DE102015114794A1 - Aufblasvorrichtungstreibmittel - Google Patents

Abstract

A propellant for an inflator, and an airbag inflator, and a method for producing a propellant are disclosed. The propellant comprises a plurality of granules which adhere to each other so that voids exist between the granules. Choosing the size of the granules and the volume of cavities allows to control the rate of combustion of the propellant.

Description

The present invention relates to a propellant for an inflator, in particular to a solid propellant for an airbag inflator. The present invention also relates to an airbag inflator comprising a solid propellant and to methods of making the solid propellant.

background

Airbags are a commonly used vehicle safety device. They are provided at one or more locations in the vicinity of an occupant seating position to protect an occupant in the event of a collision from impacting on interior portions of the vehicle. Airbags typically include a flexible pad and an inflator system that is designed to fill the pad with gas in the event that a required deployment condition is met.

Several types of air bag inflators are known. Pyrotechnic inflators receive a source of gas from a combustible gas generating material which when ignited generates a sufficient amount of gas to inflate an air bag. Gas storage inflators use a quantity of stored, pressurized gas that is deliberately released to inflate an air bag. Hybrid inflators combine the use of a gas generating material and an amount of stored pressurized gas to inflate an air bag.

Pyrotechnic inflators or hybrid inflators typically utilize a solid, flammable propellant formulation of fuel, oxidizer and binder. Sodium azide is an example of a known solid chemical blowing agent that, when ignited, rapidly generates nitrogen gas that fills the airbag. Recently, alternative propellants have been proposed which are more efficient, less toxic and cheaper, and may, for example, contain a combination of nitroguanidine, ammonium nitrate or other non-metallic oxidants and a non-azide nitrogen-rich fuel such as tetrazoles, triazoles and their salts.

The solid propellant is typically formed in a pellet, for example by pressing or extruding. For a given propellant formulation, the amount of gas yield is determined by the propellant mass and the efficiency of the combustion. The rate of combustion and the increase may be determined by varying the surface area to mass ratio of the pellet (s) comprising the inflator, e.g. Example by selecting the pellet size or by controlling the extrusion profile of the pellet. While extruded propellants offer the potential for a well-controlled surface area to mass ratio, they tend to be less preferred because extruded propellant requires the use of a binder that allows the propellant to be extruded, and this binder affects outflow levels. In addition, care must be taken to allow the extruded propellant to dry crack-free, as any small cracks in the fractures alter the surface area of the resulting propellant and thus the rate of combustion.

Accordingly, there is a need to improve the control of burn rate and / or increase in solid propellant for use in air bag inflator systems.

Information on the invention

According to a first aspect of the present invention there is provided a blowing agent for an air bag inflator system, the blowing means comprising a plurality of granules tacked together to form a propellant body, and wherein a plurality of cavities are present in the propellant body between the granules.

The propellant is therefore a solid body having a granular structure which can be advantageously used as a propellant for a pyrotechnic or hybrid inflator system. The granules preferably have a curved surface and / or have a substantially spherical shape. Therefore, due to the surface curvature of the granules, gaps and voids between the granules are maintained when adhered to each other. Alternatively, the granules may be disc-shaped or generally cylindrical. The void areas between the granules of the propellant body serve to increase the surface area to mass ratio of the propellant. Due to the internal gaps created between the granules, the propellant can be considered as a solid yet air permeable body.

Advantageously, the combustion rate and / or the increase in combustion can be better controlled by choosing the size of the granules and / or the volume of void areas inside the propellant body. The increased surface area to mass ratio increases the rate of combustion of the propellant and thus allows the choice of a chemical propellant formulation having a slower burning rate. This has a number of consequential benefits for the inflator, since such formulations tend to exhibit an improved combustion process, include reduced combustion pressure and / or lower effluent levels.

The leavening granules preferably comprise a fuel, an oxidizer and a binder. Alternatively, the granules comprise a fuel and an oxidizer, with an adhesive binder serving to staple the granules together. As a further alternative, oxidizer granules may be provided with an adhesive binder such as wax, which also serves as a fuel.

The propellant may include sodium azide, or it may, for. From guanidine nitrite, 5-amino-tetrazole, potassium aminotetrazole or potassium nitrate. Other propellant families include ammonium nitrate, potassium perchlorate, dibasic nitrocellulose, SINCO (tradename of Dynamite Nobel). Numerous other propellant formulations are contemplated within the scope of the present disclosure.

Therefore, the ability to achieve a slower burn rate / increase means that more recently developed non-azide propellant formulations can be used. These alternative formulations benefit from their lower cost, tend to be easier to produce, and / or tend to have lower outflow levels. A reduction in combustion pressure allows for providing simplified generator housing concepts. For example, it is contemplated that an inflator system according to the present disclosure may use a plastic housing for the propellant under circumstances where this is sufficient to withstand the lower combustion pressure.

The propellant body can be advantageously formed to a specific, required shape and size, which provides good repeatability in terms of mass and thus gas yield. It is therefore possible to tailor the shape of the propellant body so that the propellant, allowing faster and / or more effective ignition of the propellant, can be mounted near the igniter of the airbag inflator.

In a normal pellet-type inflator, an anti-vibration plate is used to minimize movement of the pellets so as to prevent the formation of pellet dust or cracks which may adversely affect the rate of combustion. Advantageously, the present propellant may not require the use of an anti-vibration plate. Optionally, small deformable elements or tips may be added to the outer surface of the propellant body, thereby further reducing the need for the use of anti-vibration plates as part of the inflator assembly.

The size / diameter of the granules can be a few microns - z. B. a fine powder - reach up to a few millimeters. Therefore, the diameter or the cross-sectional width of the granules may be between 2 microns and 10 mm.

Various methods of forming the propellant granules are contemplated in the present disclosure. In addition to conventional methods such as pressing or extruding and cutting, other methods may be possible. For example, the granules may be formed by a method similar to the manner in which shot pellets are made, wherein molten lead is dropped from a great height into cold water, or alternatively, in which ball bearings are formed by rolling between two plates become. Various other methods of forming the granules are understood by the skilled reader.

The granules can be formed as a powder. Optionally, each of the granules comprises a propellant "pellet" - therefore, the propellant may be formed of a plurality of pellets stapled together to form the propellant body, the individual pellets being considered to constitute the granules forming the propellant. In this case, the pellet granules can be prepared by pressing or extruding. A propellant formulation which is pressed or extruded may be cut to obtain a pellet granule of the required size.

Optionally, the granules are tacked together by means of an adhesive or adhesive. The adhesive may be a solvent-based adhesive, a thermosetting adhesive, a pressure sensitive adhesive, or a hot melt adhesive which is applied in molten form and cured upon cooling to form a bond between the granules. In the case of a thermoplastic or pressure-sensitive adhesive, the granules may be coated with a thin film of adhesive and then compressed in a mold to form the propellant body. Alternatively, the granules may be stapled together by wax or a plastic material. The wax / plastic acts to bind the granules together and can also supplement the fuel in the propellant.

Alternatively, the propellant granules may exhibit magnetic properties such that it it becomes possible to magnetize the granules to adhere to each other. For example, the granules could comprise iron oxide.

The size of the gaps between the granules forming the solid propellant block depends on the size of the individual granules. The size of the voids may also depend on the properties of the adhesive used to adhere the granules. Therefore, it is possible to choose exactly the granule size and void volume (and thus the permeability of the propellant body) to control or "fine-tune" the rate of combustion.

According to another aspect of the present invention, there is provided an airbag inflator, the airbag inflator comprising a solid propellant body, the propellant body formed of a plurality of granules adhered to each other so that a plurality of voids are provided inside the propellant body between the granules.

According to another aspect of the present invention, there is provided a method of producing a blowing agent according to the first aspect.

Brief description of the drawings

For a better understanding of the present invention and to show how the same may be carried into effect, the attached exemplary drawings are explained in which:

1 Fig. 12 is a diagram of an air bag inflator according to a first example;

2 a propellant according to a second example; and

3 shows an inflator housing containing a propellant according to a third example.

Detailed description

1 shows an air bag inflator system comprising a crash sensor 3 an inflator comprising an igniter and a housing 4 , a chemical blowing agent 5 and a safety airbag 6 containing. In this particular example, the air bag inflator system is provided in the steering wheel of a vehicle. It is contemplated, however, that the present disclosure extends to airbag inflators designed for use in a variety of locations in the vehicle.

When in use, an impact by the impact sensor 3 is detected - z. By detecting a sudden deceleration - a signal is sent to the ignition device which ignites the propellant and initiates combustion of the propellant which generates gas to the airbag 6 to fill, leading this through the module cover 7 unfolded through. Filling the airbag causes the airbag to fill the space directly in front of the driver's chest and chest, thus preventing injury to forward movement.

According to the present example, the propellant is 5 a solid, air-permeable body in granular form. The gaps between the granules allow air, the surface area to mass ratio, and thus the rate of combustion, to be extruded through the propellant, as compared to extruded or compressed propellant blocks, in which all voids or voids are forced out during manufacture.

2 In more detail, illustrates the granular structure of a semipermeable propellant body 10 according to a second example. As in 2 shown are the granules 11 essentially spherical and stapled together, leaving gaps 12 to be preserved between the granules. A thin coating of adhesive binds the grains together.

3 shows an inflator comprising an igniter 13 and a housing 15 that is a propellant 16 contains. In this example, the propellant comprises granules 17 with a generally rectangular or square cross section. The granules were formed from an extruded pellet of propellant and then cut to form the granules 17 to form blowing agent. The cut pellets or granules are coated with a wax which serves to staple the granules together while still ensuring that voids 12 to be maintained between the granules.

Optionally, the method of making the propellant body may include a step of coating propellant granules in an adhesive, e.g. B. by rolling the granules in adhesive. For example, the granules may be coated in a thin film of thermosetting adhesive and pressed together in a mold. This step should preferably ensure that the space between the granules is not filled.

Alternatively, the granules may be coated with a wax or a thermoplastic. Advantageously, the wax can supplement the fuel in the propellant granules. Preferably, the wax / plastic has a melting point that is between 120 degrees Celsius and 400 degrees Celsius.

As another alternative, the permeable propellant body can be made by sintering the propellant granules to weld them together.

As still another alternative, the leavening body may be prepared by aerating a mixture, or slurry, of grain and binder by means of a foaming agent or by blowing gas through the mixture. A free-drying step (lyophilization) converts the aerated liquid into a solid propellant body.

Examples of the present invention show a number of technical advantages demonstrated by a variety of chemical blowing agent formulations. The choice of granule size and void volume provides an effective mechanism for controlling or fine tuning the burn rate of a given propellant formulation. The increased surface area to mass ratio resulting from the presence of voids in the propellant body allows for slower burn rates for producing the same volume of gas required to inflate the airbag in a timely manner. This may allow the selection of alternative propellant families that may offer:

• Lower combustion pressure

• • Higher gas yield with less residue. Increasing the surface area may result in easier ignition of the propellant mass so that higher combustion pressures are not required to reduce residue. Typical pressures of 150 bar to 300 bar are required in inflators. More efficient combustion at lower temperatures would also reduce filter requirements and costs.

• Reduced gas delivery variability

These advantages potentially lead to further indirect benefits in simplifying the inflator design, particularly the propellant housing or propellant vessel. It has also been shown that propellant according to the present disclosure advantageously has improved combustion linearity, particularly at the extreme ends of normal vehicle operating temperatures.

It will be understood by one skilled in the art that although the invention has been described by way of example with reference to one or more examples, it is not limited to the examples disclosed and alternative examples could be formed without departing from the scope of the invention as defined by the appended claims ,

Claims (12)

 Propellant for an airbag inflator system, the propellant comprising a plurality of granules adhered to one another to form a propellant body, with voids present between the granules.  Propellant according to claim 1, wherein the granules adhere to each other by means of an adhesive.  Propellant according to claim 2, wherein the adhesive comprises wax.  The propellant of claim 2, wherein the adhesive comprises a thermosetting adhesive or a pressure-sensitive adhesive.  Propellant according to any one of the preceding claims, wherein the granules are substantially spherical.  Propellant according to any of the preceding claims, wherein the granules are formed as a powder.  Propellant according to any one of the preceding claims, wherein the granules have a diameter between 2 microns and 10 mm.  Propellant according to any one of the preceding claims, wherein the granules comprise sodium azide.  An airbag inflator comprising propellant according to any one of claims 1 to 8.  A method of producing a blowing agent according to any one of claims 1 to 8.  The method of claim 10 including the step of selecting the size of the granules and the volume of voids within the propellant body to control the intended rate of combustion of the propellant. Propellant, airbag inflator and method of making a propellant substantially as described herein with reference to the accompanying drawings.

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