Abstract:
To achieve an air bag activation device that does not require the use of a mechanical safing sensor, the air bag activation device of the invention comprises: a first sensor for electronically detecting acceleration; second and third sensors, mounted at right and left front ends of a vehicle, for electronically detecting acceleration; a squib driver inserted between a power supply and a squib; a microcomputer for generating from outputs of the first, second, and third sensors a driving signal for driving the squib driver; safing signal generating means for generating a safing signal from the outputs of the second and third sensors; and an AND gate for receiving the driving signal and the safing signal as inputs, and for producing an output which is supplied to the squib driver.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority of Japanese Patent Application No. 2002-044831, filed on Feb. 21, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a device for activating an air bag, for occupant protection, in the event of a vehicle collision. 
   2. Prior Art 
     FIG. 1  shows the configuration of a prior art air bag activation device. In the figure, reference numeral  100  is a power supply for igniting an air bag, which usually comprises a battery and a backup capacitor. Reference numeral  101  is an acceleration sensor, generally known as a mechanical safing sensor, for mechanically detecting impact severity. Reference numeral  102  is an acceleration sensor, generally known as a G sensor, for electronically detecting impact severity. Reference numerals  103  and  104  are acceleration sensors mounted at the right and left front ends of a vehicle and used to electronically detect the severity of the impact applied to the vehicle; this type of sensor is generally known as a front sensor. 
   Further, reference numeral  105  is an igniter (hereinafter called the squib) which, when energized, ignites and causes a chemical to undergo a chemical reaction to generate gas. The gas is used to inflate the air bag. Reference numeral  106  is a microcomputer which processes the acceleration signals supplied from the G sensor  102  and the right and left front sensors  103  and  104 , determines whether the impact applied to the vehicle is of a severity that warrants the activation of the air bag, and if it is warranted, produces a signal for igniting the squib. 
   The section enclosed by dashed lines in  FIG. 1  is a squib ignition circuit which is usually implemented using an integrated ASIC. The ignition circuit  107  contains a decoder  108  for decoding the signal supplied from the microcomputer  106 , and for supplying a conduction signal to the bases of transistors  109  and  110  which together constitute a squib driver. The ignition circuit  107  further contains a receiving circuit  111  for receiving signals from the right and left front sensors  103  and  104 . Outputs of the receiving circuit  111  are sent to the microcomputer  106  which detects the mode of crash based on such factors as the difference between the impact severities detected by the right and left sensors. The detected information is used to determine the mode of air bag deployment. 
   In the air bag activation circuit described above, the acceleration (G) signals from the G sensor  102  and the right and left front sensors  103  and  104  are processed by the microcomputer  106  to determine whether the impact is due to a crash and to determine the mode of crash. If it is determined that a crash has occurred, the microcomputer  106  produces a signal to turn on the transistors  109  and  110 ; this signal is decoded by the decoder  108  and applied to the bases of the transistors  109  and  110 . As a result, the transistors  109  and  110  are turned on, and an ignition current is thus supplied to the squib. 
   On the other hand, the mechanical safing sensor  101  mechanically detects impact severity, independently of the G sensor  102  and the right and left front sensors  103  and  104 , and if the impact severity is greater than a predetermined value, the contact is closed to form a state in which a current can be supplied to the transistors  109  and  110 . The magnitude of impact severity that causes the mechanical safing sensor  101  to close the contact is chosen to be smaller than the magnitude of impact with which the G sensor  102  determines that a crash has occurred. 
   The reason is that the mechanical sensor  101  is provided primarily for safing purposes, that is, to prevent an erroneous activation of the air bag due to malfunctioning of the G sensor  102  or the microcomputer  106 ; more specifically, when an impact is distinctly detected by the mechanical sensor  101  and, on top of that, the G sensor  102  detects the occurrence of a crash, then the current is supplied to the transistors  109  and  110 . 
   Accordingly, in this ignition circuit, if the G sensor  102  or the microcomputer  106  malfunctions due to noise caused by an external electric wave or the like, and outputs a signal indicating the occurrence of a crash when actually a crash has not occurred, since such noise does not cause the mechanical safing sensor  101  to close its contact, an erroneous activation of the air bag is prevented. 
   As described above, in the prior art air bag activation circuit, a safing system is constructed by providing the mechanical sensor in addition to the electronic sensors in order to prevent an erroneous activation of the air bag due to malfunctioning of the electronic G sensor, the microcomputer, or the like. 
   SUMMARY OF THE INVENTION 
   However, such a mechanical safing sensor is large in size and expensive in construction, and thus remains a major barrier to achieving cost and size reductions in the commercial implementation of the activation device. There is therefore a need for an air bag activation device equipped with a safing system that does not use a mechanical sensor. 
   To solve the above problem, the present invention aims to develop a novel electronic safing system that utilizes the outputs of the right and left front sensors, and thus provide an air bag activation device that does not use a mechanical safing sensor. 
   To achieve this, a first air bag activation device according to the present invention comprises: a first sensor for electronically detecting acceleration; second and third sensors, mounted at right and left front ends of a vehicle, for electronically detecting acceleration; a squib driver inserted between a power supply and a squib; a microcomputer for generating from outputs of the first, second, and third sensors a driving signal for driving the squib driver; safing signal generating means for generating a safing signal from the outputs of the second and third sensors; and an AND gate for receiving the driving signal and the safing signal as inputs, and for producing an output which is supplied to the squib driver. 
   As described above, in the present invention, the safing system is constructed by utilizing the outputs of the second and third sensors mounted at positions entirely different from the position of the first sensor which is usually located near the center of the vehicle. Accordingly, even when the first sensor or the microcomputer malfunctions due to noise or other external disturbances, the safing system mounted in an entirely different position is unaffected by the noise and thus prevented from malfunctioning. Conversely, if the safing system malfunctions due to some kind of noise, the G sensor and the microcomputer are unaffected by the noise and are thus prevented from malfunctioning. 
   In this way, according to the present invention, the safing system and the G sensor/the microcomputer do not malfunction simultaneously; therefore, by making provisions to drive the squib driver by the AND of the two inputs, a device that can reliably activate the air bag by reliably detecting the occurrence of a crash can be constructed. 
   In the above-described device, the safing signal generating means, the squib driver, etc. are integrated into a single IC, and the microcomputer is provided separately from the IC. This serves to protect the safing signal generating means from a runaway of the microcomputer. 
   Further, in the device of the present invention, the microcomputer has a function to produce a safing signal from the outputs of the second and third sensors, and the fail-safe mechanism is improved by making provisions to generate the safing output only when the safing signal produced by the microcomputer matches the safing signal produced by the safing signal generating means. 
   A second air bag activation device according to the present invention comprises: first acceleration detecting means ( 5 ) for electronically detecting acceleration to determine if a crash has occurred; second acceleration detecting means ( 2 ,  3 ) mounted at a different position from the first acceleration detecting means ( 5 ) in order to identify a crash mode; and control means ( 12 ) for performing air bag ignition control based on signals supplied from the first ( 5 ) and second acceleration detecting means ( 2 ,  3 ) wherein first switching means ( 9 ) whose switching operation is controlled by the control means ( 12 ) based on the signal output from the first acceleration detecting means ( 5 ) and on the crash mode identified from the signal output from the second acceleration detecting means ( 2 ,  3 ), and second switching means ( 10 ), whose switching operation is controlled based on the signal output from the first acceleration detecting means ( 5 ), are connected in series in an air bag ignition current path. 
   According to the above device, the second switching means, whose switching operation is controlled based on the output of the second acceleration detecting means, for example, the left and right front sensors, is connected in series with the first switching means; therefore, as long as the second switching means is not turned on, based on the output of the second acceleration detecting means, a current does not flow in the series circuit consisting of the first and second switching means and the air bag is not activated. As a result, even when the control means or the first acceleration detecting means and the control means malfunction due to noise or the like, causing the first switching means to turn on, as the second switching means is not turned on, the current for activating the air bag does not flow and an erroneous activation of the air bag is thus prevented. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram showing the configuration of a prior art air bag activation device; 
       FIG. 2  is a diagram showing the configuration of a device according to one embodiment of the present invention; 
       FIG. 3  is a diagram showing the arrangement of various kinds of acceleration sensors on a vehicle; 
       FIG. 4  is a diagram showing the configuration of a device according to a second embodiment of the present invention; 
       FIG. 5  is a diagram showing one embodiment for a safing determination according to the present invention; 
       FIG. 6  is a diagram showing another embodiment for a safing determination according to the present invention; 
       FIG. 7  is a diagram showing the configuration of a device according to a third embodiment of the present invention; and 
       FIG. 8  is a diagram showing the configuration of a device according to a fourth embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiments of the present invention will be described below with reference to drawings. 
     FIG. 2  is a block diagram showing the configuration of an air bag activation circuit according to a first embodiment of the present invention. In the figure, reference numeral  1  is a power supply, and  2  and  3  are right and left front sensors mounted at the front ends of a vehicle and used primarily to detect the mode of crash. Further, reference numeral  4  is a microcomputer,  5  is a G sensor, and  6  is a squib. These component elements are the same or similar in configuration to the corresponding elements in the prior art circuit, and will not be described in detail here. 
   Reference numeral  7  is an ignition circuit which constitutes a unique feature of the present embodiment, and comprises: a decoder  8  for decoding the signal supplied from the microcomputer  4 , and for supplying a signal for igniting the squib  6  to the transistors  9  and  10  which together constitute a squib driver, a safing determination circuit  11  for performing a safing determination by detecting signals from the right and left front sensors  2  and  3 ; and a logic circuit  12  for signal processing. The logic circuit  12  comprises an OR circuit  13  for ORing the determination outputs corresponding to the right and left front sensors  2  and  3 , and an AND circuit  14  for ANDing the output of the OR circuit  13  with the output of the decoder  8 . 
     FIG. 3  shows the positions of the right and left front sensors  2  and  3  relative to the position of the air bag activation circuit  15  on the vehicle. The air bag activation circuit  15  includes the microcomputer  4 , the G sensor  5 , the squib  6 , and the ignition circuit  7 . 
   In the present embodiment, the safing determination circuit  11  is provided within the ignition circuit  7  which is implemented as an integrated ASIC separately from the microcomputer  4 . Generally, the microcomputer has the risk of runaway; in that case, if the safing determination circuit  11  were integrated into the microcomputer, the safing determination circuit  11  might erroneously recognize a non-crash event as being a crash and activate the air bag when actually a crash has not occurred. To prevent such a situation, in the present embodiment, the microcomputer  4  is provided outside the IC so that the safing determination circuit  11  will not be affected in the event of runaway of the microcomputer. 
   As shown in  FIG. 3 , the G sensor  5  and the right and left front sensors  2  and  3  are located at different positions on the vehicle so as to prevent the two types of sensors from malfunctioning simultaneously. Taking advantage of this, the safing system in the present embodiment is constructed using the front sensors and does not use the traditional mechanical safing sensor. 
   Accordingly, when the safing determination circuit  11  determines from the outputs of the right and left front sensors  2  and  3  that at least one of the sensors has detected a crash, the resulting signal is input to the AND circuit  14  via the OR circuit  13 . In this case, if a crash detection signal from the G sensor  5  is also input to the AND circuit  14  via the microcomputer  4  and the decoder  8 , the AND circuit  14  opens its gate and supplies its output signal to the base of the transistor  9  which is thus turned on. As the transistor  10  is already turned on by the output of the decoder  8 , a current flows from the power supply  1  to the squib  6  and the air bag is thus activated. 
   On the other hand, when neither of the front sensors  2  and  3  detects a crash and the gate of the OR circuit  13  is not opened, if the G sensor  5  detects a crash and the microcomputer  4  outputs a crash detection signal to turn on the transistor  7 , the transistor  9  remains off because the gate of the AND circuit  14  is closed. As a result, no current flows to the squib  6 , so that the air bag will not be activated. That is, in this case, the crash detection by the G sensor  5  is judged to be an erroneous detection due to noise. 
   The safing determination circuit  11  performs a safing determination using a crash determining threshold which is set lower than that of the determination that the microcomputer  4  makes based on the output of the G sensor  5 . As a result, in the air bag activation circuit of the present embodiment, a current flows to the squib and the air bag is activated, only when at least either one of the right and left front sensors has detected a severe impact and, at the same time, the G sensor  5  has detected the occurrence of a crash. Accordingly, if the G sensor malfunctions due to some kind of noise, as neither front sensor detects a severe impact, the safing system does not operate and an erroneous activation of the air bag is thus prevented. 
     FIG. 4  is a diagram showing the configuration of an air bag activation circuit according to a second embodiment of the present invention. In this embodiment, the outputs of the right and left front sensors  2  and  3  in the activation circuit shown in  FIG. 2  are introduced into the microcomputer  4  where a safing determination is performed, and the output of the determination is fed to a second AND circuit  15  via the decoder  8 . The other input of the AND circuit  15  is supplied with the safing signal output from the OR circuit  13 . Accordingly, the AND circuit  15  produces an output only when the safing determination made in the microcomputer  4  matches the safing determination made in the integrated ASIC. 
   In this way, the embodiment of  FIG. 4  achieves further stabilization of the safing system by employing a kind of fail-safe mechanism which requires that the safing determination made in the microcomputer match the safing determination made in the integrated ASIC. 
     FIG. 5  shows one embodiment for the safing determination performed in  FIGS. 2 and 4 . First, when the signal from the right front sensor  2  is input in step S 1  in serial form to the safing determination circuit  11 , the serial signal is converted to parallel form (step S 2 ), after which the signal is decoded into G data (step S 3 ) and stored in a G data register. The thus stored G data is compared bit by bit with the contents of the register in which a predetermined safing determination value is prestored, and if it is determined that the G data exceeds the level of the determination value, a safing signal is output (step S 4 ). 
   After being held for a predetermined time (step S 5 ), the signal is input to the OR circuit together with the safing signal from the left front sensor obtained through similar steps (steps S 11  to S 15 ) performed in parallel with the above steps, and a final safing output is thus obtained (S 6 ). In steps S 5  and S 15 , the output after the safing determination is held for a predetermined time in order to adjust the time difference relative to the crash detection performed in the G sensor. 
     FIG. 6  is a diagram showing another embodiment for the safing determination. In this embodiment, after the serial/parallel conversion in step S 2 , S 12 , the signal is converted from digital to analog (step S 7 , S 17 ), and the level of the resulting analog value is discriminated using an integrator circuit (low-pass filter) (step S 8 , S 18 ). The feature of this integrator circuit is that the discrimination reference voltage level is predetermined and the safing determination is performed using this voltage level as the threshold value. 
   In this embodiment, the threshold value in the integrator circuit can be easily changed, for example, by changing the value of an external resistor  20  shown in FIG.  7 . Thus, the circuit is easily adaptable for a change in the crash G characteristic resulting from a change of the vehicle. 
     FIG. 8  is a diagram showing a further embodiment of the present invention. In this embodiment, the ignition circuit  7  shown in  FIG. 2  is provided, for example, in the driver-side air bag, and the safing output (the output of the OR gate  13 ) produced by the ignition circuit  7  is also supplied to ignition circuits  7   a ,  7   b , and  7   c  for other air bags such as the passenger-side air bag, rear seat air bag, etc. 
   Since the air bag ignition circuits  7   a ,  7   b , and  7   c  are identical in configuration, the configuration will be described by taking the air bag ignition circuit  7   a  as an example. Reference numeral  8   a  is a decoder to which the output of the microcomputer  4  is input,  14   a  is an AND circuit to which the output of the decoder  8   a  and the safing output of the ignition circuit  7  are input, and  9   a  and  10   a  are transistors constituting a driver circuit for activating a squib  6   a.    
   As shown, the air bag ignition circuit  7   a  is configured to utilize the safing output produced by the air bag ignition circuit  7 , which means that the air bag ignition circuits for seats other than the driver&#39;s seat need not be equipped with a safing determination circuit or an OR circuit. This simplifies the configuration of the ASIC for each of these circuits, and contributes to reducing the cost of the device. 
   The above embodiments have each been described by taking the electronic G sensors mounted at the left and right front ends of the vehicle as examples of the sensors used in the safing system, but it will be appreciated that other types of sensors can also be used to detect the mode of a crash by mounting the sensors at positions different from the position of the electronic G sensor located in the center of the vehicle. Furthermore, other than the electronic G sensors, various types of sensors such as strain sensors can also be used. 
   Further, in each of the above embodiments, the transistor  9  is turned on based on the ANDing between the signal from the safing determination circuit  11  and the signal from the microcomputer  4  but, alternatively, the transistor  9  may be turned on based only on the signal from the safing circuit  11 . 
   As described with reference to the various embodiments above, as the air bag activation device of the present invention does not require the use of a mechanical safing sensor as used in the prior art device, the invention offers a significant effect in reducing the size and cost of the device.