Abstract:
A vehicle impact sensing system for detecting impact events to a vehicle, and allowing deployment decisions of passive restraint devices based on information gathered and relayed regarding such impact events. The sensing system includes one or more sensor elements capable of directly detecting vehicle deformation occurring as a consequence of the impact event. The sensor elements generate an output that varies upon deformation of the element. The sensor elements are in communication with a restraints control module. Upon deformation of the sensor element, the control module receives impact signals from the sensor elements based upon the altered output, and discriminates between impact events that warrant deployment of a passive restraint, such as a side air bag, and those that do not. The control module utilizes information gathered from the sensor elements to make deployment decisions, such as which restraint to deploy and the appropriate degree of deployment.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application No. 60/156,165, filed Sep. 27, 1999. 

   FIELD OF THE INVENTION 
   The present invention relates to a sensing system employed to detect vehicular impact events; and more particularly to a vehicular impact sensing system that utilizes sensors to directly detect vehicle deformation by impact events and actuate restraints, such as inflatable restraints, in the motor vehicle. 
   BACKGROUND OF THE INVENTION 
   Almost all passenger motor vehicles presently produced include some type of impact deployed restraint system to protect vehicle occupants, or others, during a vehicle impact event. Such restraint systems may include, for example, front and side airbags within the passenger compartment, side curtains, inflatable seat belts, and seat belt pretensioners. A restraint system may also include deployable restraints for the protection of pedestrians involved in impacts with the vehicle, such as pedestrian airbags and hood release mechanisms. Sensing systems typically control the deployment of such restraints by detecting the occurrence of a vehicle impact event. 
   During most impact events, the opportunity to provide occupant restraint exists only for a very brief period of time. Furthermore, inadvertent deployment of a restraint, such as an airbag, is undesirable. Therefore, to be most effective, impact deployed restraints must deploy quickly when needed, and only when actually needed. To this end, impact sensors must be able to discriminate between severe and relatively harmless impact events and also be insensitive to mechanical inputs which are not associated with crash events. Most importantly, however, the design of the sensor must allow for rapid detection of the impact event and transmission of relevant information to allow for effective deployment decisions. The need for a sensor which allows for rapid deployment decisions is particularly great with side airbags, where the crush zone is much smaller than that associated with front airbags, and the time available for a deployment decision is likewise shorter. 
   Several types of sensors have been used for detection of impact events in vehicles. For example, sensors comprised of piezoelectric cables, accelerometers, pressure sensors and crush-zone switches, have been utilized. While these sensors can operate adequately, it is desirable to improve the ability of vehicle impact sensing systems to discriminate between impact events, such as vehicle crashes, that warrant deployment of a passive restraint, and those that do not, such as a minor impact with a shopping cart. Furthermore, it is desirable to improve the ability of the sensor to provide information regarding the impact, such as its location and relative size, thereby increasing the effectiveness of subsequent deployment decisions. 
   Consequently, there is a need for an impact sensing system that utilizes sensors capable of relaying information about an impact and making deployment decisions based on such information. 
   SUMMARY OF THE INVENTION 
   In its embodiments, the present invention comprises a vehicle sensing system that utilizes sensor elements to directly detect deformation of the vehicle and provide information regarding the impact. Direct detection of vehicle deformation, as opposed to indirect detection, allows the sensor to relay more accurate and detailed information regarding the impact event. As a consequence, the sensing system according to the present invention has an ability to discriminate among impact events, and allows for effective deployment decisions. 
   The sensing system of the present invention includes a sensor element for such direct detection of vehicle deformation. The sensor is mounted in a manner that allows the sensor to directly detect an impact event. That is, the sensor operates as a consequence of its direct physical involvement in the impact. The sensor is in electronic communication with a controller, which receives and interprets electronic signals from the sensor. 
   The sensing system of the present invention can be utilized to directly obtain information about impact events in a variety of vehicle locations. For example, sensors can be located in the vehicle door to gather information concerning side impacts. Likewise, a sensor can be embedded directly into a vehicle bumper to obtain information regarding frontal impacts. Wherever located, the sensor elements provide information regarding an impact, allowing for more effective deployment decisions. The sensor element preferably constitutes a bend sensitive resistance element having conductive layers such as an ink which has been printed onto a substrate and treated to produce cracks in its structure. When the bend sensitive resistance element is bent, such as occurs in a vehicle crash, the cracks open and increase the resistance of the element. The bend sensitive resistance element may be a single unitary element, or a plurality of independent elongate elements horizontally situated so as to be capable of providing azimuthal resolution of the impact event. The bend sensitive resistance element may either be disposed on a structural element of the vehicle, such as within a vehicle door, or contained within a sealed housing. Use of a sealed housing protects it from environmental contamination while also imparting a modular design that facilitates installation. Furthermore, the housing may define functional elements that increase the capabilities of the sensing system. For example, the housing may define crush actuators that facilitate the transmission of the impact to the resistance element. Means are adapted for mounting the housing adjacent a structural member of the vehicle, and extending generally along the member. 
   The controller subsequently makes deployment decisions based on the signals received from the sensor element. The present invention further contemplates a method of discriminating among impact events, the method comprising the steps of: directly sensing vehicle deformation via the sensor; producing a corresponding electronic deformation signal; determining the severity of the impact as compared to a threshold value; and actuating at least one deployable restraint if the threshold is exceeded by the severity of the impact. 
   Accordingly, an object of the present invention is to provide a sensing system that employs a sensor element to directly detect vehicle deformation and subsequently to provide an electronic signal containing information regarding the deformation. 
   Another object of the present invention is to provide a restraints control module which utilizes the information within the electronic signal to make deployment decisions for the restraints of the vehicle. 
   An advantage of the present invention is that the sensing system can include sensor elements arranged in a manner that provides a degree of azimuthal resolution regarding deformation caused by an impact event, allowing the sensors to provide more specific information regarding the impact. 
   Another advantage of the present invention is that the sensor element provides a variable output that is used to discriminate between various impact situations, thus improving passive restraint deployment decisions. 
   Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers reflect the same feature, element or component. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic plan view of a vehicle, including sensor elements, in accordance with the present invention; 
       FIG. 2  is a schematic side view of a vehicle door, with a sensor element mounted thereon in accordance with the present invention; 
       FIG. 3  is a schematic plan view of a vehicle bumper with a sensor assembly associated therewith in accordance with the present invention; 
       FIG. 4  is a schematic view of a unitary bend sensitive resistance element in accordance with the present invention; 
       FIG. 5  is a schematic view of a plurality of deformation sensor elements capable of providing azimuthal resolution in accordance with the present invention; 
       FIGS. 6   a – 6   c  are graphical illustrations of the approach of the side of a vehicle containing a deformation sensor element to a pole and impact therewith, in accordance with the present invention; and 
       FIGS. 7   a – 7   c  are graphical illustrations of the sensor output, corresponding to the impact depicted in  FIGS. 6   a – 6   c , respectively. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A vehicle  10  having several deployable restraints and including the present invention is illustrated in  FIGS. 1 and 2 . The vehicle has front  12  and rear  14  seats in a passenger compartment  16 . Mounted in proximity to each seat is a seat belt  18 , each of which may be equipped with pretensioners  20  as deployment restraints. Mounted in front of the two front seats  12  are front airbags  22 . The illustrated vehicle  10  includes two front doors  24  and two rear doors  25 , all of which may include a side airbag  26  mounted alongside, adjacent the front  12  and rear  14  seats. The vehicle  10  has a front bumper  28  with a pedestrian airbag  30  mounted in proximity to the bumper  28 . 
   The vehicle  10  may be equipped with accelerometers, a first frontal accelerometer  32  oriented to sense longitudinal acceleration of the vehicle and a second side accelerometer  34  oriented to sense side-to-side (i.e., lateral) acceleration. Alternatively, the two accelerometers  32 ,  34  can be replaced with a single dual-axis acceleration sensor if so desired. These accelerometers  32 ,  34  are electronically connected to and in communication with a restraints control module  36 . 
   The impact sensing system  35  of the present invention comprises deformation sensor elements  38  located at various positions throughout the vehicle, a restraints control module  36 , and electrical connections  40  between the sensor elements  38  and the restraints control module  36 . The sensor elements  38  of the current invention may be utilized in several areas of the vehicle. Generally, the sensor elements  38  will be mounted in areas around the body of the vehicle  10  in which impact sensing is desired, i.e., areas in which impact events are known to occur. For example, the sensor elements  38  may be disposed within a door  24  of the vehicle  10  for detecting side impact events. Also, a sensor element  38  may be disposed near or within a bumper  28  of the vehicle  10 . So disposed, the element  38  can be utilized to monitor for impact events involving pedestrians. Other locations may, of course, be desirable. No matter where located, the sensor element  38  is disposed in a manner that allows direct detection of an impact event. That is, the sensor element  38  is disposed in a manner that ensures its physical involvement in an impact event generating sufficient deformation of the vehicle  10 . The term deformation sensor is used to describe sensors capable of this direct physical involvement in vehicle impact events causing sufficient deformation of the vehicle  10 . For example, as shown in  FIG. 2 , the sensor element  38  may be disposed on a structural element of a vehicle door  24 . In this configuration, the sensor element  38  will directly participate in a side impact event affecting the vehicle door  24 . Also, for monitoring pedestrian and frontal impact events, the sensor element  38  may be directly embedded in the compressible material of the bumper  28 . The position of the sensor element  38  allows the sensing system  35  to discriminate among impact events. For example, the outer skin  42  of a vehicle door  24  and the outer layer of a vehicle bumper  28  are frequently exposed to impact events not warranting deployment of a passive restraint. A slight indentation to either of these structural elements does not warrant deployment. Therefore, positioning the sensor element  38  on the surface of either of these structural elements may lead to unnecessary deployment. Positioning the sensor element  38  sufficiently underneath the outer skin  42  of the structural element while ensuring its participation in significant impact events eliminates such unnecessary deployments. 
     FIG. 2  illustrates an example of the sensor element  38  mounted in a vehicle door  24 . The sensor element is positioned underneath the outer skin  42  and near a main structural element, such as a structural reinforcement beam  44 . The sensor element  38  can be mounted thereto via attachment points  46 . Alternatively, the sensor element  38  can be disposed within a housing member (not illustrated), and the housing member can be mounted securely to the reinforcement beam  44  via attachment points  46 . The attachment points  46  can be fasteners, welding, etc., so long as the sensor element  38  and/or housing is securely and rigidly mounted to the reinforcement beam  44 . 
     FIG. 3  illustrates an example of the sensor element  38  mounted near the front bumper  28 . The sensor element  38  is located behind the outer layer of the bumper  28 , and may either be directly embedded in the compressible material of the bumper  28 , or be mounted behind the bumper  28  in a manner similar to that described above for the sensor element  38  located within a vehicle door  24 . This sensor element  38  will detect impacts to the front bumper  28 , and demonstrates the ability of the sensing system  35  to discriminate among impact events based on the severity of the event. Depending on the severity and the force of the impact detected by the sensor element  38 , the restraints control module  36  may deploy either a pedestrian airbag  30 , for minor impacts typical of those with pedestrians, or the front  22  and/or side  26  airbags for major impacts such as vehicle crashes. The ability to discriminate between these two very different types of impacts is developed more fully below. 
   Each sensor element  38  is in electrical communication with the restraints control module  36  via electrical connections  40 . There may be a signal-processing module  48  electrically situated between the sensor elements  38  and the restraints control module  36 , i.e., the signal processing module  48  is electrically connected to both the sensor elements  38  and the restraints control module  36 . The restraints control module  36  is electrically connected to and in communication with the deployable restraints of the vehicle  10 . 
   In the preferred embodiment, the sensor element  38  constitutes a bend sensitive resistance element  50 . Bend sensitive resistance elements, such as the flexible potentiometer disclosed in U.S. Pat. No. 5,583,476 to Langford, provide electrical signals that vary as the element is deformed. A bend sensitive resistance element  50  is only one example of the type of sensor that can be used as the sensor element  38  in the sensing system  35  of the present invention. As such, the specific example of a bend sensitive resistance element  50  is only illustrative in nature and is not intended to limit the scope of the present invention in any way. 
   Preferably, the bend sensitive resistance element  50  is comprised of a rectangular ink strip  52  composed of a conductive ink which has been treated to produce cracks in the ink, a flexible substrate  54 , and electrical connectors  56  for connecting the conductive ink strip  52  and the restraints control module  36 . The flexible substrate  54  is preferably about 1″ wide and has a length approximately equal to the structural element being monitored. In one embodiment, the ink strip  52  constitutes a single continuous strip of the conductive ink having a length slightly less than that of the flexible substrate. Preferable in this embodiment, the ink strip  52  is approximately ¼″ in height, and has a length approximately equal to the length of the structural element to be monitored. For example, for a bend sensitive resistance element  50  utilized to monitor for side impacts, the ink strip  52  preferably has a length approximately equal to the length of the appropriate vehicle door  24  and is disposed on a flexible substrate  54  slightly longer in length. 
   It will be appreciated that the flexible substrate  54  can vary significantly from the dimensions detailed above. For example, the substrate  54  can take a size and form approximately equal to the interior space of a door  24  panel. In this configuration, ink strips  52  could be disposed in a variety of patterns along the flexible substrate  54 , providing a multitude of deformation sensors. The patterns could be designed to mimic high-probability impact sites. It will be further appreciated that the ink strips  52  can vary from the dimensions detailed above to meet specific impact monitoring needs. 
   In an alternate embodiment illustrated in  FIG. 5 , the conductive ink is arranged into several smaller strips  52  each in independent electrical communication with the restraints control module  36 . In this embodiment, the smaller ink strips  52  are disposed horizontally relative to each other, i.e., end-to-end, along a unitary flexible substrate  54 . The smaller ink strips are preferably about ¼″ in height by approximately 4″ in length. As in the previous embodiment, the flexible substrate  54  is preferably about 1″ in height and has a length approximately equal to the structural element being monitored. An appropriate number of smaller ink strips  52  necessary to span the length of the flexible substrate  54  is disposed on the flexible substrate  54 . It has been determined that, for a typical front vehicle door  24 , seven ink strips  52  of the preferable dimensions, laid end-to-end on the flexible substrate  54  provide adequate coverage of the span. 
   Arranged in this manner, the smaller ink strips  52  act as individual bend sensitive resistance elements  50 , providing a degree of azimuthal resolution. For example, when an impact event occurs near the latch of the door  24 , causing deformation only in that area, the element  50  located in that area will deform, and therefore it will be the only element  50  that relays a deformation signal to the restraints control module  36 . This localization of the impact will allow the restraints control module  36  to better discriminate among severe and non-severe impact events. In contrast, if the element  50  constitutes a single, continuous ink strip  52  along the span, no such localization of the impact occurs. For example, when an impact occurs near the latch, the element  50  relays an impact signal. Because localized elements  50  were not present, though, the signal does not relay information regarding the locality of the impact beyond the general area of the vehicle door  24 . Consequently, the restraints control module  36  does not have information regarding the precise location of the impact when making a subsequent deployment decision. Furthermore, this arrangement of a plurality of bend sensitive resistance elements  50  provides an ability to resolve the location and width of an impact event relative to the vehicle  10  by comparing the extent of deformation between neighboring bend sensitive resistance elements  50 . 
   The conductive ink strip  52  of the bend sensitive resistance element  50  is printed onto the flexible substrate  54 . Preferably, the substrate  54  is a flexible material such as polyamide. Polyester or other suitable materials capable of providing the necessary flexibility may also be used. The flexible nature of the substrate  54  allows the bend sensitive resistance element  50  to be disposed along a non-linear surface. Also, the flexible substrate  54  provides the flexibility necessary to allow the ink strip  52  to structurally react in response to impact events, which is necessary for proper operation of the bend sensitive resistance element  50 , and consequently the sensing system  35 . The flexible substrate  54  may have an adhesive backing which facilitates placement on structural elements or in a housing. 
   The cracks are small, interspersed fissures in the ink strip  52  of the bend sensitive resistance element  50 . The cracks are randomly spaced and oriented throughout the ink strip  52 . The cracks are disposed along a single side of the strip  52 , making the bend sensitive resistance element  50  sensitive in only one direction. When used to monitor for the occurrence of side impact events in a vehicle door  24 , the surface having the cracks is typically directed toward the passenger compartment  16  of the vehicle  10 . As the bend sensitive resistance element  50  is bent inward, such as when a side impact occurs, the cracks open and increase the resistance of the element  50 . This change in resistance can be detected by the restraints control module  36 , which continually monitors the resistive output of the element  50 . 
   In addition to bend sensitive resistance elements  50 , the sensor element  38  may be any other type of sensor element  38  capable of being disposed in a manner that allows direct physical involvement in an impact and gathering and relaying information regarding the impact. That is, the sensor element  38  may be any other type of deformation sensor element. For example, the sensor element  38  may be a piezoelectric cable or a fiber-optic cable. No matter the type of deformation sensor utilized, the sensor element  38  can be either a unitary item spanning the length of a vehicle structural element, or may be a plurality of elongate sensor elements  38  horizontally situated so as to be capable of providing azimuthal resolution of impact events. 
   Turning now to the operation of the sensing system  35  of the present invention. As discussed above, the sensor element  38  of the present invention is able to directly participate in a vehicle impact event occurring in the area of the vehicle  10  in which the sensor element  38  is positioned. The sensor element  38  provides a variable output that is proportional to the extent of deformation induced in the sensor element  38  by an intruding object driving the impact event. It will be noted that the bend sensitive resistance element  50  of the preferred embodiment, due to its flexible nature and ability to have an adhesive backing on the flexible substrate  54 , is particularly easy to mount in various locations of the vehicle  10  such that it will directly participate in and therefore detect an impact, and subsequently relay information regarding the impact event. 
     FIGS. 6   a – 6   c  show an impact event involving a pole  58  and a vehicle  10  containing a sensing system  35  according to the present invention. The door  24  of the vehicle  10  contains a sensor element  38  in communication with a restraints control module  36 . The sensor element  38  is positioned underneath the outer skin  42  of the door  24 . The figures illustrates the physical consequences of the impact over time. As the impact progresses, the pole  58  first deforms the outer skin  42  of the vehicle door  24 . As shown in  FIG. 6   b , the sensor element  38  is not involved at this point due to its position relative to the outer skin  42 . However, as shown in  FIG. 6   c , once the impact progresses to a point where the sensor element  38  is situated, the pole  58  actually deforms the sensor element  38 . At this point, the sensor element  38  is directly participating in the impact event, which is necessary for the operation of deformation sensors. As the impact progresses further, the sensor element  38  deforms further. The sensor element  38  provides an output signal  60  that, when altered, indicates the occurrence of an impact event. For example, fiber optic deformation sensors provide an output signal  60  that consists of the transmission of light. In the preferred embodiment, the resistance of the bend sensitive resistance element  50  is the output signal  60 , and increases as deformation progresses due to increased opening of the cracks in the ink strip  52 . The restraints control module  36  detects any change in the output signal  60 , as described below, and makes a deployment decision based thereon. 
     FIGS. 7   a – 7   c  illustrate a corresponding output signal  60  transmitted by the sensor element  38  during the impact event depicted in  FIGS. 6   a – 6   c . As the impact event progresses over time, the output signal  60  varies depending on the extent of deformation of the sensor element  38 . For the preferred embodiment, which utilizes a bend sensitive resistance element  50 , the output signal  60  corresponds to the resistance of the sensor element  38 . In  FIG. 7   a , before the impact event has occurred, the output signal  60  remains constant at a threshold output level  62 . As the pole  58  deforms the outer skin  42  of the door  24  but has yet to reach the sensor element  38 , the electrical output signal  60  remains constant at the threshold level  62 , as illustrated in  FIG. 7   b . Once the sensor element  38  is involved in the impact event, and deformation of the sensor element  38  occurs, the output signal  60  changes to reflect the severity of the impact. 
   The amplitude  64  of the change in the output signal  60  indicates the extent of the deformation. That is, as more deformation is imposed on the sensor element  38 , the output signal  60  changes more dramatically from the threshold output level  62 . For the preferred embodiment utilizing bend sensitive resistance elements  50 , it has been observed that the resistance typically changes by a factor of approximately ten when deployment-type events are encountered. The output signal  60  of the sensor element  38  will return to its original value, i.e., the threshold output level  62 , when and if the sensor element  38  returns to its original and undeformed state. The slope  66  of the change in the output signal  60  indicates the rate at which the deformation occurred. If deformation occurs rapidly, the time required to achieve the change in the output signal  60  is relatively brief, producing a steep slope  66 . Conversely, if the deformation occurs relatively slowly over time, the slope  66  will be correspondingly gradual in nature. Both the amplitude  64  and the slope  66  of the change in the output signal  60  can be used by the restraints control module  36  to make more effective deployment decisions. For example, if the amplitude  64  indicates a relatively severe impact event, the restraints control module  36  can deploy restraints to a greater extent, such as involving more restraints or deploying one restraint more fully. Also, if the slope  66  indicates a relatively slow impact event, the restraints control module  36  can slow down the rate of deployment. 
   The output signal  60  is sent via the signal-processing module  48  to the restraints control module  36 , which then interprets the signal  60  to discriminate between different types and severity of impacts. Given that different types of objects involved in impact events, such as poles  58 , barriers, pedestrians and other vehicles, will produce different output signals  60  for a given speed and acceleration of the vehicle  10  during the impact event, the signal  60  will vary accordingly. The ability of the sensing system  35  of the present invention to provide azimuthal resolution of an impact event adds another degree of variance to the output signal  60 . The resulting ability to distinguish, for example, pole-impact events from low-speed barrier impacts, will provide a more accurate decision from the restraints control module  36  for when to deploy a restraint device, which restraint to deploy, and the extent of such deployment. Furthermore, the ability to determine the location and width of impact with the vehicle  10  will allow for more effective decisions regarding which restraints need be deployed. 
   The restraints control module  36  includes hardware and/or software for processing incoming output signals  60 , determining if a passive restraint threshold has been met and sending a deployment signal to the passive restraints, such as the front airbags  22 , the side airbags  26 , and/or the pedestrian airbag  30 . 
   In order to further improve impact determination and passive restraint firing decisions, one may wish to employ the output signal  60  from the sensor elements  38  of the present invention along with the output from the accelerometers  32 ,  34 . The accelerometers  32 ,  34  are illustrated in  FIG. 1  and also provide output signals processed by the restraints control module  36 . While accelerometers are illustrated in the preferred embodiment, they are not necessary for the operation of the sensor elements  38  of the present invention. 
   For example, the particular sensor element  38  near the impact location may be used as the primary impact detection sensor, with the centrally mounted accelerometers employed as safing sensors. In this way, the characteristics of the strain detected by the sensor element  38  may be tempered by the amount of acceleration experienced by the vehicle as is detected by one or both of the accelerometers  32 ,  34 . Another example of impact detection in which the different sensors are employed may include employing the accelerometers  32 ,  34  as the primary sensors for impact events, and modifying the thresholds for the deployment decision based upon the strain detected by a particular one of the sensor elements  38 . No matter if the sensor element  38  or the accelerometers  32 ,  34  are utilized as the primary sensors, the azimuthal resolution provided by the sensor elements  38  can be utilized in conjunction with output from the accelerometers  32 ,  34  to resolve the localization and/or width for an impact event. This combination of impact information provides for a further degree of tempering, and increasing the number of possible deployment scenarios. 
   The foregoing disclosure is the best mode devised by the inventors for practicing the invention. It is apparent, however, that vehicle impact sensing systems incorporating modifications and variations will be obvious to one skilled in the art of impact sensors and systems. Inasmuch as the foregoing disclosure is intended to enable one skilled in the pertinent art to practice the instant invention, it should not be construed to be limited thereby but should be construed to include such aforementioned obvious variations and be limited only by the spirit and scope of the following claims: