Abstract:
A sensing device for actuating an airbag system in a motor vehicle comprises an airbag having a stowed condition and an inflated condition, an inflator operationally coupled with the airbag responsive to electrical actuation for inflating the airbag with a gas, an impact detection sensor for generating a signal upon an offset impact event, and a controller for processing the signal generated by the sensor and electrically actuating the inflator upon computing a predetermined impact severity to a forward corner of the motor vehicle. The motor vehicle further comprises a front bumper beam attached proximate a distal end of a front rail and the sensor comprises a flexible electro-resistive sensor mounted to a rear side of an outboard portion of the front bumper beam.

Description:
CLAIM OF PRIORITY AND CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to currently pending, commonly assigned U.S. application Ser. No. 14/082,443 now U.S. Pat. No. 9,266,496 issued in Feb. 23, 2016, titled FLEXIBLE ELECTRO-RESISTIVE IMPACT DETECTION SENSOR FOR FRONT RAIL MOUNTED AIRBAG and is also related to U.S. application Ser. No. 14/082,438 now U.S. Pat. No. 9,004,216, issued on Apr. 14, 2015, titled “FRONT RAIL MOUNTED AIRBAG” and U.S. application Ser. No. 14/082,455 now U.S. Pat. No. 9,127,968 issued on Sep. 8, 2015, titled “FLEXIBLE OPTICAL IMPACT DETECTION SENSOR FOR FRONT RAIL MOUNTED AIRBAG,” the contents of which are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to an airbag for a motor vehicle to minimize intrusion into the vehicle during an impact event, specifically a front side rail airbag that is triggered to inflate in the event of and to mitigate small offset rigid barrier impacts. 
     BACKGROUND OF THE INVENTION 
     Airbag systems for use in motor vehicles are generally well-known in the art. Traditionally, such airbag systems have been used within motor vehicle interiors to mitigate and reduce occupant impacts with motor vehicle interior components and structures, such as steering wheels, dashboards, knee bolsters, side door panels, and body pillars. 
     The present disclosure, however, addresses the application of such airbag systems in combination with exterior motor vehicle components to manage and control motor vehicle impact events with external objects. In particular, the airbag system is adapted to manage and control an impact event to the front corner of the motor vehicle. That is, various testing protocols and standards are being and have been developed to address vehicle integrity in the event of such a collision. For example, the Insurance Institute for Highway Safety (IIHS) has adopted a new small offset frontal crash test, where the test objective is to manage and control damage and injuries resulting from actual motor vehicle impacts with stationary rigid poles (offset from the motor vehicle center of gravity and outside the main longitudinal rail), vehicle to vehicle collinear offset impacts (again, offset from the motor vehicle center of gravity), and vehicle to vehicle frontal oblique impacts. The IIHS test protocol involves the evaluation of such impacts against a rigid pole and currently envisions using a 25 percent overlap rigid barrier with a curved end simulating a 6-inch pole radius. The test impact velocity is 40 mph (64 kilometers per hour). The contemplated testing protocol is referred herein as the 40 mph Small Offset Rigid Barrier (“SORB”) impact test. 
     In view of the SORB test protocol, current front end structures are being evaluated to optimize vehicle performance in small offset pole impact events. Hence, solutions for mitigating SORB impacts would be advantageous. 
     The airbag assembly disclosed herein particularly accomplishes the foregoing optimization of vehicle performance by providing a deployable structure mounted to the front side rail of the vehicle behind the bumper. Upon vehicle impact with the SORB, a front bumper mounted sensor sends a signal to an electronic control unit or ECU. Once the signal is processed, the ECU activates a side rail mounted inflator deploying the airbag. The airbag design is configured such that the airbag will deploy in a triangular shape, preferably creating a 30 degree angle with the longitudinal axis of the side rail and the motor vehicle. The 30 degree angular end of the triangular deployed airbag is preferably closest to the front bumper system of the vehicle. This deployment configuration allows for the vehicle to generate a very high Y-force against the rigid barrier to propel the vehicle away from the barrier and thus redirect impact energy by lateral movement of the motor vehicle and thereby minimize vehicle intrusion. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present disclosure, an airbag system is disclosed that mitigates intrusion in the event of an offset rigid barrier impact to a forward corner of a motor vehicle. The airbag system comprises a motor vehicle front rail having a forward projecting distal end and an airbag attached proximate the distal end of the front rail, the airbag having a stowed condition and an inflated condition, wherein the airbag in the inflated condition has an inclined angular leading edge. An inflator is operationally coupled with the airbag and is responsive to electrical actuation for inflating the airbag with a gas. An impact detection sensor generates a signal upon an impact event, whereby a controller processes the signal generated by the detection sensor and electrically actuates the inflator upon computing a predetermined impact severity to the forward corner of the motor vehicle. The inclined angular leading edge of the airbag in the inflated condition acts against the offset rigid barrier so as to generate a lateral force against the offset rigid barrier to push the motor vehicle away from the barrier and thereby redirect impact energy by lateral movement of the motor vehicle. 
     Still another aspect of the present disclosure is an airbag system having a pair of airbags, wherein one of the pair of airbags is mounted on each side of the motor vehicle. 
     Yet another aspect of the present disclosure is an airbag system wherein the motor vehicle has a front wheel mounted proximate the front rail, and the airbag is mounted forward of the front wheel. 
     An additional aspect of the present disclosure is an airbag system wherein the motor vehicle includes a body panel having an exterior and an interior surface, the airbag being disposed proximate the interior surface to act through the body panel to generate the lateral force against the offset rigid barrier. 
     Another aspect of the present disclosure is an airbag system utilizing an airbag having a substantially triangular configuration when in the inflated condition, where an angular leading edge corresponds to the hypotenuse of the triangular configuration, a forward end of the airbag corresponds to the apex of the triangular configuration, and a rearward end corresponds to the base of the triangular configuration. 
     Still another aspect of the present disclosure is an airbag system where the apex of the triangular configuration has an angle of about 30 degrees. 
     A further aspect of the present disclosure is an airbag system, wherein the motor vehicle is equipped with an automatic occupant restraint system having occupant restraint system deployment sensor, and the impact detection sensor is also the deployment sensor for the automatic occupant restraint system. 
     Yet a further aspect of the present disclosure is an airbag system having an impact detection sensor mounted to an interior surface of the outboard portion of the front bumper. 
     An additional aspect of the present disclosure is an airbag system having an impact detection sensor that detects bending of the outboard portion of the front bumper during the impact event. 
     Yet another aspect of the present disclosure is an airbag system having an impact detection sensor comprised of a conductive film that generates an electrical signal when bent. 
     A still further aspect of the present disclosure is an airbag system having an impact detection sensor comprising a fiber optic cable that generates a variable output signal in response to bending of the fiber optic cable. 
     Another aspect of the present disclosure is an airbag system for a motor vehicle comprising a front rail, an airbag attached to the front rail, the airbag when inflated having an angular leading edge, an inflator, a sensor for generating a signal upon an impact to the corner of the vehicle by an object, and a controller for receiving the signal from the sensor and actuating the inflator, wherein the angular leading edge of the airbag generates a lateral force against the object. 
     A yet additional aspect of the present disclosure is an airbag system utilizing a front rail having a distal end and an outer side surface, wherein the airbag is attached to the distal end of the front rail on the outer side surface of the front rail. 
     A further aspect of the present disclosure is an airbag system utilizing a pair of front rails extending forward from each side of the motor vehicle, with one each of a pair of the airbags is mounted on each of the outer side surfaces thereof. 
     Still another aspect of the present disclosure is a method of employing an airbag system to generate a lateral force against an offset rigid barrier to push the motor vehicle away from the barrier and thereby redirect impact energy by lateral movement of the motor vehicle, wherein the method comprises the steps of providing a motor vehicle front rail having a forward projecting distal end, attaching an airbag proximate the distal end of the front rail, the airbag having a stowed condition and an inflated condition, wherein the airbag in the inflated condition creates an inclined angular leading edge, equipping the airbag with an inflator operationally coupled with the airbag responsive to electrical actuation for inflating the airbag with a gas, providing an impact detection sensor for generating a signal upon an impact event, and providing a controller for processing the signal generated by the detection sensor, electrically actuating the inflator upon a predetermined impact severity to the forward corner of the motor vehicle, and presenting the inclined angular leading edge of the airbag in the inflated condition to act against the offset rigid barrier so as to generate a lateral force against the offset rigid barrier to push the motor vehicle away from the barrier and thereby redirect impact energy by lateral movement of the motor vehicle. 
     Yet another aspect of the present disclosure is a method wherein the airbag has a substantially triangular configuration when in the inflated condition, wherein the angular leading edge corresponds to the hypotenuse of the triangular configuration, a forward end of the airbag corresponds to the apex of the triangular configuration having an angle of about 30 degrees, and a rearward end corresponds to the base of the triangular configuration. 
     These and other aspects, objects, and features of the present disclosure will be understood and appreciated by those skilled in the art upon studying the following specification, claims, and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a front perspective view of a motor vehicle front side frame rail incorporating the first embodiment of the airbag for the airbag system in accordance with the present disclosure in the inflated condition; 
         FIG. 2  is a rear perspective view of a motor vehicle front side frame rail incorporating the first embodiment of the airbag for the airbag system in accordance with the present disclosure in the inflated condition; 
         FIG. 3  is a bottom view of the first embodiment of the airbag for the airbag system of the present disclosure in the inflated condition; 
         FIG. 4  is a front view of the first embodiment of the airbag in the inflated condition in accordance with the present disclosure; 
         FIG. 5  is a side view of the first embodiment of the airbag in the inflated condition in accordance with the present disclosure; 
         FIG. 6  is a front perspective view of a second embodiment of the airbag in the inflated condition in accordance with the present disclosure; 
         FIG. 7  is a top view of the second embodiment of the airbag in the inflated condition contacting the impact barrier in accordance with the present disclosure; 
         FIG. 8  is a top view of the second embodiment of the airbag in the stowed condition in accordance with the present disclosure; 
         FIG. 9  is a rear perspective view of the first embodiment of the installed bumper bending impact sensor for use with the airbag system of the present disclosure; 
         FIG. 10  is a top perspective view of the first embodiment of the bumper bending impact sensor for use with the airbag system of the present disclosure; 
         FIG. 11 a    is another perspective view of the first embodiment of the bumper bending impact sensor for use with the airbag system of the present disclosure; 
         FIG. 11 b    is yet another perspective view of the first embodiment of the bumper bending impact sensor for use with the airbag system of the present disclosure; 
         FIG. 12  is a schematic view of the second embodiment of the bumper bending impact sensor for use with the airbag system of the present disclosure; 
         FIG. 13  is perspective view of the second embodiment of the bumper bending impact sensor for use with the airbag system of the present disclosure; and 
         FIG. 14  is a rear perspective view of the second embodiment of the installed bumper bending impact sensor for use with the airbag system of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
     Referring to  FIGS. 1-4 , a motor vehicle  10  includes a front frame  12  including a pair of front rails  16  of the motor vehicle. In the one embodiment of the present disclosure, the front frame  12  may extend substantially the length of the body, but in other configurations may extend outwardly and forward of a unibody body structure of the motor vehicle  10 , as is typical of smaller vehicles. Each of the front rails  16  may have a beam configuration with integrated ribs  18  and flanges  20  for reinforcement, as shown in  FIGS. 1-8 . The front rails  16  may also have a tubular configuration, as shown in  FIGS. 9 and 14 . In either case, each of the front rails  16  include a front distal end  22  provided with a flange  24 , to which a bumper assembly  26  may be attached, either directly or indirectly through an intermediate bumper bracket  28 . 
     The bumper assembly  26  can adopt one of many possible configurations, but, as is typical, preferably includes a steel reinforcement beam  30  to which is attached an outer body fascia  32  having a decorative finish and color coordinated to the overall exterior color of the motor vehicle  10 . The attachment of the bumper assembly  26  to the front rail  16  can also include a low speed (i.e., 5-9 mph) impact mitigator  154 , such as a polygel mitigator having a displaceable ram and tube assembly capable of absorbing impact energy from a low speed impact without damage to the distal end  22  of the front rails  16  and minimal damage to the outer body fascia  32 , as shown in  FIGS. 9 and 14 . 
     The front rails  16 , as well as other front body structures and engine components (in the case of front mounted engine motor vehicles) provide a deformable forward section  34  (which may also be used for impact mitigation), as is known in the art. It is contemplated and intended that the forward section  34  will deform upon contact with an object in a forward collision, such as in the aforementioned NCAP testing, to absorb the impact energy associated with such a forward collision. As is common on such systems, one or more accelerometers is used as a sensing device to generate an electrical signal upon the sudden de-acceleration of a frontal impact. This signal is then detected by an on-board electronic control unit or ECU  60  and then used to determine whether the installed occupant restraint system, such as one or more airbag assemblies, should be deployed within the occupant compartment in the event that a predetermined de-acceleration is detected. 
     A further optimization of vehicle structural performance for SORB impacts can be obtained by providing a front rail mounted airbag system  35  to mitigate intrusion in a 40 mph SORB impact. An airbag  36  is mounted in the stowed condition to an outer surface  38  of the “crash can” or deformable segment  156  of the distal end  22  of the front side rail  16 , as best seen in  FIG. 8 . The front side rail mounted airbag  36  in the stowed condition preferably includes a number of predetermined folds  40 ,  42 ,  44 ,  46  to manage deployment, as noted below. Preferably, one each of a pair of the front side rail mounted airbags  36  is disposed forward each of the front wheels  48 . Thus, the front side rail mounted airbag  36  is mounted to the front rail  16  of the motor vehicle  10  behind the front bumper assembly  26 . Further, for cosmetic purposes, the motor vehicle  10  may also include a front side body panel  50 , such as a forward fender shown in  FIG. 7 , having an exterior surface  52  and an interior surface  54 , where the airbag  36  is disposed proximate the interior surface  54  and acts through the body panel  50  to generate a lateral force against the SORB barrier  56 , as discussed below. 
     Upon vehicle impact with the SORB barrier  56 , a sensor  58  sends a signal to an electronic control unit or ECU  60 . Once the signal is processed, the ECU  60  activates an inflator  62  operationally coupled with the front side rail mounted airbag  36 , deploying the front side rail mounted airbag  36 . The airbag  36  is preferably configured such that the airbag  36  will deploy in a substantially triangular configuration when in the inflated condition, thereby creating an angular leading edge  64  corresponding to the hypotenuse of the triangular configuration, a forward end  66  of the airbag corresponding to the apex of the triangular configuration and preferably having an angle of about 30 degrees, and a rearward end  68  corresponding to the base of the triangular configuration. This deployment configuration allows for the vehicle to generate a very high lateral or Y-force against the SORB barrier  56  to propel the motor vehicle  10  laterally away from the SORB barrier  56  and thus redirect impact energy by lateral movement of the motor vehicle  10  and thereby minimize vehicle intrusion, as best shown in  FIG. 7 . 
     As shown in  FIGS. 6-8 , the forward end  66  of the airbag may be extended laterally outwardly to form an offset wall  70  in order to fill the space between the folded airbag and the interior surface  54  of the front side panel  50 . However, it will be noted that the angular leading edge  64  is disposed at the same approximately 30 degree angle with the longitudinal axis of the motor vehicle so as to generate the Y-force necessary to laterally move the motor vehicle  10 . Also, as shown in  FIG. 6 , it may be helpful to mount the stowed airbag  36  within a frame  72 , preferably fabricated from steel or aluminum, to create a reinforced space within which the airbag  36  can be inflated and thus maintain the shape of the angular leading edge  64  when deployed and in contact with the SORB barrier  56 . 
     As noted previously, accelerometers may be used as a sensing device to generate an electrical signal upon the sudden de-acceleration of a frontal impact to deploy airbag(s) within the occupant compartment in the event that a predetermined de-acceleration is detected. These accelerometers may also be employed to signal a vehicle impact with the SORB. However, under certain circumstances, such as small overlap frontal impacts, the time taken by the traditional frontal impact sensing systems may not be ideal and may not provide adequate time for proper deployment of the disclosed airbag structure. These kinds of impacts may need additional sensing systems especially designed for sensing small overlap frontal impacts, depending on vehicle front structure, impact velocity, and the object with which the impact occurs. 
     Thus, preferably a separate front bumper mounted sensor  58  is used to send a signal to the ECU  60  (such as that shown in  FIG. 12 ) for inflation of the airbag  36  upon impact with a SORB barrier  56 , preferably within 5 to 15 milliseconds after the impact event begins. Indeed, the front side rail airbag  36  is preferably fully deployed and in position before front rails  16  and crash can  154  starts deforming (roughly 10 to 20 milliseconds), depending on the vehicle front end structure. Therefore, in addition to traditional motor vehicle crash sensors, a front bumper mounted sensor  58  for determining bending in the bumper reinforcement beam  30  can be employed to more rapidly send a signal to the ECU  60  assigned to the front bumper mounted sensor  58  mounted to an outboard portion of the front bumper. This location provides the ideal signal for sensing the SORB impact event, regardless of sensor design. However, it is a hostile environment, subject to temperatures of 105° C. and salt spray from wheel splash when driving during precipitation. Two preferred concepts are one or more electro-resistive beam bending sensors  74  mounted on the front bumper beam or one or more front bumper beam bending sensors  76  based on optical fiber technologies. 
     The first concept, a flexible electro-resistive sensor  74 , is a flexible sensor design which monitors for bending of the bumper reinforcing beam  30  located behind the front fascia  32 . The flexible electro-resistive sensor  74  includes a force-resistive film  78 , which consists of a conductive ink  80  printed on a clear plastic membrane  82 . The conductive ink  80  changes resistance in response to material stress experienced when the membrane  82  bends. By applying a voltage and measuring the change, the amount of bending in the flexible electro-resistive sensor  74  can be measured, as shown in  FIG. 9 . Thus, in an impact event, the membrane  82  bends and an electrical signal generated to measure and compare the actual impact severity against the predetermined impact severity to determine if airbag  36  actuation is required. If the deflected signal equals or exceeds a signal level corresponding to a predetermined impact severity, airbag  36  deployment is initiated. Since the flexible electro-resistive sensor  74  operates on current levels that are insufficient to engage automotive grade communication protocol, the current level of the flexible electro-resistive signal  74  must be increased in a separate step, after which the signal is output at automotive voltage levels. 
     The flexible electro-resistive sensor  74  is mounted to a rear surface  31  of the outboard portion  33  of the frontal bumper beam  30 , forward of the front frame side rail  16 , to detect a small offset impact event that initially causes bending only in the outboard portion  33  of the front bumper beam  30 . Such bending occurs only when impacting an object of sufficient mass to deflect the sheet metal bumper beam  30  and is not subject to localized, short duration impacts which are largely resonant and does not result in significant displacement in the bumper beam  30 . This improves the discrimination capabilities of the flexible electro-resistive sensor  74  versus an accelerometer, which is subject to oscillatory signals from vibrations. To provide a timely decision signal, the flexible electro-resistive sensor  74  is preferably mounted directly to a rear surface  31  of the outboard portion  33  of the front bumper beam  30 , as shown in  FIG. 9 . This mounting location is superior to mounting the electro-resistive front bumper beam bending sensor  74  on the bumper fascia  32 , in that the front bumper beam  30  is more structurally robust than the fascia  32 , and does not bend due to incidental impacts with lower mass objects, such as shopping carts and bicycles. 
     In order for a flexible membrane sensor to function and survive in this environment, the force-resistive film sensor preferably employs a conductive ink  80  that retains its electrical properties at high temperatures (i.e., above 100° C.). The flexible electro-resistive sensor  74  is also preferably coated with a waterproof, but flexible, coating  86  to protect the ink  80  from water and salt spray, as shown in  FIG. 10 . The coating  86  may be a separate, solid piece wrapped around the flexible electro-resistive sensor  74  or a tube which surrounds the flexible electro-resistive sensor  74  and is sealed at the ends. The coating  86  may be dipped or sprayed over the flexible electro-resistive sensor  74 . The coating  86  thus protects the flexible electro-resistive sensor  74  from temperature extremes and liquid exposure that occurs on the front bumper assembly  26 . The coating  86  materials must be flexible enough when applied that they do not interfere with the bending properties of the flexible electro-resistive sensor  74 . 
     In addition, the flexible electro-resistive sensor  74  may be bonded to the metal of the bumper beam  30  with an adhesive, so the entire length of the flexible electro-resistive sensor  74  is fixed and must expand and contract along with the bumper. However, the different thermal expansion coefficients of the force-resistive film sensor ink  80  and membrane  82  and the sheet metal of the front bumper beam  30  to which it is mounted induces an inherent drift in the signal with temperature changes, which can be significant when compared to the output of the flexible electro-resistive sensor  74  when bent. To minimize such drift, the flexible electro-resistive sensor  74  is preferably mounted at fixed points along its length. These could be wire clamps  88  attached to the flexible electro-resistive sensor  74  or built into the protective coating  86 , as shown in  FIG. 11 a   . It could also be a channel  90  rigidly attached or built into the bumper beam  30 , within which the flexible electro-resistive sensor  74  loosely lies, as shown in  FIG. 11 b   . Such arrangement allows the flexible electro-resistive sensor  74  elements, that is, ink  80 , membrane  82 , and coating  86 , to thermally expand and contract without regard to the thermal expansion and contraction of the front bumper beam  30 , reducing the amount of signal drift incurred from the thermal cycling of the system. The flexible electro-resistive sensor  74  can thus be utilized for detecting a SORB impact event in a timely manner. Further, the flexible electro-resistive sensor  74  is relatively low cost and robust to the environment, maintaining its sensing capabilities through liquid spray and temperature changes. 
     Alternatively, a flexible fiber optic sensor  76  may be used to detect an SORB impact. The flexible fiber optic sensor  76  consists of a fiber optic cable  92 , light source  94 , photodiode  96 , and amplifier  98 , as shown in  FIG. 12 . The light source  94 , preferably an infrared light-emitting diode (LED), sends a light signal through the fiber optic cable fiber  92 , which is received by the photodiode  96 , preferably an infrared detector, which in turn outputs an electrical signal from an amplifier  98  proportional to the quantum of light received. 
     The flexible fiber optic cable  92  consists of a core material  100  surrounded by a thin layer of cladding material  102  having a different index of refraction than that of the core material  100 . Normally, any light that bounces off the walls  104  of the core material  100  is reflected back into the core material  100  and no light is lost due to bending of the cable. However, if a partial portion of the cladding is removed to form a bare portion  106  on the core material  100 , as shown in  FIG. 13 , a portion of the light which strikes the wall  104  of the core material  100  at an angle will escape the core material  100 . Bending the flexible fiber optic cable  92  allows even more light to escape. The quantum of light striking the photodiode  96  will be thus changed by being reduced, and the signal of the photodiode  96  will be changed by being reduced, indicating the degree of bending of the fiber optic cable  92 . Further, if the cladding  102  is removed on only one side of the fiber optic cable  92 , the photodiode  96  can be used to detect a directional signal, indicating whether the fiber optic cable  92  is bending towards the bare portion  106  of the modified side of the fiber optic cable  92  or away from it. 
     As noted above, in the SORB test mode, the impact is preferably detected within 5 milliseconds of initial contact in order to provide timely activation of the front side rail airbag  36 . By carefully placing the fiber optic cable  92  in the area of interest and modifying the cladding  102  to produce bare portions  106  in a defined pattern, the flexible optical sensor  76  can be adapted to provide a signal to specifically detect the SORB crash mode. As shown in  FIG. 14 , the fiber optic cable can be mounted to the back surface  31  of the outboard portion  33  of the bumper reinforcement beam  30  and also to the distal portion  22  of the frame rail  16  near the flange  24 . In this configuration, the flexible optical sensor  76  senses any rearward bending of the outboard portion  33  of the front bumper assembly  26 . In order to accommodate this specific mode, the cladding  102  is removed to form bare portions  106  in specific areas of the fiber optic cable  92 . That is, the section of the fiber optic cable  92  directly mounted to the outboard portion  33  of the front bumper reinforcement beam  30  preferably has cladding  102  removed to form bare portions on one side at regular intervals to detect any local deformation of the bumper reinforcement beam  30  outside the frame rail  16 . The cladding  102  is preferably removed to form bare portions  106  at smaller intervals in the bend radius to give a timely indication of deformation between the bumper reinforcement beam  30  and the front side rail  16  and flange  24 . The cladding  102  is preferably only removed in these sections of the fiber optic cable  92  to form bare portions  106  on one side of the cable in order to differentiate inward bending from outward bending. 
     The detection of the specific SORB impact mode of interest is obtained by comparing the detected light intensity signal to a predetermined light intensity signal corresponding to an impact severity justifying airbag deployment and deployment of the airbag when the detected light signal equals or exceeds the predetermined light intensity signal. The section of the fiber optic cable  92  mounted to the front rail  16  has no cladding removed, since the deformation of the front rail  16  will occur too late in the event to be of use for activating front side rail airbag system  35 . Using this selective cladding removal technique, a single length of fiber optic cable  92  can be designed to perform timely flex sensing in a specific orientation and direction. The optical cable sensor can be bonded to a rear surface of the front bumper beam with an adhesive along substantially the entire length of the sensor in contact with the bumper and the front rail. The optical fiber sensor can also be mounted to the rear of the front bumper beam and the distal portion of the front rail at fixed points along its length by wire clamps  88  attached to the sensor as shown in  FIG. 11   a.    
     The SORB front rail mounted airbag system  35  disclosed herein is lightweight, requires minimum packaging, and utilizes well-proven inflator technology. Further, the disclosed SORB front rail mounted airbag system  35  does not interfere with efforts to optimize motor vehicle performance of the New Car Assessment Program (NCAP) 35 mph full frontal crash mode. That is, the disclosed SORB front rail mounted airbag system  35  may be deployed in all cases when a frontal crash component may exist (e.g., full frontal, offset frontal and angular impacts). While the SORB impact event may be sensed by the traditional front crash sensors for restraint deployment in frontal crashes, separate front bumper reinforcement beam-mounted sensors  58  provided improved performance. 
     It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.