Abstract:
A vehicle occupant protection apparatus includes an occupant protection device, a control unit, and a sensor module. The sensor module includes an acceleration sensor for detecting first acceleration caused by a collision and second acceleration caused by a fault diagnosis of the sensor module, a signal processing circuit for producing first and second data corresponding to the first and second acceleration, respectively, and a signal output circuit for outputting a signal having the first data or the second data to the control unit. The control unit includes a diagnostic unit for performing the fault diagnosis based on the second data and a controller for controlling the protection device based on the first data. The signal output circuit adds a first code to the signal having the first data and adds a second code to the signal having the second data.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and incorporates herein by reference Japanese Patent Application No. 2006-58149 filed on Mar. 3, 2006. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a vehicle occupant protection apparatus for protecting an occupant of a vehicle in the event of a collision. 
       BACKGROUND OF THE INVENTION 
       [0003]    Typically, a vehicle occupant protection apparatus includes a sensor module having an acceleration sensor for outputting an acceleration signal corresponding to acceleration caused by a collision. The occupant protection apparatus detects collision based on the acceleration signal. 
         [0004]    In such an occupant protection apparatus, fault diagnosis of the sensor module is performed to ensure proper operation of the apparatus. For example, in an occupant protection apparatus disclosed in JP 2003-2157A, a control section outputs a diagnosis start signal to a sensor module and fault diagnosis of the sensor module is performed in response to the start signal. Then, the sensor module returns a result signal indicating the result of the diagnosis to the control section. The control section determines based on the result signal whether the sensor module is at fault. 
         [0005]    The control section cannot distinguish between the acceleration signal and the return signal, because each signal is the same type of signal. Specifically, each of the acceleration signal and the return signal is a voltage signal outputted from the acceleration sensor. Therefore, the control section interprets the first signal, which is inputted to the control section immediately after the control section outputs the start signal to the sensor module, as the result signal. 
         [0006]    However, there are fears that the control section misinterprets the return signal as the acceleration signal. Therefore, the control section may activate an occupant protection device (e.g., airbag) despite the fact that the collision does not occur. 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the above-described problem, it is an object of the present invention to provide a occupant protection apparatus in which an acceleration signal and a diagnostic signal can be clearly distinguished from each other to prevent an occupant protection device from being accidentally activated by the diagnostic signal. 
         [0008]    An occupant protection apparatus for a vehicle includes an occupant protection device, a control unit, and a sensor module. 
         [0009]    The occupant protection device may be, for example, an airbag device or a seat belt pretensioner device to absorb impact applied to an occupant in the event of a collision. The sensor module includes an acceleration sensor for detecting first acceleration caused by the collision, a signal processing circuit for producing first data corresponding to the first acceleration, and a signal output circuit. 
         [0010]    The control unit includes a diagnostic unit for performing a fault diagnosis of the sensor module and a controller for controlling the protection device based on the first data and a result of the fault diagnosis. 
         [0011]    The diagnostic unit outputs a start signal to the sensor module to perform the fault diagnosis of the sensor module. The sensor module further includes a start circuit for causing the acceleration sensor to detect second acceleration in response to the start signal. For example, the acceleration sensor performs self-vibration, i.e., vibrates itself in response to the start signal to detect the second acceleration. The signal processing circuit produces second data corresponding to the second acceleration. 
         [0012]    The signal output circuit of the sensor module outputs a signal having the first data or the second data to the control unit. The diagnostic unit performs the fault diagnosis of the sensor module based on the second data and the controller controls the protection device based on the first data. The signal output circuit adds a first code to the signal having the first data and adds a second code to the signal having the second data. 
         [0013]    Thus, the signal having the first data related to the collision and the signal having the second data related to the diagnosis can be clearly distinguished from each other. Therefore, the controller can be prevented from controlling the occupant protection device based on the second data so that the occupant protection device can be prevented from accidentally activated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The above and other objectives, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
           [0015]      FIG. 1  is a block diagram of a vehicle occupant protection apparatus according to an embodiment of the present invention; and 
           [0016]      FIG. 2A  shows a signal outputted from an output circuit of a sensor module of the occupant protection apparatus of  FIG. 1 ,  FIG. 2B  shows the signal containing first data related to a collision, and  FIG. 2C  shows the signal containing second data related to a fault diagnosis. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    As shown in  FIG. 1 , an airbag apparatus  1  according to an embodiment of the present invention includes an occupant protection device  10 , an electronic control unit (ECU)  20 , and a sensor module  30 . 
         [0018]    The protection device  10  may be, for example, an airbag installed in a steering wheel hub to protect a driver in the event of a frontal collision. 
         [0019]    The ECU  20  includes a controller  21  and a diagnostic unit  22 . The diagnostic unit  22  outputs a diagnosis start signal S 1  to the sensor module  30  to start fault diagnosis of the sensor module  30 . The sensor module  30  returns a response signal S 2  to the diagnostic unit  22 . The diagnostic unit  22  performs the fault diagnosis of the sensor module  30  based on the response signal S 2 . Then, the diagnostic unit  22  outputs a result signal S 3  indicating a result of the diagnosis to the controller  21 . The controller  21  activates the protection device  10  based on the response signal S 2  and the result signal S 3 . For example, if the result signal S 3  indicates that the sensor module  30  is at fault, the controller  21  does not activate the protection device  10 . 
         [0020]    The sensor module  30  includes an acceleration sensor  31 , a filter circuit  32 , an amplifier circuit  33 , an analog-to-digital (A/D) converter  34 , a start circuit  35 , first and second diagnostic circuits  36 ,  37 , and a signal output circuit  38 . 
         [0021]    The acceleration sensor  31  detects acceleration of a vehicle. For example, the collision vibrates the acceleration sensor  31  and the acceleration sensor  31  detects a first acceleration caused by the collision. Then, the acceleration sensor  31  outputs a first analog signal corresponding to the first acceleration to the filter circuit  32 . Also, the acceleration sensor  31  performs self-vibration, i.e., vibrates itself in response to the start signal S 1  outputted from the start circuit  35 . The acceleration sensor  31  detects a second acceleration caused by the self-vibration and outputs a second analog signal corresponding to the second acceleration to the filter circuit  32 . The first and second analog signals are the same type of signal so that the first and second analog signals cannot be distinguished from each other. 
         [0022]    The filter circuit  32  eliminates noise components from the first and second analog signals. The amplifier circuit  33  amplifies the filtered first and second analog signals. The A/D converter  34  converts the amplified first and second analog signals to first and second digital data D 1 , D 2 , respectively. For example, each of the first and second digital data D 1 , D 2  is a 12-bit data. 
         [0023]    The start circuit  35  receives the start signal S 1  from the ECU  20  and outputs the start signal S 1  to each of the acceleration sensor  31 , the first diagnostic circuit  36 , and the second diagnostic circuit  37 . 
         [0024]    Upon receiving the start signal S 1 , the first diagnostic circuit  36  checks functions of internal devices of the sensor module  30  and diagnoses whether the internal devices operate normally. For example, the internal devices include a read only memory (ROM), which is not shown in the drawings. Then, the first diagnostic circuit  36  outputs a result signal S 4  indicating a result of the diagnosis to the output circuit  38 . 
         [0025]    Upon receiving the start signal S 1 , the second diagnostic circuit  37  enables input from the A/D converter  34 . Thus, the second diagnostic circuit  37  receives the second digital data D 2  that is outputted from the A/D converter  34  immediately after the second diagnostic circuit  37  receives the start signal S 1 . Based on the second digital data D 2 , the second diagnostic circuit  37  diagnoses whether each of the acceleration sensor  31 , the filter circuit, the amplifier circuit  33 , and the A/D converter  34  operates normally. For example, the second diagnostic circuit  37  compares the second digital data D 2  with a correct data prestored in the ROM. Then, the second diagnostic circuit  37  outputs a result signal S 5  indicating a result of the diagnosis to the output circuit  38 . 
         [0026]    The output circuit  38  receives the first and second digital data D 1 , D 2  from the A/D converter  34  and also receives the result signals S 4 , S 5  from the first and second diagnostic circuits  36 ,  37 , respectively. The output circuit  38  generates the response signal S 2  based on the result signals S 4 , S 5  and the digital data D 1 , D 2  and then outputs the response signal S 2  to the ECU  20 . 
         [0027]    The response signal S 2  is a 16-bit digital signal. As shown in  FIG. 2A , the twelve high-order bits of the response signal S 2  is the first digital data D 1  or the second digital data D 2  and the four low-order bits of the response signal S 2  is a 4-bit code. 
         [0028]    The code represents whether the response signal S 2  includes the first digital data D 1  or the second digital data D 2 . Specifically, as shown in  FIG. 2B , when the code is a first code C 1 , the response signal S 2  includes the first digital data D 1 . For example, the first code C 1  is “1010”. In contrast, as shown in  FIG. 2C , when the code is a second code C 2 , the response signal S 2  includes the second digital data D 2 . The second code C 2  indicates whether the sensor module  30  is at fault. For example, when the second code C 2  is “1001”, the sensor module  30  operates normally. When the second code C 2  is “0110”, the sensor module  30  is at fault. 
         [0029]    In a first case where the diagnostic unit  22  of the ECU  20  does not output the start signal S 1  to the start circuit  35  of the sensor module  30 , the output circuit  38  does not receive the result signals S 4 , S 5  from the first and second diagnostic circuits  36 ,  37 , respectively. In this case, the outputs circuit  80  interprets the digital data received from the A/D converter  34  as the first digital data D 1  and generates the response signal S 2  consisting of the first digital data D 1  and the first code C 1  of “1010”. 
         [0030]    Then, the output circuit  38  outputs the response signal S 2  to each of the controller  21  and the diagnostic unit  22  of the ECU  20 . The diagnostic unit  22  performs the fault diagnosis of the sensor module  30  only when the code of the response signal S 2  is the second code C 2 . Since the code of the response signal S 2  is the first code C 1 , the diagnostic unit  22  ignores the first digital data D 1  and does not perform the fault diagnosis of the sensor module  30  based on the first digital data D 1 . 
         [0031]    In contrast, the controller  21  controls the protection device  10  only when the code of the response signal S 2  is the first code C 1 . Since the code of the response signal S 2  is the first code C 1 , the controller  21  determines based on the first digital data D 1  whether the collision occurs. If the controller  21  determines that the collision occurs, the controller  21  outputs a drive signal S 6  to the protection device  10 . The protection device  10  is activated by the drive signal S 6 . 
         [0032]    In a second case where the diagnostic unit  22  outputs the start signal S 1  to the start circuit  35 , the output circuit  38  receives the result signals S 4 , S 5  from the first and second diagnostic circuits  36 ,  37 , respectively. In this case, the outputs circuit  80  interprets the digital data received from the A/D converter  34  as the second digital data D 2  and generates the response signal S 2  consisting of the second digital data D 2  and the second code C 2 . If both the result signals S 4 , S 5  represent that the sensor module  30  operates normally, the outputs circuit  80  sets the second code C 2  to “1001”. If at least one of the result signals S 4 , S 5  represents that the sensor module  30  is at fault, the output circuit  38  sets the second code S 2  to “0110”. 
         [0033]    Then, the output circuit  38  outputs the response signal S 2  to each of the controller  21  and the diagnostic unit  22  of the ECU  20 . Since the code of the response signal S 2  is the second code C 2 , the diagnostic unit  22  performs the fault diagnosis of the sensor module  30 . Specifically, the diagnostic unit  22  determines whether the second code C 2  is “1001” or “0110”. When the second code C 2  is “1001”, the diagnostic unit  22  determines that the sensor module  30  operates normally. In contrast, when the second code C 2  is “0110”, the diagnostic unit  22  determines that the sensor module  30  is at fault. Then, the diagnostic unit  22  outputs the result signal S 3  indicating the result of the diagnosis to the controller  21 . 
         [0034]    The controller  21  ignores the second digital data D 2  and does not control the protection device  10  based on the second digital data D 2 , because the code of the response signal S 2  is the second code C 2 . 
         [0035]    Thus, the ECU  20  can accurately determine whether the response signal S 2  includes the first digital data D 1  related to the collision or the second digital data D 2  related to the fault diagnosis. Therefore, the ECU  20  can be prevented from accidentally activating the protection device  10 . 
       (Modifications) 
       [0036]    The embodiment described above may be modified in various ways. For example, the protection device  10  may be a seat belt pretensioner or the like. 
         [0037]    Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.