Title of Invention

A ROTATING ELECTRIC MACHINE

Abstract

A rotating electric machine includes a housing having a hole for receiving a rotating shaft, an approximately cylindrical inner peripheral surface, and at least one rib-shaped first projection which has a substantially trapezoidal transverse cross section and projects radially inwards from the inner peripheral surface and is elongated in an axial direction of the housing. A brush apparatus which is provided on the inner peripheral surface of the housing has a base having at least one rib-shaped second projection which has an approximately trapezoidal transverse cross section and which projects radially outwards from an outer periphery of the base and which is elongated in the axial direction of the housing. The first and second projections are aligned with and oppose each other in a radial direction of the housing to radially position the brush apparatus with respect to the housing.

Full Text

Background of the Invention 1. Field of the Invention This invention relates to a rotating electric machine having a brush apparatus secured to a housing by fastening screws. 2. Description of the Related Art Figures 5 and 6 Illustrate a portion of an example of a rotating electric machine of the type to which the present Invention relates which has been proposed In the past. Figure 5 is a front elevation of a portion of the rotating electric machine, and Figure 6 is a cross-sectional view taken along tine VI-VI of Figure 5. This example of a rotating electric machine includes an unillustrated cylindrical yoke, unillustrated field permanent magnets which are secured inside the yoke, an unillustrated shaft which is rotatably supported by an unillustrated bearing In the yoke, an unillustrated armature which is secured to the shaft, an unillustrated commutator which Is secured to an end of the shaft, a brush apparatus 1 which is secured by fastening screws 3 to a housing 2 having a through hole 15 through which the shaft passes, a grommet 4 which elastically engages with a cutout 2a In the housing 2, and lead wires 5 which pass through the grommet 4. The brush apparatus 1 Includes a base 7 which is formed by insert molding with a plate 6 inside it, four metal brush holders 8 which are secured to the base 7, and four brushes 10, each of which is held inside one of the brush holders 8 and urged into contact with the commutator by a spring 9. Electric current from the exterior of the rotating electric machine is supplied to the armature through the brushes 10 contacting the commutator, and as a result the armature rotates with the shaft. In a rotating electric machine having the above-described structure, the brush apparatus 1 is positioned with respect to the housing 2 and held in place by the fastening screws 3 which pass through loosely fitting holes 12 formed in the base 7 and screw into screw holes 11 in the housing 2. Since the fastening screws 3 pass through the holes 12 with a clearance, it is possible for the position of the brush apparatus 1 to deviate from a desired position by the amount of the clearance. As a result of the deviation, the state of contact between the brushes 10 and the commutator can become nonuniform, causing the performance of the rotating electric machine to become poor, shortening the life span of the brushes 10, and Increasing brush noise. Another possible problem with the rotating electric machine of Figures 5 and 6 relates to the installation of the lead wires 5. The lead wires 5 are normally spot welded to exposed portions of the plate 6. There are many cases in which the position in which the lead wires 5 are welded to the plate 6 deviates from prescribed positions. In such cases, after welding, when the grommet 4 is engaged with the cutout 2a in the housing 2, the lead wires 5 exert a lopsided force acts on the brush apparatus 1 due to the spot welded position of one or both of the lead wires 5 deviating from the prescribed position, and the position of the brush apparatus 1 ends up deviating from a properly centered position by the amount of the clearance between the fastening screws 3 and the holes 12. As a result, the above-described problems of poor performance, a shortened life span of the brushes 10, and increased brush noise occur. It is conceivable to prevent the above-described positional deviation of the brush apparatus 1 by decreasing the clearance between the fastening screws 3 and the holes 12 in the base 7. However, doing so requires high precision molding of the base 7 and so requires an increase in the manufacturing costs of the brush apparatus 1 as well as an increase in the time required to assemble the brush apparatus 1 in the housing 2. Summary of the Invention The present invention provides a rotating electric machine in which brushes can be made to more uniformly contact a commutator and yet which is easy to assemble. According to one form of the present invention, a rotating electric machine includes a housing having a hole for receiving a rotating shaft, an approximately cylindrical inner peripheral surface, and at least one rib-shaped first projection which has a substantially trapezoidal transverse cross section and projects radially inwards from the inner peripheral surface and is elongated in an axial direction of the housing. A brush apparatus which is provided on the inner peripheral surface of the housing has a base having at least one rib-shaped second projection which has an approximately trapezoidal transverse cross section and which projects radially outwards from an outer periphery of the base and which is elongated in the axial direction of the housing. The first and second projections are aligned with and oppose each other in a radial direction of the housing to radially position the bmsh apparatus with respect to the housing. In preferred embodiments, a plurality of the first and second projections are formed at intervals in the circumferential direction on the inner peripheral surface of the housing and the outer peripheral surface of the base, respectively. At least one of the first and second projections may have an end which is tapered towards an open end of the housing. The rotating electric machine may further include a circumferential direction positioning mechanism which positions the brushes in the circumferential direction with respect to the commutator. At least one of the first projections and second projections may be an elastic body. In preferred embodiments, the rotating electric machine includes a grommet which elasticaliy engages with a cutout in the housing, and lead wires are supported by the grommet and electrically connected to the brushes. In a preferred embodiment, at least the portion of the lead wires between the grommet and the brushes is flexible. Brief Description of the Drawings Figure 1 is a front elevation of a portion of an embodiment of a rotating electric machine according to the present invention. Figure 2 is a cross-sectional view taken along line 11-11 of Figure 1. Figure 3 is a front elevation of a portion of another embodiment of a rotating electric machine according to the present invention. Figure 4 is a cross-sectional view taken along Line IV-IV of Figure 3. Figure 5 is a front elevation of a portion of a rotating electric machine which has been proposed in the past. Figure 6 is a cross-sectional view taken along line VI-VI of Figure 5. Description of Preferred Embodiments A number of preferred embodiments of a rotating electric machine according to the present invention will be described while referring to the accompanying drawings. In the drawings. Figure 1 is a front elevation of a portion of a first embodiment of a rotating electric machine according to the present invention, and Figure 2 is a cross-sectional view taken along line 11-11 of Figure 1. Like the rotating electric machine of Figures 5 and 6, this embodiment includes an uniUustrated cylindrical yoke, a plurality of uniUustrated field permanent magnets secured inside the yoke and forming magnetic poles of the rotating electric machine, an uniUustrated shaft which is rotatably supported by an uniUustrated bearing in the yoke, an uniUustrated armature which is secured to the shaft, and an uniUustrated commutator which is secured to an end of the shaft. This embodiment further includes a brush apparatus 1 which is secured by fastening screws 3 to a housing 22 having a through hole 16 through which the shaft passes, a grommet 4 v\^ich elastically engages with a cutout 17 in a housing 22, and lead wires 5 which pass through the grommet 4 and supply electric current for driving the rotating electric machine. The brush apparatus 1 has an approximately disk-shaped base 7 which is formed by insert molding with a plate 6 inside it, four metal brush holders 8 which are secured to the base 7, and four brushes 10, each of which is held inside one of the brush holders 8 and is urged into contact with the commutator by a spring 9. The housing 22 has a recess having a substantially cylindrical inner peripheral surface 22b, and the brush apparatus 1 is housed in the recess. A plurality of rib-shaped first projections 22a are formed at equal intervals in the circumferential direction in a plurality of locations, such as at four locations, on the inner peripheral surface 22b of the recess in the housing 22. Each of the first projections 22a projects radially inwards from the inner peripheral surface 22b of the housing 22 and has an approximately trapezoidal transverse cross section and is elongated in the axial direction of the housing 22 over a portion of the length of the recess of the housing 22. As shown in Figure 4, the inner diameter of the housing 22 where the first projections 22a are formed, i.e., the diameter of a circle tangent to the top surfaces of the four first projections 22a isDh. A plurality of rib-shaped second projections 27a each having an approximately trapezoidal transverse cross section and projecting radially outwards from the outer peripheral surface of the base 7 and elongated in the axial direction of the housing 22 over a portion of the length of the recess of the housing 22 are provided on the base 7. The second projections 27a are disposed at equal Intervals at four locations around the circumference of the base 7. The outer diameter of the portion of the base 7 where the second projections 27a are provided, i.e., the diameter of a circle tangent to the top surfaces of the second projections 27a is Db. The angular spacing between adjoining second projections 27a matches the angular spacing between adjoining first projections 22a so that when the base 7 is installed inside the housing 22, each of the first projections 22a can be aligned with an opposing one of the second projections 27a. When the base 7 is inserted into the housing 22, each of the first projections 22a is aligned with one of the second projections 27a, and then the second projections 27a are guided by sliding along the first projections 22, and the base 7 is thereby radially positioned with respect to the housing 22. The inner diameter Dh of the housing 22 in the region where the first projections 22a are formed is slightly larger than the outer diameter Db of the base 7 where the second projections 27a are formed, i.e., Dh > Db, but the difference in diameter is sufficiently small that there is only a slight amount of play between opposing projections 22a and 27a, and the base 7 can undergo only a very small amount of radial movement with respect to the housing 22. In Figure 1, the difference in size between Dh and Db has been exaggerated for the purpose of clarity. As shown in Figure 2, each of the first projections 22a may be tapered at the end nearest to the open end of the housing 22 to make it easier to install the base 7 in the housing 22. The length of the first and second projections 22a and 27a in the axial direction of the housing 22 is a fraction of the total height (the radial dimension) of the bnjsh apparatus 1. In this embodiment of a rotating electric machine, the first projections 22a are formed at four locations spaced at equal intervals around the inner peripheral surface 22b of the housing 22, and the second projections 27a are formed at four locations spaced at equal intervals around the outer peripheral surface of the base 7. Therefore, if the opposing surfaces of the projections 22a and 27a are made to contact each other and then the base 7 is inserted into the housing 22, due to the guiding action of the projections 22a and 27a, the brush apparatus 1 can be smoothly inserted into the recess of the housing 22. The radial position of the brush apparatus 1 with respect to the housing 22 is determined by the projections 22a and 27a, so the state of contact of the brushes 10 with respect to the commutator is made more uniform. The guiding action of the projections 22a and 27a can be made smoother by contacting two opposing projections 22a and 27a against each other. The first and second projections 22a and 27a are each provided in only a portion in the circumferential direction of the brush apparatus 1, and they extend over only a portion of the axial length of the recess of the housing 22, so the transmission of brush noise from the brush apparatus 1 to the housing 22 can be further decreased. In addition, control of the dimensional accuracy of the projections 22a is easier compared to when projections are formed around the entire periphery of the housing 22, and productivity is increased. The number of projections 22a and 27a is not restricted. The brush apparatus 1 can be stably positioned in the radial direction by 3 or more of the first and second projections 22a and 27a. However, an even number of each of the first and second projections 22a and 27a is advantageous because with an even number, it is possible to check the dimensions of the projections by measuring with calipers or a micrometer the distance between diametrically opposed projections. Four is a convenient number for the number of projections 22a and 22b because it Is a small even number greater than 3, so it is advantageous from the standpoint of shutting off vibrations, processing, and measurement of dimensions. There are no particular restrictions on the material used to form the projections 22a and 27a. However, if at least the first projections 22a or at least the second projections 27a are formed of an elastic material such as rubber or a synthetic resin, a certain amount of dimensional errors in the projections 22a and 27a can be compensated for, assembly of the brush apparatus 1 becomes easier, and vibrations such as brush noise can be absorbed or attenuated. When an elastic material is used for the first projections 22a and/or the second projections 27a, it may be convenient for the outer diameter Db of the base 7 where the second projections 27a are formed to be slightly larger than the inner diameter Dh of the housing 22 where the first projections 22a are formed. This enables the bnjsh apparatus 1 to be smoothly inserted into the inner peripheral surface 22b of the housing 22, and the radial position of the brush apparatus 1 with respect to the housing 22 can be accurately controlled by the projections 22a or 27a, so the state of contact between the brushes 10 and the commutator becomes more uniform. When the first projections 22a and/or the second projections 27a are made of an elastic material, the end portions 5a of the lead wires 5 between the grommet 4 and the plate 6 are preferably flexible. As mentioned above, the lead wires 5 are normally secured by spot welding to an exposed location on the plate 6, and sometimes the positions in which the lead wires 5 are spot welded to the plate 6 deviate from prescribed positions. However, if the end portions 5a of the lead wires 5 are flexible, deviation of the welded positions of the lead wires 5 from prescribed positions can be absorbed by the flexible end portions 5a of the lead wires 5. Therefore, the application of a lopsided force to the brush apparatus 1 due to the deviated position of one or both lead wires 5 when the grommet 4 is elastically engaged with the cutout 17 in the housing 2 can be reduced, so positional deviation of the brush apparatus 1 due to the clearance between the fastening screws 3 and the holes 12 can be further decreased. Figure 3 is a front elevation of a portion of another embodiment of a rotating electric machine according to the present invention employing a somewhat different brush apparatus 21 from the brush apparatus 1 of the previous embodiment, and Figure 4 is a cross-sectional view taken along line IV-IV of Figure 3. In the following explanation, only those aspects of this embodiment which are different from in the preceding embodiment will be described. In this embodiment, the rib-shaped first projections 22a of the embodiment of Figures 1 and 2 have been replaced by rib-shaped first projections 22c which are similar to first projections 22a but extend over a great axial length of the recess of the housing 22. For example, in this embodiment, the first projections 22c extend continuously from the bottom wall of the recess to the open end of the housing 22. The base 7 of the brush apparatus 21 is equipped with second projections 27a, each of which opposes one of the first projections 22c. Except for the greater length of the first projections 22c, the various features of the projections 22c and 27a such as their transverse cross-sectional shape, their radial dimensions and separation, the materials of which they are made, and the number of the projections can be the same as for the projections 22a and 27a of the preceding embodiment. In this embodiment, because the first projections 22c extend over the entire length in the axial direction of the inner peripheral surface 22b of the housing 22, Insertion of the brush apparatus 21 Into the recess of the housing 22 can be accomplished more smoothly. In addition, the brush apparatus 21 can be slid to the bottom end of the housing 22 after the first and second projections 22c and 27a have been aligned with each other, so it is unnecessary to adjust the position of the brush apparatus 21 in the circumferential direction by rotating the base 7 when it is already located deep inside the recess of the housing 22. As shown in Figure 4, this embodiment includes a circumferential direction positioning device 49 for engaging the base 7 of the brush apparatus 21 with the housing 22 so as to maintain a prescribed positional relationship in the circumferential direction between the brush apparatus 21 and the housing 22. The circumferential direction positioning device 49 comprises a hole 50 formed in the bottom wall of the recess of the housing 22 and a projection 51 which is provided on the base 7 of the brush apparatus 21 opposing the bottom wall of the recess and can fit Into the hole 50. The circumferential direction positioning device 49 makes it possible to always perform correct positioning so that the brush apparatus 21 does not rotate inside the housing 22 and so that positional deviation in the circumferential direction (deviation due to rotation) does not develop. The embodiment of Figures 1 and 2 may be equipped with a similar circumferential direction positioning device. As described above, a rotating electric machine according to the present invention can provide benefits such as the following. (1) By providing a first projection on the inner peripheral surface of a housing and a second projection on the outer peripheral surface of a base of a brush apparatus, the state of contact between the brushes and the commutator of the rotating electric machine becomes more uniform, the performance of the rotating electric machine is improved, the life span of the brushes is increased, and the generation of brush noise is decreased. In addition, by contacting the projections with each other when inserting the brush apparatus Into the housing, due to the guiding action of the projections, the brush apparatus can be smoothly housed in the recess In the housing, the projections can accurately position the brush apparatus with respect to the housing In the radial direction, and the state of contact of the brushes with respect to the commutator becomes more uniform. Furthermore, by making the projections rib-shaped, the transmission of brush noise from the brush apparatus to the housing can be further decreased, the control of dimensional accuracy can be simplified, and productivity can be increased. A rotating electric machine according to the present invention is particularly advantageous when used in an electric power steering apparatus, which requires a rotating electric machine having decreased generation and transmission of brush noise compared to a conventional rotating electric machine. (2) By providing a plurality of first and second projections at intervals in the circumferential direction of the brush apparatus, guiding of the brush apparatus into the housing can be accomplished all the more smoothly by contact between opposing first and second projections. In addition, transmission of brush noise from the brush apparatus to the housing c&n be further decreased, control of dimensional accuracy becomes easier, and productivity is increased. (3) By tapering the end closest to the open end of the housing of the first or second projections, the brush apparatus can be more smoothly introduced into the housing. (4) By providing a circumferential direction positioning device for positioning the brush apparatus with respect to the housing in the circumferential direction, the brush apparatus can always be properly positioned with respect to the housing without it being necessary to rotate the brush apparatus after inserting it into the housing. (5) By forming the first or second projections from an elastic material, a certain amount of dimensional errors in the projections can be absorbed, assembly becomes easier, and vibrations due to brush noise and the like can be absorbed or attenuated. Furthermore, the state of contact of the brushes with respect to the commutator becomes more uniform. (6) By making the end portions of the lead wires between the grommet and the brushes flexible, deviations in the positions in which the lead wires are welded in place can be prevented from affecting the position of the brush apparatus. WE CLAIM: 1. A rotating electric machine comprising a housing having a hole for receiving a rotating shaft, an approximately cylindrical inner peripheral surface, and at least one rib-shaped first projection which has a substantially trapezoidal transverse cross section and projects radially inwards from the inner peripheral surface and is elongated in an axial direction of the housing; an armature which is secured to the shaft: a commutator which is secured to an end of the shaft; and a brush apparatus which is secured to the housing by a fastening screw and which has a base having a hole through which the fastening screw loosely passes and a plurality of brushes which are mounted on the base and which contact the commutator, the base having at least one rib-shaped second projection which has an approximately trapezoidal transverse cross section and which projects radially outwards from an outer periphery of the base and which is elongated in the axial direction of the housing, the first and second projections being aligned with and opposing each other in a radial direction of the housing to position the brush apparatus with respect to the housing in the radial direction. 2. The rotating electric machine as claimed in claim 1 comprising a plurality of the first and second projections formed at intervals in the circumferential direction of the housing, each of the first projections being aligned with and opposing one of the second projections. 3. The rotating electric machine as claimed in claim 1 wherein the housing has an open end, and at least one of the first and second projections has an end which is tapered towards the open end of the housing. 4. The rotating electric machine as claimed in claim I comprising a circumferential direction positioning device which positions the brush apparatus with respect to the housing in a circumferential direction of the housing. 5. The rotating electric machine as claimed in claim I wherein at least one of the first and second projections comprises an elastic material. 6. The rotating electric machine as claimed in claim 5 comprising a grommet which elastically engages with a cutout in the housing and a lead wire which is supported by the grommet and which is electrically connected to the brushes, wherein at least a portion of the lead wire between the grommet and the brushes is flexible.

Documents:

787-mas-2002 abstract duplicate.pdf

787-mas-2002 abstract.pdf

787-mas-2002 claims duplicate.pdf

787-mas-2002 claims.pdf

787-mas-2002 correspondence others.pdf

787-mas-2002 correspondence po.pdf

787-mas-2002 description (complete) duplicate.pdf

787-mas-2002 description (complete).pdf

787-mas-2002 drawings duplicate.pdf

787-mas-2002 drawings.pdf

787-mas-2002 form-1.pdf

787-mas-2002 form-19.pdf

787-mas-2002 form-26.pdf

787-mas-2002 form-3.pdf

787-mas-2002 form-5.pdf