Abstract:
An apparatus ( 10 ) for controlling a vehicle actuatable occupant restraining system including a crash accelerometer ( 32 ) for sensing frontal crash acceleration and providing a first crash acceleration signal indicative thereof. A side crash accelerometer ( 46, 48 ) senses transverse crash acceleration and provides a second crash acceleration signal indicative thereof. A controller ( 50 ) actuates the actuatable occupant restraining system in response to the first crash acceleration signal and the transverse crash acceleration signal.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for controlling a vehicle actuatable occupant restraining device and is particularly directed to a method and apparatus for controlling a front actuatable restraining device using a specific safing function. 
     BACKGROUND OF THE INVENTION 
     Air bag restraining systems in vehicles for vehicle occupants are known in the art. An air bag restraining system may include a multistage inflator device where the stages are actuated at different times in response to sensed vehicle crash conditions. 
     U.S. Pat. No. 5,935,182 to Foo et al., assigned to TRW Inc., discloses a method and apparatus for discriminating a vehicle crash condition using virtual crash sensing. U.S. Pat. No. 6,036,225 to Foo et al., assigned to TRW Inc., discloses a method and apparatus for controlling a multistage actuatable restraining system in a vehicle using crash severity index values. U.S. Pat. No. 6,186,539 to Foo et al., also assigned to TRW Inc., discloses a method and apparatus for controlling a multistage actuatable restraining device using crash severity indexing and crush-zone sensors. U.S. Pat. No. 6,529,810 to Foo et al., also assigned to TRW Inc., discloses a method and apparatus for controlling an actuatable multistage restraining device using switched thresholds based on transverse acceleration. 
     The use of safing functions in the control of actuatable restraining devices is also known in the art. Early known systems used a discrimination inertia switch and a series connected safing switch. When both the discrimination switch and the safing switch closed, the restraining device was actuated. Other known systems included a crash accelerometer, a discrimination algorithm for analyzing the crash accelerometer output signal, and a sating switch. When the discrimination algorithm determined a deployment crash event was occurring and the safing switch closed, the restraining device was actuated. Still other known systems used a discrimination crash acceleration sensor oriented in a direction of expected crash and a safing crash acceleration sensor oriented in the same direction. Associated algorithms process the signals from the two sensors and control the restraint when both determined a deployment crash event was occurring. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method and apparatus for controlling a frontal actuatable occupant restraining system using side satellite safing sensors. 
     An apparatus for controlling a vehicle actuatable occupant restraining system comprising a crash accelerometer for sensing frontal crash acceleration and providing a first crash acceleration signal indicative thereof. A side crash accelerometer senses transverse crash acceleration and provides a second crash acceleration signal indicative thereof. A controller actuates the actuatable occupant restraining system in response to the first crash acceleration signal and the transverse crash acceleration signal. 
     A method is provided for controlling a vehicle actuatable occupant restraining system comprising the steps of sensing frontal crash acceleration and providing a first crash acceleration signal indicative thereof, sensing transverse crash acceleration and providing a second crash acceleration signal indicative thereof, and actuating the actuatable occupant restraining system in response to the first crash acceleration signal and the transverse crash acceleration signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the invention will become apparent to one skilled in the art upon consideration of the following description of the invention and the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of a vehicle having an actuatable occupant restraining system in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a schematic block diagram of a portion of the actuatable occupant restraining system shown in  FIG. 1  in more detail; 
         FIG. 3  is an electrical schematic block diagram of the actuatable occupant restraining system shown in  FIG. 1 ; 
         FIG. 4  shows graphical representations of determined crash related values and thresholds used in an exemplary embodiment of the present invention; 
         FIG. 5  is a logic diagram showing deployment control logic in accordance with an exemplary embodiment of the present invention; and 
         FIG. 6  is a diagram showing inflator mapping in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1-3 , an actuatable occupant restraining system  10 , in accordance with an exemplary embodiment of the present invention, for use in a vehicle  12 , includes a driver&#39;s side, multistage, front actuatable restraining device  14 , and a passenger&#39;s side, multistage, front actuatable restraining device  18 . Other actuatable restraining devices could be included such as a driver&#39;s actuatable side restraining device  16  and a passenger&#39;s actuatable side restraining device  20 . The actuatable occupant restraining system  10  could further include a driver&#39;s side pretensioner  22 , and a passenger&#39;s side pretensioner  24 . The present invention is not limited to use with a multistage air bag restraining system responsive to frontal crash events. The present invention is applicable to any actuatable restraining device triggered in response to a frontal crash event. A front air bag having plural actuatable stages is described here for purposes of explanation. 
     The system  10  includes a central control unit (“CCU”)  30  located at a substantially central location of the vehicle. In accordance with an exemplary embodiment, CCU  30  includes a crash acceleration sensor  32  having its axis of sensitivity substantially oriented to sense crash acceleration in the vehicle X-direction (i.e., parallel with or substantially parallel with the front-to-rear axis of the vehicle) that provides a crash acceleration signal designated herein as CCU_ 1 X. The crash acceleration signal from the crash sensor  32  can take any of several forms. The crash acceleration signal can have amplitude, frequency, pulse duration, etc., or any other electrical characteristic(s) that varies as a function of the sensed crash acceleration. In accordance with a preferred embodiment, the crash acceleration signal CCU_ 1 X has frequency and amplitude characteristics indicative of the sensed crash acceleration. 
     In addition to the crash acceleration sensor  32 , the system  10  includes forwardly located, crush-zone satellite acceleration sensors (“CZS”)  40  and  42  located in a crush-zone location of the vehicle  12 . The crush-zone sensor  40  is located on the driver&#39;s side of the vehicle and has an XY-axis of sensitivity substantially oriented to sense crash acceleration parallel with the vehicle&#39;s X-axis, i.e., front-to-rear axis. The crush-zone sensor  42  is located on the passenger&#39;s side of the vehicle and has an axis of sensitivity substantially oriented to sense crash acceleration parallel with the vehicle&#39;s X-axis, i.e., front-to-rear axis. The signal from the driver&#39;s side, crush-zone sensor  40  is designated herein as CZS_ 3 X. The signal from the passenger&#39;s side, crush-zone sensor  42  is designated herein as CZS_ 4 X. 
     The signals from the crush-zone sensors  40  and  42  also have frequency and amplitude characteristics indicative of the crash acceleration experienced and sensed by those sensors at those sensor locations of the vehicle. The crush-zone sensors  40 ,  42  are in one exemplary embodiment mounted at or near the radiator location of the vehicle and serve a two-fold purpose. First, they serve to provide a safing function in frontal crash events using the CCU_ 1 X sensor as the main discriminatory sensor in accordance with the present invention. Also, the crush-zone sensors function in selecting the thresholds to be evaluated in the main crash discrimination algorithm. 
     A driver&#39;s side-satellite crash acceleration sensor (“RAS”)  46  is mounted on the driver&#39;s side of the vehicle such as at the B-pillar and has its axis of sensitivity substantially oriented to sense crash acceleration parallel with the vehicle&#39;s Y-axis, i.e., substantially perpendicular to the vehicles front-to-rear axis. The crash acceleration sensor  46  provides a crash acceleration signal designated herein as RAS_ 1 Y having frequency and amplitude characteristics indicative of crash acceleration in the Y-axis direction with acceleration into the driver&#39;s side of the vehicle having a positive value. 
     A passenger&#39;s side-satellite crash acceleration sensor (“RAS”)  48  is mounted on the passenger&#39;s side of the vehicle such as at the B-pillar and has its axis of sensitivity substantially oriented to sense crash acceleration parallel with the vehicle&#39;s Y-axis, i.e., substantially perpendicular to the vehicles front-to-rear axis. The crash acceleration sensor  48  provides a crash acceleration signal designated herein as RAS_ 2 Y having frequency and amplitude characteristics indicative of crash acceleration in the Y-axis direction with acceleration into the passenger&#39;s side of the vehicle having a positive value. In accordance with the present invention, the side satellite sensors  46 ,  48  provide a safing function for frontal crash events. It will be appreciated that the sensors  46 ,  48  may be used to control the side restraints  16 ,  20  in accordance with known algorithms such as U.S. Pat. No. 5,758,899 to Foo et al. 
     The crash acceleration signals CCU_ 1 X, CZS_ 3 X, CZS_ 4 X, RAS_ 1 Y; and RAS_ 2 Y are provided to a controller  50  in the CCU  30 , through associated hardware, high-pass/low-pass filters  52 ,  58 ,  60 ,  62 , and  64 , respectively. The controller  50  may be a microcomputer. Although a microcomputer is described in this exemplary embodiment, the invention is not limited to the use of a microcomputer for a controller. The present invention contemplates that the functions performed by the controller could be carried out by other digital and/or analog circuitry and/or could be assembled on one or more circuit boards and/or as an application specific integrated circuit (“ASIC”). 
     The filters  52 ,  58 ,  60 ,  62 , and  64 , filter their associated crash acceleration signals to remove frequency components that are not useful in analyzing and evaluation of a vehicle crash event, e.g., frequency components resulting from road noise. Frequencies useful for crash evaluation and analysis can be determined through empirical testing of a vehicle platform of interest. 
     The controller  50  monitors the filtered crash acceleration signals and performs one or more crash algorithms to determine whether a vehicle deployment or non-deployment crash event is occurring. Each crash algorithm measures and/or determines values of the crash event from the crash acceleration signals. These values are used in deployment and actuation decisions. Such measured and/or determined crash values are referred to herein as “crash metrics” and include but are not limited to crash acceleration, crash energy, crash velocity, crash displacement, crash jerk, etc. Based upon the crash acceleration signals, the controller  50 , in accordance with the present invention, controls the actuatable restraining devices  14 ,  18 . 
     Other driver associated sensors could be used to detect characteristics of the driver (for the driver&#39;s side restraints) and provide inputs used by the controller  50  in its control algorithm to control the actuatable restraining devices  14  and  16 . These sensors could include a driver&#39;s buckle switch sensor  70  that provides a signal to controller  50  indicating whether the driver has his seatbelt buckled. Driver&#39;s weight sensors  72  located in the driver&#39;s seat  74  provide a signal indicative of the driver&#39;s sensed weight. Other driver associated sensors  76  provide other driver related information to the controller  50  such as position, height, girth, movement, etc. The sensors  76  may take the form of cameras, infrared sensors, ultrasonic sensors, etc. All of this information is further useful in the control of the driver&#39;s associated restraining device(s). 
     Other passenger associated sensors could be used to detect characteristics of the passenger and provide inputs for the controller  50  in its control algorithm to control the actuatable restraining devices  18  and  20 . These sensors could include a passenger&#39;s buckle switch sensor  80  that provides a signal to controller  50  indicating whether the passenger has his seatbelt buckled. Passenger&#39;s weight sensors  82  located in the passenger&#39;s seat  84  provide a signal indicative of the passenger&#39;s sensed weight. Other passenger associated sensors  86  provide other occupant information to the controller  50  related to the passenger such as position, height, girth, movement, etc. The sensors  86  may take the form of cameras, infrared sensors, ultrasonic sensors, etc. Other sensors  88  provide signals to the controller  50  indicative of whether a passenger is present on the seat  84 , whether a child restraining seat is present on the seat  84 , etc. The sensors  88  may take the form of cameras, infrared sensors, ultrasonic sensors, etc., also. All of this information is further useful in the control of the passenger&#39;s associated restraining device(s). 
     In accordance with an exemplary embodiment of the present invention, the air bag restraining device  14  includes a first actuatable stage  90  and a second actuatable stage  92 , e.g., two separate sources of inflation fluid in fluid communication with a single air bag restraining device  14 . Each stage  90 ,  92 , has an associated squib (not shown) that, when energized with sufficient current for a sufficient time period, initiates fluid flow from an associated fluid source. When one stage is actuated, a percentage less than 100% of the maximum possible inflation of the air bag restraining device  14  occurs. To achieve 100% inflation, the second stage must be actuated within a predetermined time of the first stage actuation. More specifically, the controller  50  performs a crash algorithm using determined crash metrics and outputs one or more signals to the actuatable restraining device  14  for effecting actuation of one or both actuatable inflation stages  90  and  92  at times to achieve a desired inflation profile and pressure. As mentioned, other actuatable restraining devices such as a pretensioner  22 , or other devices such as side restraining devices  16  would also be controlled. 
     As mentioned, each of the actuatable stages  90 ,  92  includes an associated squib (not shown) of the type well known in the art. Each squib is operatively connected to an associated source of gas generating material and/or a bottle of pressurized gas. The squibs are ignited by passing a predetermined amount of electrical current through them for a predetermined time period. Each squib ignites its associated gas generating material and/or pierces its associated pressurized gas bottle. The amount of gas released into the bag is a direct function of the number of stages actuated and the timing of their actuation. The more stages actuated during predetermined time periods, the more gas present in the air bag. In accordance with an exemplary embodiment, the air bag restraining device  14  includes two actuatable stages. If only one stage is actuated, less than 100% of the maximum possible inflation pressure occurs. If the two stages are actuated within 5 msec. of each other, 100% of the maximum possible inflation pressure occurs. If the stages are actuated approximately 20 msec. apart, a different, lesser percentage of the maximum possible inflation occurs. By controlling the actuation timing of the multiple stages, the dynamic profile of the bag is controlled, e.g., the inflation rate, the inflation pressure, etc. 
     The passenger&#39;s side restraining device  18  includes a first actuatable stage  94  and a second actuatable stage  96  controlled as described above with regard to the driver&#39;s side restraining device  14  to control the inflation profile/inflation pressure of the air bag. 
     In accordance with the present invention, a deployment controller  100  within the controller  50  controls the actuation of the first actuatable stages  90 ,  94  and second actuatable stages  92 ,  96  using determined crash metrics and other monitored sensor inputs. 
     Referring to  FIGS. 4 and 5 , a control process performed by the controller  50  to control actuation of the first and second stages will be better understood for the driver&#39;s side, multistage restraining device  14 . It should be understood that the passenger&#39;s side, multistage restraining device  18  is similarly controlled. As mentioned, the controller  50  is, in accordance with an exemplary embodiment, a microcomputer programmed to perform these described and illustrated functions. 
     The acceleration sensor  32 , an accelerometer in an exemplary embodiment, outputs the acceleration signal CCU_ 1 X having a characteristic (e.g., frequency and amplitude) indicative of the vehicle&#39;s crash acceleration upon the occurrence of a crash event. Since the axis of sensitivity of the accelerometer is oriented substantially parallel with the front-to-rear axis of the vehicle, the sensor  32  is particularly sensitive to crash events in the forward direction. The acceleration signal CCU_ 1 X is filtered by, in the exemplary embodiment, a hardware (i.e., separate from the controller  50 ) high-pass-filter (“HPF”)/low-pass-filter (“LPF”)  52  to eliminate frequencies resulting from extraneous non-crash vehicle operating events and/or input signals resulting from such things as road noise. The frequency components removed through filtering are not indicative of the occurrence of a crash event for which deployment of the restraining device  14  is desired. Empirical testing is used to determine the frequency values of relevant crash signals for a particular vehicle platform of interest under a variety of crash conditions. Extraneous signal components that may be present in the crash acceleration signal not indicative of a crash event are appropriately filtered and signal characteristics indicative of a deployment crash event are passed for further processing. 
     The accelerometer  32 , in accordance with an exemplary embodiment, has a nominal sensitivity of ±100 g&#39;s (g being the value of acceleration due to earth&#39;s gravity, i.e., 32 feet per second squared or 9.8 m/s 2 ). In a multistage actuatable restraining system, it is desirable to continue sensing crash acceleration during the crash event, even after a first or initial trigger threshold is reached. Since a first stage actuation is desired upon the occurrence of crash acceleration well within ±100 g&#39;s, the further need for sensing is facilitated with the accelerometer  32  having a nominal sensitivity of ±100 g&#39;s. 
     The filtered output signal from accelerometer  32  is provided to an analog-to-digital (converter), that is, in an exemplary embodiment, internal to the controller  50  (e.g., an A/D input of a microcomputer) or could be to an external A/D converter. The A/D converter converts the filtered crash acceleration signal CCU_ 1 X into a digital signal. The output of the A/D converter is filtered, in the exemplary embodiment, with another high-pass/low-pass filter having filter values empirically determined for the purpose of eliminating small drifts and offsets associated with the A/D conversion. In a microcomputer embodiment of the present invention, the filter could be digitally implemented within the microcomputer. A determination function of the controller  50  determines two crash metric values Vel_Rel_ 1 X (“crash velocity”) and Displ_Rel_ 1 X (“crash displacement”) from the filtered crash acceleration signal CCU_ 1 X. These metric values are determined by first and second integrations of the acceleration signal from CCU_ 1 X. 
     The crash displacement value and crash velocity value may be determined using a virtual crash sensing process as described in U.S. Pat. No. 6,186,539 to Foo et al. and U.S. Pat. No. 6,036,225 to Foo et al. using a spring mass model of the occupant to account for spring forces and damping forces. A detailed explanation of a spring-mass model is found in U.S. Pat. No. 5,935,182 to Foo et al. 
     The crash metric values determined in crash velocity and crash displacement determination functions are used to compare the Vel_Rel_ 1 X value as a function of Displ_Rel_ 1 X against crash displacement varying thresholds in a comparison function of the controller  50 . The comparison function  124  compares the Vel_Rel_ 1 X value against a LOW threshold  130  and a SWITCHED LOW threshold  132  and also compares the Vel_Rel_ 1 X value against a HIGH threshold  134 . Crossing of the thresholds  130  or  132  is the discrimination portion of what controls actuation of the first stage  90  of the restraining device  14 . Which one of the two low thresholds  130  and  132  that is selected for discrimination control of the deployment of the first stage actuation  90  of the restraining device  14  is controlled in response to a determined CZS value in the X direction compared against an associated threshold values (referred to herein as asymmetric CZS segment value that varies as a function of the Displ_Rel_ 1 X value) or a determined RAS value in the Y direction compared against an associated threshold value (referred to herein as asymmetric RAS segment value that varies as a function of the Displ_Rel_ 1 X value) as discussed below. The control of the first stage actuation is further controlled in response to the crossing of a safing threshold value by at least one of CZS_ 3 X, CZS_ 4 X, RAS_ 1 Y, or RAS_ 2 Y. 
     Assuming the safing function is satisfied, the second stage  92  is actuated as a function of the time between a LOW (or SWITCHED LOW) threshold crossing and a HIGH threshold crossing ( 134 ) and in accordance with a predetermined inflator mapping function shown in  FIG. 6 . All three thresholds  130 ,  132 , and  134  vary as a function of the crash displacement Displ_Rel_ 1 X value and are empirically determined for a particular vehicle platform of interest. 
     In particular, the controller  50  determines the time period from when the determined crash velocity value Vel_Rel_ 1 X crosses the LOW threshold  130  or the SWITCHED LOW threshold  132  to when it exceeds the HIGH threshold  134 . This time period is referred to herein as the “Δt measurement”. This time period is a measure of the crash intensity. The shorter the time period Δt, the more intense the vehicle crash. It is this measure of Δt that is used in the control actuation of the second stage  92 . The second stage is not necessarily deployed at the time of the HIGH threshold crossing, but as a function of the Δt measurement in accordance with an inflator mapping function as described below and shown in  FIG. 6 . Again, this assumes actuation of the first stage because of both crossing of the threshold  130  or  132  and a TRUE of the safing function, i.e., the first stage is actuated. 
     In accordance with the present invention, the crush-zone sensors  40  or  42  or the side satellite sensors  41  or  43  detection of one of a plurality of a certain types of crash events can select the switched LOW threshold  132  rather than the LOW threshold value  130  for discrimination control of the deployment of the first stage  90 . 
     The crush-zone sensor  40  provides signal CZS_ 3 X having signal characteristics (e.g., frequency and amplitude) indicative of the vehicle&#39;s crash acceleration upon the occurrence of a crash event as sensed at the forward, front left location of the vehicle in the direction along the vehicle&#39;s X axis. The acceleration signal CZS_ 3 X is filtered by, in one exemplary embodiment, a hardware high-pass-filter (“HPF”)/low-pass-filter (“LPF”)  58  to eliminate frequencies resulting from extraneous vehicle operating events and/or inputs resulting from road noise. The frequency components removed through filtering are those frequencies not indicative of the occurrence of a crash event. Empirical testing is used to establish a frequency range or ranges of the relevant crash signals so that extraneous signal components present in the crash acceleration signal can be filtered and frequencies indicative of a crash event passed for further processing. 
     The filtered output signal is provided to an associated analog-to-digital (“A/D”) converter that may be internal to the controller  50  (e.g., an A/D input of a microcomputer) or an external A/D converter. The A/D converter converts the filtered crash acceleration signal CZS_ 3 X into a digital signal. The output of the A/D converter is further filtered with high-pass/low-pass filters having values empirically determined for the purpose of eliminating small drifts and offsets resulting from the conversion. In a microcomputer embodiment of the present invention, the filter would be digitally implemented within the microcomputer. The filtering functions provide filtered acceleration signal CSZ_ 3 X. 
     The controller  50  determines acceleration value designated A_MA_CZS_ 3 X from the CZS_ 3 X signal. This value is determined by calculating moving average value of the associated filtered acceleration signal from the crush-zone sensor  40 . A moving average is a sum of the last predetermined number of samples of the filtered acceleration signal. The average is updated by removing the oldest value, replacing it with the latest sample, and then determining the new average. 
     The determined crush-zone sensor acceleration value A_MA_CZS_ 3 X is first compared against a safing threshold  218  by a comparison function  226 . When A_MA_CZS_ 3 X crosses the safing threshold  218 , a safing flag is set TRUE. The safing flag of controller  50  must be true before the first stage actuation can occur. 
     The determined crush-zone sensor acceleration value A_MA_CZS_ 3 X as a function of the determined displacement value Displ_Rel_ 1 X is next compared against an asymmetric CZS_ 3 X segment threshold  220 , and a CZS_ 3 X special mapping segment threshold  222  in the threshold comparison function  226 . The threshold  222  and the threshold  220  vary as a function of Displ_Rel_ 1 X in a predetermined manner to achieve a desired control. The thresholds  220 ,  222  may be determined empirically for a particular vehicle platform of interest. The result of the comparison function  226  is output to an ORing function  230 . 
     The side satellite sensor  41  provides signal RAS_ 1 Y having characteristics (e.g., frequency and amplitude) indicative of the vehicle&#39;s crash acceleration upon the occurrence of a crash event in the direction along the vehicle&#39;s Y axis. Even during a frontal crash event, the sensor RAS_ 1 Y will output a signal that can be used for the safing purposes. The acceleration signal RAS_ 1 Y is filtered by, in an exemplary embodiment, a hardware high-pass-filter (“HPF”)/low-pass-filter (“LPF”)  62  to eliminate frequencies resulting from extraneous vehicle operating events and/or inputs resulting from road noise. The frequency components removed through filtering are those frequencies not indicative of the occurrence of a crash event. Empirical testing is used to establish a frequency range or ranges of the relevant crash signals so that extraneous signal components present in the crash acceleration signal can be filtered and frequencies indicative of a crash event passed for further processing. 
     The filtered output signal is provided to an associated analog-to-digital (“A/D”) converter that may be internal to the controller  50  (e.g., an A/D input of a microcomputer) or an external A/D converter. The A/D converter converts the filtered crash acceleration signal RAS_ 1 Y into a digital signal. The output of the A/D converter is further filtered with high-pass/low-pass filters having values empirically determined for the purpose of eliminating small drifts and offsets resulting from the conversion. In a microcomputer embodiment of the present invention, the filter would be digitally implemented within the microcomputer. The filtering functions provide filtered acceleration signal RAS_ 1 Y. 
     The controller  50  determines acceleration value designated A_MA_RAS_ 1 Y from the RAS_ 1 Y signal. This value is determined by calculating moving average value of the associated filtered acceleration signal from the side satellite sensor  41 . A moving average is a sum of the last predetermined number of samples of the filtered acceleration signal. The average is updated by removing the oldest value, replacing it with the latest sample, and then determining the new average. 
     The determined satellite sensor acceleration value A_MA_RAS_ 1 Y is first compared against a safing threshold  231  by a comparison function  236 . When A_MA_RAS_ 1 Y crosses the safing threshold  231 , a safing flag is set TRUE. The safing flag of controller  50  must be true before the first stage actuation can occur. 
     The determined satellite sensor acceleration value A_MA_RAS_ 1 Y as a function of the determined displacement value Displ_Rel_ 1 X is compared against an asymmetric RAS_ 1 Y segment threshold  232  and a RAS_ 1 Y special mapping segment threshold  234  in the threshold comparison function  236 . The threshold  232  and the threshold  234  vary as a function of Displ_Rel_ 1 X in a predetermined manner to achieve a desired control. The thresholds  232 ,  234  may be determined empirically for a particular vehicle platform of interest. The result of the comparison function  236  is output to the ORing function  230 . 
     The crush-zone sensor  42  is an accelerometer providing a signal CZS_ 4 X having characteristics (e.g., frequency and amplitude) indicative of the vehicle&#39;s crash acceleration in the X directions upon the occurrence of a crash event as sensed at the forward, front right location of the vehicle. The acceleration signal CZS_ 4 X is filtered by, in one exemplary embodiment, a hardware high-pass-filter (“HPF”)/low pass filter (“LPF”)  60  to eliminate frequencies resulting from extraneous vehicle operating events and/or inputs resulting from road noise. The acceleration signal CZS_ 4 X is filtered by, in one exemplary embodiment, a hardware high-pass-filter (“HPF”)/low pass filter (“LPF”)  60  to eliminate frequencies resulting from extraneous vehicle operating events and/or inputs resulting from road noise. The frequency components removed through filtering are those frequencies not indicative of the occurrence of a crash event. Empirical testing is used to establish a frequency range or ranges of the relevant crash signals so that extraneous signal components present in the crash acceleration signal can be filtered and frequencies indicative of a crash event passed for further processing. 
     The filtered output signal is provided to an associated analog-to-digital (“A/D”) converter that may be internal to the controller  50  (e.g., an A/D input of a microcomputer) or an external A/D converter. The A/D converter converts the filtered crash acceleration signal into a digital signal. The output of the A/D converter is filtered in one exemplary embodiment with high-pass/low-pass filter having filter values empirically determined for the purpose of eliminating small drifts and offsets resulting from the conversion. In a microcomputer embodiment of the present invention, the filter would be digitally implemented within the microcomputer. The filtering function outputs filtered acceleration signals CSZ_ 4 X. 
     The controller  50  determines acceleration values designated A_MA_CZS_ 4 X. This value is determined by calculating a moving average value of the filtered acceleration signal of the crush-zone sensors  42 . A moving average is a sum of the last predetermined number of samples of the filtered acceleration signal. The average is updated by removing the oldest value, replacing it with the latest sample, and then determining the new average. 
     The determined crush-zone sensor acceleration value A_MA_CZS_ 4 X is first compared against a safing threshold  248  by a comparison function  256 . When A_MA_CZS_ 4 X crosses the safing threshold  248 , a safing flag is set TRUE. The safing flag of controller  50  must be true before the first stage actuation can occur. 
     This determined crush-zone sensor acceleration value A_MA_CZS_ 4 X as a function of the determined displacement value Displ_Rel_ 1 X is compared against an asymmetric CZS_ 4 X segment threshold  250  and a special-mapping segment threshold  252  in a threshold comparison function  256  of the controller  50 . The threshold  252  and the threshold  250  vary as a function of Displ_Rel_ 1 X in a predetermined manner to achieve a desired control. The thresholds  250 ,  252  may be determined empirically for a particular vehicle platform of interest. The result of the comparison from the comparison function  256  is an input to the ORing function  230 . 
     The side satellite sensor  43  provides signal RAS_ 2 Y having characteristics (e.g., frequency and amplitude) indicative of the vehicle&#39;s crash acceleration upon the occurrence of a crash event in the direction along the vehicle&#39;s Y axis. Even during a frontal crash event, the sensor RAS_ 2 Y will output a signal that can be used for the safing purposes. The acceleration signal RAS_ 2 Y is filtered by, in an exemplary embodiment, a hardware high-pass-filter (“HPF”)/low-pass-filter (“LPF”)  64  to eliminate frequencies resulting from extraneous vehicle operating events and/or inputs resulting from road noise. The frequency components removed through filtering are those frequencies not indicative of the occurrence of a crash event. Empirical testing is used to establish a frequency range or ranges of the relevant crash signals so that extraneous signal components present in the crash acceleration signal can be filtered and frequencies indicative of a crash event passed for further processing. 
     The filtered output signal is provided to an associated analog-to-digital (“A/D”) converter that may be internal to the controller  50  (e.g., an A/D input of a microcomputer) or an external A/D converter. The A/D converter converts the filtered crash acceleration signal RAS_ 2 Y into a digital signal. The output of the A/D converter is further filtered with high-pass/low-pass filters having values empirically determined for the purpose of eliminating small drifts and offsets resulting from the conversion. In a microcomputer embodiment of the present invention, the filter would be digitally implemented within the microcomputer. The filtering functions provide filtered acceleration signal RAS_ 2 Y. 
     The controller  50  determines acceleration value designated A_MA_RAS_ 2 Y from the RAS_ 2 Y signal. This value is determined by calculating moving average value of the associated filtered acceleration signal from the side satellite sensor  43 . A moving average is a sum of the last predetermined number of samples of the filtered acceleration signal. The average is updated by removing the oldest value, replacing it with the latest sample, and then determining the new average. 
     The determined satellite sensor acceleration value A_MA_RAS_ 2 Y is first compared against a safing threshold  220  by a comparison function  266 . When A_MA_RAS_ 2 Y crosses the safing threshold  266 , a safing flag is set TRUE. The safing flag of controller  50  must be true before the first stage actuation can occur. 
     The determined satellite sensor acceleration value A_MA_RAS_ 2 Y as a function of the determined displacement value Displ_Rel_ 1 X is next compared against an asymmetric RAS_ 2 Y segment threshold  262  and a RAS_ 2 Y special mapping segment threshold  264  in a threshold comparison function  266 . The threshold  262  and the threshold  264  vary as a function of Displ_Rel_ 1 X in a predetermined manner to achieve a desired control. The thresholds  262 ,  264  may be determined empirically for a particular vehicle platform of interest. The result of the comparison function  266  is output to the ORing function  230 . 
     With the ORing function  230 , the controller  50  controls which threshold  130  or  132  is used to actuate the first stage deployment. If none of the determined values A_MA_CZS_ 3 X, A_MA_RAS_ 1 Y, A_MA_CZS_ 4 X, OR A_MA_RAS_ 2 Y cross their associated thresholds  220  (Asymmetric CZS_ 3 X Segment),  232  (Asymmetric RAS_ 1 Y Segment),  250  (Asymmetric CZS_ 4 X Segment), OR  262  (Asymmetric RAS_ 2 Y Segment), then threshold  130  is used. If any of them cross their associated thresholds, then the threshold  132  is used. The threshold  130  is also referred to herein as the Symmetric CCU 1 st  Stage Threshold. 
     Referring to  FIG. 5 , the logic process used by controller  50  is depicted to initiate a first stage deployment. As can be seen, if any of the CZS_ 3 X OR CZS_ 4 X OR RAS_ 1 Y OR RAS_ 2 Y safing comparisons crosses their associated thresholds, the ORing function  300  is TRUE or, HIGH. If (1) the output of the ORing function  300  is HIGH AND (ANDing function  302 ) (2) the VEL_REL_ 1 X value exceeds the low threshold  130 , the first stage is actuated. If (1) the output of the ORing function  300  is HIGH AND (2) (a) if any of the CZS_ 3 X OR CZS_ 4 X OR RAS_ 1 Y OR RAS_ 2 Y values exceed their associated switching thresholds  220 ,  250 ,  232 , or  262  (all by ORing function  230 ), AND (ANDing function  306 ) (b) the switched low CCU_ 1 X threshold  132  is exceeded by VEL_REL_ 1 X, the first stage is actuated. Second stage deployment is based on the time for crossing the second threshold  134  and the inflator mapping shown in  FIG. 6 . 
     Referring to  FIG. 6 , mapping for control of second stage deployment is shown for an exemplary embodiment of the present invention. Two inflator mappings exist for this exemplary embodiment. A normal inflator map and a special inflator map. The inflator map is selected in response to the CZS values, the RAS values, and the comparisons in functions  226 ,  236 ,  256 , and  266 . If all of the A_MA_CZS_ 3 X, A_MA_RAS_ 1 Y, A_MA_CZS_ 4 X, OR A_MA_RAS_ 2 Y values as a function of Disp_Rel_ 1 X are below the special mapping thresholds  222 ,  234 ,  252 , and  264 , respectively, then the normal inflator mapping is used. If any of the A_MA_CZS_ 3 X, A_MA_CZS_ 3 Y, A_MA_CZS_ 4 X, OR A_MA_CZS_ 4 Y values as a function of Disp_Rel_ 1 X is greater than the special mapping thresholds  222 ,  234 ,  252 , and  264 , respectively, then the special inflator mapping is used. 
     In the special-mapping, one-to-one timing occurs between the crossing of the second threshold and the deployment signal for the second actuation from 1-30 milliseconds. In the normal mapping, actuation of the second stage would occur 10 milliseconds after the first stage actuation if the second threshold crossing was between 1-10 milliseconds of the first stage crossing, a one-to-one timing control is used between 10-20 milliseconds, and second stage deployment occurs 30 milliseconds after first stage actuation if the second crossing occurred between 21-30 milliseconds after the first stage deployment occurred. 
     Other sensors  88  could be used to make further control adjustments in the actuation. For example, if a rearward facing child seat is detected on the passenger&#39;s seat  84 , actuation of the first and second stages  94 ,  96  could be prevented. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes, and/or modifications within the skill of the art are intended to be covered by the appended claims.