GB2216342A

GB2216342A - Plastics brush holder for an electric motor

Info

Publication number: GB2216342A
Application number: GB8806744A
Authority: GB
Inventors: Georg Strobl
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1988-03-22
Filing date: 1988-03-22
Publication date: 1989-10-04
Also published as: GB8806744D0

Abstract

The brush holder 12 is formed from first and second separate plastics parts (19 and 20, respectively) which together define brush receiving cages in which respective brushes (31) are mounted. Preferably, one of the plastics parts also supports motor terminals (39), contact between terminal and brush being for example by a conductive resilent strip interposed between the brush flank and radially extending portion of the terminal. <IMAGE>

Description

An electric motor This invention relates to an electric motor and in particular a fractional horsepower electric motor.

Known permanent magnet direct current (p.m.d.c.) motors have a can-like metal casing and an end cap which closes the open end of the casing and which supports brushgear. Generally speaking the brushgear comprises brushes supported by respective brash leaves or brushes slidably mounted in respective brush cages. In known p.m.d.c. motors utilising brush cages, the cages are of metal and either secured to a plastics end cap or secured to a metal end cap with electrically insulating material between the end cap and the brush cages.However, in motors operating at a high voltage it is not always easy when using metal brush cages to comply with regulations governing creepage distances between metal parts particularly as motors get smaller, and the present invention seeks to mitigate this drawback, not only in p.m.d.c. motors but also in a.c. and universal motors utilising brush cages. According to the present invention, there is provided an electric motor comprising a motor frame, an armature having a commutator mounted for rotation in the frame, and a brush holder at one end of the frame, the brush holder being formed from first and second separate plastics parts which together define brush receiving cages in which respective brushes are mounted for slidable movement under the urging force of resilient means into contact with said comtor.

The use of a plastics brush holder has the advantage that one does not have to provide a required creepage distance between the brush cage and adjacent metal parts and a two part plastics brush holder is much easier to mould than a single part brush holder.

moreover, the number of component parts can be reduced.

Preferred and/or optional features of the invention are set forth in claims 2 to 9, inclusive.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view partly in section of one embodiment of a motor according to the invention, Figure 2 is a view taken in the direction of arrow A of Figure 1, Figure 3 is a plan view of the first part of the brush holder on an enlarged scale with brushes and torsion springs shown mounted thereon, Figure 4 is a section taken along line IV-IV of Figure 3, Figure 5 is a plan view of the second part of the brush holder on an even larger scale, Figure 6 is a section taken along line VI-VI of Figure 5, Figure 7 is a sectional view of one of the motor terminals on a much enlarged scale, and Figure 8 is a fragmentary sectional view showing a motor terminal in its respective terminal housing.

Referring firstly to Figures 1 and 2 of the drawings, the electric motor shown therein is a fractional horsepower permanent magnet direct current electric motor and comprises a frame in the form of a cylindrical steel can-like casing 10 closed at one end by an integral end plate 11 and a brush holder 12 and metal end closure 13 at its other eflo. T- stator magnets 14 (only one is shown) are fixed within the casing 10 in conventional manner against angular movement relative to the casing by a U-shaped spring (not shown) between adjacent axial edges of the magnets 14 urging the other axial edges of the magnets into engagement with ears (not shown) pressed out of the casing.

An armature 15 provided with a commutator 16 is supported for rotation within the casing 10 and between the stator magnets 14 by bearings 17 and 18 mounted, respectively, in the end plate 11 and the end closure 13.

The brush holder 12 is formed from two separate plastics parts 19 and 20. As best shown in Figures 3 and 4, the part 19 comprises a generally cylindrical sleeve-like outer wall 21 which is push-fittable in the said other end of the casing 10, four projections 22 which extend radially outwards from the wall 21 and which fit in notches in the other end of Whe casing 10, and two inner portions 23 and 2e. The inner portions 23, 24 each comprise a platforr 25 from which cylindrical post 26 and projection 27 upstand, and three sides 28, 29 and 30 of a brush cage. A brush 31 is mounted in each brush cage for slidable movement under the urging force of a torsion spring 32 into contact with the commutator 16.Each torsion spring 32 is mounted about a respective post 26; one end of the torsion spring 32 engages upstanding projection 27 and the other end of the torsion spring 32 enters a respective brush cage through a recess in side 30 and engages the radially outer end of a respective brush 31.

A post 33 projects from the inner surface of the side 29 of each brush cage to make contact with and axially locate a respective magnet 14.

As best shown in Figures 5 and 6, the plastics part 20 comprises an annular portion 34, two terminal housings 35 integral with the free ends of wing portions 36 extending radially outwards from the annular portion 34, and two ears 37 each having an aperture 38 therein.

The terminal housings 35 fit into recesses 39 in the outer wall 21 of the plastics part 19 and the apertures 38 receive the free ends of the cylinorical posts 26. The wing portions 36 define the fortn sides of the brush cages.

As shown in Figure 1 the terminal housings 35 each support an L-shaped motor terminal 39 having a first limb extending externally of the motor and a second limb extending radially inwards within a respective brush cage. As best shown in Figure 7 this second limb has a resilient leaf 40 secured thereto, such as by an integral upset rivet on the second limb. This leaf 40 bears against the brush 31 and electrically connects the terminal 39 to the brush 31.

Alternatively, however, the terminal 39 could be electrically connected to a respective brush 31 by a conventional pigtail (not shown).

As shown in Figure 8, the terminal 39 is firmly located in the housing 35 by portions 41 which are splayed out after insertion of the-terminal 39 in the terminal housing 35.

The metal end closure 13 has an integral, drawn bearing housing 42, two recesses 43 which receive the terminal housings 35, and four radial projections which fit in said notches in the said other end of the casing 10. Portions of the casing uzall bordering the said notches are deformed to secure the brush holder 12 and the end closure 13 to the casing 10.

The casing 10, the two parts 19 and 20 of the brush holder 12, and the end closure 13 may all be designed so as to fit together in only one angular position thus enabling the end closure 13 to be given a polarity coding for the terminals 39, during manufacture.

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. For example, the invention may be applied to an a.c. or universal motor.

Claims

1. An electric motor comprising a motor frare, an armature having a commutator mounted for rotation in the frame, and a brush holder at one end of the frame, the brush holder being formed from first and second separate plastics parts which together define brush receiving cages in which respective brushes are mounted for slideable movement under the urging force of resilient means into contact with said commutator.

2. A motor as claimed in claim 1, wherein one of the plastics parts also supports motor terminals.

3. A motor as claimed in claim 1 or claim 2, wherein the first plastics part defines three sides of a brush cage and the second plastics part defines the fourth side of the brush cage.

4. A motor as claimed in claim 3, wherein the resilient means urging each brush into contact with the commutator is a torsion spring and the torsion spring is mounted about a post integral with the first plastics part.

5. A motor as claimed in any one of claims 1 to 4, wherein the first and second plastics parts fit together and are push fittable in the one end of the frame.

6. A motor as claimed in any one of claims 1 to 5, wherein a metal bearing support is secured to the one end of the frame and the brush holder is disposed on the inner side of the bearing support.

7. A motor as claimed in any one of the preceding claims, wherein the motor is a permanent magnetic direct current electric motor and the frame is in the form of a casing having the brush holder at one end of the casing'and permanent magnet means supported in the casing.

8. A motor as claimed in claim 7, wherein the other end of the casing has an integral end plate supporting a motor bearing.

9. A motor as claimed in claim 7 or claim 8, wherein the casing is metal.

10. An electric motor substantially as hereinbefore described with reference to the accompanying drawings.