An assembled commutator

Abstract: An assembled commutator has an insulating commutator body (1 to 4) having a cylindrical outer surface (1), radially extending axial support means (2) and an axial extension (15) on the opposite side of the axial support means (2) to the cylindrical outer surface (1). Three commutator segments (5 to 8) each have an arcuate brush-contacting portion (5) seated on the cylindrical outer surface (1) of the commutator body (1 to 4), an axial terminal stem (7) extending through a passage (3) formed in the axial support means (2), and a radial terminal stem (8) seated in one of three equiangularly extending radial grooves (11) formed in the axial support means (2). An apertured insulating clamping member (9) which is press-fitted on a first part (16) of the axial extension (15) clamps an apertured varistor (10) which is seated on a second part (21) of the axial extension (15) in electrically conductive engagement with the radial terminal stems (8).

Description: Field of the Invention The invention relates to an assembly in which the components of an assembled commutator and an electromagnetic interference suppressor element, such as a varistor, are formed separately and subsequently fitted together. Background Art One way to fasten metallic commutator segments to the insulating body of a commutator is to provide these segments as inserts in a moulded plastics commutator body. However, this moulding process requires precise and time-consuming positioning of the commutator segments and the resultant moulded commutators have to be individually hand finished to remove the inevitable unwanted excessive pieces of plastics material. To avoid this difficulty, the commutator body and the commutator segments are formed separately so as to cooperate with each other and are subsequently assembled in a manner which ensures that the segments are securely fastened to the commutator body by means of an insulating clamping member. Where an assembled commutator such as this is to be provided with an electromagnetic interference suppressor element, this element may also be held in place by the insulating clamping member. Thus, as disclosed in the specification of UK Patent No. 2 183 933 it is known to provide a commutator comprising an insulating commutator body having a cylindrical outer surface and integral, radially extending axial support means; at least three commutator segments mounted on the body, each having an arcuate brush contacting portion seated on the cylindrical outer surface of the body, radial positioning means extending axially from one end of the brush contacting portion, and a radial terminal stem; an apertured electromagnetic interference suppressor element; and an insulating clamping member for clamping the radial terminal stems and the suppressor element together between the axial support means and the insulating clamping member. In this known construction, the radial terminal stem of each commutator segment extends radially from one end of the arcuate portion of the segment forming the brush contacting portion and two axial projections extend on opposite sides of the radial terminal stem. The suppressor element is an elastomeric annular ring which must be fitted over the cylindrical outer surface of the commutator body and the clamping member is an annular ring which must be press-fitted over the brush contacting portions of the commutator segments so as to clamp the segments to the commutator body and to clamp the radial stems against the suppressor element. As a result, difficulty is encountered in fitting the clamping member. The two axial projections on each segment must also be inserted between the cylindrical outer surface of the commutator body and the suppressor element and this is accomplished as a result of resilient deformation of the elastomeric suppressor element. However, when the segments are secured in position by the clamping member, the radial loading on the segments is provided solely, or almost solely, by the clamping member. Disclosure of Invention The purpose of the present invention is to provide an assembled commutator-suppressor assembly in which the components can be more easily and effectively assembled and in which the suppressor element is not necessarily of resiliently deformable elastomeric construction. This is achieved by constructing the commutator so that the commutator body is provided with an axial extension on the opposite side of the axial support means to the cylindrical outer surface; the axial support means are formed with axially extending openings which each have a passage which extends right through the axial support means; the radial positioning means comprise axial terminal stems disposed respectively within the passages; the radial terminal stems extend respectively from the axial terminal stems on the opposite side of the axial support means to the brush contacting portions of the commutator segments; and the apertured suppressor element is mounted on the axial extension between the radial terminal stems and the clamping member. Thus, according to the invention, there is provided an assembled commutator-suppressor assembly comprising an insulating commutator body having a cylindrical outer surface, radially extending axial support means formed with axially extending openings each having a passage which extends right through the axial support means, and an axial extension on the opposite side of the axial support means to the cylindrical outer surface; at least three commutator segments mounted on the body, each having an arcuate brush contacting portion seated on the cylindrical outer surface of the body, radial positioning means, comprising an axial terminal stem, extending axially from one end of the brush contacting portion into one of the axially extending openings so that the axial terminal stems are respectively disposed within the passages, and a radial terminal stem extending from the axial terminal stem on the opposite side of the axial support means to the brush contacting portion; an apertured electromagnetic interference suppressor element mounted on the axial extension; and an insulating clamping member for clamping the radial terminal stems and the suppressor element together between the axial support means and the insulating clamping member. Each commutator segment is formed initially with a strip extending from one end of its brush contacting portion. During assembly, this strip is passed through one of the passages in the axial support means and the free end of the strip is bent radially outwards so that the axially extending and radially extending portions of the strip form axial and radial terminal stems. This form of construction simplifies the provision, as part of the assembly, of an electromagnetic suppressor element such as a varistor which may be clamped in contact with the radial terminal stems between the axial support means and the clamping member. The apertured suppressor element may be mounted around the axial terminal stems, between the axial support means and the radial terminal stems. However, in this case, because suppressor elements such as varistors are sometimes made of relatively brittle and/or friable sintered material which could be damaged while bending the commutator segment strips to form the radial terminal stems, the electromagnetic interference suppressor element is preferably mounted between the radial terminal stems and the clamping member. The axial support means therefore may be provided with radial grooves extending from the axially extending passages for accommodating the radial terminal stems. Each such groove must be shallower than the thickness of the radial terminal stem accommodated in said groove so that the radial terminal stem stands axially clear of the axial support means and is able to contact the adjacent clamping member or suppressor element. In order to connect armature leads to the commutator segments, a "U"-shaped configuration may be formed at the outer extremity of each radial terminal stem, with an inner axially extending arm which rests on the clamping member and an outer arm joined to the inner arm so that each armature lead can be clamped between the inner and outer arms of the "U"-shaped configuration. Where this clamping operation is performed with the application of heat, to effect welding between the inner and outer arms, the clamping member may be made of a heat and pressure resistant material, such as glass fibre impregnated epoxy resin, capable of withstanding the pressures and temperatures encountered in the hot staking process adopted to effect the welding. The axial extension of the commutator body is provided on the opposite side of the axial support means to the cylindrical outer surface to simplify mounting of the clamping member and the suppressor element. The axial extension may be provided with a first part for seating the clamping member and the clamping member may be provided with an aperture which receives the first part of the axial extension. In this case, the axial extension is preferably circular in cross-section. This simplifies construction and assembly of the components. Where the diameter of the first part of the axial extension is larger than the diameter of the cylindrical outer surface of the commutator body, the first part may be formed with axially extending grooves aligned with the passages for receiving the strips extending from the brush contacting portions of the commutator segments when these strips are passed through the passages formed in the axial support means. In this case, where a "U"-shaped configuration is formed at the outer extremity of each radial terminal stem and the inner axially extending arms of these configurations rest on circumferentially spaced portions of the clamping member, the clamping member may be provided with at least one inwardly projecting portion seated in one of said axially extending grooves. This ensures that the circumferentially spaced portions are angularly aligned with the "U"-shaped configurations. The axial extension may also be provided with a second part, having a greater diameter than the first part, for seating the suppressor element. As in the case where the first part of the axial extension is larger than the diameter of the cylindrical outer surface of the commutator, where the diameter of the second part of the axial extension is larger than the diameter of the outer cylindrical surface, the second part may be formed with axially extending slots aligned with the passages to enable the commutator segments to be mounted on the commutator body. Although separate fastening means may be provided for holding the clamping member in place, the clamping member is preferably press-fitted on the first part of the axial extension. An assembled commutator-suppressor assembly according to the invention and incorporating various optional features is hereinafter described, by way of example, with reference to the accompanying drawings. Brief Description of the Drawings Figure 1 is an elevational view of one of three commutator segments of an assembled commutator; Figure 2 is an exploded sectional side elevation of an insulating commutator body and a segment as shown in Figure 1; Figure 3 is a perspective view of the commutator body and the segment of Figure 2, showing the parts at a later stage of assembly; and Figures 4 and 5 are exploded and assembled perspective views of an assembly, according to the invention, incorporating an assembled commutator and an electromagnetic interference suppressor element. Best Modes for Carrying-Out the Invention The commutator segment shown in Figures 1 and 2 comprises an arcuate brush contacting portion 5 and, extending from one end of the brush contacting portion 5, two radial positioning members 6 and an integral strip 22 having, at its inner end, between the members 6 an axial terminal stems 7 which serves as an additional radial positioning member. As shown in Figure 2, the commutator body has a cylindrical outer surface 1, an annular radially extending axial support 2 and a circular-section axial extension 15 on the opposite side of the axial support 2 to the cylindrical outer surface 1. Three equiangularly-spaced axially extending openings comprising passages 3 for the strips 22 and laterally disposed blind recesses 4 for the two radial positioning members 6 are formed in the axial support 2 and axially extending grooves 18, respectively formed in the axial extension 15, are aligned with the passages 3. The axial extension 15 has first and second parts 16 and 21 engaging apertures 17 and 23 respectively formed in an insulating clamping member 9 of glass fibre impregnated epoxy resin and a varistor 10, as shown in Figures 4 and 5, and three axial projections 24 for attachment to the armature portion of the rotor of an electric motor. Each commutator segment is mounted on the commutator body by passing the strip 22 through one of the passages 3 and into the aligned axially extending groove 18, as shown in Figure 3. The segment is then secured to the commutator body by moving the segment axially until the radial positioning members 6 are seated in the blind recesses 4 on opposite sides of the passage 3 and bending the free end of the strip 22 radially outwards so that it seats in one of three radial grooves 11 formed in the axial support 2. The outer extremity of the strip 22 is bent to form a "U"-shaped configuration 12 which has an inner axially extending arm 13 and an outer arm 14, for clamping an armature lead. Each strip 22 thus provides an axial terminal stem 7, adjacent the brush contacting portion 5 of the commutator segment, which serves as an additional radial positioning member, a radial terminal stem 8, and a "U"-shaped configuration 12 In this construction, the grooves 11 are shallower than the thickness of the radial terminal stems 8 and the varistor 10 projects axially beyond the second part 21 of the axial extension 15 so that the varistor 10 is held in contact with the radial terminal stems 8 by the clamping member 9 which is press-fitted to the first part 16 of the axial extension 15. As shown, the aperture 17 in the clamping member 9 has three inwardly projecting portions 19 respectively seated in the grooves 18 and the clamping member 9 has three circumferentially spaced outer surfaces 20 arranged respectively as radial supports for the inner arms 13 of the "U"-shaped configurations 12 at the ends of the radial terminal stems 8. Armature leads (not shown) can therefore be attached to each commutator segment by being placed between the inner and outer arms 13 and 14 of a "U"-shaped configuration 12 and then clamping the two arms 13 and 14 in a hot staking operation in which heat and pressure cause the two arms 13 and 14 to be welded together.

Claims: An assembled commutator comprising: an insulating commutator body (1 to 4) having a cylindrical outer surface (1) and integral, radially extending axial support means (2); at least three commutator segments (5 to 8) mounted on the body (1 to 4), each having an arcuate brush contacting portion (5) seated on the cylindrical outer surface (1) of the body (1 to 4), radial positioning means (6 and 7) extending axially from one end of the brush contacting portion (5), and a radial terminal stem (8); an apertured electromagnetic interference suppressor element (10); and an insulating clamping member (9) for clamping the radial terminal stems (8) and the suppressor element (10) together between the axial support means (2) and the insulating clamping member (9); characterised in that: the commutator body (1 to 4) is provided with an axial extension (15) on the opposite side of the axial support means (2) to the cylindrical outer surface (1); the axial support means (2) are formed with axially extending openings (3, 4) which each have a passage (3) which extends right through the axial support means (2); the radial positioning means (6 and 7) comprise axial terminal stems (7) disposed respectively within the passages (3); the radial terminal stems (8) extend respectively from the axial terminal stems (7) on the opposite side of the axial support means (2) to the brush contacting portions (5) of the commutator segments (5 to 8); and the apertured suppressor element (10) is mounted on the axial extension (15) between the radial terminal stems (8) and the clamping member (9). A commutator, according to Claim 1, in which the apertured suppressor element (10) is mounted between the radial terminal stem portion (8) and the clamping member (9). A commutator, according to Claim 2, in which:- the axial support means (2) are provided with radial grooves (11) extending from the passages (3) for accommodating the radial terminal stems portions (8); and each groove (11) is shallower than the thickness of the radial terminal stem portion (8) accommodated in said groove (11) so that the radial terminal stem portion (8) stands axially clear of the axial support means (2). A commutator, according to any preceding claim, in which a "U"-shaped configuration (12) is formed at the outer extremity of each radial terminal stem portion (8) and has an inner axially extending arm (13) which rests on the clamping member (9) and an outer arm (14) joined to the inner arm (13). A commutator, according to Claim 4. in which the clamping member (9) is made of a heat and pressure resistant material. A commutator, according to any preceding claim, in which:- the clamping member (9) is formed with an aperture; and the axial extension (15) has a first part (16) for seating the clamping member (9) and a second part (21), having a larger cross-section than the first part (16) for seating the apertured suppressor element (10). A commutator, according to Claim 6, in which the clamping member (9) is press-fitted on the first part (16) of the axial extension (15). A commutator, according to Claim 6, in which the cross-section of the first part (16) of the axial extension (15) is larger than the cross-section of the cylindrical outer surface (1) of the commutator body (1 to 4) and the first and second parts (16 and 21) are formed with axially extending grooves (18) aligned with the passages (3). A commutator, according to Claim 8, in which;- the clamping member (9) has at least one inwardly projecting portion (19) seated in one of said axially extending grooves (18) and a plurality of circumferentially spaced portions (20) which are angularly aligned with the radial terminal stem portions (8); and a "U"-shaped configuration (12) is formed at the outer extremity of each radial terminal stem portion (8) and has an inner axially extending arm (13), resting on one of the circumferentially spaced portions (20) of the clamping member (9), and an outer arm (14) joined to the inner arm (13).

Inventors: STROBL GEORG, STROBL, GEORG
Applicants: JOHNSON ELECTRIC SA, JOHNSON ELECTRIC S.A.
Application year: 1992
Main classification: H01R39
IPC codes: H02K11, H01R39, H02K13