Patent Publication Number: US-9418807-B2

Title: Electrical switch forming a fast-acting circuit breaker

Description:
BACKGROUND 
     In numerous applications, it is necessary to have electric switches that are fast and reliable that make it possible to open a faulty circuit in order to isolate one or more components, in particular when they have failed, and also making it possible, where appropriate, to act simultaneously to close a branch circuit. 
     Document FR 2 953 322 describes an example of an electric switch of the above-specified type in which electrical contact between the sliding assembly and the conductive tabs takes place via tightly-engaged rings, either because the rings are split rings, thereby imparting a certain amount of resilience to the electrical connection, or else because the sliding assembly is engaged in the rings by forced engagement. Nevertheless, in the long run split rings lose their shape and tend to become oval under the effect of stresses relaxing. Under such circumstances, the electrical contact between the rings and the sliding assembly can become uncertain or might even be lost. As for mounting the sliding assembly by force between the annular rings of the conductive tabs, that can turn out to be difficult. 
     SUMMARY 
     The present invention relates to an electric switch acting in particular as a circuit breaker. More particularly, the invention relates to an electric switch having a sliding assembly, and in particular an electric switch of the type comprising a hollow body defining a cavity, a sliding assembly comprising at least one conductive portion and adapted to move in said cavity from an “initial” first position to a second position, an actuator arranged to co-operate with said sliding assembly and to move it in said cavity, and at least two primary electrically conductive tabs, respectively an upstream tab and a downstream tab, each comprising a ring penetrating into said cavity, said rings being on the same axis and being offset axially in the travel direction of the sliding assembly, wherein the conductive portion of the sliding assembly is in at least tight electrical contact with the two primary electrically conductive tabs when the sliding assembly is in its first position, and when the sliding assembly is in its second position, the upstream electrically conductive tab is separated from the conductive portion of said sliding assembly. 
     The electric switch of the present description is used mainly as a circuit breaker, and it can also be used as an electric changeover switch. It is particularly suitable for high-current electrical circuits. 
     Throughout the present description, the term “primary electrically conductive tab” is used to designate electrically conductive tabs that are connected to the conductive portion of the sliding assembly while it is in its first position, i.e. while the electric switch is in its initial state. 
     In contrast, the term “secondary electrically conductive tab” is used to designate electrically conductive tabs that are connected to the conductive portion of the sliding assembly only after it has moved into its second position (as when a component of the first electrical circuit has been isolated, e.g. because it is considered to have failed, and a second electrical circuit has been closed). 
     An object of the present invention is to propose an electric switch that avoids the above-mentioned drawbacks. 
     In particular, an object of the present invention is to propose an electric switch of the above-specified type that is capable of being assembled very simply, that can respond in a very short period of time, and that provides electrical connections that are reliable over time. 
     More precisely, the invention provides an electric switch comprising a hollow body defining a cavity, a sliding assembly comprising at least one conductive portion and adapted to move in said cavity from an “initial” first position to a second position, an actuator arranged to co-operate with said sliding assembly and to move it in said cavity, and at least two primary electrically conductive tabs, respectively an upstream tab and a downstream tab, each comprising a ring penetrating into said cavity, said rings being on the same axis and being offset axially in the travel direction of the sliding assembly, wherein the conductive portion of the sliding assembly is connected by a clamping force with the two primary electrically conductive tabs when the sliding assembly is in its first position, and when the sliding assembly is in its second position, the upstream electrically conductive tab is separated from the conductive portion of said sliding assembly, said switch being characterized in that the sliding assembly comprises at least one tube split by a slot extending along its entire length, and in that the conductive portion of the sliding assembly is constituted by all or part of said split tube, the clamping force between the conductive portion and the primary electrically conductive tabs being provided by the resilience of the split tube. 
     In the above definition, the terms “upstream” and “downstream” are used to designate the position of one element relative to another while using as a reference the travel direction of the sliding assembly when it is actuated. 
     By means of the above provisions, the electrical circuit connecting together the primary electrically conductive tabs is closed by electrical contacts that are reliable, so long as the electric switch is in its initial position. Since the connection between the primary electrically conductive tabs and the conductive portion of the sliding assembly is a permanent electrical junction obtained by construction by the initial clamping of the split tube, the electrical contact between those elements is well controlled and does not degrade over time, even if the electric switch is subjected to vibration or to impacts. Undesirable phenomena such as intermittent contact, Joule effect losses, electric arcs, etc., are avoided. When, under drive from the actuator, the sliding assembly goes from its first position to its second position, at least one of the tabs is no longer electrically connected to the conductive portion of the sliding assembly. The electrical connection between the two primary electrically conductive tabs is broken, and the electrical circuit is open. 
     The slot gives the split tube resilience that makes it easier to set up the electrical junction. The split tube can thus be engaged as a force fit between the rings of the electrically conductive tabs. 
     The term “force fit” is used in particular to designate a substantially radial force being applied against the longitudinally free ends of the tube so as to move those ends towards each other and reduce the radial size of the tube, and then once the tube has been inserted between the rings, its ends are released so that under the effect of the elastic resilience of the tube, it presses against the inside faces of the rings. 
     With such a split tube, any relaxing of stress leads to an increase in the diameter of the tube and thus contributes to improving electrical contact and during assembly within the ring, it is limited by the inside diameter of the ring. 
     The resilience of the split tube provides a clamping force that is strong enough to ensure that electrical resistance is very low, while nevertheless limiting the force required for moving the split tube when the switch is operated. 
     In practice, the tight force may be determined by selecting a split tube that has a rest diameter that is about 4% to 5% greater than the inside diameter of the ring that is to receive said tube, and by assembling the split tube in the ring by making use of the elasticity of the material constituting the tube. Under such conditions, it is possible to obtain contact resistances of the order of 30 microohms (μΩ) to 50μΩ. 
     In more general manner, it is possible to adjust the clamping force by acting on:
         the clamping clearance between the diameter of the rings in the conductive tabs and the outside diameter at rest of the split tube, and in particular the initial stress applied to the split tube when moving together the two free ends of the tube that define the slot;   the thickness of the split tube (whether the length of the tube is a function of the desired movement, for reasons associated with maximum voltage); and   the nature of the materials.       

     The fact of having a clamping force that is orthogonal to the travel axis made available by construction makes it possible to reduce the force needed for moving the split tube. 
     Furthermore, the resistance to movement of the split tube inside the cavity varies little with varying magnitude of the clamping between the rings and the split tube. 
     It should be observed that the split tube can be obtained very simply, starting from a standard tube and then splitting it by a simple milling or cutting operation. 
     In the present invention, it is preferred to use annular rings that are continuous (i.e. that are not slit radially). Such rings may be obtained easily by punching or stamping using industrial techniques with satisfactory tolerances and without any risk of losing shape by relaxing stresses (as would happen with split rings since they generally become oval in the vicinity of the slot). 
     In an embodiment of the invention, the slot extends in the axial direction of the tube. 
     Advantageously, the width of the slot made in the tube may be selected to compensate at most for the difference in diameter between the conductive tabs and said split tube, the diameter of the tube being greater prior to force assembly than the diameter of the rings of the conductive tabs. 
     In an embodiment, the sliding assembly includes an additional clamping element inserted inside the split tube and configured to apply an outwardly directed radial clamping force on the tube towards the electrically conductive tabs. Preferably, the additional clamping element is made of insulating material. 
     In an embodiment, the actuator is a pyrotechnic gas generator (e.g. a micro gas generator and its pyrotechnic initiator, or a pyrotechnic initiator) and the sliding assembly includes a piston movable inside said cavity, a gas expansion chamber being defined between said pyrotechnic gas generator and said piston. In preferred manner, the piston is made of insulating material. 
     In an embodiment, the piston includes at least one circumferential groove adapted to receive a sealing ring. 
     In an embodiment, the piston is made of insulating material and comprises a first portion adapted to slide along the cavity, and a second portion that is situated in line with the first portion and that is suitable for being inserted, at least in part, inside the split tube in order to constitute a guide element for said tube. 
     In an embodiment, the second portion is mounted by force inside the split tube. The guide element thus has an additional function of forcing the split tube to open radially, thereby reinforcing its electrical connection with the rings of the conductive tabs. 
     In an embodiment, the piston presents a cavity that is axially open upstream, the space defined by said cavity constituting at least a portion of the gas expansion chamber. 
     In an embodiment, the switch includes at least one secondary electrically conductive tab arranged downstream from said first and second primary electrically conductive tabs, and wherein the stroke of the sliding assembly is such that when it is in said second position, said second primary electrically conductive tab is electrically connected to said secondary electrically conductive tab by said conductive portion of the sliding assembly. 
     The above-defined structure is favorable to extending the number of circuit breakers and/or changeover switches. On these lines, and in a possible variant, the switch is characterized in that at least two groups of two primary conductive tabs arranged in line one with another from upstream to downstream and in that said sliding assembly includes a corresponding number of conductive portions that are mutually electrically insulated, each of said conductive portions interconnecting only the conductive tabs of each group when said sliding assembly is in its initial position. 
     It should be observed that in above-described variant, the upstream primary conductive tab of a group of two primary conductive tabs situated downstream from another tab may act as a secondary conductive tab relative to that group. 
     In this same type of embodiment having a plurality of primary conductive tab groups, it is also possible to ensure that the arrangement of said sliding assembly and of the conductive tabs of the two groups is such that for an intermediate position of said sliding assembly, the electrically conductive tabs of the two groups are electrically interconnected via said conductive portions. 
     For example, in order to obtain this result, said two conductive portions may be separated by insulation of thickness that is smaller than the thickness of a conductive tab, so that at a given moment of the stroke, the two conductive portions of the sliding assembly are electrically connected together by the thickness of a ring of one of the conductive tabs. This transient position makes it possible, for example, to close a branch circuit momentarily so as to ensure continuity of an electrical circuit during the travel of the sliding assembly. 
     In an embodiment, the cavity in the hollow body is terminated in its downstream end by a guide portion for guiding the sliding assembly when it goes from its first position to its second position. The guide portion serves to position the conductive sliding split tube appropriately when it is in its second position. When, in this second position, the electric switch is to close one or more branch circuits, the guide portion serves to ensure reliable electrical contact of good quality between certain electrically conductive tabs and the conductive portion(s) of the sliding assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood and other advantages therefore appear more clearly in the light of the following description of embodiments of an electric switch in accordance with the principle of the invention, given purely as examples and described with reference to the accompanying drawings, in which: 
         FIGS. 1A and 1B  are diagrammatic longitudinal section views showing the structure and the operation of an electric switch forming a circuit breaker; 
         FIG. 2  is an exploded perspective view of one possible technological embodiment of an electric switch as shown in  FIGS. 1A and 1B ; 
         FIGS. 3A to 3C  are diagrammatic views showing the structure and the operation of another embodiment; 
         FIGS. 4A to 4C  are views similar to  FIGS. 3A to 3C  showing yet another variant; and 
         FIG. 5  shows yet another variant piston suitable for use with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     With reference more particularly to  FIGS. 1 and 2 , there can be seen a first embodiment of an electric switch  11  in accordance with the invention and in this example constituting more particularly a circuit breaker for any electrical circuit connected to two primary electrically conductive tabs  13  and  14  in the meaning as defined above. 
     The circuit breaker switch  11  has a hollow body  16  of electrically insulating material defining a cavity  19 , an actuator  23 , and the two primary electrically conductive tabs  13  and  14  projecting into the cavity  19 . 
     The electric switch  11  also has a sliding assembly  20  suitable for being moved inside the cavity. In the example shown, the cavity  19  is cylindrical and the sliding assembly  20  is itself essentially cylindrical. 
     The sliding assembly  20  comprises a split tube  21  having at least one conductive portion. In the example shown in  FIGS. 1 and 2 , the split tube  21  is entirely conductive. 
     The sliding assembly  20  also has a slide  22  of insulating material forming a kind of piston and adapted to move inside the cavity so as to entrain the split tube  21  therewith. 
     In the example shown, the actuator  23  is a pyrotechnic gas generator of conventional type installed in the hollow body so as to communicate with the cavity  19 . 
     A gas expansion chamber  25  is defined between the pyrotechnic gas generator  23  and one of the axial end faces of the piston  22 . More particularly, in the example shown, the piston  22  has a cavity  26  in its upstream face that faces towards the gas generator  23 , and the cavity  26  constitutes a portion of the gas expansion chamber  25 . 
     In the initial position in which the slide  22  is practically in contact with the actuator  23 , i.e. with the expansion chamber  25  reduced to its minimum volume, the two electrically conductive tabs  13  and  14  are electrically connected together via the split tube  21  in a first position referred to as an “initial” position. Electrical contact is established via the conductive portion of the split tube  21 , i.e. the entire tube in this example. 
     As shown, the split tube  21  moves towards a second position in the cavity ( FIG. 1B ) under the effect of the actuator  23 , i.e. when the pyrotechnic gas generator is fired, and under such circumstances, the electrical connection between the two conductive tabs  13  and  14  is broken such that the upstream primary electrical conductive tab  13  is separated from the split tube  21 . 
     According to a remarkable characteristic of the invention, the two conductive tabs comprise two rings  13   a  and  14   a  on the same axis that are axially offset along the travel direction of the sliding assembly  20 , and these rings  13   a  and  14   a  are at least in tight contact with the conductive portion of the sliding assembly (in this example the split tube  21 ) when it is in said first position. In this example, the inside faces of the rings  13   a  and  14   a  are flush with the wall of the cavity  19 . When the sliding assembly is in its second position, the ring  13   a  is separate from the conductive portion of the sliding assembly (i.e. the split tube  21 ). 
     Advantageously, in said first position, the split tube  21  is engaged as a force fit between the rings  13   a  and  14   a  of said primary conductive tabs  13  and  14 , thereby guaranteeing excellent electrical connection between said primary conductive tabs throughout the period prior to actuating the electric switch  11 . 
       FIG. 2  shows how it is possible in simple and inexpensive manner to make an electric switch in accordance with the above-described circuit breaker. 
     The hollow body  16  is defined by assembling together two housing elements  30  and  31 , respectively a left element  30  and a right element  31 . 
     The housing element  30  includes two tapped blind holes  32  surmounted by a laterally open indentation  33  of shape that is defined to receive a portion of each electrically conductive tab  13 ,  14  and a portion of a gas generator support  12 . 
     Each electrically conductive tab has a ring  13   a ,  14   a  extended laterally by a connection bar  13   b ,  14   b  that projects outside the insulating hollow body so as to be capable of being connected to the electrical circuit external to the circuit breaker. 
     The second housing element  31  has two through holes  36  enabling fastener bolts  37  to be inserted. In the same manner as the first housing element  30 , it likewise has a laterally open indentation  34  of shape that is defined to receive a portion of each electrically conductive tab  13 ,  14  and a portion of the gas generator support  12 . 
     The gas generator support  12  is mounted between the two housing elements  30 ,  31  and has a hole  38  that receives the gas generator  23  at its end. The gas generator  23  is mounted inside said support  12  so as to define the gas expansion chamber  25  inside said hole  38 . 
     As mentioned above, the split tube  21  is engaged by force in each of the two rings  13   a  and  14   a.    
     In this manner, in said first or “initial” position, the two rings  13   a  and  14   a  that are axially offset on the same axis are electrically interconnected by the split metal tube  21 . 
     In the example shown, the slide  22  is inserted inside the sliding split tube  21 . The slide  22  thus performs the following functions: 
     A first portion or upstream portion  41  of cylindrical shape and of diameter substantially equal to the diameter of the cavity  19  slides along the inside face of said cavity. 
     In its upstream face that faces upwards in  FIGS. 1 and 2 , the first portion  41  includes a cavity  26 , in this example likewise substantially cylindrical, that defines a portion of the initial volume of the expansion chamber  25 . 
     As can be seen in  FIG. 2 , the first portion  41  has two circumferential grooves  61  and  62  that are axially spaced apart from each other, each receiving a sealing O-ring  63 ,  64 . Thus, the piston  22  closes the gas expansion chamber  25  and enables pressure to rise quickly in the closed environment of this chamber. The gas generated in the gas expansion chamber  25  is prevented from infiltrating towards the conductive rings  13   a  and  14   a.    
     A notch  65  is advantageously formed in at least one of said grooves and configured to form a calibrated passage for allowing air to escape from the gas expansion chamber while the piston  22  is being mounted in the gas generator support  12 . 
     The piston  22 , which is situated at least in part upstream from the split tube, has the function of transmitting to said tube  21  the pressure force generated by the gas in the gas expansion chamber  25  so as to enable the circuit to be broken by moving said tube  21 . 
     This first portion  41  is extended downstream by a second portion  42  of slightly smaller diameter that is selected to enable it to be inserted, possibly as a force fit, inside the split tube once the split tube has been inserted between the rings  13   a  and  14   a.    
     This second portion may act as a guide element for the split tube while it is moving inside the cavity  19 . 
     In an advantageous embodiment, it may also form an additional clamping element for pressing the split tube against the rings  13   a  and  14   a.    
     After the pyrotechnic gas generator  23  has been triggered, the situation is as shown in  FIG. 1B . The electrical connection between the two tabs  13  and  14  has been interrupted. 
     It should be observed that in this example the piston  22  presents on a portion situated directly upstream from the split tube a diameter that is equal at most to the outside diameter of the tube once inserted between the rings. In the example shown, the diameter of the upstream portion of the piston is even slightly smaller than that of the split tube, such that on entraining the split tube the piston can slide easily between the rings without remaining jammed between them. This is made possible in this example by a small difference in diameter between the furthest upstream portion of the cavity along which the piston slides (formed in this example by the bore of the generator support) and its downstream portion (formed by the housing elements), which is larger and into which the rings project. 
     As can be seen in the drawings, the cavity  19  is extended downstream by a guide portion  45  that serves to guide the split tube  21  when it passes from the first position to the second position, and serves to ensure that it follows a straight path. 
     A damper pad  9  is inserted in the end of the cavity  19 . Where necessary, this damper pad  9  has the function of reducing the impact energy from the conductive split tube  21  and the insulating piston  22  when these two parts come into contact with the end of the switch body  16 . 
     With reference more particularly to  FIGS. 3A to 3C , it may be observed that the electric switch  11 A that forms both a circuit breaker and a changeover switch is obtained in simple manner using the same modules as those described above. 
     More particularly, when the sliding assembly  20  is in the first or “initial” position, the situation from an electrical point of view is as shown in  FIG. 3A , i.e. the two primary electrical conductive tabs  13  and  14  are interconnected by the split tube  21 , as in the above example. 
     Nevertheless, in addition to the two primary conductive tabs  13  and  14 , the electric switch  11 A includes a secondary electrically conductive tab  50  situated downstream from the downstream primary conductive tab  14 , also having a ring  50   a  that is extended on one side by a conductive bar  50   b  that projects outside the body of the switch. 
     When the sliding assembly is in its first position, the secondary conductive tab is disengaged from the split tube  21 . 
     In contrast, when, after the pyrotechnic gas generator  23  has been triggered, the sliding assembly  20  is to be found in its second position ( FIG. 3C ), the downstream primary electrically conductive tab  14  is electrically connected to said secondary electrically conductive tab  50  by the split ring  21 , while the upstream primary electrically conductive tab  13  is separated from the conductive split tube  21 . The length of the split tube  21  is such that, for a short instant, during the stroke of the sliding assembly  20 , all three tabs  13 ,  14 , and  50  are electrically interconnected by the split tube  21 . This is the situation shown in  FIG. 3B . Thus, a branch circuit can be closed prior to the circuit breaker opening. 
       FIGS. 4A to 4C  show another embodiment of a switch  11 B that may be made using components that are generally similar to those shown in  FIG. 2  and in which several groups of pairs of primary conductive tabs that are arranged in line with one another from upstream to downstream can all be associated with a single sliding assembly. In the example, only two groups of such pairs of primary conductive tabs are shown, but it is clear that the device could be “extended” in modular manner to have a larger number of groups of such tabs. 
     There can be seen a hollow body  16  of electrically insulating material defining a cavity  19  that is axially longer than in the above-described embodiments, and a pyrotechnic actuator  23  mounted at one end of the hollow body to define a gas expansion chamber  25  in association with the adjacent end of the piston  22 A. 
     The piston  22 A, which is shown in greater detail in  FIG. 5 , in this example is different in shape from the piston of the above-described embodiment, in that it is not extended by an additional guide portion for penetrating into the split tube. In other words, in this example, the split tube  21 A is dissociated from a movable piston  22 A inside the cavity  19 . The piston  22 A is then interposed between the split tube  21 A and the pyrotechnic gas generator, the expansion chamber  25  being defined between the piston  22 A and the actuator  23 . 
     The piston  22 A, which comprises a single portion  41  of diameter suitable for sliding along the cavity  19 , thus urges the split tube  21 A in an axial direction only for the purpose of moving it from the first position to the second position. 
     In this example, there can be seen a first group of two primary conductive tabs  113  and  114  and a second group of two primary conductive tabs  213  and  214 , and the split tube has a corresponding number, i.e. two in this example, of conductive portions  58  and  59  that are electrically insulated from each other. In this example, the split tube  21 A has two metal portions that are separated by an insulating portion  60  that extends in the initial position between the two groups of pairs of primary conductive tabs. In this way, each of said conductive portions  58 ,  59  interconnects only the conductive tabs of each of the groups while the sliding assembly is in its initial position, as shown in  FIG. 4A . After the pyrotechnic gas generator has been actuated, the situation is that shown in  FIG. 4C , i.e. the split tube  21  is completely disengaged from the upstream primary conductive tab  113  of the first group (the upstream group), the downstream primary conductive tab  114  of the first group is in contact with the upstream primary conductive tab  213  of the second group via the upstream split tube  58 , while the downstream primary conductive tab  214  of the (downstream) second group is in electrical contact with the downstream portion of the split tube  59  but is electrically insulated from all of the other conductive tabs because the insulating portion  60  lies between the two primary conductive tabs of the (downstream) second group. Thus, in this arrangement, a changeover function is performed between the two groups of primary conductive tabs, i.e. the upstream primary conductive tab  213  of the second group acts as a secondary conductive tab relative to the first group. 
     As can be seen in the drawings, said two conductive portions of the split tube  21 A are separated by insulation  60  of thickness that is smaller than the thickness of a conductive tab, and in particular of the upstream conductive tab  213  of the second group. Thus, and as shown in  FIG. 4B , while the sliding assembly is moving, and because contact between the upstream portion of the split tube  21 A and the upstream conductive tab of the first group has not yet been broken, all of the conductive tabs of the two groups are interconnected for a short time interval via the split tube. 
     In all of the embodiments, a passage of small section may advantageously be provided between the cavity  19  and the outside through the body  16  in order to facilitate moving the sliding assembly  20 . 
     In addition, the combustion products from the gas generator may be conductive or may contain metal particles. If the circuit for breaking is under high voltage, an electric arc or metal plating may occur inside the chamber  25  after the piston  22  has moved. The piston  22  is thus advantageously made of an insulating material so that after actuation the two rings  13   a  and  14   a  are separated by an insulating portion.