Abstract:
An apparatus ( 10 ) comprises seat belt webbing ( 24 ). An elongated member ( 30 ) is connected with the seat belt webbing ( 24 ). Tension in the seat belt webbing ( 24 ) is transmitted to the elongated member ( 30 ). An arm ( 106 ) is associated with the elongated member ( 30 ). The arm ( 106 ) receives a force from the elongated member ( 30 ) when tension in the seat belt webbing ( 24 ) increases. The force acts on the arm ( 106 ) through a moment arm creating a torsion force on the arm ( 106 ). At least a portion of the arm ( 106 ) moves in response to the torsion force. A device ( 102 ) is responsive to movement of the at least a portion of the arm ( 106 ) due to the torsion force to provide an output signal indicative of the tension in the seat belt webbing ( 24 ).

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to an apparatus for measuring tension in seat belt webbing of a seat belt assembly associated with a vehicle seat.  
         BACKGROUND OF THE INVENTION  
         [0002]    A system for determining the weight of an occupant on a vehicle seat is known. The system outputs a signal indicative of the weight of the occupant to a controller. The controller controls actuation of a vehicle safety device, such as an air bag or pretensioner. The controller, upon the occurrence of a crash condition, considers the weight of the occupant when determining whether the vehicle safety device is should be actuated. The vehicle safety device is actuated when the weight on the seat is determined to be greater than a threshold level.  
           [0003]    When a child safety seat is located on the seat, it may be desirable to prevent actuation of the vehicle safety device. Typically, seat belt webbing associated with the seat holds a properly installed child safety seat is firmly on the seat. The tension of the seat belt webbing holding the child safety seat on the seat may result in the weight sensed by the vehicle occupant weight sensor being above the threshold level. When the tension in the seat belt webbing is known, the controller of the system may determine a “true” weight on the seat by subtracting the load on the seat caused by the tension in the seat belt webbing from the weight sensor measurement.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention relates to an apparatus comprising seat belt webbing. The apparatus also comprises an elongated member connected with the seat belt webbing. Tension in the seat belt webbing is transmitted to the elongated member. An arm is associated with the elongated member. The arm receives a force from the elongated member when tension in the seat belt webbing increases. The force acts on the arm through a moment arm creating a torsion force on the arm. At least a portion of the arm moves in response to the torsion force. The apparatus still further includes a device responsive to movement of the at least a portion of the arm due to the torsion force to provide an output signal indicative of the tension in the seat belt webbing.  
           [0005]    In another aspect, the present invention relates to an apparatus comprising seat belt webbing. An elongated member is connected with the seat belt webbing. Tension in the seat belt webbing is transmitted to the elongated member. The apparatus also includes a sensor comprising an arm and a device. The arm is associated with the elongated member. The elongated member moves at least a portion of the arm in response to a change in tension in the seat belt webbing. The device is responsive to movement of the at least a portion of the arm to provide an output signal indicative of the tension in the seat belt webbing. The apparatus still further includes structure for reducing a variable moment acting on the arm as a result of off-axis loading of the seat belt webbing.  
           [0006]    In yet another aspect, the present invention relates to an apparatus comprising seat belt webbing. An elongated member is connected with the seat belt webbing. Tension in the seat belt webbing is transmitted to the elongated member. An arm is associated with the elongated member. The elongated member moves at least a portion of the arm in a first direction in response to an increase in tension in the seat belt webbing. An overtravel stop extends through a portion of the arm. The overtravel stop contacts the arm after movement of the arm in the first direction by a predetermined amount. The overtravel stop prevents continued movement of the arm in the first direction and carries loads associated with further increases in tension in the seat belt webbing. The apparatus also includes a device responsive to movement of the at least a portion of the arm to provide an output signal indicative of the tension in the seat belt webbing.  
           [0007]    In a further aspect, the present invention relates to an apparatus comprising seat belt webbing. An elongated member is connected with the seat belt webbing. Tension in the seat belt webbing is transmitted to the elongated member. An arm is associated with the elongated member and receives a load from the elongated member. The elongated member moves at least a portion of the arm in a first direction in response to an increase in tension in the seat belt webbing. The apparatus also comprises a biasing element for biasing the arm in a second direction opposite the first direction and a sensor responsive to movement of the at least a portion of the arm to provide an output signal indicative of the tension in the seat belt webbing. The biasing element and the sensor are located out of a path of the load applied by the elongated member to the arm.  
           [0008]    In another aspect, the present invention relates to an apparatus comprising seat belt webbing. The apparatus also includes a seat belt webbing pretensioner comprising an elongated member connected with the seat belt webbing. Tension in the seat belt webbing is transmitted to the elongated member. The pretensioner also comprises an actuatable source of energy for, when actuated, moving the elongated member to tension the seat belt webbing. The apparatus still further includes a sensor for sensing tension in the seat belt webbing. The sensor comprises an arm that is supported by the pretensioner and is associated with the elongated member. The elongated member moves at least a portion of the arm relative to the pretensioner in response to a change in tension in the seat belt webbing. The sensor further comprises a device that is responsive to relative movement between the at least a portion of the arm and the pretensioner to provide an output signal indicative of tension in the seat belt webbing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is a schematic view of an apparatus, constructed in accordance with the present invention, and mounted adjacent a vehicle seat;  
         [0011]    [0011]FIG. 2 is a perspective view of the apparatus of FIG. 1;  
         [0012]    [0012]FIG. 3 is an elevation view of the apparatus of FIG. 2 illustrating a cable holder of the apparatus in an initial position;  
         [0013]    [0013]FIG. 4 is an elevation view of the apparatus of FIG. 2 illustrating a cable holder pivoted away from an initial position;  
         [0014]    [0014]FIG. 5 is an elevation view of a second embodiment of the apparatus of the present invention;  
         [0015]    [0015]FIG. 6 is an elevation view of a third embodiment of the apparatus of the present invention;  
         [0016]    [0016]FIG. 7 is an elevation view of a fourth embodiment of the apparatus of the present invention illustrating a cable holder in an initial position; and  
         [0017]    [0017]FIG. 8 is an elevation view of the embodiment of FIG. 7 illustrating a cable holder in a position away from the initial position;  
         [0018]    [0018]FIG. 9 is an elevation view of a fifth embodiment of the apparatus of the present invention illustrating a cable holder in an initial position;  
         [0019]    [0019]FIG. 10 is an elevation view of the embodiment of FIG. 9 illustrating the cable holder in a position away from the initial position;  
         [0020]    [0020]FIG. 11 is a perspective view of a sixth embodiment of the apparatus of the present invention;  
         [0021]    [0021]FIG. 12 is a cutaway view of the embodiment of FIG. 11;  
         [0022]    [0022]FIG. 13 is an exploded view of the embodiment of FIG. 11;  
         [0023]    [0023]FIG. 14 is an elevation view of the embodiment of FIG. 11 illustrating an arm in an initial position;  
         [0024]    [0024]FIG. 15 is a cross-sectional view of the apparatus of FIG. 11 illustrating an arm in an initial position and further illustrating a cover and a mounting bolt;  
         [0025]    [0025]FIG. 16 is an elevation view of the embodiment of FIG. 11 illustrating the arm in a position away from the initial position; and  
         [0026]    [0026]FIG. 17 is a cross-sectional view of the apparatus of FIG. 11 illustrating the arm in a position away from the initial position and further illustrating a cover and a mounting bolt. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    [0027]FIG. 1 illustrates an apparatus  10 , constructed in accordance with the present invention, mounted adjacent a vehicle seat  12  in the passenger compartment  14  of a vehicle  16 . Although the seat  12  illustrated is a front passenger seat, the apparatus  10  may be associated with any of the vehicle seats. The seat  12  includes a cushion portion  18  and a back portion  20 .  
         [0028]    A seat belt assembly  22  is associated with the seat  12  for helping to restrain an occupant of a vehicle  16  in the vehicle seat  12 . The seat belt assembly  22  illustrated in FIG. 1 is a three-point continuous loop seat belt assembly. The seat belt assembly  22  includes a length of seat belt webbing  24  that is extensible about a seated occupant. A tongue  26  is attached to the seat belt webbing  24 . The position of the tongue  26  on the seat belt webbing  24  is adjustable.  
         [0029]    A buckle assembly  28  for receiving the tongue  26  is shown on the left side, as viewed in FIG. 1, of the seat  12 . An anchor line or cable  30  extends from the buckle assembly  28  to a pretensioner  32 . The anchor cable  30  is preferably a wire rope cable. As an alternative to the anchor cable  30 , seat belt webbing, a metal strap, or any other elongated and relatively flexible member may be used. As is shown schematically in FIG. 1 at  34 , the pretensioner  32  is electrically connected to a controller  36 . Upon receipt of an actuation signal from the controller  36 , the pretensioner  32  is actuatable to tension the seat belt webbing  24 . When actuated, the pretensioner  32  pulls the anchor cable  30 , causing the buckle assembly  28  to move downwardly toward a floor  38  of the vehicle  16 . When the tongue  26  is fastened in the buckle assembly  28 , the downward motion of the buckle assembly  28  creates tension in the seat belt webbing  24 .  
         [0030]    The pretensioner  32  may be any known type of pretensioner  32 . Preferably, the pretensioner  32  includes a first cylinder  40 , as is shown in FIG. 2. The first cylinder  40  extends along axis A and includes a first end  42  and a second end  44 . A piston  46  (FIGS. 3 and 4) is centrally located within the first cylinder  40 . A first end  48  of the anchor cable  30  is attached to the piston  46 . The first end  42  of the first cylinder  40  includes an opening  50  through which the anchor cable  30  passes.  
         [0031]    A second cylinder  52  intersects the first cylinder  40  near the first end  42  of the first cylinder. The second cylinder  52  also includes a first end  54  and a second end  56 . The second end  56  of the second cylinder  52  includes external threads (not shown) for receiving a cap  58  having internal threads (not shown). A pyrotechnic charge (not shown) is located in the first end  54  of the second cylinder  52  and is positioned relative to the piston  46  such that when actuated, the pyrotechnic charge forces the piston toward the second end  44  of the first cylinder  40 . A squib (not shown) is located in the second end  56  of the second cylinder  52  for igniting the pyrotechnic charge. A lead wire, shown schematically in FIG. 1 at  34 , extends through the cap  53  on the second end  56  of the second cylinder  52  for connecting the squib to the controller  36 .  
         [0032]    The pretensioner  32  also includes a support member  60 . The support member  60  extends axially outwardly from the first end  42  of the first cylinder  40 . As shown in FIG. 2, the support member  60  includes a base wall  62  and first and second side walls  64  and  66  that extend perpendicularly upwardly from the base wall  62 . The first side wall  64  includes a circular opening  68 . A channel  70  having a width that is less than the diameter of the opening  68  extends from an upper surface  72  of the first side wall  64  into the first side wall  64  and intersects the opening  68 .  
         [0033]    The second side wall  66  (FIG. 2) of the support member  60  is provided by a guide wall  74  that is substantially larger than the first side wall  64 . As best seen in FIG. 3, the guide wall  74  has a generally flat main body portion  84  that becomes wider or taller as it extends axially away from the first cylinder  40 . The main body portion  84  of the guide wall  74  extends along axis A between a narrow end edge (not shown), which connects the guide wall  74  to the first end  42  of the first cylinder  40 , and a wide end edge  82 . The axial length of the guide wall  74  is approximately equal to the axial length of the first cylinder  40 . The guide wall  74  also includes a narrow end  76  adjacent the narrow end edge and a wide end  77  adjacent the wide end edge  82  of the guide wall  74 . A first side surface  86  of the guide wall  74  is located nearest the first side wall  64  of the support member  60 . A second side surface (not shown) of the guide wall  74  is located opposite the first side surface  86 .  
         [0034]    A circular opening  79  (FIG. 2) extends through the narrow end  76  of the guide wall  74 . The opening  79  in the narrow end  76  of the guide wall  74  aligns with the opening  68  on the first side wall  64  of the support member  60 . A channel  78  having a width that is less than the diameter of the opening  79  extends from an upper edge  80  of the second side wall  66  into the narrow end  76  of the guide wall  74  and intersects the opening  79  in the guide wall  74 .  
         [0035]    An extension  88  extends downwardly from the wide end  77  of the guide wall  74  in the plane of the guide wall  74 . The extension  88  includes a first side surface  90  and an opposite second side surface (not shown). A first protrusion  92 , located on a lower end  94  of the first extension  88 , extends outwardly from the first side surface  90  in a direction generally parallel to the base wall  62  of the support member  60 .  
         [0036]    A second protrusion  96  extends outwardly from the first side surface  86  of the main body portion  84  of the guide wall  74  near a lower edge  98  of the guide wall  74 . A slot  100  extends through the second protrusion  96 . The slot  100  extends in a direction perpendicular to axis A and provides a means for attaching a sensor  102  to the second protrusion  96 .  
         [0037]    A cylindrical protrusion  104  also extends outwardly of the first side surface  86  of the guide wall  74  from a central portion of the guide wall  74 . The cylindrical protrusion  104  extends outwardly approximately one-half the distance between the first side wall  64  and the second side wall  66  of the support member  60 . As will be discussed in greater detail below, the cylindrical protrusion  104  acts as an overtravel stop for limiting movement of a movable arm or cable holder  106  beyond a predetermined amount.  
         [0038]    The movable arm or cable holder  106  includes a main body portion  120  that widens from a narrow end  122  to a wide end  124 . The main body portion  120  of the cable holder  106  has an axial length, defined as a distance along axis A between a narrow end edge  123  and a wide end edge  140 , that is less than the axial length of the guide wall  74 . The main body portion  120  of the cable holder  106  includes a first side surface  126  and a second side surface (not shown), opposite the first side surface.  
         [0039]    The cable holder  106  also includes a pivot member  108  for pivotally attaching the cable holder  106  to the support member  60  of the pretensioner  32 . The pivot member  108  includes a top wall  110 , a first side wall  112 , and a second side wall  114  (FIG. 2). A short shaft of a pivot  116  extends outwardly of the first side wall  112  in a direction opposite to the second side wall  114  of the pivot member  108 . The top wall  110  of the pivot member  108  connects the first side wall  112  to the second side wall  114 . An arched channel  118  is formed between the first and second side walls  112  and  114  and below the top wall  110 . The arched channel  118  provides access for the anchor cable  30  through the pivot member  108  and into the first cylinder  40  of the pretensioner  32 .  
         [0040]    The narrow end  122  of a main body portion  120  of the cable holder  106  forms the second side wall  114  of the pivot member  108 . A short shaft (not shown) of the pivot  116  extends outwardly of the second side wall  114  of the pivot member  108  in a direction opposite to the first side wall  112 .  
         [0041]    An outer lip  128  extends outwardly from the first side surface  126  of the main body portion  120  of the cable holder  106 . A first end  130  of the outer lip  128  is located adjacent a lower edge  132  of the main body portion  120  of the cable holder  106  approximately one-half the distance between the wide end  124  and the narrow end  122  of the cable holder. The outer lip  128  curves from the first end  130  along an edge of the wide end  124  of the cable holder  106  and terminates at a second end  134 . The second end  134  is located at the intersection of an upper edge  136  of the main body portion  120  and the wide end  124 .  
         [0042]    The outer lip  128  includes an inner surface  138  and an outer surface  140 . A protrusion  142  extends outwardly from the outer surface  140  of the outer lip  128  in a direction parallel to axis A. The protrusion  142  is centered vertically between the upper edge  136  and the lower edge  132  of the main body portion  120 .  
         [0043]    A guide  144  extends outwardly from the first side surface  126  of the main body portion  120  of the cable holder  106 . The guide  144  includes a cylindrical inner surface  146  and a curved outer surface  148 . The cylindrical inner surface  146  of the guide  144  defines an opening  150  (FIGS. 3 and 4) that extends completely through the main body portion  120  of the cable holder  106 . The opening  150  has a diameter that is larger than the diameter of the cylindrical protrusion  104  from the guide wall  74  of the pretensioner  32 . A portion of the curved outer surface  148  of the guide  144  extends parallel to the outer lip  128  on the wide end  124  of the cable holder  106 .  
         [0044]    A channel  152  is formed in the cable holder  106  between the inner surface  138  of the outer lip  128  and the outer surface  148  of the guide  144 . The channel  152  receives the anchor cable  30 , which is supported and guided through the cable holder  106  to the pretensioner  32  by surfaces  138  and  148 .  
         [0045]    To attach the cable holder  106  to the pretensioner  32 , the cable holder  106  is aligned with the guide wall  74  of the pretensioner  32  such that the first end  130  of the outer lip  128  of the cable holder  106  is adjacent the second protrusion  96  of the guide wall  74 . The second end  134  of the outer lip  128  of the cable holder  106  extends in a direction opposite the first extension  88  of the guide wall  74 . The cylindrical protrusion  104  of the guide wall  74  is inserted into the opening  150  in the cable holder  106 . The pivot member  108  of the cable holder  106  is then moved toward the support member  60  of the pretensioner  32 . When the pivot  116  is aligned with the channels  70  and  78  leading to the openings  68  and  79  in the side walls  64  and  66  of the support member  60 , the pivot member  108  is moved toward the base wall  62  of the support member  60 . As a result, the pivot  116  passes through the channels  70  and  78  and into the openings  68  and  79  in the side walls  64  and  66  of the support member  60 . A bushing  154 , only one of which is shown, is then placed in each opening  68  and  79  for supporting the pivot  116  on side walls  64  and  66  and retaining the cable holder  106  on the support member  60 .  
         [0046]    When the pivot member  108  of the cable holder  106  is attached to the support member  60  of the pretensioner  32 , the anchor cable  30 , which is attached to the piston  46  within the first cylinder  40  of the pretensioner  32 , passes through the arched channel  118  formed in the pivot member  108 . The anchor cable  30  is then threaded through the channel  152  formed in the cable holder  106 . A second end  156  of the anchor cable  30 , opposite the end  48  secured to the piston  46 , is attached to the buckle assembly  28  in a known manner.  
         [0047]    A helical spring  158  is then attached between the pretensioner  32  and the cable holder  106 . A first end  160  of the spring  158  is attached to the protrusion  92  on the first extension  88  of the pretensioner guide wall  74 . A second end  162  of the spring  158  is attached to the protrusion  142  extending outwardly of the outer lip  128  of the cable holder  106 .  
         [0048]    The spring  158  applies a force on the protrusion  142  of the cable holder  106  that tends pull the cable holder toward the protrusion  92  on the first extension  88 . The force of the spring is indicated in FIGS. 3 and 4 at F s . The spring force F s  creates a moment, indicated at M s , that tends to rotate the cable holder  106  in a clockwise direction, as viewed in FIGS. 3 and 4, about pivot  116 . As a result, the spring  158  biases the cable holder  106  into an initial position. As shown in FIG. 3, when the cable holder  106  is in the initial position, the cylindrical protrusion  104  of the guide wall  74  contacts an upper portion of the cylindrical inner surface  146  of the guide  144  of the cable holder  106  and prevents clockwise rotation of the cable holder about pivot  116 .  
         [0049]    When the tongue  26  of the seat belt webbing  24  is fastened in the buckle assembly  28 , tension in the seat belt webbing  24  pulls the buckle assembly  28  in the direction indicated by arrow T w  in FIGS. 3 and 4. As a result, a force in the direction T w  pulls on the second end  156  of the anchor cable  30  and tensions the anchor cable. Tension in the anchor cable  30  results in the anchor cable pulling upwardly, in the direction T w , on the cable holder  106  with a force equivalent to the tension in the anchor cable. As a result, a moment, indicated at M w  in FIGS. 3 and 4, is created that tends to rotate the cable holder  106  in a counterclockwise direction as viewed in FIGS. 3 and 4. The moment M w  is approximately equal to the force applied on the cable holder  106  by the anchor cable  30  multiplied by a distance between pivot  116  and the portion of the anchor cable extending in the direction T w .  
         [0050]    As shown in FIG. 4, the cable holder  106  may be pivoted relative to the pretensioner  32  by a predetermined amount. Pivotal movement of the cable holder  106  relative to the pretensioner  32  is about the pivot  116 . The predetermined amount of pivotal movement of the cable holder  106  relative to the pretensioner  32  is an amount between the initial position and a stop position. As shown in FIG. 4, in the stop position, the cylindrical protrusion  104  of the guide wall  74  contacts a lower portion of the cylindrical inner surface  146  of the guide  144  of the cable holder  106  and further pivoting of the cable holder  106  about the pivot  116  in the counterclockwise direction is prevented.  
         [0051]    When moment M w  exceeds moment M s , the cable holder  106  pivots in the counterclockwise direction about pivot  116  and away from the initial position. As the cable holder  106  moves away from the initial position, the spring  158  is stretched and the spring force F s  is increased. As a result, moment M s  increases. The cable holder  106  pivots away from the initial position until moment M s  equals moment M w .  
         [0052]    At a threshold tension in the anchor cable  30 , the cable holder  106  will have pivoted away from the initial position by the predetermined amount. Further pivoting away from the initial position will be prevented by the cylindrical inner surface  146  of the guide  144  of the cable holder  106  contacting the cylindrical protrusion  104  of the guide wall  74 . Any tension in the anchor cable  30  above the threshold tension will not result in movement of the cable holder  106  relative to the pretensioner  32 .  
         [0053]    When the cable holder  106  is away from the initial position and the tension in the anchor cable  30  decreases below the threshold tension, the cable holder pivots in the clockwise direction toward the initial position until moment M s  equals moment M w . If moment M s  is greater than moment M w , the cable holder  106  will be returned to the initial position and further rotation in the clockwise direction will be prevented.  
         [0054]    A sensor  102  is mounted on the second protrusion  96  of the guide wall  74  for monitoring the movement of the cable holder  106  relative to the guide wall  74  of the pretensioner  32 . The position of the sensor  102  is adjustable in the slot  100 . Preferably, the sensor  102  is a magnetic position sensor, such as a Hall effect device. When a Hall effect device is used, a magnet  164  (FIGS. 3 and 4) is secured to the outer surface  140  of the outer lip  128  of the cable holder  106  in a position adjacent the sensor  102 . The magnetic flux sensed by the sensor  102  decreases as the cable holder  106  pivots away from the initial position. As shown schematically in FIG. 1 at  166 , the sensor  102  provides an output signal to the controller  36  that is indicative of the position of the cable holder  106  relative to the pretensioner  32 .  
         [0055]    In the event that the pretensioner  32  is actuated, ignition of the pyrotechnic charge forces the piston  46  toward the second end  44  of the first cylinder  40  of the pretensioner. The piston  46  moves a distance, parallel to axis A, as a result of the actuation. Since the first end  48  of the anchor cable  30  is attached to the piston  46 , the anchor cable also moves the same distance as the piston. The buckle assembly  28  is attached to the second end  156  of the anchor cable  30 . Movement of the anchor cable  30  effects movement of the buckle assembly  28  in a direction indicated at P in FIGS. 3 and 4. Since the anchor cable  30  has a constant length between its first and second ends  48  and  156 , the buckle assembly  28  moves in the direction P a distance equal to the distance that the piston  46  moves along axis A. When the buckle assembly  28  is moved in the direction P, tension in the seat belt webbing  24  is increased.  
         [0056]    The apparatus  10  of the present invention may be fixed either to the vehicle  16  or to the seat  12 . Preferably, as shown in FIG. 1, the pretensioner  32  is fixed to the floor  38  of the vehicle  16  and the anchor line  30  extends between the buckle assembly  28  and the pretensioner  32 . Alternatively, the pretensioner  32  may be fixed to the seat  12  or to another portion of the vehicle, such as a pillar. As an alternative to the anchor line  30  attaching to the buckle assembly  28 , the anchor line  30  may be attached to a D-ring (not shown), a retractor (not shown), or an end (not shown) of the seat belt webbing  24 .  
         [0057]    The controller  36  includes a look-up table that includes data correlating the output signal from the sensor  102  to tension in the seat belt webbing  24 . From the output signal of the sensor  102 , the controller  36  can determine tension in the seat belt webbing  24  ranging from the tension required to move the cable holder  106  away from the initial position to the threshold tension. Those skilled in the art will recognize that the threshold tension and the tension required to move the cable holder  106  away from the initial position are both functions of the spring constant of the spring  158  and may be adjusted by replacing the spring  158  with a spring having the desired properties.  
         [0058]    With reference again to FIG. 1, a weight sensor  168  is associated with the seat  12  for sensing the weight of an occupant of the seat  12 . The weight sensor  168  may be any known weight sensor. The weight sensor  168  illustrated in FIG. 1 is located in the cushion portion  18  of the seat  12 . As shown at  170  in FIG. 1, the weight sensor  168  is electrically connected to the controller  36 . The weight sensor  168  provides an electrical signal to the controller  36  indicating the load acting downwardly on the seat cushion  18 .  
         [0059]    The vehicle  16  also includes a crash sensor  172 . The crash sensor  172  is a known device that senses a vehicle condition indicating the occurrence of a crash. Such a condition may comprise, for example, vehicle deceleration. The crash sensor  172  is electrically connected to the controller, as shown at  174 . Upon the occurrence of a crash condition, the crash sensor  172  sends a signal to the controller  36 .  
         [0060]    The vehicle  16  also includes an air bag module  176 . The air bag module  176  is secured in the instrument panel  178  of the vehicle  16  and is actuatable for helping to protect the occupant of the vehicle  16 . The air bag module  176  includes a reaction can  180 , an inflator  182 , and an air bag  184 . The air bag module  176  may be of any known design.  
         [0061]    As shown at  186 , the air bag module  176  is electrically connected to the controller  36 . The air bag module  176  is actuatable by the controller  36 . When the controller  36  determines that actuation of the air bag module  176  is desirable, the controller  36  sends an actuation signal to a squib  188  in the inflator  182 . Upon receiving the actuation signal, the squib  188  ignites, causing gas from the inflator  182  to flow into the air bag  184 . The air bag  184 , upon receiving gas from the inflator  182 , expands through an opening in the instrument panel  178  and rearward into the passenger compartment  14  of the vehicle  16 . Solid lines in FIG. 1 show the air bag  184  in a deflated condition. Dashed lines in FIG. 1 show the air bag  184  in an inflated condition.  
         [0062]    When determining whether or not to actuate the air bag  184  and the pretensioner  32 , one factor considered by the controller  36  is the weight of the occupant. Since the controller  36  receives a signal indicative of the weight of the occupant from the weight sensor  168  and a signal indicative of the tension in the seat belt webbing  24  from sensor  102 , the controller  36  can determine the “true” weight of the occupant on the seat  12 . To determine the “true” weight of the occupant of the seat  12 , the controller  36  subtracts the load on the seat  12  resulting from tension in the seat belt webbing  24  from the weight measurement from the weight sensor  168 .  
         [0063]    A second embodiment of an apparatus  210  constructed in accordance with the present invention is shown in FIG. 5. Unlike the guide wall  74  and the pretensioner  32  of FIGS.  2 - 4 , which are formed as one piece, the guide wall  212  and the pretensioner  214  in FIG. 5 are separate parts that are attached together using fasteners  216 . The guide wall  212  includes a fastening portion  218  and a guiding portion  220 . The fastening portion  218  extends perpendicular to the longitudinal axis A of the pretensioner  214  and includes a central opening (not shown) through which the anchor cable  222  passes. Two fastener openings (not shown), one above and one below the central opening, extend through the fastening portion  218  for receiving fasteners  216  to attach the guide wall  212  to the pretensioner  214 .  
         [0064]    The guiding portion  220  of the guide wall  212  extends perpendicular to and outwardly from the fastening portion  218  in a direction parallel to the longitudinal axis of the pretensioner. The guiding portion  220  includes a first side surface  224  and a second side surface (not shown). The first side surface  224  of the guiding portion  220  is nearest the fastening portion  218  of the guide wall  212 . An opening (not shown) extends through the guiding portion  220  of the guide wall  212  near the fastening portion  218  for receiving a portion of a torsion bar  226 . The guiding portion  220  also includes a cylindrical protrusion  228  that is located outwardly along axis A and a short distance above, as viewed in FIG. 5, the opening. The cylindrical protrusion  228  extends outwardly of the first side surface  224  a distance of approximately one-half the width, into the plane of the paper as viewed in FIG. 5, of the fastening portion  218  of the guide wall  212 .  
         [0065]    The cable holder  230  shown in FIG. 5 includes a narrow end  232  and a wide end  234 . Unlike the cable holder  106  of FIGS.  2 - 4 , the cable holder  230  of FIG. 5 does not includes a guide  144  that extends outwardly of the main body portion of the cable holder. Instead, the cable holder  230  includes a bent portion  236 . The bent portion  236  has a semi-circular cross section that first bends rearward, into the plane of the paper as viewed in FIG. 5, and then curves to extend forwardly and terminates in the same plane as a first surface  231  of the cable holder  230 . The bent portion  236  extends along a lower edge  238  and a wide end edge  235  of the cable holder  230 . An inner surface of the bent portion  236  defines a channel  240  for receiving the anchor cable  222 .  
         [0066]    The cable holder  230  has a first opening  246  located near the narrow end  232  of the cable holder  230  for receiving a portion of the torsion bar  226 . The first opening  246  is located above a first end  242  of the channel  240 , as viewed in FIG. 5. A second opening  248  is located outwardly along axis A and a short distance above, as viewed in FIG. 5, the first opening  246 . The second opening  248  has a diameter that is larger than the diameter of the cylindrical protrusion  228  of the guide wall  212 .  
         [0067]    The torsion bar  226  connects the cable holder  230  to the guide wall  212 . A first end (not shown) of the torsion bar  226  is received in the opening of the guide wall  212  and a second end  250  of the torsion bar  226  is received in the first opening  246  of the cable holder  230 . The torsion bar  226  allows the cable holder  230  to pivot relative to the pretensioner  214  and the guide wall  212 .  
         [0068]    When the apparatus  210  is assembled, the second opening  248  in the cable holder  230  receives the cylindrical protrusion  228  of the guiding portion  220  of the guide wall  212 . As described in detail with regard to the apparatus  10  illustrated in FIGS.  2 - 4 , the cylindrical protrusion  228  and the surface that defines the second opening  248  form an overtravel stop for limiting the amount of pivotal movement of the cable holder  230  relative to the guide wall  212  to a predetermined amount. The anchor cable  222  is threaded through the channel  240  of the cable holder  230  and is attached to the buckle assembly  252 . As discussed with regards to apparatus  10 , the anchor cable  222  may alternatively be attached to a D-ring (not shown), a retractor (not shown), or an end (not shown) of the seat belt webbing  24 .  
         [0069]    The pretensioner  214  of the apparatus  210  is fixed to either the vehicle  16  or the seat  12 . When the tongue  26  is fastened in the buckle assembly  252 , tension in the seat belt webbing  24  pulls the buckle assembly  252  in the direction indicated by arrow T w . As a result, a force in the direction T w  pulls on the anchor cable  222  and tensions the anchor cable. Tension in the anchor cable  222  results in the anchor cable pulling upwardly, in the direction T w , on the cable holder  230  with a force equivalent to the tension in the anchor cable. As a result, a moment indicated at M w  is created that tends to rotate the cable holder  230  in the counterclockwise direction as viewed L in FIG. 5. The moment M w  is approximately equal to the force applied on the cable holder  230  by the anchor cable  222  multiplied by a distance between the torsion bar  226  and the portion of the anchor cable extending in the direction T w .  
         [0070]    Another moment, indicated at M tb , is a moment caused by torsion of the torsion bar  226 . The value of moment M tb  is a function of the spring constant of the torsion bar  226  and the angular rotation or torsion of the torsion bar.  
         [0071]    Similar to the cable holder  106  illustrated in FIGS. 3 and 4, the cable holder  230  in FIG. 5 has an initial position where the cylindrical protrusion  228  of the guide wall  212  contacts an upper portion of the surface defining the second opening  248  in the cable holder  230  and prevents clockwise rotation of the cable holder about torsion bar  226 . The cable holder  230  may pivoted relative to the pretensioner  214  by a predetermined amount. Pivotal movement of the cable holder  230  is about the torsion bar  226 . The predetermined amount of pivotal movement of the cable holder  230  relative to the pretensioner  214  is in a counterclockwise direction between the initial position and a stop position. In the stop position, the cylindrical protrusion  228  of the guide wall  212  contacts a lower portion of the surface defining the second opening  248  in the cable holder  230  and further pivoting of the cable holder  230  about the torsion bar  226  in the counterclockwise direction is prevented.  
         [0072]    When the moment M w  exceeds moment M tb , the cable holder  230  pivots in a counterclockwise direction about the torsion bar  226 . As the cable holder  230  moves away from the initial position, the torsion bar  226  twists and moment M tb  increases. The cable holder  230  pivots away from the initial position until the moment M w  equals moment M tb .  
         [0073]    At a threshold tension in the anchor cable  222 , the cable holder  230  will have pivoted away from the initial position by the predetermined amount and further pivoting away from the initial position will be prevented. The predetermined amount of pivotal movement of the cable holder  230  relative to the guide wall  212  is an amount that is well below the yield point of the torsion bar  226 .  
         [0074]    When the cable holder  230  is away from the initial position and the tension in the anchor cable  222  decreases below the threshold tension, the cable holder pivots in the clockwise direction toward the initial position until moment M w  equals the moment M tb . If moment M tb  is greater than moment M w , the cable holder  230  will be returned to the initial position and further rotation in the clockwise direction will be prevented.  
         [0075]    In the event that the pretensioner  214  is actuated, ignition of the pyrotechnic charge forces the piston  254  toward the second end  258  of the first cylinder  256  of the pretensioner. The piston  254  moves a distance, parallel to axis A, as a result of the actuation. Movement of the anchor cable  222  effects movement of the buckle assembly  252  in a direction indicated at P in FIG. 5. Since the anchor cable  222  has a constant length, the buckle assembly  252  moves in the direction P a distance equal to the distance that the piston  254  moves along axis A. When the buckle assembly  252  is moved in the direction P, tension in the seat belt webbing  24  is increased.  
         [0076]    The sensor (not shown) in FIG. 5 is preferably a torsion sensor that senses the torsion in the torsion bar  226  and that provides an output signal indicative of the torsion to the controller  36 . The pivotal movement of the cable holder  230  relative to the guide wall  212  is a function of the properties of the torsion bar  226  and may be adjusted by changing the torsion bar  226 .  
         [0077]    [0077]FIG. 6 shows a third embodiment of an apparatus  310  constructed in accordance with the present invention. The general design of the guide wall  312  of FIG. 6 is similar to the design of the guide wall  212  in FIG. 5, and the structure of the guide wall  312  will be referenced with the same reference numbers as those in FIG. 5 except that  100  will be added to each number used in FIG. 5. The cable holder  330  of FIG. 6 includes an elongated main body portion  332 . The main body portion  332  includes a portion  334  that extends along axis A and an angled portion  336 . A channel  338  for receiving the anchor cable  322  extends through the main body portion  332  of the cable holder  330 .  
         [0078]    A first extension  340  extends upwardly from the axially extending portion  334  of the main body portion  332  near a first end  342  of the main body portion  332 . A first opening  344  is located in the first extension.  340 . A second extension  346  extends between the axially extending portion  334  and the angled portion  336  of the main body portion  332 . The second extension  346  defines a second opening  348  for receiving the cylindrical protrusion  328  of the guide wall  312 . The second opening  348  has a diameter that is greater than the diameter of the cylindrical protrusion  328 .  
         [0079]    A beam  350  extends partially along the axially extending portion  334  of the cable holder  330 . The beam is preferably welded to the axially extending portion  334  of the cable holder  330 . A first end  352  of the beam  350  is located adjacent the first opening  344  of the cable holder  330  and a second end  354  of the beam  350  is located adjacent the second opening  348  of the cable holder.  
         [0080]    The pretensioner  314  of the apparatus  310  is fixed to either the vehicle  16  or the seat  12 . The anchor cable  322  extends between a buckle assembly  358  and the pretensioner  314 . As discussed with regards to apparatus  10 , the anchor cable  322  may alternatively be attached to a D-ring (not shown), a retractor (not shown), or an end (not shown) of the seat belt webbing  24 .  
         [0081]    The cable holder  330  of FIG. 6 is fixed to the guide wall  312  using a fastener  356 , as opposed to a torsion bar. When the tongue  26  of the seat belt webbing  24  is fastened in the buckle assembly  358 , tension in the seat belt webbing  24  pulls the buckle assembly  358  in the direction indicated by arrow T w  in FIG. 6. As a result, a force in the direction of T w  pulls on the anchor cable  322  and tensions the anchor cable. Tension in the anchor cable  322  results in the anchor cable  322  pulling upwardly, in the direction T w , on the cable holder  330  with a force equivalent to the tension in the anchor cable. The force in the direction T w  may be broken into a force vector F a  that is parallel to the axially extending portion  334  of the cable holder  330  and a force vector F b  that is perpendicular to the axially extending portion  334  of the cable holder  330 .  
         [0082]    Since fastener  356  is rigid and does not twist when subjected to force vector F b , force vector F b  tends to bend an end of the axially extending portion  334  opposite the fastener  356  in an upward direction as viewed in FIG. 6. The axially extending portion  334  may bend a predetermined amount from an initial position where an upper portion of the cylindrical protrusion  328  of the guide wall  312  contact a surface defining the second opening  348  in the cable holder  330  to a stop position where a lower portion of the cylindrical protrusion  328  of the guide wall  312  contact a surface defining the second opening  348  in the cable holder. The axially extending portion  334  of the cable holder  330  will be in the stop position when a threshold tension, in the direction T w , is applied to the anchor cable  322 .  
         [0083]    When the axially extending portion  334  of the cable holder  330  bends, the beam  350  is bent. The beam  350  bends in proportion to the axially extending portion  334  of the cable holder  330 . As the tension of the seat belt webbing  24  decreases, the resiliency of the axially extending portion  334  of the cable holder  330  returns the cable holder to the initial position.  
         [0084]    In the event that the pretensioner  314  is actuated, ignition of the pyrotechnic charge forces the piston  360  toward the second end  364  of the first cylinder  362  of the pretensioner. The piston  360  moves a distance, parallel to axis A, as a result of the actuation. Movement of the anchor cable  322  effects movement of the buckle assembly  358  in a direction indicated at P in FIG. 6. Since the anchor cable  322  has a constant length, the buckle assembly  358  moves in the direction P a distance equal to the distance that the piston  360  moves along axis A. When the buckle assembly  358  is moved in the direction P, tension in the seat belt webbing  24  is increased.  
         [0085]    The sensor (not shown) in FIG. 6 is a strain gauge that is mounted on the beam  350 . Preferably, the strain gauge is a silicon-based or a resistive ink-based piezoresistive strain gauge. The strain gauge measures the strain of the beam  350  and provides an output signal indicative of the strain to the controller  36 .  
         [0086]    A fourth embodiment of an apparatus  410  constructed in accordance with the present invention is shown in FIGS.  7 - 8 . The guide wall  412  of FIGS.  7 - 8  is similar to the guide wall of FIGS. 5 and 6 with the addition of a third opening. Structures of the guide wall  412  in FIGS.  7 - 8  that are similar to structures of guide wall  312  in FIG. 6 will have the same reference number plus  100 . The third opening (not shown) in guide wall  412  is located above the second opening and near an upper edge  430  of the guide wall  412 .  
         [0087]    The cable holder  432  of FIGS.  7 - 8  includes a narrow end  434  and a wide end  436 . The cable holder also includes a bent portion  438  that first extends rearward, into the plane of the paper as viewed in FIGS.  7 - 8 , and then curves forwardly and terminates in the same plane as a first surface  433  of the cable holder  432 . The bent portion  438  has a semi-circular cross-section that includes an outer surface (not shown) and an inner surface  442 . The inner surface  442  defines a channel  446  for receiving a portion of the anchor cable  422 . The bent portion  438  extends along a lower edge  440  and a wide end edge  444  of the cable holder  432 .  
         [0088]    A first opening  448  is located near the narrow end  434  of the cable holder  432  above, as viewed in FIGS.  7 - 8 , the lower edge  440  of the cable holder  432 . A second opening  450  for receiving the cylindrical protrusion  428  of the guide wall  412  is located outwardly along axis A and a short distance above, as viewed in FIGS.  7 - 8 , the first opening  448 . The second opening  450  has a diameter that is greater than the diameter of the cylindrical protrusion  428 . A third opening  452  is located above the second opening  450 . Two parallel slots  456  extend from a point adjacent the first opening  448  to a point adjacent the third opening  452 . The portion of the cable holder  432  between the slots  456  is effectively a beam  454 . A fastener  458  is inserted into the first opening  448  of the cable holder  432  and the first opening of the guide wall  412 . The fastener  458  connects the cable holder  432  to the guide wall  412 . A torsion bar  460  is inserted into the third opening  452  of the cable holder  432  and the second opening of the guide wall  412 . The torsion bar  460  also connects the cable holder  432  to the guide wall  412 .  
         [0089]    The pretensioner  414  of the apparatus  410  is fixed to either the vehicle  16  or the seat  12 . The anchor cable  422  extends between the pretensioner  414  and a buckle assembly  462 . The anchor cable  422  may alternatively be attached to a D-ring (not shown), a retractor (not shown), or an end (not shown) of the seat belt webbing  24 .  
         [0090]    When the tongue  26  of the seat belt webbing  24  is fastened in the buckle assembly  462 , tension in the seat belt webbing  24  pulls the buckle assembly  462  in the direction indicated by arrow T w  in FIGS. 7 and 8. As a result, a force in the direction of T w  pulls on the anchor cable  422  and tensions the anchor cable. Tension in the anchor cable  422  results in the anchor cable  422  pulling upwardly, in the direction T w , on the cable holder  432  with a force equivalent to the tension in the anchor cable. As a result, a moment indicated at M w  is created that tends to rotate the cable holder  432  in the counterclockwise direction as viewed in FIGS. 7 and 8. The moment M w  is approximately equal to the force applied on the cable holder  432  by the anchor cable  422  multiplied by a distance between the torsion bar  460  and the portion of the anchor cable extending in the direction T w .  
         [0091]    Another moment, indicated as M tb , is a moment caused by torsion of the torsion bar  460 . The value of moment M tb  is a function of the spring constant of the torsion bar  460  and the angular rotation or torsion of the torsion bar.  
         [0092]    When moment M w  exceeds moment M tb , the cable holder  432  attempts to pivot relative to the guide wall  412 . Fastener  458  resists the pivoting movement, while torsion bar  460  allows the pivoting movement. As a result, the wide end  436  of the cable holder  432  begins to pivot about an axis centered at the torsion bar  460 . Because the fastener  458  resists movement of the narrow end  434  of the cable holder  432 , the pivotal movement of the wide end  436  of the cable holder  432  is movement relative to the narrow end  434  of the cable holder. The movement of the wide end  436  of the cable holder  432  relative to the narrow end  434  of the cable holder  432  causes the cable holder  432  to bend. The bend of the cable holder  432  is concentrated in an area between the fastener  458  and the torsion bar  460 . As a result, the center of the beam  454  of the cable holder  432  bends, or buckles, as is shown in FIG. 8.  
         [0093]    The movement of the cable holder  432  relative to the guide wall  412  is limited to a predetermined amount. When the cable holder  432  is in the initial position, shown in FIG. 7, an upper portion of the cylindrical protrusion  428  of the guide wall  412  contacts a surface defining the second opening  450 . When subjected to a threshold tension, the wide end  436  of the cable holder  432  will be rotated about the torsion bar  460  by the predetermined amount, as shown in FIG. 8. When the cable holder  432  is rotated by the predetermined amount, a left side portion of the cylindrical protrusion  428  of the guide wall  412  contacts the surface defining the second opening  450  of the guide wall  412 . As the tension on the seat belt webbing  24  decreases, the resiliency of the cable holder  432  returns the cable holder to the initial position.  
         [0094]    In the event that the pretensioner  414  is actuated, ignition of the pyrotechnic charge forces the piston  464  toward the second end  468  of the first cylinder  466  of the pretensioner. The piston  464  moves a distance, parallel to axis A, as a result of the actuation. Movement of the anchor cable  422  effects movement of the buckle assembly  462  in a direction indicated at P in FIGS. 7 and 8. Since the anchor cable  422  has a constant length, the buckle assembly  462  moves in the direction P a distance equal to the distance that the piston  464  moves along axis A. When the buckle assembly  462  is moved in the direction P, tension in the seat belt webbing  24  is increased.  
         [0095]    The sensor (not shown) is located on the beam  454  of the cable holder  432 . Preferably, the sensor is a strain gauge. The sensor measures the strain on the beam  454  and provides an output signal to the controller  36 . The controller  36  determines the tension in the seat belt webbing  24  from the output signal from the sensor. Alternatively, the sensor may be a torsion sensor located on the torsion bar  460 .  
         [0096]    A fifth embodiment of an apparatus  510  constructed in accordance with the present invention is shown in FIGS. 9 and 10. The guide wall  512  of FIGS. 9 and 10 includes a fastening portion  514  and a guiding portion  516 . The fastening portion  514  extends perpendicular to the longitudinal axis A and includes a central opening  518  through which the anchor cable  520  passes. Two fastener openings  522 , one above and one below the central opening  518 , extend through the fastening portion  514  for receiving bolts  524  to attach the guide wall  512  to the an anchor plate  526 .  
         [0097]    The anchor plate  526  may be a portion of the vehicle 16  or a portion of the seat  12 . As shown in FIGS. 9 and 10, a first end  528  of the anchor cable  520  is fixed to the anchor plate  526 . As will be discussed below, a second end  530  of the anchor cable  520  is attached to a portion of the seat belt assembly  22  (FIG. 1), preferably the buckle assembly  532 .  
         [0098]    The guiding portion  516  of the guide wall  512  extends perpendicular to and outwardly from the fastening portion  514  in a direction parallel to the longitudinal axis A. The guiding portion  516  includes a first side surface  534  and a second side surface (not shown). The first side surface  534  of the guiding portion  516  is nearest the fastening portion  514  of the guide wall  512 . An opening (not shown) extends through the guiding portion  516  of the guide wall  512  near the fastening portion  514  for receiving a pivot pin  536  or rivet. The guiding portion  516  also includes a cylindrical protrusion  538  that is located outwardly along axis A and a short distance above, as viewed in FIGS. 9 and 10, the opening for the pivot pin  536 . The cylindrical protrusion  538  extends outwardly from the first side surface  534  a distance of approximately one-half the width, into the plane of the paper as viewed in FIGS. 9 and 10, of the fastening portion  514  of the guide wall  512 . A cylindrical inner surface  540  of the cylindrical protrusion  538  extends through the guide wall  512  to the second side surface of the guide wall. A mounting bolt (not shown) may be received through the cylindrical inner surface  540  of the cylindrical protrusion  538  for forming an additional attachment of the apparatus  510  to the anchor plate  526 .  
         [0099]    The guiding portion  516  of the guide wall  512  also includes a wide end edge  542 , opposite the fastening portion  514 , and upper and lower edges  544  and  546 , respectively. A bushing holder  548  is located on the upper edge  544  of the guide wall  512  adjacent the wide end edge  542 . The bushing holder  548  includes two outwardly extending fingers  550  that are separated by a slot. The fingers  550  extend outwardly from the first side surface  534  of the guide wall  512  a distance that is approximately equal to the outward extension of the cylindrical protrusion  538 .  
         [0100]    A sensor support  552  is formed on the guide wall  512  near the wide end edge  542  of the guide wall. The sensor support  552  includes a channel  554  for supporting lead wires  556  of a sensor  558 .  
         [0101]    The cable holder  560  includes a generally wedge shaped main body portion  562 . The main body portion  562  widens from a narrow end  564  to a wide end  566 . The cable holder  560  has an arcuate narrow end edge  568 , a wide end edge  570 , and upper and lower edges  572  and  574 , respectively. The main body portion  562  of the cable holder  560  has an axial length, defined as a distance along axis A between the narrow end edge  568  and the wide end edge  570 , that is less than the axial length of the guide wall  512 . The main body portion  562  of the cable holder  560  also includes a first side surface  576  and a second side surface (not shown), opposite the first side surface.  
         [0102]    The narrow end  564  of a main body portion  562  of the cable holder  560  includes a circular opening (not shown). A low friction bushing (not shown) may be received in the opening.  
         [0103]    The main body portion  562  of the cable holder  560  also includes an outer lip  578 . The outer lip  578  extends outwardly from the first side surface  576  of the main body portion  562  of the cable holder  560 . A first end  580  of the outer lip  578  is located adjacent the lower edge  574  of the main body portion  562  of the cable holder  560  approximately one-half the distance between the wide end edge  570  and the narrow end edge  568  of the cable holder. The outer lip  578  also extends along the wide end edge  570  of the cable holder  560  and terminates in a notched portion  582  at the intersection of the upper edge  572  and the wide end edge  570 . A gap  584  is formed in the outer lip  578  at the intersection of the lower edge  574  and the wide end edge  570  of the main body portion  562 . The outer lip  578  includes an inner surface  586  and an outer surface  588 .  
         [0104]    A guide  590  extends outwardly from the first side surface  576  of the main body portion  562  of the cable holder  560 . The guide  590  includes a cylindrical inner surface  592  and a curved outer surface  594 . The cylindrical inner surface  592  of the guide  590  defines an opening  596  that extends completely through the main body portion  562  of the cable holder  560 . The opening  596  has a diameter that is larger than the diameter of the cylindrical protrusion  538  of the guide wall  512 . A portion of the outer surface  594  of the guide  590  extends parallel to inner surface  586  of the outer lip  578 . A notched portion  598  of the guide  590  extends into the outer surface  594  of the guide and is located adjacent the notched portion  582  of the outer lip  578 . Together, the notched portion  598  of the guide  590  and the notched portion  582  of the outer lip  578  form a spring seat  600 .  
         [0105]    A channel  602  for guiding a portion of the anchor cable  520  is defined in the cable holder  560  between the inner surface  586  of the outer lip  578  and the outer surface  588  of the guide  590 . The channel  602  orients the anchor cable  520  such that the anchor cable extends from the anchor plate  526  and through the slot in the bushing holder  548  of the guide wall  512 .  
         [0106]    The apparatus  510  of FIGS. 9 and 10 also includes a cable guide  604 . As will be discussed in detail below, the cable guide  604  reduces the occurrence of a variable moment acting on the cable holder  560 . The cable guide  604  includes a bushing  606 , shown in partial section. The bushing  606  is preferably made from a low friction material. In the embodiment of FIGS. 9 and 10, the bushing  606  is formed from plastic. The bushing  606  has a box-like shape that is defined by six outer surfaces. Upper and lower surfaces  608  and  610 , respectively, of the bushing  606  are generally square. The four side surfaces, only one of which is shown at  612 , of the bushing  606  are generally rectangular and have a height, measured between the upper and lower surfaces  608  and  610  of the bushing, of approximately one-half their width. Two notches  614  are formed in opposite side surfaces of the bushing  606 . The two notches  614  extend parallel to one another.  
         [0107]    A centrally located aperture  616  extends through the bushing  606  from the lower surface  610  to the upper surface  608 . A surface  618  of the bushing  606  defining the aperture  616  has an arcuate shape with a narrow portion of the aperture located between the upper and lower surfaces  608  and  610  of the bushing  606 . The arcuate surface  618  widens near the lower and upper surfaces  610  and  608  of the bushing  606 . The diameter of the aperture  616 , defined at the narrow portion of the aperture, is slightly larger than a diameter of the anchor cable  520 . A surface surrounding an opening to the aperture  616  on the lower surface  610  of the bushing  606  defines a spring seat  620 . The spring seat  620  may be located on the lower surface  610  of the bushing  606  or recessed slightly into the bushing  606  as shown in FIGS. 9 and 10.  
         [0108]    To assembly the apparatus  510  of FIGS. 9 and 10, the anchor cable  520  is fixed to the anchor plate  526  in a known manner. The anchor cable  520  is passed through the opening  518  in the fastening portion  514  of the guide wall  512 . The guide wall is fastened to the anchor plate  526  by inserting bolts  524  through the fastener openings  522  in the fastening portion  514  of guide wall and into the anchor plate. A mounting bolt may also be inserted through the cylindrical inner surface  540  of the cylindrical protrusion  538  to attach the guide wall  512  to the anchor plate  526 .  
         [0109]    To attach the cable holder  560  to the guide wall  512 , the cable holder is aligned with the guide wall such that the cylindrical protrusion  538  of the guide wall is inserted into the opening  596  defined by the inner surface  592  of the guide  590  of the cable holder and the spring seat  600  of the cable holder is positioned near the bushing holder  548  of the guide wall. The opening for a pivot pin  536  of the cable holder  560  is then aligned with the opening for a pivot pin of the guide wall  512 . A pivot pin  536  or rivet is extended through the openings to pivotally attach the cable holder  560  to the guide wall  512 . When attached to the guide wall  512 , the cable holder  560  is pivotal relative to the guide wall about the pivot pin  536 .  
         [0110]    The bushing  606  of the cable guide  604  is secured to the guide wall  512  by extending the fingers  550  of the bushing holder  548  into the notches  614  of the bushing. A spring  622  is inserted between the cable holder  560  and the bushing  606 . In the embodiment shown in FIGS. 9 and 10, the spring  622  is a compression spring. An end of the spring  622  is placed in the spring seat  620  of the bushing  606  and the opposite end of the spring is placed in the spring seat  600  of the cable holder  560 . The spring  622  creates a moment M s  on the cable holder  560  to rotate the cable holder clockwise as viewed in FIGS. 9 and 10. Moment Ms is approximately equal to the force exerted by the spring multiplied by a distance between a center of the pivot pin  536  and a center of the spring seat  600  on the cable holder  560 . The spring  622  rotates or biases the cable holder  560  into an initial position, shown in FIG. 9. When the cable holder  560  is in the initial position, the cylindrical protrusion  538  of the guide wall  512  contacts an upper portion of the cylindrical inner surface  592  of the guide  590  of the cable holder  560  and prevents clockwise rotation of the cable holder relative to the guide wall.  
         [0111]    The anchor cable  520  is then threaded through the channel  602  of the cable holder  560 , through the spring  622 , and through the bushing  606 . The second end  530  of the anchor cable  520  is attached to a portion of the seat belt assembly  22 , preferably the seat belt buckle assembly  532 , in a known manner. The anchor cable  520  may alternatively be attached to a D-ring (not shown), a retractor (not shown), or an end (not shown) of the seat belt webbing  24 .  
         [0112]    When a tongue associated with the seat belt webbing  24  is fastened in the buckle assembly  532 , tension in the seat belt webbing  24  results in a force on the anchor cable  520  that is generally directed in the direction T w . The force creates a tension in the anchor cable  520  and results in a force in the direction T w  on the cable holder  560 . As a result, a moment M w  is created that tends to rotate the cable holder  560  in a counterclockwise direction as viewed in FIG. 9. The moment M w  is approximately equal to the force applied on the cable holder  560  by the tension in the anchor cable  520  multiplied by a distance between the center of the pivot pin  536  and the center of the spring seat  600  on the cable holder  560  through which the anchor cable passes.  
         [0113]    When moment M w  exceeds moment M s , the cable holder  560  pivots in the counterclockwise direction about the pivot pin  536  and away from the initial position. As the cable holder  560  moves away from the initial position, the spring  622  is compressed and the spring force increases. As a result, moment M s  increases. The cable holder  560  pivots away from the initial position until moment M s  equals moment M w .  
         [0114]    At a threshold tension in the anchor cable  520 , the cable holder  560  will have pivoted away from the initial position by a predetermined amount, shown in FIG. 10. Further pivoting away from the initial position will be prevented by a lower portion of the cylindrical inner surface  592  of the guide  590  of the cable holder  560  contacting the cylindrical protrusion  538  of the guide wall  512 . Thus, the cylindrical inner surface  592  of the guide  590  of the cable holder  560  and the cylindrical protrusion  538  of the guide wall  512  collectively form an overtravel stop to prevent rotation of the cable holder beyond the predetermined amount. Any tension in the anchor cable  520  above the threshold tension will not result in movement of the cable holder  560  relative to the guide wall  512 . The overtravel stop resists increased tension beyond the threshold tension.  
         [0115]    When the cable holder  560  is away from the initial position and the tension in the anchor cable  520  decreases below the threshold tension, the cable holder pivots in the clockwise direction toward the initial position until moment M s  equals moment M w . If moment M s  is greater than moment M w , the cable holder  560  will be returned to the initial position and further rotation in the clockwise direction will be prevented.  
         [0116]    The cable guide  604  of the apparatus  510  of FIGS. 9 and 10 reduces a variable moment on the cable holder  560  that may result from off-axis loading of the seat belt webbing  24 . Off-axis loading of the seat belt webbing  24  is defined as loading of the seat belt webbing in a direction other than in the direction of T w  shown in FIGS. 9 and 10. For example, if the seat belt webbing and thus, the second end  530  of the anchor cable  520 , is moved upward and rightward, as viewed in FIG. 9, the bushing  606  of the cable guide  604  redirects the anchor cable between the bushing and the channel  602  of the cable holder  560  to maintain the angle shown in FIG. 9. Thus, when the cable holder  560  is in the initial position, the anchor cable  520  is maintained at a predetermined angle between the cable holder and the bushing  606 . Since the anchor cable  520  is maintained at the predetermined angle between the cable holder  560  and the bushing  606 , the distance between the center of the pivot pin  536  and the location of the anchor cable tension will not vary as the second end  530  of the anchor cable  520  is moved IF off-axis. As a result, for a given force, any change in the moment M w  that may result from movement of the second end  530  of the anchor cable  520  is reduced.  
         [0117]    A sensor  558  monitors the movement of the cable holder  560  relative to the guide wall  512 . The sensor  558  illustrated in FIGS. 9 and 10 includes a magnet  624  and a device  626  for measuring movement of the magnet. The magnet  624  is secured in the gap  584  formed in the outer lip  578  of the cable holder  560 . The magnet  624  is preferably a two-pole magnet. The device  626  is secured in the cavity, adjacent the location of the magnet  624  on the cable holder  560 . The device  626  is preferably a magnetic position sensor, such as a Hall effect device, for sensing the position of the magnet  624  relative to the device  626 . Lead wires  556  of the sensor  558  extend through the channel  554  formed in the guide wall  512 . The sensor  558  provides an output signal to the controller  36 .  
         [0118]    FIGS.  11 - 17  illustrate a sixth embodiment of an apparatus  710  constructed in accordance with the present invention. As shown in FIG. 11, the apparatus  710  includes a generally rectangular guide wall  712 . As shown in the exploded view of FIG. 13, the guide wall  712  is formed from a generally rectangular a steel backing plate  714  and a rectangular plastic cover plate  716 .  
         [0119]    The guide wall  712 , and particularly the plastic cover plate  716 , includes upper, lower, left, and right edges  718 ,  720 ,  722  and  724 , respectively. A sensor clip (not shown) for supporting a sensor  726  is located in a corner defined by the lower and left edges  720  and  722 . A steel pivot stop  728  extends outwardly of the guide wall  712  in a central location adjacent the lower edge  720 . A hook  730  for supporting a portion of a spring  732  extends outwardly of the guide wall  712  in a corner adjacent the lower and right edges  720  and  724 . The steel pivot stop  728  and the hook  730  are formed on the steel backing plate  714  and extend through corresponding openings  734  and  736  in the plastic cover plate  716  of the guide wall  712 , as shown in FIG. 11.  
         [0120]    As shown in FIG. 13, two apertures extend through the guide wall  712 . A first aperture  738  is located adjacent the left edge  722  of the guide wall  712  slightly nearer the upper edge  718  of the guide wall than the lower edge  720 . A cylindrical protrusion  740  formed on the plastic cover plate  716  extends outwardly of the guide wall  712  and surrounds the first aperture  738 . The cylindrical protrusion  740  forms a bushing. A second aperture  742  is located an equal distance between the left and right edges  722  and  724  of the guide wall  712  and slightly closer to the upper edge  718  than to the lower edge  720  of the guide wall. The second aperture  742  has a diameter that is approximately equal to one-third of the distance between the upper and lower edges  718  and  720  of the guide wall  712 .  
         [0121]    The apparatus  710  also includes an arm  744  (FIG. 13). The arm  744  has a generally pear shaped main body portion  746  with a narrow portion  748  and a wide portion  750 . A first aperture  752  extends through the narrow portion  748  of the main body portion  746  of the arm  744 . The first aperture  752  is sized to receive the cylindrical protrusion  740  of the guide wall  712 . A second aperture  754  extends through the wide portion  750  of the main body portion  746  of the arm  744 . The second aperture  754  is centrally located in the wide portion  750  of the main body portion  746  of the arm  744  and has a diameter that is approximately seventy five percent of the diameter of the wide portion of the main body portion of the arm. The diameter of the second aperture  754  in the arm is larger than the diameter of the second aperture  742  in the guide wall  712 .  
         [0122]    The arm  744  also includes two extensions. The first extension  756  extends from the narrow portion  748  of the main body portion  746  of the arm  744 . The first extension  756  includes an outwardly projecting target  758 . The second extension  760  extends from the wide portion  750  of the main body portion  746  of the arm  744  in a direction opposite the narrow portion  748  of the main body portion. The second extension  760  terminates in a hooked end  762 . An open portion of the hooked end  762  is located on an upper edge of the second extension, as viewed in FIG. 11.  
         [0123]    A sleeve  764  (FIG. 13) is generally cylindrical and includes a radially outwardly extending base portion  766 . The sleeve  764  is secured in the second aperture  754  of the arm  744  and a cylindrical portion  768  of the sleeve extends outwardly of the wide portion  750  of the main body portion  746  of the arm, as shown in FIG. 15.  
         [0124]    To attach the arm  744  to the guide wall  712 , the arm is positioned relative to the guide wall such that the first aperture  752  in the arm receives the cylindrical protrusion  740  of the guide wall. A pivot pin  770  or rivet is inserted into the first aperture  738  of the guide wall  712 . The pivot pin  770  includes a circular head portion  772  (FIG. 13) that secures the arm  744  on the cylindrical protrusion  740  of the guide wall  712 . When secured on the cylindrical protrusion  740  of the guide wall  712 , the main body portion  746  of the arm  744  is spaced from the guide wall  712 , as shown in FIG. 12, and is pivotal relative to the guide wall.  
         [0125]    As shown in FIG. 11, the apparatus  710  also includes an anchor arm  774 . As will be discussed in detail below, the anchor arm  774  reduces the occurrence of a variable moment acting on the arm  744  as a result of off-axis loading of the seat belt webbing  24 . The anchor arm  774  is generally pear-shaped and is preferably formed from steel. The anchor arm  774  includes a narrow portion  776  and a wide portion  778 . Two apertures extend through the anchor arm  774 . A first aperture  780  extends through the narrow portion  776  of the anchor arm  774 . A second aperture  782  (FIG. 13) extends through the wide portion  778  of the anchor arm  774 . The second aperture  782  is centrally located in the wide portion  778  of the anchor arm  774  and has a diameter that is greater than the diameter of the cylindrical sleeve  764 .  
         [0126]    The anchor arm  774  also includes first and second pivot stops  784  and  786 , respectively, each of which extend downwardly, as viewed in FIG. 11, from the wide portion  778  of the anchor arm  774 . The first and second pivot stops  784  and  786  are spaced from one another by approximately the diameter of the second aperture  782  in the anchor arm  774 .  
         [0127]    The anchor arm  774  pivotally attaches to the cylindrical sleeve  764  of the arm  744 . A bushing (not shown) may separate the anchor arm  774  from the cylindrical sleeve  764 . As shown in FIG. 11, when properly positioned on the cylindrical sleeve  764 , the pivot stop  728  of the guide wall  712  is located between the first and second pivot stops  784  and  786  of the anchor arm  774 . The pivot stop  728  of the guide wall  712  engages the first pivot stop  784  of the anchor arm  774  to limit pivotal movement of the anchor arm in a counterclockwise direction, as viewed in FIG. 14. The pivot stop  728  of the guide wall  712  engages the second pivot stop  786  of the anchor arm  774  to limit pivotal movement of the anchor arm in a clockwise direction, as viewed in FIG. 14. In the embodiment illustrated, the anchor arm  774  may pivot relative to the arm  744  over a range of approximately forty-five degrees.  
         [0128]    When the anchor arm  774  is attached to the sleeve  764  and thus, to the arm  744 , the narrow portion  776  of the anchor arm  774  extends beyond the upper edge  718  of the guide wall  712 . Thus, when a cover  788  (FIG. 13) for the apparatus  710  is attached to the guide wall  712 , the narrow portion  776  of the anchor arm  774  protrudes outwardly from the cover, as shown in FIGS. 15 and 17.  
         [0129]    A first end  792  of the anchor cable  790  is attached to the narrow portion  776  of the anchor arm  774 , preferably through the first aperture  780 . A second end (not shown) of the anchor cable  790  is attached to a portion of the seat belt assembly  22 , preferably the buckle assembly, shown generally at  28  in FIG. 1. The anchor cable  790  may alternatively be attached to a D-ring (not shown), a retractor (not shown), or an end (not shown) of the seat belt webbing  24 . When a tongue  26  associated with the seat belt webbing  24  is fastened into the buckle assembly  28 , tension in the seat belt webbing is transferred through the anchor line  790  to the anchor arm  774 .  
         [0130]    The apparatus  710  also includes an overtravel stop  794 . As shown in FIG. 12, the overtravel stop  794  extends through the cylindrical sleeve  764  and the second aperture of the arm  754  and is received in the second aperture  742  of the guide wall  712 . When received in the second aperture  742  of the guide wall  712 , the overtravel stop  794  limits the pivotal movement of the arm  744  relative to the guide wall  712 , as will be discussed in detail below.  
         [0131]    The overtravel stop  794  is generally cylindrical and includes a head portion  796  that extends radially outwardly of a cylindrical outer surface  798 . A cylindrical inner surface  800  of the overtravel stop  794  defines a path for a mounting bolt  802  (FIGS. 15 and 17) to mount the apparatus  710  to an anchor plate  804 .  
         [0132]    The apparatus  710  also includes a spring  732  (FIG. 11). The spring  732  extends between the hook  730  on the guide wall  712  and the hooked end  762  of the second extension  760  of the arm  744 . The spring  732  exerts a spring force on arm  744  in the direction of F s  in FIG. 14. The spring force creates a moment M s  on the arm that tends to rotate the arm clockwise as viewed in FIG. 14. Moment M s  is approximately equal to the spring force multiplied by a distance between the center of the first aperture  752  of the arm  744 , as indicated at C, and a point of contact between the spring  732  and the hooked end  762  of the second extension  760  of the arm  744 . The spring  732  rotates or biases the arm  744  into an initial position, shown in FIGS. 14 and 15. When the arm  744  is in the initial position, the overtravel stop  794  contacts an upper portion of the cylindrical sleeve  764 , as shown in FIG. 15, and prevents clockwise rotation of the arm  744 .  
         [0133]    Tension in the seat belt webbing results in a force on the anchor cable  790  directed in the direction T w . The force creates a tension in the anchor cable  790 . Tension in the anchor cable  790  pulls upwardly in the direction T w  on the anchor arm  774  with a force equivalent to the tension in the anchor cable  790 . As a result, the anchor arm  774  pulls upwardly in the direction T w  on the arm  744 . A moment M w  is created that tends to rotate the arm  744  in a counterclockwise direction as viewed in FIG. 14. The moment M w  is approximately equal to the force applied on the arm as a result of tension in the seat belt webbing multiplied by a distance between the center C of the first aperture  752  of the arm  744  and the center of the second aperture  754  of the arm, indicated at D.  
         [0134]    When moment M w  exceeds moment M s , the arm  744  pivots in the counterclockwise direction relative to the guide wall  712  and away from the initial position. As the arm  744  moves away from the initial position, the spring  732  is stretched and the spring force F s  increases. As a result, moment M s  increases. The arm  744  pivots away from the initial position until moment M s  equals moment M w .  
         [0135]    At a threshold tension in the anchor cable  790 , the arm  744  will have pivoted away from the initial position by a predetermined amount as shown in FIGS. 16 and 17. A lower portion of the cylindrical sleeve  764  of the arm  744  contacts the overtravel stop  794 , as shown in FIG. 17, to prevent further pivoting of the arm away from the initial position. Any tension in the anchor cable  790  above the threshold tension will not result in further movement of the arm  744  relative to the guide wall  712 . The overtravel stop  794  and the mounting bolt  802  that passes through the overtravel stop resist the increased tension.  
         [0136]    When the arm  744  is away from the initial position and the tension in the anchor cable  790  decreases below the threshold tension, the arm pivots in the clockwise direction toward the initial position until moment M s  equals moment M w . If moment M s  is greater than moment M w , the arm  744  returns to the initial position and further rotation in the clockwise direction will be prevented.  
         [0137]    The anchor arm  774  of the apparatus  710  reduces the occurrence of a variable moment on the arm that may result from off-axis loading of the seat belt webbing  24 . Off-axis loading of the seat belt webbing  24  is defined as loading of the seat belt webbing in a direction other than in the direction of T w  shown in FIG. 14. For example, if the seat belt webbing  24  and thus, the anchor cable  790 , is moved upward and rightward, as viewed in FIG. 14, with a force equivalent to T w , the anchor arm  774  pivots on the cylindrical sleeve  764  of the arm  744 . By pivoting, the anchor arm  774  aligns the force caused by tension in the seat belt webbing with the center D of the second aperture  754  of the arm  744 . Since the anchor arm  774  extends upward from the arm  744 , if for example, the anchor arm  774  was not pivotal, a force directed upward and rightward would reduce the distance between the center C of the first aperture  752  of the arm  744 , and the location of the upward force acting on the arm. Moreover, if the anchor arm  774  was not pivotal, an upward and leftward acting force would increase the distance between the center C and the location of the upward force on the arm  744 . By pivoting, the anchor arm  774  reduced a change in moment M w  that may result from tensioning of the seat belt webbing  24  in an off-axis direction.  
         [0138]    A sensor  726  monitors the movement of the arm  744  relative to the guide wall  712 . The sensor  726  illustrated is a back-biased Hall effect device. The sensor  726  includes a subassembly  806  that includes a magnet and a device for measuring magnet flux. The magnet of the subassembly  806  produces magnet flux. The magnet flux changes as the target  758  of the first extension  756  of the arm  744  moves relative to the subassembly  806 . Thus, the device detects a change in the magnetic flux that results from movement of the target  758 .  
         [0139]    As previously noted, as an alternative to the anchor cable, webbing, a metal strap, or any other elongated member may be used. The choice of material for the anchor cable will not alter the overall design of any of the embodiments of the present invention.  
         [0140]    From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.