Abstract:
The presence of a rear-facing infant seat on a motor vehicle seat is reliably and cost-effectively detected based on the buckle state and tension of the seat belt, and the position of the seat belt relative to the seat bight region where the seat bottom and back cushions meet. These seat belt parameters are measured and applied to a predefined decision matrix to detect the presence of a rear-facing infant seat.

Description:
TECHNICAL FIELD 
   The present invention relates to characterizing the occupant of a motor vehicle seat for purposes of allowing or suppressing air bag deployment, and more particularly to detecting the presence of a rear-facing infant seat on the vehicle seat. 
   BACKGROUND OF THE INVENTION 
   A variety of sensor systems have been developed for characterizing the occupant of a motor vehicle seat to determine whether to allow or suppress air bag deployment. A recurring requirement in this regard is the ability to reliably detect the presence of a rear-facing infant seat (RFIS), since nearly all vehicle manufacturers require that at least the front air bag be disabled in the case of a RFIS due to the proximity of the infant&#39;s head to the point of air bag deployment. In the past, the presence of a RFIS has been detected by measuring the occupant&#39;s weight distribution on the seat, by the state of the seat belt buckle and the seat belt tension, and/or by measuring the proximity or presence of the occupant relative to the point of deployment or the seat back or the passenger compartment ceiling. See, for example, Fu U.S. Pat. No. 6,024,378, Stanley U.S. Pat. No. 6,220,627, Patterson et al. U.S. Pat. No. 6,605,877 and Basir et al. U.S. Pat. No. 6,678,600. In some systems, the RFIS must be specially equipped with magnets or bar codes that are sensed by Hall sensors or scanners; see, for example, Meister et al. U.S. Pat. Nos. 5,678,854 and 5,570,903. What is needed is a way of simply and reliably detecting the presence of a RFIS without requiring the operator to utilize a specially equipped infant seat. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an improved method and apparatus for reliably and cost-effectively detecting the presence of a RFIS on a motor vehicle seat based on the buckle state and tension of the seat belt, and the position of the seat belt relative to the bight region where the seat back and bottom cushions meet. These seat belt parameters are measured and applied to a predefined decision matrix to detect the presence of a RFIS. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of a vehicle seat, a seat belt, a passive occupant detection system controller, and an air bag control module according to this invention; 
       FIG. 2  is a flow diagram representing a software routine executed by the passive occupant detection system controller of  FIG. 1  according to this invention; and 
       FIG. 3  is a chart depicting a decision matrix utilized by the software routine of  FIG. 2  according to this invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , the vehicle seat  10  is supported on a frame  12 , and includes foam cushions  14  and  16  on the seat bottom and back. The seat  10  is equipped with a conventional shoulder/lap seat belt  18  anchored to the vehicle floor (not shown) and B-pillar  20 . In use, the belt  18  is drawn around an occupant or through the frame of a child or infant seat, and a clip  22  slidably mounted on the belt  18  is inserted into the buckle  24  to fasten the belt  18  in place. A retractor assembly (not shown) mounted in the B-pillar  20  maintains a desired tension on the belt  18 , and locks the belt  18  in place when the vehicle experiences significant deceleration. 
   According to this invention, the presence of a RFIS on the seat cushion  14  is detected based on the operating state and tension of the seat belt  18 , and the position of the seat belt  18  relative to a bight region  26  where the seat bottom and back cushions  14 ,  16  meet. 
   The operating state of the seat belt  18 —i.e., buckled or un-buckled—is detected by a switch within the buckle  24  that is closes or opens on insertion of the clip  22  into the buckle  24 . One side of the switch is connected to an electrical ground or power terminal, while the other side is coupled to the conductor  28  to provide an electrical signal (STATE) indicative of the belt state. 
   The seat belt tension is detected by a belt tension sensor  30  that may be located in the B-pillar  20  as shown, near the floor on the outboard side of seat  10 , or in any other convenient location. The tension sensor  30  may be constructed as disclosed, for example, in the aforementioned U.S. Pat. No. 6,605,877 to Patterson et al., incorporated herein by reference, and produces an electrical signal (TENSION) on line  32  indicative of the seat belt tension. The proximity of the seat belt  18  relative to the bight region  26  is detected magnetically using a seat belt magnetic strip  34   a  and a first Hall Effect seat sensor  36 . The first Hall Effect sensor  36  is disposed in the seat back or bottom cushion  14 ,  16  in the vicinity of the central portion of the bight region  26 , and the magnetic strip  34   a  is embedded in the fabric of the seat belt  18 . When the seat belt  18  is in proximity to the central portion of the bight region  26  as shown in  FIG. 1 , the strip  34   a  is magnetically coupled with the sensor  36 , and an electrical signal (POS 1 ) produced by sensor  36  on line  38  indicates that the seat belt  18  is near the bight region  26 ; in other positions of the seat belt  18 , there is only weak magnetic coupling between the strip  34   a  and the sensor  36 , and the POS 1  signal indicates that the seat belt  18  is disposed away from the bight region  26 . 
   Optionally, a second Hall Effect Sensor  40  is disposed in the middle of the seat back cushion  16 , and detects proximity of the seat belt  18  to the seat back cushion  16  by virtue of a magnetic strip  34   b  embedded in the fabric of the seat belt  18 . When the seat belt  18  is in proximity to the back cushion  14  as shown in  FIG. 1 , the strip  34   a  is magnetically coupled with the sensor  40 , and an electrical signal (POS 2 ) produced by sensor  40  on line  42  indicates that the seat belt  18  is close to the back cushion  16 ; in other positions of the seat belt  18 , there is only weak magnetic coupling between the strip  34   b  and the sensor  40 , and the POS 2  signal indicates that the seat belt  18  is disposed away from the back cushion  16 . The magnetic strips  34   a  and  34   b  may be constituted by individual lap and shoulder portions as shown, or by a single continuous strip of magnetic material if desired. In any event, portions of the seat belt  18  containing the magnetic strips  34   a  and  34   b  will be in proximity to the first and second sensors  34  and  40  when a RFIS is present, much the same as when the seat belt  18  is buckled with an empty seat as depicted in  FIG. 1 ; and no part of the seat belt  18  will be in proximity to the sensors  34  or  40  when the seat belt  18  is used to properly secure a normally seated person or a forward-facing infant seat. 
   The electrical signals on lines  28 ,  32  and  38  (and optionally, line  42 ) are provided as inputs to a passive occupant detection system electronic control unit (PODS ECU)  50 , which in turn, is coupled to an airbag control module (ACM)  52  via bi-directional communication bus  54 . The ACM  52  may be conventional in nature, and operates to deploy one or more airbags or other restraint devices (not shown) for vehicle occupant protection based on acceleration data and occupant characterization data obtained from PODS ECU  50 . In general, ACM  52  deploys the restraints if the acceleration signals indicate the occurrence of a severe crash, unless the PODS ECU  50  indicates that a RFIS is present. Also, ACM  52  communicates the suppression status and driver warnings to a driver display device  56 . 
   In general, the PODS ECU  50  characterizes the inputs on lines  28 ,  32  and  38  (and optionally, line  42 ), and applies them to a decision matrix such as depicted by the chart of  FIG. 3  to determine if a RFIS is present. The flow diagram of  FIG. 2  represents a software routine that is periodically executed by the PODS ECU  50  according to this invention. The block  60  is first executed to read the inputs including the seat belt tension (TENSION), the seat belt status (STATUS), and the seat belt position (POS 1 ). As indicated above and explained below, the inputs may optionally include the position signal POS 2 . The block  62  then characterizes the analog inputs (TENSION and POS 1 ) by comparing them to various predefined thresholds, and applies the inputs to the decision matrix of  FIG. 3 . In the illustrated embodiment, TENSION is characterized as being either HIGH (above a tension threshold) or LOW (below the tension threshold), and the position POS 1  of the seat belt relative to the bight area of the seat is characterized as being either NEAR (above a proximity threshold) or FAR (below a proximity threshold). The decision matrix of  FIG. 3  provides an RFIS PRESENT output (yes or no) and a driver warning output, and the block  64  causes the PODS ECU  50  to supply the outputs to ACM  52 . The ACM  52  allows or suppresses air bag deployment based on the supplied outputs, and visually communicates the occupant status and any driver warnings via display  56 . 
   Referring to  FIG. 3 , the decision matrix of the illustrated embodiment comprehends the eight possible output combinations of TENSION, STATUS and POS 1 . States  1  and  2  result in a YES condition of the RFIS PRESENT output; in each case, STATUS=BUCKLED and POS 1 =NEAR. In State  1 , TENSION=HIGH, and no driver warning is produced; in State  2 , TENSION=LOW, and a driver warning (WARNING 1 ) is produced to indicate that the seat belt tension should be increased in order to properly restrain the infant seat. State  1  can also occur when the seat  10  is occupied by a normally seated person while the seat belt  18  buckled but positioned behind the occupant; accordingly, the driver warning (WARNING 1 ) should be broad enough to encompass either an improperly tensioned infant seat or an improperly restrained but normally seated person. The other states ( 3 – 8 ) result in a NO condition of the RFIS PRESENT output, because STATUS=UNBUCKLED and/or POS 1 =FAR. 
   In systems where the seat belt position signal POS 2  is provided as an additional input, the decision matrix may detect additional conditions of improper seat belt usage by a normally seated person. For example, an occupant may be utilizing the lap portion of the seat belt  28  properly, with the shoulder portion of the seat belt  28  improperly disposed between the occupant and the seat back cushion  16 ; in this case, POS 1 =FAR but POS 2 =NEAR. If this combination of position inputs occurs while STATUS=BUCKLED, the PODS ECU  50  may issue a suitable driver warning. Another improper condition can also occur when an occupant is improperly sitting on the lap portion of the seat belt  28 , with the shoulder portion of the seat belt  28  properly positioned in front of the torso; in this case, POS 1 =NEAR but POS 2 =FAR. This has the benefit of distinguishing between an improperly tensioned infant seat and a normally seated but improperly belted occupant. 
   In summary, the present invention provides a simple and cost-effective way of reliably detecting the presence of a RFIS without requiring special equipment on the infant seat. The addition of the optional seat back belt proximity sensor provides further occupant detection capability, and the ability to distinguish between an improperly tensioned infant seat and a normally seated but improperly belted occupant. 
   While the present invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the system may include additional sensors if desired, or a proximity sensor other than a Hall Effect sensor, and so on. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.