GB2284308A

GB2284308A - Electrical switch

Info

Publication number: GB2284308A
Application number: GB9500370A
Authority: GB
Inventors: Bun Wong
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-03-08
Filing date: 1991-03-08
Publication date: 1995-05-31
Anticipated expiration: 2011-03-08
Also published as: GB9104970D0; GB2284309A; GB2284308B; GB9500470D0; HK87896A; GB2253518A; GB2284309B; GB2253518B; GB9500370D0

Abstract

An electrical switch (10) comprises a casing having top and bottom parts (12 and 13) connected together by snap-fit means (36, 37). The snap fit means (36, 37) are defined by projections (36) which extend downwardly from the bottom of side walls (34, 35) of the top part (12) and by notches (37) in the bottom part (13) for receiving the projections (36). <IMAGE>

Description

ELECTRICAL SWITCH The present invention relates to an electrical switch.

According to the invention, there is provided an electrical switch which comprises a casing having a top part and a bottom part connected together by snap-fit means.

Preferably, the top part has a rectangular top wall and four depending side walls, and the bottom part is a plate closing from below the top part.

In a preferred embodiment, the snap-fit means is provided by lateral projections extending inwardly from at least one opposite pair of the side walls of the top part, and the bottom part is connected to the top part by engagement with the lateral projections.

It is preferred that both opposite pairs of the side walls have such lateral projections.

Preferably, each projection extends firstly downwardly from the bottom of the corresponding side wall and then laterally inwardly.

Advantageously, the bottom part has notches, in each of which a corresponding said projection is received and engaged.

Preferably, the top and bottom parts of the casing are moulded to shape.

In a preferred embodiment, the top part of the casing is moulded from plastics, and the bottom part is moulded from urea or phenolic material.

The electrical switch may include a plurality of conductive terminals fixed on and extending through the bottom part, and a movable operating member carrying a conductive bridging member within the casing for selectively electrically bridging across any two adjacent terminals of the terminals.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a top perspective view of an embodiment of an electrical switch according to the invention; Figure 2 is a bottom perspective view of the electrical switch of Figure 1; Figure 3 is an exploded top perspective view of the electrical switch of Figure 1; Figure 4 is a sectional end view of the electrical switch of Figure 2, taken along line IV-IV; Figure 5A to 5C are sectional side views of the electrical switch of Figure 4, taken along line V-V, in different operating conditions; Figures 6A and 6B are sectional side views of the electrical switch of Figure 4, taken along line VI-VI, in different operating conditions; and Figure 7 is a bottom perspective view of a part of the electrical switch of Figure 1.

Referring firstly to Figures 1 to 3 of the drawings, there is shown an electrical switch 10 embodying the invention, which switch 10 comprises a elongate casing 11 which is formed by connected (box-like) top part 12 and (plate-like) bottom part 13, an operating member 14, and eight terminals 15 arranged in two rows on the bottom casing part 13 along the longitudinal extent of the casing 11.

Each terminal 15 is provided by an electrically conductive metal strip having an upper end 16 folded through 90 degrees. The bottom casing part 13 has two rows of four recesses 17 in its upper side , and a slot 18 is formed in the bottom casing part 13 along the outer side of each recess 17. The upper end 16 of each terminal 15 is received in a corresponding recess 17 when the terminal 15 is inserted from above through the corresponding slot 18 in the bottom casing part 13.

Referring also to Figure 7, each terminal 15 is secured in position through the bottom casing part 13 by folding a pre-cut tab 19 of the metal strip until it bears against the lower side of the bottom casing part 13. The tab 19 is cut out from between two sides of the metal strip, leaving a hole 20 therein and without breaking the two sides. This construction does not significantly reduce the strength of the terminal 15 at the position of the hole 20, and the hole 20 can serve to retain solder when a wire is soldered to the terminal 15.

Referring also to Figure 4, the operating member 14 has a body 21 and an integral base 22. The base 22 is slidably located within the casing 11 and the body 21 projects upwards out of the casing 11 through a slot 23 in an upper wall 24 of the top casing part 12. The operating member 14 has a central compartment 25 and two side compartments 26, all extending along the longitudinal extent of the casing 11.

Inside each side compartment 26, there is located a pair of leaf springs 27 and 28. The spring 27 is electrically conductive and bends slightly upwards with two ends folded upwards. The spring 28 has an inverted V-shape and two ends bent upwards. The spring 28 is shorter than the spring 27 and is placed generally therein, and the assembly is held within the corresponding compartment 26 by bearing against the upper ends 16 of the terminals 15.

As shown in Figure 5A to 5C, in any one of the switch operating conditions, the spring 27 serves as a bridge across two adjacent terminals 15, at their upper ends 16, thereby permitting electric current to flow across the terminals 15 via the spring 27. The spring 28 serves to tension the spring 27 and to urge the two ends of the latter tightly against the corresponding terminal upper ends 16 to ensure good ohmic contact.

Concerning the central compartment 25 of the operating member 14, it extends through the base 22 and into the body 21. A plunger 29 is slidably received within the outer end of the compartment 25, and a coil spring 30 is located within the inner end of the compartment 25 so as to bias resiliently outwards. The plunger 29 has a thinner bottom end 31 which has a symmetrical flat V-shaped cross-section.

On the upper side of the bottom casing part 13, there is provided a track 32 between the two rows of recessed 17, as best shown in Figure 3. The track 32 has a serrated (zigzag) surface formed by a series of three identical symmetrical flat V-shaped recesses 33.

Referring also to Figures 6A and 6B, each recess 33 extends precisely across a corresponding pair of adjacent terminals 15. The plunger 29 is positioned symmetrically relative to the assembly of springs 27 and 28 on either side, so that when the bottom end 31 of the plunger 29 sits symmetrically within a particular recess 33, which is the only stable position under the action of the spring 30 behind the plunger 29, each spring 27 will bridge symmetrically acrOss the corresponding pair of adjacent terminals 15 on either side of the plunger 29.

Accordingly, the plunger 29 and the track 32 co-operate to define the operating position of the operating member 14 in which the springs 27 bridge across the corresponding pairs of adjacent terminals 15.

As best shown in Figure 6A, the inclined surface angle, i.e. the angle of inclination between adjacent surfaces constituting the V-shape, of each recess 33 is slightly smaller than that of the plunger bottom end 31. This arrangement minimises the contact area between the plunger 29 and the track 32 and in turn the friction against sliding movement of the plunger 29 along the track 32. The same result can be achieved by making the inclined surface angle of the recesses 33 slightly larger than that of the plunger bottom end 31.Compared with this alternative arrangement, the present arrangement ensures a more stable position of the plunger 29 with its bottom end 31 sitting in a particular recess 33 because of there being two lines of contact (on two sides) between the plunger bottom end 31 and the recess 33 as opposed to there being a single line of contact at the apex of the plunger bottom end 31 in the alternative arrangement.

In order to reduce further the sliding friction against movement of the operating member 14, the junctions between adjacent recesses 33 are rounded.

The connection between the top and bottom parts 12 and 13 to form the casing 11 will now be described. The top casing part 12 has two opposed wider side walls 34 and two opposed narrower side walls 35, depending from the periphery of the top wall 24. At the bottom of each side wall 34 or 35, there is provided a projection which extends firstly downwardly and then laterally inwardly, forming a hook 36. Four notches 37 are formed at the corresponding positions in the bottom casing part 13 to receive the corresponding hook 36. Each notch 37 has a step 38 (see Figure 7) behind which the corresponding hook 36 engages to hold the casing parts 12 and 13 together.

In this specific embodiment, the top casing part 12 is moulded from plastics and the bottom casing part 13 is moulded from urea or phenolic resin. Urea or phenolic material is particularly preferred because it is sufficiently strong and both electrically and thermally resistant. Plastics provides the required resilience to permit the top casing part 12 to be snap-fitted onto the bottom casing part 13. It is also appreciated that because the casing 11 is entirely made of electrically insulating materials, namely plastics and urea or phenolic resin, the danger of current leakage through the casing 11 will be significantly reduced.

In a slightly different construction, the top part of the switch casing may have two principal side walls (34 in the described embodiment) only, without side walls at both ends, for material saving.

The electrical switch 10 is generally known as a doublepole triple-throw switch, though it is understood that the invention is also applicable to any other types of switches having a different number of pole and/or throw (terminal) or in which the terminals are arranged in a circular manner.

The invention has been described by way of example only, and various other modifications of and/or alterations to the described embodiment may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.

Claims

1. An electrical switch comprising a casing having a top part and a bottom part connected together by snap-fit means.

2. An electrical switch as claimed in claim 1, wherein the top part has a rectangular top wall and four depending side walls, and the bottom part is a plate closing from below the top part.

3. An electrical switch as claimed in claim 2, wherein said snap-fit means is provided by lateral projections extending inwardly from at least one opposite pair of the side walls of the top part, and the bottom part is connected to the top part by engagement with the lateral projections.

4. An electrical switch as claimed in claim 3, wherein both opposite pairs of the side walls have such lateral projections.

5. An electrical switch as claimed in claim 3 or claim 4, wherein each projection extends firstly downwardly from the bottom of the corresponding side wall and then laterally inwardly.

6. An electrical switch as claimed in claim 5, wherein the bottom part has notches, in each of which a corresponding said projection is received and engaged.

7. An electrical switch as claimed in any one of claims 2 to 6, wherein the top and bottom parts of the casing are moulded to shape.

8. An electrical switch as claimed in claim 7, wherein the top part of the casing is moulded from plastics, and the bottom part is moulded from urea or phenolic material.

9. An electrical switch as claimed in any one of the preceding claims, including a plurality of conductive terminals fixed on and extending through the bottom part, and a movable operating member carrying a conductive bridging member within the casing for selectively electrically bridging across any two adjacent terminals of the terminals.

10. An electrical switch substantially as hereinbefore described with reference to the accompanying drawings.