FR2873367A1 - Solid propellant (in a block form), used in pyrotechnique generators and automobile safety systems, comprises an incision mouthing into a longitudinal canal formed in the block, on the external surface - Google Patents

Abstract

Solid propellant (in a block form) (1, 1') (A) comprises at least an incision (2) mouthing into at least a longitudinal canal formed in the block, on the external surface. An INDEPNDENT CLAIM is also included for the preparation of (A).

Description

The present invention relates to the field of gas generators, and

  more particularly in the field of solid propellants.

  The specificities of car manufacturers are always more and more specific, especially when they concern the safety of motor vehicle users. One of these specificities relates more specifically to the flow of gases when the generator operates during an accident. The first requirements related to the need to ensure a relatively constant flow with the sole purpose of inflating the cushion in a given time.

  This initial need has then evolved into more demanding demands for regimes that are no longer constant, but progressive. Today, the demand is turning towards a multiregime operation, of which a variant is a dual mode operation, also called indifferently double regime. A dual-speed operation makes it possible to meet the restraint specifications associated with the occupants who do not respect the standard position in the vehicle. This situation can occur, for example, when the front passenger is very close to or in contact with the security module. The occupant is then in a position called Out of position or OOP.

  By multi-regime, it is necessary to hear a strong bearing at the beginning of operation followed by lower levels or vice versa, the regimes not being absolutely constant. The curve illustrating the pressure as a function of time is characterized in the case of two-stage dual-stage operation.

  Regarding these multi-regimes, various known solutions of the state of the art are.

  One of them is to use a fuel whose particular composition allows access to a multi-regime. This result is achieved in various ways: by the use of titanium oxide whose quantity is varied, by the use of ingredients whose particle size is varied. US-A-5,579,634 illustrates these solutions. The method is simple in principle but still very restrictive, especially when it comes to applying the method on production lines.

  It can also provide the loading of several blocks of propellant in the same room, stacking on top of each other. These blocks may have different compositions and / or different shapes in order to obtain a stepwise combustion. This method has serious drawbacks such as multiple loading with the ensuing control difficulties and the manufacture of several tools, which necessarily implies high cost.

  Another method is to vary the section of the nozzles, or to use multi-stage nozzles. In the same way as before, the method is more complex and generates additional costs.

  Another technique, to obtain two combustion regimes, provides generators equipped with two loads in two separate combustion chambers. This solution is obviously more expensive than a standard generator.

  The desired performance in some applications requires the use of relatively long blocks. In such applications, it is common to encounter the problem of self-tightening that may lead to premature and undesired bursting of the block by internal pressurization of the block, greater than the pressure in the combustion chamber.

  Self-tightening is, by definition, the condition for which the propellant combustion gases emitted in a passage (channel, space between block and wall, then assimilated to a local nozzle) can not escape fast enough from said passage. This phenomenon results in the creation of an area in the combustion chamber, more tight than that imposed by the nozzle of the chamber. Most of the time, the phenomenon is in a channel crossing the block of propellant.

  The self-tightening configuration is obtained when the local clamping K, oca, is greater than the clamping of the combustion chamber, Kchbre.

  K1oca1 is defined by the ratio between the combustion surface located in said passage and the section of the local nozzle and which after calculation leads to the ratio equal to twice the length of the block on the diameter of the perforated channel in the block (2L / d ).

  Kchbre is defined as the ratio of the total area of combustion to the nozzle section of the combustion chamber.

  To prevent the block breaking, it must be ensured that the local clamping 10 is permanently lower than the clamping of the chamber.

  The present invention aims to obtain a propellant for multi-speed operation, while avoiding the self-tightening phenomenon encountered in certain blocks of solid propellant of excessive size.

  For this purpose, the invention consists in making modifications in the geometry of the propellant blocks.

  An object of the invention is a solid propellant in the form of a block, characterized in that it has on its outer surface at least one incision opening into at least one longitudinal channel formed in the block.

  The object of the invention notably makes it possible to access new functions of S = f (e) shape by practicing at least one incision of the solid propellant block.

  For example, at least one incision opening in at least one longitudinal channel formed in the block is flat.

  According to a first embodiment, one or more incision (s) is / are arranged transversely, i.e. perpendicular to the central axis of the solid propellant block.

  According to a second embodiment, one or more incisions (s) is / are arranged longitudinally, i.e. parallel to the central axis 30 of the solid propellant block.

  In another embodiment, the incision is helical.

  The block is for example used in pyrotechnic generators.

  A second object of the invention is a method of manufacturing a solid propellant in the form of a block, characterized in that it comprises a step of extruding the block and a step of producing each longitudinal or helical incision, during the extrusion step.

  A third object of the invention is a method for manufacturing a solid propellant in the form of a block, characterized in that it comprises a step of extruding the block and a step of producing each transverse incision after the extrusion step.

  The invention, with its features and advantages, will be better understood on reading the description which will follow, given solely by way of non-limiting example, with reference to the appended drawings, in which: FIGS. 1 a 1 represent several views of profile and three quarts of solid propellant blocks as commonly used and forming part of the state of the art, to which the invention can be applied; FIG. 2 represents the shape function of the total area S of the blocks, known from the state of the art, as a function of their burned thickness e during their combustion.

  FIG. 3 represents a schematic view of a standard block taken as a reference; - Figures 4a-4b show a schematic view of a solid propellant block according to the invention according to a first variant; - Figures 5a-5b show a schematic view of a solid propellant block according to the invention according to a second variant; and FIG. 6 represents the evolution of the geometry of the block as a function of its burned thickness according to the invention.

  To obtain new shape functions with several levels, we can play on the geometry of the blocks, and in particular on the relationship between the surface offered for combustion and the burned thickness of the block. FIGS. 1a to 1i illustrate the evolution of the profile of the blocks. FIG. 2 represents the curve S = f (e), where S is the evolution of the total area S of the block, as a function of its burned thickness e. Originally, the solid propellant block was of simple design having a full section over its entire length. As this block is consumed, its surface, which is limited to its external surface Sext, becomes smaller. This type of loading for which the combustion surface decreases continuously as a function of the progress of combustion is said to be decreasing as represented by curve a.

  FIG. 1b represents a solid propellant block comprising a central channel 3, for example for a circular cylindrical geometry. The surface offered for combustion, in this case, consists of the external surface Sext of the block 1 as well as the internal surface Si of the channel 3. When the block is consumed, the reduction of the external surface is partially compensated by the increase simultaneous channel surface as represented by the curve b. The degressive character is thus reduced.

  The multiplication of the number of longitudinal channels parallel to each other, as shown in FIG. 1c, makes it possible to obtain at first a constant surface evolution, according to the so-called neutral curve c, and even a so-called progressive evolution, according to the curve d, for which the surface offered to the combustion grows with the advancement of the combustion of the block. Figures 1 d-1 i are all possible geometries known to those skilled in the art.

  In the exemplary embodiments described below, solid propellant block 1 according to the invention is of standard geometry, like that shown diagrammatically in FIG. 3, with at least one channel 3 passing through it from one side to the other and arranged parallel to the longitudinal or central axis A of the block 1. The block 1 according to the invention may also have the forms described below with reference to Figures la to 1 i. The channel 3 has for example a circular cross section in Figures lb to 3, 4a, 4b, 5a and 5b or, as will be seen in the central portion in Figure 1f, rectilinear. For the sake of clarity, the channels do not bear the reference sign 3 in FIGS. 1c to 1i, but it goes without saying that they are the voids delimited in the solid parts of the blocks represented in these figures. For example, the standard geometry block has a generally cylindrical shape along the longitudinal axis A, having a circular outer section in Figure 3 or another. For example, the cross section of the block 1 according to the invention may also be: of generally annular and circular shape internally and externally around the central channel 3, as for example in FIG. 1b, of generally solid, circular or ellipsoidal, with several channels 3, including for example a central channel and several channels distributed around the central channel, such as the six in Figure lc, - of generally annular shape, circularly internally and formed of broken arches on the outer surface Sext, these broken arcs being those of the outer surface of small annular cylinders with circular section, which each delimit at their center a peripheral channel 3; the broken arcs and their associated peripheral channel are equidistant in a circle around the inner Si inner surface delimiting the central channel; the small cylinders are integral with each other to form together the block, as for example in Figure Id; - Of generally circular annular shape, formed of broken arches on the outer surface Sext and on the inner surface Si delimiting the central channel, these broken arcs being those of the outer surface of small annular cylinders with circular section, which each delimit in their center a channel 3 and which are integral with each other to form together the block, as for example in Figure le; the broken arcs and their associated peripheral channel are equidistant in a circle around the center of the ring; - Of circular general shape, with an outer surface Sext formed of broken arches, these broken arcs being those of the outer surface of small annular cylinders with circular section, each delimiting at their center a peripheral channel 3; the broken arcs and their associated peripheral channel are equidistant in a circle around the center of the block; the small cylinders are integral with each other as well as a central portion to form together the block, as for example in Figure 1f; this central part comprising a central channel 3 formed of radial rectilinear portions intersecting, and extending for example along diameters between peripheral channels, for example three radial portions 120 of one another in Figure 1f; of a hexagonal general shape, with an outer surface Sext formed of broken arcs of circle, of which for example one is provided at each of the six vertices of the regular hexagon and another of which is provided on each side of the hexagon between the vertices, for example according to Figure 1 g; six peripheral channels 3 are provided near the six vertices of the hexagon of the outer surface Se, <, to be arranged in turn in regular homothetic hexagon of the hexagon of the outer surface Sext; in addition another channel 3 is provided in the center of the hexagon; the broken arcs of the outer surface may not be centered on the peripheral channels, as shown in Figure 1g, but could be, in an embodiment not shown; of a hexagonal general shape, with an outer surface Sext formed of broken arcs of circle, of which for example one is provided at each of the six vertices of the regular hexagon and another of which is provided on each side of the hexagon between the vertices, for example according to Figure 1 g; six peripheral channels 3 are provided near the six vertices of the hexagon of the outer surface Sext, to be arranged in turn homothetic regular hex of the hex of the external surface Sext and six other peripheral channels 3 are provided between and in the middle of the peripheral channels of the outer tops; for example, the broken arcs of the outer surface Sext may be centered on the peripheral channels 3, as shown in FIG. 1 h; in addition, another channel 3 is provided in the center of the hexagon and six other intermediate channels 3 are provided between this central channel and the peripheral channels of the vertices in the middle, as shown in Figure 1 h; of similar shape to that described with reference to FIG. 1b, but with broken arcs of outer surface Sext of same radii, centered on the peripheral channels, whereas in FIG. 1h the broken arches of the middle of the sides of the hexagon do not necessarily have the same radius as those of the vertices; in addition, in FIG. 1, the channels are wider with respect to the radius of the broken arcs than in FIG. In the block shapes described below, the outer rings of Figures 1d, 1c and 1f may be non-circular and for example ellipsoidal.

  The solid propellant block according to the invention differs from the standard block and the blocks of Figures la to 1i, in that it has in addition at least one notch 2 opening on at least one channel 3 of these blocks. Each notch 2 may be of variable geometry and / or depth. Various embodiments are described below. In the remainder of the talk, the terms incision, streak, slit and the corresponding adjectives will be used independently to denote the notch made in the solid propellant block. This notch as described below can be provided on the blocks having the forms described above with reference to Figures la to 1 i. The cuts are flat, for example.

  According to a first embodiment shown in FIGS. 4a and 4b, the solid propellant block 1 according to the invention comprises on the external surface at least one incision 2 perpendicular to the longitudinal axis A of the block 1. These incisions 2 are said to be transverse or radial. When several incisions are made on the block 1, several identical or different layers of thickness X are formed on the block 1. These incisions are characterized by a depth p 1 determined according to the desired result and in particular according to the regime. FIG. 4b shows identical incisions made on the same block so that they open onto the peripheral channels 3 of block 1. An incision can for example go around the surface in which it is made, for example from the outer surface for interconnecting the peripheral channels 3 in Figure 4b.

  According to another variant (not shown) of this first embodiment, the incisions made on the outer surface of the block may be helical.

  According to a second embodiment, represented in FIGS. 5a and 5b, the external surface of the solid propellant block 1 'has at least one notch 2' parallel to the longitudinal axis A of the block 1 and opening into a channel 3 of the block 1 . These incisions 2 'are then called longitudinal. According to the embodiment of Figures 5a and 5b, a notch 2 'is formed for each peripheral channel 3 of the block 1'.

  In order to explain the operating principle in dual mode, the selected block 1 'is incised so that all the incisions lead to a preformed peripheral channel 3' in the block. This configuration is shown in Figure 5b.

  With reference to FIG. 6a, the curve S = f (e) is characterized by two levels Q and 6.

  The fuel is initiated in a. This results in a constant level of stability which results in the fuel being consumed at all its surfaces, including the outer surface and the internal surfaces. The internal surface decreases as the combustion increases, while the external surfaces increase, the outer surface and the internal surfaces coming closer to each other until joining in x, where there is a sudden drop in pressure. This is because momentarily there is no more fuel at this point in the block. This time is therefore very short. Once this transition has passed, the curve S = f (e) begins a new step 6. This long and degressive combustion period corresponds to the burned material in the center of the block. The segment e reflects the combustion of the remains of the block, namely what is commonly called carrots in the jargon. The existence of the level f found is precisely due to the presence of the incisions.

  According to another variant of this second embodiment, the solid propellant block is split longitudinally inside its body. This variant is possible if the geometry of the block allows it. This is for example possible when the block has a large central channel, such as those shown in Figures Id, le, or 1f.

  To practice incisions, there are various techniques.

  It is possible to perform the incisions simultaneously during the extrusion of the block. It suffices for this to have at specified intervals at the output of extruder knives, milling cutters or other cutting blades, according to the geometry of the desired notches. For technical reasons of realization, this technique is however applicable only to the blocks incised longitudinally.

  On the other hand, with regard to the blocks with radial external incisions, one of the techniques consists in practicing these cuts in a second step, after the extrusion, by slicing or machining, milling for example.

  In the particular case of helical incisions, these are obtained using a cutting tool disposed at the extruder outlet whose cutting edge is printed on the outer surface of the block as the block, in rotation on itself, leaves the extruder. It is also possible to consider a cutting tool rotating around the block while it comes out of the extruder.

  Other methods of obtaining the blocks are also conceivable such as compression, sintering, molding or any other method for obtaining solid propellant blocks.

  Thus, incising the solid propellant blocks allows access to the dual regime while remaining in a single-chamber generator configuration. Moreover, it makes it possible to satisfy this operating need by using a single block which is easy and easy to implement on the production lines. Indeed, the loading is carried out in a single operation.

  The appearance of the phenomenon self-tightening is avoided by the presence of incisions. Indeed, the fact of making such cuts increases the combustion surface compared to the standard block shown in Figure 3 and thus keep the local clamping lower than the clamping of the combustion chamber.

  Of course, the invention is not limited to the variants described above. It is thus possible to envisage other ways of streaking the solid propellant blocks according to other geometries, with any number of streaks.

  Similarly, one skilled in the art can associate, if necessary, several solid propellant blocks identical or differently striated in accordance with the invention.

  The embodiments presented above describe a dual-mode operation, which is no other than a particular case of multiregime. Those skilled in the art could apply the invention so as to obtain a muti-regime, of order greater than two.

  Thus, by combining several solid propellant blocks of different geometries, it is possible to obtain a low level and then a higher level. The solid propellant blocks according to the present invention can be used in any type of generator, short or long. Such blocks can be used either alone or by combining several blocks.

  Solid propellant blocks according to the invention are advantageously applied in the field of automotive safety without being limited thereto. Such blocks can indeed be used in many other fields such as aerospace, air navigation, maritime.

Claims (9)

  1. solid propellant (1, 1 ') in the form of a block, characterized in that it has on its outer surface at least one incision (2) opening into at least one longitudinal channel formed in the block (1).   2. solid propellant (1, 1 ') in block form according to claim 1, characterized in that at least one incision opening into at least one longitudinal channel formed in the block (1) is flat.   Solid propellant (1, 1 ') in block form according to claim 1 or 2, characterized in that at least one incision (2) is made perpendicularly to the longitudinal axis (A) of the block (1). ).   Solid propellant (1, 1 ') in block form according to claim 1 or 2, characterized in that at least one incision (2') is made parallel to the longitudinal axis (A) of the block (1 ).   Solid propellant (1, 1 ') in block form according to claim 1, characterized in that the incision is helicoidal.   Solid propellant (1, 1 ') in block form according to one or more of the preceding claims, characterized in that this block is used in pyrotechnic generators.   Solid propellant (1, 1 ') in the form of a block according to one or more of the preceding claims, characterized in that this block is suitable for automotive safety.   8. A method of manufacturing a solid propellant (1, 1 ') in block form according to one or more of the preceding claims, characterized in that it comprises a step of extruding the block and a step of performing each longitudinal or helical incision, during the extrusion step.   9. A method of manufacturing a solid propellant (1, 1 ') in block form according to one or more of the preceding claims, characterized in that it comprises a step of extruding the block and a step of performing each transverse incision after the extrusion step.