Title of Invention

A MOTOR FOR AN ELECTRIC POWER STEERING ASSEMBLY

Abstract

A motor for an electric power steering assembly indudes: an armature , secured to a shaft having a winding constructed by lap winding wiring into twenty- two slots; a commutator comprising a plurality of segments secured to an end portion of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; a second bearing disposed to an end of the shaft where a steering force of a steering is transmitted; and a first bearing disposed at the other end of the shaft, housed within a bearing housing portion of the yoke. A collision prevention member is provided between an outer ring of the first bearing and the bearing housing portion, the collision prevention member prevents the outer ring from colliding against the bearing housing portion.

Full Text

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 5 is a cross-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 6 is an enlargement of part of Figure 5. The electric motor includes: a cylindrical yoke (not shown); four permanent magnets (not shown) composed of ferrite spaced circumferentialiy and secured inside the yoke; a shaft 4 disposed inside the yoke by means of bearings so as to be able to rotate freely; 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 alternately stacking terminals 16, which are eleven equalizing members, and composed of copper plate or the like, with eleven insulating plates 17 on a basils 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 7 is a set of diagrams and graphs of magnetic attraction and torque ripples acting on an armature 5 having four poles, a lap winding, and twenty-two slots which the present inventors 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 8 is a moss-section of the intemal construction of another conventional electric motor. Parts that are similar or correspond to those shown in Fig. 5 described above will be assigned like reference numerals. The electric motor 20 comprises: a cylindrical yoke 1; four permanent magnets 2 composed of ferrite spaced circumferentially and secured inside the yoke 1; a first bearing 22 housed within a bearing housing portion 21, a shaft 4 disposed inside the yoke 1, one end of the shaft 4 supported by means of a first bearing 22 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, four banishes 9 placed in contact with the surface of the commutator 7 by the elastic force of springs 8; a brush holder 23 holding the brush 9, a housing 25 fastened to the yoke 1 by means of a screw 24, a second bearing 26 secured to the center portion of the housing 25. supporting another end portion so as to be able to rotate freely,' a boss 27 secured to the end portion of the shaft 4, and a grommet 29 wherein a lead wire 28 passes through the grommet. The armature 5 comprises: a core 12 having twenty-two slots 11 extending in the axial direction; and a winding 14 constructed by winding wiring into the slots by a lap winding method. Further, equalizing members (not shown) connect those segments 6 which should have equal electric potential with each other. That is, one end portion of the equalizing member is engaged at a hook 18 of the segment 6, another end portion of the equalizing member passes through a slot of the core 12, extends as far as the end face of the core 12 without the commutator 7, and then makes a U-tom at the end face, passes through another slot, extends as far as the hook 18 of the segment, and is finally engaged at the hook 18. 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 influence of imbalances in the electromagnetic circuit of the yoke, eccentricities in the armature 5, nonunform 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 life, in eases in torque ripples in the brushes 9 and the commutator 7 which accompany an unease in commutation generated by the brushes 9, as well as the combined effects thereof, thereby in easing operating noise. The first conventional electric motor described above is provided with the terminal 16 and the second conventional electric motor described above is provided with the equalizing member to prevent the above problem. As can be seen from figure 7, 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 valuator the torque ripples (p-p) is comparatively smaller. However, the armature 5 vibrates due to torque ripples, and this vibration creates operating noise. Further, in the case of both conventional electric motors, there is a problem that collision noise arises due to impact between the first bearing 22 and the yoke 1, the vibration from the impact is transferred to the yoke 1, and the housing 25, thereby increasing noise. 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, there is provided a motor for an electric power steering assembly includes: an armature secured to a shaft having a winding constructed by lap winding 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 portion of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; a second bearing disposed to an end of the shaft where a steering force of a steering is transmitted; and a first bearing disposed at the other end of the shaft, housed within a bearing housing portion of the yoke. A collision prevention member is provided between an outer ring of the first bearing and the bearing housing portion, the collision prevention member prevents the outer ring from colliding against the bearing housing portion. According to another aspect of the present invention, there is provided a motor for an electric power steering assembly includes: an armature secured to a shaft having a winding constructed by lap winding wiring into twenty-two slots formed on an outer drcumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end portion of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; and a second bearing disposed to an end of the shaft where a steering force of a steering is transmitted. Further, the motor for an electric power steering assembly includes: a first bearing disposed at the other end of said shaft, housed within a bearing housing portion of the yoke; a housing secured to the yoke and securing the second bearing; a grommet provided between the yoke and the housing, with a lead wire feeding the armature passing through the grommet; and an 0-ring provided between the yoke and the housing, and formed integrally with the grommet. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-section of a motor for an electric power steering assembly according to Embodiment 1 of the present invention; Figure 2 is an enlargement of part of Figure 1; Figure 3 is a front elevation of an 0-ring in Figure. 2; Figure 4 is a cross-section of the 0-ring in Figure 3 taken along the line IV-IV therein; Figure 5 is a partial cross-section of a conventional motor for an electric power steering assembly; Figure 6 is an enlargement of the equalizer main body in Figure. 5; Figure 7 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 8 is a side oases-section of another example of a conventional motor for an electric power steering assembly. DETAIED 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 side cross-section of an electric motor 50, Figure 2 is an enlargement of part of Figure 1, Figure 3 is a front elevation of an 0-ring 60 in Figure. 2, Figure 4 is a cross-section of the 0-ring 60 in Figure 3 taken along the line IV-IV therein. The electric motor 50 comprises: a cylindrical yoke 1; four permanent magnets 2 composed of ferrite spaced circumferentially and secured inside the yoke 1; a first bearing 51 housed within a bearing housing portion 21, a shaft 4 disposed inside the yoke 1, one end thereof supported by means of a first bearing 51 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, four brushes 9 placed in contact with the surface of the commutator 7 by the elastic force of springs 8; a brush holder 23 holding the brush 9, a housing 25 fastened to the yoke 1 by means of a screw 24, a second bearing 26 secured to the center portion of the housing 25, supporting another end portion so as to be able to rotate freely, and a grommet 29 with a lead wire 28 passing through the grommet 29. The armature 5 comprises: 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, equalizing members (not shown) connect those segments 6 that are to have equal electric potential to each other. That is, one end portion of the equalizing member is engaged at a hook 18 of the segment 6, another end portion of the equalizing member passes through a slot of the core 12, extends as far as a end face of the core 12 away from commutator 7, and then makes a U-tum at the end face, passes through another slot, extends as far as the hook 18 of the segment, and is finally engaged at the hook 18. The first bearing 51 which is a ball bearing, comprises a shaft ring 52 pressed on the shaft 4, balls 53 as the rolling members, a outer ring 54 provided in the bearing housing portion 21 of the yoke 1 by means of clearance fit, an 0-ring 56 composed of rubber as a collision prevention member elastically engaged in a groove 55, the groove 55 being formed on an outer circumferential surface of the outer ring 54 so as to extend in the drcumferential direction. The grommet 29 having a through hole 29a is provided between the yoke 1 and the housing 25, The lead wire 28 feeding the armature 5 passes through the through hole 29a. The grommet 29 is integrally formed with an 0-ring 60 to seal the yoke 1 and the housing 25. In this electric motor 50 as the O-fang 56 is provided between the outer ring 54 of first bearing 51 and the bearing housing portion 21, the generation of impact noise due to impact against the outer ring 54 of the first bearing 51 and the yoke 1 can be prevented. Further, the vibration transfer route which passes through the armature 5, the first bearing 51, and the yoke 1 can be cut off, enabling the reduction of the operating noise. Further, the 0-ring 60 integrally formed with the grommet 29 is provided between the yoke 1 and the housing 25, further cutting-off the vibration transfer route of the armature 5 which passes through the housing 25, enabling further reduction of operating noise. As described above, a motor for an electric power steering assembly 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 be able to rotate freely; an armature secured to the shaft having a winding constructed by lap winding 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 portion of the shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; a second bearing disposed to an end of the shaft where a steering force of a steering is transmitted; and a first bearing disposed at the other end of the shaft, housed within a bearing housing portion of the yoke; wherein a collision prevention member is provided between an outer ring of the first bearing and the bearing housing portion, the collision prevention member preventing the outer ring from colliding against the bearing housing portion. This prevents the generation of collision noise due to impact of the outer ring with the bearing housing portion, and further, cuts-off tine vibration transfer route which passes through the armature, the first bearing, and the yoke, enabling a reduction in operating noise. A motor for 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 tine inner wall of the yoke; a shaft disposed within the yoke so as to be able to rotate freely; an armature secured to tine shaft having a winding constructed by lap winding wiring into twenty-two slots famed 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 portion of said shaft; an equalizing member connecting those of the segments that should have equal electric potential with each other; a second bearing disposed to an end of the shaft a steering force of a steering is transmitted; a first bearing disposed at the other end of the shaft, housed within a bearing housing portion of the yoke; a housing secured to the yoke and securing the second bearing; a grommet provided between the yoke and the housing, with a lead wire feeding the armature passing through the grommet; and an 0-ring provided between the yoke and the housing, and formed integrally with the grommet. This cuts-off the vibration transfer route of the armature which passes through the housing, enabling a reduction in operating noise. The electric power steering assembly according to one form of the present invention includes: a housing secured to the yoke and securing the second bearing; a grommet provided between the yoke and the housing, with a lead wire feeding the armature passing through the grommet; and an 0-ring provided between the yoke and the housing, and formed integrally with the grommet. This cuts-off the vibration transfer route of the armature which passes through the housing, enabling a reduction in operating noise. WHAT IS CLAIMED: 1. A motor for an electric power steering assembly comprising: a yoke; a magnetic field portion composed of four poles secured to the inner NAZI of said yoke; a shaft disposed NA hen said yoke so as to be able to rotate freely; an armature secured to said shaft having a winding constructed by lap winding 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 portion of said shaft; an equalizing member connecting those of said segments that should have equal electric potential with each other; a second bearing disposed to an end of said shaft where a steering force of a steering is transmitted; and a first bearing disposed at the other end of said shaft, housed within a bearing housing portion of said yoke; wherein a collision prevention member is provided between an outer ring of said first bearing and said bearing housing portion, said collision prevention member preventing said outer ring from colliding against said bearing housing portion. 2. A motor for an electric power steering assembly comprising: a yoke; a magnetic field portion composed of four poles secured to the inner wall of said yoke; a shaft disposed within said yoke so as to be able to rotate freely; an armature secured to said shaft having a winding constructed by lap winding wiring into twenty-two slots formed on an outer drcumferential surface of a core so as to extend in the axial direction thereof; a commutator comprising a plurality of segments secured to an end portion of said shaft; an equalizing member connecting those of said segments that should have equal electric potential with each other; a second bearing disposed to an end of said shaft where a steering force of a steering is transmitted; a first bearing disposed at the other end of said shaft, housed within a bearing housing portion of said yoke; a housing secured to said yoke and securing said second bearing; a grommet provided between said yoke and said housing, with a lead wire feeding said armature passing through said grommet; and an O-ring provided between said yoke and said housing, and formed integrally with said grommet. 3. The motor for an electric power steering assembly according to claim 1, further, comprising: a housing secured to said yoke and securing said second bearing; a grommet provided between said yoke and said housing, with a lead wire feeding said armature passing through said grommet; and an O-ring provided between said yoke and said housing, integrally formed with said grommet. 4. A motor for an electric power steering assail substantially as herein described with reference to the accompanying drawings.

Documents:

738-mas-2002-abstract.pdf

738-mas-2002-claims filed.pdf

738-mas-2002-claims granted.pdf

738-mas-2002-correspondnece-others.pdf

738-mas-2002-correspondnece-po.pdf

738-mas-2002-description(complete)filed.pdf

738-mas-2002-description(complete)granted.pdf

738-mas-2002-drawings.pdf

738-mas-2002-form 1.pdf

738-mas-2002-form 26.pdf

738-mas-2002-form 3.pdf

738-mas-2002-other document.pdf