EP1324361A1 - Snap action switch with tiltable leaf spring - Google Patents

Abstract

The abrupt break switch has a flexible conductor strip (20) passing current from a first to a second wire when contact is made. The flexible strip has a central section (22) with a fixed (24) and free (26) end and two side arms (30,32). The arms have an open and closed position forming the switch.

Description

The invention relates to electric break switches abrupt in which an elastic blade can switch between two positions stable under the control of a push button (for example a push button manual). The electric current to be interrupted or deflected suddenly passes in the elastic blade which is therefore made of a material electrically driver.

The two stable positions of the blade generally correspond to a first position in which the current can pass through the blade from a first terminal to a second terminal, and a second position in which the current is interrupted or can pass through the blade of the first terminal towards a third terminal.

To suddenly switch from one position to another, the blade is generally mounted in a housing being subjected to a stress which prevents it from taking the form that it would naturally have at rest. Typically, if the blade is flat at rest, it is mounted with a constraint longitudinal which prevents it from keeping this flat position. The blade is therefore curves in one direction or the other and can tilt so bistable from one direction of curvature to the other, each direction corresponding to one switch positions. A push-button allows the blade to tilt from one position to another.

In the prior art, represented for example by the French patent FR-A-2 681 184, the blade may consist of three parallel branches, with a central branch cut in the middle and two lateral branches. By spreading the two strands of the central branch, we create in the branches lateral a constraint which curves them and which gives the blade its bistable operation. The two strands of the central branch serve as articulation point around which the blade can tilt from one position to the other. The ends of the strands are supported for this each in a groove in V which allows an angular movement of the blade from the first position towards the second. Figure 1 shows such an arrangement.

In this type of assembly, the point of articulation of the blade in the V-groove also serves as an electrical contact point to make pass the current from the blade to a contact terminal of the switch. This blade articulation point must withstand both mechanical stresses and constraints of passage of a high density of electric current. In practical, to maintain sufficiently high currents, of the order of ten amps or more, we have to coat with a layer of silver one side of the elastic blade, where it comes into contact with the V-shaped groove

This silver plating operation is costly in time and in material.

EP 0 015 782, FR 2 346 836 and US 2 513 804 describe other systems in which current flow is through points of articulation of a movable blade in a fixed blade, with the same drawbacks.

It has also been proposed, in US Pat. No. 4,145,587 a monostable or bistable prestressed blade switch but whose configuration and mounting require difficult adjustment of mechanical characteristics of the blade to obtain a breaking effect sudden. In addition, this switch necessarily uses a spring to return to the starting position after tilting.

The object of the present invention is to reduce the manufacturing cost while obtaining good electrical performance and a long service life high, and for this we propose on the one hand a snap switch having a particular structure, and on the other hand a manufacturing process switch.

The switch according to the invention comprises at least a first electrical terminal and a second electrical terminal, an elastic blade conductive allowing current to flow from the first terminal to the second when this blade touches both terminals, the blade elastic comprising a central strand having a foot and a free end, and two lateral arms extending from the foot of the central strand on the side and other of the latter, the two lateral arms being longer than the strand central and being rigidly connected to each other at their ends, beyond the free end of the central strand, the rigid connection between the ends of the two side arms being preloaded so that the side arms move apart necessarily on one side or the other of the central strand when the blade is at rest, characterized in that the free end of the central strand is fixed rigidly, preferably by welding, at the first electrical terminal of the switch, the blade pressing the second terminal of the switch when it is in a first state where the lateral arms tend to move apart on one side of the central strand, and the blade no longer pressing on the second terminal when in a second state where the side arms tend to move apart on the other side of the central strand.

The switch may include a third electrical terminal against which the blade comes to rest when it is in its second state, an electric current can then pass through the blade of the first terminal towards the third.

The blade can come into contact with the second terminal either through the foot of the central strand, either by the joined ends of the lateral arms. In the first case, the tilting action of the blade from a first position towards a second can be carried out by a pusher which comes to rest against the joined ends of the side arms. In the second case, the action can be make by a pusher which comes to rest against the foot of the central strand.

• fabriquer d'abord une lame élastique en découpant dans une plaque conductrice plane une lame plane d'une seule pièce comportant un brin central s'étendant entre un pied et une extrémité libre, et deux bras latéraux s'étendant en V à partir du pied de part et d'autre du brin central et sur une longueur plus grande que le brin central,
• rapprocher les deux extrémités de bras en les contraignant jusqu'à les faire se rejoindre et les solidariser rigidement de manière à créer dans la lame une contrainte mécanique interne, les bras s'écartant alors du plan du brin central,
• fixer rigidement, de préférence par soudage, l'extrémité libre du brin central sur une première borne électrique prévue dans un boítier d'interrupteur de telle manière que la lame vienne par ailleurs en contact avec une deuxième borne électrique de l'interrupteur.

The method according to the invention, for manufacturing a snap switch comprises at least the following steps:

• first make an elastic blade by cutting from a flat conductive plate a flat blade in one piece having a central strand extending between a foot and a free end, and two lateral arms extending in V from the foot on either side of the central strand and over a greater length than the central strand,
• bring the two ends of the arms together, forcing them until they join and rigidly join them so as to create an internal mechanical stress in the blade, the arms then moving away from the plane of the central strand,
• rigidly fix, preferably by welding, the free end of the central strand on a first electrical terminal provided in a switch box so that the blade also comes into contact with a second electrical terminal of the switch.

The blade is then in the stable prestressed position, and an action on a pusher at either end of the blade allows you to do tip the blade from a state in which the side arms tend to move apart from one side of the central strand to a state in which the side arms tend to move aside on the other side of the central strand.

• la figure 1, déjà décrite, représente le principe d'un interrupteur de l'art antérieur ;
• la figure 2 représente en vue de dessus une lame plane découpée à partir de laquelle on va former la lame précontrainte de l'interrupteur ;
• la figure 3 représente une vue de dessus de la lame qui est précontrainte par le rapprochement de ses bras latéraux ;
• la figure 4 représente une vue latérale de cette lame, faisant apparaítre que les bras latéraux s'écartent naturellement du plan du brin central de la lame ;
• la figure 5 représente une coupe frontale de la lame des figures 3 et 4 selon la ligne A-A de la figure 4 ;
• les figures 6 et 7 représentent des vues analogues aux figures 4 et 5, mais dans lesquelles on a forcé la lame précontrainte vers une deuxième position stable où les bras latéraux sont passés de l'autre côté du plan du brin central ;
• la figure 8 représente une vue de la lame après repliement d'une extrémité libre du brin central, en vue d'une soudure ultérieure sur une borne électrique ;
• la figure 9 représente un interrupteur dans lequel on a monté la lame de la figure 8 ;
• la figure 10 représente l'interrupteur de la figure 9, dans lequel la lame a basculé dans sa deuxième position ;
• la figure 11 représente une variante de réalisation de la lame, en vue de dessus ;
• la figure 12 représente la lame de la figure 11, en vue latérale ;
• la figure 13 et la figure 14 représentent un interrupteur dans lequel est montée la lame des figures 11 et 12, respectivement dans une première et une deuxième positions de la lame.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which:

• Figure 1, already described, shows the principle of a switch of the prior art;
• 2 shows a top view of a flat blade cut from which we will form the prestressed blade of the switch;
• Figure 3 shows a top view of the blade which is prestressed by the approximation of its lateral arms;
• Figure 4 shows a side view of this blade, showing that the side arms naturally deviate from the plane of the central strand of the blade;
• 5 shows a front section of the blade of Figures 3 and 4 along the line AA of Figure 4;
• Figures 6 and 7 show views similar to Figures 4 and 5, but in which the pre-stressed blade has been forced into a second stable position where the lateral arms have passed to the other side of the plane of the central strand;
• Figure 8 shows a view of the blade after folding of a free end of the central strand, for subsequent welding on an electrical terminal;
• Figure 9 shows a switch in which the blade of Figure 8 has been mounted;
• Figure 10 shows the switch of Figure 9, in which the blade has tilted into its second position;
• Figure 11 shows an alternative embodiment of the blade, seen from above;
• Figure 12 shows the blade of Figure 11, in side view;
• Figure 13 and Figure 14 show a switch in which is mounted the blade of Figures 11 and 12, respectively in a first and a second positions of the blade.

In FIG. 2, the first phase of production has been represented. of the tilting elastic conducting blade of the switch: we cut a shape in a thin plate made of an elastic and conductive material electricity; the material can be an alloy of copper and beryllium, combining good elasticity and conduction properties, but other materials may be suitable (especially stainless steel for greater resistance).

At this stage, the blade 20 is flat and has a central strand 22 having a foot 24 and a free end 26. Of the foot 24 of the central strand 22 leave two lateral arms 30 and 32 which extend at an acute angle with the general direction of elongation of the central strand. The side arms do not are not necessarily straight, but the angle they form with the strand main is such that we can bring them closer to the main strand (by exercising a constraint) while allowing after this reconciliation a interval between lateral arms and central strand.

In principle, the free ends, 31 and 33 respectively, do not not touch; they are separated by an interval of width D, such as bringing the two ends 31 and 33 together until they touch or even partially overlap, there is a fairly strong constraint on these arms to force them to deviate significantly from the strand plane central 22 of the blade. Of course, the distance D remains sufficiently short so that this bringing together of the arms is done while staying within the limits of elasticity of the material.

In the embodiment shown, each lateral arm 30 or 32 is terminated at its free end by a lateral extension (34, 36) facing the other arm, and the bringing together of the arms will bring in contact an edge 35 of the extension 34 along an edge 37 of the extension 36. However, to increase the solidity of the rigid connection that we will establish between the lateral extensions 34 and 36, we can consider bringing in mutual overlap extensions 34 and 36. The bringing together of the arms will then consist in bringing the extensions closer to D 34 and 36. The weld between the two lateral arms will not then be a edge-to-edge weld but a plan-to-plan weld of the extensions 34 and 36. Preferably, the general arrangement is symmetrical with respect to a median longitudinal axis of the central strand 22.

The length of the lateral arms 30 and 32, counted from the foot 24 of the central strand, is greater than the length of the central strand, so that the lateral extensions 34 and 36 of the lateral arms, once brought together of each other until touching or overlapping, lie beyond the end 26 of the central strand 22.

Figure 3 shows a top view of the blade prestressed by the bringing together of the lateral arms. The side arm ends are permanently joined to each other, for example by welding on the line joint representing the joined edges 35 and 37.

The lateral arms are deformed due to the stress exerted by so that they cease to lie in the same plane as the central strand. The bringing the lateral arms together veils these arms and causes the end, become common (31, 33), lateral arms out of the plane of the central strand.

Figures 4 (side view) and 5 (section along line A-A of the Figure 4) show these different deformations. In Figure 4, we see clearly that the lateral arms 32 (or 30) deviate from the plane of the central strand 22, so that the ends 31, 33 of these lateral arms come out completely of this plane (which can be considered as a reference plane).

Likewise, in FIG. 5, it can be seen that the lateral arms are veiled, that is to say that they are no longer plan because of the stress they undergo between the foot of the central strand and their joined ends 31, 33; in the section plane A-A, we see a sharp inclination of the arm section lateral 30, 32 with respect to the horizontal reference plane of the central strand 22.

The general shape of the cutting of the lateral, straight arms with a lateral extension 34, 36, or curved regularly between the foot and the ends, is such that the arms, when brought together, do not do not touch the central strand. A narrow gap 40 remains between the side arms and the central strand (Figure 3, Figure 5).

Finally, since this blade is intended to pass a current from one terminal of a switch to another terminal of the switch, provision is preferably made to constitute a contact pad made of material highly conductive (silver-based alloy for example) resistant to abrasion due to abrupt and repeated power interruptions. This stud is designated by the reference 44 in Figure 3; in this example of realization there is located on the foot 24 of the blade. There may be a pin 44 above the blade and a pad 46 below the blade (Figure 4) in the case where the blade must come into contact with two different terminals of the switch. The studs could be located elsewhere on the blade, and in particular on the ends 31, 33 of lateral arms as will be seen later.

The blade thus prestressed by the rigid connection between the ends of the lateral arms has a stable natural shape which is that of Figures 4 and 5. But it can also take (if only because of its symmetrical structure) a second stable natural form in which the lateral arms come from the other side of the reference plane defined by the plane from the central strand 22.

Figure 6 and Figure 7 correspond respectively to representations of Figures 4 and 5 (side view and front section), but in which we forced the blade to take this second natural form stable. The intermediate positions are unstable, and in particular the stress exerted on the arms prevents them from remaining in the plane of the central strand or close to this plane.

It is therefore seen in Figures 4 and 6 that in the first form natural of the blade the lateral arms tend to deviate from one side of the plane of the central strand, while in the second form of the blade they tend to move aside on the other side of the central strand.

FIG. 8 represents a later stage in the manufacture of the blade, in which we folded permanently (non elastic) the free end of the central strand 22. This folding is linked to the implantation particular of electrical terminals that we chose in the realization switch 9 and 10. It will be understood that other forms of folding or even a lack of folding can be envisaged according to the arrangement of electrical terminals in the switch housing. We will consider that the reference plane mentioned above and which represents the plane of the central strand in FIGS. 1 to 7 (with respect to which the side arms tend to move away) is then the plane of this strand close immediate of his foot.

Figure 9 shows the side section of a break switch abrupt in which the elastic conductive strip has been mounted and prestressing, the manufacture of which has just been described.

In this exemplary embodiment, the switch comprises three connection terminals 50, 60 and 70 partially penetrating inside a case 90, a pre-stressed elastic conductive blade 20, and a button pusher 80 for passing the blade from a first state to a second state. The blade has the function of passing an electric current from terminal 50, said common terminal, towards one or the other of terminals 60 and 70 depending on whether the blade is in its first state or in its second state. Therefore, the blade in this case carries two contacts 44 and 46 as explained in reference to FIG. 4, but it can be seen that the invention could be used even if there were only two terminals 50 and 60 instead of three terminals 50, 60, 70.

The free, folded end 26 of the central strand 22 of the blade is fixed rigidly, preferably by welding, at the end of the common terminal 50 inside the housing. The folding angle of the end of the central strand, and the arrangement of terminal 60 and pusher 80 in the housing are such that when the blade is welded in place while in its first position stable, it comes to rest by one of its ends against the button pusher 80 and by another end against the terminal. More precisely, this other end, provided with the contact pad 44, bears against a pad contact 62 corresponding mechanically and electrically secured to terminal 60. The contact force must be sufficient to establish good contact electric between the pads 62 and 44, which means that in the mounted position in the housing, the angle formed by the central strand and the lateral arms is more reduced than the angle visible in Figure 4 (Figure 4 shows the blade in its stable natural form not subject to external forces on its ends). In other words, the blade tends to take its natural form of rest of Figure 4 but does not quite take this form due to external stresses caused by the pusher and terminal 60; these constraints allow sufficient support force to remain between the electrical contacts 44 and 62.

On the right side of Figure 9, there is shown schematically the front section of the central strand 22 and the lateral arms 30 and 32, showing the position of the veiled side arms (in V, above the plane of the central strand 22) when the blade is in its first position.

In the embodiment of Figure 9, it is the foot of the strand central which comes into contact with terminal 60, and therefore the button pusher presses on the joined ends of the side arms of the blade. We will see that it is possible to do the opposite: contact on the ends of the arms lateral, and push against the foot of the central blade strand.

Figure 10 shows the same switch in its second state. By pushing the pusher 80 against the end of the blade, we lower this by reducing the angle formed (at the foot of the central strand) between the central strand and the side arms of the blade. At a certain stage, there is sudden tilting due to the internal stresses of the blade, and the angle formed by the lateral arms with respect to the central strand tends to take the value it has in Figure 6, i.e. a value opposite to that of the Figure 4. Contact 44 suddenly detaches from pad 62, cutting the circuit between the terminals 50 and 60. In the new position that it takes, the blade is constrained by the end of the pusher on one side, by the welding of the central strand on the other side. The blade end carrying the contact 46 is then applied against a contact pad 72 secured electrically and mechanically from terminal 70. This terminal 70 and this pad 72 are placed in the case in a position such that the blade does not find not completely its natural form (that of figure 6), but such as in on the contrary, there remains a pressing force of the pad 46 against the pad 72. This force support serves to establish a good electrical contact for the passage of current between terminal 70 and terminal 50. The angle formed by the central strand and the arms lateral at the foot of the central strand is therefore in principle smaller than that of FIG. 6 which represents the natural form.

On the right side of figure 10 we still see a frontal section schematically showing the position of the lateral arms relative to the strand central 22 of the blade (V-shaped arm below the central strand) when the blade is in its second state.

As long as the pusher 80 is held down, the blade remains in his second position. The central strand 22 is constrained during this depressing. When the pusher is released, the central strand also relaxes, automatically returning to the first position (that of Figure 9) at both the pusher 80 and the blade end on which the pusher presses. The recall to the first position is done as for the reverse path, with sudden tilting when the angle between the central strand and the side arms changes direction. The restoring force exerted by the central strand is more great that the prestressing force which opposes the passage of the blade its second natural form to the first. A spring 85 can be possibly provided to help this recall to the first position.

Figures 11 and 12, similar to Figures 3 and 4, show an alternative embodiment of the prestressed conductive strip. In this embodiment, provision has been made for the contact pads 44, or 44 and 46, to be welded on the blade on the side of the joined free ends (31, 33) of the lateral arms and not on the side of foot 24 of the central strand. The welding operation of the contact pads 44, 46 can also be used at the same time for the securing of the two ends 31, 33 of the arms while these are forced to get closer until touching or overlapping.

With this blade realization, the switch will be mounted as in Figure 13: the central strand has its free end 26 folded so permanent depending on the position of terminal 50, and this free end 26 is welded (or rigidly fixed in another way, for example by a screw) on this terminal. The pusher 80 presses on the blade on the side of the foot 24 of the blade. The welded ends of the lateral arms carry studs contact 44, 46 which come between terminals 60 and 70, and more precisely in look of contact pads 62, 72 welded to these terminals.

In its first position, the blade is forced to rest on both on the pusher 80 in the high position and on the pad 62, the natural shape of the blade of FIG. 12 then tending to exert a contact force sufficient on this stud.

The push-in action of push-piece 80 moves the foot of the blade until the lateral arms tend to pass on the other side of the plane of the central strand. The prestressed blade then swings suddenly towards its second stable form, which causes the pad 44 to detach from the pad 62 and the pad 46 to come to lean against the pad 72. The position of the pad 72 is, there again, such that the blade cannot deform until it sets completely its second natural stable form. It therefore remains in support against the pad 72 with sufficient contact force.

A spring similar to the spring 85 in FIGS. 9 and 10 can be designed to automatically return the blade to its first state. However, it will be noted that the deformation of the central strand of the blade pushed by the pusher 80 may be sufficient in itself to act as a spring for force recall greater than the internal prestressing force of the blade, that is to say the force which tends to oppose the passage of the blade of a first natural state to the other natural state. In this case, using a spring Additional 85 is not necessary and this is why Figures 13 and 14 do not show such a spring.

As an indication, the invention is particularly applicable for the manufacture of microswitches, which are snap-action switches the dimensions of which are no more than a few centimeters per side.

Claims (11)

Snap-action switch comprising at least a first electrical terminal (50) and a second electrical terminal (60), a conductive elastic blade (20) allowing current to flow from the first terminal to the second when this blade touches both the two terminals, the elastic blade comprising a central strand (22) having a foot (24) and a free end (26), and two lateral arms (30, 32) extending from the foot of the central strand on both sides 'other of the latter, the two lateral arms being longer than the central strand and being rigidly connected to each other at their ends (31, 33) beyond the free end of the central strand, the connection rigid between the ends of the two lateral arms being prestressed so that the lateral arms necessarily move away from one side or the other of the central strand when the blade is at rest, characterized in that the free end (26) of the central strand is rigidly fixed, preferably by welding, at the first electrical terminal (50) of the switch, the blade pressing on the second terminal (60) of the switch when it is in a first state where the lateral arms tend to deviate from 'one side of the central strand, and the blade no longer pressing on the second terminal when it is in a second state where the lateral arms tend to move away from the other side of the central strand. Switch according to claim 1, characterized in that it comprises a third electrical terminal (70) against which the blade comes to rest when it is in its second state, an electric current being able then to pass through the blade of the first terminal towards the third. Switch according to one of claims 1 and 2, characterized in that the blade comes into contact with the second terminal by the foot (24) of the central strand. Switch according to claim 3, characterized in that a pusher is provided for pressing on the joined ends (31, 33) of the lateral arms. Switch according to claim 4, characterized in that a spring (85) is provided to help bring the blade and the pusher back to a first state when the blade is in its second state. Switch according to one of claims 1 and 2, characterized in that the blade comes into contact with the second terminal by the joined ends (31, 33) of the lateral arms. Switch according to claim 6, characterized in that a pusher is provided for pressing on the foot (24) of the central strand. Switch according to claim 7, characterized in that a spring (85) is provided to help bring the blade and the pusher to a first state when the blade is in its second state. Switch according to claim 7, characterized in that the central strand is constituted so as to exert, when the blade is in its second state, a restoring force sufficient to overcome, without the aid of an additional spring, the force of prestress which opposes the passage of the blade from its first state to its second state. Method for manufacturing a snap switch, characterized in that it comprises at least the following steps: first fabricating an elastic blade (20) by cutting from a flat conductive plate a flat blade in one piece comprising a central strand (22) extending between a foot (24) and a free end (26), and two lateral arms (30, 32) extending in a V from the foot on either side of the central strand and over a length greater than the central strand, bring the two ends (31, 33) closer to the arms, forcing them until they meet and rigidly joining them so as to create an internal mechanical stress in the blade, the arms then moving away from the plane of the central strand, rigidly fix, preferably by welding, the free end (26) of the central strand on a first electrical terminal (50) provided in a switch box (90) so that the blade (20) also comes into contact with a second electrical terminal (60) of the switch. Method according to claim 10, characterized in that the central strand is folded in a non-elastic manner before welding on the first electrical terminal.

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