GB2074385A - Push-button switches - Google Patents

Abstract

A push-button switch has, mounted on its push-button a resiliently based, conductive rockable bar (20) carrying a couple of movable contacts (24, 25) and being movable with the pushbutton until one of the movable contacts 24 engages a fixed contact 26, whereafter the bar (20) rocks about the couple of contacts (24, 26) in mutual engagement until the other movable contact (25) engages a fixed contact (27). The conductive bar (20) is resiliently urged towards abutments (23) on the pushbutton. <IMAGE>

Description

SPECIFICATION Improvements in or relating to push-button switches This invention relates to push-button switches, that is, those in which the movable contact is driven by a control member which goes along a rectilinear path.

Generally speaking, these switches are comprised of a couple of fixed contacts which are adapted to coact with a movable contact consisting of a bar carried by the push-button and which can be positioned either in a remote position or in a position in which it rests against the fixed contacts to connect them electrically.

The switches of this kind should, from a merely theoretical standpoint, afford constructional advantages over the switches having a rocking movable contact, that is the toggle switches.

As a matter of fact, still from a theoretical standpoint, the two fixed contacts reach their closure position on the bar simultaneously: this fact involves the distribution over the two contacts of the dissipation of the energy evolved by the arc discharge.

In this case, the proportioning of the two breaker contacts might be lower than that of the single breaker contact.

Such an advantage, however, is rather questionable since the absolute simultaneousness of the contact break does not occur in actual practice, since it has been experienced in the majority of the cases that the cutoff is statistically distributed for one half on either contact and for the other half on the other one, assuming that the switch has correctly been constructed.

Such a distribution, however, is also influenced by the uncertainty as to the tolerance in the construction of the switch, in addition to the rigid rectilinear nature of the shift of the movable contact.

As a matter of fact it may occur that for certain switches of a manufacuring series the interruption is predominant for either contact point, and it cannot be forecast on which of the two.

It should also be borne in mind that the contact opening and closing velocity in a toggle switch is entrusted, as a rule, to the bias of a spring which overtakes a snap dead centre, the result thus being that this velocity is, within a wide range, independent of the swiftness of manipulation of the switch by the user.

Contrarywise, in the push-button switches, inasmuch as there is a direct action between the manipulating member and the movable contact, the closing or the opening velocity is a function of the rapidity of manipulation.

This manipulation can be comparatively slow and this wouid be detrimental as to the duration of the contact.

In summation, even if, theoretically speaking, the sizing of the contacts may be assumed to be smaller than that required for the contacts of the toggle switch, in practice, it must considerably be oversized due to the concurrence of the circumstances aforementioned, and this has, as a result, an increased cost of the switch.

Thus, the invention aims at offering a redress to these drawbacks by modifying the mode of operation of the component parts of the switch while substantially abating the cost of the contacts without, however, unduly sacrificing the constructional simplicity of the switch.

According to the invention, this object is achieved by providing a push-button switch having its push-button moved rectilinearly within a switch-casing to bring at least a couple of movable contacts towards or away, as the case may be, of a corresponding couple of fixed contacts, said switch being characterised in that said movable contacts are borne by the push-button in a resiliently rocking way, the distance between each fixed contact and its corresponding movable contact exceeding the distance for which current may flow between a fixed and a movable contact when the movable contacts are in their at rest position on the push-button.

In order that the objects and the features of the invention may be best understood, a practical embodiment will be described hereinafter, to be illustrated in the accompanying drawings, wherein: Figure 1 is a longitudinal cross-sectional view of a push-button switch.

Figure 2 is a cross-sectional view, taken along the line ll-ll of Fig. 1.

Figures 3, 4 and 5 show operative positions of the switch shown in Figs. 1 and 2, and Figures 6 and 7 show diagrammatic views of switches working in a manner akin to that of the devices shown in the previous Figs.

As shown in Figs. 1 and 2, a push-button switch, the general arrangement of parts of which is commonly known, comprises a casing 10 in which a push-button 11 is guided for axial movement. The push-button is moved against the bias of a compression spring 1 2 and has a conventional detent mechanism 1 3 which, alternately, clamps it in its depressed position, or allows it to reach a lifted position by sequential depressional actions thereon.

On the push-button is mounted a couple of movable contacts 20, each of them being guided by a pin 21 and urged by a spring 22 against abutments 23. The contact 20 carries contact dots 24 and 25, intended to come into touch, each, with either of two contact dots 26 and 27 mounted on terminals 28 and 29 placed in fixed position on the switch casing 10.

In its depressed position, the push-button 11 brings the contact dots 24 and 25 resiliently to rest against the contacts 26 and 27, that is, by a stroke which is adequate to have the bar 20 separated from its abutments 23, so that a reliable mutual rest between the contacts is ensured.

Figs. 3, 4 and 5 best show the mode of action of the contacts, which is the basic principle of this invention.

These Figs. diagrammatically show the operability of the contacting members and the structure of the switch has not been shown so as to simplify the pictures.

Fig. 3 shows the contacts when the switch is OFF: in this case the bar 20 rests against its abutments 23 and the dots 24-25 are away of the dots 26-27.

It is to be noted, however, that the terminals 28 and 29 have the dots 26 and 27 located at different levels, that is, at differed; distances with respect to the conjugated contacts 24-25, just for the purposes aforementioned.

As a matter of fact, as the push-button is depressed to place the switch in its ON position, the switch takes the position of Fig. 4, that is, with the dots 24 and 26 touching one another, whereas the dots 25 and 27 are still spaced apart from one another by a gap indicated at a.

This gap, a, must be of an appreciable magnitude, that is, its magnitude must exceed the gap at which, irrespectively of the switch being ON or OFF, a consistent sparking in air might occur.

For switches intended for non-special uses, the order of magnitude of a will be one millimeter or a few millimetres.

Under these conditions, it is apparent that the couple of contact dots 24 and 26 is closed under no-load conditions, that is, in open-circuit position: thus, they can correspondingly be sized and will not require the use of any precious metals.

By depressing the push-button farther, the bar 20, now abutting 24 is no longer shifted parallely of itself but, rather, it swings about 24 and is withdrawn from the abutments 23: in practice, it goes to the position of Fig. 5 and the dot 25 approaches the dot 27 at a speed which is twice the speed at which the push-button is depressed. This swing of the bar 20 requires only that the bar be mounted on the pin 21 with an appropriate clearance.

As a result, the structure suggested by the invention concurrently fulfils the requirements of increasing the closure velocity of the switch while obtaining the closure of the circuit under load conditions in correspondence with one preselectable couple of contact dots only.

It-is quite obvious that the same effect is achieved as the switch is opened, when current surges might seriously stress the switch contact dots.

As a matter of fact, the switch passes, sequentially, through the positions shown in Figs. 3, 4 and 5, that is, in the reverse order with respect to that described above with reference to the switching-on sequence.

Anyone skilled in the art may introduce modifications and changes for obtaining simi lar results with equivalent means, still within the scope of this invention.

The gap gradient between the opened contacts may thus be obtained by varying the level of the dot 25 relative to that of the dot 24, or, as an alternative, by modifying the height of the dot on the bar 20 (as shown in Fig. 6), or, also, by properly arranging the abutments which define the at rest position of the bar (as shown in Fig. 7).

Summing up, it is required that the line joining the contact dots on the bar which is moved with the push-button, and the line joining the corresponding fixed contact dots are at an angle with one another and are not parallel until such time as all the contact dots come into mutual engagement.

The configurations to be taken by the detents for the bar 20 can thus be most varied provided that they permit the resilient swing of the bar as the first couple of contact dots is in engagement.

There are no limitations, likewise, for the number of bars 20 carried by the push-button of a switch: there can be a single bar for unipolar switches and two for the bipolar ones.

It is also understood, in the instant specification, that a push-button switch is also one which can be held ON only when the pushbutton is held down or also one having the function of a plural-way switch.

Claims (4)

1. A push-button switch having its pushbutton moved rectilinearly within a switchcasing to bring at least a couple of movable contacts towards'and away, as the case may be, of a corresponding couple of fixed contacts, said switch being characterized in that said movable contacts are borne by the pushbutton in a resiliently rocking way, the distance between each fixed contact and its corresponding movable contact exceeding the distance for which current may flow between a fixed and a movable contact when the movable contacts are in their rest position on the push-button.

2. Switch according to Claim 1, characterized in that said movable contacts are borne by a metal bar mounted movably on said push-button against the bias of a resilient member which urges the bar against abutments which define its at rest position.

3. Switch according to Claim 1, characterized in that said contacts have such a size and are made of a such material which are adequate for no-load operation for the contact dots which are set at the least mutual distance, and which are adequate to operation under load for the contact dots which are set at the greatest mutual distance.

4. Switch according to Claim 1, substantially as described with reference to Figs. 1 to 5, or Fig. 6, or Fig. 7, of the accompanying drawings.