BACKGROUND 
   Embodiments of the invention relate to vehicle control systems, and more particularly to a vehicle control system to deploy an occupant restraint device. 
   Restraint devices such as airbags and seatbelts are, in general, actuated during crashes or possible crashes to protect vehicle occupants from injury. The accuracy and timeliness of deployment and actuation are factors in the effectiveness of restraint devices. 
   Some restraint devices are controlled using algorithms that process accelerations measured in various locations of a motor vehicle. The measured accelerations are analyzed using various functions such as integration (to yield velocity), a sum of squares of the measured accelerations, slopes of the measured accelerations, and the like. The outputs of the functions are compared to thresholds. If the thresholds are crossed, restraint devices are deployed. 
   SUMMARY 
   The severity of a crash is, in general, related to the energy dissipated in the vehicle during a crash. When the severity of the crash is low, restraint devices may not need to be actuated. When the severity of the crash is high, restraint devices should be actuated. In one embodiment, the invention provides an actuation system or a restraint device control system in which a signal from an acceleration sensor or an accelerometer is processed to determine a value that approximates the energy of the crash. The approximation is then compared to a dynamically determined threshold that can be based on a vehicle feature to determine whether a passenger restraint should be actuated. 
   In one embodiment, the invention provides a method of controlling a restraint device in a vehicle. The method includes sensing an acceleration or something that is representative or indicative of acceleration of the vehicle, and determining from the acceleration an energy value that indicates the energy dissipated in the vehicle during the crash. The method also includes determining from the acceleration a transformed acceleration, retrieving a threshold based on the transformed acceleration, and activating the restraint device when the energy value is above the threshold. 
   Another embodiment includes a method of controlling a restraint device in a vehicle. The method includes sensing a first signal that is indicative of the acceleration of the vehicle, and determining a second signal from the first signal indicative of the acceleration. The method also includes retrieving a threshold that is established based on the first signal and the second signal, comparing the second signal with the threshold, and activating the restraint device based on the comparison. 
   Yet another embodiment provides an apparatus for controlling a restraint device in a vehicle. The apparatus includes a sensor to sense a plurality of vehicle conditions having values that are indicative of vehicle accelerations, and an accumulator to accumulate the values to obtain an accumulated value. The apparatus also includes a transformer to transform the accumulated value into a transformed value, and a signal generator to activate the restraint device when the accumulated value exceeds a threshold determined from the transformed value. 
   Still another embodiment provides a vehicle. The vehicle includes a restraint device, a sensor to sense a plurality of values indicative of vehicle acceleration, and a transformer to generate a first signal and a second signal based on the value indicative of vehicle acceleration. The vehicle also includes a processor that has a comparator to compare the first signal with a threshold based on both the first and the second signals. The processor then generates a deployment signal when the first signal is above the threshold. The restraint device is configured to be deployed upon receiving the deployment signal. 
   Other features and advantages of embodiments will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  shows a schematic plan view of a vehicle; 
       FIG. 2  shows a block diagram of a control system in the vehicle of  FIG. 1 ; 
       FIG. 3  is a graph of a deployment threshold; and 
       FIG. 4  is a flow chart of processing carried out in embodiments of the invention. 
   


   Before any embodiments of the invention are explained 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 components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. 
   DETAILED DESCRIPTION 
     FIG. 1  shows a schematic plan view of a vehicle  100 . The vehicle  100  has four wheels  104 A,  104 B,  104 C and  104 D. The wheels  104 A,  104 B,  104 C and  104 D are connected to two axles  108 A and  108 B, as shown. The four wheels are monitored by a plurality of wheel speed sensors  112 A,  112 B,  112 C and  112 D. The wheel speed sensors  112 A,  112 B,  112 C, and  112 D are coupled to an electronic processing unit (“ECU”)  116 . The vehicle  100  also includes other sensors such as a front bumper sensor  120 , a back bumper sensor  124 , a plurality of side impact sensors  128 , and accelerometers  130 A and  130 B. The wheel speed sensors  112 A,  112 B,  112 C and  112 D, the front bumper sensor  120 , the back bumper sensor  124 , the plurality of side impact sensors  128 , and the sensors  130 A and  130 B are shown as individual sensors generically. These sensors  112 A,  112 B,  112 C,  112 D,  120 ,  124 ,  128 ,  130 A, and  130 B can also include multiple sensors in a plurality of sensor arrays, for example, that may be coupled to the ECU  116 . Other sensor types such as thermal sensors can also be used in the vehicle  100 . 
   The vehicle  100  also includes a plurality of restraint devices such as front airbags  132 , and side airbags  136 . Although  FIG. 1  shows only airbag restraint devices, other types of restraint devices such as seatbelt tensioners, and head and torso airbags can also be used in the vehicle  100 . 
   In one embodiment, a control system  200  ( FIG. 2 ) is used to separate non-deployment crash conditions from deployment crash conditions. The control system  100  receives its input from a sensor array  204  that includes sensors  112 A,  112 B,  112 C, and  112 D, the front bumper sensor  120 , the back bumper sensor  124 , the side impact sensors  128 , and the sensors  130 A and  130 B. 
   In one embodiment, each of the sensors  130 A and  130 B detects and monitors a specific condition of the vehicle  100 . For example, the sensors  130 A and  130 B are used to sense a condition of the vehicle that is indicative of an amount of acceleration experienced by the vehicle  100 . In some embodiments, the sensors  130 A and  130 B detect vehicle conditions such as the motion of the vehicle  100 . Sensed conditions are then transduced and converted into calibrated signals that are indicative of acceleration of the vehicle  100 . If the sensors  130 A and  130 B are equipped with any calibration circuitry or microprocessor therein, the motions can be converted internally to a calibrated form in the sensors  130 A and  130 B. Otherwise, the conditions can be converted into calibrated signals by other external processes in a manner known in the art. Furthermore, other sensors such as the front bumper sensor  120 , the back bumper sensor  124 , the side-impact sensors  128  are used to detect or sense events such as crashes and collisions. Collectively, values of the signals output by the sensors  112 A,  112 B,  112 C,  112 D,  120 ,  124 ,  128 ,  130 A,  130 B, or by the sensor array  204  are referred to as sensed values, or values hereinafter. 
   The ECU  116  includes a processor  212  that receives the values from the sensor array  204 . The processor  212  then filters the values from the sensor array  204  with a high-pass filter  214 , and processes the values according to a program stored in a memory  216 . Although the memory  216  is shown as being external to the processor  212 , the memory  216  can also be internal to the processor  212 . Similarly, although the high-pass filter  214  is shown being inside the processor  212 , the high-pass filter  214  can also be external to the processor  212 . Furthermore, the processor  212  can be a general-purpose micro-controller, a general-purpose microprocessor, a dedicated microprocessor or controller, a signal processor, an application-specific-integrated circuit (“ASIC”), or the like. In some embodiments, the control system  200  and its functions described are implemented in a combination of firmware, software, hardware, and the like. To be more specific, as illustrated in  FIG. 2 , the processor  212  communicates with other modules (discussed below) that are drawn as if these modules were implemented in hardware. However, the functionality of these modules could be implemented in software, and that software could, for example, be stored in the memory  216  and executed by the processor  212 . 
   In some embodiments, the high-pass filter  214  filters the acceleration values or signals from the motion sensors  130 A and  130 B. Frequency components of the acceleration signals that are above a cutoff frequency are allowed to pass through the high-pass filter  214 . In some embodiments, the high-pass filter  214  has an adjustable cutoff frequency that can be varied and adjusted to the specific vehicle and requirements at hand. For example, the measured accelerations can be discretely integrated and normalized in a predetermined window to initially obtain low-pass filtered accelerations. The low-pass filtered accelerations can then be subtracted from the sensed accelerations to obtain high-pass filtered accelerations. 
   The filtered accelerations from the high-pass filter  214  are received at an absolute value module  220 . Specifically, an absolute value of each of the filtered accelerations is obtained at the absolute value module  220 . An accumulator  224  then sums or accumulates consecutive absolute values that are sensed over a period or a predetermined window of time. For example, in some embodiments, after a first filtered acceleration and a second filtered acceleration have been received at the accumulator  224 , the first and the second accelerations are summed to obtain a value that can be indicative of the energy dissipated in the vehicle  100 . The accumulated value generally indicates an energy envelope or the energy dissipated in the vehicle  100  during a crash. While accumulating the absolute values of the accelerations provides an indication of the energy dissipated in the vehicle, other energy determining techniques such as summing of the squares of the filtered accelerations can also be used. 
   A transformer  228  transforms the filtered and absolute valued accelerations from the absolute value module  220  into at least one transformed value. In some embodiments, the transformer  228  includes a quantizer  232  that samples or quantizes the conditioned accelerations with a predetermined quantization resolution. For example, in some embodiments, acceleration amounts between 0 ms −2  and 2.99 ms −2  can be sampled or quantized to obtain a transformed value of 0 ms −2  with a quantization resolution of 3 ms −2 . Similarly, acceleration amounts between 3 ms −2  and 6 ms −2  can be sampled or quantized to obtain a transformed value of 3 ms −2  with the same quantization resolution. In some other embodiments, the transformer  228  includes a low-pass filter  236  that further filters the filtered accelerations to obtain a transformed value that can be indicative of the velocity of the vehicle  100 . 
   In yet some other embodiments, the transformer  228  includes a mapper  240  that maps the filtered accelerations to obtain a predetermined transformed value in a manner similar to the quantizer  232 . In some embodiments, the mapped transformed values used by the mapper  240  are stored in a look-up table in the memory  216 . In some embodiments, the mapped transformed values used by the mapper  240  are determined by a mapping formula stored in the memory  216 . For example, acceleration amounts between 0 ms −2  and 2.99 ms −2  can be mapped to obtain a transformed value of 1.5 ms −2 . Similarly, acceleration amounts between 3 ms −2  and 6 ms −2  can be mapped to obtain a transformed value of 4.5 ms −2 . In such a case, the mapped transformed values of 1.5 ms −2  and 4.5 ms −2  are either stored in the memory  216 , or determined by the processor  212  using a pre-determined mapping formula depending on the application at hand. In yet some other embodiments, the transformer  228  can employ a combination of the quantizer  232 , the low-pass filter  236  and the mapper  240  to determine the transformed value. In still other embodiments, the transformer  228  can employ an integrator to integrate the acceleration values to obtain transformed values that are indicative of the velocity of the vehicle  100 . 
   Once the transformed value from the transformer  228  has been obtained, the transformed value is used to retrieve a threshold from a look-up table in the memory  216 . The threshold generally corresponds to the transformed value. In some embodiments, the processor  212  processes and converts the transformed value into a memory address at which the corresponding threshold is stored in the memory  216 . Thereafter, the threshold is retrieved from the memory  216 . In some other embodiments, a signal generator  244  processes and converts the transformed value into a memory address at which the corresponding threshold is stored, and retrieves the threshold from the memory  216 . That is, the look-up table in the memory  216  can include a plurality of empirically determined transformed values based on the transformation used by the transformer  228 . 
     FIG. 2A  shows a first exemplary system  250  to calculate a value that is indicative of the energy dissipated in the vehicle  100  using the high-pass filter  214 , the absolute value module  220  and the accumulator  224 . Once the accelerations have been filtered at a high-pass filter  214 ′, the filtered accelerations are then absolute-valued at an absolute value module  220 ′ to obtain some conditioned accelerations. The conditioned accelerations are then accumulated at an accumulator  224 ′ for a period of T win . Similarly,  FIG. 2B  shows a second exemplary system  254  to calculate a value that is indicative of the energy dissipated in the vehicle  100  using the high-pass filter  214 , the absolute value module  220  and the accumulator  224 . In such a case, a high-pass filter  214 ″ is implemented with a low-pass filter  258  in a direct form structure. In this case, the low-pass filter  258  includes an integrator  262  having an integration period of T FIR , and an amplifier  266  having a gain of −1/T FIR . The low-pass filtered accelerations are then added to the accelerations to obtain a plurality of filtered accelerations at a summer  270 . The filtered accelerations are then absolute-valued at an absolute value module  220 ″ to obtain some conditioned accelerations. The conditioned accelerations are then accumulated at an accumulator  224 ″ for a period of T win . Of course, other implementations of high-pass filters such as a cascade implementation, can also be used depending on application at hand. 
     FIG. 3  shows a deployment threshold plot  300 . Transformed values are measured along an x-axis  304 , and accumulated values are measured along a y-axis  308 . Curve  312  illustrates a deployment event or crash in which restraint devices are deployed based on the transformed values and the accumulated values. Curve  316  illustrates a non-deployment event or crash in which restraint devices are disabled based on the transformed values and the accumulated values. Curve  320  illustrates an exemplary threshold that can be stored in the memory  216 . In some embodiments, the threshold curve  320  is adjusted such that all non-deployment events remain below the threshold curve  320 . In general, the threshold curve  320  is dynamically determined from the accumulated values accumulated over different times, the accumulated values accumulated over a certain number of conditions or accelerations, the transformed values generated from the accumulated values, and the like. For example, a first accumulated value can be obtained from accumulating a plurality of conditioned accelerations over a first period of time, while a second accumulated value can be obtained from the conditioned accelerations over a second period of time. In this way, the accumulated values determined from the two accumulations are different, thereby yielding different transformed values and different thresholds. Once the threshold is exceeded, a deployment event or crash is identified. More specifically in some embodiments, for each of the transformed values, an associated deployment accumulated value is determined by searching the lookup table in the memory  216 . Furthermore, the lookup table is generally calibrated using acceleration data determined during crash tests. In some embodiments, acceleration data for a non-deployment crash is also recorded. 
   Referring back to  FIG. 2 , the retrieved threshold is compared to the accumulated value from the accumulator  224  at the signal generator  244 . In some embodiments, the signal generator  244  includes a comparator  248  that compares the accumulated value to the retrieved threshold. The signal generator  244  activates the restraint device  208  when the accumulated value exceeds the retrieved threshold determined from the transformed value, or when a deployment crash has been identified. Specifically, the signal generator  244  generates a deployment signal that actuates the restraint devices when the accumulated value is above the retrieved threshold. However, the signal generator  244  generates a disabling signal that disables the restraint devices when the accumulated value is below the retrieved threshold. 
   In some embodiments, the signal generator  244  will only generate an activating signal or deployment signal when the accumulated value is above the retrieved threshold, and will not generate any disabling signal otherwise. In this way, other deployment techniques can also be used to activate the restraint devices. For example, in yet some other embodiments, the signal generator  244  can also generate the activating signal or deployment signal based on a combination of signals generated by other deployment algorithms and the outputs of the comparator  248 . That is, signals from additional deployment techniques are combined and processed in the signal generator  244  to arrive at a final deployment decision. 
     FIG. 4  includes a flow chart  400  that further illustrates processes that occur in some embodiments including processes that may be carried out by software, firmware, or hardware. As noted, the sensors sense accelerations and other parameters. This is shown at block  404 . Vehicle conditions, such as the accelerations, are high-pass filtered (as described earlier) to obtain filtered accelerations, as shown at block  408 . The filtered accelerations are then processed at the absolute value module  220  to obtain the absolute values of the filtered accelerations as shown at block  412 . The absolute values of the accelerations are accumulated (block  420 ). The accumulated values are indicative of the energy dissipated in the vehicle  100 . The values of the accelerations from block  404  are similarly transformed into a plurality of transformed accelerations or transformed values, as shown at block  416 . This may be done in a manner that is similar to the technique described above. The transformed values are used to retrieve a threshold at block  424  from a table  428  stored in the memory  216 . The retrieved threshold from block  424  is then compared to the accumulated values at block  432 . If the accumulated values are above the retrieved threshold, a deployment signal is generated at block  436 . If the accumulated values are below the retrieved threshold, a disabling signal is generated at block  440 . 
   Various features of the invention are set forth in the following claims.
A method of controlling a restraint device in a vehicle, and an apparatus employing the method. The method includes sensing accelerations of the vehicle, determining an energy value, determining a transformed acceleration, retrieving a threshold based on the transformed acceleration, and activating the restraint device when the energy value is above the threshold.