Horn membrane switch with rupturable strain relief bridging connector

An improved membrane horn switch having a first main switch section and a second main switch section connected by spaced-apart, relatively narrow first and second bridge members which are rupturable by a force created by an inflating airbag cushion. Each bridge member has a conductive coating in the form of two spaced-apart parallel strips which resist the propagation of stress cracks caused by the bending and twisting of horn actuation, and provide redundancy upon one of the two conductive strips being severed by a stress crack. Improved membrane horn switches having strain relieving bridge members are also provided. Each strain relieving bridge member, in addition to having two spaced-apart conductive strips, also forms a non-straight path between the first main switch section and the second main switch section. The non-straight paths of the strain relieving bridge members allow extra slack and leeway between the first and the second main switch sections of the horn switch, reducing stress on the bridge members. An improved membrane horn switch having a combined bridge member is also provided, and improved membrane horn switches having a combined strain relieving bridge member with a non-straight path are also provided.

FIELD OF THE INVENTION 
The present invention relates to a membrane horn switch for use in a driver 
side airbag module, and more specifically, the present invention relates 
to a membrane horn switch having an improved strain relieving bridge 
member. 
BACKGROUND OF THE INVENTION 
This invention relates to a membrane horn switch for a driver side airbag 
module. A membrane horn switch generally includes a first very thin, 
flexible, plastic sheet having a conductive coating, and a second very 
thin, flexible, plastic sheet having a conductive coating. The two plastic 
sheets are adhered together with the conductive coatings facing and 
separated by thin nonconductive spacers. Pressure on the membrane horn 
switch pushes the conductive coatings together to close a horn control 
circuit that the membrane horn switch is connected to in order to actuate 
a remote horn. 
An airbag module is employed in a vehicle for protecting an occupant 
against injury by deploying an inflated airbag cushion to physically 
restrain the occupant's body when the vehicle encounters a collision. A 
driver side airbag module is normally positioned within a hub of a 
steering wheel, where a horn switch is also traditionally positioned. 
Driver side airbag modules have, therefore, been adapted to include a horn 
switch. 
In many driver side airbag modules an inflating airbag cushion is forced 
out of the airbag module in a predetermined manner through a weakened area 
or tear seam dividing a horn actuation area of an airbag module cover. 
Membrane horn switches have been provided with two spaced-apart, 
rupturable bridge members for spanning the tear seam of the airbag module 
cover and connecting two larger sections of the horn switch. The 
rupturable bridge members accommodate the operation of the tear seams 
while providing the potential for actuation of the horn switch over a 
larger portion of the horn actuation area of the module cover. 
Because the tear seam is normally located at or near the center of the horn 
actuation area of the airbag module cover, and because the bridge members 
span the tear seam, the bridge members bend and twist upon a driver 
pressing upon the horn actuation area. Over the average life of an 
automobile, the bridge members may be subjected to hundreds or thousands 
of cycles of bending and twisting. It has been discovered that such 
bending or twisting can cause failure of the bridge members and render the 
horn switch inoperable. In particular, once a stress crack forms in the 
conductive coatings of the bridge members, the stress cracks can propagate 
and eventually sever the conductive coatings and disable the horn switch. 
The bridge members must be able to withstand thousands of cycles of 
bending and twisting during the average life of a vehicle, and there is a 
need for an improved membrane horn switch having means for preventing the 
propagation of stress cracks through the conductive coatings of the bridge 
members. 
BRIEF SUMMARY OF THE INVENTION 
A general object, therefore, of the present invention is to provide an 
improved membrane horn switch. 
A more specific object of the present invention is to provide an improved 
membrane horn switch having bridge members that are better able to 
withstand thousands of cycles of bending and twisting without failure of 
the bridge members and the membrane horn switch. 
Another object of the present invention is to provide an improved membrane 
horn switch having bridge members that are more resistant to the 
propagation of stress cracks through the conductive coatings of the bridge 
members. 
An additional object of the present invention is to provide an improved 
membrane horn switch having bridge members configured to reduce tension 
across the bridge members. 
A further object of the present invention is to provide an improved 
membrane horn switch having only one bridge member. 
The present invention meets these objects by providing a membrane horn 
switch having a first main switch section and a second main switch section 
connected by a first bridge member and a second bridge member. The first 
and the second bridge members are relatively narrow and rupturable by a 
force created by an inflating airbag cushion. Each of the first and the 
second bridge members includes an electrically conductive coating in the 
form of at least two spaced-apart, generally parallel strips connecting 
conductive coatings of the first and the second main switch sections. The 
electrically conductive coatings in the form of at least two spaced-apart, 
generally parallel strips prevent the propagation of stress cracks across 
the conductive coatings and provide redundancy, resulting in an increase 
in the useful life of the bridge members and in-turn the life of the horn 
switch. 
According to one aspect of the present invention, the first bridge member 
and the second bridge member are spaced-apart, and each bridge member 
defines a non-straight path between the first main switch section and the 
second main switch section. The non-straight path of the bridge members 
provides reduced tension across the bridge members and a greater range of 
movement to reduce the resulting stress on the bridge members during the 
bending and twisting of horn actuation. The non-straight path of the 
bridge members, therefore, increases the useful life of the bridge members 
and in-turn the horn switch. 
According to another aspect of the present invention, the first bridge 
member is superimposed on the second bridge member forming a combined 
bridge member. The at least two conductive strips of the first bridge 
member are offset from the at least two conductive strips of the second 
bridge member so that the at least two conductive strips of the first 
bridge member do not contact the at least two conductive strips of the 
second bridge member. The combined bridge member can be beneficial in 
place of two spaced-apart bridge members for at least two reasons. First, 
the combined bridge member places fewer design restrictions on a module 
cover that the horn switch is to be mounted to. Second, an inflating 
airbag cushion has to break through only one bridge member instead of two 
bridge members. 
According to an additional aspect of the present invention, the combined 
bridge member defines a non-straight path between the first main switch 
section and the second main switch section in order to reduce tension and 
stress on the combined bridge member.

The same reference numerals refer to the same elements throughout the 
various figures. 
DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 3 through 6, the present invention provides a membrane 
horn switch 64 having improved bridge members 66,68. Referring first, 
however, to FIGS. 1 and 2, a prior art membrane horn switch 10 is shown to 
provide background for the illustration of the improvements provided by 
the present invention. As shown in FIG. 1, the prior art membrane horn 
switch 10, which is connectable to a remote power source and a remote 
vehicle horn as part of horn control circuit, is mounted to a module cover 
200 for use as part of a driver side airbag module. As is known in the 
art, the membrane horn switch 10 acts to close the horn circuit and 
activate the remote horn upon being compressed by a vehicle driver. 
The membrane horn switch 10 includes rectangular, relatively large first 
and second main switch sections 12,14 connected by relatively small, i.e. 
narrowed, spaced-apart first and second bridge members 16,18. The 
relatively narrow first and second bridge members 16,18 provide readily 
rupturable areas for a force produced by an inflating airbag, and each 
bridge member is provided with one or more and preferably at least two 
opposing notches 19 which enhance the ability of the bridge members to 
rupture during airbag deployment. 
Referring also to FIG. 2, the first main switch section 12 includes a flat, 
thin and flexible top nonconductive sheet 22 having a bottom surface 23 
substantially covered with an electrically conductive coating 30, and a 
flat, thin and flexible bottom nonconductive sheet 38 having a top surface 
39 substantially covered with an electrically conductive coating 46. The 
top and the bottom nonconductive sheets 22,38 of the first main switch 
section 12 are overlaid, with the conductive coatings 30,46 facing each 
other, and are held together with a layer of adhesive 54 extending around 
the periphery of the conductive coatings 30,46. The first main switch 
section 12 also includes a nonconductive spacer in the form of a plurality 
of spaced-apart, plastic raised protrusions 52 arranged on and facing 
upwardly from the conductive coating 46 on the bottom nonconductive sheet 
38. The plurality of raised protrusions 52 prevent contact of the 
conductive coatings 30,46 until sufficient actuation pressure is exerted 
against the of the first main switch section 12. Raised protrusions can 
additionally or alternatively be arranged on and facing downwardly from 
the conductive coating 30 on the top nonconductive sheet 22. 
The second main switch section 14 includes a flat, thin and flexible top 
nonconductive sheet 24 having a bottom surface 25 substantially covered 
with an electrically conductive coating 32, and a flat, thin and flexible 
bottom nonconductive sheet 40 having a top surface 41 substantially 
covered with an electrically conductive coating 48. The top 24 and the 
bottom nonconductive sheets 40 of the second main switch section 14 are 
overlaid, with the conductive coatings 32,48 facing each other, and are 
held together with a layer of adhesive 56 extending around the periphery 
of the conductive coatings 32,48. The second main switch section 14 also 
includes a nonconductive spacer in the form of a plurality of 
spaced-apart, plastic raised protrusions 52 arranged on and facing 
upwardly from the conductive coating 48 on the bottom nonconductive sheet 
40. The plurality of raised protrusions 52 prevent contact of the 
conductive coatings 32,48 until sufficient actuation pressure is exerted 
against the second main switch section 14. Raised protrusions can 
additionally or alternatively be arranged on and facing downwardly from 
the conductive coating 32 on the top nonconductive sheet 24. 
The first bridge member 16 includes a flat, thin and flexible top 
nonconductive bridge sheet 26 having a bottom surface 27 substantially 
covered with a conductive coating 34, and a flat, thin and flexible bottom 
nonconductive bridge sheet 42. The top and the bottom nonconductive bridge 
sheets 26,42 of the first bridge member 16 are overlaid, with the 
conductive coating 34 therebetween, and secured together with a layer of 
adhesive 58. The top nonconductive bridge sheet 26 connects the top 
nonconductive sheet 22 of the first main switch section 12 to the top 
nonconductive sheet 24 of the second main switch section 14 and the 
conductive coating 34 connects the conductive coating 30 on the top 
nonconductive sheet 22 of the first main switch section 12 to the 
conductive coating 32 on the top conductive sheet 24 of the second main 
switch section 14. The bottom nonconductive bridge sheet 42 connects the 
bottom nonconductive sheet 38 of the first main switch section 12 to the 
bottom nonconductive sheet 40 of the second main switch section 14. 
The second bridge member 18 includes a flat, thin and flexible bottom 
nonconductive bridge sheet 44 having a top surface 45 substantially 
covered by a conductive coating 50, and a flat, thin and flexible top 
nonconductive bridge sheet 28. The top and the bottom nonconductive bridge 
sheets 28,44 of the second bridge member 18 are overlaid, with the 
conductive coating 50 therebetween, and secured together with a layer of 
adhesive 60. The top nonconductive bridge sheet 28 connects the top 
nonconductive sheet 22 of the first main switch section 12 to the top 
nonconductive sheet 24 of the second main switch section 14. The bottom 
nonconductive bridge sheet 44 connects the bottom nonconductive sheet 38 
of the first main switch section 12 to the bottom nonconductive sheet 40 
of the second main switch section 14, and the conductive coating 50 
connects the conductive coating 46 on the bottom nonconductive sheet 38 of 
the first main switch section 12 to the conductive coating 48 on the 
bottom nonconductive sheet 40 of the second main switch section 14. Each 
of the nonconductive sheets of the horn switch 10 can be made from a 
suitable material such as polyethylene or polyester, and each of the 
conductive coatings of the horn switch can be made from a suitable 
material such as copper, silver or conductive ink which can be screened on 
the nonconductive sheets. 
Referring back to FIG. 1, an inner surface 201 of the module cover 200 
defines a central tear seam 202 extending between two opposed side tear 
seams 203,204, and the tear seams form first and second airbag deployment 
doors 206,208. The module cover 200 also includes a first raised ridge 210 
substantially extending around the first deployment door 206, and a second 
raised ridge 216 substantially extending around the second deployment door 
208. 
As shown, the membrane horn switch 10 is positioned against the module 
cover 200, with the first main switch section 12 positioned against the 
first deployment door 206 and peripherally surrounded by the first raised 
ridge 210, and the second main switch section 14 positioned against the 
second deployment door 208 and peripherally surrounded by the second 
raised ridge 216. The first and the second bridge members 16,18 extend 
through a first and second opening 212,213 in the first raised ridge 210 
and a first and second opening 218,219 in the second raised ridge 216 and 
transverse the central tear seam 202 formed in the module cover 200. A 
first lead 62 of the membrane horn switch 10 extends through an opening 
214 in the first raised ridge 210 and a second lead 63 extends through an 
opening 220 in the second raised ridge 216. The leads 62,63 are 
connectable to a vehicle horn control circuit. Two rigid backing plates 
222,224 are secured inside the first and the second raised ridges 210,216 
to contain the membrane horn switch 10 against the module cover. 
Depression of the airbag module cover 200 by a vehicle driver compresses 
the membrane horn switch 10 against the rigid backing plates 222,224 to 
activate a remote horn. 
Whenever the module cover 200 is depressed, however, the first and the 
second bridge members 16,18 are bent and flexed, causing unwanted stress 
in the bridge members. The bending and flexing of the bridge members 16,18 
over hundreds of cycles of horn actuation can lead to cracks forming in 
the conductive coatings 34,50 of the bridge members. Once a stress crack 
forms in one of the conductive coatings 34,50 of the bridge members 16,18, 
the crack can continue to spread essentially unimpeded to sever the 
conductive coating, requiring the replacement of the membrane horn switch 
10. Replacement of the membrane horn switch 10 is especially unwanted 
since the entire module cover 200 might have to be replaced, depending 
upon whether the backing plates 222,224 are welded to the raised ridges 
210,216. The unwanted stress can also be intensified since, as shown, each 
of the bridge members 16,18 forms a straight line between the first and 
the second main switch sections 12,14, which can additionally place the 
bridge members in tension. 
Referring to FIGS. 3 through 6, the membrane horn switch 64 according to 
the present invention includes improved first and second bridge members 
66,68 which are resistant to the propagation of stress cracks. The 
membrane horn switch 64 is similar to the prior art horn switch 10 of FIGS 
and 2, and parts which are the same have the same reference numeral. As 
shown, the first improved bridge member 66 includes an electrically 
conductive coating in the form of two (2) spaced-apart, parallel strips 
70,71 on the bottom surface 27 of the top nonconductive bridge sheet 26, 
with each strip extending between the electrically conductive coatings 
30,32 on the top nonconductive sheets 22,24 of the first and the second 
main switch sections 12,14. The second improved bridge member 68 also 
includes an electrically conductive coating in the form of two (2) 
spaced-apart, parallel strips 72,73 on the top surface 45 of the bottom 
nonconductive bridge sheet 44, with each strip extending between the 
electrically conductive coatings 46,48 on the bottom nonconductive sheets 
38,40 of the first and the second main switch sections 12,14. 
The two spaced-apart strips 70,71 of conductive coating of the first 
improved bridge member 66, and the two spaced-apart strips 72,73 of 
conductive coating of the second improved bridge member 68 prevent the 
propagation of stress cracks across the entire conductive coating of each 
bridge member. Even if one of the two strips 70,71 of conductive coating 
of the first improved bridge member 66, or one of the two strips 72,73 of 
conductive coating of the second improved bridge member 68 is severed by a 
stress crack, the crack will not continue across the other of the two 
strips. In addition, depending on the conductive material used to form the 
strips, each strip is suitably wide and thick enough to individually 
handle the electrical load (of about 100 to 500 milliamperes for example) 
that passes through the horn switch 64. The two strips 70,71 of conductive 
coating of the first improved bridge member 66, and the two strips 72,73 
of conductive coating of the second improved bridge member 68, therefore, 
provide redundancy in addition to preventing stress cracks, resulting in 
an increase in the useful life of the bridge members and in-turn the life 
of the horn switch 64. Each improved bridge member 66,68 can have more 
than two spaced-apart conductive strips. As shown in FIG. 6, the layer of 
nonconductive adhesive 60 securing the top nonconductive bridge sheet 28 
to the bottom nonconductive bridge sheet 44 of the second improved bridge 
member 68 preferably fills in between the two strips 72,73 of conductive 
coating to further prevent propagation of stress cracks. Although not 
shown, the layer of nonconductive adhesive 58 securing the top 
nonconductive bridge sheet 26 to the bottom nonconductive bridge sheet 42 
of the first improved bridge member 66 also fills in between the two 
strips 70,71 of conductive coating. 
As shown in FIG. 7, as an alternative to the layer of nonconductive 
adhesive 60, the second improved bridge member 68 (and also the first 
improved bridge member 66) can include two strips 160,161 of adhesive 
securing the outer peripheries of the top nonconductive bridge sheet 2S to 
the outer peripheries of the bottom nonconductive bridge sheet 44 with the 
strips 70,71 of conductive coating positioned between the two strips 
160,161 of adhesive. As shown in FIG. 8 the second improved bridge member 
68 (and also the first improved bridge member 66) can further include a 
strip 162 of adhesive positioned between the two strips 72,73 of 
conductive coating. If each improved bridge member 66,68 has more than two 
spaced-apart conductive strips, the bridge members can include further 
strips of adhesive positioned between some or all of the additional strips 
of conductive coating. 
Referring to FIG. 9 through 11, improved, strain relieving bridge members 
76,78,80 according to the present invention are shown in place of the 
second improved bridge member 68 of FIGS.3 through 6. The bridge members 
76,78,80 are similar to the second improved bridge member 68 of FIGS. 3 
through 6, and parts which are the same have the same reference numeral. 
Although not shown, similar improved strain relieving bridge members are 
also provided in place of the first improved bridge member 66 of FIGS.3 
through 6. 
In addition to being resistant to the propagation of stress cracks, the 
improved, strain relieving bridge members 76,78,80 have non-straight paths 
between the first and the second main switch sections 12,14, and the 
non-straight paths reduce tension and compression across the bridge 
members. As shown, the bridge members 76,78,80 each have a first juncture 
j1 with the first main switch section 12 and a second juncture j2 with the 
second main switch section 14. Each bridge member 76,78,80 has, 
respectively, an overall length L1,L2,L3 between a central point c1 of the 
first juncture j1 and a central point c2 of the second juncture j2 that is 
greater than the length of an imaginary straight line S1,S2,S3 between the 
central point of the first juncture and the central point of the second 
juncture. 
The first juncture j1 of the bridge member 76 of FIG. 9 is offset from the 
second juncture j2 of the bridge member, and the bridge member has a 
serpentine path generally in the form of an "S" between the first juncture 
and the second juncture. The first juncture j1 of the bridge member 78 of 
FIG. 8 is offset from the second juncture j2 of the bridge member, and the 
bridge member has a serpentine path generally in the form of a "Z" between 
the first juncture and the second juncture. The first juncture j1 of the 
bridge member 80 of FIG. 11 is aligned with the second juncture j2 of the 
bridge member, and the bridge member has a serpentine path generally in 
the form of an omega between the first juncture and the second juncture. 
The non-straight paths of the improved strain relieving bridge members 
76,78,80 allow extra slack and leeway between the first and the second 
main switch sections 12,14 of the horn switch, thereby reducing tension 
and compression across the bridge members. The non-straight paths also 
provide a greater freedom of movement for the bridge members 76,78,80, 
thereby allowing easier bending and twisting. This reduced tension and 
compression, and greater freedom of movement, in combination, reduces the 
resulting stress on the bridge members 76,78,80 during the bending and 
twisting of horn actuation. The non-straight paths of the bridge members 
76,78,80, therefore, increase the useful life of the bridge members and 
in-turn the life of the horn switches. It should be noted that improved 
strain relieving bridge members can be provided having paths forming sharp 
angles such as a "V" for example, although paths forming curved turns are 
preferred to reduce tension. Also improved strain relieving bridge members 
can be provided having non-straight paths in the form of shapes other than 
an omega, "S" or "Z". 
Referring to FIGS. 12 through 14, an additional membrane horn switch 82 
according to the present invention is shown and includes a combined, 
improved bridge member 84. The horn switch 82 is similar to the prior art 
horn switch 10 of FIGS. 1 and 2, and parts which are the same have the 
same reference numeral. The combined, improved bridge member 84 basically 
combines two spaced-apart bridge members into superimposed bridge members. 
The membrane horn switch 82 having the combined bridge member 84 in place 
of two spaced-apart bridge members is beneficial, for example, because the 
first and the second raised ridges 210,216 of the module cover 200 (see 
FIG. 1) each need only one opening for the bridge member instead of two. 
The design of the module cover 200, therefore, is less restricted. In 
addition, an inflating airbag cushion only has to break through a single 
bridge member instead of two spaced-apart bridge members. 
The combined, improved bridge member 84 includes a bottom nonconductive 
bridge sheet 86 connecting the bottom nonconductive sheets 38,40 of the 
first and the second main switch sections 12,14. The bottom nonconductive 
bridge sheet 86 has a top surface 87 covered with a conductive coating in 
the form of two (2) spaced-apart, parallel strips 88,89 extending between 
the conductive coatings 46,48 on the bottom nonconductive sheets 38,40 of 
the first and the second main switch sections 12,14. The combined bridge 
member 84 also includes a top nonconductive bridge sheet 90 connecting the 
top nonconductive sheets 22,24 of the first and the second main switch 
sections 12,14. The top nonconductive bridge sheet 90 has a bottom surface 
91 covered with a conductive coating in the form of two (2) spaced-apart, 
parallel strips 92,93 extending between the conductive coatings 30,32 on 
the top nonconductive sheets 22,24 of the first and the second main switch 
sections 12,14. The top and the bottom nonconductive bridge sheets 86,90 
are superimposed and secured with a layer 95 of nonconductive adhesive to 
form the combined bridge member 84, and the two conductive strips 92,93 on 
the top nonconductive bridge sheet 90 are offset from the two conductive 
strips 88,89 on the bottom nonconductive bridge sheet 86. 
Because the two conductive strips 92,93 on the top nonconductive bridge 
sheet 90 are offset from the two conductive strips 88,89 on the bottom 
nonconductive bridge sheet 86, the top and the bottom nonconductive bridge 
sheets can be superimposed without the risk of the conductive strips on 
the bottom nonconductive sheet contacting the conductive strips on the top 
nonconductive sheet to inadvertently actuate the horn switch 82 prior to 
the first or the second main switch sections 12,14 being compressed. 
Referring to FIG. 14, the layer 95 of nonconductive adhesive acts as a 
nonconductive spacer between the conductive strips 88,89 on the bottom 
nonconductive bridge sheet 86 and the conductive strips 92,93 on the top 
nonconductive bridge sheet 90, to prevent contact and inhibit the 
propagation of stress cracks among the conductive strips. 
It should be noted that the combined, improved bridge member 84 could 
include, in place of the layer 95 of adhesive, two strips of adhesive 
positioned on either side of the four strips 88,89,92,93 of conductive 
coating, or five strips of adhesive positioned on either side and in 
between the four strips of conductive coating similar to the bridge member 
of FIGS. 7 and 8. Also, each of the top nonconductive bridge sheet 90 and 
the bottom nonconductive bridge sheet 86 can have more than two 
spaced-apart conductive strips. In addition, the combined improved bridge 
member 84 can be made with a non-straight path similar to the improved, 
strain relieving bridge members 76,78,80 of FIGS. 9 through 11, in order 
to reduce stress on the bridge member. 
Since other changes and modifications varied to fit particular operating 
requirements and environments will be apparent to those skilled in the 
art, the invention is not considered limited to the examples chosen for 
purposes of illustration, and includes all changes and modifications which 
do not constitute a departure from the true spirit and scope of this 
invention as claimed in the following claims and equivalents thereto.