Abstract:
A method and system for controlling a vehicle occupant safety system based on crash severity. The system uses an acceleration signal indicating the acceleration of the vehicle upon occurrence of a crash to determine whether to trigger a restraint device. A controller implements a crash sensing algorithm to determine whether the severity of the crash warrants deployment of the safety restraint. The algorithm uses a predicted velocity and an acceleration peak time derived from the acceleration signal. The predicted velocity is indicative of the relative velocity between the passenger and the vehicle at a predetermined time following detection of a crash event. The acceleration peak time is the time period between peak acceleration values that correspond to contacting of significant structural elements of the vehicle, such as the bumper and the radiator. The two values are compared to their respective thresholds and if both of them exceed their thresholds then a deployment signal is generated to trigger the safety restraint.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicle occupant safety system and more particularly to a method and system for determining the severity of a vehicle crash and controlling an occupant safety system in response to the crash severity. 
     2. Related Art 
     It is known in the art relating to vehicle safety systems to trigger a passenger safety restraint in response to a vehicle crash. Such systems typically include an accelerometer mounted on the vehicle to sense vehicle acceleration crash condition. A controller is operatively connected to the accelerometer to receive an acceleration signal. The controller analyzes the acceleration signal to determine the severity of the crash and then based on the analysis the controller activates the safety restraint as required. The controller may determine the severity of the crash by using various calculated values of velocity, crash displacement and energy. 
     Such vehicle safety systems often include an air bag that inflates and cushions a passenger in the event of a crash. It is particularly desirable for the air bag to be activated only when the crash conditions require such activation. Unnecessary activation of the air bag may startle and distract the driver and may require costly replacement work to be done. Thus, it is desirable to provide a system that can accurately discriminate between fire and non-fire events. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and system for controlling a vehicle safety system based upon crash severity. 
     In one embodiment, the method and system determines a predicted velocity from a sensed vehicle acceleration signal, compares the predicted velocity with a velocity threshold and activates the safety restraint, for example, an air bag, if the predicted velocity exceeds the velocity threshold. 
     The predicted velocity is the velocity of the passenger relative to the vehicle at a time equal to the present time plus the airbag inflation time. A high predicted velocity generally indicates a severe crash condition. 
     In another embodiment, the method and system determines a predicted velocity from a sensed vehicle acceleration signal, and compares the predicted velocity with a velocity threshold. The method and system also determines an acceleration peak time from the sensed acceleration signal, and compares the acceleration peak time with an acceleration peak time threshold and activates the safety restraint if the predicted velocity exceeds the velocity threshold and the acceleration peak time is less than the acceleration peak time threshold. 
     The acceleration peak time is the time period measured from the detection of a first predetermined maximum acceleration value, to a predetermined minimum acceleration value and to a second predetermined maximum acceleration value. The detection of maximum acceleration times indicates the contacting of the bumper and then the contacting of the radiator support area of the vehicle as the vehicle structure collapses. With a higher speed crash, the contacts occur closer in time than for a lower speed crash. By determining the time interval between the contacts, the present invention better discriminates between high and low severity crashes. 
     In another embodiment, the method and system determine a predicted velocity from a vehicle acceleration signal, and compares the predicted velocity with a velocity threshold. The method and system also determines an acceleration peak time from the vehicle acceleration signal, and compares the acceleration peak time with an acceleration peak time threshold. The method and system also determines from the sensed acceleration signal whether a pole crash event has occurred and activates the safety restraint if the predicted velocity exceeds the velocity threshold and the acceleration peak time exceeds the acceleration peak time threshold, and the acceleration signal indicates that a pole crash event has occurred. 
     These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a block diagram of a vehicle occupant safety system having an air bag in accordance with the present invention; 
     FIG. 2 is a flowchart of the operation of a vehicle occupant safety system in accordance with an embodiment of the present invention; 
     FIG. 3 is a flowchart of the operation of a vehicle occupant safety system in accordance with another embodiment of the present invention; and 
     FIG. 4 is a flowchart of the operation of a vehicle occupant safety system in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1 of the drawings, numeral  10  generally indicates a vehicle occupant safety restraint system including sensor  12 , such as an accelerometer, controller  14 , firing circuit  16  and safety restraint  18 , such as an air bag. Accelerometer  12  is mounted on the vehicle frame (not shown) to provide an analog signal corresponding to the acceleration, positive or negative, along the longitudinal axis of the vehicle caused by a crash. The acceleration signal is applied to an input of analog-to-digital (AND) converter  20  of controller  14  to convert the signal from analog to digital. Controller  14  analyzes the acceleration signal by using a crash-sensing algorithm to determine whether air bag  18  should be deployed. If air bag  18  is to be deployed, controller  14  generates a deployment signal, which is applied to firing circuit  16 . Upon receipt of the deployment signal, firing circuit  16  causes the deployment of air bag  18 . 
     Controller  14  may be a conventional microcontroller, which includes such elements as a central processing unit (CPU), read only memory (ROM) devices, random access memory (RAM) devices, input/output circuitry (I/O) and the A/D converter. When activated, controller  18  carries out a series of operations stored in an instruction-by-instruction format in ROM for providing deployment control of safety restraints within safety restraint system  10 . One such operation is the analysis of the acceleration signal to determine whether a crash exists warranting deployment of an air bag. 
     In the present invention, controller  18  derives a predicted velocity from the sensed acceleration signal and uses the predicted velocity to determine the crash severity. The predicted velocity is the velocity of the passenger relative to the vehicle at a time equal to the present time plus the airbag inflation time. A high predicted velocity generally indicates a severe crash condition. The predicted velocity is compared to a velocity threshold that is also derived from the sensed acceleration. If the predicted velocity exceeds the velocity threshold, controller  14  generates a deployment signal to trigger the deployment of air bag  18 . 
     As shown in FIG. 2, operation  200  is initiated at step  210  upon application of power to controller  14  and proceeds from step  210  to carry out general initialization operations at step  212 . Such initialization operations include setting pointers, flags, registers and RAM variables to their starting values. Following the general initialization operations, controller  14  samples the acceleration signal and converts the analog signal to a digital signal at step  214 . The rate of conversions is selected in accordance with known sampling criteria to assure reliable representation of the analog acceleration signal is obtained. At step  216 , the acceleration signal is averaged and filtered. 
     To determine the predicted velocity, steps  218 - 222  are executed. At step  218 , a filtered jerk signal is determined by taking the derivative of the acceleration signal to form a raw jerk signal and then filtering the raw jerk signal. The derivative is found by sending the acceleration signal to a ring buffer having a 0.004-second buffer length, taking the difference between the first and last values and then scaling the value by 1/0.004. At step  220 , the acceleration signal is integrated and stored in a RAM location as a velocity signal. 
     The predicted velocity is determined at a future time which account for the time required to inflate air bag  18  once a deployment signal is issued. This is done by estimating the predicted velocity in accordance with the velocity signal, filtered jerk signal, acceleration signal and the airbag inflation time. The predicted velocity is determined by integrating an acceleration signal having the assumed form y=at+b. The solution to the equation implemented by the controller at step  212  is as follows: 
     
       
         ∫ y dt=[ 0.5 aT   2   +bT+c]   
       
     
     {evaluated from time t to t+T} 
     where: 
     ∫y dt=predicted velocity; 
     a=filtered jerk signal; 
     b=filtered acceleration signal; 
     c=velocity signal; and 
     T=inflation time of the air bag. 
     Next, the predicted displacement of the vehicle occupant is determined similarly to the predicted velocity of the vehicle occupant at step  224 . The predicted displacement of the occupant is determined at a future time which accounts for the time required to inflate air bag  18  once a deployment signal is issued. This is done by estimating the predicted displacement in accordance with the displacement signal, velocity signal, acceleration signal and the required deployment time. The above equation is used to determine the predicted displacement value except “a” equals acceleration, “b” equals velocity and “c” equals displacement. 
     The velocity threshold, which is compared to the predicted velocity to determine the severity of the crash, is determined at step  226 . The velocity threshold is determined by combining a predetermined velocity reference value and a displacement factor. The displacement factor is proportional to an amount the predicted displacement exceeded a predetermined displacement threshold. 
     Next, at step  228 , the predicted velocity is compared to the velocity threshold to determine whether the predicted velocity is greater than the velocity threshold. This is done by subtracting the predicted velocity from the velocity threshold. Then, the resulting difference is multiplied by a weighting factor, which limits the predicted velocity between zero and one. By determining the predicted velocity in this manner, the operation will not proceed to the next step unless the predicted velocity exceeds the velocity threshold. If the predicted velocity exceeds the velocity threshold, controller  14  generates a deployment signal in step  230 . Otherwise, controller  14  returns to step  214  and performs another cycle of sampling the acceleration signal and determining whether a severe crash event has occurred. 
     It may be desirable to rely on factors other than the predicted velocity when determining the severity of a crash event. In that regard, another useful factor is the time between acceleration peaks. The detection of an acceleration peak may indicate contacting of significant structural elements of a vehicle. During the course of a crash event, the maximum acceleration peaks typically indicate, among other events, the contacting of the bumper and the contacting of the radiator support area as the vehicle structure collapses. With a higher speed crash, the contacts occur closer in time than for a lower speed crash. By determining the time interval between the acceleration peak points, the present invention better discriminates between high and low severity crashes. 
     In an alternative embodiment, controller  14  determines the severity of the crash using predicted velocity and acceleration peak time derived from the sensed acceleration signal. The steps for determining crash severity using predicted velocity and acceleration peak time is shown in FIG.  3 . Steps  310 - 328  correspond to steps  210 - 228  of FIG. 2, respectively, and relate to determining predicted velocity and the velocity threshold, and comparing the predicted velocity to the velocity threshold. 
     Steps  330 - 338  relate to determining an acceleration peak time, which corresponds to the time period between acceleration peaks indicative of the contacting of significant structural elements of the vehicle. In step  330 , a first maximum acceleration peak is detected by accumulating the acceleration data points until the data point is greater than a predetermined maximum, and that data point is stored in a RAM location as the first maximum acceleration peak value. At step  332 , the acceleration points are accumulated until a data point is less than a predetermined minimum value, and that data point is stored in a RAM location as the minimum acceleration peak value. Next, at step  334 , a second maximum acceleration peak that exceeds a second predetermined maximum is detected. Finally at step  336 , the time between the first and second maximum acceleration peaks is measured to form the acceleration peak time. 
     At step  338 , the acceleration peak time is compared to a predetermined acceleration peak time threshold. The predetermined acceleration peak time threshold may vary for different vehicle models and is set as necessary. If the acceleration peak time is less than the predetermined acceleration peak time threshold, controller  14  continues to step  340 . Otherwise, controller  14  returns to step  314  to sample the accelerometer. Likewise, if the predicted velocity exceeds the velocity threshold as indicated in step  328 , controller  14  continues to step  340 , otherwise controller  14  returns to step  314 . If the predicted velocity exceeds its threshold and the acceleration peak time is less than its threshold, as indicated in step  340 , controller  14  generates a deployment signal in step  342 . 
     Another factor that may be considered in determining crash severity is whether the crash is a pole crash event. In a pole crash event, the crash severity may be greater than the predicted velocity or acceleration peak time may indicate. During a pole crash, the acceleration signal tends to be moderate until the pole contacts the engine and then the acceleration signal increases rapidly. It is desirable to recognize the pole crash event well in advance of the engine contact because the air bag deployment delay time must be considered to ensure full deployment of the air bag when the rapid acceleration increase occurs. 
     In another embodiment, the present invention determines the presence of a pole crash event and deploys air bag  18  accordingly. The steps for determining crash severity that recognizes the presence of a pole crash event, is shown in FIG.  4 . In FIG. 4, steps  410 - 428  correspond to steps  310 - 328 , respectively, and relate to determining whether the predicted velocity exceeds the velocity threshold. Likewise, steps  430 - 436  correspond to steps  330 - 336 , and relate to determining the acceleration peak time. The determination of whether a pole crash exists is made at step  437 . A pole crash condition is determined to exist if the following requirements are met: the minimum acceleration peak is very small, near zero or another predetermined level; the difference between the first maximum peak and the minimum acceleration peak is very large; and the second maximum acceleration peak is greater than the first maximum acceleration peak. 
     If a pole crash condition exists, the acceleration peak time between the first and second acceleration peak times is determined and compared to a predetermined pole crash time threshold. Controller  14  performs the comparison by subtracting the acceleration peak time from the pole crash time threshold at step  439 . However, if a pole crash does not exist, the acceleration peak time is compared to the predetermined acceleration peak time threshold by subtracting the acceleration peak time from the predetermined acceleration peak time threshold at step  438 . Then, the resulting difference is multiplied by a weighting factor limiting the acceleration peak time value to between zero and one. 
     Finally, if the predicted velocity exceeds the velocity threshold and the acceleration peak time is less than the peak time threshold, a deployment signal is generated to trigger the air bag. At step  440 , the predicted velocity is added to the acceleration peak time value. The sum can only be greater than one when the predicted velocity exceeds the velocity threshold, and the acceleration peak time is less than the acceleration peak time threshold or the pole acceleration peak time is less than the pole crash peak threshold. When the sum is greater than one, controller  14  generates the deployment signal at step  442 . Otherwise, controller  14  returns to step  414 . 
     Although the invention has been described by reference to a specific embodiment, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. For example, different weighting factors may be used for the differences of the various values in order to adjust the performance of the safety system. Accordingly, it is intended that the invention not be limited to the described embodiment, but that it have the full scope defined by the language of the following claims.