GB2203596A - Winding connections retention in an armature for an electric motor - Google Patents

Abstract

In order to prevent movement of connector portions 32 of windings within the terminal support housings 18, which receive integral terminal 36 of commutator segments 34 to grip the respective connector portion 32, each housing contains a mass of set material (8), e.g. epoxy resin, in which the respective connector portion is supported. Thus fretting of the connector portions is prevented. The material (8) may contain an electrically conductive material and extend between each pair of adjacent housings to form a resistive bridge between the commutator segments for suppression purposes. <IMAGE>

Description

An Armature for an Electric Motor This invention relates to an armature for an electric motor.

In our British Patent No. 2128818B we describe a connection between the armature winding and a commutator segment which avoids the application of heat to effect the connect ion and which utilises the principle of insulation displacement in which a wire having an insulating cover is forced into a slot narrower than the wire diameter to form a clean metal to metal contact between the wire and a terminal integral with the commutator segment.

In the aforesaid Patent the commutator segments are mounted on a base which includes a plurality of integral housings for receiving the aforesaid terminals. The housings could however be part of a terminal support which is sepate from the terminal base. Indeed this is advantageous in that the terminal support can be of a flexible plastics material to allow the terminals to flex during insertion of the terminals, whilst the base is of a material which is able to withstand higher temperatures than the material of the terminal support. In either case, the wires are not rigidly supported in respective housings and these wires are therefore free to move about slightly during movement or operation of the motor. This could lead to fretting of the wires.

In order to mitigate this drawback, the present invention provides an armature for an electric motor, comprising a winding having connector portions, a plurality of commutator segments each having an integral terminal which grips a respective connector portion, a commutator base for supporting said commutator segments and a. terminal support having a plurality of housings in which the terminals are located, each housing containing a mass of set material in which the respective connection portion is supported.

Preferably, the set material contains electrically conductive material and extends between each pair of adjacent housings to form a resistive bridge between the commutator segments.

The set material can be any appropriate material which can be cured without the application of an excessive amount of heat, although in a preferred embodiment the set material is essentially an epoxy resin.

Preferred and/or optional features of the invention are set forth in claims 4 to 7, inclusive.

The set material hence supports the wires in the housings so that these wires cannot move and fret.

The set material has the additional advantage that it may contain an appropriate quantity of electrically conductive material, e.g. copper powder or graphite, and may extend between each pair of adjacent housings to form a resistive bridge between the commutator segments and thus provide a suppression element into which inductive energy from the windings can be discharged.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows in plan view a terminal support forming part of the armature and is partially sectioned to illustrate the configuration of one of the terminal housings; Figure 2 is a plan view of a commutator segment and terminal in blank form; Figure 3 is an end elevation of the commutator segment and terminal of figure 2 showing the operational configuration of the segment and terminal;; Figure 4 is an enlarged view of one portion of the terminal shown in figure 2, Figure 5 is a perspective view of an assembled commutator including the base and commutator segments mounted thereon prior to being offered up to the terminal support, and Figure 6 is a vertical sectional view of the terminal support of Figure 1 and'of the assembled commutator of Figure 5 with the assembled commutator connected to the support.

Figures 1 and 6 show a terminal support in the form of a body 12 of moulded thermoplastics material, e.g.

thermosoftening nylon. The body 12 has two sections 14 and 16 and is mounted fast on the shaft (not shown) of an armature of an electric motor. The section 14 comprises three housings 18 and the section 16 acts as a spacer to space the section 14 of the body 12 frbm the base of the armature stack (not shown). The body 12 co-operates with a commutator base 10 (Figures 5 and 6) to support the commutator segments and the terminals integral therewith in a manner which will be described. The base 10 is of a material which will withstand a higher temperature than the body 12, e.g.

is of moulded thermosetting plastics material such as a phenolic resin, or of metal provided with an insulating layer of metal oxide, e.g. anodised aluminium, to avoid softening and distortion when current, particularly full stall current, is passing through the brush/commutator interface. The base 10 is essentially a hollow cylinder with three arcuate ears 38 at its rear end, the ears 38 being equally spaced around the circumference of the base 10 and being each a close fit in the section 14 of the body 12 between an adjacent pair of housings 18.

The three housings 18 of the body 12 are equally spaced around the circumference of the body 12. Each of the housings 18 is used in effecting connection between a respective portion of the armature winding and one of the commutator segments.

One of the housings 18 is shown in section in Figure 1. The housing has side walls 20, an end wall 22 and a cover 24. The end wall 22 is adjacent the spacer 16 and an opening 26 which faces away from the spacer 16 is provided by the walls 20, 22 and cover 24. The side walls are parallel with the longitudinal axis of the body 12.

A boss 28 projects centrally from the internal surface of the end wall 22 and extends within the housing 18 for approximately half the length of the side walls 20. The boss 28 extends parallel with the longitudinal axis of the body 12 and is only connected to the body 12 by the end wall 22. Each side wall 20 of the housing 18 has a slot 30 which extends parallel to the ' longitudinal axis of the body 12, from the commutator end of the housing 18 for a length which terminates at the level of the free end of the boss 28. A portion 32 of the armature winding is passed through the slots 30 of one of the housings 18 and the winding portion 32 rests on the end of the boss 28.

The external surfaces of the side walls 20 are bevelled so as to facilitate entry of the winding portion 32 into the slots 30. Each housing 18 contains a mass 8 of settable material, e.g. epoxy resin, which when set will support the winding portion 32 against movement.

A combined commutator segment 34 and terminal 36 is illustrated in Figures 2 and 3. Figure 2 shows the combination in the form of a blank and Figure 3 is an end elevation of the combination when formed into its operational configuration. A lug 42 of reduced width is provided at the front end of the segment 34 and the lug 42 has a central struck-up tag 44.

At its rear end, the commutator segment 34 is connected to the terminal 36. The terminal 36 is rectangular with its minor axis coincident with the longitudinal axis of the commutator segment 34. The terminal 36 has a central cut out portion 46 which is symmetrical with respect to both the major and minor axis of the terminal 36. The cut out 46 reduces from its largest width at the centre of the terminal to two key hole shaped portions 48 which terminate -either end of the cut out 46. A triangular barb 50 is provided on either side of the minor axis of the terminal 36 along the edge furthest from the commutator segment 34.

As can be seen from Figure 3, the commutator segment 34 is of arcuate form which conforms to the external radius of the cylindrical base 10. The lug 42 extends below and back along the length of the commutator segment 34 with the tag 44 projecting below the lug 42. Terminal 36 is bent upright from the commutator segment 34 and the arms 52 of the terminal 36, which include the respective key hole formations 48, are bent at 90 degrees to the central portion 54 of the terminal. The arms 52 therefore extend parallel to each other and to the longitudinal axis of the commutator segment 44, and forward along the length thereof. The free ends 56 of the terminal 36 are bent so as to be inclined towards each other when the arms 52 have been bent parallel to each other.

Figure 4 shows one half of the terminal 46 of Figure 2, on an enlarged scale. Areas 58 are shown in which bending occurs between the central portion 54 and the arm 52. Area 60 is also indicated in which bending between the arm 52 and the extreme end portion 56 occurs. However, the main purpose of Figure 4 is to illustrate the detailed structure of the key hole cut out section 48. It is this feature which ensures contact with the armature winding portion 32. The reduction in size from the centre of the cut portion 46 to the start of the key hole portion 48 provides a funnel for guiding the arm 52 onto the winding portion 32. A short distance into the key hole portion 48 there are located two cutters 62 which have sharp edges 64 projecting into the cut out 48.The cutters 62 are formed from the arm 52 but are partially severed therefrom such that the sharp edges 64 are resiliently urged into the cut out 48. Along the cut out 48, behind the cutters 62, there is a further small reduction in width. Circular end 66 of cut out 48 ensures that the edges of the cut out 48 have a certain resilience to separation by the winding portion 32.

Figure 5 shows an assembled commutator in which shaped commutator segments 34 and the terminals 36 are in position on the base 10. The terminals 36 are located between a pair of adjacent ears 38. The front end of the base 10 is provided with three longitudinal recesses 70 which are cut away at the forward ends so as to meet the curved external surface of the base 10. Lug 42 of commutator segment 34 is received in the recess 70 and tag 44 of lug 42 is forced into the material of the base 10 so as to rigidly restrain the lug 42 within recess 70.

Figure 6 shows the assembled commutator of Figure 5 connected to the support of Figure 1. Each terminal 36 enters a respective housing 18 containing a mass 8 of settable material and the central portion 54 of the terminal 36 passes over the boss 28. The winding portion 32 is guided into the key hole cut out 48. As the terminal 36 passes over the wire 32 the sharp edges 64 of the cutters 62 sever the insulation on the wire 32 and further entry of the terminal 36 forces the wire 32 into the narrow portion 68 of cut out 48.

The slight resilience provided by circular portion 66 and the relative sizes of the wire and the section 68 ensure that the arms 52 continue to bear against the wire 32 with a residual spring tension which maintains high contact pressure ensuring a reliable long term connection.

The barbs 50 grip the cover 24 of the housing 18 and therefore retain the terminal 36 within the housing 18. Additional retention may be provided by contact between the central portion 54 of the terminal 36 and the boss 28. The arms 52 of the terminal 36 can be bent at an angle slightly less than 90 degrees from the central portion 54 so as to provide retention of the terminal 36 by action against the side wall 20 of the housing 18. Further retention is provided if the width of the terminal 36 is a close fit to the internal dimensions of the housing 18.

After the terminals 36 have been inserted in respective housings 18 the settable material 8 is allowed to set around the wire 32 to support the latter and prevent it from fretting.

The armature may be assembled as follows: The body 12 is first placed on the armature shaft with the spacer 16 against the base of the lamination stack. Settable material 8 is then introduced into the housings 18. Thereafter, the lead wire of the armature winding is inserted into the housing 18 by laying the end of the wire 32 in the slots 30 provided in the side wall 20 of the housing 18.

The wire 32 is drawn back into the housing 18 until it rests against the boss 28. From this start, the first armature coil is wound. At the end of the first coil winding the armature is indexed and the wire 32 is layed in the same manner in the next housing 18 without breaking the continuity of the wire 32.

This process is repeated until all coils have been wound and the tail end of the winding is then laid in the slots 30 of the first housing 18 and pushed back until it is adjacent to the lead end which was placed against the boss 28 at the beginning of the winding operation. The wire 32 is then cut and the armature removed from the winding machine.

The body 12 now has a winding portion 32 comprising insulated wire laying -in each of the housings 18.

Each of the winding portions 32 is under tension and is pulled tight against the respective boss 28.

Moreover, each housing18 contains settable material 8 around the winding portions 32.

The commutator segments 34 are pre-assembled on the base 10. To do this they are placed on the outer surface of the base 10 and are slid along the base 10 so that - the terminals 36 slide between a pair of adjacent ears 38 and the lugs 42 enter the respective recesses 70. The segments 34 may be held on the base 10 by a ring (not shown) which can be snipped off after connecting the terminals 36 to the body 12.

The base 10 together with commutator segments 36 is slid along the armature shaft before the material 8 has set and as the terminals 36 approach the winding portions 32 held in the housings 18, the slots provided by cut outs 48 move over the wires 32. The sharp edges 64 of the cutters 62 sever the insulation on the wires 32 which is deformed as the slots, formed by cut outs 48, move over the wires 32. Intimate metal to metal contact is thereby provided between the wires 32 and the terminals 36.

The material 8 is then allowed to set.

The material 8 preferably extends between the housings 18 and contains an appropriate quantity of electrically conductive material, e.g. copper powder or graphite, to form a resistive bridge between the commutator segments and thus provide a suppression element into which conductive energy from the windings can be discharged. The material 8 can simply be caused to extend around the top of the ears 38 of the base 10 after the latter is inserted into the support 12. However, alternatively the ears 38 could be of shorter axial length to provide a gap - within the support 12 on one or other side of the ears 38 for occupation by the material 8, or could be of smaller radial extent so as not to be a close fit in the support 12 to leave a circumferentially extending gap for occupation by the material 8.

As described above the settable material 8 is introduced into the housing 18 before the wires 32.

It could however, be introduced into the housings 18 after the wires 32 and before the commutator is offered up to the support 12 or even after the commutator has been connected to the support 12.

The above embodiment is given by way of example only and various modifications will be apparent to a person skilled in the art without departing from the scope of the invention. For example, the commutator could be in the form of a face plate commutator in which the commutator segments lie in a common plane perpendicular to the axis of the armature. Moreover, the base 10 and support 11 could be integral with one another and formed for example as a unitary plastics moulding. Indeed, the slots in the terminals could be arranged so that the terminals can be located in respective housings of the terminal support prior to connection of the winding portions to the terminals.

This invention is particularly but not exclusively applicable to armatures of fractional horsepower electric motors.

Claims (9)

1. An armature for an electric motor, comprising a winding having connector portions, a plurality of commutator segments each having an integral terminal which grips a respective connector portion, a commutator base for supporting said commutator segments and a terminal support having a plurality of housings in which the -terminals are located, each housing containing a mass of set material in which the respective connector portion is supported.

2. An armature as claimed in claim 1, wherein the set material contains electrically conductive material and extends between -each -pair of adjacent housings to form a resistive bridge between the commutator segments.

3. An armature as claimed in claim 1 or claim 2, wherein the set material comprises an epoxy resin.

4. An armature as claimed in anyone of claims 1 to 3, wherein the terminal support is formed of thermoplastics material and the commutator base is made of a material which will withstand higher temperatures than the thermoplastics material of the terminal support.

5. An armature as claimed in anyone of claims 1 to 3, wherein the terminal support and commutator base are integral with one another.

6. An armature as claimed in anyone of the preceding claims, wherein the connector portions are coated with insulation and each terminal has a slot provided with two cutting edges for cutting through the insulation of the connector portion as it is drawn into the slot to establish electrical contact between the connector portion and the terminal, the slot maintaining said electrical contact by straddling and gripping said connector portion.

7. An armature as claimed in anyone of the preceding claims, wherein each terminal has at least two parallel arms, each having a slot which straddles and grips said connector portion.

8. An armature for an electric motor, substantially as hereinbefore described with reference to the accompanying drawings.

9. An electric motor provided with an armature according to anyone of the preceding claims.