Title of Invention

MOTOR FOR AN ELECTRIC POWER STEERING ASSEMBLY

Abstract

ABSTRACT OF THE DISCLOSURE A motor for an electric power steering assembly includes: a yoke; a magnetic field portion composed of four poles; a shaft disposed within the yoke; an armature secured to the shaft having a winding constructed by lap winding a wiring into twenty-two slots; a commutator comprising a plurality of segments secured to an end of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; a concave housing having a hole through which the shaft passes; a brush placed in contact with the commutator; a brush holder for holding the brush; and protrusions for positioning the center axis of the brush holder so as to be aligned with the center axis of the commutator, provided between an outer circumferential surface of the brush holder and an inner wall of the housing.

Full Text

4. Field of the Invention The present invention relates to a motor for an electric power steering assembly for assisting the steering force of an automotive steering wheel. 2. Description of the Related Art Figure 3 is a aoss-section of the internal construction of an electric power steering assembly (hereinafter "electric motor") described in Japanese Patent Laid Open No. 2000-224822, and Figure 4 is an enlargement of part of Figure 3. The electric motor includes: a cylindrical yoke (not shown); four permanent magnets (not shown) composed of ferrite spaced circumferentially and secured inside the yoke; a shaft 4 disposed inside the yoke by means of bearings so as to be able to rotate fi-eely; an armature 5 secured to the shaft 4; a commutator 7 comprising a plurality of segments 6 secured to an end portion of the shaft 4; four brushes (not shown) spaced equidistantly and placed in contact with the surface of the commutator 7 by the elastic force of springs (not shown); and an equalizer main body 10 secured to the shaft 4 between the armature 5 and the commutator 7. The armature 5 includes: a core 12 having twenty-two slots 11 extending in the axial direction; and a winding 14 constructed by winding wiring 13 into the slots 11 by a lap winding method. The equalizer main body 10 is assembled by altemately stacking terminals 16, which are eleven equalizing members, and composed of copper plate or the like, with eleven insulating plates 17 on a basel 5 composed of phenolic resin. Each of the terminals 16 has a pair of equalizing portions 16a extending radially outwards in opposite directions. The equalizing portion 16a is bent along a hook 18 and electrically connected with the hook 18 at a total of twenty-two places such that those segments 6 which should have equal electric potential with each other are connected through the terminal 16. Figure 5 is a set of diagrams and graphs of magnetic attraction and torque ripples acting on an amiature 5 having four poles, a lap winding, and twenty-two slots which the present inventas obtained by magnetic field analysis. As can be seen from the figure, in the case of a 22-slot lap-wound armature, the total magnetic attraction acting on the armature is also zero and operating noise due to rotational vibrations does not arise. Figure 6 is a front elevation of a brush holder of another conventional electric motor, Figure 7 is a side aoss-section taken along line Vll-Vll in Figure 6, wherein parts with the same as or corresponding to those of Figure 3 above have the same numbering. The electric motor includes: a cylindrical yoke; a magnets secured inside the yoke; a shaft 4 supported by means of bearings inside the yoke so as to be able to rotate freely; an armature 5 secured to the shaft 4; a commutator 7 secured to an end portion of the shaft 4; a brush holder 20 secured to a housing 22 having hole through which the shaft 4 passes by means of a screw 23; a grommet 24 engaged elastically in the concave portion 22a of the housing 22; and a lead wire 25 passing through the grommet 24. The bmsh holder 20 includes a base 27 constructed by insert molding a conductor 26; four holder portions 28 composed of metal secured to the base 27; a brush 30 held within each holder portion 28 with the brush 30 placed in contact with the commutator 7 by the elasticity of a spring 29; and a pigtail 40 having one end thereof connected the brush 30, and the other end thereof connecting with a connection 26a of the conductor 26. In the above electric motor, external current leads in by the lead wire 25, is supplied to the armature 5 via the conductor 26, the pigtails 40 and brushes 30. As a result, the armature 5 is rotated together with the shaft 4 due to electromagnetic action. In the case of lap winding, there are problems in that differences arise in the electromotive forces induced among the circuits of the winding 14 of the armature 5 due to the irrfluence of imbalances in the electromagnetic circuit of the yoke, eccentricities in the armature 5, nonuniform electric currents flowing through the brushes 9, engineering errors, etc., giving rise to circulating currents within the armature 5 flowing through the brushes 9. As a result, the commutating action of the brushes deteriorates, leading to increases in temperature, shortened working life, inaeases in torque ripples in the brushes 9 and the commutator 7 vi/hich accompany an inaease in commutation spari The conventional electric motors described above are provided with the equalizing members to prevent the above problems. As can be seen from Figure 5, in the case of a 4-pole 22-slot lap-wound armature, torque ripples (peak to peak or p-p) represented by the ratio of vertical variance in the torque wave to the total torque are 0.876 percent, the value of the torque ripples (p-p) is comparatively small. However, one problem has been that the armature 5 vibrates due to the torque ripples, to aeate operating noise. In the second conventional electric motor, one problem has been that the brush holder 20 is fixed to the housing 22 by being screwed to housing 22 with the saew 23 passing through a saew hole 31 formed in the housing 22. That is, as there is some clearance between the saew 23 and the loose hole 32 formed in the base 27, the brush holder 20 can be displaced from ifs proper position by the clearance, making contact between the brush 30 and the commutator 7 uneven, causing the performance of the electric motor to deteriorate, and shorting the wori Further, in the second conventional electric motor, another problem has been that since each of the pigtails 40 has a different bent shape, making contact between each of the brushes 30 and the commutator 7 uneven. SUMMARY OF THE INVENTION The present invention is aimed at solving the above problems and an object of the present invention is to provide a motor for an electric power steering assembly that allows operating noise to be reduced. To this end, according to the present invention, a motor for an electric power steering assembly indudes: a yoke; a magnetic field portion composed of four poles secured to an inner wall of the yoke; a shaft disposed within the yoke so as to rotate freely; and an armature secured to the shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof. The motor for an electric power steering assembly also indudes: a commutator comprising a plurality of segments secured to an end of said shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other, a concave housing having a hole through which the shaft passes; a brush placed in contact with the commutator; a brush holder for holding the bmsh; and a positioning means for positioning the center axis of the bmsh holder so as to be aligned with the center axis of the commutator, provided between an outer circumferential surface of the brush holder and an inner wall of the housing. According to another aspect of the present invention, a motor for an electric power steering assembly indudes: a yoke; a magnetic field portion composed of four poles secured to an inner wall of the yoke; a shaft disposed within the yoke so as to rotate freely; and an armature secured to the shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer drcumferential surface of a core so as to extend in the axial direction thereof. The motor for an electric power steering assembly also indudes: a commutator comprising a plurality of segments secured to an end of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other, a concave housing having a hole through which the shaft passes; a plurality of brushes placed in contact with the commutator; a brush holder having a plurality of holders for holding each of the brushes; a conductor provided in the brush noiaer, connected with an end of a lead wire which leads in external current; and a plurality of pigtails of uniform length, one end of each pigtail connected with one of the brushes respectively, the other end thereof connected with the conductor, wherein each connection of the conductor connected with one of the other ends of the pigtails, and each of the brushes are respectively disposed axisymmetrically to a center line which passes through the center of the brush holder, and extends in the radial direction thereof According to still another aspect of the present invention, a motor for an electric power steering assembly includes; a yoke; a magnetic field portion composed of four poles secured to an inner wall of said yoke; a shaft disposed within the yoke so as to rotate freely; and an armature secured to the shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof The motor for an electric power steering assembly includes; a commutator comprising an plurality of segments secured to an end of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; a concave housing having a hole through which the shaft passes; a plurality of brushes placed in contact with the commutator; and a brush holder supported through an elastic member by the housing, having a plurality of holders for holding each of the brushes. Accordingly, the present invention provides a motor for an electric power steering assembly comprising a yoke; a magnetic field portion composed of four poles secured to an inner wall of said yoke; a shaft disposed within said yoke so as to rotate freely; an armature secured to said shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of said shaft; an equalizing member connecting those of said segments that should have equal electric potential with each other; a concave housing having a hole through which said shaft passes; a brush placed in contact with said commutator; a brush holder for holding said brush; a positioning means for positioning the center axis of said brush holder so as to be aligned with the center axis of said commutator, provided between an outer circumferential surface of said brush holder and an inner wail of said housing; a conductor provided in said brush holder, connected with an end of the lead wire which leads in external current; a plurality of pigtails of uniform length, one end of each pigtail connected with one of said brushes respectively, the other end thereof connected with said conductor, wherein each connection of said conductor connected with one of said other ends of said pigtails, and each of said brushes are respectively disposed axisymmetrically to a center line which passes through the center of said brush holder and extends in the radial direction thereof Accordingly, the present invention also provides a motor for an electric power steering assembly comprising: a yoke; a magnetic field portion composed of four poles secured to an inner wall of said yoke; a shaft disposed within said yoke so as to rotate freely; an armature secured to said shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of said shaft; an equalizing member connecting those of said segments that should have equal electric potential with each other; a concave housing having a hole through which said shaft passes; a plurality of brushes placed in contact with said commutator; a brush holder having a plurality of holders for holding each of said brushes; a conductor provided in said brush holder, connected with an end of a lead wire which leads in external current; and a plurality of pigtails of uniform length, one end of each pigtail connected with one of said brushes respectively, the other end thereof connected with said conductor, wherein each connection of said conductor connected with one of said other ends of said pigtails, and each of said brushes are respectively disposed' axisymmetrically to a center line which passes through the center of said brush holder, and extends in the radial direction thereof Accordingly, the present invention further provides a motor for an electric power steering assembly comprising: a yoke; a magnetic field portion composed of four poles secured to an inner wall of said yoke; a shaft disposed within said yoke so as to rotate freely; an armature secured to said shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of said shaft; an equalizing member connecting those of said segments that should have equal electric potential with each other; a concave housing having a hole through which said shaft passes; a plurality of brushes placed in contact with said commutator; a brush holder supported through an elastic member by said housing, having a plurality of holders for holding each of said brushes; a conductor provided in said brush holder, connected with an end of the lead wire which leads in external current; a plurality of pigtails of uniform length, one end of each pigtail connected with one of said brushes respectively, the other end thereof connected with said conductor, wherein each connection of said conductor connected with one of said other ends of said pigtails, and each of said brushes are respectively disposed axisymmetrically to a center line which passes through the center of said brush holder and extends in the radial direction thereof The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention take in conjunction with the accompanying drawings. Fig. 1 is a front elevation of a motor for an electric power steering assembly according to the present invention. Fig. 2 is a side cross-section taken along the line II-II in Fig. 1. Fig. 3 is a cross-section of the internal construction of an electric power- steering assembly. Figure 4 is an enlargement of the equalizing main body of Figure 3. Figure 5 is a set of diagrams and graphs explaining magnetic attraction acting on an armature having four poles, a lap winding, four brushes, and twenty-two slots. Figure 6 is a front elevation of a brush holder of another example of a conventional motor for an electric power steering assembly. Figure 7 is a side aoss-section taken along the line VII-VII in Figure 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 An example of a motor for an electric power steering assembly (hereinafter "electric motor") according to the present invention will now be explained, and parts the same as or corresponding to those of the conventional examples will be given the same numbering. Figure 1 is a front elevation of a brush holder 50 of an electric motor of the present invention, Figure 2 is a side -section taken along the line ll-ll in Figure 1. The electric motor includes: a cylindrical yoke 1; magnets 2 secured inside the yoke 1, a shaft 4 supported so as to be rotatable freely by means of bearings inside the yoke 1; an armature 5 secured to the shaft 4; a commutator 7 secured to an end portion of the shaft 4; a housing 22 having hole through which the shaft 4 passes; a brush holder 50 secured to the housing 22 by means of a saew 23 through an elastic member 52; a grommet 24 engaged elastically in a concave portion 22a of the housing 22; and a lead wire 25 passing through the grommet 24. The protrusions 22b which serve as positioning means are formed equi-spaced in the drcumferential direction at four spots of the inner wall of the housing 22. The protrusions 22b may also be formed on the base 27. The armature 5 includes: a core 12 having twenty-two slots extending in the axial direction; and a winding 14 constructed by winding wiring into the slots by a lap winding method. Further, segments that should have equal electric potential are electrically connected with each other by an equalizing member (not shown). That is, one end portion of the equalizing member passes through a slot of the core12, extends as far as the end face of the core 12 away from the commutator 7, then makes a U-tum at the end face, passes through another slot, extends as far as the hook 18 of the segment 6, and is finally engaged at the hook 18. The bnjsh holder 50 includes a base 27 constructed by insert molding a conductor 26; four holder portions 28 composed of metal secured to the base 27; a brush 30 held within each holder portion 28 with each brush 30 placed in contact with the commutator 7 by the elasticity of spring 29; and pigtails 51 where one of each pigtail connects with the brush 30, with the other end thereof connecting with a connection 26a of the conductor 26. The length of the pigtails 51 is uniform. Further, each of the connecting portions 26a of the conductor 26 and each of the trushes 30 are respectively disposed axisymmetrically to the center line A, B which pass through the center of the brush holder 50, extending in the radial direction thereof. In this electric motor, the protmsions 22b are formed equiv-spaced in the circumferential direction at four spots of the inner wall of the housing 22. Therefore, the brush holder 50 is fixed to the housing 22 and the center axis line of the brush holder 50 are aligned with the center axis line of the commutator 7, making contact between the brush 30 and the commutator 7 more uniform. Further, as the lengths of the pigtails 51 are uniform, each of the connecting portions 26a of the conductor 26 and each of the brushes 30 are respectively disposed axisymmetrically to the center line A, B which passes through the center of the brush holder 50, extending in the radial direction thereof, variations in the state of contact of the brushes 30 to the commutator 7 can be minimized so that variations in brush noise among brushes 30 can be reduced. Furthermore, the brush holder 50 is supported on the housing 22 by the elastic members 52. Therefore, vibrations from the brush holder 50 to the housing 22 and brush sliding noise are absorbed by the elastic members 52, reducing the occurrence of brush noise due to vibration of the brushes 30 As explained above, a motor fa an electric power steering assembly according to one aspect of this invention includes: a yoke; a magnetic field portion composed of four poles secured to the inner wall of the yoke; a shaft disposed within the yoke so as to rotate freely; an armature secured to the shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; a concave housing having a hole through which the shaft passes; a brush placed in contact with the commutator; a brush holder for holding the brush; and a positioning means for positioning the center axis of the brush holder so as to be aligned with the center axis of the commutator, provided between an outer circumferential surface of the brush holder and an inner wall of the housing. Therefore, the contact condition of brushes to the commutator is more uniform, reducing the occurrence of vibrations and noise due to sliding of the brushes. Furthermore, an electric power steering assembly according to another aspect of the present invention includes: a yoke; a magnetic field portion composed of four poles secured to an inner wall of the yoke; a shaft disposed within the yoke so as to rotate freely; an armature secured to the shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; a concave housing having a hole through which the shaft passes; a plurality of brushes placed in contact with the commutator; a brush holder having a plurality of holders for holding each of the brushes; a conductor provided in the brush holder, connected with an end of the lead wire which leads in external current; and a plurality of pigtails of uniform length, one end of each pigtail connected with each one of the brushes respectively, the other end thereof connected with the conductor, wherein each connection of the conductor connected with one of the other ends of the pigtails, and each of the brushes are respectively disposed axisymmetrically to a center line which passes through the center of the brush holder and extends in the radial direction thereof Therefore, variations in the contact condition to the commutator among the brushes become small, reducing the occurrence of vibrations and noise due to sliding of the brushes. Furthermore, a motor for an electric power steering assembly according to still another aspect of this invention includes: a yoke; a magnetic field portion composed of four poles secured to the inner wall of the yoke; a shaft disposed within the yoke so as to rotate freely; an armature secured to the shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other, a concave housing having a hole through which the shaft passes; a plurality of brushes placed in contact with the commutator; and a brush holder supported through an elastic member by the housing, having a plurality of holders for holding each of the brushes. Therefore, vibrations from the brush holder to the housing, and brush sliding noise is absorbed by the elastic members, reducing the occurrence of brush noise due to vibration of the brushes. According to one form of the motor for an electric power steering assembly, the motor further may include: a positioning means for positioning the center axis of the brush holder so as to be aligned with the center axis of the commutator, provided between an outer circumferential surface of the brush holder and an inner wall of the housing. Therefore, the contact condition of bmshes to the commutator is more uniform, reducing the occurrence of vibrations and noise due to sliding of the brushes. According to another form of the motor for an electric power steering assembly, the motor includes: a conductor provided in the brush holder, connected with an end of the lead wire which leads in external current; a plurality of pigtails of uniform length, one end of each pigtail connected with one of the brushes respectively, the other end thereof connected with the conductor, wherein each connection of the conductor connected with one of the other ends of the pigtails, and each of the brushes are respectively disposed axisymmetrically to a center line which passes through the center of the brush holder and extends in the radial direction thereof. Therefore, variations in the contact condition to the commutator among the brushes become small, redudng the occurrence of vibrations and noise due to sliding of the brushes. While the invention has been desaibed in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the sprit and scope of the appended claims. WE CLAIM: 1. A motor for an electric power steering assembly comprising a yoke; a magnetic field portion composed of four poles secured to an inner wall of said yoke; a shaft disposed within said yoke so as to rotate freely; an armature secured to said shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of said shaft; an equalizing member connecting those of said segments that should have equal electric potential with each other; a concave housing having a hole through which said shaft passes; a brush placed in contact with said commutator; a brush holder for holding said brush; a positioning means for positioning the center axis of said brush holder so as to be aligned with the center axis of said commutator, provided between an outer circumferential surface of said brush holder and an inner wall of said housing; a conductor provided in said brush holder, connected with an end of the lead wire which leads in external current; a plurality of pigtails of uniform length, one end of each pigtail connected with one of said brushes respectively, the other end thereof connected with said conductor, wherein each connection of said conductor connected with one of said other ends of said pigtails, and each of said brushes are respectively disposed axisymmetrically to a center line which passes through the center of said brush holder and extends in the radial direction thereof 2. A motor for an electric power steering assembly comprising: a yoke; a magnetic field portion composed of four poles secured to an inner wall of said yoke; a shaft disposed within said yoke so as to rotate freely; an armature secured to said shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of said shaft; an equalizing member connecting those of said segments that should have equal electric potential with each other; a concave housing having a hole through which said shaft passes; a plurality of brushes placed in contact with said commutator; a brush holder having a plurality of holders for holding each of said brushes; a conductor provided in said brush holder, connected with an end of a lead wire which leads in external current; and a plurality of pigtails of uniform length, one end of each pigtail connected with one of said brushes respectively, the other end thereof connected with said conductor, wherein each connection of said conductor connected with one of said other ends of said pigtails, and each of said brushes are respectively disposed axisymmetrically to a center line which passes through the center of said brush holder, and extends in the radial direction thereof 3. A motor for an electric power steering assembly comprising: a yoke; a magnetic field portion composed of four poles secured to an inner wall of said yoke; a shaft disposed within said yoke so as to rotate freely; an armature secured to said shaft having a winding constructed by lap winding a wiring into twenty-two slots formed on an outer circumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end of said shaft; an equalizing member connecting those of said segments that should have equal electric potential with each other; a concave housing having a hole through which said shaft passes; a plurality of brushes placed in contact with said commutator; a brush holder supported through an elastic member by said housing, having a plurality of holders for holding each of said brushes; a conductor provided in said brush holder, connected with an end of the lead wire which leads in external current; a plurality of pigtails of uniform length, one end of each pigtail connected with one of said brushes respectively, the other end thereof connected with said conductor, wherein each connection of said conductor connected with one of said other ends of said pigtails, and each of said brushes are respectively disposed axisymmetrically to a center line which passes through the center of said brush holder and extends in the radial direction thereof 4. The motor for an electric power steering assembly as claimed in claim 3, further comprising : a positioning means for positioning the center axis of said brush holder so as to be aligned with the center axis of said commutator, provided between an outer circumferential surface of said brush holder and an inner wall of said housing. 5. A motor for an electric power steering assembly, substantially as herein described with reference to the accompanying drawings. Dated this 25 day of October 2002 (R RlNAIR) of DePENNING & DePENNING AGENT FOR THE APPLICANTS Dated this 25 day of October 2002 (R RlNAIR) of DePENNING & DePENNING AGENT FOR THE APPLICANTS

Documents:

0790-mas-2002 abstract-duplicate.pdf

0790-mas-2002 abstract.pdf

0790-mas-2002 claims-duplicate.pdf

0790-mas-2002 claims.pdf

0790-mas-2002 correspondence-others.pdf

0790-mas-2002 correspondence-po.pdf

0790-mas-2002 description (complete)-duplicate.pdf

0790-mas-2002 description (complete).pdf

0790-mas-2002 drawings-duplicate.pdf

0790-mas-2002 drawings.pdf

0790-mas-2002 form-1.pdf

0790-mas-2002 form-19.pdf

0790-mas-2002 form-26.pdf

0790-mas-2002 form-3.pdf

0790-mas-2002 petition.pdf