Abstract:
A tension sensing switch assembly for a seat restraint system in a vehicle includes a housing for operative connection to the seat restraint system and a spring at least partially disposed in the housing for operatively cooperating with vehicle structure. The tension sensing switch assembly also includes a switch disposed in the housing and cooperable with the spring to indicate a first tension level and a second tension level in the seat restraint system when the spring is deflected.

Description:
TECHNICAL FIELD 
     The present invention relates generally to seat restraint systems for vehicles and, more particularly, to a tension sensing switch 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 on inflatable restraint 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 restraint. 
     Although the above seat restraint system has worked, it is desirable to provide a switch for sensing tension in a seat restraint system of a vehicle. It is also desirable to provide a switch 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 a switch for a seat restraint system in a vehicle that provides information used in determining inflatable restraint deployment levels. 
     SUMMARY OF THE INVENTION 
     It is, therefore, one object of the present invention to provide a switch assembly for sensing tension in a seat restraint system of a vehicle. 
     It is another object of the present invention to provide a dual resistance switch for sensing tension in a seat restraint system of a vehicle. 
     To achieve the foregoing objects, the present invention is a tension sensing switch assembly for a seat restraint system in a vehicle includes a housing for operative connection to the seat restraint system and a spring at least partially disposed in the housing for operatively cooperating with vehicle structure. The tension sensing switch assembly also includes a switch disposed in the housing and cooperable with the spring to indicate a first tension level and a second tension level in the seat restraint system when the spring is deflected. 
     One advantage of the present invention is that a tension sensing switch assembly is provided for a seat restraint system in a vehicle. Another advantage of the present invention is that the tension sensing switch 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 switch assembly has a dual resistance switch that is diagnosable. Still another advantage of the present invention is that the tension sensing switch assembly provides information useful in determining deployment of an inflatable restraint system. 
     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 switch 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 switch assembly of FIG. 1 illustrating a low tension condition. 
     FIG. 3 is a view similar to FIG. 2 illustrating the tension sensing switch assembly in a high tension condition. 
     FIG. 4 is a schematic view of a circuit for the tension sensing switch 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 switch 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  and the tension sensing switch assembly  10  interconnected by suitable means such as belt webbing  26 . The tension sensing switch assembly  10  is connected to the vehicle structure  20  in a manner to be described. It should be appreciated that the latch plate has an aperture extending therethrough and is engageable and disengageable with the buckle assembly  24 . It should be appreciated that, except for the tension sensing switch 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 switch assembly  10 , according to the present invention, includes an anchor plate  28  connected to vehicle structure by suitable means such as an anchor bolt  30 . The anchor bolt  30  has a head portion  32  extending radially and a shaft portion  34  extending axially from the head portion  32 . The shaft portion  34  is generally cylindrical in shape and the head portion  32  is generally circular in shape. The head portion  32  has a diameter greater than a diameter of the shaft portion  34 . The shaft portion  34  extends through an aperture  44  to be described in the anchor plate  28  and the vehicle structure  20  and is secured in place by a nut (not shown). It should be appreciated that the anchor bolt  30  is conventional and known in the art. 
     The anchor plate  28  has a base portion  36  and a tongue portion  38  extending axially and upwardly from the base portion  36 . The base portion  36  has a first portion  40  that is generally rectangular in shape. The base portion  36  also has a second portion  42  extending axially from the base portion  36 . The second portion  42  has a width less than the first portion  40 . The second portion  42  has an elongated aperture or slot  44  extending therethrough and axially to receive the anchor bolt  30 . It should be appreciated that the second portion  42  of the base portion  36  is disposed between the head portion  32  of the anchor bolt  30  and the vehicle structure  20 . It should also be appreciated that the anchor plate  28  is movable longitudinally relative to the anchor bolt  30 . 
     The tongue portion  38  is generally rectangular in shape and has a width the same as the second portion  42  of the base portion  36 . The tongue portion  38  includes an aperture  46  extending therethrough. The aperture  46  is generally rectangular in shape and receives one end of the belt webbing  26 . The base portion  36  and tongue portion  38  are made of a metal material and formed as a monolithic structure being integral, unitary and formed as one-piece. 
     The tension sensing switch assembly  10  also includes a housing  48  disposed about and enclosing the first portion  40  of the base portion  36  of the anchor plate  28 . The housing  48  has a cavity  49  with an aperture  50  at a forward end for a function to be described. The housing  48  has a pair of posts  52  disposed in the cavity  49  and being laterally spaced and extending upwardly adjacent the aperture  50 . The housing  48  is generally rectangular in shape and made of a rigid material such as plastic. It should be appreciated that only one half of the housing  48  is illustrated in FIGS. 2 and 3. 
     The tension sensing switch assembly  10  includes a spring  54  at least partially disposed in the cavity  49  of the housing  48 . The spring  52  is of a leaf type having a first end  56  disposed about one of the posts  52  in the housing  48  and a second end  58  disposed about the other post  52  in the housing  48 . The spring  54  has a bowed or arcuate shape to cooperate with the shaft portion  34  of the anchor bolt  30 . The spring  54  is made of a metal material. The spring  52  is tuned to a predetermined force for comfort. The spring  54  may also be of a coil spring type. It should be appreciated that the anchor bolt  30  deflects the spring  54  when the anchor plate  28  is moved relative to the anchor bolt  30 . 
     Referring to FIGS. 2 through 4, the tension sensing switch assembly  10  includes an electrical circuit, generally indicated at  60 , for diagnosing usage of the seat restraint system  12 . The electrical circuit  60  includes a switch  62  for cooperating with the spring  54 . The switch  62  is diagnosable and has two positions. Preferably, the switch  62  is of a micro type that is actuated by an arm or bail  64  pivotally connected to the switch  62 . The switch  62  may also be of another suitable type such as a reed or Hall effect type. The bail  64  will move or pivot when the spring  54  engages the bail  64 . The spring  54  moves the bail  64  from an open or first position with the switch  62  illustrated in FIG. 2 to a closed or second position illustrated in FIG.  3 . It should be appreciated that the position of the bail  64  relative to the switch  62  changes the state of the switch  62 , giving a different output current from the switch  46 . It should also be appreciated that the bail  64  is preloaded by a spring (not shown) to return the bail  64  to the first position. 
     The circuit  60  also includes a first resistor  66  interconnecting one end of the switch  62  and ground  68 . The first resistor  66  has a predetermined value such as one hundred ohms (100 Ω). The circuit  60  includes a second resistor  70  connected in parallel with the switch  46  with one end interconnecting the switch  62  and the first resistor  66  and another end connected to a source of power  72  such as a controller (not shown) of the vehicle  14 . The second resistor  70  has a predetermined value such as three hundred ohms (300 Ω). The circuit  60  is mounted on a circuit board (not shown) connected to the housing  48  and is potted and connected by electrical leads or wires to the source of power  72  and ground  68 . 
     In operation of the tension sensing switch assembly  10 , the occupant buckles the seat restraint system  12  and the tension in the belt webbing  26  is lower than a predetermined load required to deflect the spring  54  as illustrated in FIG.  2 . In this state, the tension sensing switch assembly  10  will send an open signal to the controller. Current from the source of power  72  flows through the second resistor  70  and first resistor  66  to ground  68 . The flow of current through the both resistors  66  and  70  causes the controller to determine that a normal or large mass adult is present in the seat  18 . It should be appreciated that the anchor plate  28  of the tension sensing switch assembly  10  is spring loaded to an initial position by the spring  54 . 
     When a child seat (not shown) is placed in the seat  18  and the seat restraint system  12  is buckled, the seat belt webbing  26  is cinched to pull the child set tightly in to the seat  18 . The tension in the seat belt webbing  26  is above the predetermined level to deflect the spring  54  as illustrated in FIG.  3 . In this state, the deflection of the spring  54  causes the switch  62  to change states, sending a closed contact signal to the controller. Current from the source of power  72  flows through the switch  62  and first resistor  66  to ground  68 . The flow of current through only one resistor  66  causes the controller to determine that a child seat is present in the seat  18 . Also, if the controller receives no signal from the switch  62 , the controller determines that there is an unplugged wiring connector (not shown) to the seat restraint system  12 . Further, if the controller receives a signal from the switch  62  approximately equal to the current from the source of power  72 , the controller determines that there is a shorted wiring connector to the seat restraint system  12 . It should be appreciated that the when the belt webbing  26  is tensioned past a predetermined force, the spring  54  will deflect or travel approximately three millimeters (3.0 mm), causing the switch  62  to change states. 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 the predetermined level. 
     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.