Abstract:
A collision protection system for protecting a pedestrian that uses a sensor that provides a width output signal that varies in relation to the width of an object contacting the vehicle. The sensor includes a resistive conductor that is shorted out by a conductive conductor of a portion of the length of the resistive conductor. A second sensor may be provided that provides an output only upon exceeding an impact threshold. Several sensors may be used to provide an indication of the location and width of the object contacted.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to sensors for measuring the location and the width of an impacted object.  
           [0003]    2. Background Art  
           [0004]    Sensors and sensing systems for active restraints on vehicles generally include accelerometers, speed sensors, piezoelectric sensors, flex tape switches, ribbon switches and the like. Such prior art sensors and systems do not have the capability of determining the width of an object struck by the sensor on the vehicle. The systems also fail to provide a mechanism for determining the location of an impact on the sensor. Ribbon switches or tape switches such as those disclosed in U.S. Pat. Nos. 3,694,600; 5,847,643; or 6,009,970 produce an output indicating that the strip switch or ribbon switch has been contacted but fail to provide any indication as to the width, of the area contacted or the location of the area contacted on the elongated switches.  
           [0005]    Information regarding the size and location of a collision would be useful for pedestrian protection systems or airbag deployment systems. If a pedestrian is struck by a vehicle, the greatest risk of injury is the risk of injury to the pedestrian. If, on the other hand, a pole, bridge abutment or another vehicle is contacted by a vehicle, the principal risk of injury is to the driver and passengers of the vehicle. In such instances, impact sensors are used to activate interior active restraint systems such as dashboard airbags or side curtains.  
           [0006]    There is a need for sensors that can sense the location and size of an object struck by a vehicle. In side or front impacts, the location and width of the impact zone, if sensed, could assist the vehicle&#39;s crash mitigation system to determine what active restraints should be deployed. Information regarding the location, width and severity of an impact can also be used to control the speed of actuation or selection of particular active restraints that would be most appropriate for the protection of vehicle occupants or pedestrians.  
           [0007]    There is a need for a simple, inexpensive device for sensing the severity, location, and width of an impact. This information may be integrated with other sensor outputs by a control system to provide an intelligent crash mitigation system.  
         SUMMARY OF INVENTION  
         [0008]    According to the present invention, a collision protection system is provided that controls a collision protection apparatus such as an inflatable member or the like. A sensor located on an exterior surface of a vehicle is adapted to provide a width output signal that varies in relation to the width of an object contacting the vehicle. A controller is provided for the collision protection apparatus that receives the width output signal from the sensor and compares the width output signal to a threshold value to determine if the width of the object is less than a predetermined width. The controller actuates the pedestrian collision protection apparatus if the object is less than the predetermined width and exerts a force on the sensor between a lower and an upper threshold.  
           [0009]    The system described above may include a collision protection apparatus such as an external inflatable member that is deployed between the object, such as a pedestrian, and the vehicle. The collision protection apparatus may also comprise a hood release that shifts the hood of the vehicle to a raised position that permits the hood to absorb forces applied thereto by the object or pedestrian. The collision protection apparatus may also be an interior active safety restraint system that is actuated either with other restraint systems or independently thereof to protect an occupant of the vehicle from injury caused by a pedestrian who is struck by the vehicle.  
           [0010]    According to another aspect of the invention, the sensor may be an elongated strip that extends in a generally horizontal direction across an exterior panel of the vehicle such as the bumper or fender. The strip has electrical contacts that are at least partially compressed in the event of an impact. The width output signal of the sensor is related to the portion of the strip that is compressed. The strip may be a tubular member having at least two spaced electrodes that are normally held apart by the tube. The two spaced electrodes are pressed together along a portion of their length in the event of an impact. The two spaced electrodes provide an electrical signal that indicates the portion of the length of the tube that is compressed. The two spaced electrodes may comprise a carbon ink strip and a copper electrode that are held apart by dielectric dots.  
           [0011]    The system may also include an interior sensor secured to a vehicle or location recessed from the surface of the vehicle. The interior sensor may generate an impact force signal in the event of an impact of sufficient force to actuate the interior sensor. The controller may receive the impact force signal from the interior sensor and may disable the collision protection apparatus if it determines that the object struck is not a pedestrian. The interior sensor may be disposed in a cavity formed in a structural foam bumper member.  
           [0012]    According to another aspect of the invention, an apparatus for determining if a pedestrian is struck by a vehicle is provided. The apparatus comprises an elongated sensor extending across an exterior region of the vehicle. The sensor has at least two spaced electrodes that are supported on a compressible member. The compressible member is locally compressible along a portion of the region of the vehicle across which the sensor extends. The two spaced electrodes provide an electrical signal that varies in proportion to the portion of the compressible member that is compressed. A controller receives the electrical signal and calculates the length of the portion of the compressible member that is compressed. An impact absorbing member is deployed if the length of the portion of the compressible member compressed is less than a threshold length corresponding to the approximate, predetermined width of a pedestrian at the height of the sensor on the vehicle. The system then determines whether the object struck by the vehicle is a pedestrian.  
           [0013]    According to other aspects of the invention, the electrical signal provided by the sensor may also vary in response to the location of the portion of the compressible member that is compressed. If so, the controller may determine the location of-the portion of the compressible member that was compressed. The impact absorbing member may be an external inflatable member, a hood raising mechanism, or the like.  
           [0014]    According to another aspect of the invention, a sensing system is provided for determining the width of an object in the event of an impact force being applied thereto. The sensing system includes a strip having first and second portions that are spaced apart that connect to a conductive electrode attached to the first portion, and a resistive electrode that is attached to the second portion. A voltage source is connected to the resistive electrode to provide a constant current through the resistive electrode. Upon impact, the conductive electrode contacts the resistive electrode and shorts out the portion of the resistive electrode that is contacted by the conductive electrode. This decreases the resistance of the resistive electrode which decreases the voltage developed.  
           [0015]    The sensing system may also comprise a resistive electrode formed as a first part that increases in resistivity from right to left and a second part that increases in resistivity from left to right. The first and second parts are positioned adjacent to one another so that the conductive electrode contacts both parts during an impact thereby shorting the first and second parts of the resistive electrode. By comparing the voltages developed in each part, the width and location of the impact may be determined.  
           [0016]    According to another aspect of the invention, the resistive electrode may be formed as a plurality of discrete conductive lines that are located in a generally linear array. Each line is connected to one of a series of resistors so that when the conductive electrode contacts one or more of the conductive lines upon impact, the conductive electrode circumvents the resistors corresponding to the conductive lines. This circumvention reduces the resistance of the resistive electrode and decreases the voltage developed.  
           [0017]    These and other aspects of the invention will be better understood in view of the attached drawings and the following detailed description of the several embodiments of the invention disclosed. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0018]    [0018]FIG. 1 is a fragmentary side elevation view of a vehicle having a bumper including a sensor made in accordance with the present invention;  
         [0019]    [0019]FIG. 2 is a cross-sectional view of one embodiment of a sensor made in accordance with the present invention in its non-compressed state;  
         [0020]    [0020]FIG. 3 is a cross-sectional view similar to FIG. 2 showing the sensor in its compressed state;  
         [0021]    [0021]FIG. 4 is a perspective view of a portion of a section of a sensor strip made in accordance with the present invention;  
         [0022]    [0022]FIG. 5 is a schematic diagram of a circuit for a sensor for detecting the width and center of an impact;  
         [0023]    [0023]FIG. 6 is a side elevation view of a bumper having a surface sensor and recessed sensor that is only contacted when the impact force exceeds a certain level;  
         [0024]    [0024]FIG. 7 is a cross-sectional view of a floating electrode sensor strip showing two conductive strips and two resistive strips in its uncompressed state;  
         [0025]    [0025]FIG. 8 is a cross-sectional view of a floating electrode sensor strip showing two conductive strips and two resistive strips in their compressed state;  
         [0026]    [0026]FIG. 9 is a perspective view of a double sensor;  
         [0027]    [0027]FIG. 10 is an electrical schematic of the floating electrode sensor made in accordance with the present invention;  
         [0028]    [0028]FIG. 11 is an electrical schematic showing an alternative embodiment of the present invention having a discrete resistor circuit having a terminated electrode;  
         [0029]    [0029]FIG. 12 is an electrical schematic showing a floating electrode discrete resistor circuit; and  
         [0030]    [0030]FIG. 13 is a logic diagram for determining if a struck object is a pedestrian according to a two variable model. 
     
    
     DETAILED DESCRIPTION  
       [0031]    Referring now to FIG. 1, a portion of a vehicle  20  is shown including a bumper  22  having a sensor  24  that senses the width of an object contacted by the sensor.  
         [0032]    Referring now to FIG. 2, the sensor  24  is shown in greater detail including a hollow tube  28  having an inner wall  30  and an outer wall  32 . A conductive electrode  36  preferably made of copper or other highly conductive material is connected to one of the walls  30 ,  32  and as illustrated is connected to the outer wall  32 . A resistive electrode  38  is attached to one of the walls  30 ,  32  and as illustrated is connected to the inner wall  30 . The resistive electrode  38  may be a carbon electrode in the illustrated embodiment. A resistive electrode  38  is defined as an electrode having a relatively higher resistance than the conductive electrode  36 . An air gap  40  is formed between the conductive electrode  36  and the resistive electrode  38  when the sensor  24  is in its normal, non-compressed state as shown in FIG. 2.  
         [0033]    As shown in FIG. 3, the conductive electrode  36  and resistive electrode  38  are placed in contact with each other as the outer wall  32  is compressed towards the inner wall  30 .  
         [0034]    Referring now to FIG. 4, a schematic representation of the sensor  24  is shown wherein a first substrate  42  and a second substrate  44  are shown in parallel spaced relationship to each other. The substrate may be formed of a wide variety of material, for example, polyester sheet. A copper electrode  46  is provided on the first substrate  42  and carbon ink  48  is deposited on the second substrate  44 . A plurality of dielectric dots  50  are provided in the air gap  40  that hold the copper electrode  46  and carbon ink  48  apart unless a force is applied to one of the substrates to compress them together. An adhesive gasket  52  is provided on the perimeter portions of the substrates  42 ,  44 . The two substrates  42 ,  44  are sealed together at their periphery by the adhesive gasket  52  so that the two electrodes  46  and  48  face each other and are separated by the dielectric dots  50 . When the sensor  24  is backed by a rigid material such as the structural foam forming a portion of a bumper or a fender or door of a car, and sufficient force is applied to the external surface thereof, the outer substrate  42 ,  44  bends and allows the electrodes  46 ,  48  to make contact between the dielectric dots  50 . A similar technique is used in vehicles in the manufacture of horn switches in steering wheels for vehicles. In contrast to horn switches, however, the sensor  24  provides location and width information as is more particularly described below.  
         [0035]    Referring now to FIG. 5, one method of measuring resistances is illustrated. In FIG. 5, a circuit  60  is provided that includes a current source  62 . Voltages V 1  and V 2  are measured to calculate the width and center of the impact.  
         [0036]    The arrangement shown in FIG. 5 may be referred to as a terminated electrode embodiment wherein electrical connections are made to both ends of the resistive electrode  38  and to some point on the conductive strip  36 . All three connections to the conductive electrode  36  and resistive electrode  38  may be made with a single connector at one end of the sensor  24 . When the sensor strip  24  is struck-in a collision, it collapses in the impact zone represented by the portion of the conductive electrode  36  that is placed in contact with resistive electrode  38  and is identified as the impact contact area  68 . If the resistance of the strip before impact is R 0 , and during the impact resistances of those portions of the strip to the left and right of the impact are R L  and R R , respectively, the width and center of impact, normalized to the length of the strip, are given in terms of these quantities by:  
             W   =     1   -         R   L     +     R   R         R   0                             C   =       1   2          (     1   +         R   L     -     R   R         R   0         )                                   
 
         [0037]    If a constant current is sent through the resistive strip as shown in FIG. 5, the two voltages V 1  and V 2  are measured. The width and center are given in terms of these quantities and V 0 , the value of V 1  prior to the impact by:  
                   W   =     1   -       V   1       V   0                             C   =       1   2     +         V   2     -       1   2          V   1           V   0                       (   1   )                               
 
         [0038]    Referring to FIG. 9, the sensor can be used to detect front bumper impacts with a pedestrian based upon the low pressure that a pedestrian&#39;s leg is able to produce against the bumper and the distinctive small impact width. This may be accomplished by providing two separate strips as shown in FIG. 6 or by adding another pair (or double pair) of electrodes in a three layer sandwich as shown in FIG. 9. Two separate strips could be used as shown in FIG. 6 with one sensor  74  near the front of the bumper  72  and the other sensor  76  located in a cavity within the structural foam of the bumper. Alternatively, the second sensor could be mounted behind another structural member so that it is protected from the impact unless the foam or other member is deformed. Regarding the embodiment of FIG. 9, the spacing and/or thickness of the dielectric dots may be adjusted so that the outer pair of electrodes is brought into contact with a relative low force that would be produced when a pedestrian is struck. The inner pair of electrodes requires a much larger force, such as would be generated in striking another car, or tree, etc. Either the,terminated electrode embodiment or the floating electrode embodiment can be used to detect the force of a collision by using two sensors, as in FIG. 6, or a three layer sandwich, as in FIG. 9.  
         [0039]    The embodiment shown in FIG. 6 can also be used to determine the speed of impact for an impact that activates both sensors  74  and  76 . Knowledge of impact speed may be useful, for example, in determining the force with which to fire an airbag. The exterior sensor  74  closes immediately upon striking an object. The interior sensor  76  does not close, however, until the cavity in which it is located has been collapsed by the intruding foam or structural member in front of it. If the cavity had an original depth d and the second sensor  75  closes a time δt after the first sensor  74 , then the speed of impact is d/δt. (The timing will be affected if the foam in front of the cavity does not move as a rigid body but is compressed during the collision; however, this effect can be calibrated based upon the relative rigidity of the foam.)  
         [0040]    Referring to FIG. 9, the alternative embodiment of the sensor  94  is described more specifically, The sensor includes a first substrate  96 , a second substrate  98 , a third substrate  100 , and a fourth substrate  102 . The substrates are preferably formed of a flexible material such as polyester or can also be formed as an extruded polymeric material. A first copper electrode  104  and second copper electrode  106  are shown secured to the first and third substrates  96 ,  100 . A first strip of carbon ink  108  and a second strip of carbon ink  110  are provided on the second and fourth substrates  98 ,  102 . A first set of dielectric dots  112  is provided between the first copper electrode  104  and the first strip of carbon ink  106  while a second set of dielectric dots  114  are provided between the second copper electrode  106  and the second strip of carbon ink  110 . The second set of dielectric dots  114  is more closely spaced than the first set of dielectric dots  112 . The portion of the sensor having a higher dot density is preferably disposed closer to the bumper.  
         [0041]    Referring now to FIGS. 7 and 8, an alternative embodiment of a floating electrode sensor system is shown. Like the embodiments of FIGS. 2 and 3, the sensor includes a hollow tube  78  having an inner wall  80  and an outer wall  82 . First and second conductive electrodes  84  and  86  are shown on the outer wall  82 . However, it should be understood that the conductive electrodes can also be placed on the inner wall  82 . First and second resistive electrodes  88  and  90  are shown disposed on the inner wall  80 . An air gap  92 , as illustrated in FIG. 7, represents the sensor in its uncompressed stage while the air gap  92  is substantially diminished or eliminated in FIG. 8 which shows the sensor as compressed after impact.  
         [0042]    Referring now to FIG. 10, a floating electrode circuit embodiment  116  of the electrical circuit is illustrated that may be used with the embodiment shown in FIGS. 7 and 8. In the floating electrode embodiment, each electrode is split into two parts. No electrical connections are required to the conductive electrode which remains electrically “floating.” The resistivity (ohm per meter) of the resistive electrodes varies along their length as described below.  
         [0043]    The floating electrode circuit  116  includes a current source  118  that is connected to a resistive electrode  88  and a second resistive electrode  90 . The resistive electrodes  88  and  90  are also connected to a common electrical lead  91 . A first voltage V 1  may be measured across resistive electrode  88  and lead  91  while a second voltage V 2  is measured across resistive electrode  90  and lead  91 . An impact area  120  is shown across a portion of resistive electrode  88  and  90 . In the impact area, the resistive electrodes  88  and  90  are shorted out by conductive electrodes  84  and  86 , respectively, thereby reducing the resistance of the circuit including the resistive electrodes  88  and  90 .  
         [0044]    The resistivity r of each resistive electrode  88  and  90  increases linearly from one end of the strip to the other. That is, r is a function of the distance x along the strip as given by the following formula:  
           r ( x )= r   c   +r   v   x    (2)  
         [0045]    where r c  and r v  are design constants. The total resistance of the strip of length L is:  
               R   0     =         ∫   0   L            r        (   x   )               x         =           r   c        L     +       1   2          r   v          L   2         ≡       R   c     +     R   v                   (   3   )                               
 
         [0046]    The electrodes are oriented in opposite directions so that as one electrode increases in resistivity from left to right, the other increases in resistivity from right to left. The electrodes are electrically connected as shown in FIG. 10. As described above with reference to FIG. 5, an impact collapses the portion of the strip causing each conductive electrode to short out a portion of the corresponding resistive electrode behind it. In this case, the normalized width and center of impact are given by:  
                   W   =     1   -         R   1     +     R   2         2        R   0                               C   =       1   2          (     1   +         R   2     -     R   1         2                 α                   R   0        W         )                     (   4   )                               
 
         [0047]    where R 1  and R 2  are measured resistances of the first and second resistive electrodes under impact conditions, and α/R v /R 0  is a design constant. A preferred method of measuring resistance is to send a constant current through the resistive electrodes and measure the voltages developed. In terms of voltages, W and C are:  
                   W   =     1   -         V   1     +     V   2         2        V   0                               C   =       1   2          (     1   +         V   2     -     V   1         2                 α                   V   0        W         )                     (   5   )                               
 
         [0048]    The error associated with measuring the partially-shorted resistances during impact may be shown as resultant errors as follows:  
                     Error                   (   W   )       =       -     1   2          Error                   (   R   )                     Error                   (   C   )       =         1   +     α        (       2      C     -   1     )           2                 α                 W          Error                   (   R   )                                                α   →   1                         C   W        Error                   (   R   )                     (   6   )                               
 
         [0049]    By selecting parameters R c  and R v , the effect of the error in the calculated quantities can be minimized. Error (W or C) is the error in estimating W or C for a given Error(R) in measuring R 1  or R 2 , where Error (R) is expressed as a fraction of R 0  the resistance in the absence of impact. To minimize Error (C) in estimating the location of impact, o( should be close to 1 and thus the ratio of resistivity at the two ends of the strip, (r c +r v L)/r c  should be substantially larger than 1. Location error also depends inversely on impact width W. For this reason, it is desirable to make the device stiff enough along its length so that a narrow object collapses the tube over some minimum length (for example 5% of the strip).  
         [0050]    [0050]FIG. 11 is a schematic drawing of a terminated electrode circuit  26  that includes a plurality of discrete resistors  28  that are connected to a plurality of corresponding switch contacts  130 . Upon impact, one or more of the switch contacts  130  are closed which short circuits or circumvents the resistors  128  to which the switch contacts  130  are connected.  
         [0051]    The array of switch contacts  130  can be formed in a number of ways. The contacts could, for example, be a plurality of conductive electrode pairs spaced apart by dielectric dots similar to the configuration shown in FIG. 4, wherein one or more of the pairs being closed by an impact. Alternatively, a plurality of switches  130  could be closed by an associated non-contact sensor operating on the basis of capacitive, ultrasonic, or other principles. An impending collision could be detected by each non-contact sensor within its own immediate field of detection. Actuation of the switches  130  by non-contact sensors could allow the width and location of the colliding object to be estimated before collision occurs.  
         [0052]    Referring now to FIG. 12, a floating electrode circuit  132  is illustrated that includes a first set of resistors  134  and a second set of resistors  136  that are connected, respectively, to a first set of switch contacts  138  and a second set of switch contacts  140 . In the event of an impact of sufficient severity to close at-least some of the first and second set of switch contacts  138 ,  140 ,an indication of the width of the object contacted is provided. The resistors  134 ,  136  that are circumvented reduce the resistance of the circuit. As in the configuration of FIG. 11, the switches  138  and  140  could be actuated by non-contact sensors to estimate the width and location of a colliding object before the collision occurs.  
         [0053]    Referring now to FIG. 13, a logic diagram for determining if the struck object is a pedestrian is shown. The logic diagram is generally indicated by reference numeral  142 . At  144 , the system determines whether both of the sensor strips have collapsed. If so, it is determined that the object struck is not a pedestrian at  146 . If both strips are not collapsed, then the system determines whether the impact is greater than a predetermined width that is set as a threshold at  148 . If it is greater than the predetermined width, the system determines that the object struck is not a pedestrian at  146 . If the impact width is less than the threshold, it is determined that the object struck is a pedestrian and a collision protection system is activated.  
         [0054]    While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.