Gas generator with slotted ignition tube

Abstract

Gas generator for a vehicle safety system with an igniter (12) and a combustion chamber (16) in which a pyrotechnic propellant is received, and with an ignition tube (20) whose first end (22) faces the igniter (12) and whose second end (24) extends into the combustion chamber (16) and through which the hot gas from the igniter (12) to the propellant can be conducted after activation of the gas generator (10), wherein at least before activation of the gas generator (10) a flow cross-section of the ignition tube (20) is narrowed in a slit-like manner over at least a part of the axial length of the ignition tube (20) in at least one spatial direction, characterized in that the cross-section of the ignition tube (20) is constant over its entire length at least in the region of the combustion chamber (16).

Description

[0001] The invention relates to a gas generator with an igniter and a combustion chamber containing a pyrotechnic propellant, and with an ignition tube, the first end of which faces the igniter and the second end of which extends into the combustion chamber and through which, after activation of the gas generator, hot gas can be directed from the igniter into the propellant. The invention further relates to a module comprising a gas generator, a gas bag inflatable by the gas generator, and a mounting device for attaching the module to a vehicle. The invention also relates to a vehicle safety system, particularly for the protection of a person, for example, a vehicle occupant or pedestrian, comprising a gas generator, a gas bag inflatable by the gas generator as part of a module, and an electronic control unit by means of which the gas generator can be activated in the event of a triggering situation.

[0002] Ignition tubes of this type, also called flame guide tubes, are used to direct the hot gas generated by the igniter deep into the propellant, thus achieving uniform ignition of the entire propellant bed. US Patent 7,950,692 B2, for example, shows a gas generator with an ignition tube.

[0003] From the generic document DE 11 2004 000 592 T5, a gas generator for a vehicle safety system is known, comprising an igniter and a combustion chamber in which a pyrotechnic propellant is contained, and an ignition tube, the first end of which faces the igniter and the second end of which extends into the combustion chamber and through which, after activation of the gas generator, hot gas can be directed from the igniter into the propellant, wherein, at least before the activation of the gas generator, a flow cross-section of the ignition tube is narrowed in a slot-like manner over at least a part of the axial length of the ignition tube in at least one spatial direction.

[0004] However, the ignition tube takes up a relatively large amount of space in the combustion chamber, which cannot be filled with fuel. Furthermore, an unevenly distributed gas flow from the ignition tube is a disadvantage.

[0005] The object of the invention, with regard to the gas generator, is to achieve uniform ignition of the propellant in a space-saving manner.

[0006] Furthermore, it is an object of the invention to provide a module comprising such a gas generator, an inflatable gas bag from the gas generator, and a mounting device for attaching the module to a vehicle. It is also an object of the invention to provide a vehicle safety system, particularly for the protection of a person, for example, a vehicle occupant or pedestrian, comprising such a gas generator, an inflatable gas bag from the generator as part of a module, and an electronic control unit by means of which the gas generator can be activated in the event of a triggering situation.

[0007] The problem with regard to the gas generator is solved according to the invention by ensuring that the cross-section of the ignition tube remains constant along its entire length, at least in the region of the combustion chamber. The ignition tube can therefore, for example, be flat with a narrow cross-section. Such a shaped ignition tube occupies relatively little space in the propellant bed, yet still allows a sufficiently large quantity of gas to be delivered in a sufficiently short time to ignite the propellant evenly.

[0008] According to the invention, the problem is solved with regard to the module by the subject matter of claim 12, and with regard to the vehicle safety system by the subject matter of claim 13.

[0009] The ignition tube preferably extends over at least half the axial length of the combustion chamber. However, it can also extend substantially through the entire combustion chamber. It is advantageous to arrange the ignition tube parallel to the longitudinal axis of the combustion chamber.

[0010] The use of such an ignition tube is particularly advantageous in a tubular gas generator that has a cylindrical combustion chamber whose axial length is greater than its diameter.

[0011] The ignition tube can have a substantially oval or rectangular cross-section over at least part of its length, in which the long sides are significantly longer than the short sides, preferably at least twice, and in particular three times, as long. It would also be possible to design the ignition tube, at least in sections, with a cross-shaped or star-shaped cross-section. All these cross-sectional shapes are well suited to ensuring good gas flow to all sections of the propellant charge while requiring little space in the combustion chamber.

[0012] To allow gas to escape from the ignition tube, the ignition tube preferably has several lateral openings along its longitudinal extent.

[0013] The spacing between the openings can decrease along the length of the ignition tube, i.e., in the axial direction of the combustion chamber. Preferably, the spacing decreases the further the openings are from the igniter, in order to compensate for the decreasing gas pressure in the ignition tube, so that the amount of energy transferred by the outgoing gas remains constant for each opening. In this way, a particularly uniform ignition behavior can be achieved for the entire propellant charge along the entire length of the combustion chamber.

[0014] The shape of the ignition tube can be formed by plastically deforming an initially annular tube in cross-section. This allows the ignition tube to be manufactured from a readily available and inexpensive raw material.

[0015] The second end of the ignition tube, facing away from the igniter, is preferably open so that the gas escaping here can also ignite the propellant. However, it is also possible to close the second end of the ignition tube completely or partially, for example by welding, folding, or bending.

[0016] In the axial direction, the ignition tube preferably connects directly to the igniter in order to direct the gas released by the igniter directly into the propellant. The igniter can include a booster charge adjacent to the ignition charge of the igniter, so that the booster charge is positioned between the actual ignition charge of the igniter and the ignition tube.

[0017] At the transition to the igniter, the ignition tube preferably has a circular cross-section to facilitate the gas introduction from the igniter into the ignition tube.

[0018] In one possible embodiment, the ignition tube is designed such that, after activation of the gas generator, its cross-section can be plastically expanded, preferably by changing its cross-sectional geometry. This allows for a space-saving arrangement of the ignition tube within the propellant while maintaining a high gas flow rate through the ignition tube. Before activation of the gas generator, the cross-section of the ignition tube is narrowed to a slot. After activation, when the propellant begins to burn and thus space is freed up in the combustion chamber, the cross-section of the ignition tube increases, allowing a larger volume of gas to flow through it.

[0019] The increase in cross-sectional area can be based, for example, on the pressure and / or temperature effects of the gas generated by the igniter. In particular, the wall thickness of the ignition tube can be selected in relation to the internal pressure such that the ignition pressure can plastically deform the ignition tube outwards. Such deformation of the ignition tube due to activation of the gas generator can, for example, approximately restore the original circular cross-sectional shape.

[0020] It is also conceivable to manufacture the ignition tube, or at least the section of the ignition tube which has a slot-shaped narrowed cross-section before the activation of the gas generator, from a shape memory alloy, whereby, if the conversion temperature is exceeded by heating through the gas produced by the igniter, an original, preferably circular, cross-sectional shape is restored.

[0021] Furthermore, the invention provides a module comprising a previously described gas generator, a gas bag inflatable by the gas generator, and a mounting device for attaching the module to a vehicle. The module is particularly suitable for use in a gas bag module or an airbag module.

[0022] Furthermore, the invention comprises a vehicle safety system, in particular for the protection of a person, for example a vehicle occupant or pedestrian, with a previously described gas generator, an inflatable gas bag from this, as part of a module, in particular as described above, and an electronic control unit by means of which the gas generator can be activated in the event of a triggering situation.

[0023] Further advantages of the invention will become apparent from the following description using an exemplary embodiment with reference to the accompanying figures. The figures show: - Fig. 1 a schematic perspective representation of a gas generator according to the invention; - Fig. 2 a schematic side view of a section of the gas generator made of Fig. 1 with the lighter and the ignition tube; and - Fig. 3 den in Fig. 2. Section of the gas generator shown in a 90° rotated side view.

[0024] Fig. Figure 1 shows a gas generator 10, here a tubular gas generator, which has a pyrotechnic igniter 12 at one longitudinal end, which can be ignited by an external electrical impulse. The igniter 12 is inserted into a partition 14, which separates a combustion chamber 16 containing a propellant (not shown) made of a suitable pyrotechnic material, preferably pressed into tablets, wherein the propellant can also be in the form of granules or of at least one shaped body, for example produced by extrusion. The cylindrical outer wall 18 of the gas generator 10 is only schematically indicated.

[0025] The gas generator 10 also has outlet openings, optionally a diffuser, and mounting fittings for attaching the gas generator 10 in a gasbag module or to a vehicle, which are designed in a known manner and are not shown here.

[0026] Inside the combustion chamber 16, an ignition tube 20 extends along the axial direction A of the gas generator 10. In the example shown here, the ignition tube 20 runs centrally in the combustion chamber 16 and ends at approximately half the length L of the combustion chamber 16, but it could also be longer or shorter and, for example, extend through the entire length of the combustion chamber 16.

[0027] The ignition tube 20 extends through the partition 14 at an axial first end 22 and is connected to the igniter 12. This axial first end 22 has a substantially circular cross-section and is arranged such that the gas supplied by the igniter 12 during activation of the gas generator 10 flows into the ignition tube 20.

[0028] Over most of the length of the section of the ignition tube 20 that runs within the combustion chamber 16, the cross-section of the interior of the ignition tube 20 is narrowed to a slot. The cross-section 28 forms a narrow rectangle or oval, in which the long sides are considerably longer than the short sides. The aspect ratio can be greater than 10:1.

[0029] Fig. Figure 2 shows a top view of the ignition tube 20 on the long side of the cross-section, while Fig. Figure 3 shows a top view of the short side of the cross-section of the ignition tube 20.

[0030] This cross-sectional shape 28 of the ignition tube 20 can be achieved by flattening a tube that originally had an annular cross-section in one direction.

[0031] The second end 24 of the ignition tube 20, which here terminates in the propellant in the combustion chamber 16, is open in this example. However, it could also be completely or partially closed.

[0032] Openings 26 are provided along the length of the ignition tube 20 on its flat, wide sides 29, through which the gas supplied by the igniter 12 flows. For clarity, only some of the openings are labeled in the figures. In this example, two parallel rows of openings 26 are provided on the two opposite wide sides 29 of the ignition tube 20.

[0033] The distance between the openings 26 decreases in the axial direction A as the openings 26 are further away from the igniter 12. The distance between the openings 26 is dimensioned such that the gas flow or the energy transferred by the gas is the same at all openings 26.

[0034] The ignition tube 20 is manufactured by mechanically deforming a metal tube with an annular cross-section over its entire length except at its first end 22 and compressing it to a slot-shaped inner cross-section 28.

[0035] When the gas generator 10 is activated and the igniter 12 is ignited, the gas produced by the igniter 12 flows through the first end 22 into the ignition tube 20 and exits through the openings 26 or the open end face 24, whereby the hot gas enters the propellant in the combustion chamber 16 evenly and ignites it almost simultaneously via the effective extension of the ignition tube 20 in the combustion chamber 16.

[0036] In an embodiment not shown in detail here, the ignition tube 20 is designed such that it is plastically deformed perpendicular to the axial direction A by the gas flowing through it when the gas generator 10 is activated, so that the cross-section 28 increases and therefore more gas can flow through the ignition tube 20 per unit of time.

[0037] This change in cross-section can be caused, for example, by the internal pressure of the gas flowing from the igniter 12 into the ignition tube 20. In this case, the wall thickness of the ignition tube 20, as well as the distribution and total area of ​​the openings 26, are adapted so that the internal pressure can cause the ignition tube 20 to expand.

[0038] Another possibility is to manufacture at least the flattened section of the ignition tube 20 from a shape-memory alloy that has a transformation temperature which is exceeded when the hot gas generated by the igniter 12 flows through the ignition tube 20. In this case, the temperature increase initiates the deformation so that the ignition tube 20 returns to its original, for example, annular, cross-section.

Claims

[1] Gas generator for a vehicle safety system comprising an igniter (12) and a combustion chamber (16) in which a pyrotechnic propellant is received, and an ignition tube (20) whose first end (22) faces the igniter (12) and whose second end (24) extends into the combustion chamber (16) and through which the hot gas after activation of the gas generator (10) can be directed from the igniter (12) into the propellant, wherein at least before the activation of the gas generator (10) a flow cross-section of the ignition tube (20) is narrowed in a slit-like manner over at least a part of the axial length of the ignition tube (20) in at least one spatial direction, characterized by , that the cross-section of the ignition tube (20) is constant at least in the area of ​​the combustion chamber (16) over its entire length. [2] Gas generator according to claim 1, characterized by that the ignition tube (20) extends over at least half the axial length of the combustion chamber (16). [3] Gas generator according to any one of the preceding claims, characterized by , that the ignition tube (20) has an oval or rectangular cross-section over part of its length, in which the long sides are significantly longer than the short sides. [4] Gas generator according to any one of the preceding claims, characterized by that the ignition tube (20) has several openings (26) along its longitudinal extent. [5] Gas generator according to claim 4, characterized by , that the distance between the openings (26) in the longitudinal direction (A) of the ignition tube (20) decreases. [6] Gas generator according to any one of the preceding claims, characterized by , that the ignition tube (20) is formed by plastic deformation of a tube that was originally circular in cross-section. [7] Gas generator according to any one of the preceding claims, characterized by , that the second end (24) of the ignition tube (20) is open or closed. [8] Gas generator according to any one of the preceding claims, characterized by , that the ignition tube (20) connects to the igniter (12) in the longitudinal direction (A). [9] Gas generator according to any one of the preceding claims, characterized by , that the ignition tube (20) has a circular cross-section at the transition to the igniter (12). [10] Gas generator according to any one of the preceding claims, characterized by , that the ignition tube (20) is designed in such a way that, after activation of the gas generator (10), it can be plastically expanded by increasing the cross-section. [11] Gas generator according to claim 10, characterized by , that the cross-sectional enlargement is based on the pressure and / or temperature effect of the gas produced by the igniter (12) and the wall thickness of the ignition tube (20) is chosen in relation to the pressure inside the ignition tube (20) such that the ignition pressure can plastically deform the ignition tube (20) outwards. [12] Module comprising a gas generator (10), a gas bag inflatable by the gas generator (10) and a fastening device for attaching the module to a vehicle, characterized by , that the gas generator (10) is designed according to at least one of claims 1 to 11 [13] Vehicle safety system for the protection of a person, for example a vehicle occupant or pedestrian, comprising a gas generator (10), an inflatable gas bag as part of a module, and an electronic control unit by which the gas generator (10) can be activated in the event of a triggering situation, characterized by , that the gas generator (10) is designed according to at least one of the preceding claims 1 to 11.

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