GB2172754A

GB2172754A - Electric motor

Info

Publication number: GB2172754A
Application number: GB08603517A
Authority: GB
Inventors: Michio Hoshino
Original assignee: Mabuchi Motor Co Ltd
Current assignee: Mabuchi Motor Co Ltd
Priority date: 1985-02-25
Filing date: 1986-02-13
Publication date: 1986-09-24
Also published as: CN86100374A; KR900003399Y1; JPS61144765U; GB8603517D0; GB2172754B; HK35791A; KR860006860A; DE3604583A1; DE3604583C2

Abstract

An electric motor has a metallic motor case 12 and an end cap or motor case cover therefor which has a surface 8 at its periphery engaged with an interior surface of the motor case at one axial end of the motor case cover. A spark-quenching capacitor 10 is mounted on the internal side of the and cap or motor case cover and is electrically connected between the motor case and a terminal of the brush gear. To achieve this, the spark-quenching capacitor has a first lead wire 11 electrically coupled to the terminal and a second lead wire 11 so disposed relative to the end cap or motor case cover as to be placed in electrical engagement with the motor case when the peripheral surface of the end cap or motor case cover is engaged with the internal surface of the motor case. <IMAGE>

Description

SPECIFICATION Electric motor Description This invention relates to electric motors.

It is a common practice to provide so-called "miniature" electric motors with a shielded construction to prevent electrical noise, and/or to connect a spark quenching capacitor between a terminal of the motor and a metallic case for the motor, the capacitor tending to quench sparks generated between the commutator and the brushes in use. The usual practice has been to mount the capacitor externally of the motor by soldering or spot welding lead wires of the capacitor to a motor terminal and to the motor case.

The present Applicants regard such externally mounted capacitor as obtrusive. Its presence requires special consideration in handling and packaging to prevent the capacitor from being damaged or detached. Additionally, the operations of soldering or spot welding the capacitor lead wires to the motor case is cumbersome and inefficient.

In contrast, the present invention provides an electric motor comprising: a metallic motor case; an end cap or motor case cover therefor having a surface at its periphery engaged with an interior surface of the motor case at one axial end thereof; a rotor shaft rotatably supported by said end cap or motor case cover; brush gear for the motor supported by the end cap or motor case cover and including terminal portions extending from the internal side of said end cap or motor case cover through terminal apertures therein in electrically insulated relation therewith and being adapted for connection in an external electric circuit; and a spark-quenching capacitor mounted on the internal side of said end cap or motor case cover and being electrically connected between the motor case and said terminal portion, the spark-quenching capacitor having a first lead wire electrically coupled to said terminal portion and a second lead wire so disposed relative to the end cap or motor case cover as to be placed in electrical engagement with the motor case when the said surface of the end cap or motor case cover is engaged with the said internal surface of the motor case.

The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a motor constructed in accordance with the present invention, the end cap or motor case cover being shown detached from the motor case; and Figure 2 is a side elevational view, partly in section, of the motor of Fig. 1.

The end cap or motor case cover 1 of the illustrated motor is formed of two components, namely a brush holder 2 made of an electrically insulating material, such as a synthetic resin, and a case plate 3 made of metal and fitted to the brush holder 2 to form the end cap or motor case cover 1 as a whole.

The brush holder 2 mounts brush gear 4 including brushes proper 5 and terminals 6 which extend through respective terminal holes 7 to the exterior of the end cap or motor case cover 1 for connection in an external electric circuit. The end cap or motor case cover has a surface 8 at its periphery adapted for engagement with an interior surface of the motor case at one axial end thereof. Formed in this surface is a shallow groove 9 adapted to receive a lead wire 11 of a capacitor 10.

To the interior of the motor case 12 is mounted one or more permanent magnets to provide the motor stator. The rotor 14 is mounted on a shaft 15 together with a commutator 16.

With the end cap or motor case cover mounted on the motor case 12 with the peripheral surface 8 engaged with the motor case 12, the brushes 5 make contact with the commutator 16, and the motor rotating shaft 15 is supported by the end cap or case cover 1. The terminal 6, which is either integrally formed with the brush mounting brush proper 5 or is joined thereto, is passed through the terminal hole 7 provided on the brush holder 2 to be led out of the motor for external connection.

As will be seen, lead wire guide groove 9 for accommodating one lead wire 11 (shown in Fig. 2) of the spark-quenching capacitor 10 (as shown in Fig. 2) is provided on the surface 8 of the brush holder 2 and the metallic case plate 3. The depth of the lead wire guide groove 9 is smaller than the diameter of the lead wire 11. The end cap or case cover 1 is engaged with the motor case 12 after a second lead wire 11 of the capacitor 10 is passed through the terminal hole 7, together with the terminal 6 to be led out of the motor, while the first lead wire 11 is placed in the lead wire guide groove 9. In this state, the said first lead wire 11 is crimped by the inner circumferential surface of the motor case 12, and thereby electrically connected securely to the motor case 12 since the depth of the lead wire guide groove 9 is smaller than the diameter of the lead wire 11.Consequently, what has to be done in assembly is to connect only the second lead wire 11 to the terminal 6 by soldering, for example. This can be accomplished at the same time as the motor lead wire is connected to the terminal 6. Unnecessary parts of the lead wires 11 may be cut off.

Although the lead wire guide groove 9 is here formed on both the surface 8 of the brush holder 2 and the metallic case plate on the example shown in Fig. 1, the same effect can be achieved by forming the lead wire guide groove 9 only on the surface 8.

It will be seen from the above description, that the present invention enables a sparkquenching capacitor to be readily installed on a miniature electric motor by simple and positive means. Only a single soldering operation is necessary in this embodiment and this can be combined with another and unavoidable soldering operation. Since the capacitor when installed is not exposed to the outside of the motor, ease of handling of the motor is facilitated.

It will be appreciated that by providing the end cap or motor case cover with a metallic case plate in addition to the resin end cap integral brush holder, the shielding effect is enhanced.

Claims

1. An electric motor comprising: a metallic motor case; an end cap or motor case cover therefor having a surface at its periphery engaged with an interior surface of the motor case at one axial end thereof; a rotor shaft rotatably supported by said end cap or motor case cover; brush gear for the motor supported by the end cap or motor case cover and including terminal portions extending from the internal side of said end cap or motor case cover through terminal apertures therein in electrically insulated relation therewith and being adapted for connection in an external electric circuit; and a spark-quenching capacitor mounted on the internal side of said end cap or motor case cover and being electrically connected between the motor case and said terminal portion, the spark-quenching capacitor having a first lead wire electrically coupled to said terminal portion and a second lead wire so disposed relative to the end cap or motor case cover as to be placed in electrical engagement with the motor case when the said surface of the end cap or motor case cover is engaged with the said internal surface of the motor case.

2. An electric motor according to Claim 1, wherein the said second lead wire is located in a shallow groove formed in the periphery of the end cap or motor case cover, the groove having a depth less than the diameter of the said second lead wire so that the said second lead wire is crimped to the internal surface of the motor case as the end cap or motor case cover is engaged therewith.

3. An electric motor substantially as hereinbefore described with reference to and as shown in the accompanying drawing.