GB2140623A

GB2140623A - Push button switch

Info

Publication number: GB2140623A
Application number: GB08413234A
Authority: GB
Inventors: Yasuo Matsui
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1983-05-24
Filing date: 1984-05-23
Publication date: 1984-11-28
Also published as: GB2140623B; DE3419451A1; GB8413234D0; KR890001960Y1; KR840006409U

Abstract

A push button switch including a casing (1), a movable contact (4), a stem (5) extending through an opening in said casing (1) and an elastomeric cover (6) for said stem (5) and opening. The cover (6) includes a collar portion (6b) fitting within a step portion (1b) around said opening. The upper portion of the opening is bent over to press the collar portion (6b) against the step portion. Moreover, this push button switch may also comprise a rigid annular sealing ring fitting between the bent portion and the collar, and the step portion may have an annular rim (1d) pressing into the collar portion (6b). <IMAGE>

Description

SPECIFICATION Push Button Switch Field of the Invention This invention relates to a push button switch wherein a movable contact is placed in contact or separated from fixed contacts held in the bottom portion of a recess formed within a casing through elastic deformation of the movable contact by movement of a stem having a portion extending outwardly from the casing.

Background of the Invention A conventional push button switch of this kind, includes fixed contacts held in the bottom portion of a recess formed within a switch casing. A movable contact is placed over the fixed contact and is movable by a stem having a portion extending through an opening leading to the recess. The stem is held resiliently for movement within the casing, and a holding plate is provided around the opening receiving the stem to engage a flange portion of the stem to hold the stem within the casing, but enabling it to reciprocate therewithin.

However, in such conventional push button switches the holding plate does not make a tight seal with the stem and thus flux generated during soldering the switch to a printed circuit board, or dust, may enter the switch to degrade operation.

Additionally, cleaning of the switch is very troublesome because it cannot be dipped in a solvent which may leak into the switch between any clearance between the stem and its holding plate.

Summary of the Invention Considering such problems of the prior art, the present invention has an object of providing a push button switch which prevents deterioration of the switching performance and simplifies the washing operation by providing an elastomeric cover over the stem to prevent entry of flux, dust or solvent into the switch. Moreover, the sealing characteristics between the edge of the elastomeric cover and opening edge of the opening receiving the stem are improved by forming an annular projected portion which presses the edge part of the elastomeric cover.

Therefore, it is an object of the present invention to provide a push button switch which has a more reliable prevention of entry of foreign matter by improving the sealing characteristic of an elastomeric cover by providing an annular sealing ring to the edge of the elastomeric cover.

Brief Description of the Drawings Attached drawings show embodiments of the push button switch of this invention, wherein: Fig. 1 is a sectional view of the push button switch of the present invention; Fig. 2 is a disassembled perspective view of the push button switch of Fig. 1; Fig. 3 is a sectional view of another embodiment of the present invention, and; Fig. 4 is a disassembled perspective view of the switch of Fig. 3.

Detailed Description of the Invention This invention is described in detailed with reference to the attached drawings. Fig. 1 and Fig.

2 indicate respectively a first embodiment of the present invention which includes a casing 1 forming a central recess A. Fixed contacts 2 and 3 are held in the bottom portion of the recess A.

Moreover, a movable contact 4 and a stem 5 are accommodated within the recess A and this stem 5 extends through an opening in the casing. An elastomeric cover 6 extends over the stem 5 as shown and is fitted in the side of the opening to the casing.

More specifically, the movable contact 4 is formed like a dome and can be elastically deformed. It is accommodated in the recess A in such a manner that the edge thereof always abuts against the fixed contact 2, while the central portion is normally separated from the other fixed contact 3. The stem 5 has a central portion 5a extending upwardly like a pillar, and a flange portion 5b extends circumferentially from the lower portion of the pillar portion 4a. A semispherical pressing portion Sc abuts against the center of the movable contact 4 to engage the movable contact 4.By moving the stem 5 inwardly of the casing, the movable contact 4 is elastically deformed to connect the fixed contacts 2 and 3 electrically together, and when pressure is released from the stem 5, the resiiience of the movable contact 4 serves to return the stem to its normal position.

Moreover, an elastomeric cover 6 is formed in the general shape of a hat from a material, such as a chlompene rubber, experiencing little swelling when contacted by solvents such as Freon. The cover 6 has a main portion 6a fitting over the pillar portion 5a of the stem in order to cover the pillar portion 5a and a collar portion 6b which fits against edge 1 a of the opening to the recess A. A step portion 1 b is formed in the internal wall-portion of the edge lain order to allow placement of the collar portion 6b, while an overhanging portion 1 c is formed by bending over an edge of the opening in the upper part of case 1 in order to hold the collar part 6b in combination with the step portion 1 b.Moreover, an annular rim portion id is formed in the step portion 1 b and engages the underside of the collar portion 6b. In this way, the collar portion 6b is firmly held between the step portion 1 b and the over hanging portion 1 c.

To assemble the push button switch having such structure, the elastomeric cover 6 is first mounted to the stem 5 by covering the-pillar portion 5a of stem with the main portion 6a.

Then, the stem 5 with the elastomeric cover 6, and the movable contact 4 are placed within the recess A and simultaneously the collar portion 6b of the elastomeric cover 6 is placed on the step portion 1 b of the opening edge 1 a of the recess.

Thereafter, as shown in Fig. 1, the collar portion 6b of the elastomeric cover 6 is held between the overhanging portion 1 c and the step portion 1 b by spin caulking or thermal caulking of the overhanging part 1 c. At this time, since the annular rim portion 1 d is pressed into the collar portion 6b when the overhanging portion is bent down upon the collar portion, the clamping force of the collar portion increases, and the sealing characteristic between the elastomeric cover 6 and casing 1 is improved over that of a switch not having the annular rim portion 1 d. In such a condition, the stem 5 and opening of recess A are covered and sealed with the elastomeric cover 6.

Such a push button switch maintains the switching operation and characteristics of the conventional switch without allowing flux generated during operation from entering the casing because the stem 5 and opening of the recess A are covered with the elastomeric cover 6 and, moreover, the sealing characteristics is improved by the annular rim portion 1 d. In addition, a solvent used for washing or cleaning this switch, such as Freon, cannot enter the casing and, moreover, since the elastomeric cover 6 uses a material having a small coefficient of swelling to this solvent, the elastomeric cover 6 is not deformed even when it is dipped into the solvent. The switch can, therefore, then be washed as a whole without considering the entrance of solvent into the recess A and accordingly the washing process can be simplified easily.Further, since the annular rim portion 1 d presses the collar 6b, the sealing characteristic is improved as described above and stronger fixed condition can also be obtained. Accordingly, the elastomeric cover 6 is firmly fixed to the case 1 and does not separate from it.

Operation of this push button switch is described below. When the main portion 6a of the elastomeric cover 6, namely the pillar portion 5a of stem is pressed, the stem 5 is pushed downward with deformation of the collar portion of the elastomeric cover 6. The center portion of the movable contact 4 is depressed by the pressing portion Sc of the stem 5, and thereby the center portion of the movable contact 4 is placed in contact with the fixed contact 3 provided at the bottom of the recess A. Thereafter, when the stem 5 is released from a pressing force, the movable contact 4 returns to the initial condition to separate it from the fixed contact 3. The stem 5 is pushed upwards by a recovery force of the movable contact 4, and returns to the initial position.During such operation, the elastomeric cover 6 also operates as a conventional holding plate, not allowing the stem 5 to pop out from the recess A.

Another embodiment of this invention is described with reference to Fig. 3 and Fig. 4. The components similar to those in the embodiment shown in Fig. 1 and Fig. 2 are given the same symbols and description thereof is ommited here.

An annular sealing ring 7 formed of a rigid material such as stainless steel, for example, has an annular shape almost the same size as the collar 6b of the elastomeric cover. An annular groove 7a is formed in the entire circumference of the sealing ring in such a manner so as to extend toward the collar portion 6b.

The push button switch shown in Fig. 3 and Fig. 4 can be assembled almost in the same way as the switch shown in Fig. 1 and Fig. 2. But, assembling of the annular sealing ring 7 is additionally described. The collar portion 6b of elastomeric cover 6 is placed on the slip portion 1 b of the opening edge 1 a of recess A and the annular sealing ring 7 is placed on said collar portion 6b. Thereafter, the collar portion 6b of the elastomeric cover and annular selaing ring 7 are fixed and held as shown in Fig. 1 between the overhanging portion 1 c and the step portion 1 b by spin caulking of thermal caulking of the overhanging portion 1 c.Under this condition, the rigid annular sealing ring 7 is directly pressed by the overhanging portion part 1 c and thereby the collar portion 6b of the elastomeric cover is held between the annular sealing ring 7 and the step portion 1 b. Thereby, even if a caulking force of the overhanging part 1 c is different at each position, a more uniform force is transmitted to the collar portion 7 because of the rigid annular sealing ring 7 placed between the collar portion 6b and the overhanging portion 1 c. Thereby, a uniform force is applied, in the total circumference, to the collar portion 6b to stably secure the elastomeric cover 6.Particularly, since the annular groove 7a of the annular sealing ring 7 and annular ring portion 1 d at the upper part of the step portion 1 b compress the collar portion 6b, owing to the caulking force applied to the overhanging portion 1 c, a pressing force applied to the collar portion 6b and is increased and the stem 5 and aperture of recess A are covered with the elastomeric cover 6 under the conditions that the sealing characteristic of this part is improved over that of the case where the annular groove 7a and annular rim portion 1 d are not provided.

As described above, according to this invention, entrance of flux, dust, water or solvent, etc. into the switch is prevented by providing an elastomeric cover, and moreover, this invention more rel-iably prevents entrance of foreign matter into the switch through improved sealing characteristics by provision of an annular rim portion, showing splendid effects that deterioration of switch characteristic can be prevented and simultaneously the washing process can be simplified.

Moreover, entrance of flux, dust, water or solvent etc. into the recess part of the switch can be prevented more reliably by providing an elastomeric cover and annular sealing ring to improve the sealing characteristics.

Claims

1. A push button switch having a casing with a recess, fixed contacts held in a bottom portion of said recess, a movable contact engaging at least one of said fixed contacts, a stem movable slidably within said recess and having a first portion adapted to engage said movable contact for urging it towards the other of said fixed contact and an actuation portion extending outwardly of said casing through an opening therein, and an elastomeric cover extending over said actuation portion of said opening to seal said recess, said cover having a peripheral collar portion fitting within a complementary step portion formed around said opening.

2. A push button switch according to claim 1, including bendable means formed at the edge of said opening for pressing the upper surface of said collar portion upon being bent downwardly thereover.

3. A push button switch according to claim 2, said step portion having an upstanding rim adapted to press into the lower surface of said collar portions.

4. A push button switch according to claim 1, said elastomeric cover being formed of a material having little tendency to swell from contact with a solvent.

5. A push button switch according to claim 2, including an annular ring of rigid material held between said bendable means and the upper surface of said collar portions.

6. A push button switch according to claim 5, said annular ring having an annular groove extending into pressed contact with the upper surface of said collar portion.

7. A push button switch according to claim 6, said step-portion having an upstanding rim adapted to press into the lower surface of said collar portions.

8. A push button switch according to claim 5, said step portion having an upstanding rim adapted to presginto the lower surface of said collar portions.

9. A push button switch substantially as hereinbefore described with reference to the accompanying drawings.