GB2142192A

GB2142192A - Electric motor

Info

Publication number: GB2142192A
Application number: GB08411983A
Authority: GB
Inventors: Riyouichi Someya
Original assignee: Mabuchi Motor Co Ltd
Current assignee: Mabuchi Motor Co Ltd
Priority date: 1983-05-10
Filing date: 1984-05-10
Publication date: 1985-01-09
Also published as: JPH0139084Y2; HK34691A; GB8411983D0; GB2142192B; JPS59176350U

Abstract

An electric motor has a casing which comprises a cylindrical case 4 which is generally closed at one end and a synthetic resin end cap 8 for the other end thereof. A rotor shaft 1 has a commutator 10 and is supported for rotation in a bearings 9,2. The brush gear for the commutator has a plurality of electrically conductive brushes 11 formed of strip stock mounted in brush mounts. Corresponding terminals 12 extend through respective terminal holes formed in the end cap. The terminals each have a terminal portion (16 Fig. 3) which extends externally of the casing and is adapted for connection in an external electric circuit. The terminals also each have a fixing portion (17) located internally of the casing and provided with a fixing hole (21). The terminal is fixedly fitted to the end cap together with and in electrical connection with a respective brush by fixing means 5 passing through the fixing hole. <IMAGE>

Description

SPECIFICATION Electric motor This invention relates to electric motors.

Miniature electric motors are incorporated in a wide variety of electrical equipment. Desirably such motors should exhibit reliability and ruggedness in use. As we shall explain below with particular reference to Figure 1,we have found that the necessary electrical and mechanical connection to other electrical equipment causes problems in previously proposed motors of this kind.

The present invention has arisen from our work in seeking to improve upon the prior proposals and to provide a solution to these problems.

In accordance with the present invention, we provide an electric motor, comprising: a casing having a generally cylindrical motor case generally closed at one end and an end cap or motor case cover for the other end thereof, the motor case being formed of a magnetic material and being provided with means defining at least one magnetic pole of the motor stator, and the end cap or motor case cover being formed of a synthetic resin material and forming a press fit within the said other end of the motor case; a rotor shaft on which a commutator is mounted adjacent one end, the said one end being supported for rotation in a bearing mounted in the end cap or motor case cover, and the other end of the shaft being supported for rotation in a bearing mounted in said one end of the motor case; brush gear for the commutator comprising a plurality of electrically conductive brushes formed of strip stock and brush mounts therefor provided internally of the end cap or motor case cover; and a corresponding plurality of terminals each extending through a respective terminal hole formed in said end cap or motor case cover and each having a terminal portion extending externally of said casing and adapted for connection in an external electric circuit and a fixing portion internally of said casing and provided with a fixing hole, said terminal being fixedly fitted to the end cap or motor case cover together with and in electrical connection with a brush by fixing means passing through said fixing hole.

The present invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a partial cross-sectional view of a previously proposed miniature electric motor; Figure 2A is a similar partial cross-sectional view of an embodiment of motor constructed in accordance with the present invention; Figure 2B is an end elevational view of the motor of Figure 2A as seen from the right; Figure 2C is a partial side elevational view as seen in the direction of the arrow X in Figure 2A; Figure 3 is an exploded perspective view of the end cap or motor case cover illustrating the manner of fixing of a terminal; Figure 4A is a top plan view of a terminal in the motor of Figures 2A to 3; Figure 4B is a side elevational view of the terminal of Figure 4A;; Figure 4C is a right-hand end elevation of the terminal of Figures 4A and 4B; Figure 5 is a perspective view of the end cap or motor case cover end of the motor of Figures 2A to 3.

Referring first to the previously proposed miniature motor illustrated in Figure 1, it will be seen that its rotor shaft 1 is supported in bearings 2 and 9 respectively mounted in a generally closed end of a cylindrical motor case 4 formed of a magnetic material and an end cap or motor case cover 8 formed of a synthetic resin or plastics material. The rotor windings 3 and a commutator 10 are mounted on the shaft 1. Brush gear comprising brushes 11 formed of thin metal strip stock are mounted on the interior of the end cap or motor case cover 8 by fixing means 5. The brushes 11 each include an integral portion 7 adapted to extend through a terminal hole 6 to the exterior of the motor and to serve as a terminal therefor for connection in an external electric circuit.

It has heretofor been the general practice in the miniature motor art two form the strip brushes with integral terminal portions for ease of manufacture and reduced cost. The configuration of the terminals was generally as simple as possible. With this construction we have found that it is necessary to balance two conflicting requirements, namely that the motor terminal portion should be of adequate thickness and that the strip brush be as thin as practicable so that it may adopt a suitably bent configuration to maintain pressure and area of contact with the commutator at the desired and consistent levels. As a result, in order to obtain reliable functioning of the brush gear, the terminals have been manufactured with a lesser thickness than would be desirable.Good electrical connection with external electrical equipment is not easy and the mechanical strength of the terminals has proved insufficiently good for our purposes. As will become apparent, the present invention adopts a quite different approach.

Superficially the construction of the embodiment of motor constructed in accordance with the present invention which is described in detail hereinbelow is similar to that of the previously proposed motor of Figure 1, and where appropriate like reference numerals are employed. Indeed, as will become apparent from the description below, an embodiment of motor in accordance with the present invention can be produced by an absolute minimum of re-tooling of the apparatus employed for producing the motor of Figure 1.

As will be seen from Figure 3, the brushes 11, which here comprise brush arms formed of metallic strip stock carrying carbon brushes adjacent their ends, are formed separately from terminals 12. Each terminal 12 is formed as a generally L-shaped metal strip of thickness substantially greater than that of the brush arm. The shorter limb of the Forms a fixing portion 17, while the longer limb of the L extends through a terminal hole 13 in the plastics motor case 8, extending to the exterior of the casing to form a terminal portion 16 adapted for connection in an external electric circuit. The fixing portion 17 has a fixing hole 21 which enables the fixing portion ofthe terminal to be fitted to the end cap or motor case cover together with and in electrical connection with a respective brush.To fix the terminal in position, terminal portion 16 is inserted into terminal hole 13 until fixing portion 17 comes into contact with a base portion 15 of a brush 11 in position on a brush mount 14. Insertion of a fixing means 18, for example a rivet, through fixing hole 21 and a corresponding hole in brush base 15 and into a corresponding hole in the brush mount 14will fix the terminal and the brush in position. A locking effect of the same kind as found with a spring washer is obtained by providing a cut from fixing hole 21 to the adjacent outside edge ofthe fixing portion and by raising at least one edge 20 of the cut out of the plane of the fixing portion. Preferably this procedure results in a sharp edge such as that at 24 adapted to bite into the material of the brush base 15 as the terminal is fixed in position thereover.This enhances electrical connection. As will be seen from Figures 3, 4A and 5 the terminal portion 16 is provided with a series of shoulders 19 by which the width of the terminal increases step-wise with distance from the distal end of terminal portion 16. This increased width provides not only reinforcement for the terminal portion 16 but also enables the terminal 12 to be firmly secured to the end cap or motor case cover 8 by staking or deforming the shoulders 19 as shown at 23 in Figure 5.

It should be understood that although the terminal portion 16 is here shown as being flat, other configurations of terminal portions are possible. In particular, the terminal portion 16 may take a round or flare configuration.

Comparison between Figures 2A and 2B on the one hand and Figure 1 on the other hand will show that the only significant difference in construction of the end cap or motor case cover in the two motors is the provision in the motor in accordance with the present invention of the terminal holes 13 which are located on the radially inner side of the brush mount 14 and substantially closer to the axis of the shaft 1 than the terminal hole 6 of the embodiment of Figure 1. It will be seen, however, in Figures 2A and 2B that a a hole is retained in the position of the terminal hole 6. A portion of the brush base fits into the slot so defined, as can be seen in Figure 2A.Thus, an embodiment of motor constructed in accordance with the present invention as shown in Figures 2A to 5 can readily be produced with a minimum of retooling of the manufacturing apparatus for manufacture of the motor of Figure 1.

In contrast with the motor of Figure 1,we have found that embodiments of motor constructed as shown in Figures 2Ato 5 of the accompanying drawings exhibit substantially enhanced mechanical strength in external connection of the motor by means of its terminals in an external electrica circuit with reliable electrical connection. The cut and raised edges 20,27 ensure positive electrical connection between the brushes and their associated terminals. Embodiments of motor in accordance with the present invention as described above make it possible to realise reliable and sturdy reinforce mentoftheterminal portion and electrical and mechanical connection of the miniature motor directly to other equipment. The terminal is firmly connected to the plastics end cap or motor case cover.

Claims

1. An electric motor, comprising: a casing having a generally cylindrical motor case generally closed at one end and an end cap or motor case coverforthe other end thereof, the motor case being formed of a magnetic material and being provided with means defining at least one magnetic pole of the motor stator, and the end cap or motor case cover being formed of a synthetic resin material and forming a press fit within the said other end of the motor case; a rotor shaft on which a commutator is mounted adjacent one end, the said one end being supported for rotation in a bearing mounted in the end cap or motor case cover, and the other end of the shaft being supported to rotation in a bearing mounted in said one end of the motor case; brush gearforthe commutator comprising a plurality of electrically conductive brushes formed of strip stock and brush mounts therefor provided internally of the end cap or motor case cover; and a corresponding plurality ofterminals each extending through a respective terminal hole formed in said end cap or motor case cover and each having a terminal portion extending externally of said casing and adapted for connection in an external electric circuit and a fixing portion internally of said casing and provided with a fixing hole, said terminal being fixedly fitted to the end cap or motor case cover together with and in electrical connection with a brush by fixing means passing through said fixing hole.

2. An electric motor according to Claim 1, wherein a cut extends from said fixing hole to an outside edge of said fixing portion, and at least one edge of said cut being bent out of the plane of said fixing portion.

3. An electric motor according to Claim 2, wherein the said edge of said cut is bent in a direction to bite into the material of said brush.

4. An electric motor according to any preceding Claim, wherein each said terminal is formed of strip stock of thickness greater than that of said brushes and is bent generally into an L-shape, the shorter limb of said L forming said fixing portion, and the longer limb of said L extending through said terminal hole and forming said terminal portion.

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