widthwise edges on spring receiving portions 64 which are formed on the respective raised portions 42 at opposite positions thereof to further protrude above the raised portions 42. By virtue of this arrangement, even when the leaf spring 62 receives an external force in the direction in which it presses the brush 48, (in the direction of the arrow A ) the coil portions 62A are prevented from unraveling into a so-called bamboo shoot or telescope phenomenon in which their inner winding layers coaxially slip out from their outer winding layers in the axial direction thereof. Incidentally, these spring receiving portions 64 are formed at the same angle ϑ of inclination as the inclined surface 42A. Spring receiving walls 66 respectively protrude from end faces on through hole 32 sides of the spring receiving portions 64 to confront the cut pieces 56. Each spring receiving wall 66 has, on the opposite side thereof to the brush holder 44, an end portion which is bent at a substantially right angle with respect to the remaining portion of the wall, and is formed into the shape of a letter L , so that the spring receiving wall 66 encloses, in cooperation with the corresponding cut piece 56, the coil portion 62A to hold the same. Thus, the cut piece 56 and the spring receiving wall 66 do not restrain the coil portion 62A at the axis thereof, but constitute a receiving portion which holds the coil portion 62A correspondingly with its circumference. These receiving portions support the circumferences of the respective coil portions 62 to prevent an unnecessary external force from acting on the coil portions 62 when the leaf spring is drawn out or wound up, and further serve to support the leaf spring 62 when the brush 48 is assembled. Incidentally, opposite side faces 64A of the spring receiving portions 64, which portions are respectively raised at opposite positions on each raised portion 42, are arranged to abut against the outer sides of the respective leg portions 44B at positions close to the inclined surface 42A and the through hole 32. This prevents the leg portions 44B of each brush holder 44 from spreading outwardly. As shown in Fig. 10, in heightwise intermediate parts of each brush holder 44, enlarged width portions 68 are formed to widen the widthwise size for receiving the brush 48. These enlarged width portions 68 are provided for receiving holding portions 62C of the leaf spring 62. The holding portions are positioned on opposite sides of the brush 48 when the same is held in the brush holder 44. The holding portions 62C are continuously formed on both sides of the pressing portion 62B so that the pressing portion 62B and the holding portions 62c present substantially the shape of an inverted letter U as shown in Fig. 9. Accordingly, the enlarged width portions 68 stretch to the respective rectangular cut-out portions 58, and the leaf spring 62 has the holding portions 62C which are received in the enlarged width portions 68 and respectively stretch through the corresponding rectangular cut-out portions 58 to the coil portions 62A. Consequently, the holding portions 62C hold the leaf spring 62 in a direction of rotation of the commutator 38, or tangential directions thereof as indicated by arrows B , to eliminate the play of the brush 48 in this direction. In addition, as the pressing portion 62B presses, within the brush holder 44, the brush 48 in the arrow A direction against the commutator 38, the brush 48 is supported at its interconnecting part of the bottom face 48A and the abutment face 48D by an end face of the inclined surface 42A which is close to the through hole 32. This produces the moment in which an interconnecting part of the top face 48B is pressed against an inside of the top portion 44A of the brush holder, so that the brush is securely received in the brush holder 44 without any play so as to eliminate the play in the plane which includes the axis of rotation of the commutator. Incidentally, in the leaf spring 62, the coil portions 62A which respectively serve as hair springs always exert spring forces in directions in which the respective holding portions 62C are wound up. These spring forces are constant in magnitude, owing to the characteristics of hair springs, irrespective of amounts of the respective holding portions 62C being wound up into or drawn out from the coil portions 62A, and therefore, a substantially uniform biasing force can be exerted in the direction of the arrow A on the brush 48 irrespective of its size. The operation of the present embodiment will now be described. When each brush holder 44 has been fixed onto the insulator plate 28 by means of the fixing pieces 44C of the holder 44, the leaf spring 62 is brought into a state in which the coil portions 62A are mounted on the respective spring receiving portions 64. In this state, the pressing portion 62B of the leaf spring lies at the front end of the brush holder 44. Upon inserting the brush 48 into the brush holder 44 from the through hole 32 side thereof in the opposite direction to the arrow A direction, the pressing portion 62B is pressed by the rear face 48C of the brush 48 to move in the direction away from the through hole 32 while drawing out parts of the coil portions 62A. By the above insertion, the pig tail 54 of the brush 48 is received in the elongated hole 52. Then, the connection of this pig tail 54 is completed, and the insulator plate 28 is fixed to the bracket 18 as shown in Fig. 2 to be attached to the motor case 12 via the bracket 18. In this installation, the rotary shaft 14 is inserted through the bearing 22 in the bracket 18, and the commutator is disposed in the through hole 32. As a result, the respective brushes 48 are pressed against the outer periphery of the commutator 38 by the biasing forces of the leaf springs 62. During the rotation of the rotary shaft 14, as each brush 48 is inclined at the angle ϑ , within the plane including the axis S of the rotary shaft 14, with respect to the direction which intersect the axis at right angle, the brush 48 abuts at its front end and rear end against the inclined surface 42A of the corresponding raised portion and the top portion 44A of the brush holder, respectively, and play thereof is prevented. Further, in the direction of rotation of the commutator 38, the holding portions 62C hold the brush to eliminate play thereof in this direction. When the brush 48 become worn due to the rubbing against the commutator 38, the coil portions 62A of the leaf spring gradually wind up the respective holding portions 62C, while continuing to always press the brush 48 against the commutator 38 with a uniform force by the biasing of their coil springs. Additionally, as the leaf spring is supported at its widthwise opposite edges by the rectangular cut-out portions 58 of the holder, it does not come off the brush holder 44 inadvertently. Incidentally, although in the above embodiment, the direction of pressing of each brush (the arrow A direction) is inclined with respect to the radial direction of the axis S of rotation in such a manner as to get near the coil 24 as shown in Fig. 2, it may be inclined with respect to the radial direction of axis S of rotation in the opposite direction to that in the embodiment.

Claims: A brush holding structure for a motor disposed in a motor case (12) comprising: a brush (48) to be pressed against a commutator (38) to make contact therewith; a spring (62) for pressing the brush (48) against the commutator (38), the spring (62) comprising coiled end portions (62A), a flat pressing portion (62B) provided at an intermediate portion thereof to contact and press the brush (48) toward the commutator (38), and a pair of holding portions respectively provided between each of the coiled end portions (62A) and the flat pressing portion (62B); and guide means (28,42,44) for holding and guiding the brush (48) in a direction in which the brush (48) comes into contact with the commutator (38) characterized in that the guide means has an inclined portion (42A) which is inclined with respect to the radial direction of the commutator (38) within a plane including the axis of rotation of the commutator (38); the guide means (28,42,44) include an insulator plate (28) which is connected to the motor case (12); the insulator plate is integrally provided with spring seat portions (64) to support end faces of the coil portions (62A) of the spring (62); and the spring seat portions (64) have an inclined surface which is parallel to the inclined portion (42A) of the guide means (28,42,44). A brush holding structure for a motor according to claim 1, characterized in that the guide means (28,42,44) has a holder (44) fixedly attached to the insulator plate (28) for receiving the brush (48), thereby maintaining an angle of inclination of the brush with accuracy. A brush holding structure for a motor according to claim 1, characterized in that the inclined portion (42A) is formed on the insulator plate (28) for guiding the brush (48) in an inclined direction. A brush holding structure for a motor according to claim 3, characterized in that the brush (48) is formed in a rectangular shape in a cross section which is taken perpendicularly to the direction in which the brush (48) is guided, the bottom of the brush (48) being guided along the inclined portion (42A), and the top and both lateral sides of the brush (48) being guided by said holder (44). A brush holding structure for a motor according to claim 2, characterized in that the holder (44) is comprised of a top portion (44A) and leg portion (44B) with fixing pieces (44C), the top portion (44A) being formed in a plate-like shape disposed so as to be parallel to the inclined portion (42A) of the insulator plate (28) and corresponds to the top face of the brush (48), the leg portions (44B) being bent at substantially right angles from the top portion (44A), and the fixing pieces (44C) being fixedly attached to the insulator plate (28). A brush holding structure for a motor according to claim 5, characterized in that the leg portions (44B) of the holder (44) are respectively provided at in inner sides thereof with an enlarged width portion (68) for receiving the pair of holding portions of the spring (62). A brush holding structure for a motor according to claim 5, characterized in that the leg portions (44B) at their parts closer to the commutator (28) are respectively provided, with cut-out portions (58) for guiding interconnections of the holding portions and the coiled end portions (62A) of the spring (62), both edges of the cut-out portions facing widthwise ends of the spring (62) to restrain said spring (62) from moving widthwise, the spring (62) being led from inside of the holder (44) to the outside thereof. A brush holding structure for a motor according to claim 1, characterized in that the end faces of the coiled end portions (62A) of the spring (62) are supported on the pair of spring seat portions of the insulator plate (28) parallel to the inclined portion (42A) of the insulator plate (28). A brush holding structure for a motor according to claim 1, characterized in that a spring receiving wall (66) is formed on each of the spring seat portions (64) of the insulator plate (28) to protrude therefrom to constitute a receiving portion facing and supporting an outer surface of each of the coiled end portions without being restrained at a central parts of said coiled end portions (62A). A brush holding structure for a motor according to claim 9, characterized in that the holder (44) comprises a cut-out portion (58) formed by bending cut sections (56) outwardly in a continuous and integral manner from one end of the cut-out portion (58), the cut-sections (56), respectively, accomodating the coiled end portions (62A) of the plate-like spring (62) between the cut-sections (56) and the spring receiving walls (66). A brush holding structure for a motor according to claim 5, characterized in that a space between the spring seat portions (64) constitutes a portion for allowing insertion of the leg portions (44C) of the holder (44), thereby preventing that the distance between the leg portions of the holder is widened inadvertently.

Inventors: NAKATA MASASHI, SHIMMURA TETSURO, NAKATA, MASASHI, SHIMMURA, TETSURO
Applicants: ASMO CO LTD, ASMO CO., LTD.
Application year: 1990
Main classification: H01R39
IPC codes: H02K13, H02K5, H01R39, H02K23