Patent Abstract:
A vehicle occupant restraint system has a gas generator and a gas bag. A method for inflating a gas bag for restraining an occupant comprises the following steps: providing a gas generator for producing gas which is flowingly connected to the gas bag, providing at least one propellant charge within the gas generator, providing at least one igniter within the gas generator, the gas generator blowing gas into the gas bag over more than one second, preferably over more than three seconds, in order to achieve a high service time.

Full Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a method for inflating a gas bag, a gas generator to carry out the method and an inflatable vehicle occupant restraint system operating by means of the proposed method.  
         BACKGROUND OF THE INVENTION  
         [0002]    Vehicle occupant restraint systems comprising a gas generator and a gas bag are usually constructed such that the gas bag is inflated by the gas generator within a few milliseconds and the gas bag provides its protective effect after approximately 20 ms. This protective effect is, however, maintained only over a few milliseconds. Then the gas bag collapses. In so-called window bags, i.e. gas bags which cover the side windows of a vehicle across a large area, the so-called service time of the gas bag, i.e. the time during which it remains inflated and offers a protective effect, is extended in that the gas bag is constructed in a gas-tight manner. This gas-tightness is, however, only to be achieved with a high expenditure. A disadvantage also is that the inflated gas bag can be a hindrance when rescuing or on leaving the vehicle.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    The invention provides a method which provides for longer service times in a more reliable manner and avoids the above disadvantages. The method for inflating a gas bag according to the invention comprises the following steps: providing a gas generator for producing gas which is flowingly connected to said gas bag, providing at least one propellant charge within the gas generator, providing at least one igniter within the gas generator, the gas generator blowing gas into the gas bag over more than one second. The method, therefore, follows a contrary direction to the prior art, by not exclusively providing the entire quantity of gas within the shortest period of time, but rather by, for the first time, permanently blowing gas into the gas bag over a very long period of time until after the first contact of the occupant with the gas bag (primary impact). The invention is not only limited to side gas bags, rather the method is also able to be used in drivers&#39;, passengers&#39; and knee gas bags.  
           [0004]    Preferably the gas generator will provide so much gas after its activation that within a maximum of 30 ms, preferably 20 ms after activation of the gas generator, the gas bag is fully inflated.  
           [0005]    Through the method proposed, such great demands with respect to tightness no longer have to be made on the gas bag, in order to increase its service time. Furthermore, it is possible that the gas bag automatically collapses after a few seconds and hence it is no longer a hindrance when the occupant is being rescued or when he is climbing out of the vehicle.  
           [0006]    To carry out the method proposed, it is theoretically possible to use gas generators which provide the entire quantity of gas rapidly and introduce it into an intermediate reservoir which directs the gas to the gas bag with the desired chronological sequence.  
           [0007]    Preferably, however, the method is carried out by means of one gas generator which for its part produces gas over more than one second, preferably even over three or five seconds. This time is the total time within which gas is blown out from the gas generator, it of course being possible that a plurality of propellant charges is used and between the igniting of individual propellant charges a specific time elapses, within which no gas flows out from the gas generator and within which therefore also no gas is generated.  
           [0008]    As explained, the gas generator proposed is equipped with at least one propellant charge and at least one igniter, the propellant charge having such a nature and being accommodated in the gas generator such that it generates gas over more than one second, preferably over more than three or even more than five seconds. With three seconds, sufficient restraining energy is still made available in particular for a secondary impact; with five seconds, a sufficient protective effect is still present even in the case of a roll-over of the vehicle.  
           [0009]    The gas generator proposed preferably has several propellant charges which are able to be activated chronologically in succession and which preferably are comprised of different fuels.  
           [0010]    According to the preferred embodiment, a propellant charge is ammonium nitrate, a particularly slow-burning fuel.  
           [0011]    The propellant charge of ammonium nitrate forms a propellant charge which is to be ignited after a primary propellant charge.  
           [0012]    Preferably the gas generator is constructed such that the propellant charge to be ignited subsequently burns at a maximum of 2 bar combustion pressure, in order to thus ensure a slow burning. 2 bar is approximately the pressure inside the gas bag, which is necessary for restraining. This is therefore deliberately far from the higher combustion pressures usual hitherto, which are present on burning of the propellant charge.  
           [0013]    The propellant charge which is to be activated first is constructed such and accommodated in the gas generator such that it burns completely within a maximum of 30 ms and therefore provides the quantity of gas necessary for the primary impact.  
           [0014]    The propellant charge or propellant charges which are to be activated subsequently have either their own igniters or ignite by auto-ignition and staggered over time due to they being heated, so that a so-called ignition transfer takes place.  
           [0015]    The propellant charge or propellant charges which are subsequently to be activated are preferably insulated thermally with respect to other propellant charges, although they are arranged for example adjoining each other. Thereby, the staggering of time on igniting of the individual propellant charges is to be achieved or increased. A thermally insulating wall and a thermally insulating packing in which the propellant charge is accommodated are provided for this. The thermal insulation is to be constructed such that only at the end or, preferably, after the end of the burning of the fuel of the previously activated propellant charge does the auto-ignition of the following propellant charge take place.  
           [0016]    The inflatable vehicle occupant restraint system proposed, which operates by the method proposed, provides a gas generator and a gas bag which is inflated by the gas generator. The fabric and the coating of the gas bag are coordinated with the gas generator with regard to their gas-permeability such that the gas bag has a service time of at least three seconds. The service time should be defined by the time the gas bag has at least approximately 2 bar internal pressure.  
           [0017]    Preferably, however, a service time of six seconds is provided. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 shows a vehicle occupant restraint system operating in accordance with the method according to the invention, with a first embodiment of the gas generator according to the invention,  
         [0019]    [0019]FIG. 2 shows a longitudinal sectional view through a second embodiment of the gas generator according to the invention,  
         [0020]    [0020]FIG. 3 shows a longitudinal sectional view through a third embodiment of the gas generator according to the invention,  
         [0021]    [0021]FIG. 4 shows a longitudinal sectional view through a fourth embodiment of the gas generator according to the invention and  
         [0022]    [0022]FIG. 5 shows a longitudinal sectional view through a fifth embodiment of the gas generator according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    In FIG. 1 a vehicle occupant restraint system is illustrated, which has a gas generator  10  and a gas bag  12 , connected with it with regard to flow and able to be inflated by it. The gas bag  12  is a so-called window bag, i.e. a side gas bag having a large area and covering the side windows of the vehicle in the case of restraint. In FIG. 1 it is shown that the gas generator  10  is arranged inside the gas bag  12 , but it is also possible to connect gas generator  10  and gas bag  12  with each other with regard to flow via a gas-directing pipe.  
         [0024]    The gas generator  10  is an elongated tubular gas generator, at one axial end of which an igniter  14  is arranged, which is connected with a control unit  16  which activates the igniter  14 . A so-called primary propellant charge  18  which adjoins the igniter  14  and is to be ignited first in the case of restraint, consists of rapidly burning fuel in tablet form. The propellant charge  18  is accommodated in a combustion chamber  20 . A conical filter cone  22  projecting into the interior of the combustion chamber  20  separates an expansion chamber  24  from the combustion chamber  20 . Adjoining the expansion chamber  24  is a filter chamber  26  with cylindrical filters  28 , in the outer region of which filter chamber the outer housing of the gas generator  10  has numerous outflow openings. Adjoining the axial end of the gas generator  10  opposed to the igniter  14  is a second propellant charge  30  which is to be ignited after the primary propellant charge  18 , which second propellant charge  30  is likewise in flow connection with the filter chamber  26  but in the non-activated state is separated from the filter chamber  26  by a thermally insulating wall  32 .  
         [0025]    The gas bag  12  is coated on the inner face for example by means of a foil and is constructed such as to be almost (e.g. in parts) or completely gas-tight.  
         [0026]    In the case of restraint, the gas generator inflates the gas bag according to the following method. The igniter  14  is activated and ignites the primary propellant charge  18 . The fuel burns within a few milliseconds and the generated gas flows via the conical filter  22  with a large area very rapidly into the expansion chamber  24  and the filter chamber  26  and arrives through the filter  28  into the gas bag  12 . The gas generator here provides a quantity of gas within a few milliseconds, which fully inflates the gas bag in approximately 20 ms. After the complete burning of the fuel of the propellant charge  18 , the propellant charge  30  ignites itself. This takes place in that the housing and also the wall  32  heat up intensively with the outflow of the gas. With a specific chronological delay, this heat also arrives at the propellant charge  30 , until the latter ignites itself. The propellant charge  30  has a fuel which burns substantially more slowly than that of the propellant charge  18 . The propellant charge  30  preferably consists of the very slow-burning ammonium nitrate. The wall  32  is constructed with regard to its thermally insulating characteristics such that it directs to the propellant charge  30  in less than one second that amount of energy which is necessary for auto-ignition of the propellant charge  30 . The latter then burns over more than one second, even preferably more than three seconds. The gas thus generated likewise arrives into the gas bag  12  via the filter chamber  26 . The gas generator  10  consequently blows gas into the gas bag  12  over more than one second, preferably over more than three seconds, which gas bag  12  has a correspondingly long service time.  
         [0027]    The gas-permeability of the gas bag and the gas generator are coordinated with each other such that the gas bag has a service time of more than three seconds, which means that it develops a protective effect over more than three seconds and in so doing preferably has more than 2 bar internal pressure.  
         [0028]    The burning of the fuel of the propellant charge  30  takes place with a combustion pressure of a maximum of 2 bar, whereby the burning time can be very long.  
         [0029]    In the embodiments according to FIGS.  2  to  5 , for simplification the gas bag is no longer illustrated. For all the parts already explained hitherto, which also have a corresponding function in the following embodiments, the reference numbers already introduced are maintained. If the function or construction of the parts is different compared with the embodiment according to FIG. 1, then the corresponding parts are given a reference number increased by the number  100 .  
         [0030]    In the embodiment according to FIG. 2, the filter chamber  26  is arranged at the opposite end of the gas generator  110  to the igniter  14 . The combustion chamber  120  not only contains the primary propellant charge  18  but also propellant charges  130 ,  130 ′ and  130 ″ which are subsequently to be ignited and which are constructed in a ring shape and extend around the conical filter  122 . The individual propellant charges  130  to  130 ″ differ from each other in the geometry and/or the fuel composition.  
         [0031]    After the igniting of the propellant charge  18 , the gas flows via the tip of the filter  122  into the expansion chamber  24  and the filter chamber  26 , from where it arrives into the gas bag and fully inflates the latter within a few milliseconds. During or at the end of the burning of the fuel of the propellant charge  18 , through the generated hot gas the propellant charge  130 , which is subsequently to be activated, is ignited. The corresponding gas likewise arrives via the filter  122  into the expansion chamber  24  and the filter chamber  26 . The burning time of the fuel of the propellant charge  130  is, however, distinctly higher than that of the fuel of the propellant charge  18 , so that over approximately one second gas is generated by the propellant charge  130 . After the propellant charge  130  is burnt, the propellant charge  130 ′ arranged adjacent and then the propellant charge  130 ″ is activated, so that a gradual burning of the propellant charges takes place and the gas generator  110  conveys gas into the gas bag over more than three seconds. Through the provision of still more propellant charges, the inflation time and hence the service time of the gas bag is increased to more than five or six seconds, which is sufficient to also offer protection in a rollover of the vehicle.  
         [0032]    In the embodiment according to FIG. 3, a single propellant charge  230  to be subsequently ignited, is accommodated in a thermally insulating packing  40 . The propellant charge  230  is cylindrical in construction and has an axially through-opening  42 . The propellant charge  230  adjoins the igniter  14 , but is arranged in the combustion chamber  220  as in the embodiment according to FIG. 2. The primary propellant charge  18  adjoins the propellant charge  230 .  
         [0033]    Through the opening  42 , the igniter  14  ignites the fuel of the propellant charge  18 . The generated gas arrives through the filter  222  into the expansion chamber  224  and from there into the filter chamber  26 . The packing  40  is constructed such that on igniting of the propellant charge  18 , no auto-ignition of the propellant charge  230  takes place. Only after the fuel of the propellant charge  18  is burnt does so much thermal energy arrive at the propellant charge  230  via the packing  40  that the propellant charge  230  ignites itself with a predeterminable time delay. Gas is generated over several seconds on burning of the fuel of the propellant charge  230 , which keeps the gas bag inflated.  
         [0034]    In the embodiment illustrated in FIG. 4, several propellant charges  330 ,  330 ′,  330 ″ are provided, spaced apart from each other by thermally insulating walls  44 . Also in the region of the opening  42 , the propellant charges  330  to  330 ″ are thermally insulated, so that they ignite themselves in succession, staggered chronologically, after the propellant charge  18  has been activated. In this embodiment, service times of six seconds and more are able to be achieved for the gas bag, and the gas generator generates gas over more than five seconds.  
         [0035]    In the embodiment illustrated in FIG. 5, a primary propellant charge  18  and a propellant charge  430 , which is to be ignited subsequently, are each equipped with one own igniter  14 ,  14 ′. The propellant charges  18 ,  430  are separated from each other via a wall  50 . The propellant charge  18  serves for making the gas bag available quickly. Staggered chronologically to this, via the igniter  14  the propellant charge  430  is ignited, which consists of a very slow-burning fuel and provides for a long service time of the gas bag. In this embodiment, separate combustion chambers are provided for the individual propellant charges.

Technology Classification (CPC): 1