GB2203291A

GB2203291A - Heat resistant commutator insulation

Info

Publication number: GB2203291A
Application number: GB08706842A
Authority: GB
Inventors: Patrick Shui-Chung Wang
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1987-03-23
Filing date: 1987-03-23
Publication date: 1988-10-12
Anticipated expiration: 2007-03-23
Also published as: HK131794A; GB8706842D0; GB2203291B

Abstract

An assembled commutator 10 comprises a plurality of commutator pieces 15 mounted on a support 11 including a supporting portion 11b of the support 11 below the terminal is of a first material, the remainder 11a, 11c being of a second material; the materials being chosen to give required resistance to heating effects. Terminals 17 of the commutator pieces 15 are bent into a U shape. A wire is joined by electric forging to the terminal 18. A phenolic resin layer 11b protecting thermoplastic areas 11a, 11c. Alternatively, areas 11a, 11b may be a powder filled phenolic resin to tolerate energy dissipation in motor stabled conditions. <IMAGE>

Description

ASSEMBLED COMMUTATOR This invention relates to assembled commutators and more particularly to the provision of an assembled commutator having an improved base which will withstand heat applied to the base when connecting wire of armature coils to terminals of the commutator segments and/or during use of a motor incorporating the commutator.

Assembled commutators for small electric motors comprise a plurality of commutator pieces mounted on an insulating cylindrical support, typically of plastics material, and held in position by an insulating washer and tangs which engage in recesses in the support. The support is mounted on a motor shaft with portions of the commutator pieces extending axially and terminals of the commutator pieces extending generally radially. Wires from armature windings mounted on the shaft are connected to the respective terminals by bending the terminals to form a U shape, enclosing the wire in the U shape and collapsing the U onto the wire. The wire and terminal may be welded or forged together to produce a firm electrical connection. The pressure and heat required for this operation results in distortion of low temperature supports, upsetting the geometry of the commutator.This may be overcome by using a high temperature resistant support such as glass filled phenolic resin. However this material has a semi-crystalline structure and on colling after moulding will not adopt the cylindrical shape required for supporting brush contacting portions of the segments, adopting instead a generally oval cross-section. Powder filled phenolic resin may be used as this does not have a "crystalline" structure, but such materials are relatively expensive. The wire may be connected to the terminal by soldering, allowing a relatively low temperature to be used if a wire having a low temperature coating is used.This allows a thermoplastic material to be used for the base, which is readily moulded into a cylindrical structure, but such materials will not withstand the heat which is generated in the vicinity of the segment brush contacting portions when the motor is in a stall condition. Accordingly there is a need to balance the material of the base against the manner of connecting the wire to the terminals and the operating conditions of the motors.

The present invention provides an assembled commutator comprising an electrically insulating support and a plurality of commutator segments, each segment comprising a brush contacting portion and an outwardly extending terminal for connection to a wire by a method involving heat, wherein the insulating support comprises a first portion of a first material ~supporting the brush contacting portions and a second portion of a second material supporting the terminals.

The invention also comprehends a fractional horsepower PMDC motor including a rotor assembly comprising a commutator as hereinbefore defined and a wound armature, the commutator and armature being mounted on a shaft and each coil of the winding being connected to a commutator segment by bending a terminal of the commutator segment to clamp a wire of the coil and applying heat to electrically connect the terminal and wire.

The invention allows the material of the commutator base to be selected to meet the constraints imposed by the structure and operating conditions of the motor.

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 cross-section taken along an axis of a first embodiment of a commutator according to the invention; Figure 2 is an end view in the direction of arrow A of Figure 1, with a fibre washer removed; Figure 3 is a schematic side view of a top half of a rotor assembly; Figure 4 is a perspective view of a commutator piece; Figure 5 is a cross-sectional view along an axis of second embodiment of the invention; and Figure 6 is an end view of a third embodiment of the invention.

In Figure 1, an assembled commutator 10 comprises a support 11, the support 11 comprises a first cylindrical portion 12 for receiving a motor shaft, and a radially extending collar 13. The collar 13 has recesses 16 to receive tangs 14 of a copper commutator segment 15 (Figure 3) which position the commutator piece on the support 11 in the circumferential direction.

The commutator pieces 15 have a brush contacting portion 19 and an upwardly turned terminal 17 which is bent to lie against the radial and circumferential faces of the collar 13, as seen in Figure 1, with the outer portion of the terminal being bent to form a U shape 18.

In accordance with the invention, the support 11 comprises an integrally formed first part lla, llc and a second part llb. The first part llb is in the form of a cylindrical collar which is a tight fit on a cooperating cylindrical collar llc which is formed integrally with cylindrical portion 12, the two collar parts llb, llc cooperating to form the collar 13 supporting the commutator tangs.

To assemble the commutator, the commutator pieces 15 are first stamped and bent to the shape illustrated in Figure 4 and then fitted on the support 11 by sliding them against the collar 13 to insert the tangs 14 in the recesses. A fibre washer 21 is then slid over the commutator pieces to hold them against the cylindrical portion 12.

To connect a wire to the commutator terminals the wire is placed in the U of the terminal 17, this may be done during a winding operation (see Figure 3) and pressure is then applied radially to the end of the terminal in the direction of arrow B so that the terminal is bent over to clamp the wire. Heat is applied by means of an electric current to burn off enamel from the wire surface and to heat the wire and terminal to forge a joint therebetween, or solder may be applied to the wire and terminal whilst heating to a lower temperature, and at lower pressure, to form a soldered joint. Such techniques are well known in the art.

The material of the first and second parts is selected according to the construction of the motor and the intended operating conditions.

If the motor is to utilise a wire having a high temperature coating then the wire and terminals will normally be forged together. In this case a high temperature material, such as a thermoset resin, for example a glass or powder filled phenolic resin may be used to form the second part, llb. This is able to withstand the heat and pressure applied to the base during forging without substantial deformation or cracking. The resin material is expensive and the glass filled material ovalises on cooling.

Accordingly the first part lla, llc is formed of thermoplastics material. The parts may be moulded separately and the ring llb slid on the first part during assembly.

As seen clearly in Figure 1, the part of the collar beneath the terminal 18 is of thermoset resin and this is better able to withstand the combination of heat and pressure applied to the collar 13 during the forging operation than the underlying thermopastics collar portion llc and serves to insulate the thermoplastics portion from the full effect of the heat and pressure.

If the wire has a low temperature coating it may be joined to the terminal by soldering. In this case a thermoplastics material, which softens or distorts on heating, may be used for the second part llb.

However, thermoplastics material when used for the first part lla, llb will distort in the vicinity of the brush contacting portions 19 under stall conditions because a considerable amount of energy, in the form of heat, is dissipated in this area.

Accordingly the first part lla, llc is formed of powder filled phenolic material which has a greater tolerance to high temperatures.

Figure 3 shows schematically a rotor comprising the commutator of Figure 1 mounted on a motor shaft 22.

A shoulder 23 on the inside wall of the commutator 10 abuts against a shoulder on the shaft 22 to position the commutator in the axial direction.

A winding of the armature coil is shown schematically at 25 and has an end of its wrie looped around the terminal 17 during the winding, prior to connecting of the wire 24 and terminal 17 as described previously.

Figure 5 shows a second embodiment of the invention in which like parts to those of the embodiment of Figure 1 have like reference numerals. In this embodiment the base 11 comprises a first portion lla which is cylindrical and supports commutator segments 15 and a second portion llb which comprises the whole of the collar 13. The first and second portions are both a push fit on the shaft, cf Figure 3.

Figure 6 shows a third embodiment which is a view similar to that of Figure 2, and shows the second portion llb to comprise three inserts in the collar 13, just below the tags 18. The inserts are held in place against radially outward movement by the tags 18.

The terms thermosoftening plastics and thermoplastics are used synonymously and are intended to refer to plastics materials which will soften on heating.

Thermoset resin and thermoset plastics are used synonymously and refer to plastics materials which do not soften substantially with increasing temperature but usually char, physical change generally taking place at a higher temperature than that of thermosoftening plastics.

The heat resistant portion material used for the first or second could be of metal, for example anodised aluminium in place of resin material, provided as a collar on the shaft or an insert or band on a low temperature base portion.

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

Claims

1. An assembled commutator comprising an electrically insulating support and a plurality of commutator segments, each segment comprising a brush contacting portion and an outwardly extending terminal for connection to a wire by a method involving heat, wherein the insulating support comprises a first portion of a first material supporting the brush contacting portions and a second portion of a second material supporting the terminals.

2. A commutator as claimed in claim 1, wherein the first portion is a thermoplastic material and the second portion is a phenolic resin material.

3. A commutator as claimed in claim 2, wherein the second portion is a glass filled phenolic resin.

4. A commutator as claimed in claim 1, wherein the first portion is a phenolic resin material and the second portions a thermoplastic material.

5. A commutator as claimed in claim 4, wherein the first portion is a powder filled phenolic resin material.

6. A commutator as claim in claim 1, wherein the first portion is a thermoplastic material and the second portion is a heat resistant material.

7. A commutator as claimed in claim 6, wherein the second portion is of anodised aluminium.

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8. A commutator as claimed in claim 1, wherein the first portion is of anodised aluminium and the second portion is of thermoplastics material.

9. A commutator as claimed in claim 4, 5 or 8 wherein a wire is electrically connected to the terminal by soldering.

10. A commutator as claimed in claim 2, 3 or 6 or 7 wherein a wire is electrically connected to the terminal by soldering.

11. An assembled commutator as claimed in any one of claims 1 to 10, wherein the second portion is a cylindrical collar mounted about the first portion.

12 An assembled commutator as claimed in any one of claims 1 to 11, wherein the second portion comprises a cylindrical collar mounted directly on a shaft of the motor and the first portion is a cylinder mounted directly on the shaft adjacent the second portion.

13. An assembled commutator as claimed in any one of claims 1 to 11, wherein the second portion ts comprises a plurality of inserts each radially inward of a respective commutator segment terminal and housed in a collar of the first portion.

14. An assembled commutator substantially as hereinbefore described with reference to Figures 1 to 4, Figure 5 or Figure 6 of the accompanying drawings.

15. A fractional - horsepower electric motor including a rotor assembly comprising an assembled commutator as defined in any one of claims 1 to 14 and a wound armature, the commutator and armature being mounted on a shaft and each coil of the winding being connected to a commutator segment by applying heat to electrically connect the terminal and the wire.

16. An assembled commutator comprising an electrically insulating support and a plurality of commutator segments mounted on the support, each segment comprising a brush contacting portion and a terminal portion for connection to a wire of an armature coil, wherein said support comprises a first portion of a first material supporting the brush contacting portions and a second portion of a second material supporting the terminals, one of said first and second materials being resitant to deformation at relatively high temperature and the other deforming at a relatively low temperature.

17. A commutator as claimed in claim 1, wherein the high temperature deformation resistant material is of thermoset resin or anodised aluminium.