REDUCED STRESS INFLATABLE BAND FOR VEHICLE OCCUPANT RESTRAINT SYSTEM

Abstract: An inflatable band occupant restraint system includes an inflatable band that is configured to lower the stresses encountered by the band fabric during inflation and secondary impact. This reduction is accomplished by including a pleat pattern that better approximates the ideal cylindrical curvature of the band when inflated, attaching the band to a seat belt using a smaller radius attachment portion, and stitching the pleated portion of the band to the belt while maintaining the center of the band stitching-free.

Description: REDUCED STRESS INFLATABLE BAND FOR VEHICLE OCCUPANT RESTRAINT SYSTEM Description Cross-Reference to Related Application This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/051 ,995, filed July 9, 1997, the entire contents of which are expressly incorporated herein by reference. Background of the Invention Field of the Invention The present invention relates to vehicle occupant restraints. More particularly, the present invention relates to an inflatable band restraint that is configured to reduce stresses and strains on the band material. Description of the Related Art Inflatable band restraint systems are increasingly being considered as safe, cost-effective replacements for air bags and seat belts in automobiles. An inflatable band restraint system is typically incorporated into a three-point seat belt harness and, like conventional air bag restraint systems, inflates to protect the occupant upon impact. Unlike an air bag, however, the inflatable band is in contact with the occupant prior to inflation in a manner similar to conventional seat-belt arrangements. This contact practically eliminates the delay between inflation and occupant restraint. Air bag systems decelerate the occupant by contacting him somewhere between the occupant's original position and the dashboard as he travels towards the dashboard while the vehicle decelerates during the crash. In contrast, an inflating band simultaneously tightens the belt, thereby maintaining the occupant in his seat to decelerate at a rate approaching the deceleration of the vehicle itself, a rate which has been shown to reduce the risk of injury to the occupant. The inflated band supports the head, torso and chest of the occupant from the side of the vehicle during deceleration. The band's large contact area better distributes deceleration forces across areas of the body less prone to critical injury than the head. One of the difficulties encountered in the inflatable seat band results from the high stresses in the connection region generated by the internal pressure combined with the axial load resulting from body impact. In the past, most efforts at strengthening inflatable bands have focused on using bulkier, higher strength fabrics. These bulky fabrics are not compact when stitched into a flat, thin shape for the band's uninflated, "seat belt" function, and tend to be abrasive, causing cuts and abrasions when deployed. In light of the foregoing, there is a need for an inflatable belt with a more structurally efficient design to reduce the stresses and strains present in the band connection regions, thereby allowing the use of lighter weight and softer fabrics. Summary of the Invention The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purpose of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises an inflatable band for use in a vehicle occupant restraint system comprising a center plane and a plane of symmetry perpendicular to the center plane. A first inner pleat and a second inner pleat are also included, the second inner pleat being further away from the plane of symmetry, but closer to the center plane, than the first inner pleat. In another aspect, the invention includes an inflatable vehicle occupant restraint comprising an inflatable band of material including a plurality of pleat pairs. Each pleat pair should be comprised of an inner pleat and an outer pleat spaced from the inner pleat by an intra-pleat span of material having a first width. Adjacent pleat pairs are connected to each other by an inter-pleat span of material having a second width. The second width of the inter-pleat span of material is wider than the first width of the intra-pleat span of material. ln yet another aspect, the invention includes an inflatable band for use in a vehicle occupant restraint system comprising a plurality of inner pleats and outer pleats, and a stitch pattern whose curvature corresponds to the curvature of the inflated portion of the band in the connection region of the band. In a further aspect, the invention comprises an inflatable band for use in a vehicle occupant restraint system comprising a first plurality of inner pleats and outer pleats located on one side of a center line and a second plurality of inner pleats and outer pleats located on the other side of the center line. The inflatable band is folded at the pleats and attached to a belt by stitching which pierces through a portion of the band between the inner and outer pleats such that a region between the first and second inner pleats is not stitched. This band can also use adhesives instead of, or combined with, stitching to make the attachment. In yet a further aspect, the invention includes a vehicle occupant restraint system comprising a belt and an inflatable band which is attached to the belt at a concave attachment region having a radius equal to or smaller than the inflated radius of curvature of the inflatable band. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. Brief Description of the Drawings The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. In the drawings, Fig. 1 is a cross-sectional view of a conventional inflatable band; Fig. 2 illustrates the ideal expansion state of an inflatable band; Fig. 3 illustrates the actual path lengths of a conventional inflatable band in the expanded state; Fig. 4 is a partial cross-sectional view of an inflatable band according to the present invention; Fig. 5 is a cross-sectional view of a band according to the present invention; Fig. 6 illustrates the preferred stitching location of a conventional inflatable band; Fig. 7 illustrates a preferred attachment configuration according to another aspect of the invention; Fig. 8 is a closer view of the preferred attachment configuration; and Fig. 9 is a graph illustrating the folded thickness of a band according to one embodiment of the invention. Description of the Preferred Embodiments Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Prior art inflatable bands use a simple folded structure to fold the band into a compact, flat shape resembling a seat belt as shown in Fig. 1. Outer pleats 1-6 are stacked, one above the other, and inner pleats 11-15 are similarly stacked when the band is not inflated. In order to maintain the "seat- belt" shape, the spans of fabric which connect the outer and inner pleats 11- 15 at a distance, f, from each other are folded together and the entire band is stitched to a seat belt (not shown) extending through the interior of the band. While investigating the stresses generated during the initial inflation of inflatable band restraints, the inventor discovered that the pleat arrangement of the band material greatly influences the stress distribution. Specifically, the inner pleats experience higher strains than the other portions of the band material. A cause of this strain is demonstrated in Figs. 2 and 3. The ideal inflated state of the band is shown in Fig. 2. The ideal band inflates into a cylinder surrounding the belt 7 in which all of the outer pleats 1-6 and inner pleats 11-15 are points located on the same circle of radius R. The actual inflated state of the conventional band is illustrated in Fig. 3. The width of the span of fabric, f, creates different expansion center points for the outer and inner pleats, R' and R, respectively. In this configuration, the inner pleats 11-15 are taking most of the load, while the outer pleats 1-6 are not significantly contributing to the support of the load. Thus, the stress and strains on the inner pleat material are much higher than the other portions of the band, and a large center-line load is applied to the seat belt webbing 7 where the band is attached thereto. Fig. 4 illustrates a pleat configuration in an inflatable band according to one aspect of the invention. The inflatable band of material includes a plurality of pleat pairs comprised of inner pleats 11'-15" and outer pleats 1 '-6'. The outer pleats 1'-6' are spaced from the inner pleat 11'-15' by spans of material 21-25 and 31-35. Within each pair, the inner pleats are spaced from the outer pleats by intra-pleat spans 21-25. Adjacent pleat pairs are connected to each other by inter-pleat spans of material 31-35. The inter- pleat spans of material 31-35 are wider than the intra-pleat spans of material 21-25. As shown in Fig. 4, a pair of pleats is made up of, for example, outer pleat 1' and inner pleat 11 ' which are spaced from each other by an intra-pleat span of material 21. An adjacent pair of pleats is made up of outer pleat 2' and inner pleat 12' which are spaced from each other by intra-pleat span of material 22. The two adjacent pairs are connected to each other by an inter- pleat span of material 31. This pattern may be symmetrically reproduced on the other side of the plane of symmetry 8 and the band's center plane 9. While the tuxedo pattern in Fig. 4 illustrates a pleat configuration in which the pleat directly adjacent to the belt 7 is smaller than the other pleats, the pleats may all generally be the same size. The resulting band is illustrated in Fig. 5. The inner pleats get closer to the center plane 9 of the belt as they get further away from the plane of symmetry to produce a "tuxedo fold" configuration. Moving the inner pleats out reduces the difference between the radial expansion positions of the inner and outer pleats. This difference tends to become smaller near the plane of symmetry. Similarly, the outer pleats may get closer to the center plane 9 of the belt as they get further away from the plane of symmetry 8. Also, the attachment forces are distributed across the width of the seat belt webbing, lowering the stress concentrations. The band of Fig. 4 may be about 2 inches wide so that X is about 1 inch. The adjacent pleats are extended out by distances, x, of about 1/8", as they get closer to the plane of symmetry 8. The 1/8" fold is repeated below the plane of symmetry. However, the distances, x need not be equal spacings, but can also be a variety of distances, e.g., X1 , X2, X3, X4. Expansion of the band results in a less jagged appearance or better approximation to the bulk expansion of the cylinder than that shown in Fig. 3; the band according to the invention exhibits a much smoother curvature approximation. In other words, the tuxedo fold illustrated in Figures 4 and 5, keeps the folded fabric at the most even distance to the outer periphery of the inflated cylinder. Preferably, a belt 7 is located in the plane of symmetry. The term "belt", as used herein, broadly refers to material used to maintain the position of the band. For example, the belt may be similar to a conventional seat belt that extends completely through the center of the band or it may refer to a section of material that ends within the band and secures the band in place near the upper body (shoulder or head) of the occupant or anchors the band in place near the floor of the vehicle. If the belt extends through the center of the inflatable band, the middle of the band may be folded at the pleats and attached to the belt by stitching 41 piercing through a portion of the band between the inner and outer pleats 40 such that a region between the inner pleats closest to the center plane is not stitched. This stitching configuration may be used with the tuxedo fold or with the conventional fold as shown in Fig. 6. In the tuxedo fold, the stitching arrangement is not present in the two layer fabric region 42 between the inner-most interior pleats 11' and 11" and 11 '" and 11"". Adhesive may also be used instead, or in combination, with the stitching. The inventor also discovered that the configuration of the attachment of either end of the inflatable band to a belt also plays a significant role in the overall integrity of the inflatable band restraint system. Conventional bands are attached using a flat attachment region or a "crown stitch pattern" in which a convex stitch pattern is used, i.e., the stitching bows away from the inflatable band. The inventor discovered, however, that this conventional attachment configuration promotes failure of the stitching and/or band and/or belt at the attachment region. This failure has been determined to be the result of uneven stresses at the attachment region because in actual use the inflated band is subjected to axial loading from the restraint of the occupant. This axial loading effectively reduces the radius of the inflated band, thereby altering the stresses and strains at the attachment portion. In order to remedy the uneven stresses at the attachment portion, the inflatable band may be attached to the belt at a concave attachment region as demonstrated in Figs. 7 and 8. The radius of the curved attachment region is equal to or smaller than the inflated radius, R, of curvature of the inflatable band thereby compensating for the reduced radius of the inflated band when it is subjected to axial loads, such as those produced by restraining the occupant. By attachment region, it is intended that this term refer to the leading edge of the region at which the band is attached to the belt. It is at least this portion that has the desired shape. The leading edge (i.e., the right side of the stitching region in Fig.8) is the more significant portion because this edge bears most of the strain at the attachment portion. While the left side of the region is also shown to have a radius of curvature, it may be configured otherwise and still fall within the scope of this invention. The radius of curvature of the concave attachment region may approximate an arc of a circle, a parabola, or any other curved shape that approximates the actual radius of the axially loaded, inflated band during deployment. The degree to which the attachment region radius of curvature differs from the inflatable band's radius of curvature depends on the degree to which the belt/band system will be axially stressed. For example, in a configuration in which the belt extends completely through the interior of the band, the belt will reinforce the band. The resulting axial "stretching" of the band, therefore, will be smaller than in a system in which the belt does not extend through the band. Thus, the difference between radii of curvature can be larger for the system in which the belt does not extend through the band or for other configurations tending to experience greater axial strains. The band can be attached to the belt by any number of means, such as stitching, adhesive or a combination of both, and the band may be attached to the belt at one or both of the ends using this configuration. The tuxedo fold produces an uneven fabric thickness profile across the width of the band as illustrated in Fig. 9. (which is shown without the seat belt webbing) and the scale of Fig. 9 can be adjusted by the fabric thickness. A conventional buildup typically uses 12 layers of fabric. The resulting profile may be cast or otherwise formed into the clip arrangement used to secure the belt to the band, or in a D-shaped belt routing clip similar to those used in conventional seat belts. This profile will help ensure that the pleats of the tuxedo fold are in the appropriate positions and would reflect the shape shown in Fig. 9. The invention will be further clarified by the following examples, which are intended to be purely exemplary of the invention. EXAMPLE 1 The inventor has completed a finite element analysis comparing the conventional fold pleated band and a band using the tuxedo fold configuration to compare the stresses which are generated from initial inflation. The results of the analysis demonstrated the improvements attained by the tuxedo fold pattern. This structure has similar thickness in the center of the band as the conventional pleated fold pattern (7 layers of fabric on each side of the belt.) The analytical model of the tuxedo fold was constructed of 10,148 nodes and 10,128 membrane elements. Similar loading as was used in a conventional pleated band analysis was applied to this model to allow a direct comparison of the results (20 psi inflation peak). All the warp and fill results were presented in terms of fabric capacity and the fabric thickness was factored into the color assignments. This gave a direct read on the percentage of fabric capacity in lb/in quantities normally used in fabric strength comparisons. Outside Fabric Results The shear force distribution for both the tuxedo and pleated folds were determined. The tuxedo fold reduced the shear force from 41 lb/in to 29 lb/in, but, more importantly, reduced the zone in the fabric where shear is present. The maximum strain in the outer fabric was reduced with the tuxedo fold from 10.8% to 7.7%, with widespread strain being reduced from the 7-8% range to the 6-6.3% range. The maximum fill stress distribution showed a similar reduction from 220 lb/in to 150 lb/in. In the warp direction, the reduction was from the pleated fold 42 lb/in to 34 lb/in for the tuxedo fold. The strain in the top layer of fabric extended across the spherical section of the band, toward the cylindrical portion of the structure, for both kinds of folds. This portion of fabric is loaded most aggressively by the secondary impact, because there is no pleat here and the fabric is essentially tight from the inflation only. The tuxedo fold experienced a zone of 6% fabric strain, whereas the pleated fold had a larger zone of 8.8% strain. This is a potential failure site for dynamic loading, and, here too, the tuxedo fold demonstrated significant improvement. In summary, the analysis demonstrated that the tuxedo fold configuration reduces the stress in the outer layer of fabric on the centerline to approximately 2/3 that of the pleated fold. Inside Pleat Results The tuxedo fold reduced the peak fill loading from 308 lb/in to 236 lb/in. The warp stress was low in this area since the pleats were not filled out, so these values of stress are inconsequential. Strain in the pleats demonstrated similar results to the fill, with 16.6% strain being reduced to 12.7% for the tuxedo folds. More widespread results indicated that an 11 % strain can be reduced to approximately 6-8% when the tuxedo fold structure is used. In summary, the analyses demonstrated that the tuxedo fold reduces the critical inside pleat stress by about 1/3. It will be apparent to those skilled in the art that various modifications and variations can be made in the inflatable band and restraint system of the present invention and in construction of this band and system without departing from the scope or spirit of the invention. For example, the number of pleats, span sections, and seams may be varied from those embodiments illustrated herein. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims: What Is Claimed Is: 1. An inflatable band for use in a vehicle occupant restraint system comprising: a center plane and a plane of symmetry perpendicular to said center plane; a first inner pleat and a second inner pleat, said second inner pleat being further away from said plane of symmetry, but closer to said center plane, than said first inner pleat. 2. The inflatable band of claim 1 , including a first outer pleat and a second outer pleat, said second outer pleat being further away from said plane of symmetry, but closer to said center plane, than said first outer pleat. 3. The inflatable band of claim 1 , including a belt located in the plane of symmetry. 4. The inflatable band of claim 3, wherein: said inflatable band is folded at said pleats and attached to said belt by stitching piercing through a portion of the band between the inner and outer pleats such that a region between the inner pleats closest to the center plane is not stitched. 5. The band of claim 1 including a concave attachment region having a radius equal to or smaller than the inflatable band's inflated radius of curvature. 6. The band of claim 1 including a concave attachment region having a radius smaller than the inflatable band's inflated radius of curvature. 7. An inflatable vehicle occupant restraint comprising: an inflatable band of material including a plurality of pleat pairs, each pleat pair comprised of and inner pleat and an outer pleat spaced from said inner pleat by an intra-pleat span of material having a first width, adjacent pleat pairs being connected to each other by an inter- pleat span of material having a second width; wherein the second width of the inter-pleat span of material is wider than the first width of the intra-pleat span of the of material. 8. An inflatable band for use in a vehicle occupant restraint system comprising: a first plurality of inner pleats and outer pleats located on one side of a center line; a second plurality of inner pleats and outer pleats located on the other side of the center line; wherein said inflatable band is folded at said pleats and attached to a belt by stitching piercing through a portion of the band between the inner and outer pleats such that a region between the first and second inner pleats is not stitched. 9. A vehicle occupant restraint system comprising; a belt; an inflatable band having an inflated radius of curvature, said inflatable band being attached to said belt at a concave attachment region having a radius equal to or smaller than the inflated radius of curvature of the inflatable band. 10. The band of claim 9 wherein the concave attachment region has a radius smaller than the inflatable band's inflated radius of curvature. 11. The vehicle occupant restraint system of claim 9, including stitching at the attachment region. 12. The vehicle occupant restraint system of claim 9, including adhesive at the attachment region. 13. The vehicle occupant restraint system of claim 9, including adhesive and stitching at the attachment region. 14. The vehicle occupant restraint system of claim 9, wherein the belt extends through the inflatable band. 15. The vehicle occupant restraint system of claim 10, wherein the belt ends within the inflatable band. 16. The vehicle occupant restraint system of claim 9, including two attachment regions, one at each end of the inflatable band. 17. The vehicle occupant restraint system of claim 9, wherein the radius of the curved attachment region corresponds to a loaded inflated radius of curvature of the inflatable band.

Inventors: GWINN KENNETH W, GWINN, KENNETH, W.
Applicants: PRECISION FABRICS GROUP INC, PRECISION FABRICS GROUP, INC.
Application year: 1998
Main classification: B60R21
IPC codes: B60R21, B60R22