Abstract:
A vehicular crash sensing system is provided wherein a bumper cap contacts a bumper. A chamber is at least partially fit into a side rail attached to the bumper, wherein the chamber is sealed by the bumper cap. The bumper cap and chamber together enclose a space containing a volume of air. A stop element limits movement of the chamber into the side rail. A pressure sensor detects an increased chamber air pressure during crushing of the chamber resulting from movement of the bumper with respect to the stop element.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates in general to crash sensing in motor vehicles, and, more specifically, to pressure-based sensing having a pressure chamber location that enables low cost components and avoids negatively impacting other vehicle structures or systems. 
         [0004]    Active restraint systems utilize one or more sensors to detect the occurrence of a crash in order to deploy air bags or other restraint or occupant protection devices. Sensor signals are sent to an electronic control module that monitors the signals and determines when conditions warrant activation or deployment of an air bag, for example. 
         [0005]    The most commonly used type of sensor is the accelerometer which responds to gravitational forces occurring during deceleration associated with a crash. The accelerometer has a small size, so that it has a minimal effect on the mechanical crash performance of the structures to which it is mounted. In some situations, however, an accelerometer may not perform well because of the nature of the movements of the vehicle structure to which it is mounted both prior to and during a crash. Depending on the transmission of loads, deformation, and other structural issues, certain positions on a vehicle frame wherein an accelerometer might be mounted can be subject to vibrational resonance or other motions that interfere with sensing of the overall vehicle movement. This issue is sometimes addressed by mounting extra struts to the vehicle frame in order to either create an acceptable location for an accelerometer or to modify vibrational resonance in the frame, but such struts may interfere with the intentionally-controlled deformation of vehicle structures during a crash, may be difficult or impossible to package in the available space, or may be too costly. Consequently, other types of crash sensors are also sometimes used. 
         [0006]    A different type of known crash sensor directly senses an impact. Examples of impact sensors include a moving ball sensor and a deforming chamber sensor. In a deforming chamber sensor, a pressure or temperature of a fluid (e.g., air) in a chamber being compressed or crushed during a crash can be monitored to detect a deformation. Such impact sensors typically have a greater size, so that it may be even harder to find a good packaging space with sufficient clearance. Known uses of deforming chamber sensors have been especially subject to the problem of the creation of unintended changes in the controlled deformation during a crash. 
         [0007]    It would be desirable to provide a pressure-based crash system that 1) does not add strength to the front vehicle frame structure, 2) uses components that can withstand paint oven temperatures without degradation, 3) functions over a wide temperature range, and 4) is easily assembled with low cost components. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect of the invention, a vehicular crash sensing system is provided wherein a bumper cap contacts a bumper. A chamber is at least partially fit into a side rail attached to the bumper, wherein the chamber is sealed by the bumper cap. The bumper cap and chamber together enclose a space containing a volume of air. A stop element limits movement of the chamber into the side rail. The location of the seam between the bumper cap and chamber (i.e., whether or not the bumper cap is smaller or larger than the chamber part or how much of the bumper cap extends into the side rail) can be adjusted to facilitate manufacturing of the parts. A pressure sensor detects an increased chamber air pressure during crushing of the chamber resulting from movement of the bumper with respect to the stop element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of a prior art placement of an accelerometer on a bumper/side rail system, and also showing a hollow side rail that provides a space for mounting a deformation-type crash sensor in a first embodiment of the present invention. 
           [0010]      FIG. 2  is a perspective view of a bumper/side rail system using a crush can into which the crash sensing system of the present invention can alternatively be placed. 
           [0011]      FIG. 3  is an exploded view of a first embodiment of a crash sensing system mounted in a side rail. 
           [0012]      FIG. 4  is a perspective view of the assembled crash sensing system of  FIG. 3 . 
           [0013]      FIG. 5  is a perspective view of the system of  FIGS. 3 and 4  with the side rail assembled. 
           [0014]      FIG. 6  is a perspective, partially-exploded view of the crash sensing system with a bumper. 
           [0015]      FIG. 7  is a side view showing the crash sensing system interfaced against the bumper. 
           [0016]      FIG. 8  is a top view of a crash sensing system and a bumper. 
           [0017]      FIG. 9  is an exploded view of another embodiment of the crash sensing system. 
           [0018]      FIG. 10  is a cross-sectional view of an alternative embodiment of a chamber of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    Referring to  FIG. 1 , a vehicle frame system  10  includes a front bumper beam  11  and a side rail  12 . Side rail  12  is joined approximately perpendicularly to bumper  11  by conventional means, which in this example includes a bracket  13 . An accelerometer-based crash sensor  14  is shown mounted at one potential location on frame system  10 . For some vehicle designs, it may not be feasible to install an accelerometer-based sensor in any convenient location on the frame without signal degradation from vibrational resonances unless undesirable structural changes are made (e.g., adding a strut). In some embodiments, the present invention uses an open space behind the bumper beam inside the side rail for mounting a deforming chamber-type sensor. 
         [0020]      FIG. 2  shows an alternate frame system  15  having a bumper  16  and a side rail  17 . A crush can  18  joins bumper  16  and side rail  17 . The sensor described in the following figures can also be readily adapted by one skilled in the art for placement inside crush can  18 . 
         [0021]      FIG. 3  is an exploded view of a crash sensor system  20  received inside a side rail comprised of rail members  21   a  and  21   b.  Sensor system  20  includes a bumper cap  22 , and elongated chamber  23 , and a reaction cap  24 . A pressure sensor  25  is mounted using fasteners  26  to a side of chamber  23  within a side opening  27 . Elongated chamber  23  may be generally cylindrical and may contain a flattened facet  28  to provide a flat surface for side opening  27  and pressure sensor  25 . 
         [0022]    Bumper cap  22  has a first end surface  30  that is shaped in such a way that it nests into a contoured surface of a bumper. Chamber  23  is formed by an outer wall, the major portion of which is sized to be received in the hollow side rail. Chamber  23  has an end opening  31  to receive a second end  32  of bumper cap  22  (e.g., by interference fit, threading, or welding). Bumper cap  22  substantially seals end opening  31 . 
         [0023]    Reaction cap  24  substantially closes a second end  33  of chamber  23  so that when chamber  23  is crushed by forces applied through bumper cap  22 , an increasing air pressure is created inside chamber  23  which is converted by pressure sensor  25  into an electrical signal that is transmitted to a controller (not shown) for determining whether a crash is in progress. Reaction cap  24  is a plate-like or disc-like member and is mounted against an inside surface of the outer wall of chamber  23 . It can be joined by an interference fit, welding, or may be integrally formed with chamber  23 . In one preferred embodiment, bumper cap  22 , chamber  23 , and reaction cap  24  may be all comprised of stamped sheet metal. Alternatively, they could be comprised of molded plastic or reinforced rubber. 
         [0024]    Either reaction cap  24  or chamber  23  has a stop surface at the farthest point from the bumper in order to interface with a corresponding side rail feature for limiting movement of chamber  23  axially into the side rail. If reaction cap  24  is inserted fully into chamber  23 , then the back end of chamber  23  may provide the stop surface. If reaction cap  24  extends out from chamber  23 , then it would provide the stop surface. The stop surface abuts a reaction surface that is stationary with respect to the side rail. The reaction surface may be provided by an intrusion integrally formed in the side rail, such as a stamped rib or dimple  35  in rail member  21 A. Alternatively, the reaction surface may be provided by a bracket  36  fixed to the side rail and crossing the hollow interior space of the side rail. Bracket  36  may be cup shaped, may be comprised of multiple sections, and may be joined with side rail members  21   a  and  21   b  by welding, for example. 
         [0025]      FIG. 4  shows sensor system  20  in its assembled state. In a preferred embodiment, chamber  23  includes a plurality of circumferential grooves  40 - 44  that reduce the resistance of chamber  23  to being crushed in its longitudinal direction (i.e., from the direction of bumper cap  22 ). Preferably, the circumferential grooves are concentrated toward first end  31  so that the axial crushing (created when the bumper is forced inward) is concentrated toward the front of chamber  23 . 
         [0026]      FIG. 5  illustrates sensor system  20  mounted into side rail  21  with bumper cap  22  extending outward for contact with a bumper.  FIG. 6  shows a rear perspective view wherein a bumper  45  has a contoured central groove  46 . Bumper cap  22  is formed so that its front end surface  30  has a shape that nests into (i.e., conforms with) groove  46 . As shown in  FIG. 6 , bumper cap  22  may also be provided with a circumferential groove  47 . Alternatively, an even greater portion of the longitudinal length of the chamber assembly may be provided by bumper cap  22  to facilitate manufacture of the parts by drawing or stamping, for example.  FIGS. 6-8  also show a two-piece chamber assembly wherein the “reaction cap” is integrally formed as back end  48  of chamber  23 . 
         [0027]      FIG. 7  is a side view showing the placement of first end surface  30  into groove  46  after the side rail (not shown) is joined to bumper  45 . As shown in  FIG. 8 , first end surface  30  may also be tapered (e.g., in a direction perpendicular to the longitudinal axis of chamber  23 ) to accommodate any curvature of bumper  45 . 
         [0028]      FIG. 9  shows an alterative embodiment wherein the hollow space within the side rail and the outer profile of the sensor system are non-cylindrical. Thus, a chamber  50  and bumper cap  51  may have an oval outer profile to match a hollow space created by side rail members  52   a  and  52   b  with a similar profile. A bracket comprised of bracket members  53   a  and  53   b  is sized to mate with side rail members  52   a  and  52   b  and to chamber  50  so as to limit movement of chamber  50  into the side rail. A non-cylindrical profile can reduce any tendency of the sensor system to rotate inside the side rail and tends to reduce noise and rattling.  FIG. 9  is also constructed as a two-piece unit without a separate reaction cap. 
         [0029]    As shown in cross-section in  FIG. 10 , a chamber  60  may include an integrated outer wall  61  and reaction cap  62 . The integrated structure may be fabricated using molded materials. Grooves  63  and a side opening  64  would preferably be included in a molded structure. 
         [0030]    The foregoing invention has provided an integrated bumper-side rail pressure signal device of low cost that generates a pressure signal with a fast response time, high signal quality, and low noise. The device can be used on many types of vehicle and structural elements. No additional packaging is required because the sensing system is mounted in an otherwise empty space behind the bumper and in the side rail.