GB2215141A

GB2215141A - Connection of windings to commutator preventing heat distortion

Info

Publication number: GB2215141A
Application number: GB8803444A
Authority: GB
Inventors: Georg Strobl
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1988-02-15
Filing date: 1988-02-15
Publication date: 1989-09-13
Anticipated expiration: 2008-02-15
Also published as: HK36795A; GB2244387B; GB8803444D0; GB2244387A; GB2215141B; GB9112244D0

Abstract

Each commutator segment 16 has a tang 20 with a wall portion 21 having an aperture 22 to locate the tang 20 about a projection 15 on a collar 4 formed on the commutator base 2. The tangs 20 have a U-shaped portion 23 having a lower arm 24 which rests on the collar 4 and is wider than the other arm 25, to form wings 26. 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. Heat distortion is limited to the collar portion 4 of the commutator. <IMAGE>

Description

COMMUTATOR FOR AN ELECTRIC MOTOR The present invention relates to a 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 comprises a plastics base supporting a plurality of segments. 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 tang 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.

A first aspect of the invention provides an assembled commutator comprising a base of electrically insulting material, the base comprising a cylindrical portion having a collar at one end, a plurality of commutator segments mounted on the base, each segment comprising a brush contacting portion which is supported by the cylindrical portion of the base and a generally radially extending tang which is supported by the collar, wherein an aperture is formed in a said tang and a projection is provided on the collar, the projection being received in the aperture to locate the segment on the base in the region of the collar.

During the hot forging process, an electrode is brought down onto the U-shaped tang portion to collapse it onto the wire, a second electrode contacts the segment brush contacting portion and a current is passed through the segment to heat the tang. The hot forging process often results in some distortion of the commutator base. Some distortion in the region of the collar is acceptable but distortion of the cylindrical portion is undesirable.

A second aspect of the invention provides an assembled commutator comprising a base of electrically insulating material, the base comprising a cylindrical portion having a collar at one end, a plurality of commutator segments mounted on the base, each segment comprising a brush contacting portion which is supported by the cylindrical portion of the base and a generally radially extending tang which is supported by the collar, wherein the tang has a U-shaped portion for receiving a wire of an armature coil of an electric motor, an arm of said U-shaped portion resting on a circumferential surface of the collar and being wider in the circumferential direction than the other arm of the U-shape.

In this way, the tang can be hot forged to the wire by bringing a first electrode down onto the other, radially outer arm of the U-shape to urge it against the first arm, and a second electrode is brought down onto the first arm at a position adjacent the other arm, such that current flow will be limited to the region of the tang and hence to 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. 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.l0. Ends 18 of the tabs 27 have a detent 19 to wedge the ends in the respective apertures 10 (Figure 4).

A tang 20 is formed at the rear end of each brush contacting portion 17. A tang 20 comprises a radially extending wall 2l which is slightly narrower than the width of the portion 17 The wall 2l has an aperture 22 which snugly receives a projection 15, the 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 arm 24 which rests on the circimferential surface 12 of the collar 4 and a second arm 25 extending at an acute angle to the first arm 24. The first arm 24 is wider than the second arm 24 in the circumferential direction such that it has two 11wings 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 tang 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 around respective tangs 20 at the end of each coil winding. The tangs 20 are hot forged or resistance welded to the wire in the usual manner, but with electrodes bearing on the arm 25, and, preferably, a forked 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 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 walls 21 of the tangs 20 cooperate with the protrusions 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.

Various modifications may be made to the described embodiments and it is desired to include all such modifications as fall within the scope of the accompanying claims.

Claims

1. An assembled commutator comprising a base of electrically insulating material, the base comprising a cylindrical portion having a collar at one end, a plurality of commutator segments mounted on the base, each segment comprising a brush contacting portion which is supported by the cylindrical portion of the base, and a generally radially extending tang for hot connection to an armature coil wire, the tang being supported by the collar, wherein an aperture is formed in a said tang and a projection is provided on the collar, the projection being received in the aperture to locate the segment on the base in the region of the collar.

2. A commutator as claimed in claim 1, wherein the base is of crystalline polymer material.

3. A commutator as claimed in claim 1 or 2, wherein the protrusion is provided on a wall of the collar, the wall extending radially away from the cylindrical base portion.

4. A commutator as claimed in claim 3, wherein the protrusion is spaced from the base portion by the thickness of the segment.

5. A commutator as claimed in any one of claims 1 to 4, wherein the tang comprises a U-shaped wire receiving portion, a first arm of the U-shaped portion being supported by a circumferential surface of the collar.

6. A commutator as claimed in claim 5, wherein the first arm of the U-shaped portion is wider in the circumferential direction than the other arm of the U-shaped portion.

7. An assembled commutator comprising a base of electrically insulating material, the base comprising a cylindrical portion having a collar at one end, a plurality of commutator segments mounted on the base, each segment comprising a brush contacting portion which is supported by the cylindrical portion of the base and a generally radially extending tang which is supported by the collar, wherein the tang has a U-shaped portion for receiving a wire of an armature coil of an electric motor, an arm of said U-shaped portion resting on a circumferential surface of the collar and being wider in the circumferential direction than the other arm of the U-shape.

8. A commutator as claimed in claim 7, wherein a buttress is provided on a radially extending wall of the collar distal of the cylindrical portion of the base, the buttress being provided radially beneath a said tang.

9. An assembled commutator substantially as hereinbefore described with reference to the accompanying drawings.