Abstract:
A tension sensing assembly for a seat restraint system in a vehicle includes a housing for operative connection to vehicle structure and at least one spring disposed in the housing. The tension sensing assembly also includes at least one magnet disposed in the housing and a Hall effect sensor disposed in the housing and cooperable with the at least one magnet. The tension sensing assembly further includes a movable mechanism at least partially disposed in the housing and cooperable with belt webbing of the seat restraint system and the at least one spring to move the at least one magnet relative to the Hall effect sensor to change an output of the Hall effect sensor to indicate a first tension level and a second tension level in the seat restraint system when the at least one spring is deflected.

Description:
TECHNICAL FIELD 
     The present invention relates generally to seat restraint systems for vehicles and, more particularly, to a tension sensing assembly for a seat restraint system in a vehicle. 
     BACKGROUND OF THE INVENTION 
     It is known to provide a seat restraint system such as a seat belt in a vehicle to restrain an occupant in a seat of the vehicle. In some vehicles, the seat restraint system may be a lap belt, a shoulder belt, or both. Typically, the lap belt and shoulder belt are connected together at one end. The seat restraint system includes a latch plate at the connected end. The seat restraint system also includes a buckle connected at one end by webbing or the like to vehicle structure. The buckle receives the latch plate to be buckled together. When the buckle and latch plate are buckled together, the seat restraint system restrains movement of the occupant to help protect the occupant during a collision. 
     Smart inflatable restraint systems need to know what is occupying a seat of the vehicle. Decisions on deployment of inflatable restraints depend on information supplied by sensors in the seat in determining weight of an object in the seat. When a child seat is placed in the seat and cinched down, the sensors may read a large mass instead of a child seat. With this condition, there will be high tension in the seat restraint system. Comfort studies have shown that no human occupant would wear their seat restraint that tight. With this information on seat restraint tension, the inflatable restraint system can decide on deployment of the inflatable restraints. 
     Therefore, it is desirable to provide an assembly for sensing tension in a seat restraint system of a vehicle. It is also desirable to provide an assembly for a seat restraint system in a vehicle that allows a control module to determine the difference between either a child seat or a small occupant. It is further desirable to provide an assembly for a seat restraint system in a vehicle that provides an indication of low tension forces while preventing audible noise due to rattle and provide an indication of high tension forces in the seat restraint system. 
     SUMMARY OF THE INVENTION 
     It is, therefore, one object of the present invention to provide a tension sensing assembly for sensing tension in a seat restraint system of a vehicle. 
     It is another object of the present invention to provide an assembly for dual level tension sensing in a seat restraint system of a vehicle. 
     To achieve the foregoing objects, the present invention is a tension sensing assembly for a seat restraint system in a vehicle including a housing for operative connection to vehicle structure and at least one spring disposed in the housing. The tension sensing assembly also includes at least one magnet disposed in the housing and a Hall effect sensor disposed in the housing and cooperable with the at least one magnet. The tension sensing assembly further includes a movable mechanism at least partially disposed in the housing and cooperable with belt webbing of the seat restraint system and the at least one spring to move the at least one magnet relative to the Hall effect sensor to change an output of the Hall effect sensor to indicate a first tension level and a second tension level in the seat restraint system when the at least one spring is deflected. 
     One advantage of the present invention is that a new tension sensing assembly is provided for a seat restraint system in a vehicle. Another advantage of the present invention is that the tension sensing assembly senses tension in the seat restraint system to help identify what is occupying the seat, either a child, child seat, or low mass adult. Yet another advantage of the present invention is that the tension sensing assembly has dual level tension sensing. Still another advantage of the present invention is that the tension sensing assembly employs dual level spring operation to provide sensing device travel at low tension forces, prevent rattle, and still provide output at higher forces. A further advantage of the present invention is that the tension sensing assembly has greater output at lower tensions and greater control of output. Yet a further advantage of the present invention is that the tension sensing assembly may use ortho-planar or flat springs and reduce assembly forces to ease automated assembly. 
     Other objects, features, and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a tension sensing assembly, according to the present invention, illustrated in operational relationship with a seat restraint system of a vehicle. 
     FIG. 2 is a fragmentary plan view of the tension sensing assembly of FIG.  1 . 
     FIG. 3 is a view similar to FIG. 2 illustrating the tension sensing assembly in a low tension condition and a high tension condition. 
     FIG. 4 is a graph of force versus displacement for the tension sensing assembly of FIG.  1 . 
     FIG. 5 is a fragmentary plan view of another embodiment, according to the present invention, of the tension sensing assembly of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings and in particular FIGS. 1 and 2, one embodiment of a tension sensing assembly  10 , according to the present invention, is shown for a seat restraint system, generally indicated at  12 , in a vehicle (partially shown), generally indicated at  14 . The vehicle  14  includes a vehicle body  16  and a seat  18  mounted by suitable means to vehicle structure  20  such as a floorpan in an occupant compartment  22  of the vehicle body  16 . In this embodiment, the seat  18  is a front seat of the vehicle  14 . It should be appreciated that the seat  18  could be a rear, second row, or third row seat for the vehicle  14 . 
     Referring to FIGS. 1 and 2, the vehicle  14  includes the seat restraint system  12  for restraining an occupant (not shown) in the seat  18 . The seat restraint system  12  includes a latch tongue or plate (not shown) connected to an end of either one of a lap belt, shoulder belt, or both (not shown) which have another end connected to a retractor (not shown). The seat restraint system  12  also includes a buckle assembly  24  connected by suitable means such as belt webbing  26  to the tension sensing assembly  10 . The tension sensing assembly  10  is connected to the vehicle structure  20  in a manner to be described. It should be appreciated that the latch plate is engageable and disengageable with the buckle assembly  24 . It should be appreciated that, except for the tension sensing assembly  10 , the seat restraint system  12  and vehicle  14  are conventional and known in the art. 
     Referring to FIGS. 1 through 3, the tension sensing assembly  10 , according to the present invention, includes an anchor plate  28  extending axially and connected to vehicle structure by suitable means such as an anchor bolt  30 . The anchor plate  28  has an aperture  32  extending therethrough to receive the anchor bolt  30 . The anchor bolt  30  extends through the aperture  32  in the anchor plate  28  and the vehicle structure  20  and is secured in place by a nut (not shown). The anchor plate  28  is made of a rigid material such as metal. It should be appreciated that the anchor bolt  30  is conventional and known in the art. It should also be appreciated that the anchor plate  28  is fixed by the anchor bolt  30 . 
     The tension sensing assembly  10  also includes a housing  34  mounted on or connected to the anchor plate  28 . The housing  34  is generally rectangular in shape. The housing  34  has opposed lateral side walls  35  and longitudinal end walls  36  to form a cavity  37 . One of the end walls  36  has an aperture  38  extending therethrough at a forward longitudinal end for a function to be described. The housing  34  also includes a stop  39  extending into the cavity  37  for a function to be described. The housing  34  is made of a rigid material such as plastic. It should be appreciated that the housing  34  has a bottom wall  40  and a top wall  42  that may be integral or attached thereto as illustrated in FIGS. 1 and 2. It should also be appreciated that the stop  39  may extend from either the bottom wall  40  or top wall  42 . 
     The tension sensing assembly  10  includes a slider or tongue plate  44  connected to the belt webbing  26  and cooperating with the housing  34 . The tongue plate  44  has a base portion  46  which is generally rectangular in shape and has a width the same as or less than a width of the aperture  38  of the housing  34 . The base portion  46  extends through the aperture  38  of the housing  34 . The base portion  46  has a slot  47  extending longitudinally therein to receive the stop  39  of the housing  34 . It should be appreciated that the base portion  46  moves relative to the stop  39 . 
     The tongue plate  44  also has a first end portion  48  connected to one end of the base portion  46  and disposed outside the housing  34 . The first end portion  48  has a width greater than a width of the aperture  38  of the housing  34 . The first end portion  48  includes an aperture  50  extending therethrough. The aperture  50  is generally rectangular in shape and receives one end of the belt webbing  26 . 
     The tongue plate  44  further has a second end portion  52  connected to the other end of the base portion  46  and disposed inside the housing  34 . The second end portion  52  has a width less than a width of the cavity  37  of the housing  34 . The second end portion  52  includes an aperture  54  extending therethrough for a function to be described. The tongue plate  44  is made of a rigid material and formed as a monolithic structure being integral, unitary and formed as one-piece. 
     The tension sensing assembly  10  includes an actuator  56  disposed in the aperture  54  and slot  47 . The actuator  56  is generally “T” shaped and has a first portion  58  extending longitudinally and disposed in the slot  47  for a function to be described. The actuator  56  also includes a second portion  60  extending laterally and disposed in the aperture  54 . The second portion  60  has a width greater than a width of the first portion  58  and slot  47  but less than a width of the aperture  54 . The actuator  56  is made of a rigid material and formed as a monolithic structure being integral, unitary and formed as one-piece. 
     The tension sensing assembly  10  includes a first spring  62  disposed in the slot  47  of the base portion  46  and within the cavity  37  of the housing  34  between the stop  39  and the first portion  58  of the actuator  56 . The first spring  62  has a low spring constant. The first spring  62  is tuned to a predetermined force for comfort or low tension to have an output of approximately zero pounds (0 lb.) to approximately eight pounds (8 lb.). The first spring  62  is of a coil type having a first end contacting the stop  39  in the housing  34  and a second end contacting the first portion  58  of the actuator  56 . The first spring  62  may also be of a flat or orthoplanar spring type. The first spring  62  is made of a spring material. It should be appreciated that the actuator  56  deflects the first spring  56  when the tongue plate  44  is moved relative to the housing  34 . 
     The tension sensing assembly  10  includes at least one, preferably a plurality of, more preferably two, second springs  64  disposed in the aperture  54  within the cavity  37  of the housing  34  between the second end portion  52  of the tongue plate  44  and the second portion  60  of the actuator  56 . The second springs  64  have a high spring constant. The second springs  64  are tuned to a predetermined force for a high tension condition to have an output of approximately eight pounds (8 lb.) to approximately thirty pounds (30 lb.). The second springs  64  are of a coil type having a first end contacting the second portion  60  of the actuator  56  and a second end contacting the second end portion  52  of the tongue plate  44 . The second springs  64  may also be of a flat or orthoplanar spring type. The second springs  64  are made of a spring material. It should be appreciated that the second end portion  52  of the tongue plate  44  deflects the second springs  64  when the tongue plate  44  is moved relative to the housing  34 . It should also be appreciated that the springs  62  and  64  may be replaced with one or more multi-level springs such as an ortho-planar spring developed by Brigham Young University, Provo, Utah. 
     Referring to FIGS. 2 and 3, the tension sensing assembly  10  includes at least one magnet  66  disposed in the cavity  37  of the housing  34 . The magnet  66  is mounted on the tongue plate  44 , preferably molded into the tongue plate  44 . The tension sensing assembly  10  includes a Hall effect sensor  68  disposed in the cavity  37  of the housing  34 . The Hall effect sensor  68  is spaced longitudinally from the magnet  66  and mounted to the end wall  36  of the housing  34  in a low tension condition. The magnet  66  is moved by the tongue plate  44  toward the Hall effect sensor  68  during a high tension condition. It should be appreciated that the tongue plate  44  moves as the springs  64  are deflected and this motion moves the magnet  66  closer to the Hall effect sensor  68  in a push-push arrangement. It should also be appreciated that the position of the magnet  66  relative to the Hall effect sensor  68  changes the output current of the Hall effect sensor  68 . It should further be appreciated that the Hall effect sensor  68  may be mounted on a circuit board (not shown) connected to the end wall  36  and is potted and connected by electrical leads or wires to the source of power such as a controller  70  of the vehicle. 
     In operation of the tension sensing assembly  10 , when the latch plate is not latched with the buckle assembly  24  as illustrated in FIG. 2, no signal is transmitted by the Hall effect sensor  68 . It should be appreciated that the actuator  56  of the tension sensing assembly  10  is spring loaded to an initial position by the spring  62 . 
     When the occupant buckles the seat restraint system  12 , the tension in the belt webbing  26  is higher than a predetermined load required to deflect the spring  62  and the spring  62  is deflected or compressed by the actuator  56  as illustrated by the solid lines in FIG.  3 . In this state, the seat restraint tension sensing assembly  10  will send a low voltage signal to the controller  70 , causing the controller  70  to determine that a normal or large mass adult is present in the seat  18 . It should be appreciated that the seat restraint system  12  is in a low-tension condition as illustrated by the solid lines in FIG.  3 . It should also be appreciated that the low level spring  62  prevents audible noise due to rattle of the tension sensing assembly  10 . 
     When a child seat (not shown) is placed in the seat  18  and the seat restraint system  12  is buckled, the belt webbing  26  is cinched to pull the child seat tightly into the seat  18 . As the tension is increased in the belt webbing  26 , the contact force on the tongue plate  44  increases. The resistive force of the springs  64  reacts against the increased tension. When the tension in the belt webbing  26  exceeds the predetermined load, the tongue plate  44  moves as the springs  64  are deflected or compressed, thereby moving the magnet  66  closer to the Hall effect sensor  68  in a push-push arrangement. This movement changes the output of the Hall effect sensor  68 , causing the controller  70  to determine that a child seat is present in the seat  18 . It should be appreciated that an audible tone or visual indication may be provided when the tension in the belt webbing  26  is increased above a predetermined level. It should also be appreciated that the low level spring  62  will deflect easily at low loads and, when fully compressed, transfers this load to the high level springs  64  to carry the load as illustrated at point  72  of a force-displacement graph  74  illustrated in FIG.  4 . 
     The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. 
     Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.