Abstract:
An occupant presence and child seat detection system includes several sensors to assist a capacitance based occupant presence detection system in distinguishing an occupant from a child seat on a wet vehicle seat. In one configuration, capacitance on the seating surface and wetness of the seating surface are measured. The determination of the presence of an occupant is based upon the measured capacitance and the measured wetness.

Description:
[0001]     This application claims priority to U.S. Provisional Application Ser. No. 60/491,114, filed Jul. 30, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to an occupant presence detection and classification system.  
         [0003]     One difficulty with modern day safety restraint systems is the possibility of injury to an infant seated in a child/booster seat due to airbag deployment. It is therefore desirable to have the ability to disable the airbag when a child/booster seat is present. To achieve this, a manual override switch may be used to deactivate the airbag; however such a system is reliant on the operator of the vehicle&#39;s memory to manually disable the airbag. The preferred solution is therefore a mechanism that can determine the presence of a child/booster seat and send a signal to the restraints control module (RCM) to disable the airbag automatically.  
         [0004]     Another vehicle safety application that is relevant to this invention is “after crash notification.” When a crash takes place it is quite crucial that proper medical care is identified and transported to the location of the crash so that crash victims are provided with the required medical attention. In order for health authorities to provide such service they need to be immediately informed of the number and age-class of occupants involved in the crash. To achieve this goal a mechanism is needed to identify whether a seat is occupied or not, and to identify whether the occupant is a child in a child-seat/booster or an adult, if the seat is occupied.  
         [0005]     Capacitance-based occupant presence detection systems can determine the presence of an occupant on a vehicle seat by measuring the capacitance (or permittivity) on the seating surface. A human will have a higher capacitance than an empty seat or a child seat. However, a wet seat with a child seat could produce a sufficiently high capacitance reading to indicate the presence of an occupant.  
       SUMMARY OF THE INVENTION  
       [0006]     An occupant presence and child seat detection system includes several sensors and configurations to assist a capacitance based occupant presence detection system in distinguishing an occupant from a child seat, in particular, a child seat on a wet vehicle seat. In some disclosed configurations, capacitance on the seating surface and wetness of the seating surface are measured. The determination of the presence of an occupant is based upon the measured capacitance and the measured wetness.  
         [0007]     In one embodiment, if the wetness exceeds a threshold, then the system checks the tension measured by a seat belt tension sensor. If the seat belt tension is above a threshold, it is determined that a child seat is present. Otherwise, an occupant is present on the seat.  
         [0008]     In another embodiment, the capacitance measurement is adjusted based upon a level of wetness measured on the seat. In that way, the capacitance that is due to the seat wetness can be ignored or subtracted out. Then, the system can evaluate the capacitance signal to distinguish between an occupant and a child seat. Other embodiments are disclosed as well.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0010]      FIG. 1  is a schematic illustration of the presence detection system in a vehicle.  
         [0011]      FIG. 2  is a first flowchart of the system of  FIG. 1 .  
         [0012]      FIG. 3  is an alternate flowchart of the system of  FIG. 1  using the capacitance, seatbelt, and belt tension sensors.  
         [0013]      FIG. 4  is a third flowchart of the system of  FIG. 1 , using capacitance, and belt tension sensors.  
         [0014]      FIG. 5  is a fourth flowchart of the system of  FIG. 1  using the capacitance and wetness sensors. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     An occupant and child seat detection device  20  according to the present invention is shown in  FIG. 1  installed in a vehicle  22  to detect the presence of an occupant in a vehicle seat  26 . The seat includes a seat back  28  and a seat base  30 . A seat belt  32  is attached to the seat  26  with a seat belt fastened sensor  34 , which determines whether the seat belt  32  is fastened, and a seat belt tension sensor  38 , which measures the tension in the seat belt  32 .  
         [0016]     Installed in the seat base  30  are a capacitive presence sensor  40  and a wetness sensor  42 . The presence sensor  40  works generally by measuring the capacitance of an area on the seat base  30 . The capacitance will be altered based upon the presence of a human occupant, because humans are mostly water. Based upon the capacitance measured on the seat base  30 , the presence or absence of an occupant is determined. A suitable presence sensor  40  is disclosed in co-pending U.S. Ser. No. 10/319,431, filed Dec. 13, 2002 entitled, “Occupant Presence Detection Device,” which is hereby incorporated by reference in its entirety.  
         [0017]     The wetness sensor  42  or moisture sensor may be a conductivity sensor measuring the conductivity of a portion of the seat base  30  to determine a level of wetness. The wetness measurement is combined with the capacitance measurement to construct a mapping for the various possible wetness-capacitance conditions that may occur in a seat under a range of seat wetness, occupants, and child seats. This mapping is used to detect occupants and, in addition, to sense if the seat  26  has become wet.  
         [0018]     The presence sensor  40 , wetness sensor  42 , tension sensor  38  and fastened sensor  34  send their data to a CPU  50 . The CPU  50 , in the manner described below, uses the data from the sensors  40 ,  42  to determine whether an occupant is present on the seat  26  or whether there is a child seat  46  (occupied or not) on the seat  26 . The system  20  further includes a crash detector  52 , such as an accelerometer, and an active restraint  54 , such as an airbag, associated with the seat  26 . Based upon the determination by the CPU  50  whether there is an occupant in the seat  26 , the CPU  50  determines whether to active the active restraint  54  in the event of a crash, as detected by the crash detector  52 .  
         [0019]     Referring to flowchart in  FIG. 2  to describe the operation of the schematic of  FIG. 1 , in step  70 , the presence sensor  40  acquires a capacitance signal that reflects a potential human presence. The capacitance signal is processed by a signal processing algorithm in step  72  to filter out noise and to calibrate the signal to achieve robust and stable measurement. In step  74 , the CPU  50  processes the capacitance signal to determine a human presence that is at least the size of a 5th percentile female (103 lbs-113 lbs). Based upon the capacitance measured by the presence sensor  40 , a preliminary determination of whether a person occupies the seat  26  is made in step  76 .  
         [0020]     If the seat is not wet, as determined by the wetness sensor  42  in step  78 , then the seat  26  is determined to be occupied and the active restraint  54  is enabled. If the seat is wet, as determined by the wetness sensor  42  in step  78 , then a determination of whether an occupant is present is made in step  80  based upon the tension measured in the seat belt  32  by the tension sensor  38 . If the seat belt tension is over a threshold (ten pounds, for example), then the determination is made that there is a child seat  46  on the seat  26 , because a human occupant would not tolerate belt tension over the selected threshold. If the seat belt tension is under the threshold, then the determination is made that there is an occupant on the seat  26  and the active restraint  54  is enabled.  
         [0021]     If the presence sensor  40  determines that the seat  26  is not occupied in step  76 , then in step  82 , the fastened sensor  34  determines whether the seat belt  32  is fastened. If it is, then a child seat  46  is determined to be present. If it is not, then there is either an unbuckled child seat or the seat  26  is empty.  
         [0022]      FIG. 3  illustrates the operation of an alternate embodiment, without the wetness sensor  42  of  FIG. 1 . In this case, it is determined that an occupant is present if the presence sensor  40  so indicates in step  76  as long as the belt tension is below the threshold, as determined in step  80   a.    
         [0023]      FIG. 4  illustrates the operation of another alternate embodiment, without the wetness sensor  42  and without the fastened sensor  34  of  FIG. 1 . In this embodiment, in step  76   a  it is determined that there is a child seat or an empty seat if the presence sensor  40  does not detect a sufficient capacitance on the seat base  30 .  
         [0024]      FIG. 5  illustrates an alternate operation of the embodiment shown in  FIG. 1 , without the fastened sensor  34 . In this embodiment, it is first determined whether the seat base  30  is wet in step  86 . If so, then the capacitance reading from the presence sensor  40  is adjusted in step  88  and analyzed (such as by comparison to a threshold) in step  90  to determine a presence of an occupant in step  92 . If the seat  26  is determined not to be wet in step  86 , then the original capacitance signal from the presence sensor  40  is analyzed in step  94  to determine the presence of an occupant versus an empty seat or a child seat.  
         [0025]     In accordance with the provisions of the patent statutes and jurisprudence, exemplary configurations described above are considered to represent a preferred embodiment of the invention. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope. For example, several sensors have been described, each of which can be provided in several different forms that provide the same or similar function. Also, as explained above, different combinations of such sensors could be utilized within the scope of the present invention.