GB2222319A - Attaching commutator segments - Google Patents

Abstract

A commutator comprises a plurality of segments 12 on a base 10. The segments 12 have terminals 14 including slots 28 arranged to straddle and grip connector portions 66 of an armature coil wire. The brush contacting portions 13 of the segments are glued to the base 10. To provide an even distribution of glue under the segments the surface 19 of the base 10 has grooves which extend lengthwise of the brush contacting portions 13. <IMAGE>

Description

A COMMUTATOR This invention relates to a commutator for an armature of an electric motor.

In our British Patent No. 2128818 we describe a connection between an armature winding and a commutator segment which avoids the application of heat to effect the connection 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 petal to metal contact between the wire and a terminal integral with the commutator segment.

Our published British application No.2198890 describes a commutator in which the segnnts pre-assembled on a base which can then be slic onto the armature shaft. Typically, the housings are previously mounted on the shaft, and the armature wire is wound through the housings. The specification describes a system in which the segments are locked to the base at one end by a tongue which fits in a recess in the base. At the other end, adjacent the terminals, a locking ring is fitted around the segments. In practice, it has been found that the locking ring works well for commutators with 3 and perhaps 5 segments.The segments are locked centrally at one end and, in effect, at their edges by the ring at the other end to give a three point locking system. However, as the number of segments increases to 10 or 12 or more, the circumferential width of the segment is reduced considerably and the three point locking is not as effective.

We have previously mentioned the possibility of bonding the segments to the base and it is generally known to glue segments in hot staked pre-assembled commutators. However, we have found that glue ten5s to accumulate under the segments, mid-way between the ends, causing them to bow slightly, and resulting in a joint which is good mid-way along the segments but poor at the ends. It is known to texture the noting surfaces of components before gluing to improve the bond but this does not solve the problem.

We have now found that a secure, even bond along the length of the commutator segment can be achieved by providing grooves in the circumferential surface of the commutator base, the grooves extending in the axial direction and preferably to at least one end of the base. This results in an even distribution of the glue under the segment and hence an even bond between segment and base across the whole area of the segment.

Accordingly, the present invention provides a commutator for an electric motor, comprising a plurality of commutator segments each having a brush contacting portion and an integral terminal provided with a slot which is arranged to straddle and grip a connector portion of an armature winding to form an electrical connection therewith, a commutator base having a cylindrical part on which the brush contacting portions of the segments are mounted and a housing part receiving the terminals of the segments, wherein the brush contac qng portions of he segments are held on the base at least in part by glue and a plurality of grooves are provided in a surface of the cylindrical base part supporting the brush contacting portions, the grooves extending in the length direction of respective brush contacting portions, which direction extends from said one end to the other end thereof.

Preferably the housing part and the cylindrical part of the base are separate. The housing part can be mounted on the motor shaft and the connector portions of the armature winding inserted in the housings.

The pre-assembled cylindrical base and segments are then slid onto the shaft, the terminals being pushed into the housings to connect with the connector portions.

The underside of the brush contacting portions of the segments may also be grooved, preferably in the length direction, to enhance the shear resistance of the assembly in the cirection of rotation of the commutator.

The connector portion may be formed by a part of the armature winding wire or it may be formed by a separate electrically conducting element, the armature winding wire being wound around the element to form an electrical connection with the commutator segment. This may be particularly useful when thin armature wire is being used.

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 perspective view of one embodiment of a pre-assembled part of a commutator according to the present invention; Figure 2 is a plan view of a commutator segment blank; Figure 3 is a plan view of a housing part, the support being shown partially sectioned to illustrate the configuration of one of its terminal housings, Figure 4 is a vertical sectional view of the assembly of Figure 1 connected to the support of Figure 3; Figure 5 is a perspective view of the housing part of Figure 3; and Figure 6 is a cross-section along the line VI-VI of Figure 4.

Referring firstly to Figure 1, a cylindrical part 10 of a commutator base is preferably of thermosetting plastics material, such as a phenolic resin, or of metal coated with an insulating layer of metal oxide, e.g. anodised aluminium, and carries a plurality (as shown five) of copper commutator segments 12, each having a brush contacting portion 13 and an integral terminal 14.

The part 10 is essentially right cylindrical and is provided with five arcuate raised portions 16 at one end 15, the raised portions 16 being equally spaced around the circumference of the part 10 to define recesses therebetween in which the terminals 14 of the commutator segments 12 are located.

The other end 17 of the part 10 is provided with five longitudinal recesses 18 (Figure 4) which are cut away at their outer ends to meet the cylindrical external surface 19 of the part 10. These recesses 18 receive lugs 20 provided at the end of the segments 12 remote from the terminals 14 to assist in securing the segments to the base. As an alternative to the lugs 20 and recesses 18 the segments 12 could be provided with integral formations which fit over respective posts integral with said other end of the base.

As will be described more fully hereinafter, the brush contacting portions 13 of the segments 12 are bonded to the surface 19 of the base 10.

A commutator segment 12 is illustrated in Figure 2 in the form of a blank. The lug 22 which is of reduced width is provided at the front end of the brush contacting portion 13 and has a dimple 24 to restrain the lug 22 within the recess 18 (Figure 1). At its rear end, the brush contacting portion 13 is connected to the terminal 14. The terminal 14 has a central cut out portion 26 which reduces from its largest width at the centre of the terminal to two key hole shaped cut out portions 28 which terminate either end of fine cut out 26. . triangular barb 30 is provided on either side of the terminal 14 along the edge furthest from the brush contacting portion 13.

As can be seen from Figure 1, the brush contacting portion 13 is of arcuate form which conforms to the external radius of the part 10. The lug 20 extends below and back along the length of the brush coiitacting . portion 13 with the tag 14 projecting below the lug 20. Terminal 14 is bent upright from the brush contacting portion 13 and arms 32 of the terminal 14, which include the respective key hole shaped portions 28, are bent at 90 degrees to the central portion 34 of the terminal. The arms 32 therefore extend parallel to each other and to the longitudinal axis of the commutator segment 12, and forward along the length thereof. The free ends 36 of the terminal 14 may be bent so as to be inclined towards each other when the arms 32 have been bent parallel to each other.

As described more fully in the aforesaid specifications GB2128818 and GB2198890, the cut out portion 28 may include barbs or cutting edges to cut through insulation on the armature wire connector portion to for an electrical connection with wire.

It is also possible to use bare or pre-stripped connector portions, in which case the insulation displacement cutting edges need not be provided.

As seen by reference to figures 1 and 6, the outer cylindrical surface 19 of the cylindrical commutator base part 10 has a plurality of grooves 72 which extend along its length in the axial direction. The grooves may, additionally, have a circumferential component to their direction but it is presently preferred that the extend parallel to the axial direction. Also, the underside of the brush contacting portions 13 are scored along their length, forming V-shaped grooves 74. Preferably the grooves 74 are spaced apart by a different amount to the grooves 72.

Grooves 72 extend beyond at least one end of the segments 12, or at least to an end of the base part 10 (see Figure 1). This ensures that excess glue can be squeezed out from under the segments.

Figures 3 and 5 sho a housing part 47 of the commutator base, which co-operates with the assembly of Figure 1, the assembled commutator being shown in cross-section in Figures t and 6. mhe part 47 is in the form of a body 48 of moulded thermoplastics material, e.g. thermosoftening nylon. The body 48 is mounted fast on the shaft 49 of an armature of an electric motor and comprises five housings 50 and a sleeve portion 52 which serves to space the housings 50 from the base of the armature stack (not shown).

The housings 50 are equally spaced around the circumference of the body 48. Each of the housings 50 is used in effecting connection between a respective portion of the armature winding and one of the terminals 14 of the commutator segments 12.

One of the housings 50 is shown in section in Figure 3. The housing has side walls 54, an end wall 56 and a cover 58. The end wall 56 is adjacent the sleeve portion 52 and an opening 60 faces away from the sleeve portion 52. The side walls are parallel with the longitudinal axis of the body 48.

A boss 62 projects centrally from the internal surface of the end wall 56 and extends within the housing 50 for approximately half the length of the side walls 54. The boss 62 extends parallel with the longitudinal axis of the body 48 and is only connected to the body 48 by the end wall 56. Each side wall 54 of the housing 50 has a slot 6z which extends parallel to the longitudinal axis of the body 48, from the open end of the housing 50 for a length which terminates at the level of the free end of the boss 62. A connector portion 66 of the armature winding is passed through the slots 64 of one of the housings 50 and the portion 66 rests on the end of the boss 62. The external surfaces of the side walls 54 are bevelled so as to facilitate entry of the portion 66 into the slots 64.

The armature may be assembled as follows: The cylindrical surface 19 of the base part 10 is coated with a cold setting glue suitable for bonding the segments and base part together. The segments 12 are then slid on to the base part 10. The segments are aligned at one end by the projections 16 and at the other end by the tabs 20. It will be appreciated that the tabs 20 and/or projections 16 may be omitted, the segments being aligned mechanically.

The glue is preferably sufficiently fluid to flow between the segments and base part to distribute itself evenly under the segments, and in particular will flow along the grooves 72. The glue is then allowed to set.

The body 48 is placed on the armature shaft with the sleeve portion 52 against the base of the lamination stack. The wire of the armature winding is inserted into the housing 50 by laying the end of the wire 66 in the slots 64 provided in the side walls 54 of the housing.

The wire 66 is drawn back into the housing 50 until it rests against the boss 62. From this start, the first armature coil is wound. At the end of the first coil winding the armature is indexed and the wire 66 is layed in the same manner in the next housing 50 without breaking the continuity of the wire 66.

This process is repeated until all coils have been wound and the tail end of the winding is then laid in the slots 64 of the first housing 50 and pushed back until it is adjacent to the lead end which was placed against the boss 62 at the beginning of the winding operation. The wire 66 is then cut and the armature removed from the winding machine.

The body 48 now has a winding portion 66 comprising insulated wire laying in each of the housings 50.

Each of the winding portions 66 is under tension and is pulled tight against the respective boss 62.

The commutator which has been pre-assembled, that is the segments 12 have been glued on the base part 10, is then slid along the armature shaft. As the terminals 14 approach the winding portions 32 held in the housings 50, the slots provided by cut outs 28 move over the wires 66 to grip them.

The ears 16 enter into the body 48 between the housings 50. The barbs 30 grip the cover 58 of the housing 50 and therefore retain the terminal 14 within the housing 50.

The above embodiment is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention defined by the appended claims. The grooves 72 may be spaced evenly about the surface 19 or they may be grouped to ensure that the circumferential edges 76 of the segments rest on a non-grooved portion of the surface. Also they may extend helically around the base, so as to extend both axially and circumferentially of the base, but it is preferred that any circumfrential direction be relatively small. The terminals 14 may be designed with only one arm 32 or may have more than two arms 32. Although the invention has been described with reference to a 5 segment commmutator it is particularly advantageous with commutators for small electric motors having a higher number of segments, for example 7, 10 or higher.

This invention is applicable particularly but not exclusively to a commutator of a fractional horsepower electric motor.

Claims (8)

1. A commutator for an electric motor, comprising a plurality of commutator segments each having a brush contacting portion and an integral terminal at one end of the brush contacting portion, the terminal having a slot which is arranged to straddle and grip a connector portion of an armature winding to form an electrical connection therewith, a commutator base having a cylindrical part on which the brush contacting portions of the segments are mounted and a housing part which houses the terminals of the segments, wherein the brush contacting portions of the segments are held on the base at least in part by glue and a plurality of grooves are provided in surface of the cylindrical base part supporting the brush contacting portions, the grooves extending in the length direction of respective brush contacting parts, which direction extends from the said one end to the other end thereof.

2. A commutator as claimed in claim 1, wherein the grooves are open at least at one end thereof to allow glue to escape from between the segments and base part.

3. A commutator as claimed in claim 1 or 2, wherein the sgements are mounted on a cylindrical surface of the base part and extend substantially parallel to the axis of the cylinder.

4. A commutator as claimed in claim 1, 2 or 3, wherein an underside of the brush contacting portion of each segment has a plurality of grooves therein.

5. A commutator as claimed in claim 4, wherein the grooves in the underside of the brush contacting portions extend in the length direction of the brush contacting portions.

6. A commutator as claimed in any one of claims 1 to 5, wherein the cylindrical part and the housing part of the commutator base are separate.

7. A commutator as claimed in any one of claims 1 to 6, wherein means is provided for aligning the segments on the cylindrical part.

8. A commutator substantially as hereinbefore described with reference to the accompanying drawings.