Air bag cover having a tear seam membrane switch

A snap-on air bag cover for use with an air bag container having a retaining member. The snap-on air bag cover includes a plastic front cover adapted to directly enclose an uninflated air bag. A pair of plastic side panels are connected to opposite sides of the front cover. A resilient clip member extends from each of the side panels, the clip member having an extending snap-on groove defined therein adapted to cooperate with the retaining member for affixing the air bag cover to the air bag container. The pair of side panels are connected to the front cover such that the side panels and resilient clip members are permitted to pivotably travel away from each other in opposite directions allowing the retaining member to enter and abuttingly engage the snap-on groove thereby retaining the air bag cover on the air bag container. A horn switch assembly is disposed in and substantially fills a pair of compartments formed at the inner surface of the cover. The switch assembly is separable along a tear seam with different portions of the switch assembly being located in the different compartments which are formed by a pair of spaced rear panels heat-staked to stakes formed on the inner surface of the front cover and which extend through apertures in the switch assembly.

TECHNICAL FIELD 
This invention relates to plastic air bag covers having switch assemblies 
therein and, in particular, to such covers which have a tear seam membrane 
switch. 
BACKGROUND ART 
Presently, when air bag covers are provided in automobiles on the drivers 
side of the vehicle, the air bag is stored in the steering column behind 
an air bag cover. During automatic inflation of the air bag, the air bag 
cover moves away from the steering column to permit its safety function 
between the steering column and the operator of the vehicle. 
Recent practice in the automotive industry is utilization of all plastic 
fabricated air bag covers. Conventional air bag covers used in conjunction 
with occupant restraint systems often include various connection systems 
for attaching the air bag cover to the uninflated air bag container. As 
those skilled in the art will recognize, such systems normally include a 
two piece cover construction wherein a first cover portion, usually 
manufactured from a relatively stiff material, is initially disposed 
directly over the uninflated air bag container. A second more resilient 
cover portion is next affixed over the first cover portion and used as the 
outer decorative cover. 
U.S. Pat. No. 4,325,568 issued to Clark et al. discloses a modular occupant 
restraint system 
including an inflator, a cushion, a container for the cushion and an air 
bag cover for the container assembled as a module. Clark et al. utilizes a 
two piece air bag cover construction. 
U.S. Pat. No. 5,085,462 issued to Gaultier discloses an air bag and vehicle 
horn switch assembly. Gaultier also discloses a conventional two piece 
cover construction. 
U.S. Pat. No. 5,186,490 issued to Adams et al. discloses a cover for a 
inflatable restraint system for a motor vehicle which contains a slot in 
the upper wall thereof into which a replaceable thin or membrane type 
switch assembly in inserted. Adams et al. further discloses an air bag 
cover having an injection molded thermoplastic upper wall and a soft outer 
cover exposed to the interior of the vehicle manufactured from urethane, 
vinyl or polyester. The outer cover completely encompasses and overlaps 
the upper wall structure and uninflated air bag forming two structures the 
air bag must exit to carry out its function. 
The patent to Embach, U.S. Pat. No. 4,934,735, discloses a device which has 
inner and outer covers or plates, each of which has split lines which 
separate the upper walls into upwardly and oppositely opening upper and 
lower pairs of flaps to permit deployment of the inflatable cushion. A 
switch assembly is located between either or both pair of flaps and 
includes one or more membrane switches located between the flaps and 
respective key pads projecting outwardly of the cover flap for closing 
respective pairs of circuits on the upper and lower flexible membranes of 
the membrane switch to each other. 
The patent to Heidorn, U.S. Pat. No. 5,308,106, discloses an air bag module 
cover assembly with a switch subassembly removably attached at a front 
surface of the assembly. 
The patent to Winget, U.S. Pat. No. 5,062,661, discloses a rigid plate 
attached to the substantially rigid remainder of a front panel of an air 
bag cover to define a hollow compartment which together move upon manual 
actuation of a flexible, manually operable diaphragm at the front surface 
of the front panel. Upon separation from the side panel, the front panel, 
including the diaphragm, the hollow compartment and a rigid plate move 
together to permit the inflating air bag to leave the cover. The front 
panel has a first electrically conductive inner surface for making a 
circuit path with a corresponding second electrically conductive inner 
surface of the rigid plate. 
The patent to Cooke, II, U.S. Pat. No. 5,344,185, discloses an air bag 
cover having a replaceable horn switch and a removable cover band. 
Some of the above switches are relatively small and oftentimes inaccessible 
for drivers who have large hands or for drivers who have limited manual 
dexterity. Also, such switches extend, at least to a limited extent, above 
the exterior surface of the air bag cover and may strike the occupant upon 
air bag inflation. Consequently, there is a need for a horn switch device 
which is incorporated in an air bag cover, is relatively easy to service 
and which is actuable over a relatively large surface area of the air bag 
cover and which does not extend above the generally planar exterior 
surface of the air bag cover. 
DISCLOSURE OF THE INVENTION 
An object of the present invention is to provide an air bag cover that is 
affixable directly to an air bag container and which has at least one 
switch assembly incorporated therein. 
Still another object of the invention is to provide an air bag cover having 
a single switch assembly incorporated therein which is separable along a 
prescribed tear pattern upon deployment of an air bag. 
In carrying out the above objects and other objects of the present 
invention, a plastic molded air bag cover mountable onto an air bag 
assembly is provided. The cover includes a front cover having inner and 
outer surfaces adapted to overlie an uninflated air bag and being 
separable along a first prescribed tear pattern upon deployment of the air 
bag. The cover also includes a switch assembly which has a flexural 
material lying behind the inner surface of the front cover and a pair of 
spaced rear panels secured to the inner surface of the front cover to form 
a pair of hollow compartments wherein the switch assembly is separable 
along a second prescribed tear pattern aligned with a portion of the first 
prescribed tear pattern upon deployment of the air bag. The second 
prescribed tear pattern is located between the pair of spaced rear panels. 
An air bag cover constructed in accordance with the above invention 
provides numerous advantages. For example, the switch assembly is easily 
actuable over a relatively large surface area on the outer surface cover. 
Furthermore, such a switch assembly can be relatively inexpensively 
incorporated in a conventional air bag cover without the need to modify 
the air bag cover to allow a part of the switch assembly to extend above 
the outer surface of the cover, thereby freeing up additional areas on the 
steering column. 
These and other features and additional objects of the invention will occur 
to those skilled in the art on reading the following description with 
reference to the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawing Figures, there is illustrated in FIGS. 1 and 
2, a first embodiment of an automotive air bag cover, generally indicated 
at 10. Typically, the automotive air bag cover 10 is secured at the top 
end of a vehicle drive column (not shown) at the steering wheel of the 
vehicle. 
A front cover, generally indicated at 12 of the air bag cover 10, is 
integrally formed with side panels 14, 16 and 18. Typically, the side 
panels 14, 16 and 18 are apertured, as illustrated in FIGS. 1 and 2, to 
permit the cover 10 to be fixedly secured to the vehicle drive column. 
Outer surface 23 is disposed to face the vehicle operator (not shown). 
The front and side panels 12, 14, 16, and 18 are adapted to enclose an 
uninflated automotive air bag (not shown) between the cover 10 and the 
steering column (not shown). 
The front panel 12 includes upper and lower portions 20 and 22, 
respectively. The upper and lower portions 20 and 22 are interconnected to 
the side panels 16 at break seams 24 (only one of which is shown in FIG. 
1) and to each other at a break seam 26. The break seams 24 and 26 are of 
reduced thickness, to permit the air bag, as it is inflating, to exert a 
force at the inner portion of the front panel 12 to cause the upper and 
lower portions 20 and 22 of the front panel 12 to separate from the side 
panels 16 along the break seams 24 and to separate from each other along 
the break seam 26. 
The upper portion 20 of the front panel 12 is hingedly connected to the top 
panel 18 at a hinge 28 and the lower portion 22 of the front panel 12 is 
hingedly connected to the bottom side panel 14 at a hinge 30, as best 
shown in FIG. 2. After separation from the side panels 14 and 16, the 
upper and lower portions 20 and 22 of the front panel 12 can swing 
upwardly and downwardly, respectively, and out of the way of the inflating 
air bag. 
Rear panels 31 are fixedly secured at upper and lower flanges 29 to the 
upper and lower portions 20 and 22 of the front panel 12 at their inner 
surfaces to move therewith and to form hollow compartments 32, as best 
shown in FIG. 2. Preferably, the rear panels 31 are hot plate welded, heat 
staked or otherwise attached to the upper and lower portions 20 and 22 at 
their outer periphery adjacent the break seam 26 between the upper and 
lower portions 20 and 22, respectively, and adjacent the break seams 24. 
The air bag cover 10 may include a pair of horn switch assemblies, 
generally indicated at 34. Each assembly 34 extends substantially the 
entire width of the front panel 12 between the side panels 16 within its 
respective hollow compartment 32. Each switch assembly 34 can be slidably 
removed from its respective compartment and out slits 33 formed in one or 
both of the side panels 16. In this way, each switch assembly 34 is easily 
removable from its hollow compartment 32 so that the switch assembly 34 
can be easily serviced without removing the cover 10 from its attached 
container. The rear panels 31 do not cover any of the break seams 24 or 26 
since this would hinder or possibly prevent separation along the break 
seams 24 and 26. 
As illustrated in FIG. 2, each switch assembly 34 substantially fills its 
respective hollow compartment 32. As illustrated in FIG. 3, each horn 
switch assembly 34 includes a pair of spaced flexible, transparent, 
plastic layers 36. On the inner surface of one of the plastic layers 36, 
there is formed a matrix layer 38 of interconnected hexagonal pads which 
forms an electrically conductive inner surface for making a circuit path 
with a corresponding second electrically conductive inner surface of 
another matrix of interconnected hexagonal pads formed on the other 
plastic layer 36. Upon manual actuation of the corresponding portion of 
the front panel 12, the circuit path is made. 
The circuit path is made through an insulator layer 40 which is disposed 
between and spaces the layers 38 apart so that electrical connection is 
only made between the hexagonal pads of the layers 38. The insulator layer 
40 insulates the interconnecting portions of the electrically conductive 
inner surfaces of the layers 38 from one another. The insulator layer 40 
is preferably made of foam and has a honeycomb structure. 
Preferably, the horn switch assemblies 34 are foil switch assemblies cut to 
size from a mat of material commercially available from Illinois Tool 
Works, Inc. of Glenview, Ill. Then, electrically conductive leads 42 which 
are encapsulated in plastic are electrically connected to certain pads of 
each of the layers 38 at one end thereof and to the automobile's 
electrical system at the opposite end through a breakaway connection. 
Referring now to FIG. 2, there is shown a resilient clip connector 50 
extending from side panel 18. A snap-on groove 52 is shown disposed within 
clip connector 50. Clip connector 50 is comprised of a front engagement 
section 54 and a rear shoulder section 56 with snap-on groove 52 disposed 
between front engagement section 54 and rear shoulder section 56. Snap-on 
groove 52 is configured to cooperate with a retaining rim 51 on uninflated 
air bag container 53 (shown in phantom). For proper connection and 
retainment, the snap-on groove should have a cross-sectional shape that 
corresponds to the shape of the air bag container rim. 
As shown, clip connector 50 also includes a biasing groove 58 which extends 
in a direction parallel with the snap-on groove 52. The biasing groove 58 
divides the front engagement section 54 into a first segment 60 and a 
second segment 62. The biasing groove 58 allows the first segment 60 to 
deform and move toward the second segment when the air bag container rim 
51 is initially engaged with the clip connector just prior to full 
engagement within the snap-on groove 52. 
Referring now to FIG. 1 there is shown four clip connectors 50, 70, 72, and 
74 extending from each side panel. It is contemplated in the preferred 
embodiment that each clip member extend at least one third of the length 
of the respective side panel and the snap-on groove 52 extend the entire 
length of the clip connector 50. 
Referring now to FIGS. 4 and 5, there is shown generally, an air bag cover 
76. The air bag cover 76 includes a front cover 78 having an inner surface 
82 and an outer surface 80. The inner and outer surfaces 82 and 80 
respectively define a thickness of front cover 78 which is in a range from 
2.0 to 6.0 millimeters. The air bag cover 76 is designed to be operably 
located within the automobile interior (not shown) such that the front 
cover outer surface 80 is exposed to occupant view. 
The air bag cover 76 includes four clip connectors 86, 88, 90 and 92 
connected to respective side panels 94, 96, 98, and 100. Referring now to 
FIG. 8, and using clip connector 86 as representative of the other clip 
connectors, each clip connector includes a front engagement section 102 
and a rear shoulder section 104. As with the prior embodiment, a snap-on 
groove 106 is defined between the front engagement section 102 and the 
rear shoulder section 104. The snap-on groove 106 of the second embodiment 
of the present invention has a cross sectional shape which corresponds to 
the rim 108 of the air bag container 110. The snap-on groove shown in FIG. 
8 is L-shaped to correspond to the outer shape of rim 108. Clip connector 
86 further includes an outer inclined surface 112 as shown in FIGS. 7 and 
8. 
Referring now to FIG. 6, there is shown a biasing groove 114. Biasing 
groove 114, as with the prior embodiment discussed above, extends parallel 
to the snap-on groove 106. The biasing groove divides clip connector 86 
into a first segment 116 and a second segment 118. As those skilled in the 
art will recognize, the inclined surface 112 in cooperation with the 
biasing groove 114 assist in locating and abuttingly engaging the rim 108 
of the air bag container 110 within the snap-on groove 106. 
More specifically, as the rim 108 of the air bag container 110 initially 
contacts the clip connector 86, the rim slides along the inclined surface 
112 towards the snap-on groove 106. Simultaneously, the first segment 116 
of the front engagement section is deformed and moves toward second 
segment 118. In this fashion, the snap-on connection of the air bag cover 
to the air bag container is assisted. For structural integrity and 
material cost savings it is contemplated that the front engagement portion 
may include a plurality of spaced apart, parallel supports 120 which are 
disposed perpendicular to the snap-on groove. 
It is preferred that the air bag cover of the present invention be 
manufactured from a flexible thermoplastic rubber such as commercially 
available "Santoprene" 201-87 provided by Advance Elastomers Systems of 
Auburn Hills, Mich. Santoprene is a registered trademark of the Monsanto 
Company. Santoprene 201-87 is a colorable thermoplastic general purpose 
elastomer with good fluid resistance which is processable by injection 
molding and extrusion. 
The tear strength, ultimate tensile strength, hardness, and elasticity of 
the material are characteristics important to the choice of the 
thermoplastic material used to manufacture the air bag. The preferred 
thermoplastic material used for manufacture of the air bag cover has a 
tensile strength in a range from 15.0 to 17.0 Mpa's. The preferred 
material used has a tear strength in a range from 47 to 51 kN/M at 25 
degrees celsius and 21 to 25 kN/M at 100 degrees celsius. The preferred 
material used has a durometer hardness in a range of 70 to 100 on the 
Shore A scale. The above characteristics in conjunction with the structure 
of the air bag cover satisfy the necessary conditions related to the 
inflation and exit of the air bag from the cover. 
Having described the structural characteristics of the present invention, 
attention is now turned to operation of the snap-on air bag cover. 
Referring to FIGS. 5-8, each clip connector 86, 88, 90 and 92 extends from 
a respective side panel 94, 96, 98 and 100. Each clip connector is 
attached to the respective side panel in a live hinge-like fashion such 
that the clip connectors and associated side panels move away from the 
front cover upon operative insertion of the air bag container rim 108 
within snap-on groove 106. 
For example, opposing side panels 96 and 100 move away from front cover 82 
and also away from each other as the rim 108 is abuttingly engaged against 
the inclined surfaces 112 of each clip connector 88 and 92. Further the 
cooperation of the biasing grooves in the other pair of opposing clip 
connectors 86 and 90 works to assist in locating and operatively 
connecting the air bag container 110 to the air bag cover 76. 
The particular thermoplastic rubber described above assists in providing 
the operative resilient characteristics needed to provide an air bag cover 
which is directly affixable to an air bag container. The air bag cover of 
the present invention is resilient enough to accept deformation of the 
side panels and clip connectors while the air bag cover is connected to 
the air bag container and rigid enough to contain the air bag container on 
the steering column (not shown) throughout the operative life of the 
associated vehicle. Thus, the tear strength, ultimate tensile strength, 
hardness, and elasticity of the thermoplastic rubber material, as 
described above are important to the overall operation of the air bag 
cover. 
The air bag cover of the present invention is preferably injection molded 
using conventional injection molding techniques. The preferred embodiment 
of the present invention will include clip connectors that extend at least 
one third the length of the respective side panel. It is contemplated that 
the clip connectors do not extend completely along the length of the side 
panels because this makes the air bag cover difficult to remove from the 
mold in the manufacturing process. 
Referring now to FIG. 9, there is illustrated another air bag cover 10' 
with another foil or membrane switch assembly, generally indicated at 34', 
secured thereto by a pair of spaced rear panels, generally indicated at 
31'. The rear panels 31' have apertures 201 formed completely 
therethrough. 
Parts of the air bag cover 10' which are the same or perform the same or 
similar function as the parts of the air bag cover 10 of FIG. 1 have the 
same reference numeral but a prime designation. 
The membrane switch is of a sandwich construction and is encapsulated in a 
mylar or polyester covering. The switch has a pair of copper foil layers 
separated by an insulating layer in a conventional fashion. The switch 
assembly 34' is different from prior art switch assemblies because it 
separates along a prescribed tear pattern 200 which is aligned with a 
portion 26' of the prescribed tear pattern formed in the front panel 12' 
upon deployment of the air bag. The tear pattern 200 is formed between the 
pair of spaced rear panels 31' at a scored or weakened area of the switch 
assembly 34'. The switch assembly 34' is available from The Bergquist 
Company of Edina, Minn. 
Each rear panel 31' is secured to the inner surface of the upper and lower 
portions 20' and 22', respectively, by thermal coupling at positions about 
the periphery of each rear panel 31' such as by heat staking. The switch 
assembly 34' has apertures 202 by which the switch assembly 34' is 
positioned over stakes 204 formed on the inner surface of the upper and 
lower portions 20' and 22'. The stakes 204 center the switch assembly 34' 
and the rear panels 31' on the inner surface of the cover 10' in a 
predetermined position and orientation. Then, the rear panels 31' which 
are also positioned over the stakes 204 at their apertures 201 are 
heat-staked to the stakes 204 in a conventional fashion. 
Another advantage of this embodiment is that it minimizes the number of 
leads 42' needed to electrically connect the switch assembly to the 
vehicle's electrical system. 
While only certain embodiments of the method and apparatus of the present 
invention have been shown and described, others may be possible without 
departing from the scope of the following claims.