Automotive air bag system

Abstract: An air bag system for installation in a vehicle is provided which comprises: an inflator (1) comprising an impact sensor (19) capable of measuring the magnitude of an impact exerted on the vehicle; first gas generating means (7,8,9,10) for generating a gas for inflating an air bag; a housing (2) having a wall provided with gas outlet openings (12) through which the gas is jetted into the air bag; gas flow restricting means (15) for restricting the flow of the gas through the gas outlet openings (12) of the housing (2); and second gas generating means (13,14) for operating the gas flow restricting means (15); and a controller (20) for controlling the operation of the first (7,8,9,10) and the second gas generating means (13,14) on the basis of a collision signal provided by the impact sensor (19). The controller (20) initiates the first generating means (7,8,9,10) to inflate the air bag upon the reception of a collision signal provided by the impact sensor (19), initiates the second gas generating means (13,14) to operate the gas flow restricting means (15) so that the rate of flow of the gas into the air bag is limited, when the magnitude of the impact measured by the impact sensor (19) is below a predetermined threshold value.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an automotive air bag system for protecting a passenger from injuring by an impact of a collision and, more specifically to the automotive air bag system with an inflator for inflating an air bag at a slow speed. Description of the Related Art As is generally known, an automotive air bag system has an air bag inflator which generates a gas quickly when a high acceleration is imparted to a vehicle due to, for example, a collision of the vehicle against an obstacle. The air bag is inflated under various conditions requiring different inflating speeds. Various inflating speed controllers have been proposed in, for example, JP-A Nos. 5-24498 and 7-251694, and JP-U No. 6-1029. The inflating speed controller proposed in JP-A No. 5-24498 controls the inflating speed of the air bag by operating a valve plate by a gas generated by an inflator to control the amount of intake air by closing an air inlet opening formed in a holding box when the ambient temperature is high so that the air bag can be inflated at a substantially fixed inflating speed regardless of the variation of the ambient temperature. The inflating speed controller proposed in JP-U No. 6-1029 controls the inflating speed of the air bag by breaking a resin plate formed on an air bag case by an internal pressure of the air bag to reduce the internal pressure of the air bag to avoid imparting an excessively high impact on a vehicle passenger the suddenly inflating air bag when the air bag is unable to inflate smoothly at the initial stage of inflation and starts inflating suddenly due to the sharp increase of the internal pressure of the air bag. The inflating speed controller proposed in JP-A No. 7-251694 supplies a gas generated by an inflator through a narrow passage to an air bag to inflate the air bag at a relatively low inflating speed at the initial stage of combustion in the inflator, and removes a baffle plate disposed in the gas passage by the pressure of the gas increasing with the progress of combustion in the inflator to expand the gas passage so that the inflating speed of the air bag is increased to avoid imparting a sudden impact to an infant or a vehicle passenger by the sudden inflation of the air bag at the initial stage of inflation. No prior art inflating speed controllers can control the inflation of the air bag properly and the air bag is inflated at an excessively high inflating speed when the vehicle collides lightly against an obstacle while the vehicle is traveling at a relatively low traveling speed and a relatively light shock is exerted on the vehicle. Generally, the air bag is provided with a gas discharging hole to absorb energy moderately, and the air bag is held fully inflated only a very short time. The data on the air bag are determined for appropriately securing the passenger from a strong impact that may be imparted to the passenger when the vehicle collides with an obstacle while traveling at a very high speed. Therefore, the passenger will plunge into the air bag after the air bag has been fully inflated and has started deflating if the vehicle collides against an obstacle with a relatively low impact while the same is traveling at a low traveling speed, and the function of the air bag may not fully be utilized. The document EP-A-0 580 286 discloses an airbag inflator for a passenger vehicle comprising a cylinder containing a main gas generating charge to inflate an airbag through inflator passages, and responding to signals from a diagnostic unit to terminate filling of the bag prior to full inflation in the case of an impact of limited severity. In the conventional airbag inflator according to document D1, a piston is provided which is propelled by a secondary charge which is ignited by a second signal from the diagnostic unit. The piston blocks the airbag inflation passages and simultaneously opens vents to discharge the remaining inflation gas. In the conventional airbag inflator, the piston is provided with first outlet openings and a second outlet opening. The piston itself is U-shaped in cross-section and has side walls adjacent to side walls of a cover. When the piston is moved upwards, when the ignite assembly has been triggered, the side walls of the piston clearly cover diffuser holes completely when an explosion of the secondary ignition charge forces the piston upwards. Accordingly, in the conventional airbag inflator, the piston completely cuts the flow of gas from the primary charge into the airbag through the diffuser holes, thereby terminating the airbag inflation. The diffuser holes are blocked in such a state, and the gas cannot but exit the inflator through vent holes, a screening material and further vent holes. The document US-A-5 626 359 discloses a method and an apparatus for controlling an occupant restraint system, for example an airbag. Sensors are provided for sensing at least two parameters that could affect an occupant restraining function of the restraint system. The sensors are connected to a controller. A regulating valve is connected to a reaction can of the airbag and is controlled by a control signal from the controller. For example, a seat belt buckle sensor can be provided in this context. SUMMARY OF THE INVENTION The object underlying the present invention is to provide an airbag system adapted to supply an airbag in such a manner that the airbag is inflated at a very high inflating speed to protect a passenger, when the intensity of an impact is high, and that the airbag is inflated at a reduced inflating speed, when the intensity of the impact is low. This object is solved in an advantageous manner by an airbag system comprising the features of claim 1. Further developments of the airbag system according to the invention are specified in the subclaims. In the airbag system according o the invention, a movable shutter is provided which is adapted to close the gas outlet openings only partly to the effect that the respective opening areas of the gas outlet openings are reduced resulting in a restricted gas flow through the gas outlet openings into the airbag. Hence, the gas volume in the airbag increases in two stages, wherein all the gas generated by the first gas generating means is used to inflate the airbag. In the automotive air bag system, the controller may initiate the second gas generating means when an integral of the collision signal provided by the collision sensor for a predetermined time is less than a predetermined value. In the automotive air bag system, the gas flow restricting means may be a movable shutter which reduces the area of each of the gas outlet holes to reduce the rate of flow of the gas into the air bag. Preferably, the movable shutter has a peripheral part slidably fitted in the housing, and a sealing part for defining a sealed space together with the second gas generating means, and the movable shutter may be forced to slide and held at a position to reduce the area of each of the gas outlet holes when a gas is generated in the sealed space by initiating the second gas generating means. The automotive air bag system may further comprise a seat belt sensor for monitoring whether or not a seat belt is fastened to hold a passenger on a seat, and the controller may inhibit initiate the second gas generating means when the seat belt sensor provides a signal indicating that the seat belt is not fastened. When the vehicle collides against an obstacle and a strong impact acts on the vehicle, the controller provides a gas outlet signal, and the first gas generating means generates a gas suddenly, the gas is ejected through the gas outlet holes into the air bag to inflate the air bag. At this stage, the second gas outlet signal is not provided and the gas outlet hole is not closed by the movable shutter, Therefore, the gas outlet hole has a large area and the air bag is inflated in a moment to protect the passenger. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects features and advantages of the present invention will become more understood from the following description by referring to the accompanying drawings, in which: Fig. 1 is a sectional view of an air bag inflator included in an air bag system in a first embodiment according to the present invention; Fig. 2 is a fragmentary sectional view of the air bag inflator of Fig. 1; Fig. 3 is a block diagram of a controller included in the air bag system of the present invention; Fig. 4 is a flow chart of a procedure to be carried out by the controller of Fig. 3; Fig. 5 is a flow chart of a first squib initiating procedure; Fig. 6 is a flow chart of a second squib initiating procedure; Fig. 7 is a block diagram of a controller included in an automotive air bag system in a second embodiment according to the present invention; and Fig. 8 is a graph showing the variation of the quantity of a jetted gas with time. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, an air bag inflator 1 included in an air bag system in a first embodiment according to the present invention comprises a housing 2 having opposite open ends, a circular first lid 3 and a circular second lid 4 closing the opposite open ends of the housing 2, a circular first partition wall 5 and a circular second partition wall 6 disposed inside the housing 2, axially spaced from each other and welded to the housing 2 to partition a space defined by the housing 2 into three chambers. The partition walls 5 and 6 are provided with central openings 5a and 6a, and metal sealing plates 5b and 6b are attached to the partition walls 5 and 6 so as to cover the openings 5a and 6a, respectively. The first partition wall 5, the first lid 3 and a part of the housing 2 define a combustion chamber C . The combustion chamber C is filled with an oxidizer 7, such as oxygen gas or the like. A first squib (igniter) 8 and a combustible material container 10 containing a combustible material 9, such as hydrogen gas, are disposed in the combustion chamber C and mounted on the first lid 3. The first squib 8 is initiated by a first gas outlet signal provided by a controller 20 upon the reception of a collision signal from a collision sensor 19 capable of sensing an impact exerted on a vehicle. The partition walls 5 and 6 and a part of the housing 2 define a high-pressure gas chamber G in the middle part of the space defined by the housing 2, and the high-pressure gas chamber G is filled with an inert gas 11, such as argon gas. The first squib 8, the combustible material container 10, and the members defining the combustion chamber C and the high-pressure gas chamber G constitute a first gas generating unit. The second partition wall 6, the second lid 4 and a part 2a of the housing 2 define a gas outlet chamber J . The part 2a of the housing 2 is provided with a lurality of gas outlet holes 12 at angular intervals. A gas is ejected into an air bag, not shown, through the gas outlet holes 12. As shown in Fig. 2, the second lid 4 has a cylindrical projection 4a having an open inner end 4b coaxially projecting a central part thereof into the gas outlet chamber J. A second squib 13 and a combustible material container 14 containing a combustible material are placed in the cylindrical projection 4a. The second squib 13 is initiated by a second gas outlet signal provided by the controller 20, and the combustible material container 14 ejects a gas through the open inner end 4b of the cylindrical projection 4a. The second squib 13 and the second combustible material container 14 constitute a second gas generating unit An axially movable shutter 15 is fitted in the second end of the housing 2 so as to cover the cylindrical projection 4a containing the second gas generating unit The axially movable shutter 15 has a central cylindrical projection 15b having a bottom wall 15a at its inner end, a cylindrical rim 15c fitted in the part 2a of the housing 2 and having a covering part 15d for covering the gas outlet holes 12. The cylindrical projection 4a of the second lid 4 is fitted in the central cylindrical projection 15b of the axially movable shutter 15. In an original state, the gas outlet holes 12 are not covered with the cylindrical rim 15c of the axially movable shutter 15. If the second squib 13 is initiated by a second gas outlet signal, the second gas generating unit generates a gas to shift the axially movable shutter 15 to the left, as viewed in Fig. 1, in the gas outlet chamber J so that the gas outlet holes 12 are partly covered with the cylindrical rim 15c of the axially movable shutter 15 as shown in Fig. 2 to reduce the respective areas of the gas outlet holes 12. The pressure of a gas generated by the first gas generating unit and pressing the axially movable shutter 15 to the right and the pressure of a gas generated by the second gas generating unit and pressing the axially movable shutter 15 to the left balance each other, so that the axially movable shutter 15 is held at a position to cover the gas outlet holes 12 partly with the covering part 15d of the cylindrical rim 15c thereof so that the respective areas of the gas outlet holes 12 are reduced. The shape and dimensions of the axially movable shutter 15 are designed so that the axially movable shutter 15 can be held at the position to cover the gas outlet holes 12 partly with the covering part 15d of the cylindrical rim 15c thereof so that the respective areas of the gas outlet holes 12 are reduced. Referring to Fig. 3, the controller 20 has a microcomputer as a main component comprising a CPU 21, a RAM 22, a ROM 23, an I / O interface 24, and bus lines for 25 interconnecting those components. A collision sensor 19 is connected to the input port of the I / O interface 24, and the first squib 8 and the second squib 13 are connected to the output port of the I/O interface 24. ROM 23 stores an air bag inflation control program, and fixed data for deciding the severity of a collision, i.e., a light collision and a heavy collision. The RAM 22 scores data obtained by processing the output signal of the collision sensor 19 and data processed by the CPU 21. The CPU 21 processes the output signal of the collision sensor 19, i.e., a collision signal, received through the I/O interface 24 according to a control program stored in the ROM 23, and executes a squib initiation control operation for initiating the first squib 8 and the second squib 13 on the basis of the fixed data stored in the RAM 23 and the data stored in the ROM 23. Upon the sensing of an impact, the collision sensor 19 sends a collision signal representing the waveform of the impact to the controller 20. Then, the controller 20 executes control operations expressed by flow charts in Figs. 4 to 6. In a main control program shown in Fig. 4, a first squib initiating procedure is executed in step S10, and a second squib initiating procedure is executed in step S20. Referring to Fig. 5 showing the first squib initiating procedure to be executed in step S10 of the main control program, the output of the collision sensor 19 expressing the waveform of the impact is read in step S 11. And, the collision signal provided by the collision sensor 19 is compared with the fixed data stored in the ROM 23 to decide whether or not a collision occurred in step S12. If the decision in step S12 is affirmative, i.e., if it is decided that a collision occurred in step S12, the controller 20 gives a first squib initiation signal to ignite the explosive of the first squib 8 in step S13. If the decision in step S12 is negative, i.e., if it is decided that any collision has not occurred, the program returns to step S11 to read the collision signal provided by the collision sensor 19. After the first squib 8 has been initiated, the program returns to step S20 of the main control program. When the explosive of the first squib 8 is initiated and explodes, the pressure of explosion bursts the combustible material container 10 containing the combustible material 9 and the heat of explosion ignites the combustible material 9. Then, the combustible material 9 reacts with the oxidizer 7 sealed in the combustion chamber C. Consequently, a high-temperature gas is generated in the combustion chamber C to break the first sealing plate 5b and the high-temperature gas flows into the high-pressure gas chamber G. The inert gas 11 contained in the high-temperature gas chamber G is heated by the high-temperature gas and expands suddenly, the pressure in the high-pressure gas chamber G rises sharply. Consequently, the second sealing plate 6b attached to the second partition wall 6 is broken, the high-pressure inert gas 11 flows through the gas outlet holes 12 of the gas outlet chamber J into the air bag, not shown. The controller 20 continues monitoring the waveform of the collision signal provided by the collision sensor 19 after the first squib 8 has been initiated. Referring to Fig. 6, the controller 20 reads the collision signal provided by the collision sensor 19, integrates values of impacts represented by the collision signal provided by the collision sensor 19 in step S21, and compares the integral of the collision signal with the fixed data stored in the ROM 23 in step S22 to see whether or not a light collision occurred. If an affirmative decision is made in step S22, i.e., if it is decided that a light collision occurred, the controller provides a second squib initiating signal to initiate the second squib 13 in an optimum timing. If a negative decision is made in step S22, i.e., if any light collision did not occur, the program returns to step S21. Thus, the first squib initiating signal to initiate the first squib 8 is provided when a momentary value of the collision signal provided by the collision sensor 19 is larger than a predetermined value, that is, the first squib initiating signal is given when the magnitude of an impact exerted on the vehicle corresponds to that of an impact may be exerted in case of a heavy collision. On the other hand, the second squib initiating signal to initiate the second squib 13 is provided when the integral of the collision signal for a predetermined time after the first squib initiating signal has been provided is smaller than a predetermined value. When the second squib 13 is initiated, the combustible material contained in the combustible material container 14 is ignited, and a high-pressure combustion gas generated by the combustion of the combustible material acts on the bottom wall 15a of the cylindrical projection 15b of the axially movable shutter 15 to shift the axially movable shutter 15 to the left as viewed in Fig. 1. Consequently, the gas outlet holes 12 are partly closed, so that the rate of flow of the high-pressure inert gas 11 heated by the high-temperature gas generated in the combustion chamber C into the air bag is reduced and the quantity of the high-pressure inert gas 11 inflating the air bag increases along a curve shown in Fig. 8. Thus, the air bag is inflated in two stages. The air bag system in a second embodiment according to the present invention is provided with a controller 20 shown in Fig. 7. The air bag system in the second embodiment is the same in function and configuration as the air bag system in the first embodiment, except that the controller 20 of the air bag system in the second embodiment uses the output signal of a seat belt sensor 26 in addition to the output signal of a collision sensor 19. The controller 20 included in the air bag system in the second embodiment will be described by referring Fig. 7, in which parts like or corresponding to those shown in Fig. 3 are designated by the same reference characters and the description thereof will be omitted. Plunging mode of the passenger into the air bag is decided by the fact that the seat belt is fastened to hold the passenger on the seat. In the second embodiment, the output signal of the seat belt sensor 26 is used for inflating the air bag at an optimum inflating speed. It is assumed that the upper body of the passenger falls quickly forward when the seat belt is not fastened. Therefore, when the output of the seat belt sensor 26 indicates that the seat belt is not fastened, the initiation of the second squib 13 is inhibited to avoid the inflation of the air bag from retarding. When the output of the seat belt sensor 26 indicates that the seat belt is fastened, the second squib 13 is initiated by the control procedure previously described with reference to Fig. 6. The axially movable shutter 15 may be shifted by a solenoid actuator or the like instead of by the pressure of the combustion gas. A cylindrical rotary shutter provided with openings respectively coinciding with the gas outlet holes 12 may be employed instead of the axially movable shutter 15. The cylindrical rotary shutter may be fitted in the gas outlet chamber J , and may be turned so as to cover the gas outlet holes 12 partly by a solenoid actuator or the pressure of the combustion gas. A generally used acceleration sensor may be employed instead of the collision sensor capable of sensing impacts that are exerted on the vehicle when the vehicle collides against an obstacle. As is understood from the foregoing description, the controller of the air bag system of the present invention controls the inflating speed of the air bag according to the magnitude of the impact exerted on the vehicle so that the air bag is inflated at a high inflating speed in case of a heavy collision, and the air bag is inflated at a low inflating speed in case of a light collision.

Claims: An airbag system of a vehicle having an inflator (1) for inflating an airbag with a gas and an impact sensor (19) for measuring a magnitude of an impact exerted on the vehicle, wherein the inflator (1) comprises: a housing (2) with gas outlet openings (12) in a wall thereof for letting out the gas in the housing (2) into the airbag; first gas generating means (7, 8, 9, 10) for generating the gas in the housing (2); a movable shutter (15) for restricting the flow rate of the gas exiting the gas outlet openings (12) into the airbag, the movable shutter (15) being installed in the housing (2) and being movable toward the gas outlet openings (12) to partly cover the gas outlet openings (12); second gas generating means (13, 14) for moving the movable shutter (15) toward the gas outlet openings (12); and a controller (20) for controlling the operation of the first gas generating means (7, 8, 9, 10) and the second gas generating means (13, 14) on the basis of a collision signal provided by the impact sensor (19); wherein the controller (20) initiates the first gas generating means (7, 8, 9, 10) to inflate the airbag upon the reception of the collision signal and wherein the controller (20) initiates the second gas generating means (13, 14) after initiating the first gas generating means (7, 8, 9, 10) when the collision signal is below a predetermined threshold value so that the movable shutter (15) partly covers the gas outlet openings (12) for limiting the flow rate of the gas exiting the gas outlet openings (12) into the airbag. The airbag system according to claim 1, wherein the controller (20) initiates the second gas generating means (13, 14) when an integral of the collision signal is less than the predetermined value. The airbag system according to claim 1 or 2, wherein the first gas generator means (7, 8, 9, 10) are disposed in a first end of the housing (2), wherein the second gas generating means (13, 14) are disposed in a second end of the housing (2), wherein the gas outlet openings (12) are disposed between the first and second ends of the housing (2) and wherein the movable shutter (15) is disposed between the second end of the housing (2) and the gas outlet openings (12) and is axially movable from the second end of the housing (2) toward the gas outlet openings (12). The airbag system according to claim 3, wherein the shutter (15) comprises: a cylindrical rim (15c) slidably fitted in the housing (2); and a covering part (15d) for partly covering the gas outlet openings (12). The airbag system according to any of claims 1 to 4, further comprising a seat belt sensor (26) for monitoring as to whether or not a seat belt is fastened to hold a passenger on a seat, wherein the controller (20) inhibits the initiation of the second gas generating means (13, 14) when the seat belt sensor (26) provides a signal indicating that the seat belt is unfastened.

Inventors: OTSU TAKASHI, OTSU, TAKASHI, Otsu, Takashi, c/o Fuji Jukogyo K. K.
Applicants: FUJI HEAVY IND LTD, FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1998
Main classification: B60R21
IPC codes: B60R21