Air bag deployment door

A deployment door (24) for an inflatable air bag (18) has a door panel (80), a hinge (84), and first and second stress risers (128,192). The first stress riser (128) ruptures under stress induced in the door panel (80) upon movement of the air bag (18) forcefully against the door panel (80). The hinge (84) supports the door panel (80) for pivotal movement about an axis (190) when the first stress riser (128) has been ruptured. The hinge (84) includes a pivotal hinge leaf (150) having opposite side edges (180,182). One of the side edges (180) extends alongside the axis (190). The other side edge (182) is skewed relative to the axis (190). The second stress riser (192) ruptures under stress induced in the pivotal hinge leaf (150) when the door panel (80) pivots about the axis (190).

FIELD OF THE INVENTION 
The present invention relates to a deployment door which is opened upon 
inflation of an air bag in a vehicle. 
BACKGROUND OF THE INVENTION 
An air bag is inflated to protect an occupant of a vehicle upon the 
occurrence of a vehicle collision. When the vehicle experiences a 
collision-indicating condition of at least a predetermined threshold 
level, an inflator is actuated. The inflator then emits inflation fluid 
which is directed to flow into the air bag. The inflation fluid inflates 
the air bag to an inflated condition in which the air bag extends into the 
vehicle occupant compartment. When the air bag is inflated into the 
vehicle occupant compartment, it restrains an occupant of the vehicle from 
forcefully striking parts of the vehicle as a result of the collision. 
The air bag and the inflator are typically assembled together as parts of 
an air bag module. In addition to the air bag and the inflator, the module 
includes a reaction canister which contains and supports the air bag and 
the inflator in the vehicle. The reaction canister has a deployment 
opening through which the air bag moves outward from the reaction canister 
when the air bag is inflated. A deployment door extends over the 
deployment opening to conceal the air bag and the other parts of the 
module from the vehicle occupant compartment. 
When the inflator is actuated, the reaction canister directs the inflation 
fluid to flow from the inflator into the air bag. As the inflation fluid 
enters the air bag, it moves the air bag outward through the deployment 
opening and forcefully against the deployment door. The deployment door is 
ruptured by the force of the fluid pressure in the air bag, and is thus 
released for movement away from the deployment opening. As the air bag 
continues to move outward against the deployment door, it forcefully 
deflects a hinge portion of the deployment door so as to move the 
deployment door pivotally away from the deployment opening. The deployment 
door is thus opened and moved pivotally out of the path of the air bag as 
the air bag inflates outward from the reaction canister through the 
deployment opening and into the vehicle occupant compartment. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, an apparatus for use with an 
inflatable vehicle occupant restraint, such as an air bag, comprises a 
deployment door panel, means for defining a first stress riser, and hinge 
means. The first stress riser is rupturable under stress induced in the 
door panel upon movement of the air bag forcefully against the door panel. 
The hinge means supports the door panel for pivotal movement about an axis 
when the first stress riser has been ruptured. The hinge means includes a 
pivotal hinge leaf having opposite side edges. One of the side edges of 
the pivotal hinge leaf extends alongside the axis. The other side edge of 
the pivotal hinge leaf is skewed relative to the axis. The hinge means 
further includes means for defining a second stress riser. The second 
stress riser is rupturable under stress induced in the pivotal hinge leaf 
when the door panel pivots about the axis. 
In a preferred embodiment of the present invention, the door panel has a 
curved contour which is complimentary to the curved contour of a vehicle 
part in which the apparatus is mounted. The side edge of the pivotal hinge 
leaf that extends alongside the axis is an inner side edge which is spaced 
from the door panel. The side edge of the pivotal hinge leaf that is 
skewed relative to the axis is an outer side edge which extends alongside 
the door panel. The inner and outer side edges of the pivotal hinge leaf 
are thus skewed relative to each other as a result of the curved contour 
of the door panel. The second stress riser extends along the inner side 
edge. 
The skewed relationship of the inner and outer side edges of the pivotal 
hinge leaf causes an imbalance in stresses that are induced in the pivotal 
hinge leaf when the door panel pivots about the axis. However, in 
accordance with the present invention, stress in the pivotal hinge leaf is 
relieved upon rupturing of the second stress riser so that the imbalance 
in stresses is alleviated. Additionally, energy is dissipated upon 
rupturing of the second stress riser. The second stress riser thus helps 
to ensure that the apparatus is not undesirably broken by the force of the 
air bag moving against the door panel.

DESCRIPTION OF PREFERRED EMBODIMENTS 
As shown in FIG. 1, a vehicle occupant restraint apparatus 10 comprising a 
first embodiment of the present invention includes an air bag module 12. 
The air bag module 12 is mounted in a vehicle at a location adjacent to 
the vehicle occupant compartment 14, such as in the instrument panel 16 at 
the passenger side of the vehicle. The air bag module 12 includes an 
inflatable vehicle occupant restraint 18, which is commonly referred to as 
an air bag, and includes an inflator 20 for inflating the air bag 18. 
When the inflator 20 is actuated, it inflates the air bag 18 from an 
uninflated condition, as shown fully in FIG. 1, to an inflated condition, 
as shown partially in FIG. 2. When the air bag 18 is in the inflated 
condition, it extends from the instrument panel 16 into the vehicle 
occupant compartment 14 to restrain movement of a vehicle occupant toward 
the instrument panel 16. The air bag 18 thus helps to protect the occupant 
from a forceful impact with the instrument panel 16 or other parts of the 
vehicle. 
The air bag module 12 further includes a reaction canister 22 and a 
deployment door 24. The reaction canister 22 contains the air bag 18 and 
the inflator 20. The deployment door 24 is mounted on the reaction 
canister 22, and conceals the other parts of the air bag module 12 from 
the vehicle occupant compartment 14. 
The reaction canister 22 has an upper wall 26, a lower wall 28, and a pair 
of opposite side walls 30 and 32. The upper, lower, and side walls 26, 28, 
30 and 32 of the reaction canister 22 together define a deployment opening 
34 at the outer end of the reaction canister 22. An inner wall 38 closes 
the inner end of the reaction canister 22 opposite the deployment opening 
34. 
A plurality of mounting tabs 40, one of which is shown in FIG. 1, project 
from the reaction canister 22. The mounting tabs 40 are fixed to 
corresponding supporting parts 42 of the instrument panel 16 by fasteners 
44. The structure and arrangement of the fasteners 44, the mounting tabs 
40, and the supporting parts 42 of the instrument panel 16 can vary, as 
known in the art. The reaction canister 22 is mounted in the instrument 
panel 16 in a position in which the deployment opening 34 is closely 
spaced from a surrounding edge surface 46 of the instrument panel 16. The 
deployment opening 34 is thus located within a larger opening 48 defined 
by the edge surface 46 of the instrument panel 16. Although the reaction 
canister 22 in the preferred embodiments of the present invention is a 
separate structure which is mounted in the instrument panel 16, such a 
canister could alternatively be defined by the structure of the instrument 
panel 16, or by another part of the vehicle from which the air bag 18 is 
to be inflated into the vehicle occupant compartment 14. 
As noted above, the air bag 18 is contained in the reaction canister 22 in 
the uninflated condition of FIG. 1. An open inner end portion 50 of the 
air bag 18 is wrapped around and secured to a retainer ring 52 in a known 
manner. The retainer ring 52 extends fully around the inside of the 
reaction canister 22 at a location between the inflator 20 and the 
deployment opening 34. A plurality of fasteners 54 securely fasten the 
retainer ring 52, and hence the inner end portion 50 of the air bag 18, to 
the surrounding walls 26, 28, 30 and 32 of the reaction canister 22 at 
that location. 
The inflator 20 is an elongated cylindrical structure comprising a source 
of inflation fluid for inflating the air bag 18. As known in the art, the 
inflator 20 may contain an ignitable gas generating material which, when 
ignited, rapidly generates a large volume of gas. The inflator 20 may 
alternatively contain a stored quantity of pressurized inflation fluid, or 
a combination of pressurized inflation fluid and ignitable material for 
heating the inflation fluid. 
The inflator 20 extends longitudinally between the opposite side walls 30 
and 32 of the reaction canister 22. A threaded mounting stud 56 on the 
inflator 20 projects radially outward through an opening (not shown) in 
the inner wall 38 of the reaction canister 22. A nut 58 on the mounting 
stud 56 attaches the inflator 20 securely to the reaction canister 22. 
Alternatively, the inflator 20 could be mounted in the reaction canister 
22 by any other suitable mounting structure known in the art. 
As shown in FIG. 3, the inflator 20 is included in an electrical circuit 
60. The electrical circuit 60 further includes a power source 62, which is 
preferably the vehicle battery and/or a capacitor, and a normally open 
switch 64. The switch 64 is part of a sensor 66 which senses a condition 
indicating the occurrence of a vehicle collision. The collision-indicating 
condition may comprise, for example, sudden vehicle deceleration caused by 
a collision. If the collision-indicating condition is above a 
predetermined threshold, it indicates the occurrence of a collision for 
which inflation of the air bag 18 is desired to protect an occupant of the 
vehicle. The sensor 66 then closes the switch 64, and the inflator 20 is 
actuated electrically. 
When the inflator 20 is actuated, it emits a large volume of inflation 
fluid into the reaction canister 22. The reaction canister 22 directs the 
inflation fluid from the inflator 20 into the air bag 18 to inflate the 
air bag 18 from the uninflated condition of FIG. 1 to the inflated 
condition of FIG. 2. As the air bag 18 begins to inflate, it moves rapidly 
outward from the reaction canister 22 through the deployment opening 34. 
The air bag 18 then moves forcefully against the deployment door 24 to 
open the deployment door 24, and continues to move outward into the 
vehicle occupant compartment 14 past the deployment door 24. 
As shown with the instrument panel 16 in FIG. 4, the deployment door 24 in 
the preferred embodiment of the present invention has a generally 
rectangular shape which is elongated horizontally. As shown separately in 
FIGS. 5-8, the deployment door 24 is a unitary plastic part with a 
plurality of distinct portions including a door panel 80, a lower flange 
82, and an upper flange 84. 
The door panel 80 has an inner side surface 90 facing inward toward the 
reaction canister 22 (FIG. 1), and has an outer side surface 92 facing 
outward toward the vehicle occupant compartment 14. The inner and outer 
side surfaces 90 and 92 are coextensive with each other and are bounded by 
a peripheral edge surface 94 which extends entirely around the door panel 
80. The peripheral edge surface 94 closely follows the contour of the edge 
surface 46 of the instrument panel 16. The door panel 80 thus extends 
fully across the opening 48 in the instrument panel 16, as shown in FIG. 
4. Additionally, the door panel 80 has a curved contour such that the 
outer side surface 92 continues the curved contour of the instrument panel 
16 across the opening 48. In the preferred embodiment of the present 
invention shown in the drawings, the outer side surface 92 extends 
vertically across the opening 48 with a generally S-shaped contour (FIG. 
1), and extends horizontally across the opening 48 with a concave contour 
(FIGS. 6 and 7) facing outward toward the vehicle occupant compartment 14. 
The lower flange 82 on the deployment door 24 projects inward from the door 
panel 80 near the bottom of the door panel 80. An inner edge 96 of the 
lower flange 82 extends along the length of the lower flange 82,.and has a 
plurality of recessed portions 98. The recessed portions 98 of the inner 
edge 96 extend between a plurality of mounting tabs 100 which are spaced 
apart along the length of the lower flange 82. Each mounting tab 100 has a 
downwardly projecting cylindrical boss 102, and has an aperture 104 
centered on the boss 102. The bosses 102 and the apertures 104 are 
centered together on a straight line 106 which extends along the length of 
the lower flange 82. When the deployment door 24 is mounted on the 
reaction canister 22, as shown in FIG. 1, each boss 102 on the lower 
flange 82 is closely received in a corresponding aperture 108 in the lower 
wall 28 of the reaction canister 22. Each aperture 104 in the lower flange 
82 receives a corresponding fastener 114 such that the lower flange 82 on 
the deployment door 24 is fastened securely to the lower wall 28 of the 
reaction canister 22. 
As best shown in FIG. 6, the opposite ends of the lower flange 82 are 
defined by first and second end edges 120 and 122. The end edges 120 and 
122 extend inward from the inner side surface 90 of the door panel 80 and 
are perpendicular to the line 106. As further shown in FIG. 6, the door 
panel 80 is skewed relative to the line 106. This is a result of the 
curvature of the instrument panel 16 and the complementary curvature of 
the door panel 80, as described above. Therefore, the first end edge 120 
of the lower flange 82 is substantially longer than the second end edge 
122. 
An elongated recessed surface 124 (FIG. 1) of the lower flange 82 extends 
along the lower flange 82 adjacent to the door panel 80. An elongated 
stress riser 128 is defined by the relatively thin plastic material of the 
lower flange 82 which is located between the recessed surface 124 and an 
opposite surface 130. The stress riser 128 is rupturable under stress of 
at least a predetermined elevated level. A generally slot-shaped initiator 
opening 132 (FIG. 6) extends through the lower flange 82. The initiator 
opening 132 interrupts the stress riser 128 approximately midway along the 
length of the lower flange 82. The stress riser 128 thus extends 
longitudinally in opposite directions from the initiator opening 132 to 
the opposite end edges 120 and 122 of the lower flange 82. Although the 
foregoing structure of the stress riser 128 is preferred, any other 
suitable structure for defining one or more stress risers and/or one or 
more initiator openings can be used as an alternative. 
The upper flange 84 on the deployment door 24 also projects inward from the 
door panel 80. An inclined portion 150 of the upper flange 84 projects 
inward from the inner side surface 90 of the door panel 80. A horizontal 
portion 152 of the upper flange 84 projects inward from the inclined 
portion 150. 
As shown in FIG. 7, the horizontal portion 152 of the upper flange 84 has 
an inner edge 154. The inner edge 154 extends along the length of the 
upper flange 84, and has a plurality of recessed portions 156. The 
recessed portions 156 of the inner edge 154 extend between a plurality of 
mounting tabs 158 which are spaced apart along the length of the upper 
flange 84. A plurality of apertures 160 extending through the mounting 
tabs 158 are centered on a straight line 162. The straight line 162 at the 
upper flange 84 is parallel to the straight line 106 (FIG. 6) at the lower 
flange 82. When the deployment door 24 is mounted on the reaction canister 
22, as shown in FIG. 1, each aperture 160 in the upper flange 84 is 
aligned with a corresponding aperture 164 in the upper wall 26 of the 
reaction canister 22. A plurality of fasteners 170, one of which is shown 
in FIG. 1, are received through the aligned apertures 160 and 164 to 
fasten the upper flange 84 on the deployment door 24 securely to the upper 
wall 26 of the reaction canister 22. 
The inclined portion 150 of the upper flange 84 has inner and outer side 
edges 180 and 182 extending between a pair of opposite end edges 184 and 
186. As best shown in FIG. 7, the end edges 184 and 186 are perpendicular 
to the line 162. The inner side edge 180 is spaced from the door panel 80, 
and extends between the end edges 184 and 186 in a straight line which is 
parallel to the line 162. The outer side edge 182 extends alongside the 
door panel 80. Therefore, the outer side edge 182 extends between the 
opposite end edges 184 and 186 in a curve defined by the curvature of the 
door panel 80. The outer side edge 182 is thus skewed relative to the 
inner side edge 180. As a result, the length L1 of the first end edge 184 
is substantially longer than the length L2 of the second end edge 186. 
As described above, the air bag 18 moves outward against the deployment 
door 24 when the air bag 18 is being inflated from the condition of FIG. 1 
toward the condition of FIG. 2. The inflation fluid in the air bag 18 then 
causes the air bag 18 to apply a fluid pressure force to the inner side 
surface 90 of the door panel 80. Some components of the fluid pressure 
force are transmitted within the deployment door 24 from the door panel 80 
to the lower flange 82. This induces stress in the stress riser 128. When 
the stress reaches the predetermined elevated level, the stress riser 128 
ruptures fully along its entire length. The door panel 80 is thus released 
from the lower flange 82. 
As the air bag 18 continues to inflate, it opens the door panel 80 from the 
position of FIG. 1 to the position of FIG. 2. The upper flange 84 then 
acts as a hinge which guides such movement of the door panel 80. 
Specifically, the horizontal portion 152 of the upper flange 84 acts as a 
stationary hinge leaf. The inclined portion 150 acts as a pivotal hinge 
leaf. The two portions 150 and 152 of the upper flange 84 together define 
a pivotal axis 190 about which the inclined portion 150 and the door panel 
80 pivot from the position of FIG. 1 to the position of FIG. 2. 
As shown in FIG. 7, the pivotal axis 190 extends along the length of the 
upper flange 84 at the juncture of the inclined portion 150 and the 
horizontal portion 152. The inner side edge 180 of the inclined portion 
150 thus extends in a straight line alongside the pivotal axis 190. The 
outer side edge 182 of the inclined portion 150, which is skewed relative 
to the inner side edge 180, is also skewed relative to the pivotal axis 
190. The opposite ends of the outer side edge 182 are thus spaced unequal 
distances (L1 and L2) from the pivotal axis 190 as a result of the 
curvature of the door panel 80. 
The material of the upper flange 84 is deflected and stressed by the fluid 
pressure force applied to the door panel 80 when the inflating air bag 18 
pivots the door panel 80 about the axis 190 toward the position of FIG. 2. 
The inclined portion 150 of the upper flange 84 is then deflected and 
stressed along its length between the opposite end edges 184 and 186, and 
is also deflected and stressed across its width between the inner and 
outer side edges 180 and 182. Since the outer side edge 182 is skewed 
relative to the inner side edge 180 and the axis 190, the stresses vary 
along the length of the inclined portion 150. More specifically, the 
stresses near the second end edge 186 are substantially greater than the 
stresses near the first end edge 184 because the width of the inclined 
portion 150 at the second end edge 186 is substantially less than the 
width at the first end edge 184. 
In order to alleviate the foregoing imbalance in stresses between the 
opposite ends of the upper flange 84, a stress riser 192 is provided in 
the upper flange 84. As shown in FIG. 8, the stress riser 192 is defined 
by the relatively thin plastic material of the upper flange 84 which is 
located between an elongated recessed surface 194 and an opposite surface 
196. As shown in FIG. 7, the stress riser 192 begins at the second end 
edge 186 of the inclined portion 150 of the upper flange 84, and extends a 
distance D1 along the inner side edge 180. The stress riser 192 thus 
extends alongside the portion of the axis 190 where the greatest stresses 
arise upon pivotal movement of the door panel 80 about the axis 190. Those 
stresses cause the stress riser 192 to rupture fully along its entire 
length. As a result, stress is relieved in a controlled amount. The 
imbalance in stresses between the opposite ends of the upper flange 84 is 
thus alleviated in a controlled amount. 
Another stress riser 198 is preferably included at the opposite end of the 
upper flange 84, as shown in FIG. 7. The other stress riser 198 ruptures 
in the same manner as the stress riser 192, but extends a shorter distance 
D2 along the inner side edge 180. The differing distances D1 and D2 are 
predetermined so as to cause correspondingly differing amounts of stress 
to be relieved upon rupturing of the two stress risers 192 and 198. The 
imbalance in stresses between the opposite ends of the upper flange 84 is 
alleviated accordingly. 
When the stress risers 192 and 198 in the upper flange 84 have been 
ruptured in the foregoing manner, a living hinge portion 200 of the upper 
flange 84 is defined along the pivotal axis 190 between the ruptured 
stress risers 192 and 198. The plastic material of the upper flange 84 
continues to bend along the length of the living hinge 200 as the inclined 
portion 150 of the upper flange 84 continues to pivot about the axis 190 
toward the position of FIG. 2. Since the imbalance in stresses has then 
been alleviated as described above, the plastic material bends more evenly 
along the length of the living hinge 200. The inclined portion 150 of the 
upper flange 84 then pivots more evenly along the length of the living 
hinge 200 without twisting excessively. The door panel 80 likewise pivots 
about the axis 190 more evenly along its length without twisting 
excessively. 
Additionally, when the stress risers 192 and 198 are ruptured along their 
lengths by the fluid pressure force of the inflating air bag 18, forces 
act through distances such that work is performed and energy is 
dissipated. Therefore, in addition to alleviating an imbalance in stresses 
to promote even pivotal movement of the door panel 80 about the axis 190, 
the stress risers 192 and 198 further serve to dissipate energy such that 
undesirable breakage in the deployment door 24 is avoided. 
As further shown in FIG. 2, the door panel 80 and the upper flange 84 are 
also deflected relative to each other at the juncture of the door panel 80 
and the upper flange 84. The door panel 80 and the inclined portion 150 of 
the upper flange 84 are thus moved pivotally about a second pivotal axis 
210 which extends along the length of the outer side edge 182 of the 
inclined portion 150. One or more stress risers like the stress risers 192 
and 198 could be provided at the outer side edge 182 to relieve stresses 
at the second pivotal axis 210, as desired. 
As shown partially in FIG. 9, a second embodiment of the present invention 
includes a deployment door 240. The partial view of the deployment door 
240 shown in FIG. 9 corresponds with the partial view of the deployment 
door 24 shown in FIG. 7. The deployment door 240 is thus shown to have an 
upper flange 242 projecting from an inner side surface 244 of a curved 
door panel 246. 
Like the upper flange 84 on the deployment door 24 described above, the 
upper flange 242 on the deployment door 240 has a pair of stress risers 
248 and 250 extending distances D3 and D4, respectively, from 
corresponding opposite ends of the upper flange 242. Further like the 
upper flange 84, the upper flange 242 has an inclined portion 252 with 
opposite end edges 254 and 256. The opposite end edges 254 and 256 have 
lengths L3 and L4, respectively, between a pair of skewed opposite side 
edges 258 and 260 of the inclined portion 254. However, the curvature of 
the door panel 246 differs from the curvature of the door panel 80 
described above. Specifically, the curvature of the door panel 246 is such 
that the lengths L3 and L4 are equal, rather than unequal, to each other. 
The distances D3 and D4 also are equal, rather than unequal, to each 
other. If the deployment door 240 were provided with stress risers at a 
second pivotal axis, as described above with reference to the second 
pivotal axis 210, such additional stress risers also would preferably be 
equal in length in accordance with this feature of the present invention. 
The present invention has been described with reference to preferred 
embodiments. From the foregoing description of the invention, those 
skilled in the art will perceive improvements, changes and modifications. 
For example, the shape and size of the deployment door could vary. The 
deployment door could have a different location on the instrument panel, 
such as a top-mount location. Moreover, a vehicle occupant restraint 
system may include one or more air bags that inflate upon the occurrence 
of front, rear, and/or side impacts to the vehicle. The air bags can be 
mounted in parts of the vehicle other than the instrument panel. Such 
other parts of the vehicle include, for example, the steering column, the 
doors, the pillars, the roof, and the seats. A deployment door constructed 
in accordance with the present invention could be used with an air bag at 
any of those locations. Such improvements, changes and modifications 
within the skill of the art are intended to be covered by the appended 
claims.