A GAS GENERATOR

Abstract: A gas-generating unit for an inflatable safety arrangement of the "air-bag" type has a cellulose nitrate charge of 10 grams or less. The gas generator has an igniter adapted to ignite the charge, and is arranged so that gas from the charge is directed to the interior of the "air-bag".

Description: "A gas generator" THE PRESENT INVENTION relates to a gas generator and more particularly relates to a gas generator suitable for use in a safety arrangement intended to be incor¬ porated into a motor vehicle such as a motor car. It has been proposed previously to provide motor cars with safety arrangements in the form of so- called "air-bags". Such air-bags are mounted at a convenient pos¬ ition within a motor vehicle and are arranged so that, in the event of an accident arising, the air-bag is in¬ flated to form a cushion for a passenger within the motor car. A typical conventional air-bag has an in¬ flated volume of between 60 and 160 litres. A typical prior proposed air-bag is inflated with a gas which is generated rapidly, subsequent to an accident occurring, by a gas generator. A typical gas generator utilises a material such as a mixture of sodi¬ um azide (NaN , Potassium nitrate (KNO and Silicon dioxide (SiO p ) in the form of pellets. These pellets, when ignited, produce rapidly a non-poisonous gas which consists primarily of nitrogen. 1 gram of the tablets provides 1 litre of gas and thus a total charge of be¬ tween 60 and 160 grams of pellets is required. Whilst the pellets, when ignited, produce a non-poisonous gas, the pellets also produce dust, which is poisonous. The hot dust could also damage the in¬ terior of the bag. Therefore in prior proposed air-bags which utilise the pellets as described, a filter is pro¬ vided between the pellets and the interior of the bag. U.S.A. Specification 3904221 discloses a typical prior art arrangement which is relatively expensive to produce and which is bulky. The pressure within an air-bag when inflated by a gas generator of this type is in the region of 0.5 bar and the time taken to inflate the bag is typically in the region of 25-30 s. One disadvantage of an air-bag system as des¬ cribed above is that of expense. Consequently it has been proposed that if a complement is required to a con¬ ventional air-bag, or to a safety-belt, in the form of an additional inflatable arrangement, then for economic reasons this complement must be cheap to produce. It has been considered desirable to provide an inflatable bag located to one side of the or each pass¬ enger, the volume of which is in the region of 5- 25 litres, as a complement to a conventional air-bag or safety-belt. These bags can be termed "inflatable padd¬ ings". These inflatable paddings are intended to pro¬ vide protection against the side impact, but if such in¬ flatable paddings are to be utilised they must be rel¬ atively cheap to manufacture, and thus the prior pro¬ posed gas generators are not really suitable. It is to be understood that if an inflatable padding is to be of use in protecting a passenger against the side impact, then that inflatable padding must be inflated in an extremely short period of time subsequent to the sensing of an accident. The reason for this is that in the case of a side impact, typically the door structure of the vehicle will begin to collapse as soon as the impact occurs, since the door structure is not very strong. A sensor is provided which is res¬ ponsive to a side impact. Such a sensor may respond to deformation of the door panel. However, even if the sensor responds very rapidly it is to be understoood that by the time the sensor responds the door will have significantly collapsed, and the interior of the door will be extremely close to the person sitting inside the car. Thus the bag must be inflated extremely rapidly if it is .to be of any real use. It is also to be appre¬ ciated that the ideal location for such an inflatable padding is within the door itself, and thus the bag needs to be extremely compact when de-flated, and the associated gas generator must be small. It has been found that the pressure within such an inflated padding should be somewhat higher than in a conventional air-bag, preferably in the region of 1-2 bars. It has also been proposed to use cellulose nitrate for a gas generator in an air-bag. British Pat¬ ent Specification 1371506 discloses such an arrangement in which 75 grams of propellent are utilised, consisting principally of a mixutre of nitro glycerine and nitro cellulose. Such a propellent will produce gas having a volume of approximately 180 litres when ignited. The gas produced is toxic and thus the arrangement disclosed in the British Patent Specification includes means pro¬ vided to avoid problems that may arise if the toxic gas emer'ges from the bag and is breathed by people res¬ trained by the bag. In the Specification there is a teaching that a vapourisable cooling liquid should be provided, which effects purification of the combustion gases by oxidation of the toxic constitutes thereof to form non-gaseous products. The apparatus disclosed is therefore relatively complicated. According to this invention there is provided a gas generator unit for an inflatable safety arrangement in a motor vehicle, said gas generator comprising at least one cellulose nitrate charge, means to ignite the charge and means to direct gas from the charge., when ignited, to the interior of an inflatable bag or the like, the charge of cellulose nitrate having a mass of less than 10 grams. Since a charge of nitro cellulose of less than 10 grams is utilised, the amount of toxic gas that is generated is not very great, perhaps up to 30 litres by volume at the pressure at which the gas is supplied to the air-bag. This is not a sufficient volume of gas, even though it is toxic, to harm a person, even if the gas should escape from the safety arrangement. Preferably the gas generator unit comprises a tube, with a number of holes formed in it along its length, said charge being mounted on the tube to direct gas from the charge, when ignited, to the interior of the tube, so that the gas can pass through the holes into said inflatable bag. Conveniently two said charges are provided, each charge being mounted on a respective end of the tube. Advantageously the or each charge is ignited by means of an electric ignitor. Preferably each ignitor is surrounded by gun powder which is embedded in the cellulose nitrate. Conveniently wherein the holes are spaced apart along the tube in a single line, the axis of at least some holes being inclined to the axis of the tube. Preferably the number of holes is between five holes and twenty holes. Conveniently the total area of the holes is se¬ lected to be between 20 and 100 millimetres square. Preferably the total charge of cellulose ni¬ trate is between 1 and 7 grams. The generator may be a gas generator unit in combination with an inflatable padding which initially surrounds the exterior of the tube. Said inflatable padding, when inflated may have a volume of between 5 and 25 litres. 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 perspective view of an inflatable padding in accordance with the invention when inflated with parts thereof cut away, FIGURE 2 is an enlarged view of an end portion of a tube forming part of the gas generator for the in¬ flatable padding of Figure 1 , prior to inflation of the bag, FIGURE 3 is a top plan view of a door provided with an inflatable bag in accordance with the invention, when inflated, and FIGURE 4 is a vertical sectional view taken through the door of Figure 3 > illustrating the bag when inflated. Referring initially to Figures 1 and 2, an in¬ flatable padding incorporating a gas generator in accordance with the invention consists of a bag 1 which, when inflated, has a volume of between 5 and 25 litres. Contained within the bag is a gas generating unit 2. The gas generating unit 2, as can be seen more clearly in Figure 3 » comprises an elongate tube 3 - Formed within the surface of the tube 3 are a plurality of apertures 3' > arranged in a linear manner. Each ap¬ erture 3' is inclined to the longitudinal axis of the tube 3- Mounted on each end of the tube 3 is a gas gen¬ erating element 4. Each gas generating element 4 com¬ prises a housing 5 mounted on the end of the tube 3 - A breakable seal 6, for example formed of plastics mat¬ erial is provided between the end of the tube 3 and the interior of the housing 5. The Interior of the hous¬ ing 5 is substantially filled with cellulose nitrate 7 which is retained in position by the seal 6, and em¬ bedded within the cellulose nitrate is a charge of gun powder 8 within which is embedded an electrical Ig¬ nitor 9 having leads 10 which pass through the housing 5 to an appropriate ignition circuit. In a typical embodiment of the invention the tube 3 has a length of 20 centimetres and a diameter of 2 centimetres, with twelve holes 3' being provided at spaced apart positions in a single line extending along the tube, each hole having a diameter of 3 millimetres. It is to be understood, however, that the number of holes may be selected between five holes and twenty holes, and the total area of the holes may be in the region of 20-100 mm . In the illustrated embodiment the axis of each hole 3' is inclined to the axis of the tube 3. The width of the bag 1 when inflated is greater than the length of the tube 3. The holes 3' are in¬ clined to the axis of the tube to direct gas into that part of the bag that extends beyond the end of the tube, thus ensuring that the bag is fully inflated as swiftly as possible. It is envisaged that the charge of cellulose nitrate within each of the gas producing elements will be ignited simultaneously by a signal from the ignition circuit, and the cellulose nitrate will burn very swiftly to produce carbon monoxide and carbon dioxide. The cellulose nitrate does not produce any slag dust. Because no slag dust is produced in igniting the charge there is no need to provide a filter con¬ struction, and this enables the gas generator to be relatively slim, thus facilitating the mounting of the gas generator within a door 11 of a motor vehicle as illustrated in Figures 3 and 4. The fact that there are two gas generating ele¬ ments mounted on opposed ends of the tube means that no re-coil is experienced when the gas elements are ignited because the two charges effectively balance each other. It has been found that 1 gram of cellulose ni¬ trate will provide approximately 4 or 5 litres of gas, that is to say approximately four times as much gas for the same amount of charge as compared with the con¬ ventional pellets. Consequently for the described in¬ flatable padding which has a volume of between 5 and 25 litres a charge of between 1 and 7 grams is required. Embodiments of the invention may have a charge of up to 10 grams. The cellulose nitrate burns rapidly, filling the inflatable padding in a time period of 5-10 ms. In the most preferred embodiment of the inven¬ tion the volume of the inflatable padding is 10 litres and the weight of the charge is 2.5 grams. It is to be understood that the inflatable padding, as described, will, when inflated, contains a poisonous gass, namely carbon monoxide. The body can tolerate a certain amount of carbon monoxide if it is only present for a brief period of time. Whilst it is envisaged that some carbon monoxide may leak out of the inflatable padding as described it is not thought that this leakage of potentially poisonous gas will, in actual fact, cause any harm to passengers restrained by the inflatable padding.

Claims: CLAIMS : 1. A gas generator unit for an inflatable safety arrangement in a motor vehicle, said gas generator com¬ prising at least one cellulose nitrate charge, means to ignite the charge and means to direct gas from the charge, when ignited, to the interior of an inflatable bag or the like. 2. A gas generator unit according to Claim 1 wherein the gas generator unit comprises a tube, with a number of holes formed in it along its length, said charge being mounted on the tube to direct gas from the charge, when ignited, to the interior of the tube, so that the gas can pass through the holes into said in¬ flatable bag, the charge of cellulose nitrate having a mass of less than 10 grams. 3. A gas generator according to Claim 2 wherein two said charges are provided, each charge being mounted on a respective end of the tube. 4. A gas generator according to any one of the preceding Claims wherein the or each charge is ignited by means of an electric ignitor. 5. A gas generator according to Claim 4 wherein each ignitor is surrounded by gun powder which is em¬ bedded in the cellulose nitrate. 6. A gas generator according to Claim 2 or any Claim dependent thereon wherein the holes are spaced apart along trie tube in a single line, the axis of at least some holes being inclined to the axis of the tube. 7. • A gas generator unit according to Claim 2 or any Claim dependent thereon wherein the number of holes is between five holes and twenty holes. 8. A gas generator unit according to Claim 2 or any Claim dependent thereon wherein the total area of the holes is selected to be between 20 and 100 milli¬ metres square. 9. A gas generator unit according to any one of the preceding Claims wherein the total chasrge of cellu¬ lose nitrate is between 1 and 7 grams. 10. A gas generator unit according to any one of the preceding Claims in combination with an inflatable padding which initially surrounds the exterior of the tube. 11. A gas generator unit according to Claim 10 wherein said inflatable padding, when inflated, has a volume of between 5 and 25 litres.

Inventors: OLSSON JAN, SKOETTE LARS-GUNNAR, OLSSON, JAN, SKOETTE, LARS-GUNNAR
Applicants: AUTOLIV DEV, AUTOLIV DEVELOPMENT AB
Application year: 1989
Main classification: B60R21
IPC codes: B60R21, C06D5