Note: Descriptions are shown in the official language in which they were submitted.
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Li~uid-gas generator
The invention relates to a liquid-gas generator
according to the preamble of claim 1.
With passive safety devices for motor vehicles, in
which inflatable impact protection cushions protect
drivers or front seat passengers from injuries caused
by impact against the steering wheel or dashboard (also
called Air-Bag), either gas generators having a solid
propellent charge, or gas generators having condensed
gas which is under pressure (hybrid generator,
compressed-air generator), or even generators having
liquid-gas mixtures which participate in a combustion
in a partially active way, are used for the generation
of gas. The advantages of gas mixtures in comparison
with solid propellent charges when used in a generator
are sufficiently known. One problem in the case of gas
generators, or even liquid-gas generators, is that the
gases which are under pressure must be enclosed in a
container which in the case of use, i.e. operational
triggering of the generator, must be opened in a
defined manner.
A liquid-gas generator for an inflatable impact
protection cushion for protecting a motor vehicle
passenger from injuries is known from DE 42 41 221 A1.
The liquid-gas generator has a housing in which there
is accommodated a reaction container with liquid-gas.
In order to trigger combustion of the liquid-gas, a
piercing element having a transfer duct is driven into
the reaction container. The kinetic energy for the
piercing element is produced pyrotechnically by
initiating an igniter element. The ignition vapours of
the igniter element reach the inside of the reaction
container by way of the transfer duct, and there
initiate the combustion of the liquid gas. The
combustion gases which are produced in this connection
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emerge from the reaction container by way of the
transfer duct and reach a chamber in which the piercing
element is arranged. The chamber is closed from a
discharge space (through-passage) by a rupture
membrane. This rupture membrane breaks when a minimum
pressure of the combustion gases is reached and
consequently frees the way for removal of the
combustion gases from the housing by way of the
discharge space (through-passage).
A disadvantage of this is that the piercing
element, or the firing piece, has to rest directly
against the reaction container, because otherwise a
pressure can build up behind the firing piece that
prevents the reaction container from being pierced.
Apart from this there is the danger that the firing
piece will be asymmetrically loaded, something which in
turn can lead to uncertainties with the piercing. A
substantial disadvantage is, furthermore, the rupture
membrane which is required and by means of which the
chamber is constructed as a pressure space. Firstly,
these rupture membranes are extremely expensive and
secondly, when only one rupture membrane is used, a
reaction is produced by the gas which emerges, which
reaction imparts an undesired rotational moment to the
gas generator.
The underlying object of the invention is to
improve a liquid-gas generator according to the
preamble of claim 1 in such a way that the opening or
piercing of the reaction container is simplified, and
such that for the whole duration of the operation, the
generation of gas takes place in a controlled and
reproducible manner.
In order to achieve this ob;ect, in accordance
with the invention, a liquid-gas generator is proposed,
the housing of which contains a closed reaction
container for accommodating liquid-gas. Formed in the
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housing is a chamber, which abuts the reaction
container when the latter is inserted. Displaceably
arranged in the chamber there is a piercing element,
the whole length of which is driven through the wall of
the reaction container when an igniter element is
ignited and plunges completely into the reaction
container. As a result of the piercing or puncturing
of the wall of the reaction container by the piercing
element, and the further penetration of the piercing
element into the reaction container, which was
previously closed, there is consequently a connection
with the diameter of the piercing element.
A substantial advantage lies in the fact that
there is no separate pressure space having a rupture
dis~. As a result of this, a decisive price advantage
is given. Because there is no rupture disc, a
symmetrical discharge is to be achieved simply by a
comparatively lar~e number of discharge passages over
the diameter. As a result of this a reaction or an
undesired rotational moment is prevented. A further
advantage consists in the simple structure of the gas
generator, which is to be produced almost solely from
rotationally-symmetrical components.
The piercing element is advantageously a solid
body.
In a preferred embodiment in accordance with the
invention, for better piercing/puncturing of the wall
of the reaction container, the piercing element has the
shape of a projectile, i.e. a cylinder with a cone,
sphere, cylinder, etc mounted thereon.
In an advantageous embodiment, the igniter element
contains a primer capsule.
In order to trigger the liquid-gas generator, the
igniter element or the primer capsule is ignited. The
combustion gases which are produced when the igniter
element is ignited drive the piercing element through
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the wall of the reaction container. In this case,
igniter element and piercing element are connected to
each other in such a way that a clean puncturing of the
separating wall is guaranteed in each case. Because
the hot gases which follow penetrate into the reaction
container, and the liquid gas mixture flows out into
the chamber, ignition and reaction of the liquid-gas
mixture result. The combustion gases which are
produced are led off by transfer ducts which lead off
from the chamber. As a result of shape, position and
diameter of the transfer ducts, the generation of gas
can be controlled and can take place in a reproducible
manner. As a result of this, the use of expensive
rupture discs in this region can be eliminated. The
combustion gases which enter the transfer ducts emerge
from the gas generator by way of discharge passages in
the housing, and then inflate the folded impact
protection cushion.
As already mentioned, the piercing element
advantageously has the shape of a projectile in order
to guarantee a certain and defined piercing of the
separating wall. The piercing element is
advantageously connected to the igniter element or a
sleeve by way of a tear-off edge, so that only after a
defined pressure has been produced, caused by the
combustion gases of the igniter element, can the
piercing element begin to move with high energy.
Alternatively, a radial extension can be arranged
on the piercing element and/or a radial narrowing can
be arranged in the guide sleeve.
In order to achieve the energy which is required
for piercing the wall, there is advantageously arranged
between the piercing element and the igniter element a
chamber (utilisation of the combustion gases). The
chamber is advantageously filled with a charge. The
charge is advantageously a pyrotechnic propellent
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charge powder or ignition composition such as e.g.
nitrocellulose, a boron-potassium nitrate mixture or a
black-powder mixture. In accordance with the
invention, the igniter element is advantageously
provided with a cylindrical guide sleeve for guiding
the piercing element.
The piercing element advantageously consists of a
temperature stable combustible moulded part, which,
after penetrating into the reaction container, is
combusted by the high temperature which occurs during
the reaction of the gas. A further advantage is the
fact that, in the event of the piercing element flowing
back through the opening, the piercing element can no
longer block a transfer duct during combustion. The
piercing element, the tear-off edge and the sleeve are
preferably one moulded part.
The wall of the reaction container that is to be
broken down by the piercing element is advantageously a
rupture disc, which is preferably integrated in the lid
of a sealing cap of the reaction container.
Further features arise from the figures, which are
described in the following.
~Figure 1 shows in section a liquid-gas generator
in accordance with the invention,
Figure 2 shows in part section a first embodiment
of an igniter element and
Figure 3 shows in section a second embodiment of
an igniter element.
Figure 1 shows a liquid-gas generator 1 in
accordance with the invention, which liquid-gas
generator ~ubstantially comprises a head portion ~, a
base portion or adapter 9 and a cylindrical discharge
pipe 10. Arranged in the discharge pipe 10 are
discharge passages 11. Apart from this there is
arranged in the discharge pipe 10, or in the liquid-gas
generator 1, a reaction container 7 as a self-pressure-
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resistant bottle. Liquid gas, or a liquid-gas mixture,
is located in this reaction container 7.
The reaction container 7 is used as a storage
container as well as a combustion chamber for the
liquid-gas mixture. The end face of the reaction
container 7 is closed by way of a rupture disc 5. The
rupture disc 5 is in this case integrated in the lid of
a sealing cap 18. This sealing cap 18 is screwed into
the head portion 2 by way of a thread 20, in such a way
that a chamber 19 abuts the rupture disc 5. From the
chamber 19, transfer ducts 6 lead out into the spacing
between reaction container 7 and discharge pipe 10.
Arranged in the head portion 2 there is furthermore an
igniter element holder 3 having an igniter element 4.
The front point of the igniter element 4 has a piercing
element 16 having the shape of a projectile and
pro;ects with said piercing element into the chamber
19. The igniter element 4 lies on the longitudinal
axis 21 of the reaction container 7.
The reaction container 7 is advantageously made
from tempered steel. The housing is likewise
advantageously made from steel or aluminium.
Figure 3 shows a variant of the igniter element 4.
The igniter element 4 is inserted into the igniter
element holder 3. The igniter element 4 comprises a
primer capsule 12 and a chamber between piercing
element 16 and primer capsule 12, which chamber is
filled with a charge 13. The piercing element 16 is
securely connected to the igniter element 4 by moulding
over a sleeve 14 having a tear-off edge 15. In the
event of ignition, the igniter element 4 is ignited,
the gases and heated particles which are produced
ignite the charge 13. Because the piercing element 16,
which is securely connected to the igniter element
holder 3 by way of the sleeve 14 and the tear-off edge
15, cannot start to move, a build-up of pressure
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determined by the strength of the tear-off edge 15
results. After a certain defined pressure has been
reached, then a tearing off between the piercing
element 16 and the sleeve 14 takes place very quickly
at the tear-off edge 15. As a result of the guide
sleeve 17 of the igniter element holder 3, a directed
acceleration of the piercing element 16 occurs. The
piercing element is accelerated in a defined manner in
the guide sleeve 17 by the combustion-gas pressure
(principle of a bullet in a short barrel).
After the piercing element 16 has been separated
from the igniter element holder 3 or igniter element 4,
the piercing element 16 traverses the chamber 19 of the
head portion 2 and pierces the rupture disc 5, which
separates the liquid-gas mixture in the combustion
chamber 8 from the head portion 2 or chamber 19 (see
Figure 1). The liquid-gas mixture is ignited in the
combustion chamber 8 by the hot gases and hot particles
of the igniter element 4 which follow the piercing
element 16. A volume expansion takes place into the
chamber 19 of the head portion 2 via the opening in the
rupture disc 5, and consequently the inflation of the
gas sack begins via the transfer ducts 6 and the
discharge passages 11. Gas development and pressure
increase in the chamber 19 of the head portion 2 can be
controlled in a defined manner by position, diameter
and by the number of discharge ducts 6. The piercing
element 16 can consist of a temperature stable
combustible moulded part (plastics material or metal),
which has the shape of a projectile. As a result of
the high temperature which results during the reaction
of the li~uid-gas mixture, the piercing element 16
combusts after it has penetrated into the combustion
chamber 8.
Figure 2 shows an embodiment of the piercing
element 16 and the charge 13 that is somewhat different
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to Figure 3. The piercing element 16 is here not
connected to the sleeve 14 or the igniter element 4 by
way of a tear-off edge 15. Instead of this, a radial
extension 31 is arranged on the piercing element.
Alternatively, a radial narrowing 30 can also be
provided in the guide sleeve. Both measures effect, as
does the tear-off edge 15 in Figure 3, a directed
acceleration of the piercing element 16 only after a
certain pressure has been reached.
