AN INFLATABLE MULTILAYER BOLSTER AND METHOD OF MANUFACTURE

FIELD OF THE INVENTION

The present invention relates generally to the field of safety devices for vehicles. More particularly, it concerns an inflatable bolster for use in the passenger compartment of a vehicle.

BACKGROUND OF THE INVENTION

Bolsters and the like are known in the art. A conventional bolster is mounted within a passenger compartment and includes a hollow body and an inflator for injecting a pressurized fluid into the hollow body. In order to reduce the potential for injuries caused during an impact event or the like, the inflator is activated upon detection of such an event and the bolster is inflated.

For example, the impact event may be a front, rear or side impact, a rollover, or any other event which is likely to cause a rapid change in the vehicle's momentum and thereby cause the occupant to strike some portion of the vehicle's passenger compartment. The fluid released by the inflator into the hollow body serves to inflate the bolster, bringing its outer surface closer to an occupant. By decreasing the distance between the occupant and its outer surface, the bolster can absorb more of the occupant's momentum over a longer period of time, thereby lessening the force experienced.

Bolsters may be provided as part of an instrument panel, a door panel, roof panel, a head rest, or other interior portion of the vehicle.

Known in the art are the following patent and patent applications which disclose inflatable bolsters and the like: US 2007/0108747; US 6,032,978; US 6,203,057; US 6,305,710; US 6,517,103; US 6,578,867; US 6,619,689; US 6,758,493; US 6,848,715; US 6,976,706; US 7,350,852; and WO 2006/132990.

Since bolsters are integrated within the interior of a vehicle, the aesthetic appearance of the bolsters and of the overall interior is an important factor to consider. Bolsters must often present a seamless and consistent appearance once integrated within the vehicle.

Bolsters have been manufactured using various techniques and assembly methods. Many known bolsters are made by assembling independent front and back panels using

a variety of fasteners such that the front panel can rapidly project forward when triggered. Producing separate main components to be assembled together can be time consuming and inefficient. In addition, each of the separate components must be designed and interconnected to provide an aesthetic integral whole which can be difficult.

At the same time, a bolster must have sufficient structure to be properly integrated into the vehicle and retain its form in a passive state. It is often difficult to reconcile structural capacity, efficient production and certain desired aesthetic characteristics.

There is currently a need for a technology that overcomes at least some of the drawbacks of what is known in the field.

SUMMARY OF THE INVENTION

The present invention responds to the above need by providing an inflatable multilayer bolster and a method of manufacturing an inflatable multilayer bolster.

According to one preferred aspect, the invention provides an inflatable multilayer bolster for use in a passenger compartment of a vehicle. The multilayer bolster comprises a hollow body which comprises a back wall devised to face a mating surface of the vehicle; a front wall opposite the back wall and devised to face the passenger compartment; and an air chamber formed between the front and back walls. The front wall comprises an inner layer made of a structural deformable material and an outer surfacing layer co-extruded with the inner layer. The bolster also comprises an inflator for injecting a pressurized fluid into the air chamber and thereby inflating the hollow body, the inflator being mounted to the hollow body.

According to another preferred aspect, the invention provides a method of manufacturing an inflatable multilayer bolster for use in a passenger compartment of a vehicle. The method comprises co-extruding a first polymer and a second polymer through a die to produce a parison, followed by blow-molding the parison to form a hollow body. The hollow body comprises a back wall devised to face a mating surface of the vehicle; a front wall opposite the back wall and devised to face the passenger compartment; an air chamber formed between the front and back walls; and an inflation port in fluid communication with the air chamber for receiving a pressurized fluid to inflate the hollow body. The front wall of the hollow body comprises an inner layer made of the first

polymer in a structural deformable condition and an outer surfacing layer made of the second polymer.

This multilayer bolster and this method of manufacture provide a simplified and efficient bolster construction whereby the inner layer of polymer provides the required structure and deformability while the outer surfacing layer being co-extruded with the inner layer can efficiently provide improved aesthetic appearance characteristics and is more efficiently manufactured.

Further aspects and advantages of the present invention will be better understood upon reading of preferred embodiments thereof with respect to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of an inflatable bolster according to an embodiment of the present invention.

Figure 2A is a cross-sectional view taken along line U-Il of Figure 1 , showing the multilayer structure according to one embodiment of the present invention.

Figure 2B is a cross-sectional view taken along line H-Il of Figure 1 , showing the multilayer structure according to another embodiment of the present invention.

Figure 2C is a cross-sectional view taken along line H-Il of Figure 1 , showing the multilayer structure according to yet another embodiment of the present invention.

Figure 2D is a cross-sectional view taken along line H-Il of Figure 1 , showing the multilayer structure according to still another embodiment of the present invention.

Figure 2E is a cross-sectional view taken along line ll-ll of Figure 1 , showing the multilayer structure according to another embodiment of the present invention.

Figure 3 is a cross-sectional view of an inflatable bolster according to an embodiment of the present invention.

Figure 4 is a side view sketch of a parison for making an embodiment of an inflatable bolster according to an embodiment of the method of the present invention.

While the invention will be described in conjunction with example embodiments, it will be understood that it is not intended to limit the scope of the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and

equivalents as may be included as defined by the present description and appended claims.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, similar features in the drawings have been given similar reference numerals and in order to lighten the figures, some elements are not referred to in some figures if they were already identified in a preceding figure.

Figure 1 shows an embodiment of the inflatable bolster 10. The vehicle interior into which the bolster 10 is to be installed has not been shown. It will be appreciated however that the bolster 10 could be installed, or adapted to be installed, in a variety of places within the passenger compartment of a vehicle.

The bolster 10 comprises a hollow body 12, an inflator 14 mounted thereto, and attachment means 16 for mounting the hollow body 12 to a mating surface within the vehicle. The inflator is for injecting a pressurized fluid into the air chamber and thereby inflating the hollow body.

The hollow body 12 includes a back wall 18 devised to face a mating surface of the vehicle and a front wall 18 opposite the back wall 18 and devised to face a the passenger compartment. A substantial portion of the front wall 20 will often be visible to the passenger, depending on the placement of the bolster. An air chamber (not visible in Figure 1) is formed between the front wall 18 and the back wall 20.

Referring to Figures 2A to 2E, the front wall 20 comprises an inner layer 22 made of a structural deformable material and an outer surfacing layer 24 co-extruded with the inner layer.

Before delving into further features of the preferred embodiments, the following definitions should be noted.

"Structural deformable material" means a material that in a passive state makes up part of the structural form of the bolster and is deformable in response to the fluid released by the inflator into the hollow body. It should also be understood that the term "structural deformable condition" with reference to the first polymer and the inner layer means the condition of the structural deformable material once manufacturing is complete. It should also be understood that the level of structural rigidity of the inner layer may vary depending on the dimensions, the shape and the installation location of the bolster,

among other factors Indeed, various shapes may act to reinforce the structural capacity of the inner layer It should also be understood that the inner layer may have different structural capacity, rigidity and elasticity at different locations, depending on its thickness, the polymer, additives, its relationship with other polymer layers, its shape, etc

"Passenger compartment" mans an interior compartment of the vehicle where an individual may be situated and may be used interchangeably with "occupant compartment"

"Inner layer" means the layer composed of the structural deformable material and is provided inward of the outer surfacing layer The inner layer may be the innermost layer but there may alternatively be another layer coating its interior surface

"Outer surfacing layer" means the layer that covers the outer surface of the bolster at least in the region that is visible to the passenger within the vehicle, with the understanding that paint or other finishing coating may be applied to the outer surfacing layer as well in some embodiments

It should also be understood that the multilayer bolster has at least two layers and may indeed have a third layer or further layers such as adhesive, intermediate, innermost, regrind, coating and/or structural layers

In one preferred embodiment shown in Figures 2C to 2E, the entire hollow body 12 is a one-piece co-extruded structure having the inner and outer layers Thus, the outer surfacing layer 24 surrounds the inner layer 22 in the inner layer's entirety and the back wall 18 would also include the inner layer 22 and the outer surfacing layer 24 Alternatively, as shown in Figures 2A and 2B, the outer surfacing layer 24 may be co- extruded on the front wall only, preferably wrapping around the sides

Referring to Figures 2A to 2E, the hollow 12 body further includes joining sections 26 joining the front wall 20 to the back wall 18 The joining sections may have a variety of forms, structures and shapes as desired

Figure 1 illustrates that the joining section 26 preferably surrounds the perimeter of the bolster to join the front and back walls together

Due to the co-extrusion method used to manufacture the bolster 10, the joining sections 26 may be formed in different ways

Figure 3 shows the hollow body 12 with a pair of opposed joining sections 26, here illustrated as top and bottom sections. These joining sections 26 include a pinch region 28. The pinch region 28 is devised such that only the outer surfacing layer 24 is visible to the passenger.

As shown in Figures 2C and 2D, the inner layer 22 and the outer surfacing layer 24 are preferably directly melt-bonded to each other when co-extruded.

Alternatively, as shown in Figure 2E, there may be an intermediate layer 30 provided in between the inner 22 and outer 24 layers. The intermediate layer 30 may be an additional polymer layer to provide particular properties to the hollow body 12, or an adhesive layer to help bond the inner 22 and outer 24 layers together.

The inner layer 22 is preferably composed of a thermoplastic olefin such as Salflex 245™. The outer surfacing layer 24 is preferably composed of a thermoplastic olefin or polypropylene. The polymer of the outer surfacing layer 24 further may also preferably include at least one scratch or mar resistance additive, such as calcium oxide, calcium carbonate, mica or wax or a combination of such additives. It should also be noted that inner layer 22, outer layer 24 and/or other layers may include either virgin material or scrap reground material. The inner layer 22 of the hollow body 12 may also be modified so as to provide particular structural capacity, for instance by containing additives or being shaped to provide structure. Preferably, all layers of the hollow body 12 are simultaneously co-extruded into a parison and then blow-molded.

Preferably, the inner layer 22 is composed of a first polymer and the outer surfacing layer 24 comprises a second polymer different from the first polymer. The second polymer is chosen such that it may act as an appropriate surfacing layer. For instance, the second polymer may have a lower gloss level than the first polymer. The second polymer may have a lower viscosity at a molding temperature than the first polymer, to be more conducive to graining as grain is imparted to the polymer layer by the mold. It is also preferred that the first and second polymers have a substantially similar viscosity at extrusion conditions to facilitate initial that part of the process, and the second polymer has a lower viscosity at the blow-molding conditions for graining purposes. The second polymer may have a greater acceptance of coloring agents than the first polymer; it may for instance have an improved base color for coloring. The outer surfacing layer may include a colorant or be formed of a material so as to match the appearance of other interior vehicle components.

Preferably, as shown in the embodiment of Figure 2D, the outer surfacing layer 24 has an inferior thickness compared to the inner layer 22. The outer surfacing layer may be provided as thin as possible to improve the visual appearance while minimizing material consumption. By way of example, the outer layer 24 may have a thickness between about 0.1 mm and about 2 mm and the inner layer 22 may have a thickness between about 1 and about 5 mm. It should also be noted that each of the inner 22 and outer 24 layers may variable thickness at different locations of the bolster 10. For instance, it may be desired to provide a smaller thickness at the joining sections 26 to facilitate inflation, while keeping the central parts of the bolster thicker and thus more rigid.

The following will describe an optional embodiment of a method of manufacturing an embodiment of the inflatable multilayer bolster 10.

The method includes co-extruding a first polymer and a second polymer through a die to produce a parison and then blow-molding the parison to form a hollow body.

In the blow-molding step, the hollow body 12 is molded to as to have the back wall 18, the front wall 20, the air chamber between the front and back walls, and also an inflation port 32 in fluid communication with the air chamber for receiving a pressurized fluid to inflate the hollow body 12. The inflation port 32 houses the inflator 14.

The parison is co-extruded and has a moldable temperature during subsequent blow- molding. However, once the molding is complete the hollow body 12 will be composed of the inner layer 22 which is in a structural deformable condition and the outer surfacing layer 24.

The co-extrusion may be performed by providing at least two polymer inputs and co- extruding them through a die concentrically to produce a radially inner layer and at least one layer radially adjacent to the inner layer. Additional layers may be co-extruded, each being radially adjacent to the previous inward layer. As some polymers are better bonded together by an adhesive, it may be desired to co-extrude an adhesive layer in between two layers.

When co-extruded, the parison is tubular and may have a variety of cross-sections. Preferably the parison has a circular cross-section and is substantially cylindrical. Since the parison is tubular and has two opposed open ends, the blow-molding step preferably includes pinching each open end so as to form the corresponding pinch region 28 joining the front wall 20 and the back wall 18. The pinching may be performed by orienting or

providing the pinch region 28 such that only the outer surfacing layer is visible to the passenger. The pinch region may be formed by flashless design or by other techniques whereby the pinching is placed away from the occupants line of sight.

The co-extrusion is preferably performed so that the entire parison has a double-walled structure respectively formed of the first and second polymers. In other words, the co- extruding preferably includes extruding the first polymer into a tubular form and extruding the second polymer directly to the first polymer to completely surround the same, thereby producing the parison.

Referring now to Figure 4, the parison 34 may have has tubular subsections. In the illustrated example, the parison 34 has three subsections 36A-36C along its length, but this is merely exemplary and there may be less or more subsections of various lengths along the parison 34. Each subsection has a substantially constant wall thickness T horizontally. The co-extruding may be controlled so that at least one of the tubular subsections 36A-36C has a different wall thickness T from one of the other tubular subsections. Thus, once the parison 34 is blow-molded, the hollow body 12 may have parts having differing wall thicknesses. For instance, subsection 36B of the parison 34 may be given a greater thickness and thus the corresponding central region of the front and back walls of the bolster may be thicker, less deformable and may include molded integral components. For example, the inflation port 32 may be molded from a parison subsection having a greater thickness which bestows improved properties on that part of the bolster.

As for the blow-molding step, once the parison is extruded, mold portions (usually halves) are closed over the parison and a gas is blown to the interior of the parison to expand it against the interior walls of the mold cavity defined by the mold portions. The mold cavity may be provided to have outcrops and recesses that define various elements of the hollow body, such as attachment points, the injector port, vents, etc. The mold may also be provided so as to form ribs, pleats, and other structural and inflation- facilitating shapes, particularly in the back wall and the joining sections of the bolster.

Embodiments of the inflatable multilayer bolster 10 and the method of manufacturing provide numerous advantages. There is a cost-reduction due to more efficient manufacturing, as there are fewer steps to obtain improved aesthetics of a one-piece bolster. In addition, two or more co-extruded layers may resist tear away from each other during bolster inflation. Furthermore, the chemical properties of the inner and outer

layers may be tailored to best respond to the desired conditions. For instance, the inner layer may be composed of inexpensive material; its thickness may be varied to provide the necessary structure; it may go uncolored to save on colorant, etc. The outer surfacing layer may be provided as a thin skin to allow savings on colorant; it may be composed of a certain polymer or may include additives to allow improved aesthetics or better contact with the passenger upon impact. In addition, one can tune expansion characteristics by adjusting the different layers or by adding additional layers rather than reformulating base resin which can be quite laborious. The outer surfacing layer may also be made of a polymer having better electrical conduction properties to reduce static electricity and thus facilitate subsequent paint application.

Although the present invention has been explained hereinabove by way of a preferred embodiment thereof, it should be understood that the invention is not limited to this precise embodiment and that various changes and modifications may be effected therein without departing from the scope of what has actually been invented.