GB2223888A

GB2223888A - Assembled commutator for electric motor

Info

Publication number: GB2223888A
Application number: GB8822553A
Authority: GB
Inventors: George Strobl
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1988-09-26
Filing date: 1988-09-26
Publication date: 1990-04-18
Anticipated expiration: 2008-09-26
Also published as: GB2223888B; HK132194A; JPH0288456U; DE8911461U1; GB8822553D0

Abstract

The segments 16 each having a brush contacting portion 18 and a separately formed terminal portion 20 mounted on a support 22. A terminal support 24 has housings 26 formed with recesses for the terminal portions and slots 38 for positioning portions 14 of the armature winding relative to the recesses. Each terminal portion 20 has a slot 48 which straddles and grips the portion 14 and is disposed inwardly of the outer edge of the brush contacting portions 18. The separate portions 18, 20 can be made of different thickness material, allowing a thinner material to be used for the terminal to reduce the likelihood of damaging the connector portions when they are of thin wire. <IMAGE>

Description

Commutator This invention relates to an armature for an electric motor and to an electric motor equipped with such an armature.

British Patent No. 2128818B and published application No.2198892 disclose an armature and commutators in which the commutator segments are connected to the armature winding by mechanical connections. Each commutator segment has a terminal portion provided with a slot which straddles and grips an armature winding portion. The slot may have cutting edges for cutting insulation on the winding portion as the winding portion moves into the slot. The terminal portions extend radially outwards from brush contacting portions of respective commutator segments and are located in respective recesses provided in a rose-like terminal support. Our British Application No.8815365.5 discloses a system in which the terminal portion is positioned radially inwardly of the brush-contacting portion of the commutator segment, in a barrel-type commutator.

When using such commutator and armature arrangements with armature windings having thin armature wire, there is difficulty in providing a sufficiently narrow slot with a well formed cutting edge for piercing the insulation. Also, for a long commutator life a thick material must be used for the segment brush contacting portion.

The present invention provides a commutator for an electric motor, the commutator comprising a base, and a plurality of commutator segments mounted on the base, the segments each comprising a brush contacting portion for receiving thereon a brush of an electric motor and a terminal portion, the terminal portion having a slot therein for straddling and gripping a connector portion of an armature coil, wherein the terminal portion and brush contacting portion are separately formed and are electrically connected.

Thus, the brush contacting portion and terminal portion may be of different thickness material, and may even be of different materials. The terminal portion may, for example, be rivetted or welded to the brush contacting portion. The brush contacting portions may be mounted on the base prior to attachment of the terminal portions.

The invention also provides an armature including the commutator hereinbefore defined.

Other, preferred, features and advantages of the invention will be apparent from the following description and the accompanying claims.

The present invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an exploded sectional view of part of one embodiment of an armature including a commutator in accordance with the invention; Figure 2 is a plan view of one of the commutator segments of the embodiment of Figure 1 in blank form; Figure 3 is an enlarged view of one portion of the terminal portion of the commutator segment shown in Figure 2; Figure 4 is a plan view of the terminal support of Figure 1 and is partially sectioned to illustrate the configuration of one of the housings; and Figure 5 is a perspective view of a detail of the embodiment of Figure 1.

Referring firstly to Figure 1, the armature shown therein comprises a barrel-type commutator 10 mounted on an armature shaft 12, and a wire wound armature coil 11 having winding portions 14. The commutator 10 comprises five commutator segments 16 having brush contacting portions 18 and terminal portions 20, a commutator segment support 22 on which the brush contacting portions 18 of the commutator segments 16 are seated, and a rose-like terminal support 24. The terminal support 24 has an inner sleeve 25 and five housings 26 equally spaced around the circumference of the sleeve 25. Each of the housings 26 is used in effecting connection between a respective portion 14 of the armature winding and one of the commutator segments 16.

One of the housings 26 is shown in section in Figure 4. The housing 26 has side walls 28, an end wall 30 and a cover 32. An opening 34 which faces the commutator segment support 22 is provided by the walls 28 and cover 32. The side walls 28 are parallel with the axis of the shaft 12.

A boss 36 projects centrally from the internal surface of the end wall 30 and extends within the housing 26 for approximately half the length of the side walls 28. The boss 36 extends parallel with the axis of the shaft 12 and is only connected to the terminal support 24 by the end wall 30. Each side wall 28 of the housing 26 has a slot 38 which extends parallel to the axis of the shaft 12, from the commutator end of the housing 26 for a length which terminates at the level of the free end of the boss 36. A portion 14 of the armature winding is passed through the slots 38 of one of the housings 26 and the winding portion 14 rests on the end of the boss 36. The external surfaces of the side walls 28 are bevelled so as to facilitate entry of the winding portion 14 into the slots 38.

Referring now to Figure 2 the commutator segment 16 is shown therein in blank form. The segment is in two separate parts, a first, brush-contacting, portion 18 and a second, terminal, portion 20. The brush-contacting portion 18 is of copper of thickness 0.5mm and the terminal portion is of brass of thickness 0.2mm. Thin brass is particularly suitable for forming narrow slots with well defined edges.

The terminal portion 20, which is to be connected to the rear end of the brush contacting portion 18, is rectangular with its minor axis coincident with the longitudinal axis of the commutator segment 16. The terminal portion 20 has a central cut out portion 46 which is symmetrical with respect to both the major and minor axis of the terminal portion 20. The cut out 46 reduces from its largest width at the centre of the terminal to two keyhole shaped slots 48 which terminate at either end of the cut out 46. A triangular barb 50 is provided on either side of the minor axis of the terminal portion 20 along the edge furthest from the brush contacting portion 18.

Figure 3 shows one half of the terminal portion 20 of Figure 2, on an enlarged scale. Areas 58 are shown in which bending occurs between a central portion 54 and an arm 52. Area 60 is also indicated in which bending between the arm 52 and an extreme end portion 56 occurs. However, the main purpose of Figure 3 is to illustrate the detailed structure of the keyhole slot 48. It is this feature which ensures insulation displacement-type contact with the armature winding portion 14. The slot 48 is narrower than the conducting core of winding portions 14 and the reduction in size from the ce-ntre of the cut out portion 46 to the start of the keyhole slot 48 provides a funnel for guiding the arm 52 onto the winding portion 14. A short distance into the keyhole slot 48 there are located two cutters 62 which have sharp edges 64 projecting into the slot 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 slot 48.

Along the slot 48, behind the cutters 62, there is a further small reduction in width. Circular end 66 of slot 48 ensures that the edges of the slot 48 have a certain resilience to separation by the armature winding 14.

Referring to figures 2 and 5 in particular, the brush contacting portion 16 has two lugs 70 extending from its rear end. Each lug has an aperture 72 therein.

The terminal portion 20 has two wings 74, each having an aperture 76 therein. The terminal portion 20 is folded to the shape shown in Figure 5.

Description will now be given of the assembly of an electric motor incorporating the present invention.

The commutator segments 16 are prepared ready for mounting on the support 22. The commutator segments 16 are provided in blank form as shown in Figure 2.

The brush contacting portion 18 of each commutator segment 16 is of part cylindrical form which conforms to the external radius of the commutator segment support 22. A layer of glue is applied to the cylindrical surface of the support 22 and/or the underside of the segment portions 18. The portions 18 are then mounted on the support, the lugs 42 are bent over. The lugs 42 being forced into respective longitudinal recesses 43 provided in the end of the support 22. The lugs are dimpled to form a tight fit in the recesses 43.

A ring 78 is then placed around the rear end of the segments on the support 22 to hold them securely in position. The ring has ribs 80 on its inner surface, which serves to space the ends of the brush contacting portions 18. The folded terminal portions 20 are then slid between the lugs 70 and the wings 74 rivetted to the lugs, or if desired welded, glued or otherwise attached to the lugs 70. The commutator thus formed may be turned to machine the brush contacting surfaces to the required tolerance. This may be done before or after the terminal portions are attached.

The terminal support 24 is placed on the armature shaft 12 with the inner sleeve 25 against the base of a conventional lamination stack 11. The lead wire of the armature winding is inserted into the housing 26 by laying the end of the wire 14 in the slots 38 provided in the side walls 28 of the housing 26. The wire 14 is drawn back into the housing 26 until it rests against the boss 36. From this start, the first armature coil is wound. At the end of the first coil winding the armature is indexed and the wire 14 is layed in the same manner in the next housing 26 without breaking the continuity of the wire 14.

This process is repeated until all coils have been wound and the tail end of the winding is then laid in the slots 38 of the first housing 26 and pushed back until it is adjacent to the lead end which was placed against the boss 36 at the beginning of the winding operation. The wire 14 is then cut and the armature removed from the winding machine.

The body 10 now has a winding portion 14 comprising insulated wire laying in each of the housings 26.

Each of the winding portions 14 is under tension and is pulled tight against the respective boss 36.

The support 22 is then placed on the armature shaft 12 and moved towards the terminal support 24. A plurality of fingers 80 are provided on the terminal support 24, extending along the shaft 12. These are received in recesses 82 in the segment support 22 to align the assembled commutator and housings before the terminals enter the housings. As the terminal portions 20 enter the housings 26 the central portions 54 of the terminal portions 20 pass over the bosses 36 and the slots 48 move over the wire 14.

The sharp edges 64 of the cutters 62 sever the insulation on the wire 14 and further entry of the terminal portion 20 forces the wire 14 into the narrow portions 68 of the slots 48. Intimate metal to metal contact is thereby provided between the wire 14 and the terminal portions 20.

The barbs 50 grip the covers 32 of the housings 26 and therefore retain the terminal portions 20 in the housings 26.

The arms 52 of each terminal portion 20 act as double cantilever springs and exert a continuous pressure on the wire 14.

The invention provides a simple and cheap connection between the armature winding and the commutator. No application of heat is required and the associated risk of distorting the supports 22 and 24 is therefore avoided. No embrittlement of the winding wire is caused and problems associated with oxidation are also avoided. The use of flux is negated and there is no chemical reaction or consequent corrosion resulting from the connection. The armature winding is a single continuous winding and the danger of introducing slack by breaking the winding to effect a connection to each coil is completely avoided.

Consequently, the danger of the armature winding being fretted when the motor is in operation, is reduced. It should also be noted that the commutator segments are introduced after the winding of the armature has been completed and therefore the danger of the wire being accidently stripped by abrasion on metal components during winding is very greatly reduced. Moreover, since the radial extent of the terminal portions and rose-like terminal support is small a good winding fill between the adjacent arms of the lamination stack can be achieved.

Furthermore, the commutator segment support and the rose-like terminal support can be made from different materials each adapted to the function which it has to perform. The commutator segments can be pre-assembled on the commutator segment support at a location remote from the assembly line for the armature. Also, the terminal portions may be positioned radially outwardly of the brush contacting portions.

The above embodiment is given by way of example only and various modifications may be made without departing from the scope of the invention defined by the appended claims. For example, the cutters could be omitted and the winding portions in the housings could be pre-stripped of insulation. Although described with reference to a five bar commutator the invention is particularly applicable to multi-segment commutator, for example with 10 or 12 segments.

Claims

1. A commutator for an electric motor, the commutator comprising a base and a plurality of commutator segments mounted on the base, the segments each comprising a brush-contacting portion for receiving thereon a brush of an electric motor and a terminal portion, the terminal portion having a slot therein for straddling and gripping a connector portion of an armature coil, wherein the terminal portion and brush-contacting portion are separately formed and are electrically connected.

2. A commutator as claimed in claim 1, wherein the terminal portion and brush-contacting portion are of material of different thickness.

3. A commutator as claimed in claim 1 or 2, wherein the terminal portion and brush-contacting portion are of different material.

4. A commutator as claimed in claim 1, 2 or 3, wherein the brush-contacting portion comprises a pair of spaced apart lugs extending from one end thereof and the terminal portion is received between the lugs.

5. A commutator as claimed in any one of claims 1 to 4, wherein the brush contacting portions are part cylindrical and the slots are disposed radially inwardly of the outer part-cylindrical surface of the brush-contacting portions.

6. A commutator as claimed in any one of claims 1 to 5, wherein the brush contacting portions of the commutator segments are part cylindrical and the terminal portion of each commutator segment is substantially completely radially inwardly disposed of its respective brush contacting portion.

7. A commutator as claimed in claims 5 or 6, wherein the terminal portions lie against or closely adjacent to one end of the commutator segment support.

8. A commutator as claimed in any one of claims 1 to 7, wherein each terminal portion has a cutting edge for cutting insulation on said connector portion as the connector portion enters the slot.

9. A commutator as claimed in any one of claims 1 to 8, wherein each terminal portion is provided with a barb for retaining said connector portion in a housing.

10. A commutator as claimed in any one of the preceding claims, wherein each terminal portion has two parallel arms, each arm being provided with a slot which straddles and grips the connector portion.

11. An armature for an electric motor, the armature comprising a shaft, a wound armature coil on the shaft, a commutator as defined in any one of claims 1 to 10, and a plurality of housings for receiving the terminal portions of the commutator.

12. An armature as claimed in claim 11, wherein the connector portions are located in said housings and the commutator is constructed with said slots being open at an end of the commutator, whereby the commutator can be pre-assembled and slid onto said shaft, said slots of said terminal portions straddling and gripping the connector portions as the terminal portions are slid into said housings.

13. A commutator for an electric motor, substantially as hereinbefore described with reference to the accompanying drawings.

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

15. An electric motor including a commutator as defined in any one of claims 1 to 10 and 13 and/or an armature as defined in any one of claims 11, 12 and 14.