Process for deploying air bag in air bag device

[0002] The present invention relates to an air bag device designed so that an air bag is expanded by a gas, generated by a gas generating means, upon collision of a vehicle, to hold back an occupant.

[0003] An inflater mounted in an air bag device for an automobile is generally adapted to generate a high-pressure gas by burning of a gas generating agent. The profile of the amount of gas generated per unit time by the inflater is such that the amount of gas generated is steeply increased simultaneously with the ignition and, after reaching a peak value, gently decreased. However, when the air bag is expanded by the inflater having such an output profile, the following problem is encountered: the air bag is suddenly deployed, thereby making it difficult to gently hold back the occupant.

[0004] There are air bag devices known from Japanese Patent Application Laid-open Nos. 2-293234 and 2-310143 and Japanese Patent Publication No. 52-44094, each of which includes a plurality of inflaters mounted so that they are operated with time lags, thereby preventing the sudden deployment of the air bag.

[0005] To moderate the shock received by an occupant upon deployment of the air bag, it is preferable that the output profile of the inflater is changed from having a peaky characteristic to having a flat characteristic.

[0006] The present invention has been accomplished with the above circumstance in view, and it is an object of the present invention to ensure that in an air bag device including two gas generating means providing different outputs, the timing of the ignition of two gas generating means are appropriately controlled to moderate the shock received by an occupant upon deployment of the air bag.

[0007] To achieve the above-described object, a process for deploying an air bag is provided in an air bag device comprising gas generating means having an output characteristic that the amount of gas generated per unit time subsequent to an ignition is gradually increased from zero to a peak value and then gradually decreased from the peak value to zero, so that the air bag is expanded by the gas generated by the gas generating means to hold back an occupant, wherein the gas generating means comprises a first gas generating means and a second gas generating means providing the peak value smaller than that of the first gas generating means; the process comprises steps of igniting the first gas generating means upon collision of a vehicle and then, igniting the second gas generating means; timing an ignition of the second gas generating means, so that the sum of the peak value of the output from the second gas generating means and the output from the first gas generating means at the time when such peak value of the second gas generating means is provided, is any one of equal to and smaller than the peak value outputted from the first gas generating means; and timing the ignition of the second gas generating means, before the output from the first gas generating means becomes zero.

[0008] With the above feature, the first gas generating means, providing the larger output, is first ignited upon collision of the vehicle to generate the high-pressure gas, and after such output exceeds the peak value, a first second gas generating means, providing the smaller output, is ignited to generate the high-pressure gas. Therefore, the sum of the outputs from the first and second gas generating means has the peak value, and output characteristic as a whole is flat. Moreover, the second peak value is equal to or smaller than the first peak value, and the generation of the high-pressure gas cannot be intermitted. Therefore, it is possible to prevent the sudden deployment of the air bag to moderate the shock applied to the occupant, while ensuring the smooth deployment of the air bag.

[0009] FIG. 1 is a partial side view of a vehicle having an air bag device mounted therein for a driver's seat.

[0010] FIG. 2 is an enlarged cross-sectional view taken along a line 2—2 in FIG. 1.

[0011] FIG. 3 is a cross-sectional view taken along a line 3—3 in FIG. 2.

[0012] FIG. 4 is a graph showing the output characteristics of a first combustor and a second combustor.

[0013] FIG. 5 is a graph showing the ignition timing and the total output characteristic of the first and second combustors.

[0014] FIG. 6 is a view similar to FIG. 2, but according to a second embodiment.

[0015] The mode for carrying out the present invention will now be described by way of embodiments shown in the accompanying drawings.

[0016] FIGS. 1 to 5 show a first embodiment of the present invention.

[0017] As shown in FIG. 1, an air bag device is mounted within a steering wheel 2 to hold back a driver sitting on a seat 1 upon collision of a vehicle.

[0018] As shown in FIGS. 2 and 3, the steering wheel 2 includes: a steering boss 5 non-rotatably fitted to a rear end of a steering shaft 3 and fixed by a nut 4; an annular wheel rim 6 disposed to surround the steering boss 5; a front cover 7 fixed to the steering boss 5; a rear cover 8 coupled to the front cover 7; and a plurality of spokes connecting the front cover 7 to the wheel rim 6. An air bag module 10 is accommodated in a space defined by the front cover 7 and the rear cover 8.

[0019] The air bag module 10 is comprised of an inflater 11 which generates a high pressure gas, and an air bag 12 which can be expanded by the high pressure gas generated by the inflater 11. The inflater 11 includes a cup-shaped cover member 13, and a mounting flange 13₁is integrally formed on an outer periphery of the cover member 13 and fixed by a plurality of rivets 14 to a mounting flange 8₁which is integrally formed on an inner periphery of the rear cover 8. A first combustor 18aand a second combustor 18b, partitioned by a partition wall 17, are defined within a combustor housing 16 which is fixed to the cover member 13 by a plurality of bolts 15. The volume of the first combustor 18ais set larger than that of the second combustor 18b,and a gas generating agent 19 is filled in each of the combustors 18aand 18bin an amount depending on the volume of the combustors 18aand 18b.

[0020] Igniting agents 20 are disposed within the first combustor 18aand the second combustor 18b,respectively, and tip ends of two ignitors 21, extending from a front surface of the combustor housing 16 into the first combustor 18aand the second combustor 18b,face the igniting agents 20, respectively. The air bag 12 is fixed at its base portion to an outer periphery of the combustor housing 16 by the plurality of bolts 15 in a state in which it surrounds the combustor housing 16. The air bag 12 is accommodated in a folded-up state in a space provided between the combustor housing 16 and the rear cover 8.

[0021] By fixing an outer housing 22 to an outer peripheral surface of the combustor housing 16, an annular space 23 is defined between the combustor housing 16 and the outer housing 22. The annular space 23 communicates with the insides of the first and second combustors 18aand 18bthrough a plurality of gas passages 16₁defined in the outer peripheral surface of the combustor housing 16, and also communicates with an internal space in the air bag 12 through a plurality of gas passages 22₁defined in the outer housing 22. Filters 24 are mounted in the plurality of gas passages 22₁defined in the outer housing 22 for inhibiting dusts generated by combustion of the gas generating agents 19 from being supplied to the air bag 12.

[0022] An ignition control device 26, which receives a signal from an acceleration sensor 25 for detecting an acceleration in a longitudinal direction of the vehicle, expands the air bag 12 by supplying electric current to the two ignitors 21 to operate the inflater 11, when an acceleration equal to or larger than a predetermined value is detected upon collision of the vehicle.

[0023] When the gas generating agents 19, filled in the first combustor 18a,are ignited and burned, the amount of gas generated per unit time (i.e., the output from the first combustor 18a) is gradually increased from 0 (zero) toward a peak value Ma and then gradually decreased from the peak value Ma toward 0, as shown in FIG. 4, and hence, an entirely mountain-shaped output characteristic is obtained. Since the volume of the first combustor 18ais set larger than that of the second combustor 18band the gas generating agents 19 are filled in both the combustors 18aand 18bin the amount depending on the volume of the combustors 18aand 18b,as described above, the mountain shape of the output characteristic of the second combustor 18bis smaller than that of the output characteristic of the first combustor 18a,and the peak value Mb of the output from the second combustor 18bis smaller than the peak value Ma of the output from the first combustor 18a. In the present embodiment, the time points a, when the peak value of the output is provided, as well as the time points b, when the output becomes 0 (zero), are the same in the first and second combustors 18aand 18b,but may be different in the first and second combustors 18aand 18b.

[0024] The operation of the embodiment of the present invention having the above-described arrangement will be described below.

[0025] When the ignition control device 26 has determined a shock equal to or larger than a predetermined value permitting the air bag 12 to be deployed, based on the acceleration signal from the acceleration sensor 25 upon collision of the vehicle, the ignition control device 26 outputs an igniting command to operate the ignitor 21 of the first combustor 18a,whereby the igniting agent 20 is fired to start the burning of the gas generating agents 19. The high-pressure gas generated by the burning of the gas generating agents 19 spread from the gas passages 16₁surrounding the first combustor 18ainto the annular space 23, and is then passed through the filters 24 and the gas passages 22₁in the outer housing 22 and supplied into the air bag 12.

[0026] As shown in FIG. 5A, the first combustor 18ais ignited at the time point 0, and after the output from the first combustor 18areaches the peak value Ma at the time point a, the second combustor 18bis ignited at a time point c by the igniting command from the ignition control device 26. As a result, the high-pressure gas is also generated from the second combustor 18bin addition to from the first combustor 18a,wherein the sum of the outputs from the first and second combustors 18aand 18b,shown by a thick line, is diverted again to increase and reaches a second peak value at a time point a+c when the output from the second combustor 18bbecomes the peak value Mb. The time point c for igniting the second combustor 18bis set so that the second peak value at the time point a+c is equal to the first peak value Ma of the output from the first combustor 18aat the time point a.

[0027] By igniting the first combustor 18aand the second combustor 18bso as to provide the different outputs with a time lag in the above manner, the output profile is flat as a whole, as compared with the case where the first and second combustors 18aand 18bare ignited simultaneously. Thus, it is possible to weaken the shock due to sudden deployment of the air bag. Especially, the output profile can be almost flattened by setting the time point c for igniting the second combustor 18b,so that the first peak value and the second peak value are equal to each other.

[0028] If the time point for igniting the second combustor 18bis earlier than the time point c in FIG. 5A, the second peak value exceeds the first peak value Ma, thereby causing a disadvantage that the deploying speed of the air bag 12, in a moment when the air bag 12 actually contacts with an occupant, is increased, thereby increasing the shock applied to the occupant.

[0029] When the air bag 12 supplied with the high-pressure gas generated by the inflater 11 is expanded, the thinned portion of the rear cover 8 is broken by the pressure of the gas, and the air bag 12 is deployed from an opening in the broken thinned portion to hold back the occupant.

[0030] If the time point c for igniting the second combustor 18bis further latened from the state shown in FIG. 5A, the second peak value is accordingly decreased gradually from Ma toward Mb which is the peak value of the output from the second combustor 18b. However, an effect of weakening the shock due to the sudden deployment of the air bag is still exhibited by providing the first and second peak values having the time lag to the profile of the sum of the outputs from the first and second combustors 18aand 18b. However, if the time point for igniting the second combustor 18bis later than the time point b when the combustion of the first combustor 18ais finished (see FIG. 5B), there is a possibility that the supplying of the high-pressure gas is temporarily intermitted at such time point, thereby causing the deployment of the air bag 12 to be less smooth.

[0031] From the foregoing, it is appropriate that the time point for igniting the second combustor 18bis set between the timing shown in FIG. 5A and the timing shown in FIG. 5B.

[0032] Although the embodiment of the present invention has been described in detail, it will be understood that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the subject matter of the invention.

[0033] For example, in the first embodiment, the air bag device includes the single inflater 11, and the first combustor 18aand the second combustor 18b,constituting the first and second gas generating means, are mounted within the inflater 11. However, as in a second embodiment shown in FIG. 6, a first inflater 11a,providing a larger output, and a second inflater 11b,providing a smaller output, may be separately mounted. In this case, the first inflater 11aconstitutes the first gas generating means of the present invention, and the second inflater 11bconstitutes the second gas generating means of the present invention. In addition, the air bag device for the driver's seat has been illustrated in the embodiment, but the present invention is also applicable to an air bag device for an assistant driver's seat.

[0034] As discussed above, the first gas generating means, providing the larger output, is first ignited upon collision of the vehicle to generate the high-pressure gas, and after such output exceeds the peak value, the second gas generating means, providing the smaller output, is ignited to generate the high-pressure gas. Therefore, the sum of the outputs from the first and second gas generating means has the peak value again, and the output characteristic as a whole is flat. Moreover, the second peak value is equal to or smaller than the first peak value, and the generation of the high-pressure gas cannot be intermitted. Therefore, it is possible to prevent the sudden deployment of the air bag to moderate the shock applied to the occupant, while ensuring the smooth deployment of the air bag.