GB2207292A

GB2207292A - Electric motor

Info

Publication number: GB2207292A
Application number: GB08716209A
Authority: GB
Inventors: Patrick Shui-Chung Wang
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1987-07-09
Filing date: 1987-07-09
Publication date: 1989-01-25
Also published as: GB8716209D0

Abstract

A commutator 4 in an electric motor is mounted fast on a shaft 2 with a wound armature 3. A suppression element such as a varistor 39 is provided at the end of the commutator distal of the armature. The varistor is connected to segments 31 of the commutator by forming an electrical contact with bight portions 33 of tangs 32 which help secure the segments to the commutator base 27. In another embodiment (Fig 3) capacitors (41) are connected across the segments and located in recesses (40) in the base 27. <IMAGE>

Description

Electric Motor The present invention relates to an electric motor and to a commutator for an electric motor.

Electric motors having commutators commonly incorporate a suppression element. The element may be connected between brushes of the motor or segments of the commutator.

typically the suppression element comprises a resistor, capacitor, varistor or the like.

In small motors such as fractional horsepower permanent magnet direct current (PMDC) motors space is at a premium. A suppress ion element can be incorporated on the commutator in the vicinity of the commutator tangs which are connected to the armature coils. However, this can inhibit the flow of cooling air over the brush contacting surfaces of the commutator segments.

A first aspect of the present invention provides an electric motor having a rotor assembly comprising a shaft, a wound armature and a commutator mounted fast on the shaft for rotation therewith, the commutator comprising a cylindrical base having a plurality of commutator segments thereon, wherein a suppression element is mounted at an end of the commutator distal of the armature, the suppression element being in electrical contact with two or more of the segments.

A second aspect of the invention provides a commutator for an electric motor, comprising a cylindrical base mountable on a shaft of a said motor, a plurality of commutator segments on the base, said segments having first and second ends and being each adapted at said first ends for connection to an armature winding, and a suppression element electrically connected to a plurality of said segments at said second ends thereof distal of the first ends.

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-sectional view of a fractional horsepower PMDC motor embodying the invention; Figure 2 is an enlarged cross-section on line II-II of figure 1; and Figure 3 is an end view of a variation of the commutator of Figure 2 Referring to Figure 1, a small, fractional horsepower permanent magnet direct current motor 1 is illustrated.

The motor comprises a motor shaft 2 which carries a wound armature 3 and commutator 4. The commutator 4 and armature 3 are mounted fast on the shaft and the armature is wound and connected to the commutator in the manner generally known in the art. Tangs 23 on the commutator are forged to wires 26 which form the coil windings of the armature.

The shaft 2 is mounted in a cylindrical metal casing 5.

Casing 5 is closed at one end by an integrally formed end plate 6. End plate 6 carries a bearing 7 in a housing 8, the shaft 2 being journalled in the bearing 7. A brass collar 24 is a force fit on the shaft 2 to limit the axial movement of the shaft through bearing 7. A washer 25 is mounted on the shaft between the brass collar 24 and bearing 7.

End plate 6 has a plurality, typically four, of circumferentially extending slots 9 for ventilation of the inside of the motor.

A plastics end cap 10, typically of nylon, houses a self aligning sintered bearing 11 which is held in place by axially extending tabs 12 of a washer 13 which is pressed into the end cap. The end cap supports brush gear comprising a pair of carbon brushes 14 (one is seen in Figure 1) which are urged against the commutator 4 by brush leaves (not seen in Figure 1) which are connected to power supply tags 15.

The brush leaf/tag assemblies are held on the end cap 10 by rivets 16, 17. An oil slinger 44 and a thrust washer 45 are mounted on the shaft 2 between the commutator 4 and bearing 11.

In the example shown the casing 5 carries two permanent magnets 18, which each bear at one axial edge 20 against a respective tang 19 and are urged apart at their other axial edges by a U' shape spring 21.

Circumferentially extending slots 22 are provided in the casing 5 in the region between the brushes 14 and armature 3 for ventilation.

The improvement provided by the present invention resides in the provision of a suppression element at an end of the commutator 4 distal of the armature coil 3.

Referring in particular to Figure 2, the commutator 4 shown is of the assembled type and comprises a cylindrical base 27 having a collar portion 28 at the end and a boss 29 at its other end. Commutator segments 30 are mounted on the base in known fashion. The segments comprise a brush contacting portion 31 which lies on the cylindrical base 27 and an outwardly extending tang 23 which is bent to lie on the collar 28 and is forged or soldered about armature wire 26. At the end of the segments 30 opposite the tang 23 is a second tang 32 which has a reverse bend forming a bight portion 33 and an axially directed portion 34. Bight portion 33 lies against an end wall 35 of the base 27 and axially directed portion 34 is received in recess 36 in the end wall 35.

Tabs 37 on the end of the brush contacting portion 31 extend into a recess 38 formed at the junction of the collar 28 and base part 27. Tabs 37 and tangs 32 served to hold the segments on the base. The construction thus for described is well known in the art, save for the provision of the boss 29. It has been found that bight portions 32 provide a way of electrically connecting a suppressions element across the segments. Such an element may comprise a varistor, resistor, capacitor or the like.

Illustrated in Figure 2 is a varistor ring 39 which is carried on the boss 29. The ring is soldered to the bight portions 33 on each commutator segment.

Figure 3 shows another embodiment of the invention, like parts to those of Figures 1 and 2 being given like reference numerals. The boss 29 is not provided on the base part 27. The tangs 32 with bight portions 33 and axially directed portions 34 are provided as before. In addition to recesses 36 further recesses 40 are provided.

These each house a suppression element such as a capacitor 41, leads 42 from each capacitor are connected to the circumferentially adjacent bight portion 32 by soldering.

The recesses 40, 36 may be contiguous.

Various modifications may be made. For example, the invention may be applied to insert moulded commutators.

It is desired to include all such modifications as fall within the accompanying claims.

Claims

1. An electric motor having a rotor assembly comprising a shaft, a wound armature and a commutator mounted fast on the shaft for rotation therewith, the commutator comprising a cylindrical base having a plurality of commutator segments thereon, wherein a suppress ion element is mounted at an end of the commutator distal of the armature, the suppression element -being in electrical contact with two or more of the segments.

2. A motor as claimed in claim 1, wherein a segment comprises a part cylindrical brush contacting portion and a tang extending from an end of the part cylindrical portion at said end of the commutator distal of the armature, said suppression element being electrically connected to the tang.

3. A motor as claimed in claim 2, wherein the tang lays against an end face of the commutator base.

4. A motor as claimed in claim 3, wherein an end of the tang projects into a recess in the end face.

5. A motor as claimed in any one of claims 1 to 4, wherein the suppression element is housed in the commutator base.

6. A motor as claimed in claim 5, wherein the suppression element is housed in a recess in the base.

7. A motor as claimed in anyone of claims 1 to 6, wherein a boss is provided on the or an end face of the commutator base distal of the armature.

8. A motor as claimed in claim 7, wherein the boss supports a ring shaped varistor.

9. A motor as claimed in anyone of claims 1 to 7, wherein the commutator is an assembled commutator.

10. A fractional horsepower PMDC motor as defined in anyone of the preceding claims.

11. An electric motor substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.

12. A commutator for an electric motor, comprising a cylindrical base mountable on a shaft of a said motor, a plurality of commutator segments on the base, said segments having first and second ends and being each adapted at said first ends for connection to an armature winding, and a suppression element electrically connected to a plurality of said segments at said second ends thereof distal of the first ends.

13. A commutator as claimed in claim 11, wherein the suppression element is electrically connected to a tang provided at the second end of a segment.

14. A commutator as claimed in claim 11 or 12, wherein the suppression element is housed in the base.

15. A commutator as claimed in claim 14, wherein the suppress ion element is housed in a recess in an end wall of the base.

16. A commutator as claimed in claim 11 or 12 wherein the suppression element is mounted on a boss at an end of the base.

17. An assembled commutator as defined in anyone of claims 11 to 16.

18. An assembled commutator substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.