AN AIR-BAG AND A METHOD OF DEPLOYING AN AIR-BAG

Abstract: An air-bag (8) is mounted in the roof of a motor vehicle to be deployed in front of an occupant (7) of the vehicle. The air-bag is constrained by means of tear-straps (15) within the air-bag to inflate initially as a "curtain" in front of the occupant of the vehicle, that occupant only having a relatively narrow thickness (T). When the tear-straps break, the bag has a more rounded configuration. The bag is releasably retained within a recess (9) which initially houses the bag. When the bag is fully inflated, the bag becomes totally separated from the recess, to prevent the bag forcing the head of the occupant rearwardly as the torso of the occupant moves forwardly during an accident.

Description: AN AIR-BAG AND A METHOD OF DEPLOYING AN AIR-BAG THE PRESENT INVENTION relates to an air-bag aπangement, and in particular relates to an air-bag arrangement for use in a motor vehicle, such as a motor car, to provide protection for the driver or an occupant of the vehicle in the event that an accident should arise. It has been proposed previously to provide an air-bag aπangement in a motor vehicle in which an air-bag is mounted in the roof of the vehicle and is adapted, when deployed , to occupy a position in which at least part of the air- bag is located in front of the occupant of the vehicle to be protected. US A 3795412 discloses an air-bag aπangement in which a plurality of inflatable tubes are provided which are initially stored in the roof of a vehicle, above the driver. The tubes are associated with netting that interconnects the tubes. In the event that an accident arises the tubes are inflated and extend downwardly from the roof of the car forming a cage that suπounds the occupant of the car and also the back of the seat in which the occupant of the vehicle is sitting. Thus the head and torso of the occupant are prevented from moving forwardly or laterally relative to the back of the seat. It is thought that if this system were to be used, in an accident situation, the head of the occupant, which typically moves forwardly relative to the torso - since the torso is usually restrained by a seat belt - will engage the combination of the inflatable tubes and the netting and will be bent rearwardly relative to the torso, which may lead to undesirable injuries. At the conclusion of the accident, the occupant will still be encaged by the netting, even if the inflatable tubes deflate, and thus may have great problems in leaving the vehicle. This is undesirable since in many cases it is desirable for the occupants of a vehicle to leave the vehicle as soon as possible after an accident has occurred. A further problem with this arrangement is that if the occupant of the vehicle is leaning forwardly at the instant that the air-bag aπangement is deployed, they may be held in the forward position, instead of in the upright position, which may lead to an increase in the injuries sustained, rather than a decrease. US A 3774936 discloses an aπangement in which an air-bag is mounted in the roof of a vehicle in a housing that extends transversely of the rear seat. The air-bag, when deployed, is located in front of an occupant of the vehicle seat. The air-bag is associated with wires on each side of the vehicle. Each wire is an endless loop which is connected to anchoring points in the roof and behind the shoulder of the occupant of the seat, there being a loop of fabric on the air-bag that suπounds the wire of the endless wire loop. The arrangement guides the inflating air-bag so that, when inflated, the air-bag applies a downward and rearward force on the pelvic area of the occupant of the seat, as well as providing a physical bairier in front of the seat occupant to restrain forward movement. In use of an aπangement of this type there is again a risk that the head of the occupant will engage the inflated bag before the torso, and thus the head will be bent back in an undesirable manner relative to the torso. US A 4536008 also discloses an air-bag arrangement in which an air-bag is mounted on the roof of a motor vehicle to be deployed to occupy a position in front of an occupant of the vehicle in the event that an accident occurs. The air-bag is designed so that the lower end of the air-bag engages and applies a downward force to the lap of the occupant of the vehicle to retain the occupant of the vehicle in the desired position, whilst also forming a barrier in front of the occupant. The upper part of the air-bag is mounted to the roof of the vehicle in such a way that the upper part of the air-bag can move forwardly, from its initial position, by up to a predetermined distance if the occupant of the vehicle applies a substantial force to the inflated air-bag. The upper part of the air-bag moves against a bias provided by springs. Again it is thought that if the head of the occupant makes contact with the air-bag after is has been deployed, even though the top part of the air-bag can move forwardly slightly, nevertheless, there is still a severe risk that the neck of the occupant will be bent back as the torso continues to move forwardly while the head is restrained. The present invention seeks to provide an improved air-bag aπangement. According to one aspect of this invention there is provided an air-bag arrangement in a motor vehicle to protect an occupant of the vehicle in the event that an accident should occur, said aπangement incorporating an air-bag, the air-bag initially being retained within a recess at a position above the occupant to be protected, the air-bag being associated with a gas generator means to provide gas to inflate the inflatable element and a sensor, the sensor being adapted to sense an accident and activate the gas generator means to inflate at least a main inflatable part of the air-bag, the air-bag being adapted to be deployed, on inflation, with a main inflatable part thereof located in front of the occupant of the vehicle, there being means initially connecting the main inflatable part of the air-bag to the recess, the means being adapted to release the main inflatable part of the air-bag from the recess on inflation of the air-bag so that the said main inflatable part of the air-bag is free to move downwardly out of the recess, becoming separated from the recess. According to another aspect of this invention there is provided an air- bag arrangement in a motor vehicle to protect an occupant of the vehicle in the event that an accident should occur, said aπangement incorporating an air-bag, the air-bag initially being retained within a recess at a position above the occupant to be protected, the air-bag being associated with gas generator means to provide gas to inflate the inflatable element and a sensor, the sensor being adapted to sense an accident and activate the gas generator means to inflate at least a main inflatable part of the air-bag, the air-bag being adapted to be deployed, on inflation, with the main inflatable part thereof located in front of the occupant of the vehicle, there being means initially retaining the main inflatable part of the air-bag in the recess, the means being adapted to release the main inflatable part of the air-bag from the recess on inflation of the air-bag so that the said main inflatable part of the air-bag is free to move downwardly out of the recess, becoming separated from the recess. According to a further aspect of this invention there is provided an air- bag arrangement in a motor vehicle to protect an occupant of the vehicle in the event that an accident should occur, said aπangement incorporating an air-bag, the air-bag initially being stored at a position above the occupant to be protected, the air-bag being associated with gas generator means and a sensor, the sensor being adapted to sense an accident and activate the gas generator means to inflate the air-bag, the air-bag being adapted to be deployed, on inflation, in front of the occupant of the vehicle wherein the air-bag is constrained to be inflated in such a way that during the initial stages of inflation the air-bag is relatively thin ( as measured in the direction of the axis of the vehicle) and is located in front of the occupant, and subsequently the thickness of the air-bag ( as measured in the direction of the axis of the vehicle) increases. According to another aspect of this invention there is provided an air- bag aπangement in a motor vehicle to protect an occupant of the vehicle in the event that an accident should occur, said aπangement incorporating an air-bag, the air-bag initially being stored at a position above the occupant to be protected, the air-bag being associated with gas generator means and a sensor, the sensor being adapted to sense an accident and activate the gas generator means to inflate the air-bag, the air-bag being adapted to be deployed, on inflation, in front of the occupant of the vehicle, wherein the air-bag is provided with at least one element extending from one lateral side of the bag to an anchor point located above and behind the occupant. According to another aspect of this invention there is provided an air- bag arrangement to provide protection for a driver or occupant of a motor vehicle, the air-bag aπangement comprising a sensor responsive to deceleration of an impact of the motor vehicle, gas generator means adapted to be actuated in response to a signal from the sensor, and a gas duct provided to receive gas from the gas generator means, the gas duct extending from a fixed point on the vehicle to a main inflatable part of an inflatable element, the inflatable element initially being retained in a recess, the aπangement being such that on actuation of the gas generator the gas duct becomes substantially rigid to locate at least the main inflatable part of the inflatable element in a predetermined position. According to another aspect of this invention there is provided a method of deploying an air-bag aπangement, which air-bag aπangement includes a gas duct and an inflatable element, the method comprising the steps of inflating a gas duct so that the gas duct becomes substantially rigid, inflation of the gas duct locating at least part of the inflatable element in a predetermined position, and inflating the main inflatable part of the inflatable element. According to a further aspect of this invention there is provided an air- bag arrangement to provide protection for a driver or occupant of a motor vehicle, the air-bag aπangement comprising a sensor responsive to deceleration of or an impact of the motor vehicle, gas generator means adapted to be actuated in response to a signal from the sensor, and an element to be inflated by gas from the gas generator means, the element being adapted to move the main inflatable part of an inflatable element from an initial position within a recess to a desired position. 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 view of an air-bag aπangement in a motor vehicle illustrating a problem that the present invention seeks to overcome, FIGURE 2 is a diagrammatic view of an air-bag aπangement mounted in a motor vehicle with the air-bag in an initial phase of deployment, FIGURE 3 is a view corresponding to Figure 2 showing a subsequent stage of deployment of the air-bag, FIGURE 4 is a view coπesponding to Figure 3 showing the occupant of a vehicle moving into contact with the air-bag, FIGURE 5 shows a final phase of the use of the air-bag of Figures 2 to 4 with a seat occupant not wearing a seat belt, FIGURE 6 shows a final phase of the use of an air-bag of Figures 2 to 4 with a seat occupant wearing a seat belt, FIGURE 7 is a diagrammatic illustration showing how the top of the air- bag of Figures 2 to 5 is connected to the roof of the motor vehicle, FIGURE 8 is a view coπesponding to Figure 7 showing how the top part of the air-bag of Figures 2 to 5 becomes released, FIGURE 9 is a view showing an alternative aπangement, FIGURE 10 is another view showing a further alternative aπangement, FIGURE 11 is an enlarged view of part of the aπangement of Figure 10, FIGURE 12 is a view coπesponding to Figure 3 showing a modified embodiment of the invention, FIGURE 13 is a view coπesponding to Figure 3 of another modified embodiment of the invention, FIGURE 14 is a view coπesponding to Figures 3 showing yet another modified embodiment of the invention, FIGURE 15 is a diagrammatic view of an air-bag aπangement mounted in a motor vehicle in accordance with the invention with the air-bag in an initial retained position, and FIGURE 16 is a view coπesponding to Figure 15 showing the air-bag in the deployed condition, FIGURE 17 is a diagrammatic view of an air-bag aπangement in accordance with the invention illustiating the air-bag during a preliminary stage in inflation of the air-bag, FIGURE 18 is a view illustiating the air-bag of Figure 17 at a subsequent stage during inflation of the air-bag, FIGURE 19 is a view illustrating an alternative embodiment of the invention, and FIGURE 20 is a diagrammatic part sectional view taken on the line XX- XX of Figure 19 but illustiating a modified embodiment of the invention with the air-bag inflated, FIGURE 21 is a view corresponding to Figure 20 showing a modified embodiment, FIGURE 22 is a view coπesponding to Figure 20 showing a further modified embodiment, FIGURE 23 is a view coπesponding to Figure 20 showing yet another modified embodiment, FIGURE 24 is a side view of part of a motor vehicle showing another embodiment. FIGURE 25 is a front view of part of the embodiment of Figure 24, and FIGURE 26 is a side view coπesponding to Figure 24 showing a modified embodiment. Figure 1 illustrates, schematically, part of a vehicle 1. The vehicle has a roof, 2, a windscreen or windshield 3 and an associated A-Post 4. Incorporated within the vehicle is a dashboaid 5. The front seat 6 of the vehicle is occupied by an occupant 7, and the occupant 7 is illustrated as wearing a seat belt. Figure 1 illustrates an aπangement in which an air-bag 8 is provided which is initially mounted in a recess which is formed in the roof at a position extending across the top of the windscreen or windshield 3. The air-bag 8 is illustrated in the inflated condition, showing the situation that exists some milliseconds after the commencement of a frontal-impact accident. It can be seen that as a consequence of the frontal impact, the air-bag 8 has been inflated and has been deployed to occupy a position in front of the occupant 7 of the vehicle. As a consequence of the deceleration of the vehicle, caused by the frontal impact, the occupant 7 of the seat 6 has moved forwardly relative to the seat. The seat belt has become tightened, thus retaining the pelvic region of the occupant of the seat. The main torso of the occupant of the seat has thus inclined forwardly. The head of the occupant has been the first part of the occupant to make contact with the air-bag. Thus, the forward motion of the head of the occupant, relative to the vehicle, has been retarded, whilst the forward motion of the main torso of the occupant continued. Because the torso of the occupant was moving forwardly relative to the head of the occupant, the neck of the occupant has become bent rearwardly, with the head of the occupant effectively being moved pivotally towards the rear, relative to the main torso of the occupant. Such a movement of the neck of the occupant is veiy undesirable, and may cause substantial injuries. Figure 2 again shows, schematically, part of a vehicle 1, and illustrates the roof 2, windscreen or windshield 3, and an associated A-Post 4, dashboard 5 and front seat 6. The front seat is occupied by an occupant 7 who is not wearing a seat belt. The vehicle 1 is provided with an air-bag aπangement in accordance with the invention. The aπangement includes an air-bag 8 which is initially retained, in a folded state in a recess 9 which extends transversely across at least part of the top of the windscreen or windshield 3 within the roof 2 of the vehicle 1 at a position above and in front of the occupant 7 who is to be protected. The recess may be formed in the roof of the vehicle, or in a housing mounted in the roof. The air-bag is connected, by means of a flexible hose 10 to a gas generator 11 and an associated crash sensor 12. The gas generator 1 1 and crash sensor 12 are shown as being mounted behind the dashboard 5 of the vehicle, but may alternatively be positioned at another location within the vehicle. The flexible hose 10 extends from the gas generator 1 1 along the A- Post 4 to the air-bag 8. The hose 10 is releasably mounted in position on the A- Post 4. As shown in Figure 2 the sensor 12 has sensed an accident and has activated the gas generator 1 1. Gas is being supplied by the gas generator 1 1, through the hose 10 to inflate the air-bag 8. The air-bag 8 consists of a single main inflatable part comprising a single chamber. This main inflatable part is provided with fixing means as will be described below. The air-bag 8 as shown in Figure 2 is partially inflated, and extends from the roof 2 of the vehicle to a point adjacent the upper part of the legs of the occupant. Thus the air-bag has initially occupied a position in which the entire volume of the bag is located in front of the occupant 7 before the occupant 7 has moved significantly forwardly relative to the vehicle. The occupant of the vehicle could have been in a relatively forward position at the beginning of the accident. If the illustrated occupant is the driver, and if the occupant is short in stature, the seat of the occupant could be in a forward position. If the occupant were the front seat passenger, then the occupant could be leaning forwardly, for example to gain access to the glove box. Thus it is desirable that the air-bag 8, as it inflates, is as far forward as possible, to minimise the risk that the air-bag cannot be deployed in front of the occupant. Also the air-bag, during this phase of deployment should have a minimum thickness, where thickness is understood to be the distance between the part 13 of the air-bag closest to the occupant 7 and the part 14 of the air-bag closest to the windscreen or windshield 3, as shown by the line T in Figure 2. It is to be understood that the thickness of the air-bag, as shown by the line T, is measured in a direction parallel to the axis of the vehicle. Whilst it is possible to control the deployment characteristics of an air- bag by folding the air-bag in an appropriate manner, in the described embodiment of the invention the air-bag 8 is provided with a plurality of tear straps 15 each of which extends from the part 13 of the bag closest to the occupant 7, to the part 14 of the bag which is furthest from the occupant and closest to the windscreen or windshield 3. The tear straps are relatively short and act to hold the bag in the illustrated configuration during the initial phase of deployment. Thus the tear stiaps maintain the air-bag with a minimum thickness as shown by the line T. The tear stiaps are provided with regions of mechanical weakness (or are designed to have only a predetermined strength) and are adapted to tear or break when the pressure within the inflating air-bag 8 reaches a predetermined threshold. When the tear straps tear or break the air- bag will begin to adopt a more spherical form. It is to be understood that instead of tear straps interconnecting the relevant parts 13, 14 of the air-bag 8 tear threads could be used instead, these being threads adapted to snap when subjected to a predetermined force on inflation of the air-bag. Figure 3 illustrates the phase of deployment of the air-bag 8 following the tearing of the tear stiaps 15. The thickness of the bag as measured in a direction parallel to the axis of the vehicle is now increasing, with the part 13 moving towards the occupant 7 and with the part 14 moving towards the windscreen or windshield 3. The occupant 7 is still in the initial position as during this initial phase of a typical accident the vehicle is decelerated relatively slowly as the crumple zone of the vehicle crumples. Subsequently the vehicle decelerates more rapidly and, as shown in Figure 4, the occupant 7 moves forwardly relative to the seat 6 and the rest of the vehicle 1. The occupant 7 impacts with the main inflatable part of the inflated air-bag 8. Because the occupant is not wearing a seat belt the torso 16 and the head 17 of the occupant engage the air-bag virtually simultaneously. The torso 16 of the occupant may have a substantial mass and thus a substantial momentum relative to the vehicle 1. Thus the torso, even though it has impacted with the main inflatable part of the air-bag 8, will continue to move forwardly, as shown in Figure 5, thus compressing the air-bag 8. The head 17 of the occupant is engaging a part of the air-bag 8 which is close to the roof, and if the torso 16 moved forwardly while the head 17 was retained in the position shown in Figure 5 there would be a risk that the neck of the occupant 7 of the vehicle would be bent backwardly. This bending of the neck might lead to injuries that could permanently damage the occupant of the vehicle. In the illustrated embodiment the upper part of the air-bag 8 is releasably connected to the recess within the roof 2 of the vehicle 1 in which the air-bag was initially stored or retained, as will be described below with reference to Figures 7 and 8. The aπangement is such that when the force, in a forward direction of the vehicle, applied to the air-bag by the occupant 7 exceeds a predetermined threshold the upper part of the air-bag 8 becomes disconnected from the recess within the roof 2 of the vehicle. The threshold is selected so that in the described scenario the air-bag 8 will become disconnected from the recess before the neck of the occupant of the vehicle is bent rearwardly sufficiently to cause permanent damage to the occupant. The main inflatable part of the air-bag 8, which is still connected to the gas generator 11 by the flexible hose 10 is thus released from the recess within the roof 2 of the vehicle. The main inflatable part of the air-bag 8 becomes separated from the recess within the roof 2 of the vehicle and is free to move downwardly and also to move forwardly. The head 17 of the occupant can thus move forwardly, whilst being protected and retarded by the main inflatable part of the air-bag 8, with a greatly reduced risk that the neck of the occupant 7 will be bent back in an undesirable way. There is no real risk of the air-bag leaving the desired position generally in front of the occupant 7 of the vehicle, since when the main inflatable part of the air-bag is released from the roof of the vehicle the main part of the air-bag 8 is trapped between the torso 16 of the occupant 7 and the dashboard 5. Thus the air-bag provides the desired protection for the occupant 7 of the vehicle whilst minimising the risk of the occupant suffering from undesired injuries as a consequence of backward bending of the neck. Figure 6 shows the air-bag 8 of Figures 2 to 5, when used by an occupant 7 wearing a seat belt 18, at an advanced stage during an accident. The air-bag 8 is substantially completely inflated and the occupant 7 has moved forwardly relative to the seat 6 taking up all of the slack in the seat belt 18 and also slightly stretching the belt. It can be seen that the pelvic region of the occupant has been substantially retained by the belt, but the torso 16 is leaning forwardly as a consequence of the torso pivoting about the retained hips of the occupant 7 of the seat 6. The head 17 of the occupant has made contact with the air-bag, and this has applied a force to the air-bag sufficient to disconnect or release the top part of the air-bag from the recess in the roof. It is to be appreciated, however, that if the top part of the air-bag had not been disconnected from the recess, the head 17 of the occupant 7 would have been bent back, relative to the torso, (as shown in Figure 1 ) thus bending the neck of the occupant in an undesired manner. Figure 7 shows the upper part of the air-bag 8 following deployment thereof. The air-bag 8 was initially retained in a recess 20 above the roof lining 21 behind a flap or door 22. Initially the flap or door 22 formed part of, or was mounted to be flush with or just behind, the roof lining so that the air- bag aπangement was inconspicuous. On inflation of the air-bag 8 the flap or door 22 opened to permit the air-bag to descend to the position shown in Figure 2. The air-bag 8 is provided on each lateral side thereof ( i.e. the side nearest the adjacent door, and the side adjacent the centre of the vehicle) with a loop 23. The loop passes through an aperture 24 formed in a release block 25 mounted within the recess 20. The block 25 may be made of a frangible material which is adapted to break when subjected to a predeteπnined force. In the described embodiment one part of the block suπounding the aperture is provided with a line of mechanical weakness 26. A force applied to the release block by the loop 23 in excess of a predeteπnined threshold causes it to break at the line of mechanical weakness 26, thus permitting the loop 23 to escape in a generally forward direction from the aperture 24. Referring now to Figure 8, when the occupant 7 applies a force to the main inflatable part of the air-bag 8 as a consequence of the forward movement of the head 17 or torso 16 of the occupant 7 the loop 23 will apply that force to the release block 25. If the force is in excess of a predetermined threshold, the block will break along the line 26 of mechanical weakness, thus releasing the top part of the main inflatable part of the air-bag from the roof of the vehicle. The only connection between the air-bag and the vehicle is then the flexible hose 10 that extends to the gas generator 1 1. The flexible hose 10 readily becomes disconnected from the A-Post 4 and the air-bag 8 is free to move forwardly and downwardly. Figure 9 illustrates schematically an alternative embodiment. In Figure 9 the upper part of the air-bag 8 which is provided, at each lateral side thereof, with a strap 27, by means of which the air-bag is connected to the recess in the roof 2 of the vehicle. Each strap 27 is designed to break or tear when subjected to a predeteπnined force. The straps may thus be made of weak material or, alternatively, may be provided with a specific portion adapted to snap. When a predeteπnined force is applied to the main inflatable part of the air-bag 8 the straps 27 will break, and again the main inflatable part of the air-bag will be released. Figure 10 illustrates a further alternative aπangement in which the upper part 8 of the air-bag is provided with a plurality of straps 28. Each strap 28 terminates at its upper end with a loop, the loop being mounted on a retractable pin 29. As can be seen in Figure 11, the pin 29 may be associated with a piston contained within a chamber, there being a pyrotechnic charge located between the piston and one end of the chamber. The pyrotechnic charge may be ignited to move the piston along the chamber thus drawing the pin 29 into the chamber and effectively disconnecting the pin from the loop formed at the end of the strap 28. The strap 28 will thus be released. The chamber would be in the form of a housing secured to the roof of the vehicle within the recess 2. The pyrotechnic charge associated with the piston would be ignited shortly after inflation of the air-bag so that initially the air-bag is inflated, and subsequently the main inflatable part of the air-bag is then released from the recess so as to be free to move downwardly away from the recess. Figure 12 illustrates a modified embodiment of the invention. In this embodiment the vehicle 1 and the air-bag 8 are as described above but the air- bag 8 is provided with two side stiaps, only one of which, 30, is shown. Each side strap is secured to a respective lateral side part of the air-bag 8, and is so configured that when the air-bag 8 is inflated, as shown in Figure 12 the strap 30 extends to an anchor point 3 1 in the roof of the vehicle ( or on the door frame of the vehicle) located above and to the rear of the occupant 7 of the vehicle. Each strap 30 may be of triangular form, having a substantial width in the region of the strap adjacent the end thereof that is secured to the air-bag 8. The straps 30 assist in retaining the air-bag in the desired position in front of the occupant 7 of the vehicle. Also, if the occupant of the vehicle tends to move laterally for any reason (for example if the vehicle is subjected to an oblique impact) the straps will tend to guide the occupant sitting on the seat of the vehicle into contact with the main inflated part of the inflated bag 8. Figure 13 shows another embodiment of the invention in which the vehicle 1 and the air-bag 8 are veiy similar to that described with reference to Figures 2 to 5. In this embodiment the air-bag 8 is provided with two side straps which are equivalent to the side strap 30 described above. At least one of the side straps, preferably the side strap closest to the door adjacent to the occupant of the vehicle, but most conveniently both of the side straps, are of the form of a partially inflatable side strap 32. The partially inflatable side snap 32 is generally of triangular foπn and extends from a mounting point 33 foπned in the roof ( or in the door frame) of the vehicle at a position above and behind the occupant 7 of the vehicle. The lower edge of the stop is in the foπn of a gas duct 34. The gas duct is connected to a gas generator 35 which is mounted in the roof of the vehicle together with a crash sensor 36 which is adapted to activate the gas generator should an accident occur. The gas generator and the sensor may, of course, be located at any convenient position within the vehicle. The gas duct 8 is connected to a plurality of inflatable cells 37 that are located in a triangular zone of the partially inflatable side strap 32 located above the gas duct 34. As the cells 37 inflate they adopt a cylindrical configuration, with the axes of the cells intersecting a line extending generally of the side strap 32 as defined by the gas duct 34. As the cells 37 inflate, so the side-walls of the cells adopt an outwardly bowed configuration, which effectively reduces the length of the side strap 32, defined by the cells, tending to draw the air-bag towards the occupant 7 of the vehicle. However, the inflated cells 37 also form a protective cushion located between the head 17 of the occupant 7 and the adjacent window or door. This may minimise injury, especially in a side impact or roll over situation. The gas duct 34 in the described embodiments is connected to the air- bag 8 to supply the gas to the main inflatable part of the air-bag 8 necessary for the inflation thereof from the gas generator 35. In an alternative aπangement a separate gas generator may be provided to inflate the main inflatable part of the air-bag. Figure 14 illustrates another modified embodiment of the invention which is similar to that shown in Figure 12. In this embodiment of the invention the triangular strap 30, as described in Figure 12 is connected to the roof 2 of the vehicle by means of an aπangement 40 which provides the dual effect of moving the strap 30 rearwardly, thus drawing the strap rearwardly, and consequently moving the main inflated part of the inflated air-bag 8 towards the occupant 7 of the vehicle, and also providing a force-limiting effect which permits the air-bag 8 to move forwardly, against a retarding force provided by the force limiting aπange ent. In the embodiment illustrated in Figure 14, the end of the strap 30 is connected to a shaft 41 which is connected to a piston 42 contained within a cylinder 43. A gas generator 44 is provided adapted to inject gas into the cylinder 43 so as to move the piston towards the right in the orientation illustrated. As the piston moves towards the right, so a force is applied to the strap 30, tending to draw the inflated air-bag 8 towards the occupant 7 of the vehicle. When the occupant 7 moves forwardly relative to the seat, and impacts with the main inflated part of the air-bag 8, a veiy substantial force may be transfeπed, from the air-bag 8 to the strap 30. This force will tend to move the piston 42 towards the left as illustiated. The piston 42 will be able to move towards the left, expelling gas from the cylinder 43, for example through a vent hole which suπounds the shaft 41. However, the movement of the piston in this direction is accompanied by a force limiting effect, and thus the forward movement of the piston and the strap 30 is effectively retarded by the described arrangement. Whilst one particular apparatus has been illustrated which initially applied a force to the strap 30, and which subsequently permits forward movement of the strap with a force limiting effect, alternative devices could be utilised. Figures 15 and 16 illustrate a further embodiment. In this embodiment, the roof 2 of the vehicle defines a recess 50 which extends at least partly across the top of the windscreen or windshield 3. An air-bag 51 is provided which is initially retained, in a folded condition, within the recess 50. The air-bag is retained in position by means of a door 52 which initially closes the recess 50. The door 52 may form part of the roof lining of the vehicle, but may alternatively be flush with the roof lining of the vehicle or located immediately above the roof lining of the vehicle so that the air-bag aπangement is inconspicuous. In modifications of this embodiment the air-bag maybe retained by other means, such as a fabric sleeve or retaining stiaps. The air-bag 51 is connected by means of a flexible hose or conduit 10 which extends along the A-Post 4 of the vehicle to a gas generator 1 1 which is associated with a crash sensor 12. In the event that an accident should arise, the gas generator 1 1 is activated which initiates inflation of the air-bag 51. The door 52, which initially retains the air-bag 51 in the folded condition within the recess 50, consequently opens as the air-bag begins to inflate. The opening of the door permits the main inflatable part of the air-bag 51 to fall out of the recess 50, since the door is the only element retaining the air-bag in the recess. The main inflatable part of the air-bag 51 is thus totally separated from the recess 50 and is free to fall to a position in front of the occupant of the seat. If the air-bag had been retained by a sleeve or stiaps, on inflation of the bag the sleeve or straps will break, thus allowing the air-bag to inflate and fall to a position in front of the occupant of the seat. The air-bag, as can be seen in Figure 16, may be provided with internal tear straps 53, similar to the tear stiaps described above, in order to control the configuration of the air-bag during the initial stages of inflation thereof. However, the air-bag, which was retained within the recess 51 by the door 52, is no longer retained within the recess once the door 52 has opened. The air- bag thus falls to occupy a position, as illustrated in Figure 16, which is located directly in front of the occupant 7 of the motor vehicle. Refeπing now to Figure 17 of the accompanying drawings, another air- bag arrangement is illustiated. The air-bag aπangement is adapted to provide protection for a driver or front-seat passenger (i.e. a front seat occupant) in a motor vehicle in the event that an accident should occur. The air-bag aπangement comprises a sensor 61 adapted to sense a frontal impact of the motor vehicle, the sensor 61 being adapted to actuate a gas generator 62. The sensor and gas generator may be mounted in the roof lining of the motor vehicle at a position above the rear door of the motor vehicle, that is to say to the rear of the B-Post 63 of the motor vehicle. The gas generator 62 is connected by means of a gas duct 64 to the main inflatable part of an inflatable element or air-bag 65. The inflatable element 65 is initially stored in a recess or housing, schematically illustrated as recess 66 which extends transversely of the motor vehicle in the roof of the motor vehicle at a position above and just in front of a front-seat occupant of a motor vehicle. The inflatable element 65, as illustiated, may be dimensioned to extend across half of the width of the motor vehicle. Initially the inflatable element 65 will be contained within the recess 66 which may be invisible to the ordinary occupant of the motor vehicle, and a gas duct 64 will also be stored appropriately in a concealed manner. The gas duct may be foπned of a fabric, such as the fabric used to form the inflatable element 65. The gas duct 64 may be connected to the main inflatable part of inflatable element or air-bag 65 by means of a constriction 67 which will restrict or impede the flow of gas through the gas duct. The constriction 67 will be dimensioned so that during the initial stage of inflation of the inflatable element, which will be described hereinafter, the gas duct 64 becomes rigid. When rigid, the gas duct extends substantially parallel to the axis of the vehicle, extending forwardly of the gas generator 62, and downwardly The gas duct 64 may be connected to supply gas to an extension 68 of the gas duct. The extension 68 of the gas duct extends transversely to the main part of the gas duct. The extension 68 is mounted on the exterior of the main inflatable part of the inflatable element 65, extending across the lower part of the inflatable element, thus extending transversely across the vehicle. The extension 68 does not cover the upper part 69 of the inflatable element 65. A perforated panel 70 (see Figure 18) separates the extension 68 of the gas duct and the inflatable element 65. Perforated panel 70 thus permits a restricted flow of gas from the extension 68 into the inflatable element 65. The arrangement is such that gas flowing through the constriction 67 will initially inflate, or substantially inflate, the extension 68 so that it is rigid before gas passes through the perforated panel 70 to inflate the main inflatable part of the inflatable element 65. The main inflatable part of the inflatable element 65 is illustrated as having a generally rectangular configuration before inflation, but may have an alternative configuration. In the event that the sensor 61 senses an impact of the motor vehicle, the gas generator 62 is activated, and gas is fed from the gas generator 62 to the gas duct 64. Because of the presence of the constriction 67, the gas duct 64 will initially inflate and become rigid. As the gas duct 64 inflates and becomes rigid, it occupies the position illustrated in Figure 18 and 19, extending forwardly and downwardly from the gas generator relative to the axis of the vehicle. Consequently the gas duct 64 will assist in withdrawing at least part: of the inflatable element from the recess 66 and will guide or position at least that part of the inflatable element in front of the driver of the motor vehicle. Thus the gas duct 64 locates at the main inflatable part of the inflatable element 65 in a predetermined position. Subsequently gas from the now rigid duct 64 will pass through the constriction 67 and inflate the extension 68 of the gas duct. The extension 68 extends transversely to the axis of the main part of the gas duct 64 that extends in a generally forward direction from the gas generator 2 relative to the axis of the vehicle. Extension 68 of the gas duct thus extends transversely relative to the axis of the vehicle and will locate the main inflatable part of the air-bag in a predetermined position. Subsequently gas flows from the inflated extension 68 of the gas duct through the perforated panel 70 to inflate the main inflatable part of the inflatable element 65. The inflatable element is thus fully inflated and is held in place by the rigid inflated gas duct 64, and the extension 68. This is the situation shown in Figure 18. Figure 19 illustrates a modified embodiment which is similar to that described with reference to Figures 17 and 18, but in which there are two gas generators 62, each associated with a respective gas supply duct 64 of the type shown in Figure 17. The two gas supply ducts 64 are spaced apart relative to the axis of the vehicle, and are each comiected, by means of a respective constriction 67, to a single extension 68 which extends across the lower region of the main inflatable part of the inflatable element 65. In other respects the embodiment of Figure 19 is the same as the embodiment of Figures 17 and 18. Figure 20 illustrates a modified embodiment which is similar to that of Figures 17 and 18. In this embodiment the main part of the gas supply duct 64 is joined to a transverse extension 68 of the gas duct without any constriction. The transverse extension 68 of the gas duct effectively forms the lower part of the inflatable element 65. A perforated panel 71 is provided which communicates between the extension of the gas duct 68 and the main inflatable part 72 of the inflatable element 65. The panel 71 permits a restricted flow of gas. Instead of perforated panel 71, as illustiated, the extension 68 of the gas duct 64 may be formed integrally with the rest of the inflatable element 65, and may be separated from the main inflatable part 72 of the inflatable element 65 by means of a seam, the seam comprising a plurality of slightly spaced-apart seam portions which permit a restricted flow of gas from the extension 68 of the gas duct into the main inflatable part 72 of the inflatable element. Thus, in this embodiment of the invention, as illustrated in Figure 20, on activation of the gas generator, initially the gas duct 64 which extends substantially parallel to the axis of the vehicle, extending forwardly of the gas generator 62, and the transverse extension 68 of the gas duct will be inflated and will become rigid. This will serve to draw the main inflatable part 72 of the inflatable element 65 out of the recess in which it is initially stored, this being a recess coπesponding to the recess 66. The main inflatable part is thus located in a predetermined position. Subsequently, the main inflatable part 72 of the inflatable element 65 will become inflated as gas passes through the perforated panel 71 or the seam consisting of a plurality of slightly spaced apart seam portions. Consequently the main inflatable part 72 will then become erect, with that main inflatable part being located in front of an occupant of a seat in a vehicle. Referring now to Figure 21 a further embodiment of the invention is illustrated which is similar to that of Figure 20. In this embodiment a sensor 61 is provided associated with a gas generator 62, adapted to supply gas to a gas duct 64 which is adapted to become rigid, extending substantially parallel to the axis of the vehicle, extending forwardly of the gas generator 62. The forward- most end of the gas duct 64 is provided with a transversely extending extension 68, which, when inflated, extends transversely across the vehicle. The extension 68 is connected to the lower wedge of the main inflatable part of the inflatable element 65. However, in this embodiment, there is no gas flow path from the extension 68 into the main inflatable part of the inflatable element. Instead, the main inflatable part of the inflatable element receives gas through a flexible conduit 73 from a second gas generator 74 which is shown as being associated with a second sensor 75. However, a single sensor 61 may be utilised to activate both the gas generator 62 and the gas generator 74. In the embodiment illustrated in Figure 21 it is envisaged that initially the gas duct 64 and the extension 68 will be inflated and become rigid, thus adopting the position illustiated in Figure 21, withdrawing the main inflatable part of the inflatable element 65 from a recess equivalent to the recess 66 described above with reference to Figure 17. The main inflatable part will then be inflated by gas from the gas generator 74. Such an aπangement will permit swift deployment of the air-bag aπangement. Figure 22 illustrates an embodiment which is essentially identical to the embodiment of Figure 21, with the sole exception that the gas duct 64 and the extension 68 is associated with a further vertically extending extension 76 which is provided at the junction between the gas duct 64 and the extension 68. The vertically extending extension 76 is thus located adjacent one lateral side end part of the main inflatable part of the inflatable element 65. The vertical extension 76 will be inflated simultaneously with the gas duct 64 and the transverse extension 68, thus assisting in the positioning of the transverse extension 68 at a distance spaced below the roof line of the motor vehicle. Thus the vertical extension 76, as it inflates, serves to drive the lower edge of the main inflatable part of the inflatable element 65 downwardly so that the lower edge of the main inflatable part is in the desired position, relative to the occupant of a seat in the vehicle, as soon as possible after an accident situation has been sensed by the sensor 61. Figure 23 illustrates an embodiment of the invention in which, as in the embodiment shown in Figure 19, may extend across the entire width of a motor vehicle, or may extend over one-half of the width of the vehicle to provide protection for a single occupant. In this embodiment, as in the embodiment of Figure 19, a single sensor 61 controls two gas generators, one located on either side of the vehicle, each gas generator being associated with a respective gas duct 64 which extends forwardly of the vehicle, the forward and lower-most ends of the ducts 64 being connected to the two opposed ends of a transversely extending extension 68. However, as in the embodiments of Figures 21 and 22, the transversely extending extension 68 is not in communication with the interior of the main inflatable part of the inflatable element 65. Instead, the main inflatable part of the inflatable element 65 is associated with a second gas generator 74, which is actuated by the sensor 61, and which is connected to the main inflatable part of the inflatable element 65 by means of a duct 77. In each of the embodiments shown in Figures 17 to 23 inclusive, the upper edge of the main inflatable part of the inflatable element may be retained in the recess 66, or an equivalent recess, by releasable means such as those described above with reference to Figures 7 to 11 or, alternatively, the main inflatable part may simply be located in a recess and retained in position by appropriate releasable means such as a flap or door equivalent to the flap or door 52 described above with reference to Figures 15 and 16. The embodiments described above have been intended primarily to provide protection for an occupant of a front seat of a motor vehicle, although it is to be understood that equivalent aπangements may be provided for the occupants of rear seats. Figures 24 and 25 illustrate an embodiment primarily intended to provide protection for the occupant of a rear seat in a motor vehicle. As shown in Figure 24, a motor vehicle is provided with a front seat 80 and a rear seat 81. An air-bag aπangement is provided which is mounted in the roof of the motor vehicle, in a recess or the like, which is located just in front of an occupant 82 of the rear seat. The air-bag aπangement is associated with a sensor 83 adapted to detect an accident situation and a gas generator 84. The gas generator 84 is connected to supply gas to a gas duct 85 which is adapted, on inflation, to become substantially rigid. The gas duct 85, when inflated, has a generally "U"-shaped configuration, and thus comprises a first substantially vertical limb 86 extending down adjacent one side edge of the motor vehicle, a transverse arm 87 extending transversely across substantially the entire width of a motor vehicle, and a further vertical limb 88 extending up to the roof line of the motor vehicle. The gas duct 85 thus presents a generally "U"-shaped configuration, when inflated, when viewed from the front, as shown in Figure 25. Contained within the lower part of the "U" is the main inflatable part 89 of the inflatable element which, in the described embodiment, is connected to receive gas from the gas duct 85 by means of a perforated panel equivalent to the perforated panel 71 of the embodiment illustrated in Figure 20. Of course, instead of such a panel 71, a seam comprising a plurality of slightly spaced-apart seam portions may be utilised which permits a flow of gas from the transversely extending part 87 of the gas duct 85 into the main inflatable part 89 of the air-bag. However, in a further modified embodiment, the main inflatable part 89 may be associated with a separate gas generator. It is to be appreciated that, in any event, subsequent to the sensing of an accident by the sensor 83, the gas generator 84 will generate gas inflating the gas duct 85 so that the two limbs 86 and 88 thereof located adjacent the sides of the vehicle extends substantially vertically downwardly. The main inflatable part 89 of the illustrated air-bag aπangement is thus located in front of the occupant 82 of the rear seat 81. If the occupant 82 of the rear seat 81 moves forwardly, the head and upper torso of the occupant 82 of the rear seat will engage the main inflatable part 89 of the air-bag aπangement. The main inflatable part contacts the rear part of the back-rest of the front seat 80, and thus will not move forwardly. In a modification of the embodiment illustiated in Figures 24 and 25 the limbs 86 and 88 are intended, when inflated, not to extend vertically downwardly, but to extend in a forwardly and downwardly inclined orientation. In order to ensure that the inflated limbs occupy this position one or more straps 90 may be provided which extend from the lower transverse arm 87 of the gas duct 85 to a position on the roof of the vehicle in front of the position where the upper ends of the limbs 86 and 88 are connected to the roof of the vehicle. An advantage of the aπangement shown in Figure 26 is that as the occupant 82 of the rear seat is thrown forwardly, the force applied to the main inflatable part 89 of the air-bag aπangement is not tiansmitted to the back of the front seat 80, but instead is passed to the roof of the vehicle through the limbs 86, 88. It is to be appreciated that in a typical accident situation the back of the front seat 80 of the motor vehicle may, in any event, especially if the retractor is secured to the seat back, be subjected to substantial forces, in the form of forces applied to the back of the seat 80 by the seat-belt worn by the occupant of that seat. The application of further forces to the back-rest of the seat, as a consequence of the occupant 82 of the rear seat impacting with the main inflatable part 89 of the illustrated air-bag aπangement, may foπn the back of the front seat 80 to deform. It is to be appreciated that in the embodiments of Figures 24 to 26, the main inflatable part 89 of the illustiated air-bag aπangement is not secured to the recess in which it is initially stored, so that this part of the air-bag moves downwardly to a position spaced from the recess, only being connected to the recess by the limbs 86 and 88 of the inflatable element. Although internal tear stiaps 15 have been shown only in Figures 2, 3, 4, 16 and 17, such internal tear straps may be provided in all of the embodiments described above to ensure that the main inflatable part of the inflatable element has an appropriate configuration during the early stages of inflation. In the present specification "comprise" means "includes or consists of and "comprising" means "including or consisting of. The features disclosed in the foregoing description, or the following Claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for peifoπning the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS: 1. An air-bag aπangement in a motor vehicle to protect an occupant of the vehicle in the event that an accident should occur, said aπangement incorporating an air-bag, the air-bag initially being retained within a recess at a position above the occupant to be protected, the air-bag being associated with a gas generator means to provide gas to inflate the inflatable element and a sensor, the sensor being adapted to sense an accident and activate the gas generator means to inflate at least a main inflatable part of the air-bag, the air- bag being adapted to be deployed, on inflation, with a main inflatable part thereof located in front of the occupant of the vehicle, there being means initially connecting the main inflatable part of the air-bag to the recess, the means being adapted to release the main inflatable part of the air-bag from the recess on inflation of the air-bag so that the said main inflatable part of the air- bag is free to move downwardly out of the recess, becoming separated from the recess. 2. An air-bag anangement according to Claim 1 wherein the means connecting the air-bag to the recess are adapted to release the air-bag from the recess when a force in excess of a predeteπnined force is applied to the air-bag. 3. An anangement according to Claim 2 wherein the upper part of the air- bag is secured to frangible means, comprising the connecting means, which are adapted to break to release the air-bag. 4. An aπangement according to Claim 2 wherein the means connecting the air-bag to the recess include a plurality of loops in the upper part of the air-bag, each loop passing through an aperture foπned in a release block, the release block being adapted to break to release the loop and thus to release the upper part of the air-bag. 5. An aπangement according to Claim 4 wherein the release block is provided with a line of mechanical weakness adjacent said apeiture, the release block being adapted to break at the line of mechanical weakness to release the loop. 6. An anangement according to Claim 2 wherein the connecting means comprise breakable stiaps. 7. An aπangement according to Claim 1 wherein the connecting means are means which are releasable in response to a signal from a sensor which senses an accident. 8. An aπangement according to Claim 7 wherein the connecting means are releasable by actuation of a pyrotechnic charge. 9. An arrangement according to Claim 8 wherein the pyrotechnic charge drives a piston, movement of the piston causing the release of the connecting means. 10. An air-bag anangement in a motor vehicle to protect an occupant of the vehicle in the event that an accident should occur, said aπangement incorporating an air-bag, the air-bag initially being retained within a recess at a position above the occupant to be protected, the air-bag being associated with gas generator means to provide gas to inflate the inflatable element and a sensor, the sensor being adapted to sense an accident and activate the gas generator means to inflate at least a main inflatable part of the air-bag, the air- bag being adapted to be deployed, on inflation, with the main inflatable part thereof located in front of the occupant of the vehicle, there being means initially retaining the main inflatable part of the air-bag in the recess, the means being adapted to release the main inflatable part of the air-bag from the recess on inflation of the air-bag so that the said main inflatable part of the air-bag is free to move downwardly out of the recess, becoming separated from the recess. 1 1. An aπangement according to Claim 10 wherein the means retaining the air-bag in the recess comprise a door which initially closes the recess, the door being adapted to be opened on inflation of the air-bag, to release the air-bag during inflation thereof. 12. An aπangement according to any one of the preceding Claims wherein the air-bag is provided with at least one strap extending from one lateral side of the bag to an anchor point located above and behind the occupant. 13. An arrangement according to Claim 12 wherein two said straps are provided, each extending from a respective lateral side of the air-bag. 14. An aπangement according to Claim 12 or 13 wherein the or each strap is of substantially triangular form, the end of the strap secured to the air-bag being wider than the end of the strap connected to the anchor point. 15. An aπangement according to any one of Claims 12 to 14 wherein at least one strap incorporates at least one inflatable cell. 16. An aπangement according to Claim 15 as dependent directly or indirectly on Claim 13 wherein both straps are provided with at least one inflatable cell. 17. An arrangement according to Claim 15 or 16 wherein the or each cell in the or each strap has a cylindrical foπn when inflated, the axis of the cell intersecting the line of the axis of the strap. 18. An aπangement according to Claim 16 or 17 wherein there are a plurality of cells in the or each strap. 19. An anangement according to any one of Claims 15 to 18 wherein the or each strap incorporates a gas duct to supply gas to the or each cell, the gas duct supplying gas from the gas generator to the air-bag. 20. An anangement according to any one of Claims 12 to 19 wherein the or each strap is connected to the anchor point by means of an anangement which is adapted to apply a force to the strap to draw the inflated air-bag towards the occupant of the vehicle. 21. An anangement according to Claim 20 wherein the strap is connected to the anchor point by means which are adapted to provide a force limiting effect when subjected to a force via a strap. 22. An aπangement according to Claim 21 wherein the strap is connected to the anchor point by means of a piston and cylinder aπangement, the piston and cylinder aπangement being associated with gas generator means to be actuated by a sensor which senses an accident situation to apply a force to the strap and subsequently to provide a force limiting effect. 23. An arrangement according to any one of Claims 1 to 22 in which a gas duct is provided to receive gas and become rigid on inflation with said gas, the gas duct extending from a fixed point on the vehicle to a main inflatable part of the inflatable element, the aπangement being such that when the gas duct becomes substantially rigid, the gas duct serves to locate at least the main inflatable part of the inflatable element at a predetermined position. 24. An anangement according to Claim 23 wherein the gas flow path through the gas duct extends from said gas generator means to the main inflatable part of the inflatable element, and the gas duct includes a constriction adapted to constrict the flow of gas. 25. An aπangement according to Claim 23 or 24 wherein the gas duct incorporates an extension extending transversely to a main part of the duct, the extension extending across at least part of the main inflatable part of the inflatable element. 26. An air-bag anangement according to Claim 25 wherein the extension of the gas duct is connected to the main inflatable part of the inflatable element by means permitting a restricted flow of gas from the extension to the main inflatable part. 27. An anangement according to any one of Claims 23 to 26 wherein two gas generators are provided, one being adapted to supply gas to the main inflatable part of the inflatable element, and the other being adapted to supply gas to the gas duct. 28. An aπangement according to any one of Claims 23 to 27 wherein two gas ducts are provided spaced transversely relative to the vehicle, the gas ducts each extending to the main inflatable part of a single inflatable element. 29. An anangement according to Claim 28 wherein each gas duct is associated with a respective gas generator. 30. An anangement according to any one of Claims 23 to 29 wherein the gas duct is provided with a substantially vertically extending extension thereof adapted to drive the lower edge of the main inflatable part of the inflatable element downwardly on inflation of said extension. 31. An anangement according to any one of the preceding Claims wherein the air-bag is constrained to be inflated in such a way that during the initial stages of inflation the air-bag is relatively thin ( as measured in the direction of the axis of the vehicle) and is located in front of the occupant, and subsequently the thickness of the air-bag ( as measured in the direction of the axis of the vehicle) increases. 32. An aπangement according to Claim 3 1 wherein the air-bag is provided with one or more breakable means extending from the part of the air-bag closest to the occupant to the part of the air-bag furthest from the occupant, said breakable means being dimensioned to maintain the air-bag in the relatively thin condition (as measured in the direction of the axis of the vehicle) until a predetermined pressure is present within the air-bag. 33. An air-bag aπangement in a motor vehicle to protect an occupant of the vehicle in the event that an accident should occur, said aπangement incorporating an air-bag, the air-bag initially being stored at a position above the occupant to be protected, the air-bag being associated with gas generator means and a sensor, the sensor being adapted to sense an accident and activate the gas generator means to inflate the air-bag, the air-bag being adapted to be deployed, on inflation, in front of the occupant of the vehicle wherein the air- bag is constrained to be inflated in such a way that during the initial stages of inflation the air-bag is relatively thin ( as measured in the direction of the axis of the vehicle) and is located in front of the occupant, and subsequently the thickness of the air-bag ( as measured in the direction of the axis of the vehicle) increases. 34. An aπangement according to Claim 33 wherein the air-bag is provided with one or more tear straps or equivalent breakable means extending from the part of the air-bag closest to the occupant to the part of the air-bag furthest from the occupant, said tear stiaps or equivalent breakable means being dimensioned to maintain the air-bag in the relatively thin condition ( as measured in the direction of the axis of the vehicle) until a predetermined pressure is present within the air-bag. 35. An aπangement according to Claim 33 or 34 wherein the air-bag is provided with at least one strap extending from one lateral side of the bag to an anchor point located above and behind the occupant. 36. An aπangement according to Claim 33 or 34 wherein the air-bag is provided with at least one gas duct adapted to be inflated, and to be rigid when inflated, the aπangement being such that when the gas duct becomes substantially rigid on inflation, the gas duct acts to locate at least the main inflatable part of the inflatable element in a predetermined position. 37. An aπangement according to Claim 36 wherein the gas duct incorporates an extension extending transversely to a main part of the duct, the extension extending across at least part of the main inflatable part of the inflatable element, the gas duct being comiected to the main inflatable part of the inflatable element by means permitting a restricted flow of gas. 38. An air-bag aπangement in a motor vehicle to protect an occupant of the vehicle in the event that an accident should occur, said aπangement incorporating an air-bag, the air-bag initially being stored at a position above the occupant to be protected, the air-bag being associated with gas generator means and a sensor, the sensor being adapted to sense an accident and activate the gas generator means to inflate the air-bag, the air-bag being adapted to be deployed, on inflation, in front of the occupant of the vehicle, wherein the air- bag is provided with at least one element extending from one lateral side of the bag to an anchor point located above and behind the occupant. 39. An aπangement according to Claim 35 or 38 wherein two said elements are provided, each extending from a respective lateral side of the air-bag. 40. An aπangement according to Claim 35, 38 or 39 wherein the or each element is a strap is of substantially triangular form, the end of the strap secured to the air-bag being wider than the end of the strap connected to the anchor point. 41. An aπangement according to any one of Claims 35, 38, 39 or 40 wherein at least one element incorporates at least one inflatable cell. 42. An anangement according to Claim 41 as dependent directly or indirectly on Claim 39 wherein both elements are provided with at least one inflatable cell. 43. An anangement according to Claim 41 or 42 wherein the or each cell in the or each strap has a cylindrical foπn when inflated, the axis of the cell intersecting the line of the axis of the element. 44. An aπangement according to Claim 43 wherein there are a plurality of cells in the or each element. 45. An anangement according to any one of Claims 42 to 44 wherein the or each element incorporates a gas duct to supply gas to the or each cell, the gas duct supplying gas from the gas generator to the air-bag. 46. An anangement according to any one of Claims 35 or any one of Claims 38 to 45 wherein the or each element is connected to the anchor point by means of an anangement which is adapted to apply a force to the element to draw the inflated air-bag towards the occupant of the vehicle. 47. An anangement according to Claim 46 wherein the element is connected to the anchor point by means which are adapted to provide a force limiting effect when subjected to a force via the element. 48. An air-bag aπangement to provide protection for a driver or occupant of a motor vehicle, the air-bag aπangement comprising a sensor responsive to deceleration of an impact of the motor vehicle, gas generator means adapted to be actuated in response to a signal from the sensor, and a gas duct provided to receive gas from the gas generator means, the gas duct extending from a fixed point on the vehicle to a main inflatable part of an inflatable element, the inflatable element initially being retained in a recess, the anangement being such that on actuation of the gas generator the gas duct becomes substantially rigid to locate at least the main inflatable part of the inflatable element in a predetermined position. 49. An aπangement according to Claim 48 wherein the gas duct is in communication with the main inflatable part of the inflatable element so that gas from the gas duct may inflate the said main inflatable part. 50. An aπangement according to Claim 49 wherein the gas flow path through the gas duct to the inflatable element includes a constriction adapted to restrict the flow of gas. 51. An anangement according to Claim 48 wherein, in addition to the gas generator means to supply gas to the gas duct, a separate gas generator means is present to supply gas to the main inflatable part of the inflatable element. 52. An aπangement according to any one of Claims 48 to 51 wherein the inflatable element is adapted , on inflation, to move to a position in which it is totally separated from the recess or housing in which it is initially stored. 53. An air-bag aπangement according to any one of Clams 48 to 52 wherein the gas duct incoiporates an extension extending nansversely to a main part of the duct, the extension extending across at least part of the inflatable element. 54. An air-bag anangement according to Claim 53 as dependent upon Claim 49 wherein a perforated panel provides the communication between the extension of the gas duct and said main inflatable part. 55. An aπangement according to any one of Claims 48 to 54 wherein two gas ducts are provided, spaced transversely relative to the vehicle, the gas ducts each extending to the main inflatable part of a single inflatable element. 56. An aπangement according to Claim 55 wherein each gas duct is associated with a respective gas generator. 57. An anangement according to any one of Claims 48 to 56 wherein said recess extends transversely of the axis of the vehicle and is in the roof of the vehicle. 58. An anangement according to Claim 57 wherein said recess is located above and in front of the position to be occupied by a driver or passenger in the vehicle. 59. An aπangement according to Claim 57 wherein said recess is located above the position to be occupied by a rear seat passenger in the vehicle. 60. An anangement according to any one of Claims 48 to 58 wherein the main inflatable part of the inflatable element, when inflated, is located in front of a driver or passenger in the vehicle. 61. An aπangement according to any one of Claims 48 to 58 wherein the main inflatable part of the inflatable element, when inflated, is located in front of a rear seat passenger in the vehicle. 62. An aπangement according to any one of Claims 48 to 61 wherein the gas duct is provided with an extension adapted to be inflated and to become rigid, the extension being adapted to drive the lower edge of the main inflatable part of the inflatable element downwardly to a predetermined position. 63. An aπangement according to Claim 62 wherein the extension extends from part of the gas duct where the gas duct is immediately adjacent the main inflatable part of the inflatable element. 64. An anangement according to Claim 63 as dependent upon Claim 53 wherein the extension extends from the junction between the gas duct and the extension. 65. A method of deploying an air-bag aπangement, which air-bag anangement includes a gas duct and an inflatable element, the method comprising the steps of inflating a gas duct so that the gas duct becomes substantially rigid, inflation of the gas duct locating at least part of the inflatable element in a predeteπnined position, and inflating the main inflatable part of the inflatable element. 66. A method according to Claim 65 wherein the inflatable element is inflated with gas flowing through the gas duct. 67. A method according to Claim 65 wherein the gas duct is inflated with gas from one gas generating means and the inflatable element is inflated with gas from a second gas generating means. 68. A method according to Claim 66 wherein, in inflating the inflatable element, an extension of the gas duct is inflated, and subsequently gas is passed from the extension of the gas duct to the main inflatable part of the inflatable element. 69. A method according to any one of Claims 65 to 67 wherein the inflatable element extends substantially transversely to the axis of the gas duct. 70. An air-bag aπangement to provide protection for a driver or occupant of a motor vehicle, the air-bag anangement comprising a sensor responsive to deceleration of or an impact of the motor vehicle, gas generator means adapted to be actuated in response to a signal from the sensor, and an element to be inflated by gas from the gas generator means, the element being adapted to move the main inflatable part of an inflatable element from an initial position within a recess to a desired position.

Inventors: ANDERSSON STURE, ERIKSSON DICK, HAALAND YNGVE, PERSSON JOERGEN, PIPKORN BENGT, ANDERSSON, STURE, ERIKSSON, DICK, HAALAND, YNGVE, PERSSON, JOERGEN, PIPKORN, BENGT
Applicants: ANDERSSON STURE, AUTOLIV DEV, ERIKSSON DICK, HAALAND YNGVE, PERSSON JOERGEN, PIPKORN BENGT, ANDERSSON, STURE, AUTOLIV DEVELOPMENT AB, ERIKSSON, DICK, HAALAND, YNGVE, PERSSON, JOERGEN, PIPKORN, BENGT
Application year: 2000
Main classification: B60R21
IPC codes: B60R21, B60R22