Abstract:
An impact detection system has two chambers disposed adjacent to one another. The two chambers have opposing tapered shapes, so that an impact anywhere along them will create a different pressure wave or pulse in each chamber. A pressure sensor module incorporating two pressure sensors is disposed at one end of the dual-channel unit, and comparison of the signals from the sensors can be used to discriminate both the location and severity of a pedestrian impact.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/538,197, filed Sep. 23, 2011, the disclosure of which is incorporated in its entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an apparatus and method for detecting an impact, and more specifically to such an apparatus and method adapted to detect an impact between a pedestrian or other light-weight object and a motor vehicle. 
     BACKGROUND 
     Systems have been proposed to reduce the severity of injuries suffered by pedestrians when struck by a moving motor vehicle. Some such systems are referred to as “active,” meaning that some action, response, or change is made to a portion or system of the vehicle in response to (or in anticipation of) striking the pedestrian. Examples of such active systems include bumper- or hood-mounted airbags and hood-lifting systems. Such active systems generally require some type of sensor or detection system to determine that a pedestrian impact has occurred or is about to occur. 
     A pedestrian impact detector should detect an impact occurring at any lateral location across the front end of the vehicle. It may also be advantageous to detect the lateral (left/right) location on the vehicle at which the pedestrian impact takes place. 
     U.S. Pat. No. 7,782,180B2 teaches a collision detection device installed in a bumper of an automotive vehicle that includes two deformable members each with a pressure sensor contained therein. The deformable members are arranged across the front end of the bumper so that each one covers approximately one-half of the width of the vehicle. 
     SUMMARY 
     An impact detection system is disclosed having two chambers disposed adjacent to one another. The two chambers have opposing tapered shapes, so that an impact anywhere along them will create a different pressure wave or pulse in each chamber. A pressure sensor module incorporating two pressure sensors is disposed at one end of the dual-channel unit, and comparison of the signals from the sensors can be used to discriminate both the location and severity of a pedestrian impact. 
     The disclosed dual-chamber design allows both of the pressure sensors to be located adjacent one another at one end of the IDU. This simplifies the packaging and manufacture of the impact detection system as compared with having two sensors located at separate locations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: 
         FIG. 1  is a simplified schematic view of the forward portion of a motor vehicle including a pedestrian impact detection system according to an embodiment of the invention; 
         FIG. 2  is a schematic front view of the impact detection unit and bumper shown in  FIG. 1 ; 
         FIG. 3  is a schematic top view of the impact detection unit and bumper shown in  FIG. 1 ; 
         FIG. 4  is a schematic view of an alternative embodiment of an impact detection unit; 
         FIG. 5  is a schematic view of another alternative embodiment of an impact detection unit; 
         FIG. 6  is a schematic view of another alternative embodiment of an impact detection unit; 
         FIG. 7  is a schematic view showing the setup used during a series of test runs of the system disclosed herein; and 
         FIGS. 8 through 14  are plots of data gathered during test runs of the system shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Referring to  FIG. 1 , a motor vehicle has a front bumper system  10  generally comprising a transverse bumper beam  12  supported by vehicle frame components  14 , an energy-absorbing component (EAC)  16  mounted adjacent to the front surface of bumper beam  12 , and an impact detection unit (IDU)  18  disposed in front of the EAC. Bumper system  10  may be covered or enclosed by a relatively thin front fascia  19  to provide an attractive and/or aerodynamically efficient exterior surface of the front portion of the vehicle. 
     EAC  16  may, for example, be a plastic component and may be in the form of a repeating “hat-section” adapted to deform, crush, or flatten in order to absorb kinetic energy when bumper system  11  experiences a frontal impact. EAC  16  may incorporate a transverse channel or other feature(s) for mounting IDU  18 . 
     IDU  18  comprises first and second substantially hollow, tubular chambers  20   a ,  20   b  mounted to the vehicle in an over/under arrangement. IDU  18  preferably extends across the full width of bumper beam  12  and may, if desired, be somewhat curved to integrate with the shape of bumper beam  12  and/or other forward structure of the vehicle. IDU  18  may also be curved or angled to extend around the left and right front corners of the vehicle. 
     The respective cross-sectional areas of chambers  20   a ,  20   b  (cross-sections taken in the y-z plane as shown in  FIG. 1 ) vary along the length of IDU  18  (across the width of the vehicle front end), and do so in manner inverse to one another. That is, the cross-sectional area of upper chamber  20   a  increases from left to right (with reference to the vehicle body), while the cross-sectional area of lower chamber  20   b  decreases from left to right. Therefore, the ratio of the cross-sectional area of upper chamber  20   a  to that of lower chamber  20   b  varies constantly from a minimum value at the front left corner of the vehicle to a maximum value at the right corner. 
     In the embodiment of the IDU  18  shown in  FIGS. 1-3 , chambers  20   a ,  20   b  are substantially rectangular in cross-section and the lengthwise variations in the cross-sectional areas are achieved by the respective vertical dimensions (indicated as H 1  and H 2  in  FIG. 2 ) varying along the length of IDU  18 . That is, upper chamber  20   a  has a maximum height adjacent the right end of bumper system  10  and tapers to a minimum height adjacent its right end. Conversely, lower chamber  20   b  has a minimum height adjacent its right end and tapers to a maximum height adjacent its left end. The lengthwise variation in chamber heights H 1 , H 2  may be uniform or non-uniform. Assuming that the two chambers are of approximately constant depth (measured parallel to the longitudinal or y-axis of the vehicle) along the length of IDU  18 , it is apparent that the ratio of the cross-sectional area of upper chamber  20   a  to that of lower chamber  20   b  varies from a maximum value at the right end of bumper system  10  to a minimum value at the left end. 
     IDU  18  further comprises a sensor module  22  located at one end thereof. Sensor module  22  comprises two pressure sensors  24   a ,  24   b  such that the two sensors are in communication with the hollow interiors of chambers  20   a ,  20   b  respectively. Pressure sensors  24   a ,  24   b  are thus able to detect pressure internal to the two chambers substantially independently of one another. Chambers  20   a ,  20   b  may contain air or any other gas or mixture of gasses appropriate to allow pressure sensors  24   a ,  24   b  to make accurate readings. 
     Pressure sensors  24   a ,  24   b  may be any appropriate type of pressure transducer that generates an electrical signal representative of the sensed pressure at all times the vehicle is in operation. The signals generated by sensors  24   a ,  24   b  are preferably transmitted to an electronic control unit (ECU)  26  where they may be digitized, integrated, measured, compared, or otherwise electronically and/or mathematically processed as necessary to detect characteristics such as the magnitude, the time, and the location of an impact on IDU  18 . It is also possible to use the raw signals from sensors  24   a ,  24   b  to actuate a pedestrian protection countermeasure, without significant signal processing by an ECU. 
     Packaging the two pressure sensors  24   a ,  24   b  adjacent one another in a single module  22  contributes to the efficiency of the design of the overall sensor system, as compared with locating multiple sensors at separate, spaced-apart locations. Fabrication, installation, and servicing of IDU  18  are improved by the unitary nature of sensor module  22 . 
     ECU  26  is electronically connected with other components of the vehicle&#39;s pedestrian protection system. For example,  FIG. 1  schematically indicates a pedestrian protection countermeasure including actuators  28  that raise at least a portion of the vehicle hood  29  above its normal position. This lifting creates more separation between the underside of hood  29  and rigid vehicle components (not shown) beneath the hood, as is well known in the pedestrian protection art. Such added separation allows the hood to bend or deflect downward under the pressure of a pedestrian strike. The sensor signals, when properly analyzed and/or processed by ECU  26 , may be used to trigger actuators  28  in order to lift the hood at an appropriate time. This is but one of many possible uses of the signals from the sensors. 
     The dimensions and location of IDU  18  relative to the vehicle are preferably selected so that if the vehicle strikes a pedestrian, the pedestrian&#39;s leg or legs are expected to impact the front surfaces of both upper and lower chambers  20   a ,  20   b  at approximately the same time. Because the cross-sectional areas of chambers  20   a ,  20   b  vary along the length of IDU  18 , such an impact will cause two separate and distinct pressure changes within the chambers as measured by the upper and lower sensors  24   a ,  24   b . Various properties of the signals generated by sensors  24   a ,  24   b  may be studied to gain information indicating the magnitude and lateral location of an impact on the front of the vehicle. Such information may be used to adjust the thresholds and/or other parameters used in algorithms that control deployment of pedestrian protection countermeasures. 
     Chambers  20   a ,  20   b  are shown in direct contact with one another, but they may be spaced from one another by some distance. Chambers  20   a , 20   b  need only be disposed closely enough adjacent to one another that an impact will create a measurable pressure change in both chambers. 
       FIG. 4  schematically depicts another exemplary embodiment of an IDU  118 . Upper and lower chambers  120   a ,  120   b  have vertical dimensions that are constant along the length of the IDU but have respective depth dimensions (indicated as D 1  and D 2  in  FIG. 4 ) which vary or taper along the length of the IDU, thereby achieving the lengthwise variation in cross-sectional area. The upper and lower chambers may have any cross-sectional shape (circular, oval, polygonal, etc.) to allow efficient integration into the vehicle front end structure. Both chambers need not necessarily have the same shape. 
       FIG. 5  schematically depicts another exemplary embodiment of an IDU  218  in which the respective vertical dimensions H 1  and H 2  of upper and lower chambers  220   a ,  220   b  vary non-linearly along the length of the IDU. Also in this embodiment, the upper and lower portions of IDU  218  are rounded, so that upper and lower chambers  220   a ,  220   b  are non-rectangular in cross-section. 
       FIG. 6  schematically depicts another exemplary embodiment of an IDU  318  in which chambers  320   a ,  320   b  are disposed horizontally relative to one another, rather than in an over/under arrangement. Respective depth dimensions D 1  and D 2  vary or taper along the length of IDU  318 . An impact force F directed against the forward chamber  320   a  creates a measurable pressure change in the rear chamber  320   b  as well. 
       FIG. 7  shows, in schematic form, the geometry of a test set-up in which a striker rod  30  was used to strike IDU  18  to simulate pedestrian impacts at three different locations across the length of the IDU. Pressure readings from sensors  24   a ,  24   b  were recorded during three impact tests: Test  1  is an impact at a point offset toward the end of IDU  18  most distant from the sensor module  22 . Test  2  is an impact at the approximate center of IDU  18 . Test  3  is an impact at a point offset toward the end of IDU  18  closest to sensor module  22 . The data graphs of  FIGS. 5-11  show possible ways the pressure signals may be analyzed to determine the nature of an impact. 
       FIGS. 8A ,  9 A, and  10 A show plots of the percent change in detected pressure versus time for Test  1 ,  2 , and  3  respectively.  FIGS. 8B ,  9 B, and  10 B show plots of the integral of the detected pressure versus time for Test  1 ,  2 , and  3  respectively. It is apparent from a comparison of the data from the three Tests that the pressure sensor signals may be used to detect the lateral location of an impact with the vehicle. 
       FIG. 11  shows the magnitude of the pressure signals recorded in upper chamber  20   a  for each of the three Tests.  FIG. 12  shows the pressure signals recorded in lower chamber  20   b  for each of the three Tests. These magnitude data may also be used to determine important information regarding an impact, including the lateral location of an impact. 
       FIG. 13  shows the difference between the two pressure signals recorded (lower chamber pressure minus upper chamber pressure) for each of the three Tests.  FIG. 14  shows the sum of the pressure signals recorded (lower chamber pressure plus upper chamber pressure) for each of the three Tests. These data may further aid in detecting the lateral location of an impact and/or the magnitude of the impact. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.