Pyrotechnic circuit breaker and motor vehicle with such a circuit breaker

Description

Technical field of the invention

[0001] The present invention relates generally to a pyrotechnic circuit breaker intended to be mounted on a motor vehicle, and in particular in a power electrical circuit of a motor vehicle, for example a hybrid vehicle or an electric vehicle. State of the art

[0002] It is known in the prior art for circuit breaker devices, such as the one described in US patent 20130175144, that proposes the use of a flowable insulating material. However, this system has the disadvantage of requiring a large quantity of flowable insulating material, which can lead to leakage. In the case of a material containing silicone, precautions and permits will be necessary for automotive use (due to incompatibility with paint, for example). Furthermore, the applicant noted that such a flowable insulating material can result in longer opening times and / or degraded performance during circuit breaker operation (the time taken to effectively interrupt the flow of a high-power current (e.g., at least 100 A / 100 V, or 800 A / 450 V)).Finally, it is important to be able to guarantee good insulation resistance after operation.

[0003] Document WO2020099486A1 discloses a pyrotechnic circuit breaker with an internal plastic wall that may contain reinforcing fibers, such as glass fibers. With such a device, the applicant has observed that the insulation resistances after operation may not be sufficient to meet specific or stringent requirements. Description of the invention

[0004] One object of the present invention is to address the disadvantages of the prior art mentioned above and in particular, first of all, to provide a pyrotechnic circuit breaker that is simple to manufacture, has high cutting capabilities, a fast opening time during operation, and good insulation resistance after opening.

[0005] For this purpose, a first aspect of the invention relates to a pyrotechnic circuit breaker according to claim 1.

[0006] According to the claimed design, the circuit breaker comprises a wall arranged within the internal chamber, i.e., opposite the section to be interrupted, and containing a flame retardant. The applicant observed that the insulation resistances after operation were higher than those measured on circuit breakers with the same geometric configuration but without a flame retardant material. In other words, incorporating a flame retardant into the material of one of the walls exposed to the electric arc formed during interruption significantly reduces leakage currents after the interruption.

[0007] In other words, the internal chamber includes or contains at least one internal surface formed by a wall: with a plastic material containing a flame retardant, or with a plastic material containing an additive chosen to be a flame retardant. Depending on this implementation, the flame retardant additive can be directly integrated or incorporated into the granules that will be melted to be used, for example, to inject the wall surface into the internal chamber.

[0008] According to one embodiment, said plastic material comprising the flame retardant can be a polymer, such as a polyamide, and preferably a polyphthalamide (PA 6T / 66).

[0009] According to the invention, said plastic material comprising the flame retardant can be a matrix-forming polymer, and comprising a filler material, such as fibers, preferably inorganic fibers, for example glass fibers, in a proportion from 10% to 70% by weight and preferably in a proportion from 45% to 55% by weight.

[0010] According to one embodiment, said plastic material comprising the flame retardant can self-extinguish after 10 seconds, during a flammability test according to UL94 (6th edition of March 28, 2013) carried out on a vertical test specimen, with particle loss permitted as long as the lost particles are not ignited.

[0011] According to one embodiment, the flame retardant may be a non-halogenated compound, selected from: the conversion or reaction products of melamine with cyanuric acid, the condensation products of melamine, the conversion or reaction products of melamine with polyphosphoric acid, the conversion or reaction products of the condensation products of melamine with polyphosphoric acid, metallic phosphinates, phosphoric acid esters, mixtures of these materials.

[0012] According to one embodiment, the flame retardant may be a non-halogenated compound, selected from the following compounds and mixtures thereof: melamine cyanurate, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, melem phosphate (i.e. 2,5,8-triaminoheptazine phosphate), melem pyrophosphate, dimelamine pyrophosphate, dimelamine phosphate, melem polyphosphate, phosphaphenanthrenes, metal hydroxides, phosphinic acid salts, diphosphinic acid salts.

[0013] It can be noted that glass fibers used in a known way to reinforce a plastic material, even if they do not burn or burn with difficulty, will in no way limit or delay an ignition or combustion of said plastic material.

[0014] In one embodiment, the pyrotechnic circuit breaker may include a base portion formed from a second plastic material, and said plastic material containing the flame retardant may be attached to or overmolded onto the base portion. Such an implementation allows the plastic material containing the flame retardant to be located only where it will be properly exposed to the electric arc, without requiring any additional parts.

[0015] According to one embodiment, the opening mechanism may comprise: An opening body formed from a second plastic material, with an exposed face formed by the plastic material containing the flame retardant, either overmolded or attached to the opening body and positioned opposite the part to be opened and / or the side of the internal chamber. This placement on the opening mechanism ensures that the plastic material containing the flame retardant is as close as possible to the electric arc, and is therefore fully exposed to it, thus guaranteeing high and reproducible insulation resistances.

[0016] According to one embodiment, said second material may be a polyamide, preferably a polyphthalamide (PA 6.T / XT) forming a matrix, and may include glass fibers in a proportion ranging from 40% to 50% by weight. The second material provides a robust opening body that is highly resistant to mechanical stress.

[0017] In one embodiment, the pyrotechnic circuit breaker can be arranged to generate an electric arc between two separate conductor sections when the opening mechanism moves from its initial to a final position, while the circuit breaker is connected to a live electrical circuit. The plastic material containing the flame retardant can be arranged to be ablated by the electric arc. Specifically, the plastic material containing the flame retardant, arranged for ablation, is transformed (for example, sublimated) by the intense heat flux of the electric arc. This ablated material can then condense or deposit on the walls of the internal chamber, providing high insulation resistance. Furthermore, this implementation can modify the composition and conductivity of the electric arc plasma, thereby increasing the electric arc voltage.Such electrical arcs can occur when the circuit breaker is connected to a live electrical circuit, with voltages ranging from 0V to 1000V and currents ranging from 0A to 25000A on inductive loads up to 2500µH (microhenries) for a current below 500A and up to 5µH for a current of 25000A. The circuit breaker according to the invention allows for reliable current interruption in less than 10ms and even less than 5ms, permanently, because the circuit breaker, comprising a pyrotechnic actuator, can only be used once. Once activated, the circuit breaker also exhibits good insulation resistance.

[0018] In one embodiment, the pyrotechnic circuit breaker may include at least one passage arranged to guide the electric arc between the two separate conductor portions, and the plastic material containing the flame retardant may be arranged to form or at least partially delimit the passage. In this embodiment, the plastic material containing the flame retardant is necessarily exposed to the electric arc.

[0019] According to one embodiment, the passage can be at least partially formed on the opening member.

[0020] In one embodiment, the internal chamber may include or contain at least one wall formed from a third plastic material containing silicone. According to this embodiment, at least one other wall of the internal chamber contains silicone. The applicant has observed that adding silicone to a material forming the wall ensures high insulation resistance after use. Furthermore, the applicant has observed that if another wall contains the flame retardant, the effect on insulation resistance is amplified.

[0021] In one embodiment, the pyrotechnic circuit breaker may include at least one support, and the third plastic material containing silicone may be overmolded or attached to the support. This implementation allows the third plastic material containing silicone to be located only where it will have a significant effect on the insulation resistance, without requiring an additional component. In another embodiment, the support may include a portion of the electrical conductor.

[0022] According to one embodiment, the support may include a portion of the housing.

[0023] According to one embodiment, the support may include a portion of the opening member.

[0024] According to one embodiment, the wall formed with the third plastic material containing silicone can support a leakage current path between the two separate conductor portions after opening, and preferably the shortest leakage current path between the two separate conductor portions after opening. Such an implementation, with the addition of silicone in the wall supporting the shortest leakage current path, effectively interrupts the leakage current path that would otherwise be used by a leakage current.

[0025] In one embodiment, the wall formed with the third plastic material containing silicone may cover less than 50% of the total surface area of ​​the internal chamber. This implementation makes it possible to limit the use or addition of silicone to only where it will have a significant effect on the insulation resistances.

[0026] According to one embodiment, the third plastic material comprising silicone may comprise a polyamide-type polymer, preferably a polyphthalamide of the PA6T / XT type.

[0027] According to one embodiment, the third plastic material comprising silicone may comprise silicone and / or polysiloxane, in a proportion ranging from 3.5% to 6.5% by weight, and preferably from 4.25% to 5.75% by weight.

[0028] According to one embodiment, once the opening member is in the final position, an insulation resistance between the connection terminals can be greater than 30Mohms, preferably greater than 50Mohms, preferably greater than 100Mohms, preferably greater than 500Mohms, and very preferably greater than 1Gohms.

[0029] Another aspect of the invention relates to a method for manufacturing a circuit breaker according to the first aspect, comprising the steps of: to form a housing, to form an internal electrical circuit connecting the two connection terminals and formed, for example, by an electrical conductor, to provide a movable opening member arranged to open a portion of the internal electrical circuit during movement between an initial position and a final position, so as to form at least two distinct conductor portions after opening, to provide a pyrotechnic actuator arranged to move the opening member from the initial position to the final position, to form an internal chamber receiving the portion to be opened, characterized in that the process includes a step of forming the internal chamber with at least one wall formed with a plastic material comprising silicone, by adding to a first raw material, for example in granules, intended to form the internal chamber a second raw material, for example in granules, comprising between 40% and 60% by weight of silicone.

[0030] In other words, the process according to the invention includes a step of mixing, before the manufacture of the inner chamber, the first raw material, for example in granules, intended to form the inner chamber, with the second raw material, for example in granules, comprising between 40% and 60% by weight of silicone. Typically, the wall containing the silicone is formed by an injection-molding process, and the manufacturing process includes a step of preparing the material to be injected by mixing two types of granules: the first raw material and the second raw material containing the silicone. Therefore, there is no need to prepare or handle pure silicone, simply solid granules already containing the silicone. This implementation allows for a simple process.

[0031] Another aspect of the invention relates to a motor vehicle comprising at least one circuit breaker according to the first aspect. Description of the figures

[0032] Other features and advantages of the present invention will become more apparent upon reading the following detailed description of an embodiment of the invention given by way of non-limiting example and illustrated by the accompanying drawings, in which: [ Fig. 1 ] represents a cross-sectional view of a pyrotechnic circuit breaker, comprising in particular a housing through which an electrical conductor passes, forming an internal electrical circuit, a pyrotechnic actuator, and an opening device arranged to open the internal electrical circuit when the pyrotechnic actuator is activated or triggered; Fig. 2 ] represents a detail of the circuit breaker housing of the figure 1 ; Fig. 3 ] represents a detail of the circuit breaker opening mechanism of the figure 1 ; Fig. 4 ] represents a detail of a cross-section of the circuit breaker of the figure 1after actuation or triggering of the pyrotechnic actuator; [ Fig. 5 ] schematically represents a top view cross-section of the circuit breaker of the figure 1 . Detailed description of implementation method(s)

[0033] There figure 1 represents a circuit breaker including, in particular: a housing 10 formed by a lower housing portion 12 and an upper housing portion 11, two connection terminals 21 and 22, an internal electrical circuit connecting the two connection terminals 21 and 22 and formed by an electrical conductor 31, an opening member 40, movable and arranged to open a portion to be opened 31A of the internal electrical circuit during a movement between an initial position (according to the figure 1 ) and a final position (according to the figure 4 ), so as to form at least two distinct conductor portions 32 and 33 (visible figure 4) after opening, a pyrotechnic actuator 50 arranged to move the opening member 40 from the initial position to the final position, an internal chamber 60 (comprising a lower chamber 62 and an upper chamber 61), defined by one or more internal wall(s) formed in the housing 10, and receiving the part to be opened 31A, coolers 70 arranged inside the housing 10 and defined to lower the gas temperatures during operation and thus increase the cutting capacity of the circuit breaker.

[0034] The circuit breaker of the figure 1This circuit breaker is typically integrated into the power circuit of a motor vehicle (an electric vehicle, for example) and can be used to disconnect the power circuit in an emergency. One of its functions is therefore to be able to quickly disconnect a power circuit, even when high currents are present (more than 500 amps, for example). Another function of this circuit breaker is to ensure good insulation resistance between connection terminals 21 and 22 after the internal electrical circuit has been opened.

[0035] To perform the opening function, the pyrotechnic actuator 50 (typically an electro-pyrotechnic igniter) is triggered and a high pressure is generated in the space between the pyrotechnic actuator 50 and the opening member 40, which pushes the latter upwards. figure 1 , to move from the initial position shown to the final position of the figure 4 .

[0036] During this movement, the opening element 40 comes into contact with the section of the electrical conductor 31A to be opened, thus opening the internal electrical circuit by cutting the electrical conductor 31 through mechanical shearing. Alternatively, however, the opening can be achieved by pushing one of two initially separate strands, which are in contact with each other, to separate them.

[0037] As shown by figure 3 The opening member 40 comprises two projections 45, separated by a groove 46, which form knives for cutting the part to be opened 31A. In detail, and as shown in the figure 1 , the part to be opened 31A includes a central portion supported by a return 13 of the upper housing portion 11, engaged with a bar 14 overmolded on the central portion of the part to be opened 31A and integral with an overmolded body 15, overmolded on the electrical conductor 31.

[0038] During the movement of the opening member 40 from its initial position to its final position, the projections 45 of the opening member 40 bear against the unsupported portions of the electrical conductor 31 and shear it on either side of the bar 14 and the return 13 (at the level of the section to be opened 31A opposite the upper chamber 61). Alternatively, however, a single projection 45 or more than two projections 45 may be provided, the number of projections 45 defining the number of cuts made on the electrical conductor 31 during the movement of the opening member 40.

[0039] As shown by figure 4 , the shear of the electrical conductor 31 form: two distinct lateral portions 32 each having an internal end 34 in the internal chamber 60 (and in particular in the upper chamber 61), and a central portion 33, which remained engaged with the bar 14.

[0040] Furthermore, at the very beginning of the opening, when the internal ends 34 are still close to the central portion 33, an electric arc can form (depending on whether current flows through the electrical conductor 31 or not) between each internal end 34 and the central portion 33, at the level of an arc path TA represented by dashed lines. figure 4 During the movement from the initial position to the final position, the opening member 40 pushes and causes a flexion of each distinct lateral part 32, so that the arc path TA "strets" or "lengthens" to present at the end of operation a free distance sufficient to guarantee an extinction of the electric arc and a rapid breaking or opening of the internal electrical circuit.

[0041] THE figures 2 And 3show the mounting of the opening member 40 in the housing 10, and in particular, guide units are provided between the opening member 40 and the housing 10, at the level of the overmolded body 15. Indeed, the opening member 40 ( figure 3 ) is provided with lateral projections 43 forming guide protuberances, and the overmolded body 15 with lateral grooves 613 forming guide grooves, formed in lateral walls 611 of the upper chamber 61 (visible figure 2 ).

[0042] The opening element 40 is therefore mounted in a sliding or translational connection relative to the housing 10 and slides during its movement from the initial position to the final position, which provides reproducible and controlled operation and final position to guarantee rapid opening and arc extinction at the end of operation with sufficient free distance.

[0043] However, the operation of the pyrotechnic actuator 50 can generate many hot particles and gases which are projected into the internal chamber 60, and which typically coat or condense on the walls of the latter, and in particular the walls 611, the lateral projections 43 and the lateral grooves 613. Such deposits can form a conductive or weakly conductive layer of electricity, and an insulation resistance, after opening of the electrical conductor 31, can be affected.

[0044] In addition, the electric arc can remove material by ablation from the opening member 40 and / or the housing 10 (return 13 or bar 14 in particular), which can generate gases or particles which will also cover and / or condense on the walls of the internal chamber 60 and also affect the insulation resistance.

[0045] Such insulation resistance, measured after operation, between connection terminals 21 and 22 must be high, to ensure an absence of leakage current between connection terminals 21 and 22 after opening of the internal electrical circuit of the circuit breaker.

[0046] Such leakage currents typically travel along leakage current paths between separate post-opening conductor portions, which run along the inner wall of the inner chamber 60.

[0047] There figure 5 shows a schematic cross-section (therefore not showing all the details of the figure 1 ) of the circuit breaker of the figure 1 after opening, in a plane passing through the upper face of the electrical conductor 31, seen from above.

[0048] The electrical conductor 31 has therefore been opened into three distinct conductor portions, i.e. two distinct lateral portions 32 and a central portion 33. The central portion 33 is separated from the two distinct lateral portions 32 by the lateral projections 45 of the opening member 40.

[0049] Detail A and detail B of the figure 5 show that a leakage current can travel along a CCF leakage current path formed along the inner wall of the inner chamber 60, in particular between the lower corner 32A of the separate lateral portion 32 and the lower corner 33A of the central portion 33, which is the shortest leakage current path.

[0050] It should be noted that the function of providing good insulation resistance must be ensured after operation, once the electrical conductor 31 is broken or opened. Typically, a leakage current cannot be established along the arc path TA because the resistivity of air is too high. Consequently, a leakage current can only travel along the walls of the circuit breaker, in particular the internal walls of the internal chamber 60 or the walls of the opening mechanism 40, and preferably along the shortest path, which has the lowest insulation resistance.

[0051] As shown in details A and B of the figure 5The CCF leakage current path runs or extends along the wall of the inner chamber 60. In practice, it is expected or desired that the insulation resistance between the connection terminals be greater than 30Mohms, preferably greater than 50Mohms, preferably greater than 100Mohms, preferably greater than 500Mohms, and very preferably greater than 1Gohms, even if particles or condensed gases have been deposited on the inner wall of the inner chamber.

[0052] To ensure good insulation resistance, one alternative solution is to incorporate a wall made of a flame-retardant plastic material into the internal chamber 60. The applicant has observed that adding a flame retardant, particularly to a wall exposed to the electric arc during the circuit breaker's operation, significantly increases insulation resistance after operation.

[0053] The plastic material containing the flame retardant can typically be a polyamide, and preferably a polyphthalamide (such as PA 6T / 66). Reinforcing fibers, for example glass fibers, can be provided in a ratio of 45% to 55% by weight.

[0054] The flame retardant is typically a non-halogenated compound, selected from the following materials and mixtures thereof: the conversion or reaction products of melamine with cyanuric acid, the condensation products of melamine, the conversion or reaction products of melamine with polyphosphoric acid, the conversion or reaction products of the condensation products of melamine with polyphosphoric acid, metallic phosphinates, phosphoric acid esters.

[0055] In particular, it can be predicted that the flame retardant is a non-halogenated compound, selected from the following compounds and mixtures thereof: melamine cyanurate, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, melem phosphate, melem pyrophosphate, dimelamine pyrophosphate, dimelamine phosphate, melem polyphosphate, phosphaphenanthrenes, metal hydroxides, phosphinic acid salts, diphosphinic acid salts.

[0056] The plastic material comprising the flame retardant may comprise the flame retardant between 2% and 30% by mass, and preferably between 5% and 30% by mass and more preferably between 8% and 25% by mass.

[0057] The flame retardant may further comprise at least one synergist (or synergistic compound, which further enhances resistance to ignition), said at least one synergist being selected from the group consisting of nitrogen-containing compounds, nitrogen- and phosphorus-containing compounds, metal borates, metal carbonates, metal hydroxides, metal hydroxyoxides, metal nitrides, metal oxides, metal phosphates, metal sulfides, metal stannates, metal hydroxystannates, silicates, zeolites, basic zinc silicates, silicic acids and their combinations, in particular triazine derivatives, melamine, guanidine, guanidine derivatives, biuret, triuret, tartrazine, glycoluril, acetoguanamine, butyroguanamine, caprinoguanamine, benzoguanamine, melamine derivatives of acid cyanuric acid,melamine derivatives of isocyanuric acid, melamine cyanurate, melamine condensation products, melamine pyrophosphate, pyrophosphates of melamine condensation products, dimelamine phosphate, dimelamine pyrophosphate, melamine polyphosphate, dicyandiamide, ammonium polyphosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, polyphosphates of melamine condensation products, melamine sulfate, allantoin, aluminum hydroxide, synthetic aluminum hydroxide, synthetic meta-aluminum hydroxide, natural aluminum hydroxide, natural meta-aluminum oxide, aluminum oxide, calcium borate, calcium carbonate, calcium magnesium carbonate, calcium oxide, calcium sulfide, iron oxide, magnesium borate, magnesium carbonate, magnesium hydroxide, magnesium nitride, magnesium oxide, magnesium sulfide, manganese hydroxide, oxide manganese, titanium nitride,titanium dioxide, zinc borate, zinc metaborate, zinc carbonate, zinc hydroxide, zinc nitride, zinc oxide, zinc phosphate, zinc sulfide, zinc stannate, zinc hydroxystannate, basic zinc silicate, hydrated tin oxide and their combinations.

[0058] Typically, the plastic material containing the flame retardant self-extinguishes after 10 seconds in a flammability test conducted according to UL94 (6th edition, March 28, 2013) on a vertical specimen, with some particle loss permitted as long as the lost particles do not ignite. Specifically, the specimen is 5" (127 mm) long and 0.5" (12.7 mm) wide. Its thickness must not exceed 0.5" (12.7 mm). It is secured at 1 / 4 of its upper end in a vertical position. A wire mesh covered with surgical cotton is placed 12" (305 mm) below the specimen. The burner is set to produce a 3 / 4" (19 mm) blue flame. This flame is directed from below onto the lower edge of the plastic sample at a distance of 3 / 8" (9.5 mm). It is applied for 10 seconds, then removed. The burning time of the sample is measured.As soon as combustion stops, the flame is reapplied for 10 seconds. Immediately after removal, the combustion and incandescence times are measured again. The complete test is performed on five samples.

[0059] The tested material is classified as UL 94 VO if: A) None of the five samples burns for more than 10 seconds after the burner flame is removed. B) The total burning time across all 5 tests does not exceed 25 seconds. C) None of the tested samples burns, either by flame or incandescence, down to the holding jaw. D) No incandescent droplets, capable of igniting the cotton placed below, fall from any sample. E) No sample exhibits an incandescent time exceeding 30 seconds.

[0060] In the example shown, the opening element 40 can be provided with an opening body 41 (forming a base part), onto which an exposed face 42, formed from the plastic material containing the flame retardant, is overmolded. Alternatively, the plastic material containing the flame retardant could be provided on another wall opening into the internal chamber, such as on the housing 10 or on the overmolded body 15.

[0061] The basic part, i.e. here the opening body 41, can be a second plastic material, such as a polyamide, preferably a polyphthalamide like PA 6.T / XT forming a matrix, and comprising glass fibers, in a proportion ranging from 40% to 50% by weight.

[0062] For example, after functional tests (interrupting a live circuit) carried out under various conditions, insulation resistances were measured on reference circuit breakers and on circuit breakers with an opening element incorporating a flame retardant (to form an exposed face 42 applied to the opening element 40). The results are shown in Tables 1, 2, and 3: Tests carried out under 450V / 8000A / 15µH / +125°C [Table 1] Reference part - Insulation resistance (MOhms) Part with flame retardant - Insulation resistance (MOhms) N°1 15.3 >10000 N°2 4.6 >10000 N°3 8.7 >10000 Tests performed under 475V / 8000A / 20µH / +125°C [Table 2] Reference part - Insulation resistance (MOhms) Part with flame retardant - Insulation resistance (MOhms) N°1 0.49 15.40 N°2 0.73 16.70 N°3 0.54 180 Tests performed under 450V / 8000A / 20µH / +125°C [Table 3] Reference part - Insulation resistance (MOhms) Part with flame retardant - Insulation resistance (MOhms) N°1 1.8 64.0 N°2 1.8 592.0 N°3 0.9 131.0 N°4 2.1 82.7

[0063] It can be noted that in each series of tests, the insulation resistances after opening are significantly higher with parts whose internal chamber includes an arc-exposed surface formed by the material containing the flame retardant, than on reference parts not containing flame retardant.

[0064] It should be noted that the plastic material containing the flame retardant is positioned as close as possible to the arc path TA, and for this purpose, a passage 44 is provided on the opening member 40 to guide the electric arc. This passage 44 is formed directly in the plastic material containing the flame retardant. In practice, the passage 44 is a small groove (a few tenths of a millimeter in width and / or depth) made in the plastic material containing the flame retardant, to provide a free space even when the opening member 40 is in its final position against the return 13. Therefore, an electric arc will preferentially pass through this passage 44 and remove the plastic material containing the flame retardant by ablation.

[0065] To ensure good insulation resistance, a second alternative could be proposed: the internal chamber 60 could be constructed with a third type of plastic containing silicone. The applicant has observed that adding silicone, particularly to a wall through which leakage current might flow after the circuit breaker has been activated, significantly increases the insulation resistance after operation.

[0066] In particular, the third silicone-containing plastic material comprises a polyamide-type polymer, preferably a polyphthalamide, such as PA6T / XT. Specifically, the third silicone-containing plastic material comprises silicone and / or polysiloxane, in a proportion ranging from 3.5% to 6.5% by weight, and preferably from 4.25% to 5.75% by weight.

[0067] In the example shown, it can be anticipated that the third plastic material, including silicone, will be used for overmolding the electrical conductor 31, that is, to create the visible overmolded body 15 figure 1 .

[0068] Indeed, according to the embodiment shown here, the shortest leakage current path is located on the wall of this component (the overmolded body 15), as explained above with reference to the figure 5 However, it would be possible to add silicone to other parts forming walls contained within the internal chamber 60, such as the housing 10 or the cutting element 40.

[0069] The applicant discovered that adding silicone to this overmolding increased insulation resistance. For example, after functional tests (interrupting a live circuit), insulation resistances were measured on reference circuit breakers and on circuit breakers with an overmolded body containing 10% silicone. The results are shown in Table 4: Tests carried out at 450V / 8000A / 20µH / +125°C [Table 4] Reference part - Insulation resistance (MOhms) Part with silicone - Insulation resistance (MOhms) N°1 1.8 154.0 N°2 1.8 92.2 N°3 0.9 6.2 N°4 2.1 13.1

[0070] It can be noted that the insulation resistances after opening are significantly higher with the parts whose overmolded body 15 contains 10% silicone, than with the reference parts whose overmolded body 15 does not contain silicone.

[0071] Finally, the applicant noticed that there was a sharp increase in isolation resistances if the two alternatives are combined, i.e., providing in the internal chamber; one wall with the plastic material including the flame retardant, and one wall with the third plastic material including the silicone.

[0072] Indeed, in the context of the tests reported in Tables 3 and 4, the applicant also tested circuit breakers with one wall of the internal chamber comprising flame retardant (the exposed face 42 of the opening member 40) and another wall comprising silicone (in the overmolded body 15), and the results are reported in Table 5.

[0073] Tests performed under 450V / 8000A / 20µH / +125°C [Table 5] Reference part - (MOhms) Part with flame retardant - (MOhms) Part with silicone - (MOhms) Part with flame retardant and silicone - (MOhms) N°1 1.8 64.0 154.0 2160.0 N°2 1.8 592.0 92.2 2020.0 N°3 0.9 131.0 6.2 >10000 N°4 2.1 82.7 13.1 9600.0

[0074] As shown in Table 5, the effect on insulation resistance when combining one wall of the internal chamber containing a flame retardant with another wall containing silicone goes far beyond simply adding the effects measured on parts containing only one or the other alternative. Consequently, a synergy was observed, and this configuration (one wall of the internal chamber containing a flame retardant and another wall containing silicone) demonstrates its advantages.

Claims

1. Pyrotechnic circuit breaker comprising: - a housing (10), - at least two connection terminals (21, 22), - an internal electrical circuit connecting the two connection terminals (21, 22) and formed, for example, by an electrical conductor (31), - an opening member (40), which is movable and arranged to open a part to be opened of the internal electrical circuit during a movement between an initial position and a final position, so as to form at least two separate conductor portions (32, 33) after opening, - a pyrotechnic actuator (50) arranged to move the opening member (40) from the initial position to the final position, - an internal chamber (60) receiving the part to be opened and comprising or containing at least one internal surface formed by a wall that is formed using a polymeric plastics material forming a matrix and comprising a filler material, such as fibers, preferably inorganic fibers, for example glass fibers or carbon fibers, in a proportion ranging from 10% to 70% by weight and preferably in a proportion ranging from 45% to 55% by weight, characterized in that the plastics material forming the wall and the internal surface comprises a flame retardant.

2. Pyrotechnic circuit breaker according to claim 1, wherein said plastics material comprising the flame retardant is a polyamide, and preferably a polyphthalamide (PA 6T / 66).

3. Pyrotechnic circuit breaker according to one of claims 1 to 2, wherein said plastics material comprising the flame retardant self-extinguishes after 10 seconds, during a flammability test according to standard UL94 (6th edition of 28 March 2013) performed on a vertical test specimen, particle losses being permitted as long as the particles lost are not ignited.

4. Pyrotechnic circuit breaker according to one of claims 1 to 3, wherein the flame retardant is a non-halogenated compound, selected from: - the conversion or reaction products of melamine with cyanuric acid, - the condensation products of melamine, - the conversion or reaction products of melamine with polyphosphoric acid, - the conversion or reaction products of the condensation products of melamine with polyphosphoric acid, - metal phosphinates, - esters of phosphoric acid, - mixtures of these materials.

5. Pyrotechnic circuit breaker according to one of claims 1 to 3, wherein the flame retardant is a non-halogenated compound, selected from the following compounds and their mixtures: melamine cyanurate, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, melem phosphate, melem pyrophosphate, dimelamine pyrophosphate, dimelamine phosphate, melem polyphosphate, phosphaphenanthrenes, metal hydroxides, phosphinic acid salts, diphosphinic acid salts.

6. Pyrotechnic circuit breaker according to one of claims 1 to 5, comprising a base part formed by a second plastics material, wherein said plastics material comprising the flame retardant is attached to or over-molded on the base part.

7. Pyrotechnic circuit breaker according to one of claims 1 to 6, arranged to produce an electric arc between the two separate conductor portions (32, 33) during the movement of the opening member (40) between the initial position and a final position, when the circuit breaker is connected to a live electrical circuit, wherein the plastics material comprising the flame retardant is arranged to be removed by ablation by the electric arc.

8. Pyrotechnic circuit breaker according to claim 7, comprising at least one passage (44) arranged to guide the electric arc between the two separate conductor portions (32, 33), wherein the plastics material comprising the flame retardant is arranged to form or define the passage (44) at least in part.

9. Pyrotechnic circuit breaker according to one of claims 1 to 8, wherein the internal chamber (60) comprises or contains at least one wall formed using a third plastics material comprising silicone.

10. Pyrotechnic circuit breaker according to claim 9, comprising at least one support, and wherein the third plastics material comprising silicone is over-molded on or attached to the support.

11. Pyrotechnic circuit breaker according to one of claims 9 to 10, wherein the wall formed using the third plastics material comprising silicone supports a leakage current route between the two separate conductor portions (32, 33) after opening, and preferably the shortest leakage current route between the two separate conductor portions (32, 33) after opening.

12. Pyrotechnic circuit breaker according to one of claims 9 to 11, wherein the wall formed using the third plastics material comprising silicone covers less than 50% of a total surface area of the internal chamber (60).

13. Pyrotechnic circuit breaker according to one of claims 9 to 12, wherein the third plastics material comprising silicone comprises silicone and / or polysiloxane, in a proportion ranging from 3.5% to 6.5% by weight, and preferably from 4.25% to 5.75% by weight.

14. Motor vehicle comprising at least one circuit breaker according to one of claims 1 to 13.