Air bag

Abstract: The present invention provides a method of making an air bag comprising joining pieces of fabric together by stitching in substantially straight lines so as to facilitate automated machine stitching of the pieces. Preferably a generally rectangular piece (1) is stitched to four triangular pieces (4,5). Preferably there are two large triangular (4) and two small triangular (5) pieces and each are irregular triangles with three different sides, though the large and small triangular pieces (4,5) may have one side (b,c) the same length as each other and the total sum of the lengths of the other four sides should equal the length of the long side (2) of the rectangle. Such pieces (4,5) are joined by attaching the long sides of the triangular pieces to end regions of the long sides (2) of the rectangular piece (1), folding the resultant shape aöong a transverse line (L), joining respective adjoining second sides (b,c) of the triangular pieces, displacing the apexes of the joined triangular pieces so that the third sides (d,c,f,g) of the respective triangles form a straight line with the long sides (2) of the rectangle, and joining the third sides of the respective triangles to unjoined parts (d,c,f,g) of the long sides of the rectangle.

Description: The present invention relates to inflatable cushions for vehicle occupant protection in the event of a crash, such cushions being commonly known as air bags, and specifically to a method of making an air bag. Traditionally air bags are made by sewing panels of a suitable material together to produce a hollow structure shaped and adapted to provide maximum protection for the vehicle occupant in the event of a crash. On the driver's side this is usually a generally circular structure of similar shape to the steering wheel and somewhat larger than it when inflated so as to provide a cushion barrier between the driver's head and the steering wheel. On the passenger side a larger air bag is needed since the space to be filled by the bag on inflation being that between the passenger's head and upper body and the passenger side dashboard where the uninflated air bag is stored is much larger on the passenger side. Usually a passenger air bag is made by joining a generally rectangular piece of fabric, by stitching together the short sides of the rectangle and subsequently sewing circular, near circular or oval pieces into the open ends formed by the long sides. However cutting circular pieces out of a length of fabric is wasteful of the raw material. Air bag material is expensive since it has to be woven to extremely exacting standards: it must be light, have high strength to resist inflation and crash impact pressures and have a very particular porosity to be effective in inflating quickly yet subsequently deflating within a defined time period. Hence wasted material adds significantly to the cost per item. In addition, circular seams cannot easily be sewn by machine. The need for hand sewing also makes air bags expensive. It is an object of the present invention to provide a method of making an air bag in which a higher proportion of raw material is used and for which automated sewing machinery can be used. US 5 316 337 discloses a method of making an airbag from a single piece of fabric which is formed of a cutting pattern shape of generally rectangular form with triangular extensions at each corner. However this form causes waste of fabric. The present invention provides, in one aspect, a method of making an airbag, by using a cloth of airbag fabric consisting of a generally rectangular piece (1) and four triangular pieces (4,5) bordering the long sides of the rectangular piece in such a manner that a first side of each triangle is aligned with a long side of the rectangle, one corner of each triangle touches a corner of the rectangle, part of the long sides (d,e,g,f) of the rectangle is not bordered by the triangles; the length of this part (d+e,f+g) is equal to the sum of those (second) sides (d+e,f+g), opposite the corner which touches the corner of the rectangle, of both triangles aligned with that long side; and the length of the third sides (b,c) of the triangles aligned with the same long side, are equal; the method comprising folding the cloth generally in half transversely(along line L), sewing the short abutting edges of the rectangle and respective abutting third sides (b,c) of the triangles, subsequently displacing the apexes (A,B) of the triangles so as to align the remaining unjoined second sides (d,e,f,g) of each triangle with the respective unjoined edges (d,e,f,g) of the rectangle and stitching the resultant aligned edges together in substantially straight lines, characterised in that the generally rectangular piece (1) and the four triangles (4,5) are first cut from a length of raw airbag fabric, and then sewn together, in order to reduce waste material. Preferably the generally rectangular piece has each corner truncated. The triangular pieces are sewn on one side of the long sides of the rectangle. Preferably they are right-angled triangles, which may have different length sides, though they may be obtuse angled triangles. According to a preferred embodiment, two pairs of differently sized triangles are used with the larger ones sewn to opposite sides of one end of the rectangle, and the smaller ones sewn to opposite sides of the other end. The large and small triangles preferably have one side of the same length as each other, and the total sum of the lengths of the other four sides should equal the length of the long side of the rectangle. A second aspect of the invention provides a cutting pattern for air bag fabric for use in the method of the first aspect, comprising a generally rectangular shape and four right-angled triangular shapes wherein two of the triangular shapes are substantially identical and are larger than the other two which are also substantially identical, the pairs of triangular shapes being arranged with their long sides adjacent each other and the other sides being respectively substantially parallel and perpendicular to a longitudinal edge of the fabric, and the rectangular piece being arranged with its long sides substantially parallel to the longitudinal edge of the fabric and all pieces being juxtaposed on the fabric with straight sides adjacent one another. The invention also provides an air bag made according to this method or using the cutting pattern of the second aspect of the invention. For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings in which: Figure 1 shows pieces of an air bag partially sewn together according to the method of the invention. Figure 2 shows one example of a pattern layout for pieces of air bags for use in the method of the invention. Figure 3 shows an air bag made according to the method of the invention in an inflated state. Figure 1 shows a generally rectangular piece 1 with two long sides 2 and two truncated tapering sides 3. Four triangular pieces 4 and 5 are attached to the long sides 2 at respective end regions thereof. These pieces 4 and 5 can be attached using an automated machine to sew two straight stitching lines along each of the long sides. Subsequently the rectangular piece 1 with the triangles attached is folded in half along a transverse line of approximate symmetry L-L (this step can also be automated), and further stitching is effected to join sides b together and sides c together. Then the apexes of the joined pairs of triangles are pulled in the direction of arrows A and B (again automation is possible) to position the apexes to respective points L on the long sides 2 of the rectangular piece 1 and align the third side of each triangle with the respective open parts of the long sides of the rectangular piece 1. These sides are then stitched so that corresponding edges are joined: d to d, e to e, f to f and g to g. The result is a hollow fabric structure made with only straight seams with an opening defined by neck regions 6, for the introduction of inflation gas on operation of the device. Since such an air bag design can be assembled substantially entirely using straight line stitching, it can be made by automated machines. This makes the constructions cheaper to produce then hand sewn designs. Referring to Figure 2, a suitable cutting pattern layout is shown with rectangular pieces 1 and triangular pieces 4 and 5 arranged for optimum use of raw material. It is thus seen to be more efficient to use straight-sided shaped pattern pieces such as triangles and rectangles, than curved edged pieces. The use of right-angled triangles allows pairs of triangles to fit together in square shapes so that sides of the cutting pattern pieces fall mostly either parallel or perpendicular to the long sides of the raw fabric, minimising wastage. The wasted area is shown as 7 and it has been calculated that up to 95% of the raw fabric material can be used productively in one example of a method according to this invention as compared to 86% maximum with prior art patterns. Figure 3 illustrates an inflated air bag manufactured to the method of the invention, showing how the rectangular piece 1 and triangular pieces 4 and 5 fit together in the finish product. The air bag made according to this method is strong: triangles are strong shapes and straight seams are more resilient to high inflation and impact pressures. A further advantage is that the air bag need not be turned inside out after stitching as in conventional methods.

Claims: A method of making an airbag, by using a cloth of airbag fabric consisting of a generally rectangular piece (1) and four triangular pieces (4,5) bordering the long sides of the rectangular piece in such a manner that a first side of each triangle is aligned with a long side of the rectangle, one corner of each triangle touches a corner of the rectangle, part of the long sides (d,e,g,f) of the rectangle is not bordered by the triangles; the length of this part (d+e,f+g) is equal to the sum of those (second) sides (d+e, f+g), opposite the corner which touches the corner of the rectangle, of both triangles aligned with that long side; and the length of the third sides (b,c) of the triangles aligned with the same long side, are equal; the method comprising folding the cloth generally in half transversely (along line L), sewing the short abutting edges of the rectangle and respective abutting third sides (b,c) of the triangles, subsequently displacing the apexes (A,B) of the triangles so as to align the remaining unjoined second sides (d,e,f,g) of each triangle with the respective unjoined edges (d,e,f,g) of the rectangle and stitching the resultant aligned edges together in substantially straight lines, characterised in that the generally rectangular piece (1) and the four triangles (4,5) are first cut from a length of raw airbag fabric, and then sewn together, in order to reduce waste material. A method according to claim 1, wherein the generally rectangular piece (1) has each corner truncated. A method according to claim 1 or 2, wherein each of the triangular pieces (4,5) is an obtuse angled isosceles triangle, one side of which is sewn to a long side of the rectangle. A method according to claim 1 or 2, wherein each of the triangles is an irregular triangle with three sides of different lengths. A method according to claim 1 or 2, wherein each of the triangles is a right-angled triangle. A method according to any one of claims 1 to 5 comprising using pieces comprising two pairs of respectively differently sized triangles and wherein the larger triangles are sewn to opposite sides of one end of the rectangle and the smaller triangles are sewn to opposite sides of the other end of the rectangle. A method according to claim 6, wherein each of the large triangles have one side which has the same length as one side of each of the small triangles. A method according to claim 7, wherein the total sum of the length of the other two sides of one of the large triangles and the other two sides of one of the small triangles equals the length of one of the long sides of the rectangle. An air bag made according to the method of any one of claims 1 to 9. A cutting pattern for making an air bag, the pattern comprising a generally rectangular shape (1) and four right-angled triangular shapes (4,5) wherein two of the triangular shapes (4) are substantially identical and are larger than the other two (5) which are also substantially identical, the pairs of triangular shapes (4,5) being arranged with their long sides adjacent each other and the other sides being respectively substantially parallel and perpendicular to a longitudinal edge of the fabric, and the rectangular piece (1) being arranged with its long sides substantially parallel to the longitudinal edge of the fabric and all pieces being juxtaposed on the fabric with straight sides adjacent one another. A cutting pattern according to claim 11, wherein the rectangular piece (1) has each corner truncated.

Inventors: HAMMER BAERBEL, HAMMER, BAERBEL, Hammer, Bärbel
Applicants: BREED AUTOMOTIVE TECH, BREED AUTOMOTIVE TECHNOLOGY, INC.
Application year: 1996
Main classification: B60R21
IPC codes: B60R21, D05B23, D06H5