Abstract:
An inflation system for inflating an air bag installed in a vehicle features an impact sensor for measuring an impact exerted on the vehicle and an inflator having a housing with a gas chamber and gas jettison opening for flowing the gas out of the housing and into the air bag. The inflator includes a first gas generator for inflating the air bag, a shutter for restricting gas flow through the gas jettison opening, and a second gas generator for moving the shutter to a reduced gas jettison opening area position. The housing and second gas generator are arranged such that the second gas generator directs the shutter into the outrushing gas flow leading to the jettison opening and shifts until the pressure balance on opposite sides of the axially shifting shutter are equal at which point the shuttle is in a flow limiting mode. A controller operates the first gas generator unit upon output of the impact sensor and the second gas generating unit when the output of the impact sensor is below a predetermined threshold value.

Description:
BACKGROUND OF THE INVENTION 
     1. 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. 
     2. 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. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an automotive air bag inflator for controlling an inflating speed of an air bag according to an intensity of an impact in dependency on collision modes of the vehicle against an obstacle, so that the air bag is inflated at a very high inflating speed to protect a passenger when the intensity of the impact is high, and the air bag is inflated at a reduced inflating speed when the intensity of the impact is low. 
     According to a first aspect of the present invention, an automotive air bag system mounted on the vehicle has an inflator, an impact sensor for measuring a magnitude of an impact exerted on the vehicle, first gas generating means for generating a gas for inflating an air bag, a housing with gas jetting openings in a wall, gas flow restricting means for restricting a gas flow through the gas jetting openings, second gas generating means for operating the gas flow restricting means, and a controller for controlling the first and the second gas generating means on the basis of a collision signal provided by the impact sensor. In this automotive air bag system, the controller initiates the first gas generating means to inflate the air bag upon receiving the collision signal provided by the impact sensor, and it initiates the second gas generating means to operate the gas flow restricting means so that a flow rate of the gas into the air bag is limited when the magnitude of the impact measured by the impact sensor is below a predetermined threshold value. 
     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 jettison 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 jettison 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 receives a strong impact upon collision with another object, the controller provides a gas jetting signal to the first gas generating means to generate a gas suddenly. The generated gas is jetted through the gas jettison holes into the air bag to inflate the air bag. At this stage, the second gas jetting signal is not provided and the gas jettison hole is not closed by the movable shutter, Therefore, the gas jettison 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 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  5   a  and  6   a , and metal sealing plates  5   b  and  6   b  are attached to the partition walls  5  and  6  so as to cover the openings  5   a  and  6   a , 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 jetting 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  2   a  of the housing  2  define a gas jetting chamber J. The part  2   a  of the housing  2  is provided with a plurality of gas jettison holes  12  at angular intervals. A gas is jetted into an air bag, not shown, through the gas jettison holes  12 . As shown in FIG. 2, the second lid  4  has a cylindrical projection  4   a  having an open inner end  4   b  coaxially projecting a central part thereof into the gas jetting chamber J. A second squib  13  and a combustible material container  14  containing a combustible material are placed in the cylindrical projection  4   a . The second squib  13  is initiated by a second gas jetting signal provided by the controller  20 , and the combustible material container  14  jets a gas through the open inner end  4   b  of the cylindrical projection  4   a . 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  4   a  containing the second gas generating unit. The axially movable shutter  15  has a central cylindrical projection  15   b  having a bottom wall  15   a  at its inner end, a cylindrical rim  15   c  fitted in the part  2   a  of the housing  2  and having a covering part  15   d  for covering the gas jettison holes  12 . The cylindrical projection  4   a  of the second lid  4  is fitted in the central cylindrical projection  15   b  of the axially movable shutter  15 . 
     In an original state, the gas jettison holes  12  are not covered with cylindrical rim  15   c  of the axially movable shutter  15 . If the second squib  13  is initiated by a second gas jetting 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 jetting chamber J so that the gas jettison holes  12  are partly covered with the cylindrical rim  15   c  of the axially movable shutter  15  as shown in FIG. 2 to reduce the respective areas of the gas jettison 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 jetting holes  12  partly with the covering part  15   d  of the cylindrical rim  15   c  thereof so that the respective areas of the gas jettison 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 jettison holes  12  partly with the covering part  15   d  of the cylindrical rim  15   c  thereof so that the respective areas of the gas jettison 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  stores 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 S 10 , and a second squib initiating procedure is executed in step S 20 . 
     Referring to FIG. 5 showing the first squib initiating procedure to be executed in step S 10  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 S 12 . If the decision in step S 12  is affirmative, i.e., if it is decided that a collision occurred in step S 12 , the controller  20  gives a first squib initiation signal to ignite the explosive of the first squib  8  in step S 13 . If the decision in step S 12  is negative, i.e., if it is decided that any collision has not occurred, the program returns to step S 11  to read the collision signal provided by the collision sensor  19 . After the first squib  8  has been initiated, the program returns to step S 20  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  5   b  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  6   b  attached to the second partition wall  6  is broken, the high-pressure inert gas  11  flows through the gas jetting holes  12  of the gas jetting 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 S 21 , and compares the integral of the collision signal with the fixed data stored in the ROM  23  in step S 22  to see whether or not a light collision occurred. If an affirmative decision is made in step S 22 , 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 S 22 , i.e., if any light collision did not occur, the program returns to step S 21 . 
     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  15   a  of the cylindrical projection  15   b  of the axially movable shutter  15  to shift the axially movable shutter  15  to the left as viewed in FIG.  1 . Consequently, the gas jettison 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 jettison holes  12  may be employed instead of the axially movable shutter  15 . The cylindrical rotary shutter may be fitted in the gas jetting chamber J, and may be turned so as to cover the gas jettison 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. 
     While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.