GB2275100A - Gas supply device for an air-bag - Google Patents

Abstract

A gas supply device for supplying gas to an air-bag comprises a bottle (1) containing compressed gas. The bottle is provided with a series valve mechanism comprising tubular members (22, 23) which operates to open gradually a flow passage for the compressed gas. The valve part 22 comprises a tubular portion (24) terminating with a lower inwardly turned lip (28) directed towards a tubular member (8). The air passage is defined between the free end of the lip (28) and the exterior of the tubular member (8). Various grooves or depressions (29) are provided in the outer surface of the tubular member (8) so that the flow passage area for gas increases gradually as the valve is opened. The valve may be actuated by a pyrotechnic charge or electro-magnetic arrangement. <IMAGE>

Description

DESCRIPTION OF INVENTION "IMPROVEMENTS IN OR RELATING TO A GAS SUPPLY DEVICE FOR AN AIR-BAG" THE PRESENT INVENTION relates to a gas supply device for an air-bag.

It has been proposed to provide one or more airbags in a motor vehicle, each air-bag being provided with a gas supply adapted to be activated in the event that an accident should occur, the gas inflating the bag to form a cushion to protect the driver of the vehicle or an occupant of the vehicle.

It has been proposed before, see DE 4002662A, to use compressed air initially contained in a bottle to inflate an air-bag. The bottle is opened by igniting a pyrotechnic charge which serves to separate, from the bottle, a lid which is initially formed integrally with the rest of the bottle, there being a relatively thin break line between the lid and the bottle. An arrangement of this type does not have any problems relating to the initial sealing of the bottle, but a lot of energy is expended in removing the lid from the bottle.

It has also been proposed to use compressed air contained in a bottle which is sealed by a locking element pressed against an outlet port for the bottle. DE 2121389 discloses an arrangement of this type. However, the closure element must be pressed very firmly against the outlet port to ensure a totally air-tight seal, and a lot of energy is required to remove the locking element from the sealed position.

One disadvantage in using a system in which compressed air is released from a bottle is that when compressed air is released from a bottle or other receptacle which contains the compressed air, the air tends to cool. It is a well-known law of physics that the volume of a fixed quantity of a gas, such as air, is substantially proportional to its temperature. Thus the cool air does not efficiently inflate the air-bag.

It has also been proposed to utilise a pyrotechnic source for gas to inflate an air-bag. Such a source may also provide problems in that gas from a pyrotechnic source is frequently extremely hot and can thus damage the interior of the air-bag unless special precautions are taken. Also, many of the gases generated by a pyrotechnic source may be toxic or poisonous, especially if present in a significant concentration.

Although, as explained above, the use of a pyrotechnic source is associated with problems, it is to be understood that problems are also associated with the use of compressed air initially contained in a bottle or other receptacle to inflate an air-bag. Typically the pressure of such compressed air can be 400 bar (=40 MPa). When a compressed air-bottle of this type is opened, there is a very high initial flow, that flow itself being at high pressure. This leads to a very high "volume-flow". As, at least initially, the volume of the bag is very small, the part of the bag that is actually inflated by this flow of air, travels at a very high speed. Consequently, a dangerously high momentum is imparted to the bag and to the gas associated with the bag.The part of the bag that has this momentum is the part of the bag that is closest to the person that it is desired to protect, and in some instances, the part of the bag having the high momentum can actually hit or impinge upon the person to be protected by the bag, which can cause unnecessary injuries. It is to be appreciated that as the volume of the bag increases, the pressure within the compressed air-bottle falls, which means that there is then a much lower volume-flow, and since this volume-flow is being introduced into an already considerable volume, the gas-bag only inflates at a relatively slow rate during the final stages of its inflation.

It is most desirable to have an almost opposite characteristic to that described above. The ideal situation would involve a relatively small initial flow of gas, thus causing the bag to begin inflation in a slow and gradual manner, without any part of the bag having a high speed, with the flow-rate increasing when the interior of the bag defines a significant volume, so that the air-bag is fully inflated within an acceptable period of time. It is presently felt that the maximum acceptable period of time for the inflation of an air-bag is 60 milliseconds.

Whilst a pyrotechnic or gas generator provides an almost constant flow of gas over a period of time, thus being a little closer to the desirable characteristic described above, it is to be appreciated that even a pyrotechnical gas generator (which is associated with various problems described above) is not ideal.

The present invention seeks to provide an improved gas supply device for an air-bag.

According to this invention there is provided a gas supply device for supplying gas to an air-bag, the gas supply device comprising a source of compressed gas and a valve mechanism operable to permit the compressed gas to emerge from the source to inflate an air-bag, the valve mechanism being such that, in operation, the flow passage area for gas escaping from the source of gas is substantially gradually opened in a controlled manner.

Preferably the period of time necessary to fully open the valve mechanism has a duration of at least 10 milliseconds, and is conveniently at least approximately 30 milliseconds.

Conveniently the mechanism comprises two valves in series, the first valve being gas-tight and being openable to initiate the discharge of gas from the gas supply device, the second valve being adapted to control and adjust the rate of flow of gas. In one embodiment the first valve is opened by actuation of a pyrotechnic charge.

Alternatively the first valve is opened by means of an electro-magnetic arrangement.

Advantageously the first valve comprises a sealing means adapted to seal a bottle containing the compressed gas, the sealing means being provided with one or more locking elements each adapted to engage an abutment to retain the sealing means in the sealing position, there being a further locking element, adjacent said at least one locking element, to retain the at least one locking element in position in engagement with the abutment, means being provided to move the further locking element when the device is operated, thus enabling the said one or more locking elements to become disengaged from the abutment to release the sealing means to open the first valve.

Conveniently the valve mechanism comprises a movable valve member, the valve member being movable in response to a change in pressure in at least a region within a bottle or receptacle containing compressed gas to be supplied by the gas supply device. Preferably said movable valve member comprises the second valve.

Advantageously the bottle or receptacle containing compressed gas defines at least two regions separated by a partition wall, the partition wall being movable in response to a pressure differential between the two regions, the valve member moving in response to movement of the partition wall. Conveniently the partition wall is formed integrally with the movable valve member.

Preferably the bottle or receptacle containing compressed gas defines at least two regions separated by a partition wall, the valve mechanism being such that gas from one of the regions is dispensed before gas from theother region is dispensed. Advantageously the cross-section of the flow area of the valve when fully opened is approximately twenty times larger than the cross-section of the flow area of the valve when the valve mechanism is initially opened.

Preferably the cross-sectional area of the flow opening gradually increases with the movement of the movable valve member. Conveniently the movable valve member moves past a series of grooves, enabling the grooves to become part of the flow path, thus increasing the cross-sectional area of the flow path. Preferably the first valve comprises a sealing ring initially retained in position engaging a seat, the valve being opened by removing the sealing ring from the seat.In one embodiment the movable valve member comprises a tubular portion surrounding a tube, means being provided to constrain gas from the source of compressed gas to flow between the tubular portion and the tube, the tubular portion terminating with an inturned lip defining, as the second valve, a leaky valve, the tubular portion being received slidingly within a sealing ring and being adapted to be removed from the sealing ring to fully open the second valve.

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 sectional view illustrating one embodiment of a gas supply arrangement for use with an airbag, FIGURE 1A is part of Figure 1 on an enlarged scale, FIGURE 2 is a view corresponding to Figure 1 illustrating the arrangement shortly after the arrangement has been activated, and FIGURE 3 is a view corresponding to Figure 2 illustrating the arrangement after a further brief period of time.

A gas supply for an air-bag in accordance with the invention includes not only a source of compressed gas, such as compressed air, but also a pyrotechnic device.

Referring now to the drawing, a bottle 1 adapted to contain compressed gas, such as compressed air, comprises a generally cylindrical body having inwardly turned end portions which define two opposed re-entrant openings 2,3 leading to the interior of the bottle 1. Each of the reentrant openings 2,3 defines, on its outer surface, a seat 4,5 adapted to engage the outer periphery of a respective sealing ring 6,7.

A tube 8 is provided which extends through the bottle 1. The tube 8 has an enlarged end 9, the junction between the enlarged end 9 and the main part of the tube 8 defining a seat 10 which engages the sealing ring 7 provided at the lower re-entrant opening 3 in the illustrated orientation of the bottle 1. It is to be understood that the tube 8 is inserted upwardly into the bottle 1 through the lower re-entrant opening 3.

The sealing rings 6 and 7 serve to seal the bottle to retain compressed air in the bottle, but as will be described in greater detail, the sealing rings 6 and 7 operate as valves to permit compressed air to escape from the bottle under certain circumstances.

Towards the upper end of the tube 8, the inner wall of the tube 8 is deformed inwardly to form an annular seat 11.

Partially received within the upper end of the tube 8 is a plug 12. The plug 12 presents a radially outwardly extending flange 13 which engages the end of the tube 8, and also extends radially outwardly beyond the end of the tube 8 to engage the sealing ring 6. The flange carries resilient fingers 14 which extend axially of the tube 8 along the interior of the tube, the fingers 14 carrying enlarged heads 15 which engage the annular seat or abutment 11 with an inclined or chamfered angle of contact.

With the enlarged heads 15 of the fingers 14 engaging the seat 11 the radially outwardly directed flange 13 of the plug 12 firmly engages the sealing ring 6, which in turn engages the seat 4, and thus the bottle 1 is substantially air-tight.

A piston 16 is provided which is slidably mounted within the tube 8. The piston 16 has a head 17 which is a loose non-sealing fit within the tube 8. The head 17 is connected, by a relatively narrow shank 18, to a rod 19 which has an outer diameter substantially equal to the spacing between the fingers 14. The rod 19 is located between the finger 14 and thus serves to retain the enlarged ends 15 in engagement with the seat 11. The piston may be retained in this initial position by some easily frangible means, or by friction between the rod 19 and the flanges 14. It will be appreciated that the presence of the rod 19 acts as a secondary locking element which locks the enlarged ends 15 of the fingers 14, which comprises primary locking elements, in position engaging the seat 11 so that the entire assembly is locked in position, maintaining the bottle 1 in a sealed condition.

At the lower end of the tube 8 a pyrotechnic charge 20 is provided which is illustrated as being associated with an electrical ignition arrangement 21.

Contained within the tube 8, between the pyrotechnic charge 20 and the head 17 of the piston 16 is a second pyrotechnic charge 21.

Two substantially tubular valve members 22,23 are provided within the bottle 1, the members being mirrorimages of each other. The valve member 22 only will thus be described in detail.

The valve member 22 comprises a substantially cylindrical portion 24 surrounding part of the tube 8. The upper end of the tubular portion 24 extends substantially radially outwardly thus defining a bell 25, the outer diameter of the bell being substantially equal to the inner diameter of the bottle 1. The bell 25 effectively forms a partition extending across the interior of the bottle 1.

The lower end of the tubular portion 24 is slidingly and sealingly received within an axially extending sealing ring 26 extending from a seat 27 provided on the re-entrant portion of the bottle 1 forming the lower re-entrant opening 3.

At its lower end, the tubular portion 24 of the valve member 22 is provided with an inwardly turned lip 28 which is thus directed inwardly towards and terminates adjacent the outer part of the tube 8. The lip 28 substantially seals the annular passage between the tube 8 and the re-entrant opening 3 as extended inwardly by the sealing ring 26, and thus acts as a valve as will be described hereinafter.

In the region of the tube 8 which is effectively surrounded by the sealing ring 26 a plurality of axially extending grooves or depressions 29 are provided in the outer surface of the tube 8.

As mentioned above, the tubular valve member 23 is a mirror-image of the valve member 22, and the upper end of the main tubular portion 30 of this valve member is received slidably within a sealing ring 31 which corresponds with the sealing ring 26, and the upper end is provided with an inturned lip 32 corresponding to the lip 28. The grooves corresponding to the grooves 29 may be provided in the tube 8 in the region of the sealing ring 31.

It is to be appreciated that in order to introduce the valve members 22 and 23 into the bottle 1, the bottle 1 may be made of two parts, which are subsequently joined together.

When the gas supply arrangement has been assembled, as illustrated in Figure 1, the gas bottle 1 may be filled with compressed gas, such as compressed air, by means of appropriate inlet valves provided in the gas bottle 1 (not shown). The gas cannot escape from the gas bottle, since the inlet valves are provided with non-return valves of an appropriate design and the gas cannot escape through the seals formed by the sealing rings 6 and 7.

The entire gas supply arrangement as illustrated in Figure 1 will be inserted within air-bag adapted to be inflated in the event that an accident arises.

When an accident does occur, and is sensed by the appropriate sensors, the pyrotechnic charge 20 is ignited by the electrical ignition arrangement 21. The charge 20 swiftly produces a large quantity of gas. This gas initially serves to move the second pyrotechnic charge 21 axially along the tube 8 and also causes a significant increase of pressure in the region in front of the head 17 of the piston 16. Even though some gas flows past the piston because of its loose non-sealing fit, sufficient pressure is applied to the head 17 of the piston 16 to cause the piston to move axially of the tube 8, in an upward sense if the gas bottle is in the orientation shown in Figure 1.

As the piston moves upwardly, so the rod 19 is moved upwardly, then extending beyond the end of the plug 12, the relatively narrow shank 18 then being located adjacent the fingers 14. When the relatively narrow shank 18 is in this position, the force applied to the flange 13 on the plug through the seal 6 by the compressed gas within the bottle 1 applies a force tending to move the plug 12 upwardly. Due to the chamfered angle of contact between the seat 11 and the enlarged end 15 of each of the resilient fingers 14, the enlarged end of each resilient finger 14 moves inwardly, thus enabling the plug 12 to be moved upwardly, axially of the tube 8. Once the plug has moved in this way, the sealing ring 6 becomes totally disengaged from the seat 4, since the sealing ring 6 is no longer retained in position by the flange 13. The valve defined by the sealing ring 6 is thus opened.Compressed gas from the bottle 1 can thus begin to escape through the opening 2.

The only path for gas escaping from the bottle through the opening 2 is between the tubular portion 30 of the valve member 23 and the tube 8. Thus the gas must pass the valve defined by the inturned lip 32 provided at the upper end of the tubular member 30 which valve is effectively in series, with the valve constituted by the ring 6. Because the inturned lip 32 is spaced from the exterior of the tube 8 the valve is a "leaky" valve, permitting a predetermined controlled flow of compressed gas. The rate of flow is relatively small.

It is to be understood that once the flange 13 no longer engages the sealing ring 6 and the end of the tube 8, pressure applied to the sealing ring 7 by compressed gas present within the bottle 1 tends to move the sealing ring 7 and the whole tube 8 axially downwardly, when the bottle is in the orientation illustrated in Figure 1. Thus the seal defined by the sealing ring 7 is broken, or in other words the valve constituted by the sealing ring 7 is opened and gas may also begin to escape through the lower reentrant opening 3. This gas escapes by passing the inturned lip 28 provided at the lower end of the tubular portion 24, this lip forming another "leaky" valve.

The small flow of gas will inflate an associated air-bag slowly, as is desired.

However, all the gas that is escaping from the bottle is effectively drawn from the region 33 located between the bell 25 of the valve member 24 and the opposed corresponding bell of the valve member 23. The gas passes between the tubular portions 24,30 and the tube 8 to escape through the leaky valves. As compressed gas is withdrawn from the region 33, the pressure in this region falls, and a pressure differential is established across the partition defined by the bell of the valve member 23. The higher pressure gas in the region 34, that is to say the region between the bell of the valve member 23 and the re-entrant opening 2 tends to apply force to the partition defined by the bell of the valve member 23, pushing the valve member 23 downwardly.As the valve member 23 is moved downwardly, so the inturned lip 32 provided at the upper end of the tubular portion 30 of the valve member 23 becomes aligned with the grooves corresponding to the grooves 29 formed in the tube 8. This increases the cross-sectional area available for the flow of gas, thus gradually increasing the rate of flow of the gas.

Due to the high pressure of gas within the region 35 with the bottle, located between the partition defined by the bell 25 and the lower re-entrant opening 3, the valve member 24 moves upwardly, in the illustrated orientation. The inturned lip 28 thus moves past the recesses 29, increasing the cross-sectional area available for the flow of gas. Thus, again, the rate of flow of gas through the lower re-entrant opening 3 is initially restricted by the passage available between the free end of the inturned lip 28 and the exterior of the tube 8, and then increases due to the presence of the recesses 29 adjacent the lip 28 as both the tube 8 moves downwardly and the valve member 24 moves upwardly.

As the valve members 22,23 continue to move towards each other, as gas is withdrawn from the region 33, the parts of the valve members 22,23 contained within the sealing rings 26,31, become withdrawn from those sealing rings. Consequently, an air outlet passage is then defined which is substantially larger than the initial air outlet passage defined between the ends of the inturned lips 28,32 and the exterior of the tube 8. This air passage allows gas initially in the regions 34 and 35 to be dispensed. It is preferred that the cross-sectional area of the passage then defined is approximately twenty times the crosssectional area of the initial air passage defined between the ends of the inturned lips and the exterior of the tube 8.The compressed gas contained within the regions 34 and 35 may thus escape from the bottle through the enlarged outlet openings, providing a higher flow rate.

Figure 2 illustrates the position shortly after activation of the pyrotechnic charge 20. That pyrotechnic charge is no longer visible since it has ignited, and it can be seen that the tube 8 is beginning to move downwardly. Figure 3 illustrates the position shortly thereafter, when the valve members 22 and 23 have moved to their final positions, with the inturned lips 28 and 31 being totally withdrawn from the axially extending sealing rings 26 and 31.

It can be seen that, with reference to Figure 3, the second pyrotechnic charge 21 is still in position within the tube 8. This is a slow-igniting pyrotechnic charge, and ignites when the bottle is in the fully opened position as illustrated in Figure 3. Warm gas from the first pyrotechnic charge 20 and further warm gas from the second pyrotechnic charge 21 flow past the piston 16 to emerge through the lower end 3 of the bottle in the orientation illustrated, the warm gas mixing with the decompressed compressed gas initially present within the bottle 1. The temperature of compressed gas falls as the gas decompresses. Thus the decompressed compressed gas may have a relatively low temperature. This decompressed compressed gas is mixed with the warm gas from the pyrotechnic charge, thus providing a mixture of gas which has an appropriate moderate temperature.This ensures that the air-bag is inflated with optimum efficiency, whilst not effecting any damage to the interior of the air-bag. Also the gas from the pyrotechnic charges, which may be toxic or poisonous if in a concentrated form, is mixed with the compressed gas, which is most conveniently compressed air, thus diluting the gas from the pyrotechnic charges.

In a modified embodiment of the invention, instead of utilising a pyrotechnic charge to move the piston 17 associated with the rod 19, the rod 19 may be moved by electrical means, such as an electro-magnet. Such an embodiment still provides a simple and reliable method of sealing a bottle of compressed gas, but does not provide the advantage of warming the compressed gas, when it has expanded, with gas from a pyrotechnic charge.

It is to be appreciated that the second pyrotechnic charge 21 must be considered also to be an optional feature of the invention.

It is to be understood that the duration of the procedure described above, from the initiation of the first pyrotechnic charge 20, to the time when the valve members are moved such a distance that the inwardly turned lips 28 and 33 are withdrawn from the sealing rings 26 and 31 has a duration of at least 10 milliseconds, but preferably has a duration of at least 30 milliseconds.

Claims (20)

CLAIMS:

1. A gas supply device for supplying gas to an airbag, the gas supply device comprising a source of compressed gas and a valve mechanism operable to permit the compressed gas to emerge from the source to inflate an airbag, the valve mechanism being such that, in operation, the flow passage area for gas escaping from the source of gas is substantially gradually opened in a controlled manner.

2. A gas supply device according to Claim 1 wherein, in operation, the period of time necessary to fully open the valve mechanism has a duration of at least 10 milliseconds.

3. A gas supply device according to Claim 2 wherein, in operation, the period of time necessary to open the valve fully has a duration of at least approximately 30 milliseconds.

4. A valve mechanism according to any one of the preceding Claims wherein the mechanism comprises two valves in series, the first valve being gas-tight and being openable to initiate the discharge of gas from the gas supply device, the second valve being adapted to control and adjust the rate of flow of gas.

5. A gas supply device according to Claim 4 wherein the first valve is opened by actuation of a pyrotechnic charge.

6. A gas supply device according to Claim 4 wherein the first valve is opened by means of an electro-magnetic arrangement.

7. A gas supply device according to any one of Claims 4 to 6 wherein the first valve comprises a sealing means adapted to seal a bottle containing the compressed gas, the sealing means being provided with one or more locking elements each adapted to engage an abutment to retain the sealing means in the sealing position, there being a further locking element, adjacent said at least one locking element, to retain the at least one locking element in position in engagement with the abutment, means being provided to move the further locking element when the device is operated, thus enabling the said one or more locking elements to become disengaged from the abutment to release the sealing means to open the first valve.

8. A gas supply device according to any one of the preceidng Claims wherein the valve mechanism comprises a movable valve member, the valve member being movable in response to a change in pressure in at least a region within a bottle or receptacle containing compressed gas to be supplied by the gas supply device.

9. A gas supply device according to Claim 8 as dependent directly or indirectly in Claim 4 wherein said movable valve member comprises the second valve.

10. A gas supply device according to Claim 9 wherein the bottle or receptacle containing compressed gas defines at least two regions separated by a partition wall, the partition wall being movable in response to a pressure differential between the two regions, the valve member moving in response to movement of the partition wall.

11. A gas supply device according to any one of Claims 1 to 9 wherein the bottle or receptacle containing compressed gas defines at least two regions separated by a partition wall, the valve mechanism being such that gas from one of the regions is dispensed before gas from the other region is dispensed.

12. A gas supply device according to Claim 10 wherein the valve mechanism is such that gas from one of the regions is dispensed before gas from the other region is dispensed.

13. A gas supply device according to Claim 9 wherein the partition wall is formed integrally with the movable valve member.

14. A gas supply device according to any one of the preceding Claims wherein the cross-section of the flow area of the valve when fully opened is approximately twenty times larger than the cross-section of the flow area of the valve when the valve mechanism is initially opened.

15. A gas supply device according to Claim 8 or any Claim dependent thereon wherein the cross-sectional area of the flow opening gradually increases with the movement of the movable valve member.

16. A gas supply device according to Claim 12 wherein the movable valve member moves past a series of grooves, enabling the grooves to become part of the flow path, thus increasing the cross-sectional area of the flow path.

17. A gas supply device according to any one of the Claims 4 to 16 wherein the first valve comprises a sealing ring initially retained in position engaging a seat, the valve being opened by removing the sealing ring from the seat.

18. A gas supply device according to Claim 8 or any Claim dependent thereon wherein the movable valve member comprises a tubular portion surrounding a tube, means being provided to constrain gas from the source of compressed gas to flow between the tubular portion and the tube, the tubular portion terminating with an inturned lip defining, as the second valve, a leaky valve, the tubular portion being received slidingly within a sealing ring and being adapted to be removed from the sealing ring to fully open the second valve.

19. A gas supply device substantially as herein described with reference to and as shown in the accompanying drawings.

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