Abstract:
A seat belt tension sensor assembly comprising a housing, a slider slidably received within said housing, said slider being configured for movement between a first position and a second position within said housing, a first and second magnet associated with said slider for slidable movement therewith, said first and said second magnets being positioned side by side with opposite polarization, a hall effect device being fixed relative to said housing and protruding between said first and said second magnets when said slider is in said second position, the hall effect device being configured to produce an output signal, said output signal being indicative of a seat belt tension of a seat belt as applied to said sensor assembly, and a biasing member for providing an urging force to said slider, the urging force urging said slider into said first position.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. provisional application No. 60/415,294 filed Oct. 1, 2002 entitled “SEAT BELT TENSION SENSOR ASSEMBLY,” hereby incorporated by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to a safety restraint system, and more particularly to a seat belt tension sensor assembly that can detect the tension and engagement of a seat belt and provide an electrical signal in response thereto.  
         DISCUSSION OF THE BACKGROUND ART  
         [0003]    Vehicles are provided with seat restraints systems such as a seat belts in order to restrain occupants in the seat. The proper engagement and operation of the seat belt is critical to the safety of a driver and his or her occupants.  
           [0004]    Seat belts often incorporate sensors that provide data to other vehicle restraint vehicle systems such as airbags. Deployment of an airbag may partially depend on the information supplied by the sensor in the seat belt, such as a sensor may determine the weight of an object in the seat. There are, however, several problems with detecting seat occupant weight. For example, when a seat occupant puts on the seat belt, the force of cinching the seat belt across ones&#39; lap can cause a seat weight sensor to have false and inaccurate readings. Another example is when a child&#39;s safety seat is cinched tightly in the car seat, it can appear to the sensor that a heavy person is in the seat, which is the wrong reading required for the proper operation of the restraint system. A small passenger, such as a child should cause small tension, therefore the airbag system should deactivate.  
           [0005]    A tension sensor with the ability of sensing the tension in the belt system can be used to more accurately differentiate the size of the vehicle occupant. Additionally, a tension sensor can also be used to indicate that the seat belt is properly tightened and properly engaged or latched.  
           [0006]    International Publication No. WO 02/06092 A1 discloses a seat belt tension sensor assembly, which includes a housing, a pair of magnets, and a Hall effect sensor all arranged to be coupled to an “anchor side” of a seat belt system (not the “buckle” side). The arrangement of the magnets relative to the sensor is not as integrated into the overall seat belt assembly as desired. In addition, the pair of magnets are oriented face to face wherein the direction of magnetization is in the same axis for both magnets, not in an opposite orientation. It is believed that this arrangement limits the useful tension resolving capabilities of the device.  
           [0007]    Accordingly, there is a need for a seat belt tension sensor assembly that minimizes of eliminates one or more of the problems set forth above.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to minimize or eliminate one or more of the problems set forth in the Background. One advantage of the present invention is that allows a higher level of integration of the tension sensor assembly into the seat belt system. According to the invention, a seat belt tension sensor assembly comprises a housing, a slider slidably received within the housing, the slider being configured for movement between a first position and a second position within the housing, a first and second magnet associated with the slider for slidable movement therewith, the first and said second magnets being positioned side by side with opposite polarization, a Hall effect device being fixed relative to the housing and protruding between the first and the second magnets when the slider is in the second position, the Hall effect device being configured to produce an output signal, the output signal being indicative of a seat belt tension of a seat belt as applied to the sensor assembly, and a biasing member for providing an urging force to the slider, the urging force urging the slider into the first position. In addition, the opposite orientation of the pair of magnets increases the magnetic field intensity thereby improving detection, and the accompanying signal-to-noise ratio. Moreover, the arrangement allows better use of the travel distance of the slider (i.e., the useful range over which tension sensing can occur).  
           [0009]    The invention allows detection of a tension force in the seat belt.  
           [0010]    In another aspect, a second sensor is provided to detect when the seat belt has been engaged. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention will now be described by way of example, with reference to the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is an assembly view of the seat belt tension sensor assembly used in accordance with the present invention;  
         [0013]    [0013]FIG. 2 is a simplified, perspective view of the seat belt sensor bottom cover in accordance with the present invention;  
         [0014]    [0014]FIG. 3 is an exploded view of the slider and magnets in accordance with the present invention;  
         [0015]    [0015]FIG. 4 is an exploded view of the seat belt sensor assembly in the unlatched position;  
         [0016]    [0016]FIG. 5 is an exploded view of the seat belt sensor assembly in a first latched position with a first amount of tension applied, namely zero tension;  
         [0017]    [0017]FIG. 6 is an exploded view of the seat belt sensor assembly in a second latched position with a second amount of tension applied;  
         [0018]    [0018]FIG. 7 is an exploded view showing a Hall effect device and magnets in a position corresponding to the second latched position of FIG. 8; and  
         [0019]    [0019]FIG. 8 is an exploded view showing the magnets in a position corresponding to a third latched position and with a third amount of tension applied. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring now to the drawings wherein like reference numerals are used to identify identical components, FIG. 1 an assembly view of the seat belt tension sensor assembly generally indicated by  10 . The seat belt tension sensor assembly  10  includes a bottom cover  12 , a buckle  14 , a slider  16 , spring  18 , a pair of magnets  20   a  and  20   b , hook portions  22  and  22   a , biasing members  24  and  26 , a spring  30 , a release button  32  and an upper cover  34 .  
         [0021]    Bottom cover  12  and upper cover  34  form a housing  40 , which may be constructed out of a lightweight, easily-molded material such as plastic. Bottom cover  12  includes cavity  42  configured in size and shape to receive a printed circuit board (PCB)  44 . PCB  44  may be mounted in cavity  42 , for example, as shown. Printed circuit board  44  includes a Hall effect device  48  or other sensor capable of detecting a magnetic field. Device  48  is arranged so that it protrudes generally in a normal direction outwardly from PCB  44 . PCB  44  also includes a second sensor, such as a switch  50 , configured to detect when a seat belt is engaged, as described in greater detail below. As illustrated, bottom cover  12  also includes I-beam like structures  52 ,  54 , and  56  that retain buckle  14  when slider  16 , hook  22 , 22   a , spring  18  and biasing members  24  and  26  are assembled to buckle  14 .  
         [0022]    With reference to FIG. 2, a simplified, perspective view of the seat belt sensor bottom cover  12  is provided. Bottom cover  12  includes cavity  42  whereby a printed circuit board  44  is housed. Printed circuit board  44  is standard type that allows electrical components to be surface mounted. A Hall effect sensor  48  is mounted with three connections corresponding to power, ground and signal. Additionally, surface mounted switch or sensor  50  is used to detect a latching condition. Latch  88  is shown in the unlatched position. It should be understood that with reference to the orientation of PCB  44  as shown, is exemplary only and not limiting in nature. Many other orientations with respect to the placement of PCB  44  in the bottom cover  12  are achievable and are known to those of ordinary skill in the art and are consistent with the teachings of the present invention, which relate principally to the inventive arrangement. Nonetheless, the following may be taken as a non-limiting illustrated embodiment.  
         [0023]    Referring again to FIG. 1, buckle  14  is generally rectangular shaped adapted to fit inside housing  40  and includes a generally planar base  61 . Buckle  14  provides the means for receiving the assembly of slider  16  and hook portions  22 ,  22   a . Buckle  14 , as shown, also includes a pair of J-shaped extensions  60 ,  62 . Buckle  14  also includes a centrally-disposed opening  63  defined in-part by a pair of opposing ledges  64  and  66 . Opening  63  has a preselected lateral width, whose function will be described in greater detail below. Buckle  14  further includes a pair of side rails  68   1  and  68   2  extending generally normally from base  61 , and having a preselected lateral width between inner surfaces thereof. Buckle  14  further includes elongated slots  69   1  and  69   2  which are formed into either side of side rails  68   1  and  68   2 . The elongated slots  69   1  and  69   2  function to retain hook  22   a  which provides support for release button  32 . When release button  32 , in latched condition, is pushed, button  32  pushes hook  22   a  and allows hook  22   a  to spin up releasing latch  88 .  
         [0024]    [0024]FIG. 1 shows slider  16  from the top. Slider  16  is provided to carry a magnetic array responsive to engagement with and partial and full insertion of a seat belt tongue (best shown in FIG. 2). Slider  16  includes a pair of tabs  70 , and  72 . Slider  16  further includes cavities  74 ,  76  which are configured to receive magnets  20   a  and  20   b , respectively, that define the magnetic array described above. The lateral (side-to-side) width of the cavities  74 ,  76  is selected to be no greater than the predetermined width of opening  63 . This allows the cavities to be placed “down” into opening  63  of buckle  14  during assembly. Tabs  70 ,  72  have a side-to-side lateral width that is no greater than the preselected width between the side rails  68   1 ,  68   2 . Through the foregoing, tabs  70 ,  72  can slide on top of ledges  64 ,  66 .  
         [0025]    [0025]FIG. 3 is an exploded, bottom view of slider  16  and its accommodation of magnets  20   a  and  20   b . Slider  16  comprises two cavities  74  and  76  that house magnets  20   a  and  20   b  respectively. Distance -y- indicates the width of cavities  74  and  76  in order to fit through cavity  63  of buckle  14 . The forward and aft surfaces  73 F and  73 A respectively, of cavities  74 ,  76  cooperate with the forward and aft edges of opening  63  to provide mechanical stop features, thereby defining the longitudinal travel of slider  16 . Magnets  20   a  and  20   b  are orientated side by side with opposite polarization (direction of magnetization on two parallel axis). In other words, magnets  20   a  and  20   b  are configured whereby the maximum magnetic field is created.  
         [0026]    The design of cavities  74  and  76  provide that magnets  20   a  and  20   b  are orientated in a special array whereby a higher magnetic field intensity is created relative to the known art. More specifically, magnets  20   a  and  20   b  are placed side by side wherein the north side of magnet  20   a  is facing the south side of magnet  20   b . The array of magnets  20   a  and  20   b  provide the maximum positive field at  75  and the maximum negative field at axis  77 . In addition, the opposite orientation of the pair of magnets increases the magnetic field intensity thereby improving detection, and the accompanying signal-to-noise ratio. Moreover, the arrangement allows better use of the travel distance of the slider (i.e., the useful range over which tension sensing can occur).  
         [0027]    The location of magnets  20   a  and  20   b  when assembled allow the Hall effect device  48  to protrude between magnets when slider  16  moves away from a first position (FIG. 4) where little or no tension is applied (since the tongue is unlatched) into one of a plurality of second positions (FIGS.  5 - 8 ). The second position(s) may correspond to tension levels between zero (latched but no tension), to increasing levels of tension as the seat belt is cinched. During travel of slider  16 , the Hall effect device  48  remains stationary in the bottom cover  12 . The Hall effect device  48  will sense the strength of the magnetic field of the approaching magnets  20   a  and  20   b  as the magnets travel toward the Hall effect device  48  and corresponding to the strength of the magnetic field, the Hall effect device  48  will determine the measurement of the tension, and will produce a signal that will determine whether or not to suppress any safety-related items  82  such as a hyper-tensioner, airbag, or pre-tensioner, etc. When the tension force as detected by the present invention exceeds the predetermined threshold, the system may be configured to suppress a passenger air bag.  
         [0028]    In an exemplary embodiment, the Vcc of the Hall effect device  48  is 5 volts +/−0.5 volts DC. The voltage with no magnetic field present will be approximately 2.5 v. As the magnets are brought into the proximity of the hall effect device, the voltage will increase to near Vcc or decrease to near ground, depending on the polarity of the magnet. Accordingly, as the voltage increases or decreases, so does the tension of the seat belt. Of course, Vcc may have values greater than and less than 5 volts.  
         [0029]    With continued reference to FIG. 1, slots  60  and  62  allow hook  22  to hinge and thereby allow movement of the hook  22  when a latch (not shown) of the seat belt is inserted into assembly  10 . Biasing members  24  and  26  provide biasing force and are held into place by a pair of tabs  40  and  42  of hook  22  and a pair of hooks  65   1  and  65   2  (not shown) located on either side of buckle  14 . Biasing members  24  and  26  can be of either compression or tension type. Biasing members  24  and  26  provide the urging force that slider  16  must overcome in order to move from a first position to a second position (as described above).  
         [0030]    In an exemplary embodiment, the biasing force of the members  24  and  26  is overcome when a force of 5 to 15 pounds is applied therefore causing slider  16  to move into the second position (FIGS.  5 - 8 ). Of course, and as such applications may require, the biasing force of members  24  and  26  to become overcome may vary. Accordingly, and when the urging force of members  24  and  26  are overcome, slider  16  travels towards the Hall effect device  48  and magnets  20   a  and  20   b  create a magnetic field around the Hall effect device  48  causing a resulting signal to be sent through a plurality of wires  78  and sent to the control unit  80 .  
         [0031]    [0031]FIG. 1 also shows hook  22   a  including wing like structures  23   1  and  23   2  which protrude out from elongated slots  69   1  and  69   2  (when assembled) and glide in a back and forth like manner when release button  32  is activated. Spring  30  is placed between hook  22   a  on tab  25  and stub  86  of hook  22  which allows movement of the release button  32 .  
         [0032]    Once release button  32  is in place, upper cover  34  snaps over bottom cover  12  and the integral seat belt sensor assembly is complete. Accordingly, the seat belt sensor assembly  10  is easily assembled.  
         [0033]    Referring now to FIG. 4, an exploded view of the seat belt sensor assembly  10  in an unlatched position is provided. When latch  88  is on the outside of sensor assembly, hook  22 , hinged at buckle  14 , is in the upright position as shown. The unlatched position allows slider  16   1 , accommodating magnets  20   a  and  20   b , to be urged into the first position through spring  18 . When the slider  16   1  is at the first position, magnets  20   a  and  20   b  are located over switch  50  of PCB  44 . Switch  50  is capable of reading the magnet field created by magnets  20   a  and  20   b  and registers a signal corresponding to the position. This signal may provide information to control unit  80  warning driver to latch seat belt via light  87  (FIG. 1), for example, when the vehicle is in use.  
         [0034]    [0034]FIG. 5 represents an exploded view of the seat belt sensor assembly  10  in the latched position, with zero tension. When latch  88  is inside sensor assembly  10 , hook  22  hinged at buckle  14  is in the closed position as shown in the upper part of FIG. 5. The latched position causes slider at a second position  16   2  specifically the magnets  20   a  and  20   b  thereof, to be substantially aligned with sensor  48 . Measurement X 1  is arbitrarily selected for purposes of illustration to place magnets  20   a  and  20   b  at a certain distance from the front edge of Hall effect device  48 . This distance registers a certain magnetic field strength whereby Hall effect sensor  48  produces an output signal accordingly. Magnets  20   a  and  20   b  respectively travel along axes  51   a  and  51   b . Axes  51   a  and  51   b  are offset one from another. The array of magnets  20   a  and  20   b  cooperate to provide a higher magnetic field intensity whereby the output signal is improved and the signal to noise ratio is improved. The magnetic array arrangement is also more efficient with respect to resolving varying tension levels inasmuch as it provides a higher percentage of effective use of travel compared to the total travel of the slider. This will be shown as FIGS.  6 - 8  are described, showing how changes in tension translate into an offset distance, which in turn changes the position of the sensor  48  in the magnetic field created by magnets  20   a  and  20   b . Resulting changes in the detected field strength by sensor  48  will vary the output signal (e.g., a voltage level).  
         [0035]    [0035]FIG. 6 shows tension is applied to the seat belt (not shown). Latch  88  moves in the direction of the arrow thereby creating a force necessary to move slider away from position  16   2  toward position  16   3 .  
         [0036]    [0036]FIG. 7 shows slider in position  16   2 . Distance X 2  places magnets  20   a  and  20   b , residing in slider at position  16   3 , at a certain distance from the front edge of Hall effect device  48 . This distance X 2  correspond to a certain tension applied via latch  88 . The relative positions of sensor  48  and magnets  20   a ,  20   b  register a certain magnetic field strength whereby Hall effect sensor  48  produces an output signal that corresponds to the intensity of the magnetic field created by the location of magnets  20   a  and  20   b.    
         [0037]    If additional tension is applied, FIG. 8, distance X 3  places magnets  20   a  and  20   b , residing in slider  16   4  at a distance defined by X 3  from the front edge of Hall effect device  48 .  
         [0038]    Many tension levels can be created when latch  88  is pulled and tightened, therefore measurements of X 2  and X 3  illustrate but a few of the plurality of possible tension measurements that may occur when operating the seat belt sensor tension assembly.  
         [0039]    The magnets traverse a distance with respect to the tension applied to the slider. More specifically, if the magnets travel a total distance of 8 mm with the slider, approximately 7 mm of data is captured by the Hall effect device. Additionally, if the magnets travel 5 mm total with the slider, approximately 4 mm of data is captured by the Hall effect device. Therefore the distance of the travel as compared to the total travel of the slider is more effectively translated into useful information by the Hall effect device.  
         [0040]    It will be understood that the above description is merely exemplary rather than limiting in nature, the invention being limited only by the appended claims. Various modifications and changes may be made thereto by one of ordinary skill in the art, which embody the principals of the invention and fall within the spirit and scope thereof.