GB2140218A

GB2140218A - Electric motor

Info

Publication number: GB2140218A
Application number: GB08410813A
Authority: GB
Inventors: Eberhard Gauger; Karl Gossele; Wolfgang Kofink
Original assignee: SWF Spezialfabrik fuer Autozubehoer Gustav Rau GmbH
Current assignee: SWF Auto Electric GmbH
Priority date: 1983-05-20
Filing date: 1984-04-27
Publication date: 1984-11-21
Also published as: DE3318362A1; GB8410813D0; GB2140218B; JPS59222053A; FR2546346A1

Abstract

An electric motor has a housing (11) comprising a metal shell (12) which is closed at one end by an end cap (21) which is made of an electrically non- conductive material. The end of the housing (11) is covered by a layer of electrically conductive material which is connected with the metal shell (12) in an electrically conductive manner. <IMAGE>

Description

SPECIFICATION Electric motor This invention relates to an electric motor and more particularly but not solely to windscreen wiper motors.

Electric motors often comprise a housing having a metal shell containing an armature which shell is closed by an end cap.

Recently considerable efforts have been made to reduce the weight of components fitted in a motor vehicle. One of these measures is to make the gear housing of a windscreen wiper motor of plastics material. Due to the fact that in the case of conventional windscreen wiper motors this gear housing also forms the end cap of the motor housing some problems resulted which did not occur in the case of metal gear housings. When a motor is closed by an end cap of plastics material on one front side it is a particular problem to disperse heat produced by the motor and to screen interference voltages produced by the motor. The present invention seeks to overcome or at least substantially reduce this problem.

According to the invention there is provided an electric motor comprising an armature rotatably mounted in a housing, having a metal shell and at least one end cap of the housing made of an electrically non-conductive material, characterised in that the end of the housing is covered by a layer of electrically conductive material which is connected with the metal shell in an electrically conductive manner.

In this way a kind of Faraday cage is also formed when the motor has a plastics end cap, so that interference voltages are less likely to be emitted from the motor housing. Moreover, heat produced by the motor is transmitted to the shell through the conductive layer and is thus conducted to large outside surface areas of the motor.

The conductive layer may be formed as a surface on the inner face of the end cap. In this case additional components are not necessary.

However, in a preferred embodiment an additional component, namely a metal plate or a plate provided with an electrically conductive coating, is secured between the end of the shell and the end cap.

Although an additional component is needed in this embodiment this solution has a number of advantages. This additional plate, which for example can be of sheet metal, can be braced between the end cap and the shell in a form-fit manner, so that it can serve simultaneously as a holding element for a brush plate. Thus the usual fixtures for the brush plate are no longer necessary. Moreover, interference-suppression means, for example chokes and/or capacitors, can be soldered or welded onto this conductive plate.

With regard to interference-suppression this is especially advantageous because, as a matter of fact, a mass point is created by this conductive plate.

In order that the invention and its various other preferred features may be understood more easily, an embodiment thereof will now be described, by way of example only with reference to the drawings, in which: Figure 1 is a partial section through an electric windscreen wiper motor constructed in accordance with the invention, Figure 2 is a view in the direction of arrow P in Figure 1, Figure 3 is a view of a conductive plate of the motor of Figure 1 and Figure 4 is a partial section taken on the line IV--IV in Figure 2.

Figure 1 shows a windscreen wiper motor having an armature 10 rotatably mounted in a housing 11. This housing has a metallic shell 12 on which permanent magnets 13 are fixed. A commutator 14 is fastened on the armature shaft, which commutator cooperates with brushes 15, 1 6 and 1 7 (Figure 2) in a known manner. A gear housing 20, which is made of plastics material, has a flange 21 which closes the housing 11 on one front side and thereby forms an end cap for the motor.

In the embodiment a screen 30 of sheet metal is an additional component as compared with conventional motors and is secured between the ring-shaped front face of the shell 12 and the flange 21 of the end cap. This screen 30 is formed of an electrically conductive material and is in intimate direct contact with the ring-shaped front face of the shell 12 and is thus connected with the shell in an electrically conductive manner. Thereby a Faraday cage is formed, so that even in the case of a motor with an end cap of a non-conductive material, e.g. plastics no interference voltages can be emitted or at least such voltages are reduced to a minimum.

Figure 2 shows a front view of the housing 11 in direction of arrow P in Figure 1. The screen 30 has the outline shape shown in Figure 3. Figure 4 shows that the screen 30 is fixed on a base plate 31 for securing the brushes. Thus the screen 30 and the base plate form a structural unit which is secured between the flange 21 of the gear housing 20 and the shell 1 2 without additional fastening means. This structural unit is secured to the shell 12 in a manner protected against twisting, because axially projecting tongues 32 on the flange 21 of the gear housing 20 engage in matching recesses 33 of the screen 30.

From the partial section of Figure 4 it can be seen that on the base plate 31 there are secured contact supporting points 40 and other contact supporting points 41 are directly secured on the screen 30. These contact supporting points can also serve to fix the base place 31 on the screen.

lnterference-suppression components; for example chokes 42 and capacitors 43, are secured to these contact supporting points as are connecting wires for the brushes 1 5, 1 6 and 1 7.

It can be seen that all connecting wires of the interference-suppression components, which are connected to earth, are directly connected with the screen 30, which extends over a large area and has good conductivity, that means to a single mass point or common connection. Connecting wires which may not be connected with the screen 30 in an electrically conductive manner are connected to contact supporting points 40, which are only fixed on the base plate 31. In this position the screen 30 can have a recess or can be spaced from the base plate by an indentation as is shown in Figure 4.

The advantages of the described electric motor are that a large-area earth connection between the negative brush, the interference-suppression components and the shell of the motor is created, so that interference voltages are effectively screened from interfering with radio frequencies and, moreover, heat is conducted to the outside via the screen. In order to improve the condition of heat the screen 30 can project over the rim of the shell like wings as has been indicated in Figure 1.

In the drawings an embodiment is shown in which the screen is a metallic plate, namely the screen 30 made of sheet metal. However a plate provided with an electrically conductive layer could aiso be used. This could be formed similarly to a printed circuit board which could be single or double-faced. A conductive area as large as possible in good electrical contact with the front face of the shell should be provided in order to create a large-area mass point or common connection. The current-carrying components, namely the chokes and capacitors, can then have one side directly soldered on this large area, while the other sides are secured on insulated conductors opposite to this conductive area. In this case the printed circuit board can at the same time serve as a base plate for the brushes.

In another conceivable embodiment the inside of the flange 21 of the gear housing 20 can be faced with a layer of electrically conductive material. Thereby a satisfactory interferencesuppression can be achieved, however the heat dispersion is not so good as in the example shown in Figures 1 to 4.

Claims

1. An electric motor comprising an armature rotatably mounted in a housing, having a metal shell and at least one end cap of the housing made of an electrically non-conductive material, characterised in that the end of the housing (11) is covered by a layer of electrically conductive material which is connected with the metal shell (12) in an electrically conductive manner.

2. An electric motor as claimed in claim 1, characterised in that the end cap is made of a plastics material.

3. An electric motor as claimed in claim 1 or 2, characterised in that the conductive layer is a surface layer formed onto the inner face of the end cap.

4. An electric motor as claimed in claim 1 or 2, characterised in that the conductive layer is a metal plate (30) secured between the end of the shell (12) and the end cap (21).

5. An electric motor as claimed in claim 1 or 2, characterised in that the conductive layer is formed on the surface of a non-conductive plate secured between the end of the shell (12) and the end cap (21).

6. An electric motor as claimed in claim 4 or 5, characterised in that onto the plate is fixed a base plate (31) for securing brushes (15, 16, 17) which co-operate with a commutator.

7. An electric motor as claimed in any one of claims 4 to 6, characterised in that the plate is a single or double-faced printed circuit board known in itself with a conductive area as large as possible resting upon the front face of the shell and with individual conductors and that ail current-carrying components are connected with this conductive area or with individual conductors in an electrically conductive manner.

8. An electric motor according to any one of the preceding claims, characterised in that the conductive plate (30) projects at least partly over the rim of the shell (12).

9. An electric motor according to any one of the preceding claims, characterised in that the end cap closing the shell on one front side is formed by a flange (21) of a gear housing (20) which is made of plastics material.

10. An electric motor as claimed in any one of the preceding claims, characterised in that interference-suppression components, such as chokes (42) and/or capacitors (43), are with one connection directly connected with the electrically conductive layer.

11. An electric motor substantially as described herein with reference to the drawings.