Airbag apparatus for automobile

An airbag apparatus for an automobile includes an airbag case for accommodating an airbag, a fracture-opening section of the surface panel, and a reinforcement frame member having a frame portion, at least one fracture-section reinforcement portion, and an edge reinforcement potion. The frame portion has an engagement portion to which the airbag case is connected. The fracture-section reinforcement portion is joined to the inside surface of the surface panel to cover and reinforce the fracture-opening section. The edge reinforcement portion is joined to the inside surface of the surface panel to cover and reinforce a surface panel portion surrounding the fracture-opening section.

CROSS REFERENCE TO RELATED APPLICATIONS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an airbag apparatus for an automobile for protecting a person in an automobile such as a car; for example, a driver or a passenger sitting in the front passenger seat, from impact upon head-on or side collision of the automobile to thereby ensure safety of the person. More particularly, the invention relates to an improvement in the structure for attachment of a reinforcement member.

2. Description of the Related Art

An airbag apparatus for a front passenger seat or a driver seat of an automobile, such as a car, or that to be mounted on a side pillar of the automobile basically includes an airbag, an airbag case for accommodating the folded airbag, and an inflater for inflating the airbag. The airbag apparatus is disposed inside an interior surface panel of the automobile.

A typical example of such an interior surface panel is an instrument panel cover which is made of a thermoplastic resin material, such as polypropylene, and which covers the surface of an instrument panel core formed integrally from a thermoplastic resin material, such as polypropylene.

Conventionally, a seamless-type airbag apparatus for a front passenger seat has been provided. As shown inFIGS. 1and2, the seamless-type airbag apparatus is designed to render a fracture groove of a fracture-opening section of an instrument panel cover invisible.

Specifically, as shown inFIGS. 1 and 2, the instrument panel cover10has a fracture-opening section14having a size corresponding to that of an opening portion13aof an airbag case13. The fracture-opening section14is formed through provision of front and back hinge grooves10aextending longitudinally, a center fracture groove10bextending longitudinally, and side fracture grooves10cextending transversely. These grooves10a,10b, and10care formed on the inside surface of the instrument panel cover10by use of a laser. Specifically, a pulsating laser beam is perpendicularly applied to the inside surface of the instrument panel cover10while being moved along peripheral edges of a pair of reinforcement plate members11fixed to the inside surface, thereby forming the grooves10a,10b, and10c.

The longitudinally extending center fracture groove10band the side fracture grooves10cformed perpendicularly to the fracture groove10bdivide the fracture-opening section14into a front fracture-opening subsection15aand a rear fracture-opening subsection15b. Upon inflation of an airbag, the fracture-opening subsections15aand15bare split apart from each other in a casement condition (in opposite directions) while hinging on the front and rear hinge grooves10aand10b.

When, upon inflation of an airbag, the fracture-opening section14of the instrument panel cover10is split open by pressure of the inflating airbag12, the front and rear hinge groove10amay be broken, with a resultant separation of the fracture-opening subsections15aand15bfrom the instrument panel cover10. In order to avoid this problem, the conventional air bag apparatus employs a reinforcing structure including the above-mentioned paired reinforcement plate members11, which are provided on the inside surface of the fracture-opening section14of the instrument panel cover10. Specifically, a frame-shaped reinforcement rib16is formed integrally with the instrument panel cover10in such a manner that the rib16projects from the inside surface of the instrument panel cover10, and the rib16defines a rectangular space slightly larger than the opening portion13aof the airbag case13. The paired reinforcement plate members11are disposed within the rectangular space defined by the rib16. The horizontal portions11aof the reinforcement plate members11are fixedly attached to the inside surface of the fracture-opening section14through thermal joining or like processing. Vertical portions11bof the reinforcement plate members11are bent at their hinge portions11cand extend downward along the inner surfaces of front and rear walls of the reinforcement rib16. The front and rear walls of the reinforcement rib16and the corresponding vertical portions11bof the reinforcement plate members11are engaged with corresponding hooks17attached to front and rear walls13bof the airbag case13. The reinforcement plates11prevent scattering of the fracture-opening subsections15aand15bof the fracture-opening section14of the instrument panel cover10upon inflation of the airbag.

In order to allow the fracture-opening subsections15aand15bto be split open smoothly, hook engagement holes11dformed in the vertical portions11bof the paired reinforcement plate members11assume a sufficiently large size so as to allow upward movement of the vertical portions11bwhen the fracture-opening subsections15aand15bare split open.

The thus-configured airbag apparatus functions in the following manner. Upon collision of the automobile, an impact force caused by the collision is detected by a sensor. A control unit including a CPU judges whether or not the detected impact force is equal to or greater than a predetermined value. When the control unit judges that the impact force is equal to or greater than the predetermined value, the control unit issues a signal for causing the inflater to generate a predetermined gas. The gas is fed to the airbag so as to promptly inflate the airbag.

The inflating airbag presses, from inside, the fracture-opening section14of the instrument panel cover10. The fracture-opening section14is fractured along the center fracture groove10band the side fracture grooves10c, whereby the fracture-opening subsections15aand15bare split open about the front and rear hinge grooves10a. The thus-opened front and rear fracture-opening subsections15aand15bare further opened while being turned inside out about the hinge portions11cof the reinforcement plate members11.

Simultaneously, the inflating airbag12projects outward from the instrument panel cover10through the thus-opened fracture-opening section14. Serving as a cushion, the inflated airbag12supports a front seat passenger at his/her chest and head, thereby protecting the passenger from the impact force of collision.

In the above-described airbag apparatus, the reinforcement plate members11and the reinforcement rib16are provided on the inside surface of the instrument panel cover10in a peripheral region around the fracture-opening section14. However, in order to facilitate the installation work of the airbag case13and fracture-opening of the fracture-opening subsections15aand15b, vertical play is provided between the hook engagement holes11dand the hooks17. That is, the reinforcement plate members11and the reinforcement rib16are not configured to support a pressing force imposed from above; i.e., a pressing force imposed on the instrument panel cover10. If a load is mistakenly imposed on the instrument panel cover10, the hinge grooves10a, the center fracture groove10b, and/or the side fracture grooves10cmay be fractured. As a result, the fracture-opening section14is dented or the peripheral edge of the fracture-opening section14is deformed, thereby damaging the appearance of the instrument panel cover10.

Further, conceivably, the conventional airbag apparatus has a drawback in that when the air bag apparatus operates, the inner side surfaces of the reinforcement ribs16are pushed outward at the beginning of airbag inflation, and cracks are generated in the corners at the circumferential edge of the fracture opening portion of the instrument panel cover10, with resultant scattering of the reinforcement ribs16.

In the conventional airbag apparatus, the pair of reinforcement plate members11are fixed to the inside surface of the fracture-opening section14of the instrument panel cover10so as to extend frontward and rearward, respectively, from the central fracture groove10b. However, since the reinforcement plate members11are each formed of a metallic plate, the metallic plates are exposed when the reinforcement plate members11are turned inside out upon inflation of the air bag, and this is not desirable from the viewpoint of safety. Further, during recycling, the reinforcement plate members11formed of metallic plates must be separated from the instrument panel cover10formed of plastic. However, this separation work is cumbersome, because the reinforcement plate members11are fixedly secured to the instrument panel cover10by means of thermal joining or like processing.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is to provide an airbag apparatus for an automobile exhibiting improved resistance to a pressing load imposed externally on a fracture-opening section and its peripheral region of a surface panel covering an instrument panel region, a side pillar region, or a central portion of a steering wheel of an automobile.

Another object of the present invention is to provide an airbag apparatus for an automobile in which a reinforcement frame member having a fracture-section reinforcement portion welded to a fracture-opening section of a surface panel and an edge reinforcement portion welded to a surface panel portion surrounding the fracture-opening section is formed of a thermoplastic resin material as in the case of the surface panel, to thereby enable the surface panel and the reinforcement frame member to be joined through vibration welding, facilitate assembly, and eliminate the necessity of disassembly work at the time of recycling.

To achieve the above objects, the present invention provides an airbag apparatus for an automobile which comprises an airbag case for accommodating an airbag in a folded condition, the airbag case being disposed behind a surface panel provided within the automobile; a fracture-opening section of the surface panel, the fracture-opening section facing an opening of the airbag case and being defined by means of fracture grooves formed on an inside surface of the surface panel; and a reinforcement frame member having a frame portion, at least one fracture-section reinforcement portion, and an edge reinforcement portion, which are integrally formed at an upper end portion of the frame portion. The frame portion has an engagement portion to which the airbag case is connected. The fracture-section reinforcement portion is joined to the inside surface of the surface panel to cover and reinforce the fracture-opening section. The edge reinforcement portion is joined to the inside surface of the surface panel to cover and reinforce a surface panel portion surrounding the fracture-opening section.

Preferably, the frame portion has a front side wall, a rear side wall, a left side wall, and a right side wall, which form a rectangular tubular shape; the edge reinforcement portion extends outward from an upper end portion of the frame portion in a generally horizontal direction; the fracture-section reinforcement portion extends inward from the upper end portion of the frame portion via a hinge portion having a wavy bent section; and the fracture-section reinforcement portion and the edge reinforcement portion are fixed to the inside surface of the surface panel by means of vibration welding.

The fracture-opening section of the surface panel may be defined to have a rectangular shape and to be opened toward a single direction; and the reinforcement frame member may have a single fracture-section reinforcement portion extending from the front or rear side wall of the frame portion via a hinge portion having a wavy bent section.

Alternatively, the fracture-opening section of the surface panel may be defined to have a rectangular shape and to be cut, along a longitudinally extending center line, into two fracture-opening subsections to be opened toward opposite directions; and the reinforcement frame member may have a pair of fracture-section reinforcement portions extending from the front and rear side walls, respectively, of the frame portion via corresponding hinge portions each having a wavy bent section.

Alternatively, the fracture-opening section of the surface panel may be defined to have a rectangular shape and to be cut into left-hand, right-hand, front, and rear fracture-opening subsections to be opened toward four directions; and the reinforcement frame member may have four fracture-section reinforcement portions extending from the front, rear, left, and right side walls, respectively, of the frame portion via corresponding hinge portions each having a wavy bent section.

Preferably, the reinforcement frame member is formed of a thermoplastic resin material of high flexibility such as olefin elastomer.

Preferably, the fracture-section reinforcement portion and the edge reinforcement portion of the reinforcement frame member are vibration-welded to the inside surface of the surface panel in a state in which the hinge portion is compressed toward an inclined connection portion of the edge reinforcement portion.

Preferably, the airbag case is separably connected to the frame portion of the reinforcement frame member.

Preferably, a plurality of projections, each assuming the shape of a ridge, are formed at predetermined intervals on surfaces of the fracture-section reinforcement portion and the edge reinforcement portion, the surfaces facing the inside surface of the surface panel; and the fracture-section reinforcement portion and the edge reinforcement portion are joined, by means of vibration welding, to the inside surface of the surface panel via the projections. In this case, each of the projections preferably assumes the shape of a broken ridge.

Preferably, the engagement portion of the frame portion to which the airbag case is connected is formed in each of the front and rear side walls of the frame portion and is constituted by a group of rectangular holes; and hooks of the airbag case are inserted into the rectangular holes in such a manner that the hooks engage wall surfaces of the rectangular holes when the airbag inflates.

In the airbag apparatus according to the present invention, since the edge reinforcement portion and the fracture-section reinforcement portion(s) are formed integrally with the frame portion, assembly work is facilitated. Further, when a pressing force is imposed on the upper surface of the surface panel, the edge reinforcement portion of the reinforcement frame member supports the surface panel, thereby preventing occurrence of a dent in the fracture-opening section and deformation of the peripheral edge of the fracture-opening section.

By virtue of the configuration such that the fracture-section reinforcement portion extends from the upper end portion of the frame portion via a hinge portion having a wavy bent section, the hinge portion can extend upon opening of the fracture-section reinforcement portion, to thereby suppress impact force that acts on the welded portion between the fracture opening section and the fracture-section reinforcement portion.

By virtue of the configuration such that the reinforcement frame member is formed of a thermoplastic resin material of high flexibility, such as olefin elastomer, which is the same as the material of the surface panel, the surface panel and the reinforcement frame member can be joined together by means of vibration welding, thereby facilitating welding work. Further, this configuration eliminates disassembly work which has conventionally been performed, during recycling, in order to separate frame members and reinforcement plate members formed of metallic plates from surface panels formed of plastic.

By virtue of the configuration such that the airbag case is separably connected to the reinforcement frame member, when a car is to be scrapped, the airbag case can be easily detached from the reinforcement frame member, so that an inflater and other relevant components can be easily removed for proper disposal to thereby prevent potential environmental contamination.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will next be described in detail with reference to the drawings.

FIGS. 3–8show an airbag apparatus for an automobile according to a first embodiment of the present invention and applied to use with a front passenger seat.

InFIG. 3, reference numeral40denotes an integrally molded instrument panel cover made mainly of a thermoplastic resin, such as polypropylene. The instrument panel cover40, which serves as s surface panel, covers an instrument panel core (not shown) fixed to an unillustrated car body and is fixedly attached to the instrument panel core by use of appropriate means, such as tapping screws.

As shown inFIG. 3, an accommodation section42for accommodating an airbag apparatus for an automobile41is formed behind a left-hand portion (for right-hand drive) of the instrument panel cover40in opposition to a front passenger seat. A left-hand drive automobile employs a mirror image of the configuration of the present embodiment; i.e., the accommodation section42is formed behind a right-hand portion of the instrument panel cover40.

The airbag apparatus for an automobile41includes an airbag43to be inflated by means of gas from an inflater; an airbag case44which accommodates the airbag43in a folded condition and which has an opening portion44aat its upper end; and a reinforcement frame member45which is formed of a thermoplastic resin material which is similar to that of the instrument panel cover40. The reinforcement frame member45has a frame portion46, a pair of fracture-section reinforcement portions47aand47bbranching and extending inward from an upper portion of the frame portion46and adapted to reinforce a fracture-opening section51, and an edge reinforcement portion48branching and extending outward from the upper portion of the frame portion46and adapted to reinforce a circumferential edge of the fracture-opening section51. The fracture-opening section51consists of front and rear fracture-opening subsections51aand51b, which will be described later.

The frame portion46has a front side wall46a, a rear side wall46b, a left side wall46c, and a right side wall46d, which together form the shape of a rectangular tube. The above-described edge reinforcement portion48is connected to the upper ends of the four side walls of the frame portion46via corresponding inclined connection walls46ewhich are inclined outward. The edge reinforcement portion48has a generally horizontal upper surface of a rectangular shape and surrounds the fracture-opening section51. Further, the above-described pair of fracture-section reinforcement portions47aand47bare connected to the upper ends of the front and rear side walls46aand46bof the frame portion46via hinge portions49, which are branched from the base portions of the corresponding inclined connection walls46eof the edge reinforcement portion48and are bent in a wavy shape.

In the present embodiment, the frame portion46, the edge reinforcement portion48, and the fracture-section reinforcement portions47aand47bare integrally formed, through injection molding, from a thermoplastic resin material having a high degree of flexibility (low rigidity), such as olefin elastomer.

A plurality of projections50, each formed of a broken ridge, are provided at predetermined intervals on the upper surfaces of the fracture-section reinforcement portions47aand47band on the upper surface of the edge reinforcement portion48, which upper surfaces face the inner or reverse surface of the instrument panel cover40. The fracture-section reinforcement portions47aand47band the edge reinforcement portion48are fixed, by means of vibration welding, to the inside or reverse surface of the instrument panel cover40via the projections50.

Further, the above-described fracture-opening section51is defined in the instrument panel cover40in opposition to the accommodation section42. Upon inflation of the airbag43, the fracture-opening section51is split open by pressing force of the air bag43.

The fracture-opening section51is formed as follows. Hinge grooves40aextending along the longitudinal direction (right-left direction) and side fracture grooves40cextending along the transverse direction (front-back direction) are formed on the inside surface of the instrument panel cover40through laser processing, to thereby define the fracture-opening section51assuming a rectangular shape substantially identical with that of the opening portion44aof the airbag case44. A center fracture groove40bis formed, through laser processing, on the fracture-opening section51along the longitudinal direction of the fracture-opening section51in such a manner as to extend between the centers of the side fracture grooves40c. Upon inflation of the airbag43, the fracture-opening section51is fractured at the side fracture grooves40cand the center fracture groove40b. As a result, as shown inFIG. 6, the fracture-opening section51is split into fracture-opening subsections51aand51bsuch that the fracture-opening subsections51aand51bare turned inside out, in opposite directions, about hinges52, which are implemented by the corresponding hinge grooves40a.

A plurality of square holes53serving as engagement portions are formed in longitudinally extending front and rear side walls46aand46bof the frame portion46. Hooks54fixedly provided on the front and rear side walls of the airbag case44are engaged with the square holes53.

The fracture-section reinforcement portions47aand47b, which are integrally formed with the frame portion46, are connected to the fracture-opening subsections51aand51b, so that the fracture-section reinforcement portions47aand47bcan be swung, about the hinge portions49having wavy bent sections, from a position shown inFIG. 3in which the fracture-section reinforcement portions47aand47bclose the panel-cover-side opening of the frame portion46to a position shown inFIG. 6in which the fracture-section reinforcement portions47aand47ballow inflation of the airbag43.

In the present embodiment, since the fracture-section reinforcement portions47aand47bare connected to the frame portion46via the hinge portions49having wavy bent sections, during inflation of the airbag43, initial pressure that acts on the fracture-section reinforcement portions47aand47bstemming from deformation of the fracture-opening subsections51aand51bcan be absorbed by means of the hinge portions49having wavy bent sections, whereby the fracture-opening subsections51aand51bcan be opened smoothly.

The airbag case44, which accommodates the airbag43, is disposed below the reinforcement frame member45. Hooks44bare fixedly provided on the side walls of the opening portion44aof the airbag case44. The hooks44bare passed through and engaged with the engagement portions (rectangular holes)53of the reinforcement frame member45. An unillustrated inflater for supplying gas to the airbag43is disposed at the lower end of the airbag case44.

The airbag case44is fixed via a support member55to a stationary member of the body of the automobile, such as a cross member56, by use of bolts and nuts56a.

The thus-configured airbag apparatus according to the first embodiment functions in the following manner. Upon collision of the automobile, an impact force caused by the collision is detected by an unillustrated known sensor. An unillustrated control unit including a known CPU judges whether or not the detected impact force is at least equal to a predetermined value. When the control unit judges that the impact force is at least equal to the predetermined value, the control unit issues a signal for causing the unillustrated inflater to generate a predetermined gas. The gas is fed to the airbag43so as to promptly inflate the airbag43(seeFIG. 6).

When the airbag43inflates, pressure generated at the initial stage of inflation of the airbag43is imposed on the inner surfaces of the fracture-section reinforcement portions47aand47band the inner surface of the frame portion46. However, the frame portion46is hardly affected by the inflation, because the frame portion46is connected to the edge reinforcement portion48via the outward inclined connection walls46e. Further, since the edge reinforcement portion48is pulled inward and downward, expansion of the circumferential edge of the opening of the instrument panel cover40can be reduced so as to prevent cracking. The fracture-opening subsections51aand51bwelded to the fracture-section reinforcement portions47aand47bsequentially fracture along the center fracture groove40band the side fracture grooves40c. Then, as shown inFIG. 6, the fracture-section reinforcement portions47aand47bjoined to the fracture-opening subsections51aand51bare opened outward in opposite directions while being turned inside out about the hinge portions49, each of which has a wavy bent section and can be elongated. Therefore, large force acting on the welded portion between the fracture-opening subsections51aand51band the fracture-section reinforcement portions47aand47bcan be absorbed. Further, during the final stage of inflation, that force can be absorbed by the gaps between the hooks54and the wall surfaces of the square holes53of the frame portion46. This pressure-absorbing mechanism can prevent generation of damage to the circumferential edge of the opening of the instrument panel cover40, to thereby enable the fracture-opening subsections51aand51band the fracture-section reinforcement portions47aand47bto smoothly open in a casement condition as shown inFIG. 6.

As described above, in the first embodiment, the reinforcement frame member45is composed of the frame portion46, the edge reinforcement portion48, and the paired fracture-section reinforcement portions47aand47b, which are integrally formed; the paired fracture-section reinforcement portions47aand47b, which face each other at the center of the fracture-opening section51, are connected to the front and rear side walls46aand46bof the frame portion46via the hinge portions49each having a wavy bent section; and the fracture-section reinforcement portions47aand47bare joined to the reverse surfaces of the fracture-opening subsections51aand51bby means of vibration welding. This configuration enables the hinge portions to extend upon opening of the fracture-section reinforcement portions47aand47b, to thereby suppress impact force that acts on the welded portion between the front and rear fracture-opening subsections51aand51band the fracture-section reinforcement portions47aand47b.

Further, in the first embodiment, since a portion of the instrument panel cover40around the fracture-opening section51(hereinafter referred to as an “opening surrounding portion”) is welded to the edge reinforcement portion48of the reinforcement frame member45, the opening surrounding portion is prevented from following the opening displacement of the fracture-opening section51, so that when the air bag43inflates, the fracture-opening section51quickly fractures along the fracture grooves40cinto the fracture-opening subsections51aand51b. Therefore, the fracture surfaces (peripheral end surfaces) of the fracture-opening subsections51aand51bare prevented from having sharp edges or burrs, so that the fracture-opening subsections51aand51bcan have smooth fracture surfaces.

Further, since the opening surrounding portion is reinforced by the edge reinforcement portion48of the reinforcement frame member45, the instrument panel cover40, including the fracture-opening section51, has enhanced resistance to pressing force that is applied to the instrument panel cover40from above, to thereby prevent breakage or deformation of the instrument panel cover40during periods in which the airbag is not operated.

In the first embodiment, the reinforcement frame member45is formed of a thermoplastic resin material as in the case of the instrument panel cover40; and the upper surfaces of the fracture-section reinforcement portions47aand47band the edge reinforcement portion48of the reinforcement frame member45, which surfaces face the instrument panel cover40, are joined to the instrument panel cover40by means of vibration welding, via the projections50, which assume the form of broken ridges formed on the upper surfaces of the fracture-section reinforcement portions47aand47band the edge reinforcement portion48. Thus, the work for welding the reinforcement frame member45to the instrument panel cover40can be performed easily, without generation of thermal deformation of the welded portions.

The airbag case44is separably connected to the reinforcement frame member45. Thus, when a car is to be scrapped, the airbag case44can be easily detached from the reinforcement frame member45, so that an inflater and other relevant components, which are categorized as industrial waste, can be easily removed for proper disposal to thereby prevent potential environmental contamination.

FIGS. 7A and 7Bare vertical cross-sectional views showing a modification of the reinforcement frame member of the airbag apparatus according to the first embodiment.

In this modification, a reinforcement frame member145is molded in such a manner that distal end portions of a pair of fracture-section reinforcement portions147aand147bextending from a frame portion146via wavy-shaped hinge portions149are joined together by means of a thin wall portion147c, and the thin wall portion147cis located below or above the highest points of the hinge portions149so as to increase the lengths of portions of the fracture-section reinforcement portions147aand147bfacing the reverse surface of the instrument panel cover40, to thereby increase the area of a vibration-welded portion. The fracture-section reinforcement portions147aand147band an edge reinforcement portion148are fixed to the reverse surface of the instrument panel cover40as follows. The edge reinforcement portion148is first positioned at the circumferential edge of a fracture-opening section; the fracture-section reinforcement portions147aand147bare then positioned in a state where the hinge portions149, each formed of a wavy bent section, have been compressed and shifted toward inclined connection walls146eof the edge reinforcement portion148; and the fracture-section reinforcement portions147aand147bare then joined to fracture-opening subsections151aand151bby means of vibration welding.

In this configuration, the areas of the fracture-section reinforcement portions147aand147bvibration-welded to the reverse surfaces of fracture-opening subsections151aand151bcan be increased as compared to the case of the above-described first embodiment, whereby secure welding is attained. In addition, since the extendable hinge portions149can be disposed in the vicinity of hinge portions152of the fracture-opening subsections151aand151b, the hinge portions149can be elongated to a greater extent when the fracture-section reinforcement portions147aand147bare opened outward in opposite directions. Therefore, impact force acting on the welded portion between the front and rear fracture-opening subsections and the fracture-section reinforcement portions can be eliminated.

The above embodiment employs a configuration such that the fracture-opening section51is split open in opposite directions. However, the present invention is not limited thereto and can be applied to the case where the fracture-opening section51is split open in a single direction. In this case, the configuration of the fracture-section reinforcement portion to be welded to the inner surface of the instrument panel cover40is modified appropriately.

FIGS. 8 to 10shows reinforcement frame members according to a second embodiment of the present invention, wherein each drawing shows a state in which a reinforcement frame member is applied to an instrument panel cover having a fracture-opening section which is opened toward four directions.

As shown inFIG. 8, a reinforcement frame member245according to the second embodiment has a configuration similar to that of the reinforcement frame member45of the first embodiment, except that the reinforcement frame member245has four fracture-section reinforcement portions247a,247b,247c, and247d, which are to be vibration-welded to reverse surfaces of four fracture-opening subsections251a,251b,251c, and251dof an instrument panel cover240indicated by chain lines.

Specifically, in the configuration shown inFIG. 8, the fracture-opening subsections251a,251b,251c, and251d, which are defined through formation of fracture grooves on the reverse surface of the instrument panel cover240, form a rectangular fracture-opening section, which can be opened in four directions, while fracturing along boundaries between the right-hand and left-hand triangular fracture-opening subsections251cand251dand the front and rear trapezoidal fracture-opening subsections251aand251b. Notably, the shorter sides of the trapezoids defined by the trapezoidal fracture-opening subsections251aand251bcoincide with a line connecting the vertexes of the triangles defined by the fracture-opening subsections251cand251d. The reinforcement frame member245has a horizontally extending edge reinforcement portion248, which branches outward from the upper end of a rectangular frame portion246. Further, the reinforcement frame member245has the above-described four fracture-section reinforcement portions247a,247b,247c, and247d, which branch and extend inward from the upper end of the rectangular frame portion246via corresponding hinge portions239each having a wavy bent section. Among these fracture-section reinforcement portions247a,247b,247c, and247d, the reinforcement portions247aand247b, which extend from the respective upper ends of front and rear walls246aand246bof the frame portion246, each assume a trapezoidal shape corresponding to that of the front and rear trapezoidal fracture-opening subsections251aand251b, whereas the reinforcement portions247cand247d, which extend from the respective upper ends of left and right walls246cand246dof the frame portion246, each assume a triangular shape corresponding to that of the left and right trapezoidal fracture-opening subsections251cand251d.

A plurality of projections250, each formed of a broken ridge, are provided at predetermined intervals on the upper surfaces of the fracture-section reinforcement portions247ato247dand on the upper surface of the edge reinforcement portion248. The fracture-section reinforcement portions247ato247dand the edge reinforcement portion248are fixed, by means of vibration welding, to the reverse surface of the instrument panel cover40via the projections250.

Notably, when the projections250are configured in such a manner that each projection is broken at predetermined positions along the longitudinal direction, thermal deformation during vibration welding can be reduced. However, the shape of the projections250is not limited to the shape of a broken ridge and the projections250may assume the shape of a continuous ridge.

FIG. 9shows a reinforcement frame member according to a modification of the second embodiment. The reinforcement frame member shown inFIG. 9has the same configuration as that of the reinforcement frame member according the second embodiment, except that the vertex potions of the right-hand and left hand triangular fracture-section reinforcement portions247cand247dare each formed by a curved surface. This configuration prevents formation of sharp fracture surfaces, which would otherwise be formed at the vertex potions of the opened fracture-opening subsections and the opened fracture-section reinforcement portions at the time inflation of the airbag. Notably, portions identical with or corresponding to those shown inFIG. 8are denoted by the same reference numerals, and their repeated descriptions are omitted.

FIG. 10shows a reinforcement frame member according to another modification of the second embodiment. The reinforcement frame member shown inFIG. 10has the same configuration as that of the reinforcement frame member shown inFIG. 9, except that the right-hand and left hand fracture-section reinforcement portions247cand247deach assume a semi-circular shape. Notably, portions identical with or corresponding to those shown inFIG. 8are denoted by the same reference numerals, and their repeated descriptions are omitted.

In the above-described embodiments, the hinge grooves40aand the fracture grooves40band40care formed through application of a laser beam to the inside surface of the instrument panel cover40. However, the present invention is not limited thereto. The grooves may be formed through milling or molding. When milling is to be employed, the inside surface of the instrument panel cover is grooved in such a manner as to leave a wall thickness of 0.5 mm-0.8 mm on the front surface side of the instrument panel cover. Alternatively, the grooves may be integrally formed in the course of molding of the instrument panel cover.