U.S. patent application number 09/038931 was filed with the patent office on 2001-09-20 for electro-pyrotechnic initiator built around a complete printed circuit.
Invention is credited to DUVACQUIER, DANIEL, PEROTTO, CHRISTIAN.
Application Number | 20010022146 09/038931 |
Document ID | / |
Family ID | 9504513 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022146 |
Kind Code |
A1 |
DUVACQUIER, DANIEL ; et
al. |
September 20, 2001 |
ELECTRO-PYROTECHNIC INITIATOR BUILT AROUND A COMPLETE PRINTED
CIRCUIT
Abstract
The invention relates to an initiator for a pyrotechnic gas
generator intended for motor vehicle safety. The initiator (2) is
built from a circuit support (10) on which conductive strips are
printed which include electromagnetic protection and the ends of
which are joined together by a resistive element covered with a
thermosensitive charge (6). The conductive strips are connected to
an electric cable (3). The support (10) is coated in a cylindrical
overmoulded insulation (4, 5). A fragmentable cylindrical cap (8)
containing an igniter composition (9) forms, together with the
initiator (2), an igniter (1) for pyrotechnic generators intended
for motor vehicle safety.
Inventors: |
DUVACQUIER, DANIEL;
(BORDEAUX, FR) ; PEROTTO, CHRISTIAN; (BALLANCOURT,
FR) |
Correspondence
Address: |
CUSHMAN DARBY & CUSHMAN
NINTH FLOOR
1100 NEW YORK AVENUE N W
WASHINGTON
DC
200053918
|
Family ID: |
9504513 |
Appl. No.: |
09/038931 |
Filed: |
March 9, 1998 |
Current U.S.
Class: |
102/202.2 |
Current CPC
Class: |
F42B 3/188 20130101;
F42B 3/121 20130101 |
Class at
Publication: |
102/202.2 |
International
Class: |
F42B 003/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 1997 |
FR |
97 02715 |
Claims
1. Electro-pyrotechnic initiator (2) connected to an electric cable
(3) consisting of two conductive wires (13, 14) and comprising: i)
a thermosensitive charge (6) that can be initiated by a heating
resistive element (15), ii) an electric circuit connecting the said
resistive element (15) to the said conductive wires (13, 14), iii)
means of electromagnetically protecting the said electric circuit,
characterized in that the said heating resistive element (15, 64,
74), the said electric circuit and the said means of
electromagnetic protection are integrated into a circuit of
conductive strips (11, 12) which are soldered to the said
conductive wires (13, 14) and which are formed on a printed circuit
support (10, 60, 70, 80) around which the said initiator is
built.
2. Initiator according to claim 1, characterized in that the said
heating resistive element consists of a resistive strip (16).
3. Initiator according to claim 2, characterized in that the said
thermosensitive charge (6) is deposited on the said resistive strip
(16).
4. Initiator according to claim 3, characterized in that the said
means of electromagnetic protection consist of at least one
filtering coil (61) placed on the said circuit support (60).
5. Initiator according to claim 3, characterized in that the said
means of electromagnetic protection consist of at least one
filtering coil (71) printed on the said circuit support (70).
6. Initiator according to claim 3, characterized in that the said
means of electromagnetic protection consist of at least one
capacitor (17, 18) arranged on the said circuit support (10).
7. Initiator according to claim 3, characterized in that the said
electric circuit and the said means of electromagnetic protection
are covered by a layer of insulating varnish (19).
8. Initiator according to either one of claims 3 and 7,
characterized in that the said circuit support (10) is partially
coated with overmoulded insulation (4).
9. Initiator according to claim 8, characterized in that the said
thermosensitive charge (6) is protected by a fragmentable mask
(7).
10. Initiator according to claim 8, characterized in that the said
circuit support (10) is in the form of a thin parallelepipedal card
with two opposite faces.
11. Initiator according to claim 10, characterized in that a
separate circuit (87, 89) of conductive strips, each including a
heating resistive element covered by a thermosensitive charge (86,
88) and means of electromagnetic protection (91, 93; 92, 94) is
printed on each of the two flat faces of the circuit support
(80).
12. Electro-pyrotechnic igniter (1), characterized in that an
initiator according to any one of claims 1 to 11 is surrounded by a
fragmentable cap (8) containing an igniter powder (9).
13. Use of an electro-pyrotechnic initiator according to any one of
claims 1 to 11 to ignite a pyrotechnic generator of gas intended to
inflate an air bag to protect the occupant of a motor vehicle.
Description
[0001] The present invention relates to the field of pyrotechnic
initiators and deals more specifically with an electro-pyrotechnic
initiator intended for motor vehicle safety.
[0002] Electro-pyrotechnic initiators are traditionally built from
two electrically conducting pins which are held in place by
overmoulded insulation and the upper ends of which are joined
together by a heating resistive filament which is encased in an
igniter bead consisting of a primary explosive such as lead
trinitroresorcinate or lead styphnate and the lower ends of which
are connected to a source of electrical current.
[0003] Such electro-pyrotechnic initiators are widely used to form
devices for igniting pyrotechnic gas generators intended to inflate
air bags to protect the occupants of a motor vehicle. In order to
protect these initiators against parasitic electrostatic currents
and avoid untimely undesired and possibly dangerous ignition, a
ferrite core is generally placed between the pins, as described,
for example, in the Patents U.S. Pat. No. 4,722,551 and
EP-A-0,512,682. In order further to improve the ignition
reliability, the heating resistive filament is sometimes replaced
by a printed circuit comprising a resistive and heating part as
described, for example, in Patent Application FR-A-2,704,944 or in
its counterpart U.S. Pat. No. 5,544,585.
[0004] Whatever the case may be, systematically resorting to
conductive pins appreciably increases the cost price and the
complexity of manufacturing these electro-pyrotechnic initiators.
What is more, the very frequent use of ferrite cores increases the
external dimensions of the overmoulding surrounding the pins and
does nothing to help reduce the overall volume of the pyrotechnic
gas generators intended for motor vehicle safety.
[0005] Those skilled in the art are therefore still looking for
electro-pyrotechnic initiators which are at the same time reliable
in their operation, easy and economical to manufacture and small in
volume.
[0006] The object of the present invention is specifically to
provide such an initiator by dispensing with the pins and the
ferrite cores and by integrating their functions into a complete
printed circuit, contrary to all that has been done hitherto.
[0007] The invention therefore relates to an electro-pyrotechnic
initiator connected to an electric cable consisting of two
conductive wires and comprising:
[0008] i) a thermosensitive charge that can be initiated by a
heating resistive element,
[0009] ii) an electric circuit connecting the said resistive
element to the said conductive wires,
[0010] iii) means of electromagnetically protecting the said
electric circuit,
[0011] characterized in that the said heating resistive element,
the said electric circuit and the said means of electromagnetic
protection are integrated into a circuit of conductive strips which
are soldered to the said conductive wires and which are formed on a
printed circuit support around which the said initiator is
built.
[0012] The printed circuit support will normally consist of one of
the insulating substances conventionally used for making such
supports.
[0013] According to a first preferred embodiment of the invention,
the said heating resistive element itself consists of a resistive
strip formed on the printed circuit support and the thermosensitive
charge is deposited on the said resistive strip.
[0014] The means of electromagnetically protecting the initiator
against parasitic currents may consist of at least one filtering
coil placed on the said circuit support. As a preference, in this
case, the filtering coil may itself be printed on the said circuit
support and, together with the electrical circuit, constitute a
multi-layer printed circuit.
[0015] The said means of electromagnetic protection may
alternatively consist of at least one capacitor arranged on the
said circuit support.
[0016] According to a preferred embodiment of the invention, the
said electric circuit and the said means of electromagnetic
protection are covered by a layer of insulating varnish.
[0017] The circuit support, which may or may not be covered with a
layer of insulating varnish, will moreover be partially coated with
overmoulded insulation so that only that part of the circuit
support that carries the heating resistive element covered with the
thermosensitive charge is left free. When the thermosensitive
charge is not itself at least partially held in place by the said
overmoulding, it will advantageously be protected by a fragmentable
mask. A mask made of very thin metal or a mask made of plastic, for
example of transparent plastic, are suitable.
[0018] According to a second preferred embodiment of the invention,
the said circuit support is in the form of a thin parallelepipedal
card with two opposite flat faces. This second embodiment of the
invention makes it possible to build electro-pyrotechnic initiators
in which a separate circuit of conductive strips, each including a
heating resistive element covered by a thermosensitive charge and
means of electromagnetic protection is printed on each of the two
flat faces of the circuit support. It is thus possible to build an
initiator which, for a single electrical source, has two separate
igniter heads and which is particularly dependable and
reliable.
[0019] The invention also relates to an electro-pyrotechnic
igniter, characterized in that an initiator according to the
invention is surrounded by a fragmentable cap containing a granular
igniter powder.
[0020] The invention finally relates to the use of an
electro-pyrotechnic initiator according to the invention to ignite
a pyrotechnic generator of gas intended to inflate an air bag to
protect the occupant of a motor vehicle. The initiator may be used
directly to ignite the pyrotechnic charge of the generator when the
latter is in granular or pellet form, it will advantageously be
used via an igniter like the one described above when the charge is
in the form of a compact block.
[0021] The invention thus makes it possible, using small printed
circuits which are very simple and very economic to produce, to
construct initiators or igniters which are not very bulky and are
very reliable.
[0022] A preferred embodiment of the invention will be described
hereinbelow with reference to FIGS. 1 to 8.
[0023] FIG. 1 is a view in perspective, with partial cutaway, of an
igniter built from an initiator according to the invention
depicted, for the sake of clarity, without its protective mask.
[0024] FIGS. 2, 3 and 4 illustrate the successive stages in
building an initiator according to the invention starting with its
circuit support.
[0025] FIG. 5 illustrates a printed circuit in which the
electromagnetic protection is provided by capacitors.
[0026] FIG. 6 illustrates a printed circuit in which the
electromagnetic protection is provided by a conventional filtering
coil.
[0027] FIG. 7 illustrates a printed circuit in which the
electromagnetic protection is provided by a coil printed in a
multi-layer circuit.
[0028] FIG. 8 is a sectional view through an initiator comprising
two separate igniter heads, the thermosensitive charges of which
are partially held in place by the overmoulding.
[0029] FIG. 1 depicts an igniter 1 consisting of an initiator 2
connected to an electric cable 3.
[0030] Referring more specifically to FIGS. 1 and 4, it can be seen
that the initiator 2 is contained for the most part in a
cylindrical overmoulding 4 which at the same end as the cable 3 has
a base 5 of slightly larger diameter.
[0031] At its opposite end to the base 5, the initiator 2 has an
igniter head which will be described in detail a little later but
which can be seen to have a thermosensitive charge 6 based on lead
trinitroresorcinate, which is protected by a mask 7 made of
transparent plastic, not depicted in FIG. 1. A fragmentable metal
cap 8 of cylindrical shape encases the overmoulding 4, resting
against the base S. This cap is closed at its opposite end to the
base 5 and contains a pyrotechnic charge 9 which generates gas. A
mixture of powder of the boron/potassium nitrate type, and of
single-base nitrocellulose powder is ideal.
[0032] The construction of the initiator 2 will now be described in
detail with reference more particularly to FIGS. 2 to 5. The
initiator 2 is built from a printed circuit support 10 which is in
the form of a thin parallelepipedal card with two opposite flat
faces. This support 10 is built from an epoxy resin filled with
glass fibres. Printed on one of its faces are two conductive strips
11 and 12, each of which is soldered at one of its ends to the
conductive wires 13 and 14 that constitute the electric cable 3. A
heating resistive element 15 joins the free ends of the conductive
strips 11 and 12 together. This heating resistive element 15 may be
a resistive wire but will advantageously consist of a heating
resistive strip defined by a printed sub-circuit 16 as described in
Patent U.S. Pat. No. 5,544,585 or in its counterpart
FR-A-2,704,944, the description of which is included, by reference,
in this description.
[0033] The heating resistive element 15 could equally consist of a
diode or of a semiconductor bridge as described, for example, in
Patent Application FR-A-2,720,493.
[0034] Two capacitors 17 and 18 are arranged on and connected to
the circuit formed by the conductive strips 11 and 12 and by the
resistive element 15. These capacitors constitute the means of
electromagnetically protecting the circuit by preventing the
discharge of parasitic currents through the element 15.
[0035] These means of electromagnetic protection could also consist
of a filtering coil 61 arranged on and connected to a circuit
printed on a support 60 and consisting of two conductive strips 62
and 63 joined together by a resistive element 64 as depicted in
FIG. 6. An alternative embodiment of electromagnetic protection of
this kind is depicted in FIG. 7. A circuit that consists of two
conductive strips 72 and 73 joined together by a resistive element
74 is printed on a support 70. The conductive strip 72 forms a coil
71 around the support 70, thus forming a multi-layer circuit with
the strip 73.
[0036] Referring once again to FIG. 2, it can be seen that the part
of the face of the support 10 on which the strips 11 and 12 are
printed and on which the capacitors 17 and 18 rest is covered with
a layer of insulating varnish 19. This layer 19 does not cover that
end of the support 10 that carries the resistive element 15 and
that will constitute the igniter head of the initiator. Thus
prepared, the support 10 is partially surrounded by a cylindrical
overmoulding 4 of adhesive resin based on a hot-melt polyamide.
[0037] This overmoulding 4 leaves free that surface of the support
10 which carries the resistive element 15, as depicted in FIG. 3.
This resistive element 15, together with the sub-circuit 16 used to
form it are covered with a thermosensitive charge 6, for example
based on lead trinitroresorcinate. The charge 6 is protected by a
mask 7 made of transparent plastic. The initiator 2 is thus
finished and can be used to form the igniter 1 described
earlier.
[0038] FIG. 8 depicts an initiator 82 which constitutes an
alternative form of the initiator 2 just described. The initiator
82 is built around a circuit support 80 in the form of a thin
parallelepipedal card. The essential difference between this
initiator 82 and the initiator 2 described above lies in the fact
that each of the two faces of the support 80 carries a complete
printed circuit 87 or 89 connected to the same cable 83 bringing in
electrical current. The support 80 is partially coated in a
cylindrical overmoulding 84 which has a widened base 85 and which
partially holds in place the thermosensitive charges 86 and 88 that
constitute the igniter heads. In this embodiment, the initiator
does not require a protective mask. Should current arrive via the
cable 83, the two thermosensitive charges are fired simultaneously
and the initiator 82 is thus highly effective in normal operation
and extremely safe, both with respect to parasitic currents--thanks
to its built-in electromagnetic protection 91, 93 or 92, 94, and
with respect to possible misfires--thanks to the fact that the
heads are duplicated.
* * * * *