Title of Invention

"AN AIRBAG COVER AND METHOD OF MANUFACTURING THEREOF"

Abstract An airbag cover(10a) comprising a cover material formed from a synthetic resin by molding; and a breakable portion(16) which is thinner than other portions of the airbag cover for breaking, by a pressure of an inflating airbag to thereby form a projection opening (12a) through which the airbag(4) projects, wherein the breakable portion (16) has at least one notch(16a) that is cut on the cover material, the cutting blade(37) accommodating portions (21) are recesses formed by the molding at positions corresponding to a starting end and a terminating end of the notch to accommodate therein a cutting blade of the working tool.
Full Text AIRBAG COVER
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an airbag cover formed from a synthetic resin through molding which is made to cover a folded airbag and which comprises a thin breakable portion which extends linearly so as to be broken by being pressed by the inflating air bag to thereby form a projection opening through which the airbag is allowed to project.
2. Related Art
In a conventional airbag cover which is made from a synthetic resin, a thin breakable portion was formed around a lid portion so that the lid portion can be opened to form a projection opening when the cover is pressed by an airbag (refer to, for example, JP-A-2005-289254 and JP-T-2002-538035 (Published Japanese translationof PCT patent application)). This breakable portion was made by providing a recessed groove on a rear surface side of the airbag cover which was injection molded, and furthermore, in order to enable the work of forming the breakable portion with enhanced dimension accuracy as to position and depth of the recessed groove so provided, the position and depth of a working line were measured in advance by means of an optical measuring apparatus,

and the recessed groove was formed through cutting work in which a recessed groove-shaped notch was made by makin.g use of a cutting plate of a working tool such as an ultrasonic cutter.
When forming the breakable portion of the airbag cover by the cutting work, however, there has remained room for improvement in eliminating variation in position and depth of the notch made. Namely, in the event that there exists large variation in position and depth of a notch made, a smooth breakage of the breakable portion
at such a low temperature as -20°C will be interrupted. In the case of an airbag cover which includes, as in the conventional example, two lid portions which are surrounded on their peripheries by a mounting wall portion which protrudes towards a rear surface side of the lid portions, however, a breakable portion is disposed between the lid portion- which lies in the vicinity of a side wall portion and the mounting wall portion. Because of this, in particular, since a location of the breakable portion which is disposed between the lid portions is disposed in such a way that ends thereof are situated in positions lying in the vicinity of the mounting wall portion which the location is disposed to intersect, when forming the ends, the orientation and angle of the cutter need to be changed

in order to avoid the interference with the side walL, and this serves to deteriorate the workability in forming a notch with the cutter, and hence, there still existed room for improvement in increasing the notch making workability.
Furthermore, as to the arrangement of the breakable portion, a T-shaped intersecting portion where a traversing section is made to intersect one of straight section in a T-shape fashion as viewed from the top is disposed at two locations, whereby the breakable portion was formed into an H-shape as viewed from the top (refer to, for example, JP-A-2000-264159). In the breakable portion like this, two lid portions were formed in an airbag cover which was divided by a horizontal section of the H-shape, and locations which connect together both ends of vertical rod-like portions of the H-shape which face~e"ach other are made to constitute "hinge portions which function as hinges when the lid portions are opened, whereby the breakable portion which was arranged into the H-shape was made to be broken when an airbag was deployed and inflated so as to allow the two lid portions to be opened.
However, in forming the T-shaped intersecting portions by forming the breakable portion of the conventional airbag cover through the cutting operation,

when forming the traversing section relative to one o f the straight sections through the cutting operation, there exists a risk that the cutting blade of the working tool moves across the area where the relevant straight section lies to thereby make a notch on an unexpected area of the airbag cover. The notch which happened ~o be extended to the unexpected area on the airbag cover may cause a risk that when the breakable portion is broken, the traversing section breaks across the straight line-shaped portion to thereby extend the breakage to the unexpected area and may cause further a risk that a location on the airbag which does not have to be broken is eventually broken to scatter fractures thereof.
SUMMARY OF THE INVENTION
The invention was made to solve the problems, and an o'b"je~ct thereof is to provide an airbag cover which can be manufactured while suppressing the variation in position and depth of the notch made.
Another object thereof is to provide an airbag cover in which even when the traversing section between the T-shaped intersecting portions of the breakable portion is formed through the cutting operation, the cutting operation can be implemented while preventing the generation of an unnecessary notch.

Another object thereof is to provide an airbag cover which can provided good workability in forming a threadlike breakable portion even though ends of the breakable portion which is formed with a working tool-having a cutting blade are provided in the vicinity of the mounting wall portion.
According to one aspect of the invention, there is provided an airbag cover, including: a cover material formed from a synthetic resin by molding; and a thin breakable portion for breaking by a pressure of an inflating airbag to thereby form a projection opening through which the airbag projects,
wherein the breakable portion includes at least one notch that is cut by a cutting blade of a working tool after the cover material is molded by the molding, and
cutting blade accommodating portions are recesses
• formed~bry the molding at positions corresponding to a
stating end and a terminating end of the notch to
accommodate therein the cutting blade of the working
tool.
In the airbag cover according to this aspect of the invention, when forming the breakable portion by making the notch on the cover material, the cutting blade of the working tool is inserted to be positioned in the cutting blade accommodating portion which constitutes

the starting end of a notch to be made, and following this, the working tool is moved to reach the cutting blade accommodating portion which now constitutes the terminating end of the notch that has been made, whereby the notch which makes up the breakable portion can be formed. Namely, the starting end and the terminating end of a notch to be made are specified in advance at the time of molding the airbag cover, whereby the positional accuracy with which the notch is disposed can be increased. In addition, as to the depth of a notch to be made, the cutting blade accommodating portions and the peripheries thereof are measured in advance with an optical measuring apparatus or the like, the depth of a notch to be made can easily be adjusted, and the working tool can be operated with an increased depth accuracy.
Consequently, with the airbag cover according to tlve invention, the breakable portion can be-formed while suppressing the variation in position and depth of the notch made.
Additionally, it is desirable that the breakable portion includes a T-shaped intersecting portion at which a traversing section intersects one of straight sections, and
the cutting blade accommodating portions are provided at both ends of each of the straight sections

and the traversing section. In the configuration like this, in the event that the traversing section of the breakable portion is broken by being pressed by the airbag to thereby propagate towards the straight section, the breakage so propagating can be stopped in the position of an inner circumferential surface of the cutting blade accommodating portion which is disposed at the T-shaped intersecting portion and is recessed in a width which is wider than the recessed groove-shaped notch without propagating across the cutting blade accommodating portion. Namely/ the breakage is not allowed to extend unnecessarily, thereby making it possible to prevent an unnecessary scattering of fractures of the airbag cover.
According to another aspect of the invention, it is desirable that the breakable portion further includes a recessed groove which is recessed on the rear surface of the -covex material,
the traversing section of the breakable portion is provided with the notch,
one of the cutting blade accommodating portions is provided at a position corresponding to the T-shaped intersecting portion, and
said one cutting blade accommodating portion accommodates therein the cutting blade such that no notch is formed on a surface thereof facing to the traversing

section when the cutting blade leaves the traversing section after a cutting operation in which the working tool is moved towards the T-shaped intersecting portion to produce the traversing section.
In the airbag cover according to this aspect of the invention, when producing the traversing section through the cutting operation by the working tool, the cutting blade of the working tool is moved towards the T-shaped intersecting portion so as to form the traversing section. In addition, the cutting blade of the working tool which has completed the cutting operation reaches the cutting blade accommodating portion at the T-shaped intersecting portion. As this occurs, since the cutting blade accommodating portion is formed into the configuration as described above, the cutting blade of the cutter does not contact the surface of an internal circumferential surface of the cutting blade accommodating portion which faces the traversing section (the surface which faces the cutting blade) , thereby making it possible to prevent the making of a notch on the cutting blade facing surface. As a result a breakage generated in the traversing section when the airbag cover is pressed by the inflating airbag can be prevented from propagating unnecessarily across the straight section.
Consequently, in the airbag cover according to the

invention, even though the traversing section between the T-shaped intersecting portions of the breakable portion is formed through the cutting operation, the work can be implemented while preventing the generation of an unnecessary notch, thereby making it possible to prevent the scattering of unnecessary fractures of the airbag cover when the airbag is deployed and inflated.
In addition, it is desirable that the working tool is made up of a cutter, and an edge of the cutting blade is inclined so as to be wider from a distal end toward a proximal side thereof in a direction in which the cutter is moved when the cutting operation is performed, and
said one cutting blade accommodating portion has a flat bottom surface which is in parallel to the moving direction of the cutter, and an inclined surface, which is the surface facing to the traversing section/ adjacent to' the bottTom surface on a side on whi-ch the~ as-so'ciated straight section is adjacent to the traversing section, and
the inclined surface is inclined upwardly from the bottom surface toward a direction apart from the traversing section.
In the configuration like this, even though the cutter which performs the cutting operation to produce the traversing section in the breakable portion is in

such a state that the distal end of the cutting blade thereof is biting into the flat bottom surface of the cutting blade accommodating portion, the cutting blade can be disposed in a position where the blade rests apart from the inclined surface at a location on the proximal portion side of the cutting blade which lies apart from the distal end thereof. Namely, the distal end of the cutting blade can be left biting into the flat bottom surface. On the contrary, the bottom surface of the cutting blade accommodating portion can be configured to allow the cutting blade to bite thereinto so as to increase the thickness of the relevant area of the bottom surface, thereby making it possible to prevent the reduction in thickness of the cutting blade accommodating portion, whereby the generation of a shrink mark or unevenness in gloss in an area on a front surface side of the airbag covex under which the cutting blad-e accommodating portion is formed.
When adopting the configuration described above, it is desirable that the straight section is provided with the notch cut by the cutter and traverses the flat bottom surface of said one cutting blade accommodating portion.
When adopting the configuration like this, even though the cutting operation is implemented such that

both the traversing section and the straight section bite into the flat bottom surface of the cutting blade accommodating portion or the cutting operation is implemented such that only one of the traversing section and the straight section bites into the flat bottom surface of the cutting plate accommodating portion, the breakage of the traversing section which is generated when the airbag cover is pressed by the inflating airbag can be prevented from propagating across the straight section and furthermore across the inclined surface of the cutting blade accommodating portion. Namely, in the even that the depth of the notch in the traversing section is a depth that does not reach the bottom surface of the cutting blade accommodating portion, whether the depth of the notch in the straight section does not reach or reaches the bottom surface of the cutting blade accommodatiirg po'rtitm," the breakage genera text rn- the traversing section when the airbag cover is pressed by the inflating air bag is prevented from propagating any farther than the cutting blade accommodating portion. In addition, even in the event that with the depth of the notch in the traversing section exceeding the depth of the bottom surface of the cutting blade accommodating portion, the notch in the traversing section is formed in such a way as to remain within the area of the bottom

surface of the cutting blade accommodating portion but extend across the straight section, since the inclined surface location is formed on the extension of the notch in such a manner as to abruptly increase its thickness from the bottom surface of the cutting blade accommodating portion, the breakage generated in the traversing section when the airbag cover is pressed by the inflating air bag can be prevented from propagating any farther across the inclined surface of the cutting blade accommodating portion.
According to another aspect of the invention, it is desirable that a plurality of lid portions defined by the breakable portion such that the lid portions are open when the breakable portion breaks by the pressure of the inflating airbag to thereby form the projection opening,
a substantially tubular mounting wall portion protrudes from a periphery of the lid portions on the rear side of the cover material to be mounted on a case for accommodating therein the airbag,
a section of the breakable portion which intersects with the tubular mounting wall portion is made up of the notch,
wherein a protruding portion which protrudes towards an outer circumferential side of the mounting

wall portion is formed in a wall portion of the mounting wall portion which is disposed to intersect the section of the breakable portion so as to provide a cutting blade accommodating portion in a vicinity of an end of the section of the breakable portion.
In the airbag cover according to this aspect of the invention, the cutting blade of the working tool which is connected to a working machine is moved vertically relative to the lid portions so as to be moved to a position of a starting end of the section which has already been molded in the airbag cover so as to constitute a starting end of the section forming work and is then moved along the rear surface of the lid portions so as to form the section, and after the section has been so formed, the cutting blade of the cutting tool may only has to be moved vertically relative to the lid portions in such a -manner as to cause the working-tool to move away from a position of a terminating end of the section which has also been molded in advance so as to constitute a terminating end of the section forming work. Thus, since the moving directions of the working tool can be set to be limited to the two directions, the orientation and angle of the cutting blade do not have to be changed in order to avoid the interference with the mounting wall portion when forming the ends of the

section by the cutting blade of the working tool, the construction of the working machine can also be simplified/ compared to the conventional example.
Consequently, in the airbag cover of this aspect of the invention, even though the ends of the threadlike breakable portion that is formed by the working tool having the cutting blade are provided in the vicinity of the mounting wall portion, the workability in forming (working to form) the breakable portion is improved.
In addition, in the airbag cover of the invention, since the protruding portion is formed in the mounting wall portion, this protruding portion is made to function as a reinforcement rib which enhances the strength of the mounting wall portion, the mounting wall portion can be restrained from being deformed to be expanded by being affected by the lid portions when the lid portions are pressed to open by the inflating air bag, so that the breakable portion can be broken smoothly to thereby allow the lid portions to open quickly.
Note that specifically, the invention can be applied to an airbag cover wherein
the lid portions are made up of two lid portions which are openable in opposite directions, and
the breakable portion is made up of a transverse section which is disposed between the lid portions so

as to intersect the directions in which the lid portions are caused to open and two vertical sections which are disposed on both end sides of the transverse section along the directions in which the lid portions are caused to open, so as to be formed into an H-shape as viewed from a front surface side of the lid portions, and wherein
the mounting wall portion is formed into a quadrangular tubular shape having four sides which extend along the transverse section and the vertical sections on the periphery of the H-shaped breakable portion, and the protruding portion is disposed at locations on the mounting wall portion which lie in the vicinity of both ends of the transverse section.
Further in the invention, it is desirable that the cutting blade accommodating portions are capable of accommodating therein the cutting blade of the working tool without making'a notch thereon and is provided snich that a bottom thereof is deeper than the notch of the breakable portion. In the configuration like this, no unnecessary notch is formed in the cutting blade accommodating portion, and when the breakable portion is broken by being pressed by the airbag, the breakage so made can be prevented from propagating from the cutting blade accommodating portion towards an unexpected location.

According to another aspect of the invention, there is provided a method of manufacturing an airbag cover in which a thin breakable portion is formed for breaking by a pressure of an inflating airbag to thereby form a projection opening through which the airbag projects, comprising the steps of:
molding a cover material with a synthetic resin in which a cutting blade accommodating portions are formed at positions corresponding to a stating end and a terminating end of a notch to be formed to accommodate therein a cutting blade of a working tool; and measuring a planned line on which the notch including the starting end and the terminating end is to be formed,
forming one notch constituting a part of the breakable portion by cutting with the cutting blade of the working tool after the cover material is molded, wherein the working tool is controlled based on position data obtained through the measurement to form the notch.
In the airbag manufacturing method according to the invention, when measuring in advance the planned line on which the notch is to be made by the working tool including the starting end and the terminating end between which the notch is to be made, since the starting end and the terminating end between which the notch is to be made can be measured based on the location of the

itting blade accommodating portion which is recessed .rom the surroundings, the measurement to obtain >ositional data of the notch can be made easy, and as i result, the airbag cover can be manufactured with the .ncreased accuracy as to the disposing position and depth )f the notch which makes up the breakable portion without >eing affected by a positional deviation which is caused )y a thermal expansion of the cover material which is lependent on the temperature at the time of working or _s caused when setting the cover material for working. In addition, in the event that a grain pattern is formed over a location lying in the vicinity of the )reakable portion which includes peripheries of the :utting blade accommodating portions, compared to a case /here no grain pattern is formed, when measuring the >lanned line on which the notch is to be made using an optical measuring apparatus such as a laser displacement neter, since there occurs no such reflection as is made >n a mirror, the planned line can easily be measured with :ew errors. In addition, in the event that the irregularities on the grain pattern are made up of iifferences in level or elevations which range in height :rom several to several tens of micrometers, the control )f accuracy of the depth of the notch can easily be implemented with an error of +/-0.1 mm or less.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view showing an in-use state of an airbag cover of the invention.
Fig. 2 is a sectional view of an airbag system in which the airbag cover of the invention is used, which corresponds to a location taken along the line II-II in Fig. 1.
Fig. 3 is a partial bottom view of an airbag cover of a first embodiment of the invention, which shows the vicinity of a breakable portion.
Fig. 4 is a partially omitted vertical sectional view of the airbag cover of the first embodiment, which corresponds to a location taken along the line IV-IV in Fig. 3.
Fig. 5 is a partially omitted vertical sectional view of the airbag cover of the first embodiment, which corresponds to a location taken along the line V-V in Fig. 3.
Fig. 6 is a diagram which describes a state in which a planned line is measured which is to be worked to produce a traversing section of the airbag cover of the first embodiment.
Fig. 7 is a diagram which describes a state in which a planned line is measured which is to be worked to produce a straight section of the airbag cover of the first

embodiment.
Figs. 8A and 8B are diagrams which describe a state in which a notch is made to produce the traversing section of the airbag cover of the first embodiment.
Figs. 9A and 9B are diagrams which describe a state in which a notch is made to produce the straight section of the airbag cover of the first embodiment.
Fig. 10 is a partial bottom view of an airbag cover according to a modified example of the first embodiment, which shows the vicinity of a breakable portion.
Figs. 11A and 11B are diagrams which describe cutting operation on the airbag cover shown in Fig. 10.
Fig. 12 is a partial bottom view of an airbag cover according to another modified example of the first embodiment, which shows the vicinity of a breakable portion.
Figs. 13A and 13B are diagrams which describe cutting operation on the airbag cover shown in Fig. 12.
Fig. 14 is a partial bottom view of the airbag cover of the second embodiment, which shows the vicinity of a breakable portion.
Fig. 15 is partially omitted vertical sectional view of the airbag cover of the second embodiment, which corresponds to a location taken along the line XV-XV in Fig. 14.

Fig. 16A to 16C are diagrams which describe cutting operation performed on the airbag cover of the second embodiment.
Fig. 17 is a partial bottom view of an airbag cover which shows a modified example of the second embodiment.
Fig. 18 is a partially omitted vertical sectional view of the airbag cover shown in Fig. 17, which corresponds to a location taken along the line XVIII-XVIII in Fig. 17.
Fig. 19 is a partial bottom view of an airbag cover showing another modified example of the second embodiment:.
Fig. 20 is a partially omitted vertical sectional view of the airbag cover shown in Fig. 19, which corresponds to a location taken along the line XX-XX in Fig. 19.
Fig. 21 is a partially omitted vertical sectional
view of the airbag cover of the third embodiment.
Fig. 22 is a diagram showing a modified example of cutting operation performed to produce a straight section of the airbag cover of the third embodiment.
Fig. 23 is a partially omitted vertical sectional view of the airbag cover of a fourth embodiment.
Fig. 24A to 24C are diagrams which describe cutting operation performed to produce a traversing section of

the airbag cover of the fourth embodiment.
Fig. 25 is a partial bottom view showing a modified example of an airbag cover of the fourth embodiment.
Fig. 26 is a partial bottom view showing another modified example of an airbag cover of the fourth embodiment.
Fig. 27 is a partial bottom view of the airbag cover of a fifth embodiment.
Fig. 28 is a partially enlarged bottom view of the airbag cover of the fifth embodiment.
Fig. 29 is a sectional view of the airbag cover of the fifth embodiment, which corresponds to a location taken along the line XXIX-XXIX in Fig. 27.
Fig. 30 is a sectional view of the airbag cover of the fifth embodiment, which corresponds to a location taken along the line XXX-XXX in Fig. 27.
Fig. 31 is a sectional view of the airbag cover of the fifth embodiment, which corresponds to a location taken along the line XXXI-XXXI in Fig. 27.
Fig. 32 is a schematic diagram showing a forming process of a breakable portion in manufacturing the airbag cover of the fifth embodiment.
Fig. 33A and 33B are schematic diagrams showing a forming process of the breakable portion in manufacturing the airbag cover of the fifth embodiment, which process

is a post process of the molding process shown in Fig. 32.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the invention will be described based on the accompanying drawings. Like numerals depicts like members or components to avoid duplication of explanation over the embodiments.
As is shown in Figs. 1 to 2, an airbag cover 10 according to the invention is such as to be used in an airbag system S for a passenger or occupant seated in a front passenger's seat, is made through injection molding from a synthetic resin such as an olefin-based thermoplastic elastomer, and is provided in an opening 2b on an upper surface 2 a side of an instrument panel lying in front of the front passenger's seat.
Note that used in this specification, vertical, vertical and transverse directions are understood to coincide with vertical, vertical and transverse directions of a vehicle in such a state that the vehicle travels straight ahead based on a state in which the airbag cover 10 is installed on the" vehicle in such a way as designed.
In addition, the airbag system S for the front seat passenger is made up of a folded airbag 4, an inflator 7 for supplying the airbag 4 with inflation gas, a case

8 which accommodates and holds the airbag 4 and the inflator 7, a retainer 5 for mounting the airbag 4 in place in the case 8, and the airbag cover 10 which covers the folded airbag 4.
The airbag 4 is made, when completely inflated, to take a substantially quadrangular pyramidal shape in which a front end side of the airbag constitutes an apex portion of the pyramid and a rear surface side of a bottom of the airbag, which constitutes a base of the pyramid, constitutes an occupant restraint portion. When installed on a vehicle/ this airbag 4 is folded towards the upper surface 2a side of the instrument panel 2 lying in front of the front passenger's seat for storage, and when an inflation gas flows thereinto, the airbag 4 projects upwards so as to cover a space defined between the upper surface 2a of the instrument panel 2 and a windshield provided above the instrument panel 2, while projecting rearwards to protect the front seat passenger by means of the occupant restraint portion on the rear surface side thereof.
In addition, the inflator 7 is made up of a substantially cylindrical main body portion 7a having a plurality of gas outlets 7b and a flange portion 7c via which the inflator 7 is attached to the case 8.
Furthermore, the case 8 is formed into a

substantially rectangular parallelepiped shape made of sheet metal and having a rectangular opening on an upper end side thereof and is made up of a substantially rectangular plate-shaped bottom wall portion 8a through which the inflator 7 is passed from therebelow for attachment thereto and a circumferential wall portion 8b which extends upwards from an outer circumferential edge of the bottom wall portion 8a. A plurality of locking claws 8c are formed at an upper end of the circumferential wall portion 8b for locking a side wall portion 33 of the airbag cover 10. A bracket 8d is provided on the case 8 at a location where the bottom
*
wall portion 8a lies in such a manner as to be connected to a body 1 of the vehicle-
In addition, the airbag 4 and the inflator 7 are
attached to the case 8 because of a plurality of bolts 5a of the annular retainer 5 which is provided within the airbag 4 being passed through a circumferential edge 4b of an opening 4a in the airbag 4, the flange portion 7c of the inflator 7 and the case bottom wall portion 8a so as to be fastened by corresponding nuts 6.
The airbag cover 10 according to the invention is, as is shown in Fig. 1 and 2, made up of a ceiling wall portion 11 which is formed into a rectangular plate shape which can cover the opening 2b in the instrument panel

2 and the side wall portion 33 which is formed into a substantially quadrangular tubular shape and which extends downwards from a lower surface (a rear surface) side of the ceiling wall portion 11. A plurality of locking holes 33e are formed in front and rear wall portions 33a, 33b of the side wall portion 33 so that the locking claws 8c of the case circumferential wall portion 8b pass therethrough to be locked to circumferential edges of the locking holes 33e so formed. The side wall portion 33 makes up a location which covers the periphery of the folded airbag 4 together with the case circumferential wall portion 8b-
The ceiling wall portion 11 is made to include a projection opening portion 12 which is disposed in a location surrounded by the side wall portion 33 and a circumferential edge portion 31 which lies around the projection opening portion 12. A plurality of locking legs 31a are provided on the circumferential edge portion 33 in such a manner as to protrude downwards therefrom so as to be locked to an opening circumferential edge 2c of the opening 2b in the instrument panel 2 to thereby eliminate the looseness of the airbag cover 10 when the airbag cover 10 is placed to cover the opening 2b.
When installing the airbag cover 10 on the vehicle as part of the airbag system S, the airbag cover 10 is

placed on an airbag assembly in which the folded airbag 4 in which the retainer 5 has already been accommodated and the inflator 7 are accommodated and held in place within the case 8 by making use of bolts 5a and nuts 6, and the locking claws 8c are locked to the circumferential edges of the locking holes 33e, thereafter, the airbag assembly to which the airbag cover 10 has already been assembled is inserted into the instrument panel 2 which has been installed on the vehicle in advance from the opening 2b therein, so that the individual locking legs 31a are locked to the opening circumferential edge 2c, and the bracket 8d of the case 8 is fastened to the body 1 side. Then, a predetermined operation signal inputting lead wire which extends from an airbag operation circuit is connected to the inflator 7, whereby the airbag system S can be installed on the vehicle.
When the airbag system S is activated, an inflation gas from the inflator 7 flows into the airbag 4, which is then inflated, the airbag 4 which is being inflated drastically presses against the projection opening portion 12, whereby the breakable portion 16 is broken, and the lid portions 13, 14 of the airbag cover 10 are opened forwards and rearwards, respectively, so that the airbag 4 is allowed to project largely from the projection opening 12a which is formed, so as to protect the occupant

seated in the front passenger seat. (First embodiment)
The description will now be made to a first embodiment of the invention. In the first embodiment, as best shown in Figs. 3 to 5, the projection opening portion 12 is formed into a rectangular plate shape and has provided thereon a thin breakable portion 16 which extends into a straight-line shape. This breakable portion 16 is formed by providing a recessed groove 16a which is recessed from a rear surface side towards a front surface side of the airbag cover 10A, and in the case of this embodiment, a T-shaped intersecting portion 20 is disposed at two locations so that a traversing section 19 is made to intersect straight sections 17, 18, respectively, in a T-shaped fashion as viewed from the top, whereby the breakable portion 16 is formed into an H-'shape as viewed from the top. Because of this, when the breakable portion 16 is broken, two front and rear lid portions 13, 14 between which the traversing section 19 is situated open forwards and rearwards, respectively, so as to form a rectangular opening 12a through which the airbag 4 is allowed to project. When opening, the lid portion 13 rotates upwards about a hinge portion 15 disposed on a front edge side thereof as a rotational center and then opens forwards, while when opening, the

lid portion 14 rotates upwards about a hinge portion 15 disposed on a rear edge side thereof as a rotational center and then opens rearwards. The hinge portions 15 are disposed in positions of internal surfaces of the front and rear wall portions 33a, 33b of the side wall portion 33, respectively, as locations which connect together both ends of the vertical section portions (the straight sections 17, 18) lying on both sides of the H-shape which face each other in a transverse direction.
In addition, in the event of this embodiment, the recessed groove 16a of the breakable portion is formed after the airbag cover 10A has been molded using a cutter 35 in such a manner as to make a notch without producing swarf or cuttings.
In the case of this embodiment, as is shown in Figs. 8A to 9B, the cutter 35 is an ultrasonic cutter whose main body portion 36 has a thickness ranging from 0.5 to 1. 0 mm and which includes a single-edged cutting blade 37. The cutting blade 37 is formed inclined in such a manner as to extend from a tip or distal end 37a to a heel or proximal portion 37b side thereof in a direction in which the cutter is moved when work of making a notch is performed. In addition, in the case of this embodiment, the cutter 35 is moved in its moving direction with the cutting blade 37 disposed on a front side of

the moving direction, so as to form a notch which makes up the recessed groove 16a.
In addition, in the breakable portion 16 of the airbag cover 10A, a cutting blade accommodating portion 21 which is recessed towards the front surface side of the cover 1OA is formed at both the ends of the straight sections 17, 18 and both the ends of the traversing section 19 which each constitute the T-shaped intersecting portion 20. The cutting blade accommodating portion 21 is such as to be formed in advance at the time of molding and is provided as a recessed portion whose opening on the rear surface side of the cover 10A is formed into a rectangular shape and which has a cross section which is recessed into a triangular shape along the moving direction of the cutter 35. Furthermore, with the recessed shape of the cutting blade accommodating portion 21 which is formed as described above, as is shown in Figs. 8A to 9B, when the cutting blade 37 is inserted into the cutting blade accommodating portion 21 to a position where a notch for the recessed groove 16a can be made in an attempt to make such a notch 16a, no notch is made on an inner circumferential surface of the cutting blade accommodating portion 21 by the cutting blade 37 so inserted. In addition, in the case of this embodiment,

the cutting blade accommodating portion 21 is formed inclined into an isosceles triangle in cross section in which a surface lying on a side which faces an edge side of the cutting blade 37 when the cutting blade 37 is inserted (a cutting blade's edge side facing surface)
23 and a surface lying on a side which faces a back 36a
side of the cutting plate 37 when the cutting blade 37
is inserted (a cutting blade's back side facing surface)
24 are made equal length, while a bottom portion 22 of
the recessed accommodating portion 21 constitutes an apex
of the isosceles triangle.
In the case of this embodiment, although the cutting blade's. edge side facing surface 23 is formed parallel to the cutting blade 37 which is inserted into the cutting blade accommodating portion 21, the cutting blade's edge side facing surface 23 may be inclined in such a way as to increase the angle of opening from the cutting blade' s back side facing surface 24 as an angle which produces a gap between the cutting blade 37 and the cutting blade' s edge side facing surface 23 without expanding the open area of the cutting blade accommodating portion 21 excessively. In addition, in the case of this embodiment, the cutting blade accommodating portion 21 is formed such that side wall surfaces 25, 26 are provided at the front and rear of the facing surfaces 23, 24 in such a manner ,

as to extend downwards while expanding their areas (refer to Fig. 5).
Then, of the cutting blade accommodating portions 21 which lie at both the ends of each of the straight sections 17, 18 and the traversing section 19, one constitutes a starting end side cutting blade accommodating portion 21A where the cutter starts making a notch, while the other constitutes a terminating end side cutting blade accommodating portion 21B which the cutter reaches as a result of the completion of making the notch.
In addition, as to the thickness of the airbag cover, as shown in Fig, 4, a thickness TO at the circumferential edge portion 31 which lies apart from the side wall portion 33 and a general portion lla which lies in the vicinity of centers of the lid portions 13, 14 of the ceiling wall portion 11 is set at on the order of 4 mm, a thickness at the breakable portion.16 which includes the cutting blade accommodating portions 21 is set to range from 0.6 to 1.5 mm, a thickness Tl at the periphery of the breakable portion 16 is set to range 2 to 3 mm (in this embodiment, 2 mm), a depth DO for the cutting blade accommodating portion 21 is set to range from 1.0 to 2.0 mm (in this embodiment, 1.2 mm), and a depth Dl for the recessed groove 16a is set to range from 0.8 to

1.0 ram (in this embodiment, 1.0 mm). Because of this, a thickness T2 at a location where the cutting blade accommodating portion 21 is formed is set to range from 0. 6 to 0.8 mm (in this embodiment, 0.8 mm), and a thickness T3 at a location where the recessed groove 16a is formed is set to range from 0.8 to 1.0 mm (in this embodiment, 1.0 mm).
In addition, as shown in Fig. 5, a width Wl of the bottom portion 22 side of the cutting blade accommodating portion 21 which is defined by the front and rear side wall surfaces 25, 26 is set to range from 2 to 3 nun (in this embodiment, 2 ram) , and a length LI for the cutting blade accommodating portion 21 is also set to range from 2 to 3 mm (in this embodiment, 3 mm) , Note that as will be described later on, these width HI and length LI are so set in consideration of a dimension by which a cover material -9 deviates relative to a setting table 42 on which the cover material 9 is set when it is worked to make notches.
Furthermore, a thickness B for the side wall portion 33 (see Fig. 4) is set to range from 2 to 3 mm (.in this embodiment, 2 mm) . Thin portions 28 which lie in the vicinity of the straight sections 17, 18 on the lid portions 13, 14 side and a thin portion 29 which lies on an outer circumferential side of the side wall portion

33 and reduces its thickness gradually towards the side
wall portion 33 side are provided in the vicinity of the
side wall portion 33 of the ceiling wall portion 11, and
these thin portions 28, 29 are provided in such a manner
that their thicknesses become approximate to the
thickness B of the side wall portion 33 in order not to
produce a shrink mark or unevenness in gloss on a front
surface side of a location on the ceiling wall portion
11 where the side wall portion 33 is situated.
In addition, a grain pattern 30 which is imparted at the time of molding is provided on peripheral areas of the straight sections 17, 18 and the traversing section 19 of the embodiment . In the-case of this embodiment, this grain pattern 30 is made up of a leather grain pattern of fine irregularities ranging from several micrometers to several tens of micrometers.
The cutting operation will be described below in which the recessed groove (notch) 16a is made on the cover material 9 of the airbag cover 1 OA immediately after the airbag cover 1OA has been molded. A working apparatus
34 used in this work is, as is described in Fig. 6, made
up of the cutter 35, a holding arm 39 to which an
ultrasonic transmitter, not shown, is connected and which
holds the cutter 35 operationally, a laser displacement
meter 40 as a measuring apparatus for measuring planned

lines 9a, 9b which are to be worked, a control unit 41 for controlling the drive of the holding arm 39 while activating the ultrasonic transmitter based on measured data which is obtained by the laser displacement meter 40, and a setting table 42 on which the injection molded cover material 9 is set. The holding arm 39 is made to hold the cutter 35 in such a manner as to enable a triaxial movement in directions of X, Y and Z axes which includes a horizontal movement along the setting table 42 and a vertical movement which intersects the setting table 42 at right angles. In addition, the laser displacement meter 40 is held on the holding arm 39 and measures a height (a difference in level or elevation) of the periphery of the cutting blade accommodating portion or a height along the work planned lines 9a, 9b while measuring a depth and disposing position of the bottom portion 2*2 of each cutting blade accommodating-portion 21 based on the positions of the starting end and the terminating end of the notch 16a. The setting table 42 is given a shape which faces a front surface side of the cover material 9 and has provided thereon a sucking device, not shown, for sucking the cover material 9 securely to the setting table 42 side so as to eliminate the deviation of the cover material 9 while it is being worked. Note that the planned line 9a is a line which is worked to

produce the traversing section 19, and the planned lines 9b are lines which are worked to produce the straight sections 17, 18, respectively.
As is shown in Figs. 6 and 7, when the working apparatus 34 is activated, the molded cover material 9 is set on the setting table 42, and thereafter, firstly, the laser displacement meter 40 is moved in such a way as to start from the bottom portion 22 of the starting end side cutting blade accommodating portion 21A, pass through the work planned lines 9a, 9b and reach the bottom portion 22 of the terminating end side cutting blade accommodating portion 2IB of the traversing section 19 or the straight sections 17, 18 while being caused to measure the position and difference in lever or elevation (height) . In addition, even though the cover material 9 is set on the setting table 42 in such a state that the cover material 9 deviates from the setting table 42, the width Wl and length LI of the cutting blade accommodating portion 21 are set in advance by taking such a deviation into consideration, and hence, the holding arm 39, which is adapted to move when the laser displacement meter 40 implements the designed measurement as described above, moves the laser displacement meter 40 while anticipating some extent of error in such a way that the laser displacement meter

40 starts from the bottom portion 22 of the starting end side cutting blade accommodating portion, pass through the work planned lines 9a, 9b and reach the bottom portion 22 of the terminating end side cutting blade accommodating portion 21B so as to capture precise measured data.
Then, after the measurement has been completed, the control unit 41, into which the measured data from the laser displacement meter 40 is inputted, moves the holding arm 39 while activating the ultrasonic transmitter so as to control the cutting operation of the cutter 35. As this occurs, when working to produce the traversing section 19, as is shown in Figs. 8A and 8B, the cutting blade 37 of the cutter 35 is inserted into the starting end side cutting blade accommodating portion 21A of the straight section 17 to reach the cutting depth Dl and is then stopped thereat in such a state that the cutting blade 37 is oriented towards the straight section 18, and following this, the cutting blade 37 of the cutter 35 is moved towards the T-shaped intersecting portion 20 on the straight section 18 so as to form the traversing section 19. In the event that a notch is made over the whole area of the traversing section 19 so as to form the recessed groove 16a, the cutting blade 37 of the cutter 35 which has then completed

the cutting operation reaches the terminating end side cutting blade accommodating portion 21B of the T-shaped intersecting portion 20. As this occurs, since the cutting blade accommodating portion 21B is formed into the configuration which can accommodate therein the cutting blade 37 in such a state that no notch is made on the cutting blade's edge side facing surface 23 of the cutting blade accommodating portion 21B which is disposed in the position where the facing surface 23 faces the edge side of the cutting blade 37 of the cutter 35 in a direction directed from the traversing section 19 towards the straight section 18 when the cutting blade 37 of the cutter 35 has left the traversing section 19, the cutting blade 37 of the cutter dose not contact the surface 23 making up the inner circumferential surface of the cutting blade accommodating portion 21B which faces the traversing section 19 in such a way as to make a notch thereon, thereby making it possible to prevent the cutting blade 37 from making a notch on the surface 23 which the cutting blade 37 faces. Of course, in this embodiment, also in the starting end side cutting blade accommodating portion 21A, the cutting blade 37 is prevented from cutting into the cutting blade' s back side facing surface 24 in a direction directed from the traversing section 19 towards the straight section 17.

Similarly, also in the straight sections 17, 18, as is shown in Figs. 9A and 9B, the cutting blade 37 of the cutter 35 is inserted into the starting end side cutting blade accommodating portion 21A to the cutting depth Dl and is then stopped thereat, and following this, the cutting blade 37 of the cutter 35 is moved to reach the terminating end side cutting blade accommodating portion 21B, so as to form the recessed groove 16a. As this occurs, too, in the cutting blade accommodating portions 21A, 21B, the cutting blade 37 of the cutter 35 does not contact the inner circumferential surfaces 23, 24 of the cutting blade accommodating portions 21 A, 2IB in such a way as to make an unnecessary notch thereon.
Then, in the event that: the breakable portion 16 made up of the recessed groove 16a is formed then, the manufacturing of the airbag cover 10A is completed, and the airbag cover 1 OA is removed from the setting table 42 so as to be assembled into the airbag system S. When assembling the airbag system S, the folded airbag 4 in which the retainer 5 has already been accommodated and the inflator 7 are accommodated and held in place within the case 8 by making use of bolts 5a and nuts 6, so as to form an airbag assembly. Then, the airbag cover 10A is placed on the airbag assembly, the locking claws 8c are locked to circumferential edges of the locking holes

33e, thereafter, the airbag assembly to which the airbag cover 10A has already been assembled is inserted into the instrument panel 2 which has been installed on the vehicle in advance from the opening 2b therein, so that the individual locking legs 31a are locked to the opening circumferential edge 2c, and the bracket 8d of the case 8 is fastened to the body 1 side. Then, a predetermined operation signal inputting lead wire which extends from an airbag operation circuit is connected to the inflator 7, whereby the airbag system S can be installed on the vehicle.
When the airbag system S is activated, an inflation gas from the inflator 7 flows into the airbag 4, which is then inflated, the airbag 4 which is being inflated drastically presses against the projection opening portion 12, whereby the breakable portion 16 is broken, and the lid portions 13, 14 of the airbag cover 1 OA axe opened forwards and rearwards, respectively, so that the airbag 4 is allowed to project largely from the projection opening 12a which is formed, so as to protect the occupant seated in the front passenger seat.
In addition, in the airbag cover 1OA according to the embodiment, as has already been described, the starting end and terminating end of the notch 16a are specified in advance as the cutting blade accommodating

portions 21A, 21B at the time of molding the airbag cover 10A, thereby making it possible to increase the accuracy with which the notch 16a is disposed in the designed position. In addition, also with respect to the depth Dl of the notch 16a, the peripheries of the cutting blade accommodating portions 21A, 21B are measured in advance with the laser displacement meter 40, whereby the adjustment of the depth Dl of the notch 16a can be implemented easily, so that the cutter 35 can be controlled with an increased dimensional accuracy of the depth Dl of the notch 16a.
Consequently, with the airbag cover 10A of this embodiment, the breakable portion 16 can be formed >rhile suppressing variations in position and depth of the notch 16a, whereby the breakable portion 16 can be broken smoothly with good accuracy even at low temperatures.
In addition', in the case of the embodiment, each cutting blade accommodating portion 21 can accommodate therein the cutting blade 37 of the cutter 35 without making an unnecessary notch and is provided in such a state that the bottom portion 22 which constitutes a deepest portion of the relevant portion is made deeper than the notch 16a. Because of this configuration, when working to make a notch, no unnecessary notch is formed in the cutting blade accommodating portion, whereby, when

the breakable portion 16 is pressed by the airbag 4 to thereby be broken, the breakage is prevented from propagating from the cutting blade accommodating portion 21 to an expected location.
Furthermore, in the case of this embodiment, although the breakable portion 16 is made to include the T-shaped intersecting portions 20 where the traversing section 19 is allowed to intersect either of the straight sections 17, 18 in the T-shaped fashion as viewed from the top, the cutting blade accommodating portions 21 are provided at both the ends of each of the straight sections 17, 18 and are also provided at both the ends of the traversing section 19 with the T-shaped intersecting portions 20 included in the cutting blade accommodating portions 21 so provided. Because of this, even though the traversing section 19 of the breakable portion 16 is pressed by the airbag 4 to thereby be broken, the breakage so produced propagating towards the straight sections 17, 18, the facing surfaces 23, 24 which face each other in the breakage propagating direction face the propagating breakage in the positions of the cutting blade accommodating portions 21 which are made up of recessed port ions whose widthwise dimension is made wider than the notch 16a disposed in the T-shaped, whereby the propagating breakage is not allowed to propagate further

across the cutting blade accommodating portions 21 and can be then stopped thereat. Namely, the breakage is not allowed to propagate or extend unnecessarily, thereby making it possible to prevent the scattering of unnecessary fractures of the airbag cover 10A.
In addition, in the method of manufacturing the airbag cover IDA according to the embodiment, when measuring in advance the planned lines 9a, 9b on which the notch 16a is to be made by the cutter 35 including the starting end and the terminating end between which the notch 16a is made/ since the starting end and the terminating end between which the notch 16a is made can be measured based on the bottom portions 22'of the cutting blade accommodating portions 21 A, 2IB which are recessed from the surroundings, the measurement of position data of the notch 16a is facilitated, and the adjustment of the depth Dl of the notch 16a is implemented easily by measuring the cutting blade accommodating portions 21 and the peripheries thereof. As a result, the airbag cover 1 OA can be manufactured with the increased accuracy as to the disposing position and depth of the notch 16a which makes up the breakable portion 16 without being affected by a positional deviation which is caused by a thermal expansion of the cover material 9 which is dependent on the temperature at the time of working or

is caused when setting the cover material 9 for working.
In addition, in this embodiment, the grain pattern 30 is formed over the location lying in the vicinity of the breakable portion 16 which includes the peripheries of the cutting blade accommodating portions 21, compared to a case where no grain pattern is formed, when measuring the planned lines 9a, 9b using an optical measuring apparatus such as the laser displacement meter 40 or a camera, since there occurs no such reflection as is made on a mirror/ the planned lines 9a, 9b can easily be measured with few errors. In addition, in the event that the irregularities making up the grain pattern 30 are made up of differences in level or elevations which range in height from several to several tens of micrometers, the control of accuracy of the depth of the notch 16a can easily be implemented with an error of +/-0.1 mm or less .
In this embodiment, while the blade accommodating portion 21 is formed into the recessed shape having the isosceles triangle cross section as resulting when viewed along the moving direction of the cutter 35, as with an airbag cover 10A' shown in Figs. 10, 11A, and 11B, a cutting blade accommodating portion 51 may be adopted which is recessed into a trapezoid in cross section along the moving direction of the cutter 35 so as to have a

bottom portion with a flat surface, or as with an airbag cover 10A" shown in Figs. 12, 13A and 13B, a cutting blade accommodating portion 61 may be adopted which is recessed into a rectangular triangle in cross section along the moving direction of the cutter 35. These cutting blade accommodating portions 51, 61 have rectangular openings on rear surface sides of the covers 10A' , 10A", respectively, and with the recessed shapes into which they are formed, respectively, when inserting the cutting blade 37 into the cutting blade accommodating portions to a position where a notch 16a can be made in an attempt to make the notch 16a, no notch is made on inner circumferential surfaces of the cutting blade accommodating portions 51, 61 by the cutting blade 37 so inserted. Namely, the cutting blade accommodating portions 51, 61 are made to include starting end side and terminating end side cutting blade accommodating portions 51A, 51B, 61A, 61B which are disposed in the positions of a starting end and a terminating end of the notch 16a, and a surface lying on a side which faces an edge of the cutting blade 37 when the cutting blade 37 is inserted (a cutting blade's edge side facing surface) 23 and a surface lying on a side which faces a back 36a side of the cutting blade 37 when the cutting blade 37 is inserted (a cutting blade's back side facing surface)

24 are provided in such a way as not to be brought into contact with the cutting blade 37 to thereby make a notch.
In this embodiment, while the breakable portion 16 is described as being formed into the H-shape in which the two T-shaped intersecting portions 20 are provided, the invention can be applied to an airbag cover including a breakable portion 16 which does not include the straight section 17.
In addition, the straight sections 17, 18 and the traversing section which is provided in such a way as to intersect the those straight sections 17, 18 may not be formed into the straight—line shape over the whole length thereof.
Furthermore, in the embodiment, while the ultrasonic cutter 35 is described as being used as a cutting tool with a cutting blade for implementing cutting work, a normal cold cutter or a thin rod-shaped end mill may be used to form the notch 16a. However, in the event that a cutter is used which can form the recessed groove 16a by making a notch without producing cutting or swarf, a notch 16a can be formed which facilitates the generation of stress concentration when the notch 16a is broken, and the disposal of cuttings or the like preferably becomes unnecessary. In addition, when forming the recessed groove-shaped notch 16a through

jutting work using the end mill or the like, a widthwise dimension of an opening of the notch 16a should be a dimension with which no unnecessary notch is provided on the circumferential wall of the cutting blade accommodating portion when a rotating cutting blade of the end mill or the like is accommodated in the cutting blade accommodating portion, and hence, the opening desirably has a widthwise dimension which is set to range from 0.3 to on the order of 1.5 mm.
Furthermore, in the embodiment, while the airbag covers 10A, 10A', 10A" have been each described as being a separate element from the instrument panel 2 which is used in the front passenger seat airbag system S, the invention may be applied to an airbag cover which is molded integrally with the instrument panel, and furthermore, the invention may be applied to an airbag cover for an airbag system which is installed for a driver's seat or in a side of a seat. (Second Embodiment)
Second embodiment of the invention will be now described with reference to Figs. 14 to 20.
In the second embodiment, as shown in Fig. 14, the breakable portion 16 is made up of two different types of recessed grooves 16a, 16b. The two straight sections 17, 18 are made up of recessed grooves 1 6b which are formed

through molding when the airbag cover 10B is injection molded. The traversing section 19 is made up of a recessed groove 16a which is formed by working the airbag cover 10B after it has been molded to make a notch without producing swarf or cuttings using a cutter 35.
In the case of the second embodiment, as is shown in Figs. 16A to 16C, the cutter 35 is an ultrasonic cutter whose main body portion 36 has a thickness ranging from 0. 5 to 1.0 mm and which includes a single-edged cutting blade 37. The cutting blade 37 is formed inclined in such a manner as to extend from a tip or distal end 37a to a heel or proximal portion 37b side thereof in a direction in which the cutter is moved when the cutter 35 performs work of making a notch. In addition, in the case of the second embodiment, the cutter 35 is moved in its moving direction with the cutting blade 37 disposed on a front side of the moving direction, so as to form a notch which makes up the recessed groove 16a.
In addition, a cutting blade accommodating portion 21 which is recessed towards the front surface side of the airbag cover 10B is formed at each T-shaped intersecting portion 20 of the breakable portion 16 on the cover 10B. The cutting blade accommodating portion 21 is such as to be formed in advance when the airbag cover 10B is molded and is formed into a configuration

which can accommodate therein the cutting blade 37 of the cutter 35 in such a state that no notch is made by the cutting blade on a surface 23 of the cutting blade accommodating portion which is disposed in a position where the surface is made to face the cutting blade in a direction directed from the traversing section 19 towards the straight line-shaped portion 18 when the cutting blade 37 of the cutter 35 which is moved towards the T-shaped intersecting portion 20 while performing the notch making work to produce the traversing section 19 is caused to left the traversing section 19 so produced.
In the event of the second embodiment, the cutting blade accommodating portion 21 has a bottom surface 22 lying on a side where the traversing section 19 results which is made into a flat surface which is in parallel with the moving direction of the cutter 35 in which the cutter 35 is moved to perform the notch making work to produce the traversing section 19, and the surface 23 of the cutting blade accommodating portion 21 which is disposed in the position where the surface is made to face the cutting blade 37 in the direction directed from the traversing section 19 towards the straight section 18 is made into an inclined surface which expands away from not only the traversing section 19 but also the

bottom surface 22 of the cutting blade accommodating portion 21. Note that this inclined surface 23 may be inclined in such a way as to increase the open angle from the bottom surface 22 as an angle which produces a gap between the cutting blade 37 and the inclined surface 23 itself without expanding the open area of the cutting blade accommodating portion 21 excessively. Then, in the case of the second embodiment, the cutting blade accommodating portion 21 is provided such that side wall surfaces 25, 26 extend downwards from front and rear outer circumferential edges of the bottom surface 22 in such a way as to expand in their areas as they so extend (refer to Fig. 5 in the first embodiment) and a surface 24 which faces the inclined surface 23 extends in a vertical direction from an edge of the bottom surface 22 as an entrance side wall surface 24 along which the cutting blade 37 penetrates into the cutting blade accommodating portion 21.
Furthermore, in the event of the second embodiment, since the cutter 35 is moved rightwards as if it moves from the straight section 17 towards the straight section 18 to form the traversing section 19, the inclined surface 23 is disposed on a right wall portion 33d side of the side wall 33 as a cutting blade' s edge side facing surface, while the entrance side wall surface 24 is disposed on

left wall portion 33c side of the side wall as a cutting blade's back side facing surface 3.
In addition, as to the thickness of the airbag cover 10B, as shown in Fig. 15, a thickness TO at the circumferential edge portion 31 which lies apart from the side wall portion 33 and a general portion lla which lies in the vicinity of centers of the lid portions 13, 14 of the ceiling wall portion 11 is set at on the order of 4 mm, a thickness at the breakable portion 16 which includes the cutting blade accommodating portions 21 is set to range from 0.6 to 1.5 mm, a thickness Tl at the periphery of the breakable portion 16 is set to range 2 to 3 mm (in the second embodiment, 2 mm), a depth DO for the cutting blade accommodating portion 21 is set to range from 1.0 to 2.0 mm (in the second embodiment, 1.2 mm), and a depth Dl for the recessed groove 16a is set to range from 0.8 to 1.0 mm (in the second embodiment, 1.0 mm). Because of this, a thickness T2 at a location where the cutting blade accommodating portion 21 is formed is set to range from 0. 6 to 0 . 8 mm (in the second embodiment, 0 . 8 mm) , and thicknesses T3, T4 at locations where the recessed grooves 16a, 16b are formed are set to range from 0.8 to 1.0 mm (in the second embodiment, 1.0 mm). A width W2 for the recessed groove 16b is set to range from 0.3 to 1.5 mm (in the second embodiment,

0.5 mm).
In addition, a width Wl (See Fig. 5 in the first embodiment) of the bottom portion 22 side of the cutting blade accommodating portion 21 which is defined by the front and rear side wall surfaces 25, 26 is set to range from 2 to 3 mm (in the second embodiment, 2 mm), and a transverse length LI for the cutting blade accommodating portion 21 is also set to range from 2 to 3 mm (in the second embodiment, 3 mm) , a length L2 for the bottom surface 22 being set at about 1.5 mm in the event of the second embodiment. Note that as will be described later on, these width Wl and length LI are so set in consideration of a dimension by which a cover material 9 deviates relative to a setting table 42 on which the cover material 9 is set when it is worked to make notches.
Furthermore, a thickness B for the side wall portion 33 is set to range from 2 to 3 mm (in this embodiment, 2 mm) . Thin portions 28 which lie in the vicinity of the straight sections 17, 18 on the lid portions 13, 14 side and a thin portion 29 which lies on an outer circumferential side of the side wall portion 33 and reduces its thickness gradually towards the side wall portion 33 side are provided in the vicinity of the side wall portion 33 of the ceiling wall portion 11, and these thin portions 28, 29 are provided in such a manner that

their thicknesses become approximate to the thickness B of the side wall portion 33 in order not to produce a shrink mark or unevenness in gloss on a front surface side of a location on the ceiling wall portion 11 under which the side wall portion 33 is situated.
To describe the manufacturing of the airbag cover 10B that is configured as has been described heretofore, firstly, a predetermined injection mold is used to mold a cover material 9 on which the recessed grooves 16b for the straight sections 17, 18 have been formed but the recessed groove 16a has not yet been formed. Then, this cover material 9 is removed from the mold and is then disposed on the setting table 42 of the working apparatus 34 on which the cutter 35 is provided- Note that a suction device, not shown, is provided on the setting table 42 which is adapted to suck the cover material 9 securely to the setting table 42 side so as to prevent the deviation of the cover material 9 while the material is being work. In addition, the working apparatus is made up of a holding mechanism which holds the cutter the cutter 35 in such a manner as to enable a triaxial movement in directions of X, Y and Z axes which includes a horizontal movement along the setting table 42 and a vertical movement which intersects the setting table 42 at right angles and a control circuit which control the operation of the

holding mechanism.
Namely, before starting the cutting operation by the cutter 35, an outer surface configuration of a recessed groove 16a forming location 9a (refer to Fig. 16A) on the cover material 9 set on the setting table 42 is read in advance by passing a laser displacement meter thereover in order to verify a moving distance LO (refer to Fig. 14) of the cutting blade 37 of the cutter over which the cutting blade 37 has to be moved to make a notch for the recessed groove 16a from the position of the cutting blade accommodating portion 21 at the straight section 17 (this is regarded as a starting end side cutting blade accommodating portion 21A) to the position of the cutting blade accommodating portion 21 at the straight section 18 (this is regarded as a terminating end side cutting blade accommodating portion 21 B-) , an inserting depth Dl of the cutting blade 37 of the cutter 35 along which the cutting blade 37 is inserted into the cutting blade accommodating portion 21A to make the notch for the recessed groove 16a, and furthermore, an inserting depth Dl of the cutting blade 37 along which the cutting blade 37 is inserted to form the recessed groove 16a between the recessed portions 21A, 21B. For example, as is shown in Figs. 1 6A and 16B, a bent portion between the bottom surface 22 and the wall surface 24

of the cutting blade accommodating portion 21 is used as reading reference points XI, X2 when the outer surface configuration is so read, and height positions of an outer surface of the thin portion 28 and an outer surface of the recessed groove forming location 9a of the cover material 9 from the bottom surface 22 are measured, whereby based on data obtained through such measurements, the control circuit causes the cutting blade 37 of the cutter 35 to be inserted into the starting end side cutting blade accommodating portion 2 1A without making a notch, then causes the cutting blade 37 of the cutter 35 to be moved into the terminating end side cutting blade accommodating portion 2 IB, and thereafter causes the cutting blade 37 of the cutter 35 to leave the terminating end side cutting blade accommodating portion 2IB.
Then, when performing the cutting operation, the working apparatus 34 firstly causes the cutting blade 37 of the cutter 35 to be inserted into the starting end side cutting blade accommodating portion 21A at the straight section 17 to the cutting depth Dl and stops the cutting blade 37 there with the cutting blade 37 oriented towards the straight section 18 side, and the working apparatus 34 causes then, as is shown in Figs. 16A and 16B, the cutting blade 37 of the cutter 35 to move towards the T-shaped intersecting portion 20 on the

straight section 18 side so as to form the traversing section 19. Thus, when the recessed groove forming location 9a is notched all the way through its length to cut open the traversing section 19 or the recessed groove 16a, the cutting blade 37 of the cutter 35, which has completed the cutting operation, reaches the terminating end side cutting blade accommodating portion 21B at the T-shaped intersecting portion 20, as is shown in Figs. 16B and 16C. As this occurs, the cutting blade accommodating portion 21B is formed into a configuration which can accommodate therein the cutting blade 37 of the cutter 35 in such a state that no notch is made on an inclined surface 23 of the cutting blade accommodating portion 21B which is disposed in a position where the surface faces the traversing section in a direction directed from the traversing section 19 towards the straight section 18 when the cutting blade 37 has left the traversing section 19 so produced. Because of this, the cutting blade 37 of the cutter 35 does not contact the surface 23 of an inner circumferential surface of the cutting blade accommodating portion 21B which faces the traversing section 19 in such a manner as to make a notch thereon, thereby making it possible to prevent the cutting blade 37 from making a notch on the surface 23 which faces the cutting blade 37. of course, in this

embodiment, even in the starting end side cutting blade accommodating portion 21A, no notch is made by the cutting blade 37 on the surface 24 which lies in a direction directed from the traversing section 19 towards the straight section 17.
Then, in the event that the traversing section 19 which is made up of the recessed groove 16a is formed, the manufacturing of the airbag cover 10B is completed, and the airbag cover 10B is removed from the setting table 42 so as to be assembled into the airbag system S. When assembling the airbag system S, the folded airbag 4 in which the retainer 5 has already been accommodated and the inflator 7 are accommodated and held in place within the case 8 by making use of bolts Sa and nuts 6, so as to form an airbag assembly. Then, the airbag cover 10B is placed on the airbag assembly, the locking claws 8c are locked to circumferential edges of the locking holes 33e, thereafter, the airbag assembly to which the airbag cover 10B has already been assembled is inserted into the instrument panel 2 which has been installed on the vehicle in advance from the opening 2b therein, so that the individual locking legs 31a are locked to the opening circumferential edge 2c, and the bracket 8d of the case 8 is fastened to the body 1 side . Then, a predetermined operation signal inputting lead wire which extends from

an airbag operation circuit is connected to the inflator 7, whereby the airbag system S can be installed on the vehicle.
When the airbag system S is activated, an inflation gas from the inflator 7 flows into the airbag 4, which is then inflated, the airbag 4 which is being inflated drastically presses against the projection opening portion 12, whereby the breakable portion 16 is broken, and the lid portions 13, 14 of the airbag cover 10B are opened forwards and rearwards, respectively, so that the airbag 4 is allowed to project largely from the projection opening 12a which is formed, so as to protect the occupant seated in the front passenger seat.
In addition, in the airbag cover 10B of the second embodiment, as has been described above, the terminating end side cutting blade accommodating portion 21B is formed into the configuration which can accommodate therein the cutting blade 37 of the cutter 35 in such a state that no notch is made on the surface 23 of the
)
cutting blade accommodating portion 21B which is disposed in the position where the surface faces the traversing section in the direction directed from the traversing section 19 towards the straight section 18 when the cutting blade 37 of the cutter 35 has completed the cutting operation to produce the traversing section and

reached the cutting blade accommodating portion 21B at the T-shaped intersecting portion 20 to leave the traversing section 19 so produced. Because of this, no notch by the cutting blade 37 is formed on the surface 23 of the cutting blade accommodating portion 21B which faces the interesting side location 19 in the way described above, and the breakage of the traversing section 19 which is produced when the airbag cover 10B is pressed by the airbag 4 which is being inflated can be prevented from propagating across the straight section
18 in such a way as to propagate across the cutting blade
accommodating portion 2IB.
Of course, no notch by the cutting blade 37 is formed, either, on the surface 24 of the cutting blade accommodating portion 21A which faces the traversing section 19, and the breakage of the traversing section
19 which is produced when the airbag cover 10B is pressed
by the airbag 4 which is being inflated can be prevented
from propagating across the straight section 17 in such
a way as to propagate across the cutting blade
accommodating portion 21A.
Consequently, with the airbag cover 10B of the second embodiment, even though the traversing section 19 between the T-shaped intersecting portions 20 of the breakable portion 16 is formed though the cutting

operation, the cutting operation can be implemented while preventing the generation of an unnecessary notch, thereby making it possible to prevent the scattering of unnecessary factures of the airbag cover 10B when the airbag 4 is deployed and inflated.
In addition, when implementing the cutting operation by the cutter 35, in the event that the left and right wall portions 33c, 33d of the side wall portion 33 interfere with the cutter 35 itself or the holding mechanism of the cutter 35, the problem may be deal with by expanding the areas 28 between the left and right wall portions 33c, 33d and the straight sections 17, 18, as is shown in Figs. 17 and 18. As this occurs, in the event that the whole area of the area 28 is made thin, there will be caused a risk that when installed on the vehicle, the airbag cover 10B deflects so that the whole of the lid portions 13, 14 existing area is caused to descend, whereby an unnecessary recessed portion is formed on a front surface side of the ceiling wall portion 11. To cope with this, as in airbag covers 10B shown in Figs. 17 and IB, respectively, it is desirable that at least a location lying in the vicinity of the side wall portion 33 is made thin in such a manner as not to produce any shrink mark on the front surface side of the ceiling wall portion 11 and that in order that the deflection of the

areas 28 can be prevented, elongated projections 28a having a semicircular cross section are provided as shown in Figs. 17 and 18 or a large number of triangular plate-shaped reinforcement ribs 28b are provided as shown in Figs. 19 and 20. (Third Embodiment)
While in the second embodiment, the cutting blade accommodating portion 21 is formed into the recessed shape having the trapezoidal cross section as viewed in the transverse direction along the traversing section 19, as in an airbag cover IOC of a third embodiment which is shown in Figs. 21 and 22, a cutting blade accommodating portion 41 may be adopted which is formed into a recessed shape having a triangular cross section as viewed in a transverse direction along a traversing section 19. As with the first embodiment, in the airbag cover IOC of the third embodiment not only the traversing section 19 but also the straight sections 17, 18 are formed using a cutter 35 or through cutting operation. Namely, the breakable portion 16 is made up of only a recessed groove 16a which is made through the cutting operation except for the cutting blade accommodating portions 41. Furthermore, cutting blade accommodating portions 41 are provided at both ends of each of the straight sections 17, 18. The third embodiment is identical to the first

and second embodiments in the other configurations, and hence, like reference numerals will be imparted to like portions, so that the description thereof will be omitted.
The cutting blade accommodating portion 41 of the third embodiment is also such as to be formed in advance on a cover material 39 after it has been molded, and Fig. 22, the cutting blade accommodating portion 41 is formed into a configuration which can accommodate therein a cutting blade 37 of the cutter 35 which is moved towards the T-shaped intersecting portion 20 while performing cutting operation to produce the traversing section 19 in such a state that no notch is made on a surface 43 of the cutting blade accommodating portion 41 which is disposed in a position where the surface faces the traversing section 19 in a direction directed from the traversing s-ection 19 towards the straight section 18 when the cutting blade 37 leaves the traversing section 19. This cutting blade accommodating portion 41 is made up of the surface 43 which is inclined, a wall surface 44 which is disposed in such a way as to extend along a vertical direction and wall surfaces 45, 46 which lie at the front and rear of the cutting blade accommodating portion 41.
In addition, also, in the third embodiment, the

cutting blade accommodating portion 41 at the T-shaped intersecting portion 20 on the straight section 17 Ls made as a starting end side cutting blade accommodating portion 41A into which the cutting blade 37 of the cutter 35 is inserted, and the T-shaped intersecting portion 20 on the straight section 18 is made as a terminating end side cutting blade accommodating portion 41B which the cutting blade 37 of the cutter 35 leaves.
Furthermore, in the third embodiment/ also, of the cutting blade accommodating portions 41 which aire provided at both the ends of each of the straight sections 17, 18, one of the cutting blade accommodating portions 41 is made as a starting end side cutting blade accommodating portion 41A, while the other is made as a terminating end side cutting blade accommodating portion 41B when the cutter 35 performs its cutting operation to produce the straight sections IT, 18. Then, the starting end side cutting blade accommodating portion 41A is formed into an inner circumferential configuration which allows no notch to be made on the surface 44 which extends along the vertical direction while facing the traversing section 19 or a back side of the cutting blade 37 when the cutting blade 37 of the cutter 35 is inserted into the cutting blade accommodating portion 41A. Note that widthwise and lengthwise dimensions of these cutting

blade accommodating portions 41 are set in consideration of positional deviations that would occur when the cover material 39 is set on a setting table 42.
In addition, also in the third embodiment, the cover material 39, which has been molded, is set on the setting table 42 so as to be worked to cut open the traversing section 19 and the straight sections 17, 18, and the sane function and advantage as those obtained by the first and second embodiments can also be obtained by the airbag cover IOC so manufactured. Namely, no notch by the cutting blade 37 is formed on the facing surface 43 of the cutting blade accommodating portion A IB which faces the traversing section 19 and the facing surface 44 of the cutting blade accommodating portion 41A which faces the traversing section 19, whereby the breakage of the traversing section 19 which is produced when the airbag cover IOC is pressed by the airbag 4 which is being deployed and inflated can be prevented from propagating unnecessarily across the straight sections 17, 18 in such a way as to propagate across the cutting blade accommodating portions 41A, 41B, respectively, thereby making it possible to prevent the unnecessary breakage of the airbag cover IOC.
Note that while in the third embodiment, the depth of the recessed groove 16a of the breakable portion 16

is described as being shallower than the cutting blade accommodating portion 41 as shown in Fig. 22, the recessed groove 16a provided along the straight sections 17, 18 may be formed deeper than the cutting blade accommodating portions 41 at the T-shaped intersecting portions 20 a.s shown in Fig. 23. This because since the recessed groove 16a provided along the traversing section 19 is shallower than the cutting blade accommodating portions 41 at th.e T-shaped intersecting portions 20, the propagation of the breakage of the traversing section 19 which Ls generated when the airbag cover is pressed by tb_e inflating air bag is stopped by the facing surface 44 of the cutting blade accommodating portion 41A and th,e facing surface 43 of the cutting plate accommodating portion 41B at the T-shaped intersecting portions 20 . (Fourth Embodiment)
In an airbag cover 10D of a fourth embodiment, cutting blade accommodating portions 21 are disposed which are each formed to have a similar trapezoidal cross section to that of the second embodiment, and an H-shaped breakable portion 16 which is made up of straight sections 17, 18 and a traversing section 19 may be formed by a recessed groove 16a which is formed through cutting operation except for the cutting blade accommodating portions 21.

In this airbag cover 10D, a cutting blade 37 of a cutter 35 bites into a bottom surface 22 to form the recessed groove 16a at not only cutting blade accommodating portions 21A, 21B at T-shaped intersecting portions 20 but also cutting blade accommodating portions 21A, 21B of each of the straight sections 17, 18. Namely, the cutting blade 37 is placed on a cover material 49 set on a setting table 42 and is then made to bite into the bottom surface 22 in such a way as to make no notch on a surface 24 which faces the recessed groove 16a at the starting end side cutting blade accommodating portion 21Aas shown in Fig, 24A, and following this, the cutter 35 is moved so as to form by the cutting blade 37 the recessed grooves 16a individually for the traversing section 19 and the straight sections 17, 18 as shown in Figs. 24B and 24C. In the terminating end side cutting blade accoTtimadating portion 21B, the cutting blade 37, which has left an entrance side wall surface 24, is made to leave the wall surface 24 while kept biting into the bottom surface 22 in such a state that no notch is made on an inclined surface 23, and furthermore, the cutting blade 37 is thereafter pulled up to be allowed to leave the bottom surface 22 for formation of the recessed grooves 16a individually for the straight sections 17, 18 and the traversing section 19.

In the airbag cover 10D of the fourth embodiment, the cutting blade 37 of the cutter 35 is formed inclined in such a way as to extend from a tip or distal end 37a to a heel or proximal portion 37b side thereof towards the moving direction of the cutter 35 when performing the cutting operation. Furthermore, the bottom surface 22 of the terminating end side cutting blade accommodating portion 21B which lies on a side where the traversing section 19 results is made into a flat surface which is in parallel with the moving direction of the cutter 35 which performs the cutting operation to produce the traversing section 19, and the surface 23 of the cutting blade accommodating portion 2 IB which is disposed in a position where the surface faces the traversing section in a direction directed from the traversing section 19 towards the straight section 18 is made into an inclined'surface which extends away from not only the traversing section 19 but also the bottom surface 22 of the cutting blade accommodating location 21B.
Because of the configuration like this, even though the cutter 35 which performs the cutting operation to produce the traversing section 19 of the breakable portion 16 is in such a state that the distal end 37a of the cutting blade 37 is kept biting into the flat bottom surface 22 of the cutting blade accommodating portion

21, the cutting blade 37 can be disposed in a position which is spaced apart from the inclined surface 23 at a location on the proximal portion 37b side thereof. Namely, the distal end 37a of the cutting blade 37 can be left biting into the flat bottom surface 22, and a thickness T2 at the flat bottom surface of the cutting blade accommodating portion 21 can be increased to such a thick thickness that allows the cutting blade 37 to bite thereinto, whereby the reduction in thickness at the cutting blade accommodating portion 21B can be prevented, thereby making it possible to prevent the generation of a shrink mark or unevenness in gloss on a location on a front surface side of the airbag cover 10D under which the cutting blade accommodating portion 21B is formed. Of course, the function and advantage like this can be similarly obtained at the starting end side cutting blade portion 21A of the traversing section 19a and the cutting blade accommodating portions 21A, 21B of each of the straight sections 17, 18.
Furthermore, in the fourth embodiment, the straight sections 17, 18 are made as a location which is worked to produce a notch therein using the cutter 35 and are each provided in such a way as to pass through the flat bottom surface 22 of the cutting blade accommodating portion 21 at the T-shaped intersecting portion 20.

In the configuration that has been described heretofore, even though the cutting operation is implemented such that both the traversing section 19 and the straight section 18 bite into the flat bottom surface 22 of the cutting blade accommodating portion 21A or the cutting operation is implemented such that only one of them bites into the flat bottom surface 22 of the cutting plate accommodating portion 21, the breakage of the traversing section 10 which is generated when the airbag cover 10D is pressed by the inflating air bag can be prevented from propagating across the straight section 18 and furthermore across the inclined surface 23 of the

cutting blade accommodating portion 2IB. Namely, in the even that a depth Dl at the notch 16a in the traversing section 19 is a depth that does not reach the bottom
surface 22 of the cutting blade accommodating portion 21B, whether the depth of the notch 16a in the straight section 18 does not reach or reaches the bottom surface 22 of the cutting blade accommodating portion 21B, the breakage generated in the traversing section 19 when the airbag cover 10D is pressed by the inflating air bag is prevented from propagating any farther than the cutting blade accommodating portion 21B. In addition, as is shown in Figs. 24A to 24C, even in the event that with the depth Dl of the notch 16a in the traversing section

19 exceeding the depth DO of the bottom surface 22 of the cutting blade accommodating portion 21B, the notch 16a in the traversing section 19 is formed in such a way as to remain within the area of the bottom surface 22 of the cutting blade accommodating portion 21B but extend across the area of the straight section 18 (across the notch 16a in the straight line-shaped portion 18 which lies in the area of the bottom surface 22), since the inclined surface 23 location is formed on the extension of the notch in such a manner as to abruptly increase its thickness from the bottom surface 22 of the cutting blade accommodating portion 21B, the breakage generated in the traversing section 19 when the airbag cover 10D is pressed by the inflating air bag can be prevented from propagating any farther across the inclined surface 23 of the cutting blade accommodating portion 21B. Of course, at the starting end side cutting blade accommodating portion 21A, since the facing surface 24 location is formed which abruptly increase its thickness from the bottom surface 22, even though the notch 16a in the traversing section 19 is formed in such a way as to remain within the area of the bottom surface 22 of the cutting blade accommodating portion 21A and extend across the area of the straight section 17 (across the notch 16a in the straight section 17 which lies in the

area of the bottom surface 22), the breakage of the traversing section 19 which is generated when the airbag cover 10D is pressed by the inflating air bag can be prevented from propagating across the facing surface 24 of the cutting blade accommodating portion 21A. Incidentally, in the case described above, the notch 16a in the straight sections 17, 18 which lies in the area of the bottom surface 22 may,be of either of a depth which allows the notch 16a to bite into the bottom surface 22 of the cutting blade accommodating portion 21 or a depth which does not allow the notch 16a to bite into the bottom surface 22 of the cutting blade accommodating portion 21.
In each of the embodiments that have been described heretofore, while the breakable portion 16 is described as being formed into the H-shape in which the two T-shaped intersecting portions 20 are provided, the invention can be applied to an airbag cover 10D which includes a breakable portion 16 which includes only the straight section 17 .
In addition, in the third and fourth embodiments, while the cutting blade accommodating portions 41, 21 are described as being also provided at both the ends of the straight sections 17, 18, a configuration may be adopted in which the thickness of locations on the airbag

cover where the straight sections 17, 18 are provided is made to increase as going away from the intersecting portions 20 by controlling the cutter 35 so that the breakage of the straight sections 17, 18 which is generated when the airbag cover is pressed by the airbag does not extend any farther than the ends thereof which lie on the sides where the hinge portions 15 are provided.
Furthermore/ as in the third and fourth embodiment, in the configuration in which the straight sections 17, 18 are also made up of the recessed groove 16a which results from the cutting operation/ in the event that there exists a risk that the cutter 35 itself which is used to work the relevant locations, the holding mechanism of the cutter 35 or the like interferes with the wall portions 33c, 33d, as in the airbag covers 10B shown in Figs. 17 to 20/ the configuration may be adopted in which the areas 28 between the straight sections 17, 18 and the wall portions 33c, 33d may be expanded by providing the elongated pro j ections 28a and the ribs 28b.
Moreover, the straight sections and the traversing section which is provided in such a way as to intersect the straight sections may be formed into the straight line all the way through their length or, for example, in airbag covers 10D',10D" which are shown in Figs. 25 and 26, a traversing section 19 which is provided between

straight sections 17, }8 may be formed into a curved line.
In addition, while the ultrasonic cutter 35 is shown as the working tool having the cutting blade which performs the cutting operation, the notch 16a may be formed using a normal cold cutter or a thin rod-shaped end mill. However, in the event that a cutter is used which can make a notch to form the recessed groove 16a without producing cuttings or swarf, a notch 16a can be formed which facilitates the stress concentration when the airbag cover is broken, and preferably, the disposal of cuttings and the like is also made unnecessary. In the event that a recessed groove-like notch 16a is formed through cutting work by the end mill or the like, a widthwise dimension of an opening of the notch 16a should be a dimension with which no unnecessary notch is provided by a rotating cutting blade of the end mill or the like when the rotating cutting blade is accommodated in the-cutting blade accommodating portion, and hence, the opening desirably has a widthwise dimension which is set to range from 0.3 to on the order of 1.5 mm.
Furthermore, in the second to fourth embodiments, while the airbag covers 10B, IOC, 10D have been each described as being a separate element from the instrument panel 2 which is used in the front passenger seat airbag system S, the invention may be applied to an airbag cover

which is molded integrally with the instrument panel, and furthermore, the invention may be applied to an airbag cover for an airbag system which is installed for a driver's seat or in a side of a seat. (Fifth Embodiment)
In an airbag cover 10E according to the fifth embodiment of the invention, as is shown in Figs. 27 to 31, a breakable portion 16 is formed which is made to be pressed by the inflating air bag to be broken. This breakable portion 16 is made up of a plurality of sections which intersect each other and is provided continuously on a rear surface side of the projection opening 12. In the event of this embodiment, the breakable portion 16 is made up of a transverse section l€a which is provided in such a manner as to extend linearly in a transverse direction at a vertically intermediate location of the projection opening 12 and two vertical sections 16b, 16b which are provided in such a manner as to extend linearly in both vertically forward and rearward directions from both left and right ends of the transverse section 16a and is then formed into a substantially H-shape as viewed from the top. The vertical sections 16b, 16 are provided in positions which lie in the vicinity of internal surfaces of left and right wall portions 33c, 33d. The transverse section 16a is formed by making a notch along

a boundary location between the lid portions 13, 14 with an ultrasonic cutter 35 as a working tool which will be described later on after the airbag cover 10E has been molded and is made to be connected to the vertical sections 1 6b on both the left and right end sides thereof, respectively. Each vertical section 16b is such as to be molded integrally when the airbag cover IDE is injection molded and is made into thin groove shape having a transverse opening width which is substantially constant all the way through the length thereof.
In addition, as is shown in Figs. 27 and 28, a blade edge accommodating portion 16c where a blade edge of a blade main body (a cutting blade) 36, which will be described later on, of the ultrasonic cutter 35 is accommodated is formed continuously with the vertical section 16b in such a manner as to protrude towards the left wall portion 33d side. As is shown in Figs. 33A and 33B, this blade edge accommodating portion 16c is made to accommodate therein the blade edge of the blade main body 36 when a terminating end 16ab of the transverse section 16a is formed thereby.
As is shown in Figs. 21, 28, and 31, a protruding portion 51 which protrudes towards an outer circumferential side into a substantially semi-circular cylindrical shape is provided on the left and right wall

portions 33c, 33d of the mounting wall portion 33 which are disposed in such a way as to intersect the transverse section 16a of the breakable portion 16. This protruding portion 51 is provided in such a way as to lie along the vertical direction in positions in the vicinity of the vertically centers of the left and right wall portions 33c, 33d which lie in the vicinity of a starting end 16aa and the terminating end 16ab of the transverse section 16a when it is formed. In addition, an accommodating recessed portion 51a which can accommodate therein the ultrasonic cutter 35 which forms the transverse section 16a while preventing the interference with the ultrasonic cutter 35 is formed in the protruding portion 51 by cutting away the protruding portion 51 in a substantially semi-arc-like shape.
Next, the manufacturing of the airbag cover 10E of the fifth embodiment will be described. The airbag cover 10E is injection molded using a mold of a predetermined configuration. The constituent locations of the breakable portion 16 except for the transverse section 16a are molded integrally during the injection molding of the airbag cover IDE. Thereafter, the airbag cover 10E so molded is placed on a setting table or resting jig 42 of a cutting apparatus, or working machine 34 which includes the ultrasonic cutter 35 as a working tool, and

a sucking mechanism disposed on the resting jig 42 is activated so that the airbag cover 10E is sucked to be held onto the resting jig 42. Then, as shown in Fig. 32, the blade main body 36, which functions as the blade edge disposed on a distal end side of the ultrasonic cutter 35, is brought into abutment with a position which lies between the lid portions 13, 14 on the airbag cover 10E held on to the resting jig 42 and makes up the starting end 16aa of the transverse rod-like portion 16a when it is formed. Thereafter, as is shown in Fig. 33, the ultrasonic cutter 35 is moved along a location between the lid portions 13, 14 where the transverse section 16a is to be formed to the terminating end 16ab which constitutes a terminating end of the transverse section 16a when it has been so formed in such a manner as to form a notch along the location between the lid portions 13, 14 by cutting partially the relevant location with the blade main body 36, whereby the transverse rod-like portion 16a can be formed, thereby making it possible to manufacture the airbag cover 10E.
In the event of the fifth embodiment, the ultrasonic cutter 35, which functions as the working tool, is made up of the blade main body 36 functioning as a cutting blade which is disposed on the distal end side of the cutter 35 and is inclined into a single-edged shape and

a mounting member disposed on a proximal portion side of the cutter 35 where the blade main body 36 is mounted and is configured such that ultrasonic waves of a predetermined frequency which are generated by an oscillator, not shown, are transmitted to the blade main body 36 so as to vibrate the blade main body 36 for implementation of cutting. In addition, the protruding portions 51 (the accommodating recessed portions 51a) which are formed on the mounting wall portion 33 of the airbag cover 10E are made to accommodate therein the mounting member 35a when the blade main body 36 is positioned at the starting end 16aa and the terminating end 16ab when the blade main body 36 forms the transverse section 16a, so that the mounting portion 35a does not interfere with the mounting wall portion 33 (refer to Figs. 32 and 33). Note that in the case of the fifth embodiment, the mounting member 35a of the ultrasonic cutter 35 is formed into a cylindrical shape having an
outside diameter dimension which is set at 20.
. In addition, the blade edge accommodating portion 16c, which is formed continuously with the vertical section 16b, is formed at the location which lies in the vicinity of the terminating end 16ab of the transverse section 16a which constitutes the terminating end of the transverse section 16a when it has been formed, and the

blade main body 36 of the ultrasonic cutter 35 is allowed to be accommodated within the blade edge accommodating portion 16c when the ultrasonic cutter 35 has formed the terminating end 16ab. Namely, in the fifth embodiment, when forming the terminating end 16ab of the transverse section 16a, the blade main body 36 is prevented from moving across the vertical section 16b to thereby form an unnecessary notch. Because of this, in the airbag cover 10E of the fifth embodiment, since the breakage of the transverse section 16a does not propagate across the vertical section 16b when the airbag 4 is deployed and inflated, the breakable portion 16 so formed is preferably allowed to be broken smoothly- Of course, in the event that this feature of the invention does not have to be taken into consideration, a configuration may be adopted in which the blade edge accommodating portion 16c is not provided.
Note that while in the fifth embodiment, the ultrasonic cutter 35 is used as the working tool having the cutting blade for forming the transverse section 16a, a laser cutter or a normal cold cutter may be used, and furthermore, a thin rod-shaped end mill or the like may be used. However, in the event that a cutter is used which can form the transverse section 16a by making a notch without producing swarf or cuttings, a transverse section

16 can preferably formed which facilitates the generation of stress concentration when the transverse section 16a is broken, and the disposal of swarf or the like is preferably made unnecessary. In addition, while in the fifth embodiment, the single-edged cutting blade is used as the blade main body 36, a double-edged cutting blade may of course be used.
In addition, in the airbag cover 10E of the fifth embodiment, since the protruding portion 21 which protrudes towards the outer circumferential side is formed on the left and right wall portions 33c, 20d of the mounting wall portion 33 which are disposed in such a manner as to intersect the transverse section 16a of
*
the breakable portion 16 in such a manner as to provide the accommodating recessed portion Sla which prevents
the interference with the ultrasonic cutter 35 as the working tool, the transverse section 16a can be formed by only making the notch on the rear surface of the lid portions 13, 14 which extends along the location where the transverse section 16a is to be formed to the terminating end 16ab by disposing the blade main body (the cutting blade) 36 of the ultrasonic cutter 35 in the position which constitutes the starting end 16aa of the transverse section 16a when it is formed and thereafter moving the ultrasonic cutter 35 on the rear

surface of the lid portions 13, 14 therefrom along the location where the transverse section 16a is to be formed to the terminating end 16ab. Namely, in the airbag cover 10E of the fifth embodiment, the blade main body (the cutting blade) 36 of the ultrasonic cutter 35 which is connected to the working machine 34 is moved vertically relative to the lid portions 13, 14 so as to be moved to the position of the starting end 16aa of the transverse section 16a which has already been molded in the airbag cover 10E to constitute the starting end of the transverse section forming work, and the blade main body 24 of the ultrasonic cutter 35 is then moved along the rear surface of the lid portions 13, 14 so as to form the transverse section 16a, and after the transverse section has been so formed, the blade main body 36 of the ultrasonic cutter 35 may only has to be moved vertically relative to the lid portions 13, 14 in such a manner as to cause the ultrasonic cutter 35 to move away from the position of the terminating end 16ab of the transverse section 16a which has also been molded in advance so as to constitute the terminating end of the transverse section forming work. Thus, since the moving directions of the ultrasonic cutter 35 can be set to be limited to the two directions, the orientation and angle of the cutter do not have to be changed in order to avoid the interference

with the mounting wall portion when forming the ends of the section by the cutter 35, the construction of the working machine can also be simplified, compared to the conventional example.
Consequently, in the airbag cover IDE of the fifth embodiment, even though the ends 16aa, 16ab of the threadlike breakable portion 16 that is formed by the ultrasonic cuter (the working tool) 35 having the blade main body (the cutting blade) 36 are provided in the vicinity of the mounting wall portion 33, the workability in forming the breakable portion 16 (the transverse rod-like portion 16a) is improved.
Namely, in the airbag cover 10E of the fifth embodiment, since the starting end 16aa and the terminating end 16ab which constitutes the starting end and the terminating end of the transverse section 16a forming work can be disposed in the vicinity of the left and right wall portions 33c/ 33d of the mounting wall portion 33, the vertical sections 16b, 16b of the breakable portion which are disposed along the left and right wall portions 33c, 33d of the mounting wall portion 33 in such a manner as to intersect the transverse section 16a can be disposed as near the left and right wall portions 33c, 33d as possible. Because of this, when the airbag 4 is deployed and inflated, stress is easily

concentrated on the locations of the vertical sections 16b, 16b, thereby making it possible to ensure the smooth breakage of the vertical sections 16b, 16b.
In addition, in the airbag cover 10E of the fifth embodiment, since the protruding portion 51 is formed on the left and right wall portions 33c, 33d of the mounting wall portion 33, this protruding portion is made to function as a reinforcement rib which enhances the strength of the mounting wall portion 33, the mounting wall portion 33 can be restrained from being deformed to be expanded by being affected by the lid portions 13, 14 when the lid portions 13, 14 are pressed to open by the airbag 4 which is being inflated in an initial stage of the inflation of the airbag 4, so that the breakable portion 16 can be broken smoothly to thereby allow the lid portions 13, 14 to open quickly.
Note that while in the fifth embodiment, the airbag cover 10E has been taken as an example for description of the fifth embodiment which includes the two lid portions 13, 14 which are arranged in parallel in the vertical direction and the H-shaped breakable portion 16 which is disposed on the periphery of the lid portions 13, 14, an airbag cover to which the invention can be applied is not limited thereto, and for example, the invention can be applied to an airbag cover for a driver' s

seat airbag system which includes three lid portions around which a substantially T-shaped breakable portion, is formed. In addition, while in the fifth embodiment, the airbag cover 10E is described as being molded separately from , the invention can be applied to an airbag cover which is molded integrally with an instrument panel.





We Claim,
1. An airbag cover(10a) comprising:
a cover material formed from a synthetic resin by molding; and a breakable portion(16) which is thinner than other portions of the airbag cover for breaking, by a pressure of an inflating airbag to thereby form a projection opening (12a) through which the airbag(4) projects,wherein the breakable portion (16) has at least one notch(16a) that is cut on the cover material, characterized in that the cutting blade(37) accommodating portions (21) are recesses formed by the molding at positions corresponding to a starting end and a terminating end of the notch to accommodate therein a cutting blade of the working tool.
2. An airbag cover as claimed in claim 1, wherein the breakable portion has a T-shaped intersecting portion at which a traversing section intersects one of straight sections, and the cutting blade accommodating portions are provided at both ends of each of the straight sections and the traversing section.
3. An airbag cover as claimed in claim 2, wherein the breakable portion has a recessed groove which is recessed on the rear surface of the cover material, the traversing section of the breakable portion is provided with the notch, one of the cutting blade accommodating portions is provided at a position corresponding to the T-shaped intersecting portion.
4. An airbag cover as claimed in claim 3, wherein said one cutting blade accommodating portion has a flat bottom surface which is parallel to the moving direction of the cutting blade, and an inclined surface, which is the surface facing to the traversing section, adjacent to the flat bottom surface on a side on which the straight section is adjacent to the traversing section, and the inclined surface is inclined upwardly from the bottom surface toward a direction apart from the traversing section.
5. An airbag cover as claimed in claim 4, wherein the straight section is provided with the notch and traverses the flat bottom surface of said one cutting blade accommodating portion.
6. An airbag cover as claimed in claim 2, wherein a plurality of lid portions defined by the breakable portion such that the lid portions are open when the breakable portion breaks by the pressure of the inflating airbag to thereby form the projection opening,
a substantially tubular mounting wall portion protrudes from a periphery of the lid portions on the rear side of the cover material to be mounted on a case for accommodating therein the airbag,
a section of the breakable portion which intersects with the tubular mounting wall portion is made up of the notch,
wherein a protruding portion which protrudes towards an outer circumferential side of the mounting wall portion is formed in a wall portion of the mounting wall portion which is disposed to intersect the section of the breakable portion so as to provide a cutting blade accommodating portion in a vicinity of an end of the section of the breakable portion.
7. An airbag cover as claimed in claim 6, wherein the lid portions are made up of two lid portions which are openable in opposite directions, and the breakable portion is made up of a transverse section which is disposed between the lid portions to intersect the directions in which the lid portions are caused to open and two vertical sections which are disposed on both end sides of the transverse section along the directions in which the lid portions are caused to open, so as to be formed into an H-shape. as viewed from a front surface side of the lid portions, and wherein the mounting wall portion is formed into a quadrangular tubular shape having four sides which extend along the transverse section and the vertical sections on the periphery of the H-shaped breakable portion, and the protruding portion is disposed at locations on the mounting wall portion which lie in the vicinity of both ends of the transverse section.
8. An airbag cover as claimed in claim 1 or 2, wherein the cutting blade accommodating portions are capable of accommodating therein the butting blade of the working tool without making a notch thereon and is provided such that a bottom thereof is deeper than the notch of the breakable portion.
9. A method of manufacturing an airbag cover in which a breakable portion which Is thinner than other portions of the airbag cover is formed for breaking by a pressure of an inflating airbag to thereby form a projection opening through which the airbag projects, comprising the steps of:

- molding a cover material with a synthetic resin in which a cutting blade accommodating portions are formed at positions corresponding to a starting end and a terminating end of a notch to be formed to accommodate therein a cutting blade of a working tool; and
- measuring a planned line on which the notch having the starting end and the terminating end is to be formed,
- forming one notch constituting a part of the breakable portion by cutting with the cutting blade of the working tool after the cover material is molded, wherein the working tool is controlled based on position data obtained through the measurement to form the notch.
10. A method of manufacturing an airbag cover as claimed in claim 9, wherein a grain pattern is formed over a location lying in the Vicinity of the breakable portion which has peripheries of the cutting blade accommodating portions.

Documents:

55-DEL-2007-Abstract-(14-09-2011).pdf

55-del-2007-abstract.pdf

55-del-2007-CGPA-(04-03-2014).pdf

55-del-2007-Claims-(06-03-2014).pdf

55-DEL-2007-Claims-(14-09-2011).pdf

55-del-2007-claims.pdf

55-del-2007-Correspodence Others-(22-07-2011).pdf

55-DEL-2007-Correspondence Others-(14-09-2011).pdf

55-del-2007-Correspondence Others-(15-12-2011).pdf

55-del-2007-Correspondence Others-(18-06-2013).pdf

55-del-2007-Correspondence Others-(28-01-2013).pdf

55-del-2007-Correspondence-Others-(04-03-2014).pdf

55-del-2007-Correspondence-Others-(06-03-2014).pdf

55-del-2007-correspondence-others-1.pdf

55-DEL-2007-Correspondence-Others.pdf

55-del-2007-description (complete).pdf

55-del-2007-drawings.pdf

55-DEL-2007-Form-1-(14-09-2011).pdf

55-DEL-2007-Form-1.pdf

55-del-2007-form-18.pdf

55-DEL-2007-Form-2-(14-09-2011).pdf

55-del-2007-form-2.pdf

55-del-2007-form-26.pdf

55-del-2007-Form-3-(15-12-2011).pdf

55-del-2007-Form-3-(22-07-2011).pdf

55-DEL-2007-Form-3.pdf

55-del-2007-form-5.pdf


Patent Number 259479
Indian Patent Application Number 55/DEL/2007
PG Journal Number 12/2014
Publication Date 21-Mar-2014
Grant Date 13-Mar-2014
Date of Filing 08-Jan-2007
Name of Patentee TOYODA GOSEI CO. LTD.
Applicant Address 1, AZA NAGAHATA, OAZA OCHIAI, HARUHI-CHO, NISHIKASUGAI-GUN, AICHI-KEN, 452-8564, JAPAN.
Inventors:
# Inventor's Name Inventor's Address
1 MASAKO ASAI C/O TOYODA GOSEI CO., 1, AZA NAGAHATA, OAZA OCHIAI, HARUHI-CHO, NISHIKASUGAI-GUN, AICHI-KEN, 452-8564, JAPAN.
2 YASUSHI OKADA C/O TOYODA GOSEI CO., 1, AZA NAGAHATA, OAZA OCHIAI, HARUHI-CHO, NISHIKASUGAI-GUN, AICHI-KEN, 452-8564, JAPAN.
3 RYUJI YOKOI C/O TOYODA GOSEI CO., 1, AZA NAGAHATA, OAZA OCHIAI, HARUHI-CHO, NISHIKASUGAI-GUN, AICHI-KEN, 452-8564, JAPAN.
4 TAKAYUKI ITO C/O TOYODA GOSEI CO., 1, AZA NAGAHATA, OAZA OCHIAI, HARUHI-CHO, NISHIKASUGAI-GUN, AICHI-KEN, 452-8564, JAPAN.
PCT International Classification Number B60R21
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2006-007689 2006-01-16 Japan
2 2006-007676 2006-01-16 Japan
3 2006-007688 2006-01-16 Japan