Patent Publication Number: US-2020279711-A1

Title: Pyrotechnic switching device

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the general field of electrical switching devices, and more particularly to those of the type using pyrotechnic actuation. The invention also relates to an electrical power supply system secured by a device of this type. 
     Pyrotechnic switching devices are known comprising a body in which is present a pyrotechnic initiator configured, when it is triggered, to set in motion a piston provided with a relief in the direction of a conductive bar, to cut through it. Documents WO 2016/038043 and WO 2016/038050 show examples of devices of this type which allow accomplishing switching in the event of excess current in a circuit. 
     It would be desirable to switch the current, not only in the event of excess current, but also when a non-electrical anomaly occurs (a shock for example). There exists therefore a need to dispose of a reliable, compact and low-cost switching solution to accomplish this. 
     Object and Summary of the Invention 
     The present invention therefore has the purpose of mitigating disadvantages of this type by proposing a pyrotechnic switching device comprising a first and a second pyrotechnic initiators, and a body in which are present:
         an electrically conductive portion of which at least a part is present in a chamber present in the body, and   a mobile switching element delimiting the chamber and having an electrically insulating relief which faces the conductive portion.       

     The device also comprises a fuse element connected in series with the conductive portion and configured to trip when the intensity of the current passing through it exceeds a predetermined value, the first initiator being connected to the terminals of the fuse element so that tripping the fuse element actuates the first initiator, each initiator being configured to cause the switching device to switch from a first current conducting configuration to a second current interrupting configuration, the mobile switching element being set in motion toward the conducting portion in order to break it by the impact of the relief during switching from the first to the second configuration. When the current passing through the conducting portion reaches the tripping threshold of the fuse (predetermined current value), all the current then passes through the first initiator, which also causes its tripping and the interruption of the current due to breakage of the conductive portion. When the second initiator is tripped, for example by means of a control element outside the device, the conductive portion is also broken and the current is interrupted. 
     The switching device according to the invention thus allows disposing of the advantages of a switching device tripped automatically by overrunning the current threshold (first initiator), and another switching device tripped by another anomaly (second initiator), without the bulk that mounting two devices of this type in series would produce. The use of two distinct initiators which are then tripped by separate connectors allows avoiding coupling between the fuse element and the control element which would result from the use of a single initiator which would be connected both to a fuse element and to a control element. Coupling of this type could then impair the control element in the event of overrunning the threshold value of the current at which the fuse element is tripped. The device according to the invention is thus reliable, simple and compact in design, and preserves the integrity of the control element which can be connected to the second initiator in the event of tripping in response to overrunning the current threshold. 
     Each initiator can have an output, each output being in communication with a pressurization chamber delimited by the mobile switching element. The mobile switching element can thus separate the pressurization chamber from the chamber in which the conductive portion is present. The mobile switching element can thus be a piston having a cross section of oblong shape in a plane perpendicular to an axis along which it moves in the switching device. 
     In one exemplary embodiment, the mobile switching element can be configured to break the conductive portion by the impact of the relief at a zone distinct from that where the fuse element is present during switching from the first to the second configuration. 
     In one exemplary embodiment, the fuse element can be present inside the body. In particular, the fuse element can be present in the chamber in which the conductive portion is present. 
     In one exemplary embodiment, the fuse element can be present in a second chamber present in the body and distinct from the chamber in which the conductive portion is present. This second chamber can be a cavity present inside the body, for example positioned under the conductive portion. 
     In one exemplary embodiment, the fuse element can be present in an insulating shell containing a powder of an electrically insulating material. 
     In one exemplary embodiment, the fuse element can be applied to the conductive portion. 
     In one exemplary embodiment, the fuse element can consist of a thinned zone of the conducting portion. 
     In one exemplary embodiment, the mobile switching element can comprise at least one second relief facing the conductive portion, and the conductive portion can have at least one guide slot intended to cooperate with the second relief during switching from the first to the second configuration, the second relief being closer to the conductive portion, in the first configuration, than the insulating relief. This type of positioning improves the reliability of switching. In fact, during switching from the first to the second configuration, and before the impact of the insulating relief on the conductive portion, the second relief will engage in the corresponding slot of the conductive portion and will allow the piston to be guided which still holding in position the conductive portion at the time of impact with the piston. In one exemplary embodiment, the second relief can extend transversely relative to the relief which is intended to impact on the conductive portion. In one exemplary embodiment, the second relief can extend from a lower face of the mobile switching element over a greater distance than the distance over which the relief extends which is intended to impact on the conductive portion of said face. 
     In one exemplary embodiment, the device can also comprise an additional fuse element connected in parallel to the conductive portion, said additional fuse element being configured to trip when the intensity of the current passing through it exceeds a predetermined value, said additional fuse element having a pre-arc time greater than the time taken by the switching device to switch from the first configuration to the second configuration. 
     During a normal operation of the system (i.e. when the switching device is in the first configuration), the additional fuse element is conducting, current passes through the conductive portion and the additional fuse element. On the other hand, when the intensity of the current passing through the electrical circuit exceeds the predetermined value for the fuse element connected in series with the conductive portion or when an initiator is tripped by the control element, the switching device switches into the second configuration. The additional fuse element being selected to have a pre-arc time greater than the time taken for disconnecting the conductive portion, the additional fuse element is always conducting at the time when the switching device arrives in the second configuration. In this manner, the additional fuse element short-circuits the switching device, avoiding the appearance of an electric arc within the latter. Secondly, the current circulating in the additional fuse element will melt the latter, which will cause the complete interruption of the electrical current circulating in the circuit. What is meant by “pre-arc time” is, in a manner known per se, the time that the additional fuse element takes to melt and volatilize when a current with an intensity greater than or equal to a predetermined value passes through it. 
     One advantage of the second fuse element is that the formation of an electric arc at the broken conductive portion is avoided, because the current can still circulate in the additional fuse element during a short period before the latter is tripped and interrupts the circuit. In addition, as the additional fuse element is subjected during this instant to the entire intensity circulating in the electrical circuit, its operation is reliable. This advantageously allows improving the reliability of the electrical switching performed. 
     In one embodiment, the switching current of the additional fuse element (predetermined current value) can be equal to a nominal electrical current value defined as being less than or equal to four times the maximum value of current intended to circulate in the device in normal operation. In one embodiment, the switching voltage (or breakdown voltage) of the additional fuse element can be greater than or equal to a nominal voltage value defined as being the maximum voltage value intended to be applied to the terminals of the device in normal operation. 
     The invention also has as its object a secured power supply system comprising at least:
         a switching device like that presented above,   a power supply circuit connected to the switching device, the conductive portion being connected to the power supply circuit, and   a control element configured to actuate the second initiator when an anomaly is detected.       

     In one exemplary embodiment, the anomaly can be a non-electrical anomaly. What is meant by “non-electrical anomaly” is for example a shock, i.e. a sudden movement of the control element to which the switching device can be connected, or overrunning the temperature or pressure threshold in the environment of the control element. 
     The invention also applies to a secured electrical system comprising a secured power supply system as defined above, and a device supplied by said secured power supply system. An electrical installation can comprise a secured electrical system of this type. 
     A secured electrical system of this type can be located, for example, in a motor vehicle, an airplane, a train, a photovoltaic installation, an autonomous domestic installation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will be revealed by the description given below, with reference to the appended drawings which illustrate an embodiment of it free of any limiting character. In the figures: 
         FIG. 1  is an exploded view in perspective of a switching device according to a first embodiment of the invention, 
         FIGS. 2A and 2B  show a switching device according to one embodiment of the invention, respectively in the first and in the second configuration in transverse section along planes IIA and IIB of  FIGS. 3A and 3B ,
           FIGS. 3A and 3B  show longitudinal section views of the switching device respectively in the configurations of  FIGS. 2A and 2B  along longitudinal planes IIIA and IIIB separating the two initiators,       

         FIG. 4  shows a secured electrical system comprising a secured power supply system according to one embodiment of the invention, 
         FIGS. 5 and 6  show respectively a switching device according to a second embodiment of the invention in longitudinal section and the conductive portion used in this embodiment, 
         FIG. 7  shows a switching device according to a third embodiment of the invention in longitudinal section, and 
         FIG. 8  shows a switching device according to a fourth embodiment of the invention within a secured electrical system like that of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an exploded view of a switching device  1  according to a first embodiment of the invention. The illustrated switching device  1  comprises: a body  10 , a pyrotechnic initiation system  20 , a piston  30 , a conductive portion  40 , a fuse element  50 , and a support  60 . The fuse element  50  is, according to the invention, connected in series with the conductive portion  40 . In the example illustrated, the longitudinal direction L corresponds to the direction in which the conductive portion  40  extends in the device  1 . The transverse direction T is perpendicular to the direction L in the plane of the conductive portion  40 . 
     The body  10  comprises two lateral openings  11  on two opposite faces of the body  10  (only one lateral opening  11  is visible in  FIG. 1 ) by which the support  60  can be inserted into the interior of the body  10 , a lower opening  12  ( FIGS. 2A-3B ) by which the piston  30  can be inserted into the interior of the body  10 , and two upper openings  13   a  and  13   b  protruding on an upper face of the body  10 . The pyrotechnic initiation system  20  comprises a first pyrotechnic initiator  21  and a second pyrotechnic initiator  22 , respectively equipped with electrical connectors  21   a  and  22   a  which pass through the openings  13   a  and  13   b . The lateral openings  11  continue in the longitudinal direction L and join one another inside the body  10  to form a housing in which the support  60  is retained in the body  10 . 
     Each of the electrical connectors  21   a  and  22   a  of the pyrotechnic initiators  21  and  22  is configured to initiate a pyrotechnic charge  21   b  and  22   b  to which they are connected. Each pyrotechnic charge  21   b  and  22   b  is, when it is initiated (they can be initiated separately), for example by means of a current passing through the electrical connectors  21   a  or  22   a , capable of generating a pressurization gas by its combustion. According to the invention, the first pyrotechnic initiator  21  is connected, here by means of its connectors  21   a , in parallel with the fuse element  50  (i.e. connected to the terminals of the fuse element  50 ).The second pyrotechnic initiator  22  can be connected by means of its connectors  22   a  to a control element  C  ( FIG. 4 ) configured to actuate the second pyrotechnic initiator  22  when an anomaly is detected. 
     The piston  30 , constituting a mobile switching element within the meaning of the invention, has a cross section of oblong shape in a plane perpendicular to a vertical direction Z of the switching device  1 . The direction Z corresponds to the direction in which the piston  30  moves in the switching device  1 , and here is perpendicular to the directions L and T. Here the switching device  1  comprises a single piston  30 . The piston  30  comprises a circumferential recess  31  in which a seal  32 , for example an O ring seal, is intended to be housed. When the piston  30  is in the switching device  1 , the O ring seal  32  ensures sealing between the body  10  and the piston  30 . The piston  30  can move in the direction Z inside the body  10  between a high position (first position, device in the first configuration), as in  FIGS. 2A and 3A , and a low position (second position, device in the second configuration), as in  FIGS. 2B and 3B .As long as a pyrotechnic initiator  21  or  22  has not been tripped, the piston  30  is held in the high position. Of course, the piston  30  can have a different shape from that illustrated, suited to the shape of the cavity inside the body in which it moves. 
     As illustrated in  FIGS. 2A-2B and 3A-3B , the body  10  comprises a pressurization chamber  14  in communication with the outputs S 1  and S 2  of the pyrotechnic initiators  21  and  22 , and a chamber  15  in which is present the conductive portion  40 . The piston  30  thus hermetically separates the pressurization chamber  14  from the chamber  15  by means of the seal  32 . 
     In conformity with the invention, the piston  30  has an electrically insulating relief. More precisely, the piston  30  comprises here a lower face  34  from which protrudes the relief  33 . The relief  33  is positioned facing the conductive portion  40 . The relief  33  generally extends here in the transverse direction T. The relief  33  has here a dimension in the transverse direction T which is equal to or slightly greater than the dimension, in this same direction T, of the conductive portion  40 . The relief  33  also extends in the direction L and has a nonzero thickness in this direction L. The piston  30  comprises here, on the initiators  21  and  22  side, a skirt  35  delimiting the pressurization chamber  14  and allowing guiding the piston  30  in the body  10 . 
     The conductive portion  40  takes, in the example illustrated, the shape of a plate having a dimension in the longitudinal direction L which is greater than the dimension in this same direction of the body  10  so as to protrude on either side of the switching device  1 , through the lateral openings  11 . In the example illustrated, the conductive portion  40  comprises two guide slots  41  extending here in the longitudinal direction L, which are intended to cooperate with longitudinal reliefs  36  (second reliefs) protruding on the lower face  34  of the piston  30  after the tripping of an initiator  21  or  22 . The longitudinal reliefs  36 , in the first configuration, are closer to the conductive portion  40  than the relief  33 . The cooperation of the reliefs  36  and the slots  41  allows guiding the piston  30  at the moment of breakage of the conductive portion  40  while still holding it in position, which improves the reliability of switching. 
     The fuse element  50  takes, in the example illustrated, the shape of a commercial fuse, i.e. it is present in an insulating shell containing a powder of an electrically insulating material. For example, the fuse element  50  can comprise a fusible wire present in silica powder. The fuse element  50  can, as in the example illustrated, be present outside the body or, as a variant, inside the body, as in the examples of  FIGS. 5 to 7  which will be subsequently described. When it is inside the body, the fuse element  50  can be present in the chamber  15  or in a second chamber distinct from it, as in the example of  FIG. 7  which will be subsequently described. The fuse element  50  can, as in the example illustrated here, be applied to the conductive portion  40  or, as a variant, consist of a thinned zone of the conductive portion, as in the example of  FIGS. 5 and 6  which will be subsequently described. 
     The support  60  takes, in the example illustrated, the shape of a drawer in which the conductive portion  40  is present. In the example illustrated, the support  60  is configured to retain the conductive portion in position in the switching device  1 , for example by providing a corresponding housing there. Here the support  60  is equipped with a recess  61  which extends in the transverse direction T and in which the relief  33  is intended to be received after the tripping of one of the pyrotechnic initiators  21  and  22 , once the conductive portion  40  has been cut. The recess  61  in the support thus allows locking the piston  30  in the second position and ensuring definitive cutting of the conductive portion  40 . Notches  62  corresponding to the longitudinal reliefs  36  can be present in the support  60  to house said reliefs  36  when the device  1  reaches the second configuration. 
     The operation of the device  1  will now be briefly described in connection with  FIGS. 2A-2B and 3A-3B . In  FIGS. 2A and 3A , the switching device  1  is not yet tripped and is in the first configuration, corresponding for example to a storage or transport configuration. In this configuration, the piston  30  is in a first position, or high position. The conductive portion  40  is intact and a current I ( FIG. 3A ) can pass through it. Then, two situations can occur. In a first situation, which is illustrated in  FIGS. 2A-2B and 3A-3B , the current I exceeds the predetermined value or tripping threshold of the fuse element  50  and trips it ( FIG. 3B ), generally by melting it, which has the effect of diverting the entire current to the first pyrotechnic initiator  21 , which then also trips. In a second situation which is not illustrated in the figure, it is the second pyrotechnic initiator  22  which is tripped in response to an outside signal originating for example from a control element  C  ( FIG. 4 ) in response to an anomaly. The tripping of one or the other pyrotechnic initiators  21  or  22  then generates a combustion gas which pressurizes the pressurization chamber  14  and sets the piston  30  in motion in the direction Z toward the conductive portion  40 . The piston  30  then cuts by impact the conductive portion  40  ( FIGS. 2B and 3B ) and interrupts the current in the switching device  1 . The switching device  1  then finds itself in the second configuration, the relief  33  of the piston being received in the recess  61  of the support  60 . In all the examples illustrated, the piston  30  breaks the conductive portion by the impact of the relief at a zone distinct from that where the fuse element  50  is present. In a non-illustrated variant, the piston  30  can cut the conductive portion by the impact of the relief at the zone where the fuse element is present, for example when the fuse element constitutes a thinned zone of the conductive portion. 
       FIG. 4  shows an example of a secured electrical system  100  implementing a switching device  1  according to one embodiment of the invention. The secured electrical system  100  comprises a secured power supply system  110  comprising a switching device  1  (shown very schematically) and a power supply circuit  111 . The power supply circuit  111  comprises here an electrical generator  G  connected to one end of the conductive portion of the switching device  1 . The electrical generator  G  can for example be a battery or an alternator. In the switching device  1 , the fuse element  50  is connected in series with the conductive portion  40 , and the first pyrotechnic initiator  21  is connected in parallel, by means of its connectors  21   a , to the fuse element  50 . The secured power supply system  110  also comprises a control element  C  configured to actuate the second pyrotechnic initiator  22  when an anomaly is detected. The control element  C  is connected to the second pyrotechnic initiator  22  by means of the connectors  22   a . The anomaly in response to which the control element  C  can trip the second initiator  22  can be a non-electrical anomaly such as the detection of a shock, for example a sudden deceleration of the control element, a change of temperature, of pressure, etc. In the event of the detection of an anomaly, the control element  C  is able to send an electrical current to the second pyrotechnic initiator  22  for tripping it in order to interrupt the current, as previously described. Finally, the secured electrical system  100  comprises an electrical device  D  connected to the fuse element  50  of the switching device  1  to be supplied by the secured power supply system  110 . By way of an example, a motor vehicle can comprise a secured electrical system  100 . 
     The switching device  1  described previously has a single conductive portion  40 . However, it does not depart from the scope of the present invention if the device has several conductive portions, for example two or three conductive portions, which can be broken simultaneously by the relief of the mobile switching element. 
       FIGS. 5 and 6  show respectively a switching device  1 ′ according to a second embodiment of the invention in longitudinal section, and the conductive portion  40  that it comprises. The device  1 ′ differs from the device  1  described previously by the fact that the fuse element  50 ′ constitutes a thinned zone of the conductive portion  40 , as can be seen better in  FIG. 6 . Electrical wires (shown by dotted lines) can thus be provided in the device  1 ′ to connect the connectors  21   a  of the first initiator  21  in parallel with the fuse element  50 ′, as illustrated in  FIG. 5 . The switching device  1 ′ operates in the same manner as the device  1  described previously. 
     Finally,  FIG. 7  shows a switching device  1 ″ according to a third embodiment of the invention, in longitudinal section. The device  1 ″ differs from the device  1  described previously by the fact that the fuse element  50  is present inside the body  10  and in a second chamber, consisting here of a cavity formed by the opening  12  and delimited by the support  60 , distinct from the chamber  15 . As before, electrical wires (shown by dotted lines) can be provided in the device  1 ″ to connect the connectors  21   a  of the first initiator  21  in parallel with the fuse element  50 , as shown in  FIG. 7 . The switching device  1 ″ operates in the same manner as the devices  1  and  1 ′ described previously. 
       FIG. 8  shows a secured electrical system  100  similar to that illustrated in  FIG. 4 . Thus identical reference symbols between  FIGS. 4 and 8  designate identical features. The switching device  1 ′″ according to a fourth embodiment of the invention, present in the system  100  of  FIG. 8 , also comprises a fuse element  70  (additional fuse element) connected in parallel to the conductive portion  40  in order to prevent the formation of an electrical arc at the conductive portion  40  when this breaks. The fuse element  70  is connected directly to the two ends of the conductive portion  40 . The fuse element  70  can have a cut-off current, i.e. a predetermined current value beginning at which it trips, less than or equal to four times the maximum value of current intended to circulate in the electrical circuit during normal operation; and a cut-off voltage or breakdown voltage greater than or equal to the maximum voltage value intended to be applied to the terminals of the conductive portion  40  in normal operation.