GB1574772A - Electrical switches - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRICAL SWITCHES (71) We, SOCIETY ANONYME AUTOMOBILES CITROEN, a French body Corporate, of 117-167, Quai André Citröen, 75747 Paris Cedex 15, France, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to electrical switches.

Electrical switches comprising a depressible plunger for opening and closing the switch may be mounted in the path of a movable panel so as to actuate alarm devices or lighting devices when the panel is moved.

One particular application of such switches is the control of the interior light of a motor vehicle so that the light is switched on when a door of the vehicle is opened. In such an application the switches are situated in areas that are not very watertight; moreover, they are subject to irregular thermal and hygrometric conditions and are exposed to the action of abrasive or chemically aggressive atmospheres.

In previously proposed switches. misalignment between the contacts. the relative weakness of a return spring acting on the plunger and the prolonged exposure of the contacts in their open position bring about a rapid deterioration in the conductivity of the contacts. Consequently. it often happens that the operation of the switches becomes defective; once this process has begun, it worsens very quickly. This applies in particular in the case of a switch used in a motor vehicle where dynamic forces are also present.

According to the present invention. there is provided an electrical switch comprising an actuating plunger which is depressible against a resilient bias. said plunger carrying a movable contact arranged to engage a fixed contact. the movable contact having a flat portion extending substantially perpendicularly to the direction of the movement of the plunger, the flat portion of the movable contact being arranged to engage a flat portion of the fixed contact extending substantially perpendicularly to the direction of movement of the plunger and the movable contact including a portion which forms a flexible extension of the flat portion and which is arranged to rub resiliently against a portion of the fixed contact extending generally in the direction of movement of the plunger, when the flat portion of the movable contact reaches the vicinity of the flat portion of the fixed contact.

The portion of the fixed contact extending generally in the direction of movement of the plunger may be parallel with the direction of movement of the plunger, and therefore of the movable contact, in such a manner that a constant loading is obtained. It may alternatively be inclined to this direction, in such a manner that the contact pressure increases with the movement of the movable contact towards its closing position; loading is therefore progressive.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is an axial section of a switch in accordance with the invention; and Figure 2 and Figure 3 are elevations of the switch respectively in its open and closed positions.

As is shown in the drawing. the switch.

which may be termed a "rabbet switch".

comprises a body 1 of frusto-conical form with an internal recess 5. The body 1 is solid with a lateral fixing lug 2. An earthing contact 3. constituted by a blade folded back in the manner of an S. is mounted on the body 1. This blade, which extends through an opening 4 in the lug 2, has one of its end portions 3a applied to the lug 2 while its other end portion 3b, which is flat. is applied to the small base of the body 1 and thus closes the corresponding end of the recess 5 of the body 1. The part 3c of the blade 3, defined between its end portions 3a and 3b, is applied laterally to the frusto-conical external surface of the body 1.

An actuating plunger 6 is slidably mounted in the recess 5 of the body 1 and projects beyond the two ends of the body, the plunger passing through an opening 7 in the end portion 3b of the earthing contact 3. The end 6a of the plunger which projects beyond the large base of body 1 is cylindrical, whereas the remainder of the plunger, including its opposite end portion 6b has a flat section.

A movable contact 8, also comprising a blade folded into S-shape, is fixed by a central flat portion 8a on the end portion 6b of the plunger 6; in the example shown, this fixing is effected by a clamping action by means of two prongs 9 cut out from the central portion 8a of the contact 8. When the switch is in its closed position, the end portion 8b of the contact 8 is applied resiliently on the central portion 3c of the contact 3. Its other end portion 3c is perforated with a hole 10 for the passage of a connection wire which is then welded to this portion of the contact.

It is to be noted that the portions 3b and 8a of the fixed and movable contacts 3 and 8 are substantially perpendicular to the direction of movement of the plunger.

A helical spring 11 is disposed in the recess 5 between the end portion 3b of the contact 3 and the shoulder connecting the cylindrical portion 6a of the plunger 6 to its flat portion.

The spring thus acts to move the plunger 6 in a direction from the small base of the body 1 to its large base. this movement being stopped when the central portion 8a of the contact 8 meets the end portion 3b of the contact 3.

Normally. a force which is diagrammatically represented by the arrow f and is produced by the engagement of the end portion 6a against a movable panel 12. tends to maintain the actuating plunger 6 depressed and, accordingly. the two contacts 3 and 8 spaced from each other. The circuit in which these contacts are interposed and which is. for example. the supply circuit of the interior light of a motor vehicle. is therefore open.

When panel 12 opens. the force f is removed and the spring 11 moves the plunger 6 until the central portion 8a of the contact 8 is applied against the end 3b of the contact 3. at the same time, the free end portion 8b of the contact is applied against the central portion 3c of the contact 3. During this movement. the end portion 8b of the contact 8 rubs against the central portion 3c of the contact 3 in such a manner that these contacts clean themselves so that their rubbing surfaces are free from corrosion. The closing of the circuit in which the contacts 3 and 8 are interposed is thus effected in reliable manner.

In a modified arrangement the body 1 may have a wall, cast integrally with it and forming its small base which is perforated with an opening for the passage of the end portion 6b of the plunger 6. The opening in the wall would correspond to the cross-section of the end portion 6b so as to prevent swivelling of the plunger 6 and of contact 8 supported by the plunger.

In the switch particularly described, when the switch is closed, the rubbing action which occurs between the portions 3c and 8b of the contacts 3 and 8 ensures that they are always clean and the current can, in all circumstances, pass through these portions. The length over which rubbing occurs may be relatively great, without there being a substantial increase of the strain upon the contacts. The force with which these two contact portions are pressed one against the other may be relatively small, in such a manner that the wear is small and the contacts can be light. The ranges of manufacturing tolerances may be relatively substantial.

WHAT WE CLAIM IS: 1. An electrical switch comprising an actuating plunger which is depressible against a resilient bias, said plunger carrying a movable contact arranged to engage a fixed contact, the movable contact having a flat portion extending substantially perpendicularly to the direction of movement of the plunger, the flat portion of the movable contact being arranged to engage a flat portion of the fixed contact extending substantially perpendicularly to the direction of movement of the plunger, and the movable contact including a portion which forms a flexible extension of the flat portion and which is arranged to rub resiliently against a portion of the fixed contact extending generally in the direction of the movement of the plunger, when the flat portion of the movable contact reaches the vicinity of the flat portion of the fixed contact.

2. A switch according to claim 1, wherein the said portion of the fixed contact extending generally in the direction of movement of the plunger is parallel with the direction of movement of the plunger.

3. A switch according to claim 1, wherein the said portion of the fixed contact extending generally in the direction of movement of the plunger is inclined relative to the direction of movement of the plunger. in such a manner that the contact pressure of the flexible extension increases with the movement of the movable contact towards its closed position.

4. A switch substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. to the small base of the body 1 and thus closes the corresponding end of the recess 5 of the body 1. The part 3c of the blade 3, defined between its end portions 3a and 3b, is applied laterally to the frusto-conical external surface of the body 1. An actuating plunger 6 is slidably mounted in the recess 5 of the body 1 and projects beyond the two ends of the body, the plunger passing through an opening 7 in the end portion 3b of the earthing contact 3. The end 6a of the plunger which projects beyond the large base of body 1 is cylindrical, whereas the remainder of the plunger, including its opposite end portion 6b has a flat section. A movable contact 8, also comprising a blade folded into S-shape, is fixed by a central flat portion 8a on the end portion 6b of the plunger 6; in the example shown, this fixing is effected by a clamping action by means of two prongs 9 cut out from the central portion 8a of the contact 8. When the switch is in its closed position, the end portion 8b of the contact 8 is applied resiliently on the central portion 3c of the contact 3. Its other end portion 3c is perforated with a hole 10 for the passage of a connection wire which is then welded to this portion of the contact. It is to be noted that the portions 3b and 8a of the fixed and movable contacts 3 and 8 are substantially perpendicular to the direction of movement of the plunger. A helical spring 11 is disposed in the recess 5 between the end portion 3b of the contact 3 and the shoulder connecting the cylindrical portion 6a of the plunger 6 to its flat portion. The spring thus acts to move the plunger 6 in a direction from the small base of the body 1 to its large base. this movement being stopped when the central portion 8a of the contact 8 meets the end portion 3b of the contact 3. Normally. a force which is diagrammatically represented by the arrow f and is produced by the engagement of the end portion 6a against a movable panel 12. tends to maintain the actuating plunger 6 depressed and, accordingly. the two contacts 3 and 8 spaced from each other. The circuit in which these contacts are interposed and which is. for example. the supply circuit of the interior light of a motor vehicle. is therefore open. When panel 12 opens. the force f is removed and the spring 11 moves the plunger 6 until the central portion 8a of the contact 8 is applied against the end 3b of the contact 3. at the same time, the free end portion 8b of the contact is applied against the central portion 3c of the contact 3. During this movement. the end portion 8b of the contact 8 rubs against the central portion 3c of the contact 3 in such a manner that these contacts clean themselves so that their rubbing surfaces are free from corrosion. The closing of the circuit in which the contacts 3 and 8 are interposed is thus effected in reliable manner. In a modified arrangement the body 1 may have a wall, cast integrally with it and forming its small base which is perforated with an opening for the passage of the end portion 6b of the plunger 6. The opening in the wall would correspond to the cross-section of the end portion 6b so as to prevent swivelling of the plunger 6 and of contact 8 supported by the plunger. In the switch particularly described, when the switch is closed, the rubbing action which occurs between the portions 3c and 8b of the contacts 3 and 8 ensures that they are always clean and the current can, in all circumstances, pass through these portions. The length over which rubbing occurs may be relatively great, without there being a substantial increase of the strain upon the contacts. The force with which these two contact portions are pressed one against the other may be relatively small, in such a manner that the wear is small and the contacts can be light. The ranges of manufacturing tolerances may be relatively substantial. WHAT WE CLAIM IS:

1. An electrical switch comprising an actuating plunger which is depressible against a resilient bias, said plunger carrying a movable contact arranged to engage a fixed contact, the movable contact having a flat portion extending substantially perpendicularly to the direction of movement of the plunger, the flat portion of the movable contact being arranged to engage a flat portion of the fixed contact extending substantially perpendicularly to the direction of movement of the plunger, and the movable contact including a portion which forms a flexible extension of the flat portion and which is arranged to rub resiliently against a portion of the fixed contact extending generally in the direction of the movement of the plunger, when the flat portion of the movable contact reaches the vicinity of the flat portion of the fixed contact.

2. A switch according to claim 1, wherein the said portion of the fixed contact extending generally in the direction of movement of the plunger is parallel with the direction of movement of the plunger.

3. A switch according to claim 1, wherein the said portion of the fixed contact extending generally in the direction of movement of the plunger is inclined relative to the direction of movement of the plunger. in such a manner that the contact pressure of the flexible extension increases with the movement of the movable contact towards its closed position.

4. A switch substantially as hereinbefore described with reference to the accompanying drawings.