GB2304738A

GB2304738A - A knitted air bag

Info

Publication number: GB2304738A
Application number: GB9614472A
Authority: GB
Inventors: Gerald Francis Day; Keith Jeffcoat; Giles Timothy Gregory
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1995-08-24
Filing date: 1996-07-10
Publication date: 1997-03-26
Anticipated expiration: 2016-07-10
Also published as: GB2304738B; GB9517301D0; GB9614472D0

Abstract

An air bag including a knitted fabric envelope (10) which is a 3D knitted structure comprising two single jersey webs (13)and (14) joined at their edge margins (12) e.g. through a double jersey knitted edge margin. The rear web (14) may have more courses than the front web (13). The double jersey margin may include fusible thread to prevent unravelling.

Description

A KNITTED AIR BAG This invention relates to air bags for use in motor vehicles for the protection of passengers and drivers when the vehicle is in a collision.

Air bags are typically produced from a fabric by cutting and sewing the base fabric, usually a plain weave fabric, which has been coated or laminated with a resin composition. The resin composition is generally an elastomeric composition to enhance the heat resistance, and air barrier properties of the air bag.

An air bag is stored in a confined space such as in the steering wheel or instrument panel, so the smaller its storage volume the better. Hence, the softer, lighter and thinner the base fabric the better. However, in the case of conventional air bags, a certain thickness of elastomer is provided by coating or laminating so as to improve the air bag performance, but this increases the thickness and weight, and the handle becomes harsh.

To deal with this problem a non-coated air bag which is a combination of woven and knitted fabric has been proposed in Japanese Laid-Open (Unexamined) Patent Publication No. 2-225155, the centre of which is woven bag-shaped fabric with all or part of the peripheral region being integrally connected by a knitted structure.

However, while the said air bag is soft, possesses elasticity when stretched and can be manufactured at high levels of productivity, since it is a co-called non-coated air bag it possesses the disadvantage that following cutting of the knitted fabric, fraying and laddering tend to occur from the cut regions.

Other attempts to use knitted materials are described Japanese Publication 5-319195 in which knitted fabric is laminated with a non-woven fabric.

A major disadvantages of above attempts to utilise knitted material in air bag construction lies in the use of the cut knitted material in combination with other non-knitted materials.

US Patent 4,994,225 discloses an air bag fabric knitted in the shape of a sleeve or sock on a circular knitting machine which is then shaped to a required form over the external surface of a collapsible mould.

The present invention provides an improved knitted fabric air bag.

Accordingly there is provided an air bag employing an open mouthed knitted fabric envelope which is a continuous 3 dimensional weft knitted structure comprising two single jersey webs joined at their edge margins.

Because the air bag envelope is continuously knitted there are no sewn seams and/or cut edges which may lead to fraying and/or laddering of the knitted material.

The knitted envelopes requires no further joining operation and is formed with an open mouth ready for attachment to a gas injector.

Due to the permeability of the knitted envelope it may be necessary to coat the fabric in a suitable coating which will help control the air permeability and the heat resistant properties of the envelope.

Conveniently, the edge margin are of a double jersey construction, and the inflatable portion of the bag is formed by the two single jersey webs which are integrally knitted together at the double jersey edge margins. Alternatively, the two single jersey layers are joined together by a stitch transfer techniques involving the displacement of selected selvedge loops on one or both needle beds into the corresponding loops on the opposite needle bed. Yet another alternative is to use twisted loops as disclosed in British Patent 835541.

Joining the edge margins of the two webs through a double jersey construction edge margin helps reduce permeability along the joint line as compared with a single jersey edge margin, especially when the widths of the fabric webs vary, causing stitches to be dropped from, or added to needles on a course-by-wale progression.

Preferably each single jersey web has on its reverse face a cross stitch or mis-float construction so that the floating yarn blocks holes in the fabric web and helps reduce the porosity of the knitted fabric.

The air bag may be knitted from yarns which comprises aromatic or aliphatic polyamides, aromatic or aliphatic polyester, polyether ketones, supermacromolecular polyethylene, or polyoxymethylene fibres, or combinations thereof.

The yarn should be a multifilament yarn with a decitex in the order 300-550.

Conveniently the envelope is knitted on 12-16 gauge machine using a 420 decitex nylon 66 yarn and/or a 2/167 decitex polyester yarn.

The air bag may be given shape by varying the number of active needles on a course-by-course basis and/or by one of said single jersey webs comprising more courses than the other of said two single jersey webs between the double jersey set up courses and double jersey selvedge margin courses formed on shoulders adjacent the opening in the envelope.

The excess courses in said one web are formed as two spaced apart portions which lie between portions common in both webs.

The knitted envelope may be coated to render it more impermeable to hot gas e.g. a silicone elastomer containing flame retardants, siloxanes, chloroprene rubbers, polyurethane etc.

Also according to the invention there is provided a method of manufacture of a knitted fabric envelope for an air bag in which the envelope is continuously knitted in a three dimensional form on a weft knitting machine so that the inflatable portion of the envelope is formed from two webs of single jersey construction which are joined together at said edge margins.

The envelope will be knitted on a flat V-bed knitting machine. More details on such knitting machines are to be found in the publication "Dubied Knitting Manual" Published by Edouard Dubied et Cie SA, near Chatel, Switzerland in 1967. Flat V-bed knitting machines are very well known and many such machines are now computer controlled. It has been proposed recently to manufacture upholstery fabric on such flat V-bed knitting machines and proposals have been made - see for example GB-A-2,223,034 to knit upholstery fabric suitable for use in vehicles.

The knitting of a fabric envelope by the method according to the invention uses a Stoll CMS 200 machine with 12 gauge needles. This machine is a flat V-bed machine of the types provided with sinker mechanisms to assist take-down of the knitted fabric. The machine can operate with a plurality of yarn supplies, each of which is associated with a cam system.

The cam box traverses across the needle beds supplying yarn to the needles as desired in each direction of travel.

The envelope is continuously knitted so that the pair of single jersey constructed webs are independently knitted on each of the two needle beds of the 'V' bed knitting machine with the edge margins, preferably, being of double jersey construction and being knitted on both needle beds.

The two single jersey webs form the inflatable portion of the envelope.

The double jersey portions may be knitted in the form of a ribbed construction or an interlock construction, and may comprise the set up courses and the selvedge margins. The press-off margins may be sealed using contractile or fusible threads.

The envelope may be shaped by knitting one web on one needle bed with extra courses as compared with the other web on the second needle bed.

The invention will be described by way of example and with reference to the accompanying drawings in which: - Figure 1 is a knitting pattern for an air bag envelope according to the present invention showing those portions knit only on the back needle bed as cross-hatched areas, Figure 2 is an isometric schematic view of a 3D knitted air bag made according to the pattern of Figure 1, and Figure 3 and Figure 4 are knitting diagrams for portions of the air bag envelope.

Now with reference to Figure 1 and Figure 2 there is shown a knitting pattern 11 for continuously weft knitting an air bag envelope 10 in a single operation.

The fabric is knitted on a 12 to 16 gauge flat 'V' bed knitting machine provided with a conventional presser foot device and/or other loop hold down devices for holding down a knitted fabric between opened needle beds of the machine. The direction of knitting is indicated by arrow A.

The fabric piece is of mainly single jersey construction with a single jersey web being knitted independently on each bed of the knitting machine. The two single jersey webs are joined together at their edge margins by a double jersey construction edge portion.

In Figure 1 the lines A-E represent the working length of two opposed needle beds 51, 52 (see Figures 3 and 4) of the machine on which the envelope 10 is knitted.

The needles operate to form the fabric along vertical lines only (that is in wales) course-by-course.

The knitting begins on the needles between points B and D preferably using a 470 decitex 136 filament nylon yarn preferably on 12 gauge needles. The yarn is knitted as a double jersey construction between both needle beds (51,52) for about 4 to 10 courses and as knitting proceeds needles are added after respective courses so as to gradually widen out the webs 1. After knitting the set-up courses up to points G and H to form the lower edge margin 12, the two beds of needles between points I and J are caused to knit independently so as to knit two webs 13 and 14 of single jersey fabric. The front web 13 is knitted on the front needle bed 51 and the back web 14 is knitted on the rear needle bed 52. The needles between points I and G and point J and H continue to knit in double jersey construction.The width of the double jersey position between the points I and G and J and H is preferably at least 2 needles width, and more preferably 4 to 6 needles in width.

The machine then continues to knit course by course with the single jersey wales being widened out progressively course-by-wale and the double jersey selvedge margins' 15, 16 being moved progressively outwardly whilst preferably maintaining the overall width of the selvedge double jersey margins up to points K and L.

After reaching points K and L, needles will be made progressively inactive on a course-by-course basis to begin to form the sutures 21, 22 in the single jersey webs 13 and 14 (see Figure 2).

During the course of the continuous knitting operation from the set-up edge margin 12 to the top of the air bag adjacent its mouth 20, edges of the fabric as indicated by double ended arrows are knitted together.

For example the edges indicated by double ended arrows M and N, require that the needles are made progressively inactive course-by-course between the needle lines A and I and needles E and J respectively and are then progressively reactivated to 'join' the two edges indicated by M and by N along vertical lines to form the sutures 21 and 22.

The knitting then continues forming two single jersey webs with double jersey edge margins up to the course P, thereafter the front needle bed 51 knitting the single jersey front web 13 is held up and the back needle bed 52 only continues to knit the single jersey portion 14A of the back web 14 forming the sutures 23 from the edges indicated by double headed arrows 0 in the manner described above for the sutures 21 and 22. When the back needles have knitted the portion 14A of the back web 14 as far as course Q then the front needles once again commence knitting.

After course Q the single jersey web portions 13 and 14 are gradually and progressively reduced in width and the double jersey selvedge edge margins 15 and 16 are also moved inwardly whilst preferably maintaining an overall substantially constant width. Due to potential problems with unravelling when dropping stitches from needles the outer wales of the double jersey portions may be knitted with meltable or fusible threads to prevent laddering, or held up and eventually knitted-off with fusible thread.

Both needle beds 51, 52 knit together up to Course R, thereafter the front needle bed 51 is held up and the back needle bed 52 continues to knit the single jersey portion 14B of the back web 14. The back needle bed 52 knits continuously through forming the sutures 24 and 25 from the pairs of edges indicated by double headed arrows S and T and as previously described with respect to the edges 0. When the back web has reached course 'U' the front needle bed 51 also recommences knitting.

After course 'U' the front and back needle beds knit together gradually reducing the width of the single jersey webs by rendering the needles progressively inactive wale-by-course. If the edge margins are of interlock double jersey construction the widths can be reduced by pressing the yarn off the needles. The outer wales in the double jersey edge margins 15 and 16 are again formed with a fusible or meltable thread. At course 'W the needles in the central portion 17 of course W on both single jersey webs 13 and 14 are held up and the yarn knitted at the edge portions is progressively pressed off wale-by-course up to course 'X', and then gradually the needles are reactivated to form the sutures 27 across the edges shown by double headed arrows Y and the needles in the centre portion recommence knitting.

The tubular mouth portion 28 is then formed by either conventional tube knitting or by the two single jersey webs being joined together at their selvedge margin as shown.

The press-off courses 29 at the mouth 20 are knitted with meltable or fusible threads to prevent laddering.

Now with reference to Figure 3 and Figure 4, there are illustrated stitch diagrams in which the upper row of dots represent the back needle bed 51 and the lower row of dotes represents the front needle bed 52. In Figure 3 there is shown a typical snap shot of a section across an inflatable portion of the air bag. The edge margins 15 and 16 on needles 61, 62, 63 and 66, 67, 68 are knitted as a double jersey construction with interlock as shown. (They could also be knitted as 1 x 1 rib structure). The centre portion between needles 64-65 is knitted as two single jersey webs 13 and 14. This process is described in detail in British Patent 1,265,308.

The mouth portion 28 may be formed by conventional tubular knitting as shown in Figure 4, however, such a construction is not suitable for the inflatable portion of the bag because of the tendency to create holes when widening or reducing the width of the tube. This can lead to excess permeability.

The knitted air bag envelope may if necessary or desired, then be coated in a suitable air bag coating such as silicone elastomer and chloroprene rubber compositions.

Each single jersey web 13 or 14 may be knitted with float stitches or cross-stitches on its reverse or inner face so that yarn will tend to block holes in the web and prevent gas exiting the inflated portion of the air bag.

Claims

1. An air bag employing an open mouthed knitted fabric envelope characterised in that the envelope is a continuous three dimensional weft knitted structure comprising two single jersey webs joined at their edge margins.

2. An air bag as claimed in claim 1 wherein the edge margins are of a double jersey construction, and the inflatable portion of the bag is formed by the two single jersey webs which are integrally knitted together at the double jersey edge margins.

3. An air bag as claimed in claim 2 wherein the double jersey edge margins comprise the set-up courses, and selvedge margins.

4. An air bag as claimed in claim 3 wherein the selvedge margins are at least two wales and more preferably between 4-10 wales in width, and the set-up edge is at least two and more preferably 4-10 courses in width.

5. An air bag as claimed in any one of claims 1 to 4 in which the envelope has only a single opening which is smaller in cross-sectional area than the inflatable portions of the envelope.

6. An air bag as claimed in any one of claims 1 to 5 wherein one of said single jersey webs comprises more courses than the other of said two single jersey webs between double jersey set-up courses and double jersey selvedge margin formed on shoulders adjacent the opening in the envelope.

7. An air bag as claimed in claim 6 wherein said single jersey webs includes up to 40% more courses between the set-up courses and the shoulders than said other layer.

8. An air bag as claimed in any one of claims 1 to 7 wherein air bags are knitted on 12 to 16 gauge machine preferably from one or more ends of a 470 decitex nylon 66 yarn comprising 136 filaments.

9. An air bag as claimed in any one of claims 1 to 8 wherein the two single jersey webs are formed with cross stitches or misfloat stitches on their reverse faces.

10. An air bag as claimed in claim 7 wherein the excess courses in said one web are formed as two spaced apart portions which lie between portions common in both webs.

11. A method of manufacture of an air bag having an open mouthed knitted fabric envelope in which the envelope is continuously knitted in a three dimensional form on a weft knitting machine so that the inflatable portion of the envelope is formed from two webs of a single jersey construction which are joined together at their edge margins.

12. A method as claimed in claim 11 wherein the edge margins are formed from a double jersey construction.

13. A method as claimed in claim 12 wherein said double jersey edge margins comprises the set-up courses, and the selvedge margins which are knitted continuously from the set-up courses to the final pressoff courses adjacent the open mouth of the envelope.

14. A method as claimed in any one of claims 11 to 13 wherein one of the single jersey webs is knitted with more courses therein than the other of said two single jersey webs.

15. A method as claimed in claim 14 wherein the extra courses in said one single jersey web are knitted in two spaced apart portions which lie between portions commonly formed in both webs.

16. A method as claimed in any one of claims 11-15 wherein a tubular neck portion is formed at the mouth of the envelope.

Amendments to the claims have been filed as follows

13. A method as claimed in claim 12 wherein said double jersey edge margins comprises the set-up courses, and the selvedge margins which are knitted continuously from the set-up courses to the final press-off courses adjacent the open mouth of the envelope.