Abstract:
A motor vehicle is provided that has a deployable occupant protection device, a controller that manages deployment activity, and a sensor located in a forward portion of the vehicle that produces a forward crash signal in response to crash stimulus. The forward crash signal varies between positive and negative values over time. At least some of the negative values are converted to positive values, defining a conditioned crash signal which is processed with an integrating algorithm, defining a conserved energy crash metric value that supplements processing of a central crash signal while evaluating a potential crash event(s). The conserved energy crash metric value can be used as a confirmatory factor, influencing whether to deploy the deployable occupant protection device. Or, for deployable occupant protection devices having multiple deployment stages, the conserved energy crash metric value can be used in determining whether to initiate one or more of the deployment stages.

Description:
FIELD 
       [0001]    The present invention relates to motor vehicles that use impact sensing algorithms for controlling occupant protection devices, and more particularly to motor vehicles that use crash sensor signal manipulations in concert with impact sensing algorithms so that the resultant crash metrics are highly indicative of crash occurrence and severity. 
       BACKGROUND 
       [0002]    Occupant restraint systems that include deployable occupant protection devices, such as air bags, for motor vehicles are well known in the art. Typically, these systems include one or more sensors that detect crash stimulus, for example, vehicle deceleration which is commonly referred to as crash acceleration, and an airbag that deploys when a controller energizes an igniter of the airbag. For example, when the igniter is energized, it releases or initiates a flow of inflation fluid from a reservoir or other storage device into the air bag, inflating it. 
         [0003]    In some known occupant restraint systems, the deployable occupant protection device inflates in multiple stages. This allows the device to partially inflate or deploy in crash instances that are relatively less severe or fully inflate or deploy in crash instances that are relatively more severe. Typically, multiple inflation fluid reservoirs or other storage devices and multiple sensors are used in such systems. 
         [0004]    The controller in such systems is configured to differentiate between low level deployment events, mid level deployment events, and high level deployment events, using any of a variety of known algorithms. These known algorithms typically use integration functions for signal processing and evaluating the resultant values versus predetermined criteria in determining crash occurrence or severity. Examples of such known algorithms are illustrated in, for example, U.S. Pat. No. 5,587,906; U.S. Pat. No. 5,935,182; U.S. Pat. No. 6,036,225; and U.S. Pat. No. 6,186,539. 
         [0005]    U.S. Pat. No. 5,587,906 discloses an air bag restraint system where a crash acceleration value is integrated to provide a crash velocity value and to partially determine a crash metric value. The crash metric value is compared to threshold values to determine whether to deploy the air bag. 
         [0006]    U.S. Pat. No. 5,935,182 discloses an air bag restraint system where a crash acceleration value is determined as a function of crash velocity and crash displacement using integrating functions. The crash acceleration value is then processed using an occupant spring-mass model for adjusting the crash acceleration signal. Air bag deployment decisions are made based on the adjusted crash acceleration signal. 
         [0007]    U.S. Pat. No. 6,036,225 discloses an air bag restraint system that can be deployed in multiple stages. A signal indicative of acceleration is integrated to provide a velocity signal which is processed to determine a velocity value. When the velocity value exceeds a first threshold value, a first deployment stage is initiated. When the velocity value exceeds a second threshold value, a second deployment stage or complete deployment is initiated. 
         [0008]    U.S. Pat. No. 6,186,539 discloses an air bag restraint system that can also be deployed in multiple stages. An average crash acceleration value is determined by processing signals from multiple crash sensors, and is compared against a crash severity index. When the average crash acceleration value exceeds a first threshold value, a first deployment stage is initiated. When the average crash acceleration value exceeds a second threshold value, a second deployment stage or complete deployment is initiated. 
         [0009]    Such efforts have proven beneficial and successfully increase occupant safety during crash events. Although these systems are successful and sufficient, further technological developments could prove desirable. For example, during offset deformable barrier (ODB) crash tests, and analogous actual impact or crash events, considerable signal fluctuation occurs due to energy absorption and yielding and corresponding positive and negative acceleration signals during early stages of impact, whereby innovative signal processing might prove desirable. 
         [0010]    Accordingly, it could prove desirable to provide a vehicle that incorporates a deployable occupant protection device that is controlled by processing which can accurately account for high magnitude and high frequency signal content, varying between positive and negative values. 
         [0011]    It could also prove desirable to provide a vehicle that incorporates a deployable occupant protection device that uses a supplemental algorithm to enhance performance of a known crash algorithm. 
         [0012]    It could also prove desirable to provide a supplemental algorithm that preliminarily processes crash signals transmitted by crush zone crash sensors, so that resultant values are easily accommodated by a known crash algorithm. 
         [0013]    It could also prove desirable to provide a supplemental algorithm that improves accuracy of deployment decisions during angular, oblique, or offset front end collision events. 
         [0014]    It could also prove desirable to provide a supplemental algorithm that leads to quicker deployment initiation decisions during angular, oblique, or offset front end collision events. 
       SUMMARY 
       [0015]    The present invention is directed to one or more improvements of motor vehicle crash sensing systems, crash severity determining systems, and corresponding controls for deployable occupant protection devices. A motor vehicle crash sensing system of the present invention processes a crash signal from a sensor, converting any periodic negative values within a varying signal to positive values, defining a conditioned crash signal. The crash signal is converted to the conditioned crash signal by way of, for example, processing the crash signal with an absolute value function, a squaring function, or other manipulation or operations which suitably convert negative values to positive values. 
         [0016]    The conditioned crash signal is processed by way of a crash determining algorithm, an integrating or other algorithm, to define a conserved crash energy metric. An occupant protection system controller evaluates the conserved energy metric while making deployment decisions, for example, whether to initiate deployment of the deployable occupant protection devices and/or if so, to what extent the deployment should occur. 
         [0017]    Accordingly, an object of the invention is to provide conserved energy metric values that are calculated in a manner that produces only positive values, supplementing known crash metric values used for determining crash occurrences and severity. 
         [0018]    Another object of the invention is to utilize a conserved energy metric value as a confirmatory factor for determining whether to deploy a deployable occupant protection device. 
         [0019]    A further object of the invention is to utilize a conserved energy metric value to mitigate effects of positive and negative value fluctuations of acceleration signals, such as is frequently encountered during early stages of impact, on signal processing by an occupant protection system controller. 
         [0020]    Yet another object of the invention is to consider a conserved energy metric value in determining whether to initiate a single stage of a multiple stage deployable occupant protection device. 
         [0021]    Still another object of the invention is to consider conserved energy metric values and accumulated velocity or displacement values while making occupant protection device deployment decisions. 
         [0022]    Other features and advantages of the invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating the preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
           [0024]      FIG. 1  is a top plan view of a motor vehicle equipped with a deployable occupant protection device that is controlled at least in part based on conserved energy metric values in accordance with the present invention; 
           [0025]      FIG. 2  is a flowchart of a first algorithm for use in accordance with the present invention to control a deployable occupant protection device based at least in part on conserved energy metric values; 
           [0026]      FIG. 3A  is a left-side portion of a flowchart of a second algorithm for use in accordance with the present invention to control a deployable occupant protection device based at least in part on conserved energy metric values; 
           [0027]      FIG. 3B  is a right-side portion of the flowchart of  FIG. 3A ; 
           [0028]      FIG. 4  is a graphical representation of crush zone sensor related values as a function of central vehicle sensor related values. 
       
    
    
       [0029]    Before explaining embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description and illustrated in the drawings. The invention is capable of other embodiments or being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
       DETAILED DESCRIPTION 
       [0030]      FIG. 1  illustrates a motor vehicle  20  in accordance with the present invention and generally defines crush zones  22 ,  24  at forward, lateral portions of the motor vehicle  20 . The crush zones  22 ,  24  are configured to suitably yield and thus absorb energy during front end collisions, particularly angular, oblique, or offset front end collisions. Motor vehicle  20  is equipped with an occupant protection system  26  shown in phantom in  FIG. 1 . Occupant protection system  26  includes deployable occupant protection devices  28 ,  29 , one or more crush zone sensors  30 ,  31 , and a control module, e.g., occupant protection system controller  38 , that uses crash signals from the sensors  30 ,  31  in initiating and controlling deployment of the occupant protection devices  28 ,  29 . Controller  38  typically includes a processor, such as a microcontroller or the like, along with suitable discrete digital and/or analog circuitry assembled on one or more circuit boards, optionally as an application specific integrated circuit. 
         [0031]    Deployable occupant protection devices  28 ,  29  are intended to encompass one or more airbags such as, for example, airbags that inflate in a single stage, airbags that inflate in multiple stages, airbag systems which employ multiple airbags such as a driver side airbag along with one or more of a passenger side airbag, a side curtain airbag, or other suitable airbag systems. The deployable occupant protection devices  28 ,  29  are configured to deploy or inflate when the controller  38  of the occupant protection system  26  makes a determination that a crash event warranting deployment is occurring, such as detected using one or more sensors  30 ,  31 . 
         [0032]    Still referring to  FIG. 1 , crush zone sensors  30 ,  31  can be any of a variety of suitable sensors, e.g., MEMS accelerometers, pressure sensors, or other crush zone sensors, noting that accelerometers are used for typical implementations. For example, known accelerometers having suitable nominal sensitivity values will suffice for use as crush zone sensors  30 ,  31 . The crush zone sensors  30 ,  31  are typically mounted in forward, lateral portions of motor vehicle  20 , such as crush zones  22 ,  24 , respectively. Optionally, crush zone sensors  30 ,  31  can be mounted in other portions of motor vehicle  20  that tend to absorb energy during angular front end collisions, or otherwise permit sensors  30 ,  31  to detect crash forces or stimulus indicative of straight or flat front end collisions, angular front end collisions, or offset front end collisions. Upon detecting such crash stimulus, crush zone sensors  30 ,  31  communicate crash signals along lines,  32 ,  33 , e.g., digital bus lines, to the controller  38 . 
         [0033]    Referring still to  FIG. 1 , for example, if crush zone sensors  30 ,  31  are accelerometers and vehicle  20  undergoes an angular or offset front end collision, then the resultant acceleration signals, e.g., forward crash or acceleration signals, can and frequently do exhibit considerable signal fluctuation. This can be due to variations in the rate of energy absorption by crush zones  22 ,  24  of the vehicle  20  during the crash, angular displacement of the crush zone sensors  30 ,  31  caused during the crash that displaces them off-axis relative to the direction of the transmitted crash force, as well as other factors. As a result, the forward crash signal can and often does vary between positive and negative values over time with at least some of the positive and negative values being rather large in magnitude. 
         [0034]    Regardless of the particular characteristics of the crush zone sensor signals, e.g., forward crash signals, transmitted via bus lines  32 ,  33 , they are filtered using hardware and/or software filters to eliminate, for example, high frequency and/or other noise. Such filtering can be suitably performed at or near controller  38 , but is typically performed upstream of the controller  38 , for example, onboard the crush zone sensor  30 ,  31 . It is also preferred that the crush zone sensors  30 ,  31  include analog to digital converters, allowing the signal to be transmitted through bus lines  32 ,  33 , to controller  38 , digitally. Bus lines  32 ,  33  represent cabling or other suitable conductors of a digital bus, such as a CAN bus or the like, which links crush zone sensors  30 ,  31  with controller  38 . 
         [0035]    Other sensors, namely central vehicle sensors  34 ,  36  are positioned substantially at or near a central portion of the vehicle  20 , such as adjacent a driver of the vehicle  20 . Although the controller  38  is shown in  FIG. 1  disposed in a central vehicle location with sensors  34 ,  36  onboard the controller  38 , the controller  38  can be situated in a location different from the sensors  34 ,  36  if desired. Where located onboard the controller  38 , the central vehicle sensors  34 ,  36  can be integrated into controller circuitry. 
         [0036]    As with crush zone sensors  30 ,  31 , central vehicle sensors  34 ,  36  can be any of a variety of suitable sensors, typically accelerometers, e.g., MEMS accelerometers or other suitable sensors. Known accelerometers having suitable nominal sensitivity values will suffice for use as central vehicle sensors  34 ,  36 . In at least one embodiment where sensors  34 ,  36  are accelerometers, the sensors  34 ,  36  are set up so they are out of phase with one another. The signals, e.g., central crash or acceleration signals, are filtered either on the sensors  34 ,  36  themselves or elsewhere, and converted from analog to digital format before being transmitted to and received by controller  38  for further processing. 
         [0037]    Referring generally to  FIGS. 1 ,  2 , and  3 , the controller  38  monitors the filtered and digitized forward crash signals from crush zone sensors  30 ,  31  and also the central crash signals from central vehicle sensors  34 ,  36 , and processes them to evaluate whether a crash is occurring and, if so, its severity level. Based on this, controller  38  is configured, e.g. programmed, to make a determination of whether to deploy occupant protection devices  28 ,  29 . For multi-stage versions of occupant protection devices  28 ,  29  the controller  38  is further configured to evaluate the severity level in determining to what extent the occupant protection devices  28 ,  29  will be deployed. To make such determinations, controller  38  is configured to evaluate crash stimulus and corresponding data using, for example, an occupant protection system method  40  configured in accordance with the present invention, such as depicted in the schematic diagram shown in  FIG. 2 . 
         [0038]    Referring now to  FIGS. 1 and 2 , by implementing occupant protection system method  40  into controller  38 , such as by configuring it in firmware or software, when a crash event occurs, crash stimulus is detected  140  using the crush zone sensors  30 ,  31  and/or central vehicle sensors  34 ,  36 , collectively referred to as sensors  30 ,  31 ,  34 ,  36 . The sensors  30 ,  31 ,  34 ,  36  produce and transmit  142  respective crash signals, indicative of the crash event having, for example, amplitude and frequency values which correspond to crash characteristics. As previously mentioned, the forward and central crash signals are also filtered and digitized during this step  142 , reducing the likelihood of noise compromising the integrity of the signal that is transmitted along bus lines  32 ,  33  to controller  38 . 
         [0039]    With specific reference to  FIG. 2 , these signals are processed with a primary algorithm  146  and a conserved energy algorithm  150 , either in parallel, e.g. simultaneously, or sequentially as desired, depending on factors that include the particular end use configuration of occupant protection system  26 . The algorithm used in the processing with a primary algorithm step  146  is pre-selected based on the configuration of vehicle  20  and is preferably a known or conventional crash algorithm. Those skilled in the art are well aware of such suitable known crash algorithms and how to implement the same into an occupant protection system  26 . 
         [0040]    Typical of known crash algorithms, the algorithm of the primary algorithm step  146  uses the crash signals from one or more of sensors  30 ,  31 ,  34 ,  36  in measuring or determining various values and/or characteristics of the crash event. The primary algorithm step  146  evaluates, determines, or obtains values relating to, for example, crash acceleration, crash energy, crash velocity, crash displacement, crash jerk, or other crash indicia. One suitable method includes integrating crash acceleration values to determine crash velocity values, optionally further processing the crash velocity values by integrating them to arrive at crash displacement values. 
         [0041]    Regardless of whether the primary algorithm processes acceleration, velocity, or displacement values, the values are typically processed with a summing function so that accumulated values can be considered, often referred to as “crash metrics” or “crash metric values,” represented by defining a primary crash metric value step  148 . After the primary crash metric value is defined in step  148 , it is evaluated, preferably in a known manner, against one or more predetermined threshold values  158 . This threshold value comparison step  158  can be done comparing the crash metric value with known values contained in, e.g., various look-up tables, crash event indices, or crash severity indices. Based at least in part on such comparison step  158  using the primary crash metric value, the controller  38  executes a deployment decision step  160 . In other words, for single stage deployable occupant protection devices  28 ,  29 , the controller  38  uses the comparative results to decide  160  whether to energize the igniter that will deploy the occupant protection devices  28 ,  29  where such devices  28 ,  29  are airbags. For multi-stage airbag occupant protection devices  28 ,  29 , the controller  38  uses the comparative results to decide  160  if and to what extent to deploy the occupant protection devices. Namely, during the deployment decision step  160 , controller  38  determines whether to energize the igniter(s) that deploys airbag occupant protection devices  28 ,  29 , and, if so, how many and to what extent. 
         [0042]    With continued reference to  FIG. 2 , the crash signals  142  are also processed using the conserved energy algorithm  150 . In typical implementations, the processing conserved energy algorithm processing step  150  only processes forward crash signals from the crush zone sensors  30 ,  31 . This is because the forward crash signals transmitted by the crush zone sensors  30 ,  31  tend to exhibit considerable signal fluctuation, including alternating positive and negative acceleration indications, which can be accommodated by the conserved energy metric to enhance the overall performance of the occupant protection system  26 . 
         [0043]    During execution of the conserved energy algorithm step  150 , controller  38  processes the forward crash signals from crush zone sensors  30 ,  31  in a manner that converts negative crash signal values to positive values in accordance with the present invention. The conserved energy algorithm may convert negative values of the forward crash signals to positive values using any of a variety of suitable processes, operations, or functions. For example, in one preferred conserved energy algorithm implementation, the negative values are converted to positive values using a squaring or other exponential operation. When using such an implementation, the exponential function preferably raises the negative input value to a power of an even exponent value, i.e., an exponent value that is a multiple of the integer “two,” ensuring that the negative input values are converted into positive values. In another preferred implementation, negative crash signal values are converted into positive values by processing them with an absolute value function, again ensuring that the resulting values will be positive. Regardless of the particular technique for converting negative crash signal values into positive values, doing so alone or in combination with other mathematical processes defines a conditioned crash signal according to step  152 . 
         [0044]    After the conserved energy conditioned crash signal is defined in step  152 , it is then processed with primary algorithm pursuant to step  146 . Here again, the primary algorithm is preferably known or conventional, whereby it can be processed with a function that includes or otherwise employs one or more integration and/or summing functions to arrive at an accumulated value. The result of processing the conserved energy conditioned crash signals  152  using the primary algorithm in step  146  defines conserved energy crash metric value(s) in step  154 . 
         [0045]    Intuitively, the conserved energy crash metric value has a greater magnitude than the corresponding primary crash metric value, despite being processed with the same primary algorithm  146 . Furthermore, when the primary algorithm includes summing operations, the conserved energy crash metric value accumulates or grows at a faster rate than the primary crash metric value. This is because positive and negative crash signal values transmitted in step  142  directly to the primary algorithm in step  146  for processing tend to at least partially offset or cancel one another. This contrasts with processing these same positive and negative crash signal values using the conserved energy algorithm in step  150  to define conserved energy conditioned signal(s) in step  152  before primary algorithm processing in step  146  because the negative values are converted into positive values thereby eliminating their ability to offset or cancel. 
         [0046]    After the conserved energy crash metric value is defined in step  154 , it is evaluated, preferably in a known manner, against one or more predetermined threshold values in step  158 . In at least one implementation, the conserved energy crash metric value is compared to a threshold value(s) in step  158  using the same or a similar comparative procedures as used in carrying out the primary crash metric value comparison. For example, the threshold values can be predetermined and the calculated conserved energy crash metric values can be compared directly thereto. As another example, data tables can be implemented, e.g., various look-up tables, crash event indices, or crash severity indices, against which the conserved energy crash metric values can be compared. Based at least in part on such comparison with the conserved energy crash metric, the controller  38  executes a deployment decision step  160 , e.g., determines whether to deploy one or more of the occupant protection devices  28 ,  29 , and if so, to what extent. In one preferred implementation, threshold value comparisons made in step  158  using both the primary crash metric value defined in step  148  and the conserved energy crash metric value defined in step  154  are used in making one or more deployment decisions in step  160 . 
         [0047]    Referring now to  FIGS. 1 and 3 , in at least one implementation of an occupant protection system  26  configured in accordance with the present invention, the occupant protection system method  40 ′ depicted in  FIG. 3  is configured so that the conserved energy metric value can be used to initiate quicker initial deployments, quicker subsequent stage deployments, and/or initiate deployments that might not have otherwise occurred using only the primary crash metric value. 
         [0048]    For example, when a crash event occurs  200 , the central vehicle sensors  34 ,  36  transmit an acceleration signal  205 , e.g., a central crash signal, to the controller  38 . The signal can be filtered on the central vehicle sensors  34 ,  36  themselves, and/or at the controller  38 , which integrates the signal to define a central velocity  210 . In some implementations, the central velocity values are integrated a second time, defining central displacement values pursuant to step  211 . Controller  38  uses a primary algorithm, which is preferably a known crash algorithm, to process either the central velocity  210  or central displacement  211  values to determine a primary crash metric value  213 . 
         [0049]    The controller  38  then compares the primary crash metric value  213  to a threshold value in determining whether a crash event worthy of deployment is occurring  215 . If the threshold value for the first deployment stage of occupant protection device  28 ,  29  is met or exceeded, for example, a low threshold level, then controller  38  initiates the first deployment stage  220 . 
         [0050]    Still referring to  FIGS. 1 and 3 , the crush zone sensors  30 ,  31  produce a forward acceleration signal  230 , e.g., a forward crash signal, preferably filter it, and transmit it to the controller  38 . The controller  38  processes the forward acceleration signal  230  with at least one conserved energy algorithm, resulting in at least one conserved energy conditioned crash signal. For implementations that use multiple operations to arrive at multiple resultant values, the different operations can be performed in parallel, e.g., simultaneously, or in sequence, as desired. For example, the forward acceleration signal  230 , preferably after it has been filtered, is processed using a conserved energy algorithm that converts negative values of the forward acceleration signal  230  into positive values. As one example, such negative value can be converted to positive values using an absolute value function  235 . Then, an integration step  240  is performed on the absolute values of the acceleration signal. 
         [0051]    Referring now specifically to  FIG. 3 , in processing steps that are parallel to the absolute value conversion and integration steps  235  and  240 , the filtered forward acceleration signal  230  is processed using an exponential function, e.g., squared, by way of step  265  for converting negative values to positive values. Then the squared acceleration signal values  265  can be integrated during step  270 . 
         [0052]    Referring again to  FIGS. 1 and 3 , at this point, controller  38  utilizes various ones of the resultant values of (i) integrating absolute values of the forward acceleration signal  240 , (ii) integrating squared values of the forward acceleration signal  270 , (iii) central velocity  210 , and (iv) central displacement  211 , to define various conserved energy metric values. For example, again depending on the particular algorithm(s) used by occupant protection system  26 , controller  38  can use central velocity  210  and forward acceleration integrated absolute values  240  to define a first conserved energy metric value  242 . Central displacement  211  and forward acceleration integrated absolute values  240  can be considered in defining a second conserved energy metric value  244 . Central velocity  210  and forward acceleration integrated squared values  270  can be considered in defining a third conserved energy metric value  272 . Central displacement  211  and forward acceleration integrated squared values  270  can be considered in defining a fourth conserved energy metric value  274 . 
         [0053]    Referring again to  FIGS. 1 and 3 , each of the four conserved energy metrics  242 ,  244 ,  272 , and  274  is compared to a predetermined threshold value for evaluation of crash occurrence and/or severity. Such comparisons can be done independently or along independent paths, pursuant to threshold comparison steps  246 ,  248 ,  276 , and  278 , respectively. If the threshold comparison steps  246 ,  248 ,  276 , and  278  indicate that deployment or further deployment of occupant protection devices  28 ,  29  is not justified, then controller  38  returns or goes back to the previous step for reevaluation, for example, using the most recent data. 
         [0054]    For example, when deployment is not justified pursuant to threshold comparison step  246 , controller  38  reverts to step  242 , defining a the most recent value of 1 st  conserved energy metric  242  and then evaluates such conserved energy metric  242  against the respective threshold value  246 . The same is true for the other respective pairs of the conserved energy metrics  244 ,  272 , and  274  and threshold comparisons  248 ,  276 , and  278 . Stated another way, since the absolute and squared value processing  235 ,  265  is performed in parallel, the threshold comparisons  246 ,  248 ,  276 , and  278  can be described as progressing along independent paths according to an “OR” type logic scheme or configuration. 
         [0055]    Referring still to  FIGS. 1 and 3  accordingly to step  250 , in some instances or at some point during a crash event, a mid-level or high level threshold value of one of the threshold comparisons  246 ,  248 ,  276 , and  278 , can be met or exceeded, and a first stage, low level, or initial deployment of occupant protection devices  28 ,  29  has already occurred. Under these conditions, pursuant to step  260 , then controller  38  initiates a second or subsequent stage deployment of the occupant protection devices  28 ,  29 . Again, this is preferably done according to predetermined deployment protocol, taking into account, for example, desired delay periods between sequential deployment stages, and/or other factors. 
         [0056]    Graphical representations of uses of the rapid deployment responding occupant protection methods  40  and  40 ′ of  FIGS. 2 and 3  can be seen in  FIG. 4 . Namely,  FIG. 4  shows an exemplary crash events and corresponding deployment initiation(s) when utilizing conserved energy crash metric values  155 . Referring in general terms to the graph of  FIG. 4 , it shows a plot of (i) crush zone sensor related values, e.g., integrals of absolute values or squared values of acceleration signals produced by crush zone sensors  30 ,  31 , versus (ii) central vehicle sensor related values, e.g., velocity or displacement values that result from integrating (once or multiple times) acceleration signals produced by central vehicle sensors  34 ,  36  depending on the particular underlying or primary crash algorithm that is implemented. 
         [0057]    Still referring to the general graph configuration, a low threshold value  70  corresponds, for example, to values that differentiate between non-deployment stimulus or events and deployment worthy stimulus or events. Y-values of the conserved energy crash metric  155  which are less than or below the corresponding low threshold value  70  define non-deployment events. Conversely, y-values of the conserved energy crash metric  155  which exceed the low threshold value  70  define deployment events, indicating that a crash is occurring with sufficient force to justify deploying the occupant protection device(s)  28 ,  29 . 
         [0058]    A relatively higher threshold value  80  corresponds to, for example, predetermined magnitudes that justify initiation of multiple deployment stages. Therefore, the higher threshold value  80  line is representative of a mid-level or high level deployment threshold, depending on the underlying algorithm and configuration of occupant protection system  26 . As with low threshold value  70 , the line representation of the relatively higher threshold value  80  delineates the boundary between deployment worthy events, in this case a subsequent stage of deployment, and non-deployment events. Accordingly, if the Y-value(s) of the conserved energy crash metric  155  are greater than the corresponding relatively higher threshold value  80 , then initiation of a subsequent stage of deployment will not occur. Conversely, if y-values of the conserved energy crash metric  155  are greater than the corresponding relatively higher threshold value  80 , then one or more subsequent deployment stages of occupant protection device(s)  28 ,  29  are initiated. 
         [0059]    Various alternatives are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention. It is also to be understood that, although the foregoing description and drawings describe and illustrate in detail one or more preferred embodiments of the present invention, to those skilled in the art to which the present invention relates, the present disclosure will suggest many modifications and constructions, as well as widely differing embodiments and applications without thereby departing from the spirit and scope of the invention.