GB2193602A

GB2193602A - Supporting brush gear in electric motor end covers

Info

Publication number: GB2193602A
Application number: GB08718530A
Authority: GB
Inventors: Takaichi Mabuchi
Original assignee: Mabuchi Motor Co Ltd
Current assignee: Mabuchi Motor Co Ltd
Priority date: 1986-08-05
Filing date: 1987-08-05
Publication date: 1988-02-10
Also published as: DE3725580A1; JPS6343550A; GB8718530D0; CN87105453A

Description

1 GB2193602A 1 SPECIFICATION The posts are normally made in an electri-

cally non-conductive material, and the posts Electric motors will usually comprise columns of substantially circular cross-section. Good support is prefera This invention relates to electric motors, and 70 bly established between the retainer portion of particularly to motors in which an end cover each arm and the respective post by the. cre houses the requisite brushgear for transmitting ation of line or point contact therebetween.

electric power to the commutator of the mo- The retainer portion normally defines two sub tor rotor. The invention is especially con- stantially planar divergant sections which sli- cerned with the construction of such end 75 dingly engage the post. The posts and/or the covers and the brushgear mounted thereon. retainer portions may be formed with projec- In many known designs of electric motors tions, normally annular or partannular, to brushes for making sliding electrical contact achieve good point or line contact there with the commutator are mounted at the ends between. It is desirable to ensure that the of resiliently flexible arms, the other ends of 80 curvature of the parts of the retainer portions which are fixed relative to terminals to which that makes contact with the post is greater external electrical connections are made. The than that of the post itself or any projections resilience of the arms urges the brushes into thereon.

contact with the commutator, and maintains In all embodiments of the invention, springs such contact while the motor is running. While 85 will normally be included for urging the this assembly is acceptable for many applica- brushes into engagement with the motor com tions, it can provoke problems, particularly in mutator, and the retainer portions into contact higher power motors. Cyclic flexure of the with the posts, to prevent an increase in con arms can develop, resulting in a sawing mo- tact resistance when power is fed to the tion of the brush of the commutator as the 90 brush arms. These springs typically extend be arm successively bends and straightens. tween spring receptacles and the respective To solve the above problem, it has been brush arms. Simple coil springs may be used, proposed to use rigid brush arms pivotally in tension or compression, but leaf or other supported at their radially outer ends on spring mechanisms Gan also be effective.

posts, and urge the brush against the commu- 95 The invention will now be described by way tator by means of springs which also carry of example and with reference to the accom the electric current to the brush arms. While panying drawings wherein:

this minimizes flexure of the brush arms, the Figure 1 is a plan view of an end cover for pivotal mounting of the arms can wear or an electric motor embodying this invention; otherwise deteriorate, resulting in translational 100 Figures 2 to 4 show enlarged end views of movement of the arms and movement of the brushgear in three embodiments of the inven brushes on the commutator surface. If the tion; pivotal support also transmits current to the Figures 5 and 7 are enlarged lateral cross- brush arms, dirt or foreign matter can infiltrate sections of a detail of post assemblies for use and cause sparking, thus also reducing the life 105 in the embodiernnts of Figures 2 to 4; of the equipment. Figure 6A and 6B show further enlarged end According to the present invention, views of a post assembly suitable for use in brushgear in an end cover for an electric mo- the invention; ? tor comprises substantially rigid brush arms Figure 8 shows in end view a previously each with a brush portion at its radially inner 110 proposed end cover construction; and end for making sliding electrically conductive Figures 9A and 9B are enlarged end views contact with the commutator, and a retainer illustrating the effect of wear on the pivotal portion pivotally supported on a post mounted mounting of the brush arm shown in Figure 8.

on the cover at its radially outer end, each Figure 1 shows diagramatically the inside of retainer portion having a cross-section which- 11-5 an end cover for an electric motor which em defines two divergant sections for slidingly en- bodies this invention. The remainder of the gaging a respective post; spring means contin- motor is not shown, apart from the commuta uously urging said divergant sections into such tor 1. The commutator 1 is at one end of the engagement to enable said pivotal movement motor received in a motor case supporting of the arms in a plane perpendicular to the 120 field magnets in the usual way. The commuta commutator axis about the posts; and sepa- tor 1 is engaged by brushes 2 mounted at the rate electric connectors for connecting the radially inner end of the brush arms 3 with brush portions to a source of electrical power. retainef portions 4 at their outer ends which Preferably, one of the electrical connectors is are pivotally supported on posts 5.

attached to the retainer portion of each brush 125 The brushgear is shown in more detail in arm, the cross-section 4 which is arcuate to Figures 2 to 4. As shown, the cross-sectional recieve the respective post, and one electrical shape of the arm retainer 4 is formed into connector is attached to each retainer portion. substantially U-shape so that the arm retainer The electrical connectors are normally in the 4 is engaged with the post 5 at two points form of pig-tails. 130 (when viewed cross-sectionally). With this ar- 2 GB2193602A 2 rangement, positional variations of the carbon drical shape having on the circumferential sur brushes on the commutator surface can be face thereof an appropriate number of annular substantially reduced or eliminated. Power is projections 5a at which the post 5 makes fed to the carbon brush 2 or the brush arm 3 contact wiht the arm retainer 4. Figures 5 and by means of an electrically conductive mem- 70 6 show such an embodiment. Figure 5 is a ber, such as a pig-tail 8 connected at a suit- detailed view of the contact portion between able location, preferably to the arm retainer 4. the post 5 having angular projections 5A, and The function of the post is thus limited to that Figure 6 is an enlarged view of the essential of supporting the arm retainer 4 without the parts thereof. Figures 6A and 6B are cross- power feeding function. By doing so, the 75 sectional enlarged views taken along the lines problem of abrasion due to the thermal and A-A and B-B in Figure 5. With this arrange electrical factors resulting from infiltration of ment, a clear and sharp contact is effected dirt or other foreign matter between the post between the annular projections 5A and the and the arm retainer 4 and formation of arm retainer 4. In this invention, in which the insulating substance, such as oxides, and the 80 post 5 does not serve as part of the power problem of unstable motor operation due to feeding path, but is used merely to rigidly poor contact between the post and the arm support the arm retainer 4 without deflection, retainer is substantially avoided. the material of the post 5 is not limited to an In Figures 2 to 4, the cross-section of the electrically conductive material, such as metal, arm retainer 4 is also substantially U-shaped, 85 but may be of other non- conductive materials, with both the upper and lower sides thereof such as ceramics.

being slightly opened toward the mouth The arm retainer 4 can have any suitable thereof, rather than being parallel. With this arcuate cross-section, with the upper and arrangement, the arm retainer 4 is caused to lower sides thereof being inclined in such a move towards the post 5 by the resiliency of 90 fashion as to lightly open towards the mouth a spring 6. When engaged and locked in posi- thereof and narrow towards the base. Conse tion, the upper and lower sides of the arm quently, the upper and lower sides thereof are retainer 4 come in contact with the post 5 not limited to planar surfaces, but may be each at one point or line(P, Po'). Thus, a two- inclined while describing a gentle concave or point contact is positively effected. By engag- 95 convex circular arc.

ing the arm retainer 4 with the post 5 by the Posts 5 having annular projections 5a have two-point contact, an extremely stable en- been described. In place of this construction, gagement can be realized without the fear of an appropriate number of projections 4b may chattering. This eliminates unwanted positional be provided on the inside surface of the upper variations of the carbon brush 2 on the com- 100 or lower side, or both the upper and lower mutator surface. sides, of the arm retainer 4 from the bottom Figure 3 shows a stage at which the brush of the arcuate cross-section toward the open- arm 3 has been caused to shift sideways due ing thereof. Figure 7 shows the arm retainer 4 to wear of the carbon brush 2 (as illustrated having projections 4b on both sides.

by dotted lines in Figure 1). Even when the 105 The spring 6 extends between the respec- brush arm 3 is shifted sideways, stable en- tive brush arm 3 and a receptacle or retainer gagement is maintained with the two-point 7, found on the cover 9 and thus relative to contact, although the contact points are the posts 5. As shown in Figure 4, the spring moved to points P, and P,'. may be mounted on the opposite side of the 0 Since power is fed by means of an electri- 110 brush arm 3 to the spring shown in Figure 2.

cally conductive pig-tail 8, connected to the The spring may be of any type, including a carbon brush 2 or the brush arm 3, the state coil spring.

of contact between the arm retainer 4 and the Figure 8 illustrates some of the problems of post 5 does not affect power feeding. That is, tne prior art. The figure shows the state positive power feeding is ensured, leading to 115 where part of the brushgear of a motor is stable motor operation since the electrically viewed in the axial direction of the motor.

conductive member 3 is connected to the car- The brush arm 3 is pushed by the spring 6, bon brush 2 or the brush arm 3, forming a and thereby the carbon brush 2 is forced into good and stable electrial connection. contact with the commutator 1 and the arm The shape of the post 5 is not limited to 120 retainer 4 is securely engaged with the post the cylindrical shape as shown in the embodi- 5. The post 5 and the spring retainer 7 are ment, but may be of any shape that can form fastened together,. leading to a terminal. Con the two point contact, in conjunction with the sequently, there can be two power feeding arm retainer 4 having a substantially U-shaped paths to the brush arm 3; one is through the cross-section. (The post 5 of cylindrical 125 spring 6 and the other through the post 5 and shape, which apparently forms a two-point the arm retainer 4. The post 5 is of a cylindri contact when viewed cross-sectionally, actu- cal shape, and the arm retainer 4 has a virtu ally makes contact with the arm retainer 4 in ally semi-circular crosssection so as to en a linear fashion). gage with the post 5.

The shape of the post 5 may be of a cylin- 130 The cylindrical post 5 and the arm retainer 3 GB2193602A 3 4 of semi-circular cross-section are engaged brush 2 on the commutator surface. This with each other, and forced into firm engage- leads to elimination of sparks that tend to be ment by the spring 6. The arm guide 5 serves generated due to such positional variations.

as part of the power feed circuit, and the Thus, one obstacle in realizing a high-power engagement of the arm retainer 4 and the 70 motor can be overcome. Power feeding to the post 5 serves as an electrical contact. If the brush arm 3 is stabilized since power is fed to post 5 and retainer 4 are separated due to the brush arm 3 or brush 2 through the elec infiltration of dirt or other foreign matter, trically conductive member 8, independently of sparks could be generated, resulting in wear the state of contact between the arm retainer of the contact. This would eventually cause 75 4 and the post 5. Motor operation is also chattering, and to deteriorated motor charac- stabilized as a result. Needless to say, the teristics. spring 6 can also serve the roll of the electri- If the post 5 engages snugly with the arm cally conductive member 8. Furthermore, the retainer 4, there can be no problem at least in post 5, which is independent of power feed theory. In practice, however, poor engagement 80 ing and only supports the arm retainer 4 with between the post 5 and the arm retainer 4 is out deflection, may be made of an electrically inevitable, as shown in Figure 9. Figures 9A non-conductive material so long as the ma and 9B are diagrams of asssistance in explain- terial has sufficient rigidity for a support mem ing the state of poor engagement, which are ber.

drawn in a lightly exaggerated fashion for clar-

Claims

ity's sake. The maximum clearance between CLAIMS the post 5 and the arm

retainer 4 is indicated 1. An end cover for an electric motor, by d. Figure 9A shows the brush arm 3 which cover has mounted thereon brushgear moved to its lower limit, while Figure 9B the for transmitting electric current to the commu brush moved to is upper limit. 90 tator of the rotor of the motor, the orushgear In these states of engagement, the following comprising substantially rigid brush arms each problems might result. with a brush portion at its radially inner end for making sliding electrically conductive con (1) Unwanted position variation of carbon tact with the commutator, and a retainer por brush on commutator surface. 95 tion pivotally supported on a post mounted on Assume that the commutator 1 shown in the cover at its radially outer end, each re- Figure 8 is rotated counterclockwise. As the tainer portion having a cross-section which de commutator 1 begins rotating, an upward ten- fines two divergant sections for slidingly en sile force is exerted on the right-hand carbon gaging a respective post; spring means contin brush
2 and a downward tensile force on the 100 uously urging said divergant sections into such left-hand carbon brush 2 due to the resulting engagement to enable said pivotal movement frictional force. As the commutator 1 keeps of the arms in a plane perpendicular to the rotating, both the brushes 2 tend to recover commutator axis about the posts, and sepa their respective orginal positions rather irregu- rate electrical connectors for connecting the larly. As a consequence, the brush arm 3 105 brush portions to a source of electrical power.

tends to irregularly alternate between the 2. An end cover for an electric motor ac- states shown in Figures 9A and 9b. Thus, the cording to Claim 1 wherein one of the electri carbon brush 2 changes its position on the cal connector is attached to the retainer por surface of the commutuator 1 in a so-called tion of each brush arm has, cross-section of saw-tooth motion, with the consequnce that 110 which is arcuate to recieve the respective sparks are generated, posing great difficulty in post, one electrical connector being attached high-power motors. to each retainer portion.
3. An end cover for an electric motor ac- (2) Unstable motor operation due to poor con- cording to Claim 1 or Claim 2 wherein the tact between arm gu, ide and arm retainer. 115 posts are formed with axially spaced annular As described above, the brush arm 3 irregu- projections for engagement by the divergant larly alternates the states shown in Figure 9A sections of the retainer portions.

and 913, so that the contact point between the
4. An end cover for an electric motor ac- post
5 and the arm retainer 4 also fluctuates cording to Claims 1 or Claim 2 wherein pro irregularly. In the power feeding path through 120 jections are formed on the divergant sections the post 5 and the arm retainer 4, electrical which engage the posts.

contact oetween both is continuously shifting 5. An end cover for an electric motor ac- and gradually deteriorated as the positional recording to any preceding Claim where the lationship between the post 5 and the arm spring means comnprises springs which ex retainer 4 varies. This also results in deterio- 125 tend between spring receptacles fixedly rated motor chacteristics. mounted on the cover and the respective As described above, this invention makes it brush arms.

possible to achieve a stable engagement of
6. An end cover for an electric motor ac- the brush arm 3 with the post 5, eliminating cording to any preceding Claim wherein the unwanted positional variations of the carbon 130 brush portions comprise separate brushes 4 GB2193602A 4 mounted on and electrically coupled to the brush arms.
7. An end cover for an electric motor ac- cording to any preceidng Claim wherein the electrical connectors are in the form of pig- tails.
8. An end cover for an electric motor ac- cording to any preceding Claim wherein the posts are made of an electrically non-conduc- tive material.
9. An end cover for an electric motor sub- stantially as described herein with reference to Figures 1 to 7 of the accompanying drawings.
10. An electric motor comprising a motor case with an open end; field magnets; and a rotor mounted therein for rotation between the field magnets, the rotor having a commutator at one end, and the motor having an end cover according to any preceding Claim clos- ing the open end of the motor case with the brush portions thereof engaging the commuta tor on the rotor.

Published 1988 at The Patent Office, State House, 66 /71 HighHolborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD.

Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.