GB2139820A - Electric motor - Google Patents

Abstract

An electric motor has brush gear mounted on the motor case or an end cap (1) therefor made of synthetic resin. The brush gear has brushes made of metal sheet or strip stock. They each comprise a brush proper which makes contact with the commutator of the motor in use and a terminal portion (3) integral with the brush proper. The terminal portion extends through terminal holes provided in the motor case or end cap for connection in an electric circuit externally of the motor case. At least one locking recess or hole (2) is provided on the motor case or end cap in the vicinity of each terminal hole. Respective selected auxiliary terminals (6) are electrically connected to the terminal portions of the brushes. These auxiliary terminals have root end portions (4) which are lockingly received in the terminal recesses or holes, and also have a terminal part (5) which may take various configurations and is adapted for connection in an electric circuit. <IMAGE>

Description

SPECIFICATION Electric motor This invention relates to electric motors and more particularly, though not necessarily exclusively, to those electric motors known as miniature motors.

Miniature motors are incorporated in various types of electrical equipment.

It has been the practice heretofor in miniature motors for the brush gearto comprise brushes which include an integral terminal portion since this construction reduces the numbers of parts required and allows the terminal to be of a convenient small size and simple construction. Commonly such brushes are formed of sheet or strip stock with the result that the motor terminal and the brush proper are of generally identical thickness.

The brush must make operative contact with the commutator and maintain pressure and a desired area of contact with the commutator at predeter mined levels at all times. For this reason, the brush gear is generally designed so that the brush takes up a moderately curved state in use. Best results are achieved when the brush is of relatively thin strip material. This results in the motor terminal suffering from a mechanical strength problem. In an attempt to overcome this problem, it has been suggested to bend the terminal portion, following insertion through a terminal hole or aperture in the motor case or an end cap therefor, into a generally U-shaped configuration. We have not found this to increase the mechanical strength of the terminal to the extent we would wish.A further shortcome of the above described integral brush and terminal portion has been that the thin strip configuration of the terminal portion limits the way in which connection can be made with external equipment in an electric circuit.

The present invention has arisen from our work seeking to overcome or to mitigate the above described problems.

In accordance with the present invention, there is provided an electric motor in which the brush gear therefor is mounted on a motor case or end cap made of a synthetic resin, the brush gear comprising brushes made of metal sheet or strip stock and each comprising a brush proper adapted for operative contact with the commutator of the motor and a terminal portion integral therewith and extending through terminal holes provided in said motor or end cap for connection in an electric circuit externally of the motor case; at least one locking recess or hole being provided on said motor case or end cap in the vicinity of each said terminal hole; and respective selected auxiliary terminals electrically connected to the terminal portions of the brushes, said auxiliary terminals each having root end portions formed thereon and lockingly received in said locking recesses or holes and a terminal part adapted for connection in an electric circuit.

As will become apparent from the detailed description which follows, the present invention enables the employment of mechanically strengthened terminals for connection to external equipment without any significant change in design of a previously proposed motor. All that is required is the provision of locking recesses or holes in the motor case or end cap therefor and the provision of appropriate auxiliary terminals.

The configuration of the auxiliary terminals may be selected as required in order to allow electrical connection to any selected piece of external equip ment.

The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a partial perspective view of an electric motor constructed in accordance with the present invention; Figure 2A and 2B respectively show the motor of Figure 1 in a side elevational view partly in section and in an axial end view; Figure 3 is a partly sectional side elevation of a previously proposed motor; Figure 4 is a perspective view of the one-piece brush and motor terminal of the motor of Figure 3; Figures 5A, B and C illustrate other configurations for the root end portion of the auxiliary terminal in the motor of Figures 1 to 2B; and Figures 6A, B, C and D show various configurations for the terminal part of the auxiliary terminals in the embodiment of Figures 1 to 2B.

The motor of Figure 3 has a rotatable shaft 10 mounted in bearing 11 and supporting a rotor 12 within a motor case 13 made of a magnetic material.

The motor has brushes 14 which fit in respective terminal holes 15 by means of integral motor terminals 16. Terminal holes 15 extend through motor case end cap 17 made of a synthethic resin.

Brushes 14 make contact with a commutator 18.

Magnetic poles 19 are mounted on the interior of case 13. It has been the practice heretofore for the brush 14 of a miniature motor, as here shown, to be integrally formed with the motor terminal 16 for external connection in order to provide a construction in which the motor terminal and brush are small in size, simple in construction and inexpensive. For example, an L-shaped metallic strip is bent at right angles along an extension of an internal side thereof, as shown in Figure 4, the end being used as a brush 14 and the other end as a motor terminal 20. The motor terminal 16(20) is inserted through the slot-shaped terminal hole 15 provided on the motor case end cap 17, made of a synthetic resin, to extend to the exterior of the motor case end cap 17.We have found that the motor terminal 16 (20) tends to suffer from problems of mechanical strength and of connection to other pieces of electrical equipment.

In the miniature motor of Figures 1 to 2B constructed in accordance with the present invention, a synthetic resin motor case (or end cap) 1 has at least one terminal locking recess or hole 2 in the vicinity of the motor terminal 3. An auxiliary terminal 6 is detachably fitted to the terminal locking recess or hole 2, and also has a terminal part 5 for connection to any other piece of equipment. Root end portions 4 of the auxiliary terminal 6 fit in the terminal locking recesses or holes 2. The auxiliary terminal is electrically connected to the motor terminal 3 by soldering, electrically conductive adhesive or spot welding.

This is illustrated at 7 in Figure 1 where like parts are shown with dashes. In effect, the terminal portions 3 and 3' of the brushes are reinforced by the auxiliary terminals 6 and 6' and are connected to the terminal parts 5 and 5', which may have any selected shape.

The root end portions 4 are generally locked in the terminal locking recesses or holes 2 by press fitting using jigs, etc. However, other means, such as bonding after insertion, can be employed for locking a root end portion 4 to the corresponding terminal locking recess or hole 2.

A side elevational view partly in section of the miniature motor is shown in Figure 2A, and an axial end view in Figure 2B.

Figures 5A, B and C illustrate other configurations of root end portions 4 for the auxiliary terminals 6 which we have found useful in the practice of this invention. Figure 5A shows a saw-tooth lock 22 provided on the motor terminal part 21 and serving to assist retention of the auxiliary terminal 6 in the terminal locking recess or hole 2 (refer to Figure 1).

Figure 5B shows an embossed part 23 provided on the root end portion 4to ensure press fitting of the root end portion 4 in recess or hole 2, even where the auxiliary terminal 6 may be of a lesser thickness.

Figure 5 C is a cross-sectional view of the embossed parttaken along the line A-A in Figure 5B.

Figures 6A, B, C and D illustrate a number of configurations for the terminal part 5 of the auxiliary terminal 6. Reference numerals 24, 25 and 26 indicate different shapes of tabs, i.e., a round-head tab, a fork-shaped tab and a straight tab, respectively, and 27 shows a bend-and-crimp type socket terminal part.

Thus, it will be seen that the configuration of the terminal part 5 of the auxiliary terminal 6 may be selected entirely as required in the particularcir- cumstances. The auxiliary terminal 6 is electrically connected to the terminal portion 3 of the brush providing the desired mechanical strength. Since the auxiliary terminal is mounted in position from the outside of the motor case, this operation can be accomplished at any desired stage of the manufacturing process of the motor. It will be appreciated that only the provision of the locking holes or recesses 2 and the auxiliary terminal 6 is necessary to modify a previously proposed miniature electric motor to convert it into an improved electric motor in accordance with the present invention with all the advantages which arise therefrom.

Claims (4)

1. An electric motor in which the brush gear therefor is mounted on a motor case or end cap made of a synthetic resin, the brush gear comprising brushes made of metal sheet or strip stock and each comprising a brush proper adapted for operative contact with the commutator of the motor and a terminal portion integral therewith and extending through terminal holes provided in said motor or end cap for connection in an electrical circuit externally of the motor case; at least one locking recess or hole being provided on said motor case or end cap in the vicinity of each said terminal hole; and respective selected auxiliary terminals electrically connected to the terminal portions of the brushes, said auxiliary terminals each having root end portions formed thereon and lockingly received in said locking recesses or holes and a terminal part adapted for connection in an electric circuit.

2. A motor according to Claim 1, wherein said root end portion of said auxiliary terminals have saw-tooth locks for assisting retention of said motor terminal parts into said locking recesses or holes.

3. A motor according to Claim 1, wherein said root end portions of said auxiliary terminals have embossed parts formed thereon and forming a press fit in the locking recesses or holes.

4. An electric motor substantially as hereinbefore described with reference to and as shown in Figures 1 to 2B and 5A to 6D of the accompanying drawings.