GB2323568A - Reducing airbag forward speed - Google Patents

Abstract

A gas reservoir 6 is placed between a gas generator and a manifold supplying an airbag 17. The reservoir and the manifold are connected by two flow passages, one of relatively large area, which is initially sealed 10', and another of relatively small area. In operation, the generated gas flows into the reservoir and through the small passage to begin the relatively slow inflation of the airbag and opening of the cover doors. More gas is generated than can pass through the small passage and so the pressure in the reservoir rises until a predetermined pressure is reached, when the sealing disc 10' ruptures, permitting full inflation of the airbag. Both passages may initially be sealed and the reservoir lightly pressurised with argon gas to reduce the temperature of the generated gas.

Description

DESCRIPTION OF INVENTION "IMPROVEMENTS IN OR RELATING TO AN AIR-BAG ARRANGEMENT" THE PRESENT INVENTION relates to an air-bag arrangement, and more particularly relates to an air-bag arrangement adapted for use in a motor vehicle.

It has been proposed previously to provide an airbag arrangement in a motor vehicle, the arrangement comprising an air-bag and means adapted to inflate the airbag in the event that an accident should arise, the inflated air-bag being located in a position to cushion or protect an occupant of the vehicle.

Typically, such an air-bag may be mounted in the steering wheel of the vehicle or in the dashboard of the vehicle in front of an occupant of the vehicle, within a housing that is initially closed by a pair of elements adapted to open to form doors.

The air-bag must be inflated within a very short period of time, and consequently, it has been proposed to utilise, with an air-bag, a gas generator which rapidly generates a substantial quantity of gas. The air-bag is retained initially in a folded condition, and, on activation of the air-bag, a substantial quantity of gas from the gas generator is introduced to the interior of the bag. A high pressure builds up in the bag before the elements are forced to pen to permit the bag to inflate on the exterior of the housing. Consequently, as inflation of the bag proceeds, the part of the bag which is located closest to the occupant may be given a very high acceleration. This may be enhanced by the fact that a large quantity of gas is being forced into a very small space which initially remains within the folded air-bag.

Since the portion of the bag closest to the occupant is given a substantial velocity, that portion of the bag will move towards the occupant, and may strike the occupant.

The risk of the bag striking the occupant is increased if the occupant of the vehicle is leaning forwardly, for some reason, when the air-bag is activated.

It has been proposed to try and overcome these problems by providing an air-bag with internal straps, with the straps extending from the portion of the air-bag which is most likely to strike the occupant to an anchoring point which may be adjacent the gas generator. The length of the straps is selected so that the straps will prevent the part of the air-bag which is located closest to the occupant of the vehicle actually striking the occupant of the vehicle.

Of course, if such an arrangement is to protect an occupant of the vehicle when the occupant is sitting in a forward position, the strap must be very short.

Various proposals have been made in an attempt to provide an air-bag which initially deploys in a sideways direction, and subsequently deploys towards the occupant of the vehicle. These prior attempts have included different folding arrangements and the provision of various straps.

It has also been proposed to provide a plurality of gas generators which are deployed sequentially. Such arrangements are expensive and complex.

The present invention seeks to provide an improved air-bag arrangement.

According to this invention there is provided an air-bag arrangement for use in a motor vehicle, the air-bag arrangement comprising a gas generator, means to activate the gas generator in response to an accident occurring, means to direct gas from the gas generator to a gas reservoir space, an air-bag, a relatively small crosssection flow passage to permit gas to pass from the gas reservoir space to the interior of the air-bag to commence inflation of the air-bag and a relatively large crosssection flow passage from the gas reservoir space to the interior of the air-bag, means being provided which initially seal said relatively large cross-section flow passage and which are adapted to open the relatively large cross-section passage when the air-bag has been partially inflated.

Preferably the means which seal the relatively large cross-section flow passage comprise a sealing element, the element being adapted to rupture when a predetermined pressure is present within the gas reservoir space.

Conveniently means are provided which initially seal the relatively small cross-section flow passage, the means which seal the relatively small cross-section flow passage being adapted to open said passage on activation of the gas generator.

Advantageously the gas reservoir space initially contains gas under pressure. The gas may be an inert gas or may be Argon.

Preferably the air-bag is initially located in a folded condition within a housing, the housing being provided with means defining doors, the doors initially being closed, but being adapted to open on inflation of the air-bag.

Conveniently the gas generator is a pyrotechnic gas generator, filter means being provided in the gas flow path between the gas generator and the interior of the air-bag.

The air-bag arrangement may be mounted in a motor vehicle in such a position that the air-bag, when inflated, is located in front of an occupant of the vehicle.

According to another aspect of this invention there is provided a method of inflating an air-bag in a vehicle, comprising the steps of activating a gas generator in response to an accident occurring, passing gas from the gas generator to a gas reservoir space, initially passing gas from the gas reservoir space to the interior of an air-bag through a relatively small cross-section flow passage to partially inflate the air-bag and subsequently passing gas from the gas reservoir space to the interior of the air-bag through a relatively large cross-section flow passage to complete the inflation of the air-bag.

Conveniently the relatively large diameter flow passage is initially sealed with a rupturable sealing element, the method comprising the step of generating sufficient pressure within the gas reservoir space to rupture said sealing element.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a diagrammatic sectional view of an air-bag arrangement in accordance with the invention in an initial condition, FIGURE 2 is a view corresponding to Figure 1 illustrating the air-bag shortly after an accident has been sensed, and FIGURE 3 is a view corresponding to Figure 2 illustrating the air-bag arrangement at a later instant in time.

Referring initially to the accompanying drawings, an air-bag arrangement 1 in accordance with the present invention comprises a gas generator 2 which is a pyrotechnic gas generator. The gas generator 2 is associated with a squib 3 adapted to receive a signal, along lead 4, from a sensor which is responsive to an accident situation. The sensor may comprise, for example, a decelerometer or an impact sensor.

The pyrotechnic gas generator 2 has the gas outlet thereof connected to a vessel 5 which is adapted to withstand substantial pressure, the vessel having an open interior defining a gas reservoir space 6.

Two apertures 7,8 are formed in the wall of the vessel 5, defining flow passages communicating with a manifold 9. The first aperture 7 is of relatively small cross-sectional area and the second aperture 8 is of a substantially larger cross-sectional area. The aperture 7 is open, but may in an alternative embodiment be provided with sealing means. The aperture 8 is initially closed, for example by means of a sealing disc 10'.

The manifold 9 is connected, by means of a connecting passage 10, to an air-bag 11 formed of an appropriate fabric. The air-bag, in the initial condition as illustrated in Figure 1 is folded and is accommodated within a housing 12. The housing 12 is provided with a cover 13 which may form part of the dashboard of a vehicle, or which may form part of the steering wheel assembly of the vehicle, the cover 13 being provided with a line of mechanical weakness 14 so that the cover effectively comprises two doors 15,16.

In the event that an accident should arise, a signal from the sensor activates the squib 3 which in turn activates the pyrotechnic gas generator 2. High temperature gas from the gas generator 2 is introduced into the gas reservoir space 6 within the vessel 5. Part of the gas flows through the small aperture 7, and through the manifold 9 to commence inflation of the air-bag 11.

Since gas from the gas generator is only flowing into the interior of the air-bag through the relatively small aperture 7, the air-bag is only inflated relatively slowly. As the air-bag beings to inflate, the upper part of the air-bag presses against the under-surface of the doors 15,16, causing the cover 13 to break along the line of mechanical weakness 14, thus permitting the doors 15,16 to open and allowing the air-bag to emerge from the housing 12. The relatively slow flow of gas commences the inflation of the air-bag on the exterior of the housing after the doors have opened. The pressure within the gas reservoir space 6 will be increasing, during this period of time, since the gas generator will produce more gas than it can pass through the small hole. A gas generator has optimum operating conditions when operating against a back pressure and consequently, as the pressure within the space 6 rises, the gas generator 2 will operate with an increasing efficiency. When a predetermined pressure within the space 6 is reached, which happens a few moments after actuation of the gas generator 2, when the air-bag 11 has been partly inflated, the sealing disc 10' will rupture, thus permitting gas to flow into the manifold 9 through the relatively large aperture 8 as well as through the relatively small aperture 7. The air-bag will then deploy fully without any substantial resistance, since a substantial part of the air-bag will have emerged through the open doors 15,16 before the sealing disc 10' ruptures.

As a consequence of this mode of deployment, the part of the air-bag 17 which is located closest to the occupant of the vehicle is not given a substantial acceleration towards the occupant of the vehicle.

If reference is now made to Figure 3 of the accompanying drawings, it can be seen that this drawing illustrates the situation following rupture of the disc 10'. Gas is thus flowing from the gas reservoir space 6 into the manifold 9 through both the small aperture 7 and the through the large aperture 8. This gives a substantially increased rate of flow of gas, with this flow of gas being directed into the already partly inflated airbag. Inflation of the air-bag thus continues. Since the relatively large flow of gas is not introduced into the air-bag until after the air-bag has been partly inflated, the effect of the increased flow of gas into the air-bag is not to accelerate the part 17 of the bag that is closest to the occupant in a direction towards the occupant, but instead, leads to a more general inflation of the bag, with all of the fabric that forms the air-bag being directed outwardly away from the notional centre of the bag in a substantially even manner.

In a typical air-bag arrangement as described above, the pressure within the gas reservoir space 6 may be as high as 100 bar, and the disc 10' may rupture approximately 20 milliseconds after initial activation of the gas generator.

There may be a filter between the gas generator 2 and the interior of the air-bag, with the filter either being located between the gas generator 2 and the gas reservoir space 6, or between the gas reservoir space 6 and the interior of the gas bag, in order to minimise the risk of any particles generated by the gas generator actually entering the air-bag. Means may be provided to reduce the temperature of gas leaving the chamber before the gas enters the air-bag, to minimise the risk of the gas damaging the fabric of the air-bag during the initial stages of deployment of the air-bag. Such means may comprise a lightly compressed inert gas contained initially within the gas reservoir space 6. Thus, in such an embodiment the aperture 7 will be sealed by means of a sealing disc, corresponding to the sealing disc 10', but adapted to rupture at a much lower pressure. The gas reservoir space 6 may thus be filled at a relatively low pressure with a compressed inert gas, such as Argon. In the event that the gas generator is activated, gas from the gas generator will be directed into the gas reservoir space 6 and will cause the pressure to rise initially rupturing the sealing disc that initially seals the relatively small aperture 7, permitting the commencement of inflation of the air-bag, and subsequently rupturing the disc 10 sealing the relatively large aperture 8.

It is to be appreciated that the vessel 5 may be manufactured utilising relatively cheap material, since it only has to withstand a high pressure for a very short period of time, and no high performance seals are required, as some leakage will be acceptable.

It is to be appreciated that embodiments of the invention may have the advantage that when manufacturing a number of different sized air-bags for different motor vehicles, a single "standard" gas generator may be utilised and, if necessary, the performance characteristics of the air-bag may be controlled by selecting the size of the aperture 7 and the size of the aperture 8.

Whilst in the described embodiment the larger aperture 8 in the wall of the vessel 5 is provided with a sealing disc which ruptures when predetermined pressure is present within the gas reservoir space, other types of arrangement to open the aperture 8 may be contemplated.

The aperture 8 may be opened by means which move a closure, initially sealing the aperture, a predetermined time after activation of the gas generator. The closure may be moved so that the aperture 8 is opened gradually, thus gradually increasing the flow rate of gas into the manifold.

It is believed that an arrangement as described may substantially minimise the risk of an air-bag impacting with an occupant of a vehicle in such a way as to injure the occupant of the vehicle.

Claims (13)

CLAIMS:

1. An air-bag arrangement for use in a motor vehicle, the air-bag arrangement comprising a gas generator, means to activate the gas generator in response to an accident occurring, means to direct gas from the gas generator to a gas reservoir space, an air-bag, a relatively small crosssection flow passage to permit gas to pass from the gas reservoir space to the interior of the air-bag to commence inflation of the air-bag and a relatively large crosssection flow passage from the gas reservoir space to the interior of the air-bag, means being provided which initially seal said relatively large cross-section flow passage and which are adapted to open the relatively large cross-section passage when the air-bag has been partially inflated.

2. An arrangement according to Claim 1 wherein the means which seal the relatively large cross-section flow passage comprise a sealing element, the element being adapted to rupture when a predetermined pressure is present within the gas reservoir space.

3. An arrangement according to Claim 1 or Claim 2 wherein means are provided which initially seal the relatively small cross-section flow passage, the means which seal the relatively small cross-section flow passage being adapted to open said passage on activation of the gas generator.

4. An arrangement according to Claim 3 wherein the gas reservoir space initially contains gas under pressure.

5. An arrangement according to Claim 4 wherein the gas is an inert gas.

6. An arrangement according to Claim 5 wherein the gas is Argon.

7. An arrangement according to any one of the preceding Claims wherein the air-bag is initially located in a folded condition within a housing, the housing being provided with means defining doors, the doors initially being closed, but being adapted to open on inflation of the air-bag.

8. An air-bag arrangement according to any one of the preceding Claims wherein the gas generator is a pyrotechnic gas generator, filter means being provided in the gas flow path between the gas generator and the interior of the airbag.

9. An arrangement according to any one of the preceding Claims mounted in a motor vehicle in such a position that the air-bag, when inflated, is located in front of an occupant of the vehicle.

10. A method of inflating an air-bag in a vehicle, comprising the steps of activating a gas generator in response to an accident occurring, passing gas from the gas generator to a gas reservoir space, initially passing gas from the gas reservoir space to the interior of an air-bag through a relatively small cross-section flow passage to partially inflate the air-bag and subsequently passing gas from the gas reservoir space to the interior of the air-bag through a relatively large cross-section flow passage to complete the inflation of the air-bag.

11. A method according to Claim 10 wherein the relatively large diameter flow passage is initially sealed with a rupturable sealing element, the method comprising the step of generating sufficient pressure within the gas reservoir space to rupture said sealing element.

12. An air-bag arrangement substantially as herein described with reference to and as shown in the accompanying drawings.

13. Any novel feature or combination of features disclosed herein.