Assembled Commutator With Heat-Resisting Ring

The present invention relates to an assembled commutator in which the segments have tangs arranged to be connected to an armature winding wire by a hot connection, such as forging or soldering.

When forging a connection between the segment tang and armature wire, both heat and pressure are applied to the tang. This can result in distortion of the commutator base beneath the tang. If the distortion is too great the base collapses away from beneath the tang so that it is no longer adequately supported in the forging process. The forging process typically produces a temperature of 430 degrees centigrade at the tang. Thermoplastics materials, which are most desirable for forming the commutator base, may withstand this temperature, but the combination of temperature and pressure distorts the base.

According to the present invention, there is provided an assembled commutator comprising a cylindrical base of thermoplastics material having a plurality of commutator segments mounted thereon, each segment having at an end thereof a tang for connection to an armature winding wire by a process involving heat, wherein an annular ring is provided on the base beneath the tangs, the ring being of high temperature non-softening material.

Preferably the ring is of phenolic, fibre-filled phenolic, or fibre material. Such materials may withstand temperatures higher than 500 degrees centigrade and will not soften, but rather will char at too high a temperature. The invention is particularly applicable to hot forging but also applicable to other techniques such as soldering the wire to the tangs.

Preferably the ring is held in place by fingers on the segment end which grip the ring.

Preferably the ring has a resistive coating and is in electrical contact with the segments so as to form a suppression element.

Another aspect of the invention provides an assembled commutator comprising a cylindrical base and a plurality of commutator segments mounted on the base, the segments each having a brush contacting portion having a tang at one end thereof for connection to an armature winding wire, wherein a suppression element is mounted on the base in the region of the tangs and makes electrical contact with the underside of each segment.

The accompanying single FIGURE of drawing is a side view in partial cross-section of an assembled commutator forming an embodiment of the invention.

Referring to the drawing, an assembled commutator 1 comprises a cylindrical base 2 of thermoplastics having a main segment supporting part 3, a collar 4 and a spacer part 5 at a rear end which is arranged to abut a lamination stack of an armature. A plurality of commutator segments 6 (five in the example shown) are mounted on the base 2. Each segment 6 has a brush contacting part 7 with a finger at one end which locks into a recess 8 in the front end of the base 2, and a tang 9 at other end. Tangs 9 extend radially out from the brush contacting parts 7, 12 and have apertures 10 which fit over projections 11 on the front face of the collar 4 to hold that end of the segment against the base. The brush contacting part 7 may be glued to the base. The tangs 9 end in a U-shape 13 which rests on the collar 4. A shelf 14 is formed in the rear of the collar 12. A ring 15 of phenolic material or other high temperature, non-softening material such as fibre or fibre-filled phenolic is fitted on the shelf 14 beneath the U-shape parts 13. Fingers 16 on the tangs 9 extend to either side of the U-shape parts 13 and are bent over to hold the ring 15 in place, and also help hold the segments against axial movement on the base 2.

When forging a wire to a tang 9, the wire is looped into the U-shape part 13. A first electrode bears down on the U-shape part to collapse it onto the wire and a second electrode bears onto a wing 17 to one side. The phenolic ring 15 will withstand the heat generated and the pressure of the first electrode without softening or collapsing.

The invention is also of advantage when the wire is soldered to the tang.

As shown in dotted outline, a resistor or varistor ring 18, or other suppression element may be positioned on a second shelf 19 inside the ring 15 and the fingers 16 extended down to make electrical contact with the ring. In another embodiment, the suppression element may be positioned beside the phenolic ring to make electrical contact with the underside of the tangs or fingers. In another embodiment the ring 15 has a coating of resistive material which electrically connects the fingers 16 of adjacent segments.

The shelf 14 need not be continuous but may, for example, be formed on buttresses at the rear of the collar 4.

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