CONTROLLABLE GAS GENERATOR, FOR INSTANCE FOR AN AIRBAG

Abstract: A controllable gas generator, for instance for an airbag, comprising at least one holder provided with at least one orifice, which orifice is provided with a closing means, which closing means can be removed by combustion of a propelling charge, and a method for controlling the amount of gas which is generated by a gas generator, wherein the desired mass flow is set with the aid of a measuring and calculating system, depending on external factors, subsequently the number of orifices to be opened is determined, and this number is opened by combustion of the propelling charge.

Description: Title: Controllable gas generator, for instance for an airbag. This invention relates to a controllable gas generator, for instance for an airbag. This invention also relates to a method for controlling the amount of gas which is generated by a gas generator. An airbag system generally comprises at least a diagnostic module and an airbag module. The airbag module consists of an inflatable bag and a gas generator or inflator. The gas generator consists of means providing for the release of a gaseous substance and a gas-forming substance (main charge). This gas-forming substance can be stored in the gas generator both in solid form (propelling charge) and in gaseous or liquid form (for instance compressed gases). A collision is sensed by crash sensors, which give a signal to the diagnostic module. The diagnostic module assesses on the basis of an integrated algorithm whether the airbag should go off. In general, the diagnostic module is set such that the airbag is activated in case of speeds exceeding the range of 16-19 km/h. If this is the case, the module sends an electrical signal to the means providing for the release of the gaseous substance to the inflatable bag. In the case of propelling charges, this can be an ignition mechanism, while in the case of compressed gases, a control valve or a breaking plate or other means that can provide for the release of the gas can be used. The ignition thereupon ignites the main charge of the inflator, or, in the case of compressed gases as main charge, by opening the valve or the breaking plate an orifice is cleared which passes the gas to the inflatable bag. The released gases of the ignited main charge thereupon inflate the airbag. The airbag thereupon damps the movement the body makes as a result of the collision. Directly following this, the airbag deflates again through the presence of blowout holes or through the porosity of the fabric of the airbag. The extent to which the airbag is inflated thus depends on. the net mass flow. The net mass flow is defined by the amount of gas flowing in per unit time less the amount of gas flowing out per unit time. In view of the effects that collisions at high speed can have on the human body, and the rate at which this occurs, it is requisite that an airbag can be rapidly inflated. For the mechanisms providing for the inflation of the airbag, this means that they must have a short response time. It is also requisite that the inflation or filling of the airbag can take place in a very short time. These times are generally of the order of milliseconds. A typical time for an airbag to be inflated to its full size is about 5-80 milliseconds. The effect of a collision on a body is a function of a large number of variables, such as the speed of collision, the manner of colliding, collision into a hard or a soft object, and body-dependent variables such as position, height and weight. Naturally, the presence of a body is also relevant for whether or not the airbag is inflated. This results in a large variety of conditions in a collision. To make better provision for this variety of collision conditions, it is desirable to control the amount of damping of the airbag and hence the rate at which the cushion is inflated. The control of the mass flow of an airbag is subject to equally stringent requirements as is the above-described airbag inflation. For the mechanisms controlling the mass flow, this means that the response time of such systems must be of the same order of magnitude as that of the airbag described above, that is, of the order of milliseconds, while further the total time needed for inflating the airbag may not be subject to any essential modification. To that end, measures have previously been proposed, such as described, for instance, in US 5,690,357. Also known are measures utilizing an airbag containing two pyrotechnic charges of different capacity which can be separately ignited. Through the variation in ignition possibilities (small capacity, large capacity or both), it is then possible to obtain three increasingly stronger impact- decelerating effects of an airbag. At the instant of collision, the desired impact deceleration is determined and thereupon it is determined which combinations are ignited. A disadvantage of the above-mentioned measure is that it allows only a limited control of the impact-decelerating effect. Moreover, the determination of the desired impact-decelerating effect in the prior art is basically a static control. Static control means that at the moment of impact the desired impact-decelerating power is determined a single time, and then the airbag is inflated. It is therefore an object of the invention to arrive at a better controllable impact deceleration of an airbag. It is not uncommon that during the collision changes occur in the conditions and hence in the variables. There are ongoing developments towards fitting the diagnostic module with a dynamic control. This means that at any time during the collision the variables can be determined and can be processed by the diagnostic module. It would then be desirable if the impact deceleration of the airbag could be adjusted to these changed conditions. Another disadvantage of the above-described measures is therefore that after the ignition of the pyrotechnic charges referred to it is not possible to adjust the impact-decelerating activity of the airbag during the collision. It is therefore another object of the invention to arrive at an airbag which can be controlled at more times, and also otherwise to overcome disadvantages of the prior art and to achieve a gas flow from the gas generator which is better controllable and controllable at more times. The inventors have now found that a controllable gas generator is obtained by providing one or more closing means on a holder of a gas generator, which closing means are removable by means of a propelling charge. The invention is characterized by a controllable gas generator comprising at least one holder provided with at least one orifice, which orifice is provided with a closing means, which closing means can be removed by combustion of a propelling charge. A propelling charge for removing the closing means is understood to mean a propellant. This propellant is a substance or a mixture of substances whereby energy is obtained from oxidation or decomposition or a combination thereof, while the energy is not obtained through a decomposition of the substances as a result of a shock wave. The propelling charge in the closing means can be selected, according to the invention, from blasting powder, sodium azide, PNC/KP, gunpowder/ blasting powder (single base, double base or triple base), black gunpowder and any other substance or mixtures of substances whereby energy is obtained from the oxidation or decomposition or a combination thereof. A propelling charge such as it is used to fill the airbag with gas is a gas-generating propellant. The propelling charge for removing the closing means and the propelling charge for generating gas can have a different or the same composition. In this connection, the term 'removing' the closing means should be taken to mean the physical breaking of the connection, as opposed to, for instance, the opening of a valve. A preferred embodiment concerns a gas holder where two or more orifices are present, which are all provided with the closing means referred to. In a preferred embodiment, the closing means are of the same diameter. In order to create a greater variety of mass flow control possibilities, a preferred embodiment is possible in which the orifices in the holder are of mutually the same or mutually different diameter or groups of different diameter and naturally the closing means have been adapted accordingly. In a collision, the desired impact-decelerating effect is determined by the control mechanism in the diagnostic module of the airbag. The control mechanism of the airbag comprises a measuring and calculating system which, depending on a number of factors, drives the control of the airbag. The measuring system comprises a number of sensors or other means for collecting information about external factors that are relevant to the functioning of the airbag. Examples of such factors are speed of the vehicle, presence, position, height and weight of the body, deceleration during the collision, and the like. This information is then processed in a calculating system. From the calculating system, the drive of the gas generator is controlled for achieving the desired mass flow. In order to achieve the desired impact-decelerating effect, in a further embodiment of the invention, the orifice in the holder is opened by removing the closing means. By igniting the propelling charge, the closing means are removed and the orifices opened, so that the airbag is inflated with the gases generated in the gas generator. In a preferable preferred embodiment, the closing means are removed by igniting propelling charge, with the propelling charge being caused to combust by an electronic ignition. To that end, in the closures, or in the holder adjacent the closures where the propelling charge is located, electrical means are provided, which can cause the ignition of the propelling charge. These electrical means are driven by the control mechanism of the airbag. The closures such as they are used in an embodiment of the present invention can be provided on the orifices in the holder in any suitable manner. Preferred, however, are the manners whereby the closing means of the orifice is mounted by means of a screw thread, a bayonet catch, a clamping system, a snap lock, a glued joint, or a combination of two or more of these systems. Accordingly, when removing the closing means, the connection between (the edge of) the orifice on the one hand and the closing means (cap) is broken. It is preferred to manufacture the closing means from a material that is resistant to the conditions that occur during the functioning of an airbag and simultaneously enables a simple construction, while the closing means should further be simple to remove. Also factors such as reliability and cost play a non-negligible role in the choice of the suitable material. Preferred, accordingly, are means where the closure is manufactured from ceramic materials, metal or plastic, preferably from PNC, polyethylene, polypropylene. In a preferred embodiment of the present invention, the orifice and the closing means as well as the propelling charge for removing the closing means are tailored to each other, such that the orifice is provided with an internal thread and the closure consists of a head and a bolt-shaped part, which bolt-shaped part is provided with thread, which bolt-shaped part has been fitted in the orifice, and the diameter of the head thereof being greater than the diameter of the orifice, which head is internally provided with a space for the propelling charge, as well as with means for causing the propelling charge to combust. The design of the head of the closing means is ceteris paribus also applicable to the other fastening methods for the closing means as described above. Accordingly, the invention further comprises a gas generator provided with two or more orifices, and with means for controlling the number of orifices that is opened by means of propelling charge. An embodiment of the present invention accordingly comprises a gas generator where the control mentioned is controlled on the basis of the desired mass flow. Thus, the invention further relates to a method for controlling the amount of gas that is generated by a gas generator, wherein the desired mass flow is set by means of measuring and calculating system, depending on external factors, subsequently the number of orifices to be opened is determined, and this number is opened through combustion of the propelling charge. If the conditions of the collision or the other variables change and hence the desired effect of the airbag is to be adjusted, this can be done by opening the orifices in the holder by removing more closing means. This renders the impact-decelerating effect of the airbag better controllable. In the use of solid propellants, generally an orifice for the generated gas, which is not closed off by a closing means as described in the present invention, is already present in the holder for the non-controlled discharge of the gases. Accordingly, the invention also relates to the presence of additional more closed orifices which, if necessary, can be opened in the manner indicated elsewhere in this description. In the use of gaseous propellants, such an orifice for the generated gas is, of course, by principle absent in the holder. Accordingly, the invention also relates to the presence of several closed orifices which can be opened according to need. Accordingly, the invention also relates to a method in which through determination of the external factors it is established whether the mass flow which is generated needs to be adjusted, and, if necessary, the amount of gas is adjusted by opening more orifices. The holder of the controllable gas generator is filled with a compressed or liquid gas or a solid or liquid propelling charge or a combination of two of the three (gas, solid or liquid propelling charge). In a preferred embodiment, the holder is filled with a compressed gas. Through removal of the closing means, a certain flow of gas is released; through the removal of more closing means the mass flow increases and the airbag is inflated more rapidly. The impact-decelerating effect of the airbag thereby increases. In another embodiment, the holder is at least partly filled with a solid propelling charge. The rate of combustion of propelling charge is dependent on the pressure during the combustion. With some propelling charges, a high pressure results in a rapid combustion, while a lower pressure provides for a slower combustion. As a consequence, the amount of gas generated per unit time is dependent on the pressure in the holder in which the igniting propelling charge is contained. By opening more orifices in the holder, the pressure in the holder is reduced and hence the rate of combustion of the propelling charge will decrease. As a result, less gas is generated per unit time, the mass flow decreases and the airbag will be inflated less rapidly. Thus, the impact-decelerating effect of the airbag is reduced. There are also propelling charges known which have opposite properties, that is, exhibit a negative pressure dependence. Upon opening of more orifices and the attendant pressure decrease, these propelling charges will combust faster, so that the airbag is inflated faster. The present invention has a preferred embodiment in which a gas generator based on a solid propelling charge is used, and the mass flow generated is modified by opening more orifices, the orifices in the holder being of mutually the same or different diameter or groups of different diameter.

Claims: Claims 1. A controllable gas generator, for instance for an airbag, comprising at least one holder provided with at least one orifice, which orifice is provided with a closing means, which closing means can be removed by combustion of a propelling charge. 2. A gas generator according to claim 1, wherein two or more orifices are present, which are all provided with said closing means. 3. A gas generator according to claim 1 or 2, wherein said closing means are of equal diameter. 4. A gas generator according to claims 1-3, wherein the orifices in the holder are of mutually the same or different diameter or groups of different diameter. 5. A gas generator according to claims 1-4, wherein in the holder a compressed gas, a solid or liquid propelling charge or a combination of two of the three is present. 6. A gas generator according to claims 1-5, wherein the orifice in the holder is opened by removing the closing means. 7. A gas generator according to claims 1-6, wherein the propelling charge is caused to combust through an electronic ignition. 8. A gas generator according to claims 1-7, wherein the closing means of the orifice is mounted by means of a screw thread, a bayonet catch, a clamping system, a snap lock, a glued joint, or a combination of two or more of these systems. 9. A gas generator according to claims 1-8, wherein the orifice is provided with an internal screw thread and the closure consists of a head and a bolt-shaped part, which bolt-shaped part is provided with screw thread, which bolt-shaped part is fitted in the orifice, and the diameter of the head thereof being greater than the diameter of the orifice, which head is internally provided with a space for a propelling charge, and with means for causing the propelling charge to combust. 10. A gas generator according to claims 1-9, which is provided with two or more orifices, and with means for controlling the number of orifices that is opened by means of the propelling charge. 11. A gas generator according to claim 10, wherein said control is controlled on the basis of the desired mass flow. 12. A gas generator according to claims 1-11, wherein the propelling charge in the closure is selected from blasting powder, sodium azide, PNC/KP, gunpowder/blasting powder (single base, double base or triple base) or black gunpowder. 13. A gas generator according to claims 1-12, wherein the closure is manufactured from ceramic materials, metal or plastic, preferably from PNC, polyethylene, polypropylene. 14. A method for controlling the amount of gas which is generated by a gas generator according to claims 1-13, wherein the desired mass flow is set with the aid of a measuring and calculating system, depending on external factors, subsequently the number of orifices to be opened is determined, and this number is opened by combustion of the propelling charge. 15. A method according to claim 14, wherein through continuous determination of the external factors, it is established whether the mass flow which is generated is to be adjusted and, if necessary, the amount of gas is adjusted by opening more orifices. 16. A method according to claim 14 or 15, wherein a gas generator on the basis of a sohd propelling charge is employed, and the generated mass flow is modified by opening more orifices. 17. An airbag comprising a gas generator according to claims 1-13 and an inflatable bag connected with said orifice or orifices of the gas generator.

Inventors: VAN DEN BERG RONALD PETER, VAN DEN BERG, RONALD, PETER
Applicants: DEN BERG RONALD PETER VAN, TNO, NEDERLANDSE ORGANISATIE VOOR TOEGEPAST-NATUURWETENSCHAPPELIJK ONDERZOEK TNO, VAN DEN BERG, RONALD, PETER
Application year: 2000
Main classification: B60R21
IPC codes: B60R21