Abstract:
A control unit  1  for an air bag is arranged between an inflater  2  for the air bag and a power source generating a current for operating the inflater. The control unit  2  includes a storage device  9  for storing information of whether the inflater  2  has been operated or not. A controller  13  is connected with the storage device  9  for supplying current for operating the inflater on the basis of operating information when the storage device  9  does not store the information that the inflater  2  has ever been operated. Warning device  4  is also connected with the storage device  9  for giving a warning when the storage device  9  stores information that the inflater has been previously operated. The storage device  9  stores the inflation information when the control unit  1  supplies current to the inflater  2  and operates it. The control unit 1 drives the warning device  4  if it detects the inflation information in the storage device  9  when setting the inflation. Any reuse of the control unit  21  after the inflation can thus be prevented. This improves reliability of the air bag system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a control unit for an air bag and, in particular, to the control unit for the air bag which increases reliability of an operation of the air bag. 
     2. Description of the Related Art 
     In conventional air bag systems, an inflater and a control unit are housed in separated cases, and are connected with each other through a connector or the like. Such a conventional control unit after an inflation of the air bag is not different in appearance from the same before the inflation if it is separated from the inflater. This may lead to reuse of the control unit that has ever operated the inflater. 
     In the control unit, large electric current may flow when the inflater is ignited. The switch devices or the like therein may be damaged with the large electric currents. This means that the used control unit (i. e. the control unit which has ever made inflater operate) has only little reliability. 
     A memory unit for the air bag system is disclosed in Japanese Patent Laid-Open No. 18336 in 1997. The memory unit comprises a non-volatile memory device, and a microcomputer which can write acceleration data at certain intervals for the latest certain period into the non-volatile memory device when the air bag is inflated and which can then put the memory device under a ban on writing. According to the art, it is possible to know from the acceleration data written in the memory unit whether the inflation of the air bag was performed normally or abnormally. Additionally, it is possible to also know the delay time between the detection of the certain acceleration and the inflation of the air bag, if any. 
     However, the control unit for the air bag with the above memory unit after the inflation of the air bag is not different in appearance from the same before the inflation if it is separated from the inflater. This may lead to reuse of the used control unit that has ever operated the inflater. 
     As measures to prevent reuse of the control units after the inflation, there are operation manuals distributed by manufacturers, which tell operators not to reuse the control units. 
     However, only operators removing the control unit from the car can know whether it has made inflater operate or not. Therefore, it is possible for the control unit after the inflation to be on the market. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a control unit for an air bag which ensures prevention of the reuse thereof and to increase the reliability of the air bag. 
     In order to achieve the object, the control unit for the air bag according to the present invention, which is arranged between an inflater for the air bag and a power source generating a current for operating the inflater, comprises: storage means for storing an information of whether the inflater has been operated or not; a controller connected with the storage means for supplying a current for operating the inflater to the inflater on the basis of an operating information when the storage means do not store the information that the inflater has ever been operated; and warning means connected with the storage means for giving a warning when the storage means store the information that the inflater has ever been operated. 
     The controller may preferably be connected with a sensor for detecting an acceleration, which can give an operating information to the controller. 
     The controller may also be connected with an outside control unit having input means to give an operating information to the controller. 
     The storage means may comprise non-volatile storage means, preferably an EE-PROM which an information can be electrically written into and erased from. 
     The warning means may preferably be put on an instrument panel of a car. 
     According to the present invention, the storage means of the control unit for the air bag stores the inflation information, which indicates that the inflater has been operated, when the control unit supplies the current to the inflater and operates it. The control unit drives the warning means if it detects the inflation information in the storage means when setting the inflation. Any reuse of the control unit after the inflation can thus be prevented. This improves the reliability of the air bag system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram showing circuits of a control unit for an air bag in an embodiment of the present invention; 
     FIGS. 2 and 3 are flow charts of an operation of an inside control unit in the control unit shown in FIG. 1; 
     FIG. 4 is a flow chart of an interruption operation of the inside control unit in the control unit shown in FIG. 1; and 
     FIGS. 5 and 6 are flow charts of an operation of an outside control unit in the control unit shown in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described in more detail with reference to the drawings. 
     As shown in FIG. 1, a control unit  1  for an air bag comprises: an air bag  2   a  disposed at a fixed position in a car; an inflater  2  associated with the air bag for inflating the air bag; an inside control unit  3 ; a warning lamp  4 , as an example of warning means, for warning operators on the basis of a signal from the inside control unit  3 ; an outside control unit  5  connectable with the inside control unit  3  for discarding the air bag if it has not been inflated. 
     The inside control unit  3  functions to ignite and operate the inflater  2  responsive to an acceleration of the car or to a signal from the outside control unit  5  in order to inflate the air bag. The inside control unit  3  is also adapted to operate the warning lamp  4  to warn the operators if the inside control unit  3  has ever operated the inflaters  2 . 
     The inside control unit  3  comprises: a micro controller  13  having components such as a CPU  6 , a RAM  7 , a ROM  8 , a non-volatile EE-PROM  9 , an I/O device  10 , a D/A converter (D/AC)  11  and an A/D converter (A/DC)  12  which are mutually connected through bus lines; a sensor for detecting an acceleration of the car (G-sensor)  14 ; circuits for communications (COMM)  15 ; a constant voltage circuit  16 ; a backup super capacitor  17 ; a NPN transistor  18  as a monitor switch for driving the warning lamp  4 ; and a pair of NPN transistors  19   a ,  19   b  as an inflater current switches. 
     The inside control unit  3  is also provided with: a connector  22  for connecting with a battery  20  placed in the car via an ignition switch  21 ; connectors  23  and  24  for connecting with the inflater  2 ; a connector  25  for connecting with the warning lamp  4 ; connectors  26   a ,  27   a ,  28   a  and  29   a  for connecting with the outside control unit  5  via cables; and a connector  30  for connecting with the ground. 
     The connector  22  is connected with the constant voltage circuit  16  via a diode  33 . The electric power from the battery  20  is converted into a predetermined constant voltage by the circuit  16  and is supplied into the micro controller  13  (the CPU  6 , the RAM  7 , the ROM  8 , the EE-PROM  9 , the I/O device  10 , the D/A converter  11  and the A/D converter  12 ), the sensor  14  for detecting acceleration and the circuits  15  for the communications. 
     A signal corresponding to acceleration of the car is adapted to be inputted from the sensor  14  into the I/O device  10  in the micro controller  13  connected with the sensor  14  through the A/D converter  12 . A control signal from the outside control unit  5  is also adapted to be inputted into the I/O device  10  through the circuits  15  and the connector  28   a  connected with the outside control unit  5  via bus lines. 
     The D/A converter  11  in the micro controller  13  is connected with the bases of the transistors  18 ,  19  and  19   a , respectively. 
     The micro controller  13  is adapted to output an operating signal to the bases of the transistors  19   a  and  19   b  to ignite the inflater  2  when the micro controller  13  decides the operation of the air bag on the basis of the acceleration signal from the sensor  14  or the control signal from the outside control unit  5  The EE-PROM  9  is adapted to store (be written) data indicating the acceleration of the car and the ignition of the inflater  2  or the like at that time. The micro controller  13  is adapted to output an operating signal to the base of the transistor  18  to drive (light) the warning lamp  4  when the micro controller  13  detects inflation data, which indicates that the inflater  2  has been operated. 
     The connector  22  is connected with the collector of the transistor  19   a , through the diode  33 , the backup super capacitor  17  and a safety sensor  34  which is an electromechanical type of the acceleration switch to prevent electric current from flowing due to an abnormal operation of the control unit. The emitter of the transistor  19   a  is connected with the inflater  2  via the connector  23 . 
     The connector  24  connected with the inflater  2  is connected with the collector of the transistor  19   b . The emitter of the transistor  19   b  is connected with the ground. 
     The transistors  19   a ,  19   b  are adapted to operate and ignite the inflater  2  to inflate the air bag when the micro controller  13  inputs the operating signal to the bases of the transistors  19   a ,  19   b.    
     The connectors  26   a ,  27   a  are used to supply electric power from the outside control unit  5  into the inside control unit  3 . The connector  26   a  is connected with the constant voltage circuit  16  through a diode  31  and the backup super capacitor  17 . The connector  27   a  is connected with the collector of the transistor  19   a  through a diode  32 . In this manner that the inside control unit  3  is connected with the outside control unit  5 , the electric power from the outside control unit  5  can be supplied into the micro controller  13 , the sensor  14  and the circuit  15  in the inside control unit  3  through the connector  26   a  and into the inflater  2  through the connector  27   a  even when the ignition switch  21  is off. 
     The connector  29   a  is used to connect the ground in the control unit  3  with the ground in the control unit  5 . 
     The battery  20  is connected with a terminal of the warning lamp  4  through the ignition switch  21 . A connector  25  is connected with the other terminal of the warning lamp  4 . The warning lamp  4  is preferably an air bag warning lamp put on an instrument panel or the like in order to warn effectively drivers or operators dealing with the air bag. 
     The connector  25  is connected with the A/D converter  12  and the collector of the transistor  18 . 
     The emitter of the transistor  18  is connected with the ground. The transistor  18  operates to light up the warning lamp  4  when the micro controller  13  inputs an operating signal into the base of the transistor  18 . 
     On the other hand, the outside control unit  5  can be placed outside of the car. The outside control unit  5  comprises: a micro controller  41  having components such as a CPU  35 , a RAM  36 , a ROM  37 , an I/O device  38 , a keyboard decoder (DEC)  39  and a keyboard  40  which are mutually connected through bus lines; circuits  42  for communications; a constant voltage circuit  43 ; and a battery  44 . The outside control unit  5  is also provided with: warning means (not shown) for warning operators an abnormal state of the outside control unit  5  or a mistake in a procedure for discarding the air bag or the like; and displaying means (not shown) for displaying information about the ignition of the inflater  2 . 
     The outside control unit  5  is also provided with connectors  26   b ,  27   b ,  28   b  and  29   b  which can be connected with the connectors  26   a ,  27   a ,  28   a  and  29   a  in the inside control unit  3  through the cables, respectively. 
     The battery  44  is connected with the constant voltage circuit  43  via a main switch  45  and a diode  46  in the outside control unit  5 . The electric power from the battery  44  is converted into a predetermined constant voltage by the circuit  43  and is supplied into the micro controller  41  (the CPU  35 , the RAM  36 , the ROM  37 , the I/O device  38  and the keyboard decoder  39 ) and the circuits  42  for the communications. 
     The I/O device  38  in the micro controller  41  is connected with the circuit  42  through the bus line. The circuit  42  is connected with the connector  28   b . Thus the outside control unit  5  and the inside control unit  3  can send and receive control signals to and from each other by the circuit  42  and the circuit  15 . 
     The battery  44  is also connected with the connector  26   b  through the main switch  45 . The battery  44  is also connected with the connector  27   b  through the main switch  45  and a normally-open switch  46 . Thus the electric power can be supplied to the micro controller  13 , the sensor  14  and the circuit  15  in the inside control unit  3  through the connector  26   b  and to the inflater  2  through the connector  27   b . The normally-open switch  46  prevents non-intended supply of electric power from the battery  44  to the inflater  2  due to an abnormal operation. 
     The connector  29   b  is used to connect the ground in the control unit  5  with the ground in the control unit  3 . 
     Controlling steps by the inside control unit  3  will be described hereafter. 
     As shown in FIGS. 2 and 3, the control unit  3  is initialized at the first step S 101 , where the ignition switch  21  is on, or where the outside control unit  5  is connected with the inside control unit  3  and the main switch  45  in the outside control unit  5  is on. The inside control unit  3  conducts a self-check program for detecting any abnormalities thereof at the next step S 102 . The inside control unit  3  judges the result of the self-check program at the next step S 103 . 
     If any abnormality is detected at the step S 103 , the inside control unit  3  makes the transistor  18  on in order to light up the warning lamp  4  at a step S 104 . The step S 104  is repeated as a loop. 
     If no abnormality is detected at the step S 103 , the inside control unit  3  reads the data which indicates whether the inflater  2  has ever been operated, from the EE-PROM  9  at a step S 105 . 
     The control unit  3  judges the read data at a step S 106 . 
     If the read data indicates that the inflater  2  has ever been ignited and operated at the step S 106 , the inside control unit  3  makes the transistor  18  on in order to light up the warning lamp  4  at a step S 107 . The step S 107  is repeated as a loop. Thus operators can know that this inside control unit  3  cannot be used. 
     If the ignition data indicates that the inflater  2  has never been ignited and operated at the step S 106 , the inside control unit  3  sends a request signal to the outside control unit  5  through the circuit  15  at a step S 108 . 
     Then the inside control unit  3  judges whether the outside control unit  5  sends back a response signal corresponding to the request signal to the inside control unit  3  at a step S 109 . 
     If the inside control unit  3  does not receive the signal from the outside control unit  5  at the step S 109 , the inside control unit  3  conducts an interruption pro-ram at a step S 110 . By conducting the interruption program, the inflater  2  is set to be ignited when the sensor  14  detects an acceleration below a certain value. The inside control unit  3  conducts another self-check program for detecting conditions for igniting the inflater  2  on the basis of a position of the driver or the like and for detecting any abnormality thereof at the next step S 111 . The inside control unit  3  judges whether the acceleration of the car detected by the sensor  14  is below a certain value at the next step S 112 . 
     If the detected acceleration is not below a certain value at the step S 112 , the inside control unit  3  judges the result of the self-check program at a step S 113 . If any abnormality is detected at the step S 113 , the inside control unit  3  makes the warning lamp  4  on at a step S 114 . The step S 114  is repeated as a loop. If no abnormality is detected at the step S 113 , the inside control unit  3  repeats the steps from the step S 111 . 
     If the detected acceleration is below a certain value at the step S 112 , the inside control unit  3  conducts an interruption routine at a step S 115 . After the step S 115 , the step S 114  is conducted. 
     As shown in FIG. 4, in the interruption routine, the inside control unit  3  is inputted a self-check data at a step S 201  and judges whether the inflater  2  should be ignited on the basis of the self-check data at the next step S 202 . If the inflater  2  should not be ignited at the step S 202 , the interruption routine is finished. If the inflater  2  should be ignited at the step S 202 , the inside control unit  3  makes transistors  19   a ,  19   b  on in order to ignite the inflater  2  at a step S 203 . Then the inside control unit  3  makes the EE-PROM  9  store the ignition information indicating that the inflater  2  has been ignited and the interruption routine is finished. 
     If the inside control unit  3  receives the signal from the outside control unit  5  at the step S 109 , the inside control unit  3  confirms the connection of the inside control unit  3  and the outside control unit  5  at a step S 116 . The inside control unit  3  detects the state of the ignition switch  21  to judge whether the process for discarding the air bag is normally conducted at a step S 117 . 
     If the ignition switch  21  is on at the next step S 118 , the inside control unit  3  gives an alarm for mistakes in operating the air bag at a step S 119 . 
     If the ignition switch  21  is off at the step S 118 , the inside control unit  3  stands by for an operating control signal inputted from the outside control unit  5  at a step S 120  (see FIG.  3 ). 
     If the operating control signal is inputted to the inside control unit  3  at the step S 120 , the inside control unit  3  judges whether the operating control signal is appropriate at a step S 121 . If the operating control signal is not appropriate at the step S 121 , the inside control unit  3  repeats the steps from the step S 120 . If the operating control signal is appropriate at the step S 121 , the inside control unit  3  judges whether the operating control signal is a signal for requesting an ignition of the inflater  2  at a step S 122 . 
     If the operating control signal is not a signal for requesting the ignition of the inflater  2  at the step S 122 , the inside control unit  3  judges whether the operating control signal is a signal for removing the connection between the inside control unit  3  and the outside control unit  5  at a step S 128 . If the operating control signal is a signal for removing the connection at the step S 128 , the inside control unit  3  repeats the steps from the step S 110 . If the operating control signal is not a signal for removing the connection at the step S 128 , the inside control unit  3  conducts a process corresponding to the signal at a step S 129  and repeats the steps from the step S 105 . 
     If the operating control signal is a signal for requesting the ignition of the inflater  2  at the step S 122 , the inside control unit  3  makes transistors  19   a ,  19   b  on in order to ignite the inflater  2  at a step S 123 . The inside control unit  3  makes the EE-PROM  9  store the ignition information indicating that the inflater  2  has been ignited at the next step S 124 . The inside control unit  3  sends the ignition information to the outside control unit  5  at the next step S 125 . The outside control unit  5  judges whether the ignition information is normally sent at the next step S 126 . If the ignition information is not normally sent, the inside control unit  3  repeats the steps from the step S 125 . If the ignition information is normally sent, the connection between the inside control unit  3  and the outside control unit  5  is removed at a step  127 . Thus the controlling steps are finished. 
     Controlling steps by the outside control unit  5  will be described hereafter. 
     As shown in FIG. 5, the outside control unit  5  is initialized at the first step S 301  where the connectors  26   b ,  27   b ,  28   b ,  29   b  in the outside control unit  5  are connected with the connectors  26   a ,  27   a ,  28   a ,  29   a  in the inside control unit and the main switch  45  in the outside control unit  5  is turned on to supply the electric power. The outside control unit  5  conducts a self-check program for detecting any abnormality thereof at the next step S 302 . The outside control unit  5  judges the result of the self-check program at the next step S 303 . 
     If any abnormality is detected at the step S 303 , the outside control unit  5  operates warning means (not shown) to give an alarm at a step S 304  .The step S 304  is repeated as a loop. 
     If no abnormality is detected at the step S 303 , the outside control unit  5  stands by a request signal from the inside control unit  3  at a step S 305  .If the outside control unit  5  receives the request signal, the outside control unit  5  sends back a response signal corresponding to the request signal to the inside control unit  3  at a step S 306  in order to confirm the connection. Then the outside control unit  5  reads an input from the keyboard  40  by an operator at a step S 307  .The outside control unit  5  judges whether the input is an appropriate instruction at the next step S 308  .If the input is not the appropriate instruction, the outside control unit  5  requests a reinput and repeats the steps from the step S 307 . If the input is the appropriate instruction, the outside control unit  5  sends the instruction to the inside control unit  3  at a step S 309 . 
     As shown in FIG. 6, the outside control unit  5  stands by a response to the instruction at the next step S 310 . When the outside control unit  5  receives the response, the outside control unit  5  judges whether the response is normal at the next step S 311 . 
     If the response is not normal at the step S 311 , the outside control unit  5  makes warning means (not shown) give an alarm for mistakes in operating procedures at a step S 312 . The step S 312  is repeated as a loop. 
     If the response is normal at the step S 311 , the outside control unit  5  judges whether the response is an ignition information about the inflater  2  at a step S 313 . 
     If the response is the ignition information at the step S 313 , the ignition information is displayed by displaying means (not shown) at a step S 314 . The controlling steps are then finished. 
     If the response is not the ignition information at the step S 313 , the outside control unit  5  judges whether the response is data for removing the connection between the inside control unit  3  and the outside control unit  5  at a step S 315 . If the response is the removing data at the step S 315 , the controlling steps are finished. If the response is not the removing data at the step S 315 , a process corresponding to the response is conducted at a step S 316  and the outside control unit  5  repeats the steps from the step S 305  (see FIG.  5 ). 
     Operating steps for discarding the air bag in the above embodiment will be described hereafter. 
     It is confirmed that the switches such as the ignition switch  21  of the car and the main switch  45  in the outside control unit  5  are all off. The inside control unit  3  is connected with the outside control unit  5  placed away from the car via the cables. 
     The main switch  45  is turned on to supply the electric power to the inside control unit  3 . When it is confirmed that both the inside control unit  3  and the outside control unit  5  are normally operated, the normally-open switch  46  is turned on. The ignition instruction is inputted from the keyboard  40 , so that the inflater  2  is ignited to inflate the air bag. The inside control unit  3  makes the FE-PROM  9  store the ignition information indicating that the inflater  2  has been operated. 
     The inflation of the air bag and the sending of the ignition information to the outside control unit  5  are confirmed. Thus the air bag, the inflater  2  and the inside control unit  3  or the like are removed from the car to finish the operating steps for discarding the air bag. 
     If the air bag is inflated by a collision, it is confirmed that the ignition switch  21  is off and the EE-PROM  9  stores the ignition information indicating that the inflater  2  has been operated. Thus the air bag, the inflater  2  and the inside control unit  3  or the like arc removed from the car to finish the operating steps for discarding the air bag. 
     As mentioned above, the inside control unit  3  in the embodiment makes the EE-PROM  9  store the ignition information. Therefore, in the control unit for the air bag  1  including the inside control unit  3  having ever operated the inflater  2 , the warning lamp  4  can be lighted on the basis of the ignition information when the ignition switch  21  is turned on. Thus the drivers or thc operators can know whether the switch devices in the inside control unit  3  may have little reliability because of the damage with the large electric currents at igniting the inflater  2 . Therefore the reuse of the control unit having ever operated the inflater  2  can be surely prevented. This leads to the very improved reliability of the air bag system. 
     The EE-PROM  9  can be replaced with an assembly comprising an electric driving circuit, a fuse and a circuit for detecting a current, which can store the ignition information by blowing the fuse as non-volatile storage means. 
     While the presently preferred embodiments of the present invention have 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.