Abstract:
A collision-determining device arranged to prevent a passenger protection mechanism from erroneously operating by determining the polar relationship between an acceleration signal indicative of vehicle acceleration and a pseudo signal used to determine whether a vehicle collision has occurred. A G sensor generates the pseudo signal having a polarity opposite from that of a deceleration signal based on a control signal from a microcomputer. An A-D converter receives the pseudo signal via a signal processing circuit and generates a pseudo voltage. The microcomputer determines whether a collision has occurred based on whether the pseudo voltage has been generated and based on the polarity thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to, and claims priority from, Japanese Patent Application Nos. Hei. 10-141653, 11-12350 and 11-82184, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a passenger protection system such as a vehicle air bag system, and more particularly to a collision-determining circuit of the passenger protection system for determining whether or not a collision has occurred, and for preventing erroneous system deployment. 
     2. Discussion of the Related Art 
     Conventional collision determination devices are of the type shown, for example, in U.S. Pat. No. 5,038,134. As shown in FIG. 21, such a collision determination device generates, prior to determining whether or not a collision has occurred, a pseudo signal  2  from an acceleration sensor based on a control signal  1  to determine whether an air bag system is malfunctioning based on the pseudo signal  2 . 
     However, as shown in FIG. 21, the polarity of the pseudo signal  2  is the same as that of an acceleration signal  3  generated from the acceleration sensor when the vehicle is involved in a collision. 
     Therefore, the airbag system may be activated erroneously as the pseudo signal  2  is generated when the pseudo signal  2  is erroneously output even though no acceleration signal is generated. 
     Further, when a plurality of acceleration sensors are implemented in the collision detection system, the above-discussed limitation still remains, as the control signal  1  is used in common in the respective acceleration sensors. Accordingly, the air bag system may be erroneously activated in the same manner as described above. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to solve the above-mentioned problems by providing a collision-determining circuit in a vehicle passenger protection system in which the polar relationship between an acceleration signal indicative of acceleration of a vehicle and a pseudo signal used to determine a fault prevents a passenger protecting mechanism from erroneously operating even if the pseudo signal is generated. 
     It is another object of the invention to provide a collision-determining circuit in which the polar relationship between at least two acceleration signals prevents the passenger protecting mechanism from operating erroneously. 
     The above-mentioned objects may be achieved as follows. According to one aspect of the present invention, it is possible to determine whether an acceleration detector is out of order without erroneously operating a passenger protecting mechanism of a passenger protection system by generating a pseudo signal having a polarity that is opposite from the polarity of a deceleration signal. 
     Further, even if the control signal is generated erroneously during operation of the collisiondetermining device, the passenger protecting mechanism will not operate erroneously due to the pseudo signal. This is because the polarity of the pseudo signal generated based on the control signal has a polarity that is opposite from the polarity of the deceleration signal. 
     According to another aspect of the present invention, it is also possible to determine whether or not one or more acceleration detectors are out of order without erroneously operating the passenger protecting mechanism, because the polarity of the deceleration and pseudo signals generated by at least one of the acceleration detectors are opposite from one other. 
     Even if the control signal is generated erroneously during the determination process of the collision-determining circuit, the passenger protection mechanism will not be erroneously activated by the pseudo signal when no deceleration signal caused by a collision of the vehicle is generated, because the polarity of the pseudo signal generated based on the control signal is opposite in polarity from that of the corresponding deceleration signal. Accordingly, it is possible to provide a highly reliable collision-determining device. 
     The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings in which like numerals refer to like parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a first embodiment of the present invention; 
     FIG. 2 is a perspective view showing a state in which each circuit in FIG. 1 is stored in a casing; 
     FIG. 3A is a timing diagram of a G sensor acceleration signal and pseudo signal, and 
     FIG. 3B is a timing diagram of a microcomputer control signal; 
     FIG. 4 is a flow diagram showing an operation of the microcomputer in FIG. 1; 
     FIG. 5 is a block diagram showing a second embodiment of the invention; 
     FIG. 6 is a perspective view showing a state in which each circuit in FIG. 5 is stored in a casing; 
     FIG. 7A is a timing diagram of an acceleration signal and a pseudo signal of a G sensor, 
     FIG. 7B is a timing diagram of an acceleration signal and a pseudo signal of another G sensor  21 , and FIG. 7C is a timing diagram of the microcomputer control signal; 
     FIG. 8 is a flow diagram showing an operation of the microcomputer in FIG. 5; 
     FIG. 9 is a block diagram showing a third embodiment of the invention; 
     FIG. 10 is a perspective view showing a state in which each circuit in FIG. 9 is stored in a casing; 
     FIG. 11A is a timing diagram of the acceleration signal and the pseudo signal of a G sensor, 
     FIG. 11B is a timing diagram of the acceleration signal and the pseudo signal of another G sensor, and 
     FIG. 11C is a timing diagram of the microcomputer control signal; 
     FIG. 12 is a flow diagram showing an operation of the microcomputer in FIG. 9; 
     FIG. 13 is a modified example of the third embodiment, wherein 
     FIG. 13A is a timing diagram of the acceleration signal and the pseudo signal of a G sensor, 
     FIG. 13B is a timing diagram of the acceleration signal and the pseudo signal of another G sensor, and FIG. 11C is a timing diagram of the microcomputer control signal; 
     FIG. 14 is a block diagram showing a fourth embodiment of the invention; 
     FIG. 15A is a timing diagram of the acceleration signal and the pseudo signal of a G sensor, 
     FIG. 15B is a timing diagram of an acceleration signal and a pseudo signal of another G sensor, and 
     FIG. 15C is a timing diagram of the microcomputer control signal; 
     FIG. 16 is a block diagram showing a fifth embodiment of the present invention; 
     FIG. 17 is a block diagram showing a sixth embodiment of the present invention; 
     FIG. 18 is a block diagram showing a seventh embodiment of the present invention; 
     FIG. 19 is a block diagram showing an eighth embodiment of the present invention; 
     FIG. 20 is a block diagram showing a ninth embodiment of the present invention; and 
     FIG. 21A is a timing diagram of an acceleration signal and a pseudo signal of a G sensor in a conventional collision-determining device; and 
     FIG. 21B is a timing diagram of a control signal in the collision-determining device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     FIG. 1 shows a collision-determination circuit according to the present invention applied to a vehicle air bag system. The air bag system comprises an acceleration detecting circuit mounted on a circuit board Ca within a casing C disposed within the vehicle as shown in FIG.  2 . Preferably, the circuit board Ca is supported within the casing C in parallel with a bottom wall of the casing. 
     The acceleration detecting circuit comprises an acceleration sensor  11  (hereinafter referred to as a G sensor  11 ) including an acceleration detecting section  11   a , a pseudo signal generating section  11   b  and an inverter tic. 
     The G sensor  11  is mounted in the acceleration detecting section  11   a  on the circuit board Ca to detect vehicle acceleration in the direction of arrow A in FIG. 2 (in the direction from the front to the back of the vehicle) and to generate an acceleration signal (see reference symbol SO 1  in FIG.  3 A). The G sensor  11  generates a deceleration signal when deceleration due to a collision is produced. 
     The pseudo signal generating section  11   b  generates a pulse-width pseudo signal (i.e. diagnostic signal) upon receiving a positive pulse-width control signal CS (see FIG. 3B) from a microcomputer  30 . The inverter  11   c  generates an inversion signal (see FIG. 3A, hereinafter referred to as a pseudo signal P 1 ) by inverting the pseudo signal from the pseudo signal generating section  11   b  and outputs it through the acceleration detecting section  11   a . According to the present embodiment, the acceleration detecting section  11   a  outputs the acceleration signal SO 1  or the pseudo signal P 1  from the same output terminal, with the P 1  signal having a polarity opposite from that of the positive part of the acceleration signal SO 1 . 
     Referring again to FIG. 1, the acceleration detecting circuit also comprises a signal processing circuit  12 . The signal processing circuit  12  amplifies the acceleration signal SO 1  and generates a processed pseudo signal by processing the pseudo signal P 1  from the acceleration detecting section  11   a.    
     The air bag system comprises an A-D converter  20  and a microcomputer  30  as shown in FIG.  1 . The A-D converter  20  and the microcomputer  30  are provided on the circuit board Ca within the casing C (see the reference symbol (E) in FIG.  2 ). The microcomputer  30  converts the processed acceleration signal or the processed pseudo signal from the signal processing circuit  12  into digital signals to generate acceleration voltage or pseudo voltage. 
     The A-D converter  20  executes a computer program in accordance to a flow diagram in FIG.  4  and implements an arithmetic process for controlling the pseudo signal generating section  11   b  of the G sensor  11 , a fault-determining process and a collision-determining process based on an output of the A-D converter  20 , and a process for controlling an alarm lamp  40 . 
     The collision-determining process is carried out by determining whether or not a required condition for operating an airbag mechanism  60  exists based on the acceleration voltage from the A-D converter  20 . The process determines that the vehicle has been involved in a collision when the required condition exists, or determines that the vehicle has not been involved in a collision when the required condition does not exist. 
     An activating circuit  50  activates a squib  51  when the microcomputer  30  determines that the air bag mechanism  60  must be activated. The air bag mechanism  60  operates based on the activation of the squib  51 , and correspondingly inflates the air bag. 
     When an ignition switch of the vehicle is turned on in the first embodiment constructed as described above, the microcomputer  30  starts to execute the computer program according to the flow diagram shown in FIG.  4 . 
     At Step  100 , the microcomputer  30  is initialized. After being initialized, the microcomputer generates the control signal CS necessary for generating the pseudo signal P 1  from the G sensor  11  and outputs the control signal CS to the pseudo signal generating section  11   b  of the G sensor  11  at Step  110 . 
     Then, the pseudo signal generating section  11   b  outputs the pseudo signal P 1  based on the control signal CS via the inverter  11   c  and the acceleration detecting section  11   a . Receiving the pseudo signal P 1  from the acceleration detecting section  11   a , the signal processing circuit  12  processes the signal to generate the processed pseudo signal, and outputs the signal to the A-D converter  20 . 
     When the processed pseudo signal is thus output from the signal processing circuit  12  to the A-D converter  20 , the processed pseudo signal is converted into a digital signal by the A-D converter  20  and is input to the microcomputer  30  as pseudo voltage at Step  120 . 
     It is then determined whether or not the pseudo voltage is generated correctly from the acceleration detecting section  11   a  at Step  130 . When the pseudo voltage is generated from the A-D converter  20  as described above, a YES determination is generated at Step  130 , indicating that the A-D converter is functioning properly. 
     Next, it is determined whether the polarity of the pseudo voltage is correct at Step  140 . When the pseudo signal P 1  from the G sensor  11  is negative, the processed pseudo signal from the signal processing circuit  12  is negative, and the pseudo voltage from the A-D converter  20  has a value corresponding to the processed pseudo voltage. Accordingly, the polarity of the pseudo voltage is determined to be correct, and it is determined that the acceleration detecting circuit is also functioning properly, as the answer is determined to be YES at Step  140 . 
     Subsequently, a collision-determining process is implemented at Step  150 . When the vehicle is running and the acceleration detecting section  11   a  of the G sensor  11  generates the acceleration signal SO 1 , the signal processing circuit  12  processes the acceleration signal SO 1  and generates a processed acceleration signal. Then, the processed acceleration signal is converted into a digital signal by the A-D converter  20  and is output as an acceleration voltage to be input to the microcomputer  30 . When the microcomputer  30  determines that the above-mentioned operating requirement exists based on the acceleration voltage, the activating circuit  50  activates the squib  51 , and the air bag mechanism  60  is activated to expand the air bag. As a result, a vehicle passenger is reliably protected. 
     Even when the control signal CS is generated erroneously, the polarity of the pseudo signal P 1  generated from the G sensor  11  is opposite from that of the acceleration signal SO 1  from the G sensor  11  as shown in FIG.  3 . Therefore, the output of the A-D converter  20  has a value that will not activate the airbag mechanism  60 . Accordingly, the airbag mechanism  60  will not be activated erroneously. 
     When the pseudo voltage from the A-D converter  20  is not generated correctly at Step  130  before the YES determination is made at Step  140  as described above, the determination at Step  130  turns out to be NO. This indicates that the acceleration detecting circuit is not functioning properly. 
     Even when a YES determination is made at Step  130 , a NO determination is made at Step  140  if the polarity of the pseudo voltage is not negative at Step  140 . This indicates that the acceleration detecting circuit  10  is not functioning properly. 
     When a NO determination is made at Steps  130  or  140  as described above, the collision determination processing routine  150  is inhibited, and an alarm lamp  40  is lit at Step  160 . As a result, the airbag mechanism  60  will not operate erroneously, and the alarm lamp  40  is illuminated to inform the vehicle driver of the error. 
     As discussed above, the polarity of the acceleration signal SO 1  is opposite from that of the pseudo signal P 1 . That is, the polarity of the pseudo signal P 1  is opposite from the polarity of the signal operating the air bag mechanism  60 . Therefore, the air bag mechanism  60  will not operate erroneously due to the pseudo signal P 1  prior to operation of the collision determination processing routine at Step  150 , thus increasing the reliability of the collision-determination circuit. 
     Second Embodiment 
     FIGS. 5-8 show a second embodiment of the present invention in which multiple acceleration detectors are utilized. In the second embodiment, acceleration detecting circuits  11 A and  21  and an A-D converter  20 A are adopted instead of the acceleration detecting circuit  11  and the A-D converter  20  described in the first embodiment. 
     The acceleration detecting circuit includes a G sensor  11 A instead of the G sensor  11  in the first embodiment, and has a structure in which the inverter  11 c is eliminated from the G sensor  11 . 
     Therefore, the pseudo signal generating section  11   b  outputs a positive pulse-width pseudo signal P 11  (see FIG. 7A) through the acceleration detecting section  11   a . Here, the pseudo signal P 11  has the same polarity as the acceleration signal SO 1  from the acceleration detecting section  11   a . It is noted that instead of the G sensor  11  described above, the G sensor  11 A is mounted on the circuit board Ca within the casing C so as to have the same detecting direction with the G sensor  11 . 
     The acceleration detecting circuit  20 ′ comprises a G sensor  21  and a signal processing circuit  22 . The acceleration detecting circuit  20 ′ is mounted on the circuit board Ca together with the G sensor  11 A (see FIG.  6 ), instead of with the G sensor  11  described in the first embodiment. 
     The G sensor  21  comprises an acceleration detecting section  21   a  and a pseudo signal generating section  21   b  which have the same functions with the acceleration detecting section  11   a  and the pseudo signal generating section  11   b  of the G sensor  11 A and an inverter  21   c.    
     The G sensor  21  is mounted on the circuit board Ca to detect vehicle acceleration in the direction of arrow A in FIG.  6  and to generate an acceleration signal (see reference numeral SO 2  in FIG.  7 B). 
     Receiving the control signal CS (FIG. 7C) from the microcomputer  30  described in the first embodiment, the pseudo signal generating section  21   b  generates a pulse-width pseudo signal. The inverter  21   c  inverts the pseudo signal from the pseudo signal generating section  21   b  to generate an inverted signal (hereinafter referred to as a pseudo signal P 2 . See FIG. 7B) and to output the signal through the acceleration detecting section  21   a . As a result, the acceleration detecting section  21   a  outputs the acceleration signal SO 2  or the pseudo signal P 2  from the same output terminal. 
     Here, the pseudo signal P 2  has a negative polarity, which is opposite from that of the positive part of the acceleration signal SO 2 . 
     The signal processing circuit  22  amplifies the acceleration signal SO 2  to generate a processed acceleration signal and amplifies the pseudo signal P 2  to generate a processed pseudo signal. The A-D converter  20 A converts the processed acceleration signal or the processed pseudo signal of the signal processing circuit  12  into a digital signal to generate a first acceleration voltage or a first pseudo voltage. The A-D converter  20 A also converts the processed acceleration signal or the processed pseudo signal of the signal processing circuit  22  into a digital signal to generate a second acceleration voltage or a second pseudo voltage. 
     However, the A-D converter  20 A converts the respective processed acceleration signals of both signal processing circuits  12 ,  22  so that the first and second acceleration voltages have polarities opposite from each other. The A-D converter  20 A also converts the respective processed pseudo signals of both signal processing circuits  12 ,  22  so that the first and second pseudo voltages have polarities opposite from each other. 
     In this embodiment, the A-D converter  20 A is mounted on the circuit board Ca instead of the A-D converter  20  described in the first embodiment together with the microcomputer  30  (see reference numeral (E) in FIG.  6 ). 
     In the second embodiment, the microcomputer  30  executes a computer program, in accordance with a flow diagram shown in FIG.  8 . During the execution, the microcomputer  30  implements arithmetic processing necessary for controlling the both G sensors  11 A and  21 , the fault-determining process and the collision-determining process based on the output of the A-D converter  20 A and the process for controlling the alarm lamp  40 . 
     When the control signal CS is output at Step  110  in the same manner as the first embodiment, the control signal CS is output from the microcomputer  30  to the pseudo signal generating section  11   b  and the pseudo signal generating section  21   b  of the G sensor  11 A. 
     Then, based on the control signal CS, the pseudo signal generating section  11   b  outputs the pseudo signal P 11  through the acceleration detecting section  11   a . The pseudo signal generating section  21   b  also outputs the pseudo signal P 2  through the inverter  21   c  and the acceleration detecting section  21   a.    
     Subsequently, the pseudo signal P 11  from the acceleration detecting section  11   a  is processed by the signal processing circuit  12  and is output as the processed pseudo signal. The pseudo signal P 2  from the acceleration detecting section  21   a  is processed by the signal processing circuit  22  and is output as the processed pseudo signal. 
     Next, the respective pseudo signals from the both signal processing circuits  12 ,  22  are converted sequentially into digital signals by the A-D converter  20 A and are input sequentially to the microcomputer  30  as first and second pseudo voltages at Step  120 A. 
     At Step  130 A, it is determined whether or not the first and second pseudo voltages are generated correctly from the A-D converter  20 A. When both pseudo voltages are correctly generated as described above, a YES determination is generated at Step  130 A, indicating that the A-D converter  20 A is functioning properly. 
     It is then determined whether the respective polarities of the first and second pseudo voltages described above are correct at Step  140 A. Here, the pseudo signal P 11  of the acceleration detecting section  11   a  is positive and the pseudo signal P 2  of the acceleration detecting section  21   a  is negative. Accordingly, the processed pseudo signal output from the signal processing circuit  12  is positive and the processed pseudo signal output from the signal processing circuit  22  is negative. 
     Accordingly, when both first and second pseudo voltages of the A-D converter  20 A have values corresponding to both processed pseudo signals, the polarities of the pseudo voltages are both correct, indicating that both acceleration detecting circuits  10 ,  20 A are functioning properly. At this time, a YES determination is generated at Step  130 A. 
     Subsequently, the collision determination routine  150 A is initiated. When both G sensors  11 A,  21  generate acceleration signals SO 1 , SO 2 , respectively, from the acceleration detecting sections  11   a ,  21   a , both signal processing circuits  12 ,  22  output the processed acceleration signals, respectively. Then, each of the processed acceleration signals are converted sequentially into digital signals by the A-D converter  20 A and are input sequentially to the microcomputer  30  as the first and second acceleration voltages. 
     Based on the first and second acceleration voltages, the microcomputer  30  determines whether or not a condition (e.g., a logical product of maximum values of the acceleration voltages) required to activate the  15  airbag mechanism  60  exists. When it is determined that the condition of logical product exists, the activating circuit  50  activates the squib  51 , thereby activating the airbag mechanism  60  and expanding the airbag. As a result, a vehicle passenger is reliably protected. 
     Further, even if the microcomputer  30  erroneously generates the control signal CS, one of the outputs of the A-D converter  20 A has a value that will not activate the air bag mechanism  60 , as one of the pseudo signals P 11 , P 2  generated by the G sensors  11 A,  21  has a polarity opposite from the polarity of the corresponding acceleration signal. Accordingly, the air bag mechanism  60  will not be erroneously activated. 
     A NO determination is generated at Step  130 A when at least one of the first and second pseudo voltages from the A-D converter  20 A is not generated correctly in Step  130 A prior to a YES determination is generated at Step  140 A as described above. Such a NO determination indicates that the mechanism is not functioning properly. 
     In addition, a NO determination is generated at Step  140 A when the polarities of the first and second pseudo voltages do not match, indicating that at least one of the acceleration detecting circuits  10 A and  20  is malfunctioning. 
     Consequently, the alarm lamp  40  is lit at Step  160  in the same manner as in the first embodiment to notify the driver that the device is not working properly. 
     Because the polarity of the positive part of the acceleration signal SO 2  is opposite from the polarity of the pseudo signal P 2  in the second embodiment as described above, the air bag mechanism  60  will not be erroneously activated, as the pseudo signal P 2  is generated prior to the collision judgment processing routine at Step  150 A. 
     Third Embodiment 
     FIGS. 9-12 show a third embodiment of the present invention in which an acceleration detecting circuit is utilized in addition to the acceleration detecting circuit described in the first embodiment, and an A-D converter  20 A described in the second embodiment is adopted instead of the A-D converter  20  described in the first embodiment. 
     Although the acceleration detecting circuit  20 A′ has the same structure as that of the acceleration detecting circuit  20  described in the second embodiment, a G sensor  21 A corresponding to the G sensor  21  is mounted on the circuit board Ca so that it has a detecting direction indicated by an arrow B in FIG.  10 . 
     Therefore, the acceleration detecting section  21   a  generates an acceleration signal SO 21  (see FIG. 11B) in the G sensor  21 A. This acceleration signal SO 21  has a polarity opposite from that of the acceleration signal SO 1 . The structure other than is the same with the second embodiment. 
     The polarity of the positive part of the acceleration signal SO 1  is opposite from the polarity of the pseudo signal P 1  as described above. Therefore, the air bag mechanism  60  is not erroneously activated based on the pseudo signal P 1  when a NO determination is generated at Steps  130 A and  140 A. 
     Also, the polarities of both acceleration signals SO 1  and SO 2  are different from each other. Therefore, when the A-D converter  20 A malfunctions and when one of its converted values becomes a large value, the other converted value becomes a small value. Consequently, the an airbag mechanism activation condition does not exist, and the air bag mechanism  60  is not activated erroneously due to the malfunction of the A-D converter  20 A. 
     Because the acceleration detecting sections  11   a ,  21   a  of both G sensors  11 ,  21 A are mounted on the circuit board Ca to have detecting directions opposite from each other, the above-mentioned effect may be achieved by adopting the same elements as G sensors  11 ,  21 A as shown in the second embodiment. 
     FIG. 13 shows a modified example of the third embodiment. The G sensor  21 A described in the third embodiment is mounted on the circuit board Ca to have a detecting direction indicated by the arrow A in FIG. 10 within the acceleration detecting section  21   a  in the modified example. Therefore, the acceleration detecting section  21   a  generates the same acceleration signal SO 2  described in the second embodiment. The structure other than that is the same as the third embodiment. 
     The polarity of the positive part of the acceleration signal SO 2  is opposite from that of the pseudo signal P 2  in the modified example, in addition to the polarity of the positive part of the acceleration signal SO 1  being opposite from the polarity of the pseudo signal P 1 . Therefore, the air bag mechanism  60  will not be activated erroneously by the pseudo signals P 1  and P 2  after a NO determination is generated at Steps  130 A and  140 A. Therefore, the reliability of the air bag mechanism  60  is further enhanced. 
     Fourth Embodiment 
     FIGS. 14 and 15 show a fourth embodiment in which an acceleration detecting circuit  20 B is adopted instead of the acceleration detecting circuit described in the third embodiment. The acceleration detecting circuit comprises a G sensor  21 B as well as the signal processing circuit  22  described in the third embodiment. 
     The G sensor  21 B has a structure in which the inverter  21   c  shown in the third embodiment is eliminated. In the G sensor  21 B, the pseudo signal generating section  21   b  outputs a pseudo signal P 21  based on the signal CS (see FIG. 15B) and having a positive polarity to the signal processing circuit  22  via the acceleration detecting section  21   a . The G sensor  21 B is mounted on the circuit board Ca with the detecting direction in the direction of arrow A in FIG. 10 in the same manner as the G sensor  21 A. 
     In the fourth embodiment, the acceleration signal SO 1  from the acceleration detecting section  11   a  has a polarity opposite from that of the acceleration signal SO 21 , and the pseudo signal P 1  has a polarity opposite from that of the pseudo signal P 21 . Further, the positive part of the acceleration signal SO 1  has a polarity opposite from that of the pseudo signal P 1 , and the positive part of the acceleration signal SO 21  has a polarity opposite from that of the pseudo signal P 21 . 
     As a result, system reliability is further enhanced as compared to the third embodiment in determining whether the A-D converter  20 A and both acceleration detecting circuits  10 ,  20 B are out of order on and after Step  120 A based on the control signal Cs (see FIG.  12 ). System reliability is also enhanced regarding prevention of erroneous operation of the airbag mechanism  60  due to the erroneous generation of the control signal CS in at step  150 A in the crash determination routine. All other features are the same as those in the third embodiment. 
     Fifth Embodiment 
     FIG. 16 shows a fifth embodiment of the present invention in which the acceleration detecting circuits  10 B,  20 C are utilized instead of the acceleration detecting circuits described in the third embodiment. The acceleration detecting circuit  10 B comprises a G sensor  11 B and the signal processing circuit  12 . The G sensor  11 B has a structure in which an inverter  11 C and an output circuit  11   d  arc added to the G sensor  11  described in the fourth embodiment (see FIG.  14 ). 
     In the fifth embodiment, the acceleration detecting section  11   a  generates the acceleration signal through the output circuit  11   d . The pseudo signal generating section  11   b  generates the pseudo signal through the inverter  11   c , the acceleration detecting section  11   a  and the output circuit  11   d.    
     The acceleration detecting circuit  20 C comprises a G sensor  21 C and the signal processing circuit  22 . The G sensor  21 C has a structure in which the output circuit  21   d  is added to the G sensor  21 B described in the fourth embodiment. 
     The acceleration detecting section  21   a  generates the acceleration signal through the output circuit  21   d . The pseudo signal generating section  21   b  also generates the pseudo signal through the acceleration detecting section  21   a  and the output circuit  21   d . The output circuits  11   d ,  21   d  are not the same circuit, and both G sensors  11 B,  21 C are mounted on the circuit board Ca so that both output circuits  11   d ,  21   d  are positioned opposite from each other. 
     In the fifth embodiment, directions of change of the signals in the acceleration detecting circuits  10 B,  20 C change so as to have the same polarity when the acceleration detecting circuits  10 B,  20 C are exposed to external noises and electromagnetic waves. Therefore, the directions of change of the signals change in directions opposite from each other in terms of vehicle acceleration. 
     Accordingly, it is possible to prevent the acceleration detecting circuits  10 B,  20 C from erroneously indicating a vehicle collision state when the acceleration detecting circuits  10 B,  20 C are exposed to external noises and electromagnetic waves. As a result, it becomes possible to provide a collision-determining device that is highly reliable, even in the presence of external noise and electromagnetic waves. 
     Sixth Embodiment 
     FIG. 17 shows a sixth embodiment of the present invention. In the sixth embodiment, a G sensor  13  and a signal processing circuit  14  are utilized rather than the G sensor  11  and the signal processing circuit  12  described in the first embodiment (see FIG.  1 ). 
     The G sensor  13  is structured so that the inverter  11   c  and the pseudo signal generating section  11   b  are eliminated from the G sensor  11 . Accordingly, the G sensor  13  is composed of only the acceleration detecting section  11   a  and generates only the acceleration signal SO 1  generated by the G sensor  11 . 
     The signal processing circuit  14  comprises a signal processing section  14   a  and the inverter  11   c  and the pseudo signal generating section  11   b  of the G sensor  11  described above. 
     The signal processing section  14   a  amplifies the acceleration signal SO 1  from the G sensor  13  to generate a processed acceleration signal, and outputs it to the A-D converter  20 . It also amplifies the pseudo signal P 1  from the inverter  11   c  to generate a processed pseudo signal, and outputs it to the A-D converter  20 . 
     It should be noted that the pseudo signal generating section  11   b  generates a pulse-width pseudo signal in the same manner as described in the first embodiment. All other structure is also the same as the first embodiment. 
     In the sixth embodiment arranged as described above, the signal processing circuit  14  is determined to be properly functioning when a YES determination is made at Step  140  in FIG. 4 in the same manner as with the first embodiment. The signal processing circuit  14  is determined to not be functioning properly when a NO determination is made at Step  140 . 
     Accordingly, it is possible to determine correctly whether or not the signal processing circuit  14  is out of order by providing the inverter  11   c  and the pseudo signal generating section  11   b  in the signal processing circuit  14  as described above. The other operations and effects are the same as those described in the first embodiment. 
     Seventh Embodiment 
     FIG. 18 shows a seventh embodiment in which a G sensor  15  and a signal processing circuit  16  are utilized instead of the G sensor  11 A and the signal processing circuit  12  described in the second embodiment (see FIG.  5 ), and a G sensor  23  and a signal processing circuit  24  are adopted instead of the G sensor  21  and the signal processing circuit  22  described in the second embodiment. 
     The G sensor  15  has a structure in which the pseudo signal generating section  11   b  is eliminated from the G sensor  11 A described above. Accordingly, the G sensor  15  is composed of only the acceleration detecting section  11   a  and generates only the acceleration signal SO 1 . The signal processing circuit  16  comprises a signal processing section  16   a  and the pseudo signal generating section  11   b  of the G sensor  11 A described above. 
     The signal processing section  16   a  amplifies the acceleration signal SO 1  from the G sensor  15  to generate a processed acceleration signal, and outputs it to the A-D converter  20 A. The section  16   a  also amplifies the pseudo signal P 11  from the pseudo signal generating section  11   b  to generate a processed pseudo signal, and outputs it to the A-D converter  20 A. The pseudo signal generating section  11   b  generates the pseudo signal P 11  by receiving the control signal CS from the microcomputer  30  in the same manner with the second embodiment. 
     The G sensor  23  has a structure in which the inverter  21   c  and the pseudo signal generating section  21   b  are eliminated from the G sensor  21  described in the second embodiment. Accordingly, the G sensor  23  is composed of only the acceleration detecting section  21   a  and generates only the acceleration signal SO 2  generated by the G sensor  21 . 
     The signal processing circuit  24  comprises a signal processing section  24   a  and the inverter  21   c  and the pseudo signal generating section  21   b  of the G sensor  21  described above. The signal processing section  24   a  amplifies the acceleration signal SO 2  from the G sensor  23  to generate a processed acceleration signal, and outputs it to the A-D converter  20 A. The section  24   a  also amplifies the pseudo signal P 2  from the inverter  21   c  to generate a processed pseudo signal, and outputs it to the A-D converter  20 A. 
     It should be appreciated that the pseudo signal generating section  21   b  generates the pulse-width pseudo signal and outputs it to the inverter  21   c  to generate the pseudo signal P 2  from the inverter  21   c  by receiving the control signal CS from the microcomputer  30  in the same manner as in the second embodiment. The structure other than that described above is substantially the same as in the second embodiment. 
     When the processed pseudo signals of the signal processing circuits  16 ,  24  are positive and negative, respectively, at Step  140 A (see FIG. 8) described in the second embodiment, a YES determination is generated in the seventh embodiment arranged as described above, thereby indicating that both signal processing circuits  16  and  24  are functioning properly. On the other hand, when a NO determination is generated at Step  140 A, at least one of the signal processing circuits  16  and  24  is not functioning properly. 
     The seventh embodiment enables a collision determination to be accurately made whether or not the signal processing circuits  16 ,  24  are functioning properly, instead of the whether or not the G sensors  11 A and  21  are functioning properly, as in the second embodiment, as the signal processing circuits  16 ,  24  generate the processed pseudo signal based on the control signal of the microcomputer  30 . The other operations and effects are the same as those in the second embodiment. 
     Eighth Embodiment 
     FIG. 19 shows an eighth embodiment of the present invention. In the eighth embodiment, the G sensor  13  and the signal processing circuit  14  described in the sixth embodiment (see FIG. 17) are utilized. Further, a G sensor  25  and a signal processing circuit  26  are utilized instead of the G sensor  21 A and the signal processing circuit  22  described in the third embodiment (see FIG.  9 ). 
     The signal processing circuit  14  generates the processed acceleration signal and the processed pseudo signal via the signal processing section  14   a  and outputs the processed signals to the A-D converter  20 A in the same manner as in the sixth embodiment. 
     The G sensor  25  has a structure in which the inverter  21   c  and the pseudo signal generating section  21   b  are eliminated from the G sensor  21 A described above. Accordingly, the G sensor  25  is composed of only the acceleration detecting section  21   a  and generates only the acceleration signal SO 21  generated by the G sensor  21 A. 
     The signal processing circuit  26  comprises a signal processing section  26   a  and the inverter  21   c  and the pseudo signal generating section  21   b  of the G sensor  21 A described above. 
     The signal processing section  26   a  amplifies the acceleration signal SO 21  from the G sensor  25  to generate a processed acceleration signal and outputs it to the A-D converter  20 A. The section  26   a  also amplifies the pseudo signal P 2  from the inverter  21   c  to generate a processed pseudo signal and outputs it to the A-D converter  20 A. It is noted that the pseudo signal generating section  21   b  generates the pulse-width pseudo signal by receiving the control signal CS from the microcomputer  30 , and generates the pseudo signal P 2  from the inverter  21   c  in the same manner as in the third embodiment. The structure other than that described above is substantially the same as in the third embodiment. 
     The eighth embodiment arranged as described above enables a collision determination to be made whether the signal processing circuits  14 ,  26  are functioning properly, rather than the G sensors  11  and  21 A described in the third embodiment, by implementing the process in accordance with the flow diagram in FIG.  12 . The other operations and effects are the same as those in the third embodiment. 
     It is noted that the eighth embodiment may be modified as follows. Specifically, the G sensor  25  described in the eighth embodiment is mounted on the circuit board Ca so as to have a detecting direction as indicated by the arrow A in FIG.  10 . Therefore, the G sensor  25  generates the acceleration signal SO 2  in the same manner as described in the second embodiment. The structure other than the above is the same as in the eighth embodiment. 
     In the modification arranged as described above, the polarity of the positive part of the acceleration signal SO 2 , i.e., the polarity of the processed acceleration signal of the signal processing circuit  26 , is opposite from the polarity of the processed pseudo signal of the signal processing circuit  26 . In addition, the polarity of the positive part of the acceleration signal SO 1 , i.e., the polarity of the processed acceleration signal of the signal processing circuit  14 , is opposite that of the processed pseudo signal of the signal processing circuit  14 . 
     Therefore, the airbag mechanism  60  is not activated erroneously due to a NO determination at Steps  130 A and  140 A in FIG.  12 . Thus, reliability of the airbag mechanism  60  is further enhanced. 
     Ninth Embodiment 
     FIG. 20 shows a ninth embodiment of the invention. In the ninth embodiment, the G sensor  13  and the signal processing circuit  14  described in the sixth embodiment (see FIG. 17) are adopted instead of the G sensor  11  and the signal processing circuit  12  described in the fourth embodiment (see FIG.  14 ). Also, a G sensor  27  and a signal processing circuit  28  are adopted instead of the G sensor  21 B and the signal processing circuit  22  described in the fourth embodiment. 
     The G sensor  27  has a structure in which the pseudo signal generating section  21   b  is eliminated from the G sensor  21 B described above. Therefore, the G sensor  27  is composed of only the acceleration detecting section  21   a  and generates only the acceleration signal generated from the G sensor  21 B. 
     The signal processing circuit  14  generates the processed acceleration signal and the processed pseudo signal and outputs the signals to the A-D converter  20 A in the same manner as described above. The signal processing circuit  28  comprises a signal processing section  28   a  and the pseudo signal generating section  21   b  of the G sensor  21 B described above. 
     The signal processing section  28   a  amplifies the acceleration signal from the G sensor  27  to generate the processed acceleration signal, and outputs it to the A-D converter  20 A. The section  28   a  also amplifies the pseudo signal from the pseudo signal generating section  21   b  to generate the processed pseudo signal, and outputs it to the A-D converter  20 A. It is noted that the pseudo signal generating section  21   b  generates the pulse-width pseudo signal P 21  by receiving the control signal CS from the microcomputer  30  in the same manner with the fourth embodiment. The structure other than that is substantially the same as in the fourth embodiment. 
     It is possible to determine whether or not both signal processing circuits  14 ,  28  are functioning properly, instead of the both G sensors, substantially in the same manner with the eighth embodiment. The other operations and effects are the same as those in the fourth embodiment. 
     It is noted that the invention may be applied and embodied not only in the air bag system described in the above respective embodiments but also in a vehicle belt tensioner or the like. Also, converters may be stored in the microcomputer  30  as the A-D converters  20 ,  20 A. In addition, the number of the acceleration detectors is not limited to one or two as described in the respective embodiments, and may be three or more. 
     In such a case, it is possible to arrange such that at least two acceleration detecting circuits generate acceleration signals having opposite polarities from each other by the G sensors, and generate pseudo signals having the polarity opposite from the polarity of those acceleration signals based on the control signal. It is also possible to arrange such that at least two acceleration detecting circuits generate the pseudo signals having opposite polarities from each other by the respective G sensors based on the control signal. 
     Although the invention has been describe as being applied as a collision-determining circuit for determining a collision by detecting acceleration produced in the longitudinal direction of the vehicle, the invention is applicable to a collision-determining device which determines a vehicle collision based on acceleration produced in the right and left direction of the vehicle. 
     While the preferred embodiments of the invention have been described, variations thereto will occur to those skilled in the art within the scope of the present inventive concepts delineated by the following claims.