Low permeability airbag and method

ES 2 268 005 T3

DESCRIPTION

Low permeability airbag and method.

Background of the invention

The present invention relates to low permeability airbags. More specifically, the present invention relates to airbags that must remain inflated for extended periods of time to protect the occupants of a vehicle in the event of a collision, such as a rollover. A side curtain airbag is an example of this type of airbag. One form of side airbag is described in US 6,129,377.

Traditional airbags are manufactured by fabric panels sewn together to form a three-dimensional, substantially closed bag, in which the only substantial opening of the bag (apart from the evacuation holes) is intended to receive the inflation means. Typically, airbags are made of woven fabric and bags of the desired shape have been produced by stitching panels of various shapes and dimensions. Stitched seams may be suitable for some driver and passenger applications because the required gas retention time in these bags is less than one second.

This manufacturing method is unsuitable for side curtain airbags, and the like, because holes made in the fabric during the sewing process allow gas to leak out, reducing gas retention time to unacceptable levels. Furthermore, to obtain fabrics having low air permeability, it has generally been necessary to apply a coating or a thick laminating material to the fabric, which is an expensive step in the manufacturing process.

To address this leakage problem, a solution has been proposed consisting of gluing the fabric panels together by means of welding, such as those described in US 6,042,141. Although this method can prevent or reduce leakage at seams, fabric still requires a coating or thick laminating material and it has been found difficult to directly weld fabric to fabric.

Consequently, it would be desirable to have an airbag that has low air permeability, that does not allow significant gas leakage through its seams, and that requires a minimal amount of laminating or coating material on the face of the airbag's fabric or substrate. .

In WO 01/23219 A1 a welded airbag comprising adjacent reinforcing stitched seams is described.

Objects of the invention

Therefore, an object of the present invention is to provide a low permeability airbag cushion that prevents or reduces leakage along its seams.

The present invention provides a low gas permeability airbag cushion that reduces the use of expensive sheet materials and coatings to be applied to one side of the airbag fabric.

The present invention also provides a low gas permeability air bag cushion having an inner bag confined in an outer bag, thereby forming a double layer air bag cushion.

Preferably, in the present invention a low cost fabric or nonwoven fabric is applied to the outside of the airbag, but has a low permeability internal cushion. The fabric component primarily performs the function of providing strength, rather than being a low permeability medium.

The present invention could preferably be used in driver, passenger or side airbag applications.

Still further, the present invention provides a method of producing a low gas permeability airbag, in which the process prevents the airbag from being punctured so that leakage could occur along its seams.

Preferably, an inexpensive airbag cushion and a method for manufacturing such an airbag cushion is achieved, which minimizes or eliminates the use of expensive liners and sheet materials and which addresses other problems related to the manufacture and production of airbag cushions. having low gas permeability characteristics.

Brief description of the drawings

These and other features, aspects, and advantages of the present invention will be better understood in connection with the following description, the appended claims, and the accompanying drawings, in which:

Figure 1 shows a driver's side airbag, made according to the present invention;

ES 2 268 005 T3 Figure 1A shows a side curtain airbag, made according to the present invention;

Figure 2 shows a cut-away part in cross-section of an airbag made according to the present invention, illustrating the two inner layers of film sandwiched between the two outer layers of fabric, wherein the air chamber is formed within the layers of film, producing an airbag having an inner film layer and an outer fabric layer;

Figure 3 shows a cross section of a heat-welded seam, in which the four layers shown in Figure 2 are thermally welded together and a seam is sewn through all four layers, along and through the polymeric cord formed by middle of the heat welding process.

Detailed description

Figure 1 shows a driver's side airbag 2 having low gas permeability characteristics. The airbag is made up of two different layers of material, an inner layer and an outer layer that surrounds the inner layer. The inner layer is preferably made of a film material, more preferably urethane, and is primarily used to provide a low air permeability layer in the airbag. The outer layer is preferably formed from a fabric and primarily serves to improve the strength characteristics of the airbag. Figure 1A shows a side curtain airbag 4 which may similarly be formed of an inner layer of film and an outer layer of fabric.

In an instant airbag manufacturing method, the airbag is manufactured by stacking two different layers of film material 6 between two different layers of cloth material 8, as shown in Figure 2. The two layers of film can be formed by two separate sheets (as shown) or can be made up of a single folded sheet. Similarly, the two layers of fabric can be made up of two different sheets (as shown) or they can be made up of a single folded sheet with the two layers of film stacked in between. The layers are then heat-welded to form a polymeric cord, which forms the shape and internal chambers of the bag. As used herein, the term "heat welding" refers to any method of sealing together the layers of the airbag cushion that forms a polymeric cord or fused polymeric seal, including but not limited to methods such as the radio frequency welding, ultrasonic welding, high frequency current welding, adhesive bonding, etc. In a preferred embodiment, heat welding produces a pair of polymeric cords, slightly spaced from each other, or a continuous thick cord 10, forming the seams of the airbag cushion.

The polymeric cord 10 produced by heat welding seals the four layers together, forming a film bag within a cloth bag. Within the margins of each heat welded seam, a sewn seam 12 is sewn through the polymeric cord 10, as shown in Figure 3, to give it greater strength. The stitched seam 12 can be applied prior to heat sealing of the bag or after heat sealing of the bag. Since the stitching takes place within the polymeric cord 10, as shown, the holes punched in the bag as a result of this stitching do not allow gas to leak out of the bag when the bag is inflated.

This arrangement allows the film bag to retain gas when the bag is inflated and prevents leakage through the holes in the stitched seam because none of the holes, made in the stitching step, is made on an inflated part. out of the bag. Holes are only made between or within the polymeric beads of the heat weld. The outer fabric layer provides strength and is only glued to the inner bag along its sealed seams. In the first embodiment, the non-heat-welded parts of the bags are not joined together.

Tests have been made with a polyurethane film bag welded to the inside of an unlined 420d fabric bag. The experimental sample was inflated to a maximum pressure of 96.46 kPa (14 psi) and the degree of leakage was measured. After 40 minutes the pressure in the bag had dropped by about 4.13 kPa (0.6 psi).

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Time (min)

ES 2 268 005 T3

The outer bag can be attached to the inner bag only by a stitched seam and not be glued to the inner bag by heat welding. The outer bag can be mounted on the inner bag by sewing individual panels separately (or simultaneously) at the seams of the inner bag, or the outer bag with a small opening can be mounted first and then the inner bag can be placed inside the outer bag. preassembled to stick to it.

The seam sewn at the weld interface serves to transfer the stress from the polymeric cord to the fabric, thereby reinforcing the seal against gas leaks. The polymeric cord continues to maintain its elongation properties after the weld cools, which serves to keep the structure airtight.

It is to be understood that other film materials can be used, including but not limited to polyester, silicone, polyamides, polyolefin, etc., and any combination thereof. Similarly, other fabrics may be employed for the outer bag, including but not limited to woven fabrics, nonwovens, insert weft fabrics, etc., and any combination thereof.

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Accordingly, the scope of the appended claims should not be limited to the description of the preferred versions included herein.