Assembled commutator for an electric motor

Abstract: An assembled commutator 1 comprises a base 2 carrying segments 16. Each segment 16 has a connector portion 20 with a wall portion 21 having an aperture 22 to locate the connector portion 20 about a projection 15 on a collar 4 formed on the base 2, to locate the segment 16. The connector portions 20 each have a U-shaped portion 23 having a radially inner arm 24 which rests on the collar 4 and is wider than the radially outer arm 25, to form wings 26 which can be used when hot forging the tang to an armature coil wire. A first electrode bears down on the arm 25 and a second electrode bears down on the wings 26.

Description: The present invention relates to an assembled commutator for an electric motor, and in particular to an assembled commutator for a fractional horsepower permanent magnet direct current motor. One type of assembled commutator such as described in Japanese Application 5925550 comprises a pre-formed plastics base on which a plurality of segments is mounted. The segments are form locked to the base, for example by providing tongues on the segments which are received in recesses in the base. Each segment has a connector portion which extends radially outwards and has a U-shaped portion supported by a collar on the base. To connect an armature coil to the segment, the coil wire is wrapped into the base of the U-shape which is then collapsed onto the wire and heated in a hot forging or resistance welding process to burn off the insulation covering on the wire and form an electrical and mechanical connection with the wire. According to the invention there is provided an assembled commutator comprising a pre-formed cylindrical base, the base comprising a cylindrical portion having a collar at one end, a plurality of separable commutator segments mounted against the surface of the base, each segment comprising a brush contacting portion which is held against the cylindrical portion of the base by mechanical connections thereto adjacent both ends and a generally radially extending connector portion for hot connection to an armature coil wire, the connector portion being supported by the collar, characterised in that apertures are formed in said connector portions and projections are provided on the collar, the projections being received in respective apertures to locate the segments on the base in the region of the collar. Other preferred features and advantages of the invention will be apparent from the following description and the accompanying claims. The invention will be further described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a side view of an assembled commutator in accordance with the invention; Figure 2 is an end view of the commutator of Figure 1; Figure 3 is a view of the other end of the commutator of Figure 1; and Figure 4 is a cross-section along the line IV-IV of Figure 2. The drawings show an embodiment of an assembled commutator 1 constructed in accordance with the invention. The commutator 1 comprises an electrically insulating base 2 which is integrally moulded from plastics material, preferably a crystalline polymer material. One such material is marketed under the trade name XYDAR sold by DARTCO Manufacturing Co. of the U.S.A. The base 2 comprises a cylindrical portion 3 having a collar 4 formed at one end, and a stub-like extension 5 extending beyond the collar 4. The base 2 has a cylindrical inner bore 6 for mounting on a motor shaft (not shown). An end wall 7 of the cylindrical portion 3 opposite the collar 4 has recesses 8 which connect the outer surface 9 of the portion 3 with apertures 10 extending into the base from the end wall 7. The collar 4 is generally cylindrical and has a circumferential outer surface 11, a radially extending front wall 12 and a radially extending rear wall 13. Five, evenly spaced buttresses 14 are formed on the rear wall 13. Five evenly spaced cuboid protrusions 15 are formed on the front wall 12. The protrusions 15 are spaced from the outer surface 9 of the cylindrical portion 1 and level with the outer circumferential surface 11 of the collar 4. The base 2 carries five commutator segments 16. The segments are stamped from copper sheet and folded to shape. Each segment comprises an arcuate brush contacting portion 17 which sits on the surface 9 of portion 3. A reentrant tab 27 is formed at a front end of the portion 17. Tab 27 sits in a respective recess 8 and projects into an aperture 10. Ends 18 of the tabs 27 have a detent 19 to wedge the ends in the respective apertures 10 (Figure 4). A connector portion 20 is formed at the rear end of each brush contacting portion 17. A connector portion 20 comprises a radially extending wall 21 which is slightly narrower than the width of the brush contacting portion 17. The wall 21 has an aperture 22 which snugly receives a projection 15, the brush contacting portion 17 fitting between the projection 15 and the surface 9 (see Figure 4). A U-shaped wire receiving portion 23 is formed at the outer end of the wall 21. This has a first, radially inner arm 24 which rests on the circumferential surface 11 of the collar 4 and a second, radially outer arm 25 extending at an acute angle to the first arm 24. The first arm 24 is wider than the second arm 25 in the circumferential direction such that it has two "wings" 26 which extend to either side of the second arm 25 when it is pressed down onto the first arm. The segments 16 are spaced apart on the surface of the cylindrical portion 3. To assemble the commutator the segments 16 are slid onto the base 2 along the surface 9. Ends 18 of the tabs 27 are pushed into the apertures 10, the wall portions 21 sliding over the protrusions 15. The base 1 has chamfered edges to facilitate the mounting of the segments 16. In use, the assembled commutator is mounted on a motor shaft, the extension 5 abutting the armature core. Coils are wound on the armature and the wire looped into respective U-shaped portions 23 at the end of each coil winding. The connector portions 20 are hot forged or resistance welded to the wire in the usual manner, but with a first electrode bearing on the arm 25, and, preferably, a forked second electrode bearing on the wings 26 of the arm 24. Hence, heat evolved during the forging process is largely limited to the region of the connector portion 20 and the collar 4. It is usual to machine the surface of the segments 16 to ensure that the segments form a cylindrical surface to close tolerances. The wall 21 of the connector portions 20 cooperate with the protrusions 15 to limit circumferential movement of the segment ends against the collar 4 during machining, the tabs 27 fitting in the recesses 8 to limit movement at the other ends of the segments.

Claims: An assembled commutator comprising a pre-formed cylindrical base (2), the base (2) comprising a cylindrical portion (3) having a collar (4) at one end, a plurality of separable commutator segments (16) mounted against the surface of the base (2), each segment (16) comprising a brush contacting portion (17) which is held against the cylindrical portion (3) of the base (2) by mechanical connections thereto adjacent both ends and a generally radially extending connector portion (20) for hot connection to an armature coil wire, the connector portion (20) being supported by the collar (4), characterised in that apertures (21) are formed in said connector portions (20) and projections (15) are provided on the collar (4), the projections (15) being received in respective apertures to locate the segments on the base (2) in the region of the collar (4). A commutator as claimed in claim 1, characterised in that the base (2) is of crystalline polymer material. A commutator as claimed in claim 1 or 2, characterised in that the projections (15) are provided on a wall (12) of the collar (4), the wall (12) extending radially away from the cylindrical base portion (3). A commutator as claimed in any one of claims 1 to 3, characterised in that each projection (15) is spaced from the cylindrical base portion (3) by the thickness of the segments (16). A commutator as claimed in any one of claims 1 to 4, characterised in that each connector portion (20) comprises a U-shaped wire receiving portion (23) having a first radially inner arm (24) and a second radially outer arm (25), the first radially inner arm (24) being supported by a circumferential surface (11) of the collar (4). A commutator as claimed in claim 5, characterised in that the first radially inner arm (24) is wider in the circumferential direction than the second radially outer arm (25). A commutator as claimed in any one of claims 1 to 6, characterised in that buttresses (14) are provided on a radially extending wall of the collar (4) remote from the cylindrical portion (3) of the base, the buttresses (14) being provided radially inward of an axial portion of respective connector portions (20).

Inventors: STROBL GEORG, STROBL, GEORG
Applicants: JOHNSON ELECTRIC SA, JOHNSON ELECTRIC S.A.
Application year: 1989
Main classification: H01R39
IPC codes: H01R39, H01R43, H02K13