Abstract:
An improved occupant detection system and method includes a fluid-filled polymeric seat cushion bladder defining multiple fluid-filled chambers corresponding to different areas of the seat cushion, with no fluid flow between such chambers. Fluid pressures in the various individual chambers are detected and processed to develop a weight estimation that is compensated for occupant position. The chambers are configured to detect occupant weight in at least forward, rearward, inboard and outboard regions of the bottom seat cushion. When the detected pressures are unevenly distributed and the pressure in the forward, rearward, inboard or outboard regions of the seat exceeds the average pressure by at least a predetermined amount, a composite pressure indicative of occupant weight is adjusted in a direction to bias the suppression status in favor of allowing restraint deployment, unless the occupant is forwardly positioned on a seat that is also forwardly positioned.

Description:
TECHNICAL FIELD 
     This invention relates to a system and method of detecting the weight and position of an occupant of a motor vehicle for purposes of allowing or suppressing air bag deployment. 
     BACKGROUND OF THE INVENTION 
     Vehicle occupant detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and how forcefully, to deploy the restraint. One fundamental parameter in this regard is the weight of the occupant, as weight may be used as a criterion to distinguish between an adult and an infant or small child. 
     One prior weight estimation technique is to install an array of variable resistance pressure sensitive elements in the seat, and to sum the individual pressures to determine occupant weight. A restraint system based on this technique is shown and described in the U.S. Pat. No. 5,474,327, issued on Dec. 12, 1995, and assigned to the assignee of the present invention. In practice, however, such systems tend to be relatively costly to implement, and require a significant amount of signal processing for proper calibration and weight estimation. 
     Another approach for determining occupant weight, disclosed for example in U.S. Pat. No. 5,987,370, issued on Nov. 16, 1999, and assigned to the assignee of the present invention, involves installing a fluid-filled polymeric bladder in or under the bottom cushion of a vehicle seat, and measuring the fluid pressure in the bladder. As disclosed in the U.S. Pat. No. 6,101,436, issued on Aug. 8, 2000, and also assigned to the assignee of the present invention, the bladder may have multiple cells formed by a pattern of spot welds between top and bottom layers of the bladder, creating an array of generally circular or hexagonal cells between which the fluid can freely flow. This approach can maximize the pressure response for improved sensitivity, and minimize the amount of fluid required to detect occupant weight, thereby minimizing the weight of the fluid-filled bladder. However, the position of the occupant on the seat can influence the indicated weight, and therefore, the decision as to whether to allow or suppress air bag deployment. Also, the decision as to whether to allow or suppress air bag deployment may depend on occupant position, as well as occupant weight. For example, if the occupant is very close to the point of deployment, it may be desired to disable deployment regardless of the occupant weight. For this reason, a number of position detection systems have been devised for independently determining if the occupant is out of position and in danger of injury due to air bag deployment. However, the use of multiple independent sensing systems significantly increases the system cost and complexity, and introduces a number of implementation issues, such as sensor placement and calibration. Accordingly, what is desired is a simple and cost-effective occupant detection system that takes into consideration both occupant weight and occupant position. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved occupant detection system involving a fluid-filled polymeric seat cushion bladder defining multiple fluid-filled chambers corresponding to different regions of the seat cushion, with no fluid flow between such chambers, and where the fluid pressures in the various individual chambers are detected and processed to develop a weight estimation that is compensated for occupant position. According to the invention, the chambers are configured to detect occupant weight in at least forward, rearward, inboard and outboard regions of the bottom seat cushion. When the detected pressures are unevenly distributed and the pressure in the forward, rearward, inboard or outboard regions of the seat exceeds the average pressure by at least a predetermined amount, a composite pressure indicative of occupant weight is adjusted in a direction to bias the suppression status in favor of allowing restraint deployment, unless the occupant is forwardly positioned on a seat that is also forwardly positioned. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a system diagram illustrating a passenger seat of a vehicle equipped with a fluid-filled bladder, a passenger occupant detection electronic control unit (PODS ECU), an airbag control module (ACM) according to this invention. 
     FIGS. 2A-2F depict alternate implementations of the fluid-filled bladder of FIG.  1 . FIGS. 2A and 2B depict four-chamber configurations, FIG. 2C depicts a nine-chamber configuration, FIGS. 2D and 2F depict eight-chamber configurations, and FIG. 2E depicts a five-chamber configuration. 
     FIGS. 3,  4 ,  5  and  6  depict a flow diagram representative of a software routine executed by the PODS ECU of FIG. 1 in carrying out the method of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is disclosed in the context of a restraint system for an occupant of a vehicle passenger seat  10  that is adjustable at least in forward and rearward directions, where deployment of an inflatable restraint such as a frontal air bag is subject to being disabled or suppressed based on a characterization of the occupant weight and position. Referring to FIG. 1, the vehicle seat  10  is supported on a frame  14 , and includes foam cushions  16  and  18  on the seat bottom and back. The bladder  12  is disposed in or under the foam bottom cushion  16  substantially parallel with the central seating surface, and has multiple chambers containing a fluid such as silicone which is non-corrosive, and not subject to freezing at extreme ambient temperatures. In addition, a rigid back-plate may be placed under the bladder  12  to provide a suitable reaction surface, as disclosed for example in the U.S. patent application Ser. No. 09/311,576, (Attorney Docket No. H-203753), assigned to the assignee of the present invention, and incorporated herein by reference. 
     As described more completely below in reference to FIGS. 2A-2F, the bladder  12  is constructed to define a plurality of individual, mutually isolated, fluid-filled chambers  12   a ,  12   b , etc., each such chamber being equipped with a pressure sensor  20   a ,  20   b , etc. for detecting the fluid pressure in such chamber. Conductors carrying the pressure signals developed by the pressure sensors  20   a ,  20   b , etc. are joined to connector  21 , and communicated to a microprocessor-based passenger occupant detection system electronic control unit (PODS ECU)  30  via a pressure signal bus  22 . The PODS ECU  30  processes the pressure signals along with a cushion temperature signal on line  24  to determine if restraint deployment for the occupant of seat  10  should be allowed or suppressed in a sufficiently severe crash event. The temperature signal on line  24  is developed by a temperature sensor  26  that may be separate from bladder  12  as indicated in FIG. 1, or integrated with one of the pressure sensors  20   a ,  20   b , etc. The suppression status (i.e., allow or suppress) is communicated from PODS ECU  30  to an airbag control module (ACM)  32  via bi-directional communication bus  34 . The ACM  32  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 the acceleration signals obtained from one or more acceleration sensors (A)  36 , and the suppression status obtained from PODS ECU  30 . In general, ACM  32  deploys the restraints if the acceleration signals indicate the occurrence of a severe crash, unless the PODS ECU  30  indicates that deployment should be suppressed. Of course, other more sophisticated controls are also possible, such as controlling the deployment force of the restraint devices based on occupant characterization, for example. Also, ACM  32  may be configured to communicate the suppression status to a driver display device  38  to enable the driver to verify that the suppression status is appropriate. 
     As indicated above, FIGS. 2A-2F depict alternate implementations of the fluid-filled bladder  12  of FIG.  1 . FIGS. 2A and 2B depict four-chamber or quadrant designs for bench and side-bolster seat configurations, respectively, FIG. 2C depicts a nine-chamber configuration, FIGS. 2D and 2F depict eight-chamber configurations, and FIG. 2E depicts a five-chamber configuration. In each case, the hatched portions of the bladder  12  represent a weld pattern between upper and lower layers of the bladder that define the various individual fluid chambers  12   a ,  12   b , etc., and in each case, conductors  40  carrying the pressure signals from the chambers  12   a ,  12   b , etc. are joined at a connector  21  coupling the pressure signal bus  22  to PODS ECU  30 . The pressure sensors  20   a ,  20   b , etc. may be thin-film, piezoelectric or another type of pressure sensor. 
     In the embodiments of FIGS. 2A and 2B, pressure sensors  20   a ,  20   b ,  20   c ,  20   d  for detecting the fluid pressures in the four fluid-filled chambers  12   a ,  12   b ,  12   c ,  12   d  are disposed in a rearward portion of the bladder  12 . In FIG. 2A, the pressure sensors  20   c ,  20   d  are simply positioned at the rearward edge of the chambers  12   c ,  12   d , while the pressure sensors  20   a ,  20   b  are coupled to the respective chambers  12   a ,  12   b  by the fluid channels  42 ,  44 . The bladder  12  of FIG. 2A includes two large chambers  12   a ,  12   b  at the front of the cushion  16 , and two smaller chambers  12   c ,  12   d  toward the rear of the cushion  16 . The bladder  12  of FIG. 2B includes a large chamber  12   d  centered in the rear of cushion  16 , a smaller chamber  12   b  centered in the front of cushion  16 , and two bolster chambers  12   a ,  12   c , with the chamber  12   b  coupled to the pressure sensor  20   b  by the fluid channel  42 . 
     In the embodiments of FIGS. 2C-2F, the pressure sensors  20   a ,  20   b , etc. are disposed within the respective fluid-filled chambers  20   a ,  20   b , etc., and the conductors  40  carrying the pressure signals are routed to the connector  21  through weld areas of the bladder  12 , as shown. In the bladder  12  of FIG. 2C, there are nine chambers  12   a ,  12   b ,  12   c ,  12   d ,  12   e ,  12   f ,  12   g ,  12   h ,  12   i  of approximately equal size, each having a pressure sensor  20   a ,  20   b ,  20   c ,  20   d ,  20   e ,  20   f ,  20   g ,  20   h ,  20   i . The bladder  12  of FIG. 2D is a side-bolster design having six small chambers  12   b ,  12   c ,  12   e ,  12   f ,  12   g ,  12   h  of approximately equal size in a central area of the cushion  16 , and two larger bolster chambers  12   a ,  12   d . The bladder  12  of FIG. 2E is also a side-bolster design; in this case, there is a large central chamber  12   d , two smaller chambers  12   b ,  12   e  in the forward-central and rearward-central areas of cushion  16 , and two large bolster chambers  12   a    12   c . Finally, the bladder  12  of FIG. 2F includes a large central chamber  12   f , a smaller chamber  12   g  in the rearward-central area of cushion  16 , two small chambers  12   b ,  12   c  in the forward-central area of cushion  16 , and two bolster chambers  12   a    12   h ;  12   d ,  12   e  in either side-bolster area of the cushion  16 . 
     The variety of the above-described configurations illustrates that the chamber configuration for a given application will depend to a large degree on the shape and size of the seat  10 . Also, the chambers  12   a ,  12   b , etc. may be configured to facilitate reliable identification of an infant or child seat, as opposed to a normally seated occupant. In general, however, each of the illustrated embodiments enable the PODS ECU  30  to identify a portion of the seat cushion  16  where the highest of the sensed pressures occurs for purposes of compensating the composite or overall pressure as explained below. 
     The flow diagrams of FIGS. 3-6 illustrate a software routine periodically executed by the PODS ECU  30  for carrying out this invention. The flow diagram of FIG. 3 represents a main or executive routine, whereas the flow diagrams of FIGS. 4-6 detail various steps of the main routine. At the initiation of each period of vehicle operation, the PODS ECU  30  executes an initialization routine as indicated by block  150  of FIG. 3 for initializing various registers, parameters and flags to zero or some other default setting. In the case of this invention, for example, the suppression status (STATUS) may be initialized to a default setting, or to a setting determined in the previous ignition cycle. A similar initialization also occurs in the event of a dynamic reset. Following initialization, the blocks  200 - 216  are repeatedly executed as shown. The blocks  200  and  202  read all of the sensor information (which may include seat belt latch and seat belt tension information) and perform diagnostic testing of the system and components. If the diagnostic testing detects a disabling fault, the block  204  is answered in the affirmative, and the block  205  sets the suppression status to FAULT. If there is no fault or the diagnostic tests detect a fault that is not disabling, such as a loss of fluid in one of the chambers  12   a ,  12   b , etc., the blocks  206 - 212  are executed to determine the suppression status. The block  206  determines a position compensation factor POS_COMP_FACTOR based on a detected position of the occupant on the cushion  16 , as explained below in reference to the flow diagram of FIG.  4 . If the occupant is positioned forwardly on the cushion  16  (i.e., POS_COMP_FACTOR has been set to a forward factor FF) and the position (SEAT_POS) of seat  10  is substantially full forward, the block  208  is answered in the affirmative, and the block  209  sets the suppression status to SUPPRESS. Otherwise, the blocks  210  and  212  are executed to determine the composite pressure and the suppression status, as respectively detailed in the flow diagrams of FIGS. 5 and 6. The block  214  then sends the determined suppression status to ACM  32 , and the block  216  checks for removal of system power. When system power is removed, the block  218  is executed to perform shut-down tasks, and the routine is exited. 
     Referring to FIG. 4, determining the position compensation factor POS_COMP_FACTOR is achieved by executing the blocks  220 - 252  as shown. In general, this routine determines the relative position of the occupant based on the distribution of weight at each of the various chambers  12   a ,  12   b , etc., and then assigns a corresponding value to POS_COMP_FACTOR. The process begins at block  220 , where the pressure sensor signal values are low-pass filtered to average each of the respective pressure sensor signals. Then the block  222  identifies the highest (MAX_PRESSURE) and lowest (MIN_PRESSURE) of the filtered pressure signals, and the block  224  computes an average pressure (AVG_PRESSURE) by summing all of the filtered pressure signals and dividing the sum by the total number of pressure signals. If the difference between MAX 13  PRESSURE and MIN_PRESSURE is less than a reference value (Knormal), as determined at block  226 , the occupant is considered to be normally seated, and the block  252  sets POS_COMP_FACTOR to one. If block  226  is answered in the negative and block  228  determines that the MAX_PRESSURE identified at block  222  occurs in a forward chamber (cell) of the bladder  12 , the blocks  230  and  232  set POS_COMP_FACTOR equal to a calibrated forward factor FF such as 1.30, provided that the sensed pressure in any of the forward chambers exceeds AVG_PRESSURE by at least a predetermined value Kforward. Otherwise, the block  252  sets POS_COMP_FACTOR to one. If the block  228  is answered in the negative, the block  234  is executed to determine if the MAX_PRESSURE identified at block  222  occurs in an outboard chamber (cell) of the bladder  12 . If so, the blocks  236  and  238  set POS_COMP_FACTOR equal to a calibrated outboard factor OF, such as 1.20, provided that the sensed pressure in any of the outboard chambers exceeds AVG_PRESSURE by at least a predetermined value Koutboard. Otherwise, the block  252  sets POS_COMP_FACTOR to one. If the block  234  is answered in the negative, the block  240  is executed to determine if the MAX_PRESSURE identified at block  222  occurs in a rearward chamber (cell) of the bladder  12 . If so, the blocks  242  and  244  set POS_COMP_FACTOR equal to a calibrated rearward factor RF, such as 1.50, provided that the sensed pressure in any of the rearward chambers exceeds AVG_PRESSURE by at least a predetermined value Krearward. Otherwise, the block  252  sets POS_COMP_FACTOR to one. And if the block  240  is answered in the negative, the block  246  is executed to determine if the MAX_PRESSURE identified at block  222  occurs in an inboard chamber (cell) of the bladder  12 . If so, the blocks  248  and  250  set POS_COMP_FACTOR equal to a calibrated value inboard factor IF, such as 1.20, provided that the sensed pressure in any of the inboard chambers exceeds AVG_PRESSURE by at least a predetermined value Kinboard. Otherwise, the block  252  sets POS_COMP_FACTOR to one. 
     It will be appreciated that with certain implementations of the bladder  12 , a given fluid-filled chamber  12   a ,  12   b , etc. may be considered as both a forward or rearward chamber and an inboard or outboard chamber. In the implementation of FIG. 2C, for example, the chamber  12   a  can be considered as both a forward chamber (for purposes of blocks  228 - 230 ) and an outboard chamber (for purposes of blocks  234 - 236 ). Thus, the order of the blocks  228 ,  234 ,  240  and  246  may be important for such implementations, with the most significance (highest priority) being attached to the first block to be executed. In general, detection forward-leaning occupants is accorded highest priority for a frontal air bag, so block  228  is executed prior to blocks  234 ,  240  and  246 . In the case of a side air bag on the other hand, it may be desired to execute block  234  prior to blocks  228 ,  240  and  246 , for example. 
     As explained below in reference to the flow diagram of FIG. 6, POS_COMP_FACTOR is applied to a weighted and filtered composite pressure FILT_PRESSURE to form a compensated pressure COMP_PRESSURE that is compared to predetermined thresholds to determine the suppression status. For example, if COMP_PRESSURE is greater than a threshold Kadult indicative of a child occupant, the PODS ECU  30  concludes that the seat  10  is occupied by an adult and STATUS is set to ALLOW so that restraint deployment is enabled in a sufficiently severe crash event. However, if the same occupant is positioned toward an edge of the cushion  16 , FILT_PRESSURE tends to be lower than if the occupant were normally seated, and the block  208  sets POS_COMP_FACTOR to a calibrated value (FF, IF, OF or RF), which has the effect of increasing COMP_PRESSURE to a value that more accurately indicates the occupant weight. 
     Referring to FIG. 5, determining COMPOSITE_PRESSURE involves weighting and summing the various sensed pressures, and then filtering the result. The block  254  initializes the process by setting a sensor position value P to one, and resetting COMPOSITE_PRESSURE to zero. The block  256  then increases COMPOSITE_PRESSURE by the product PRESSURE(P) * WEIGHT_FACTOR(P), where PRESSURE(P) is the filtered pressure sensor value for the Pth sensor position, and WEIGHT_FACTOR(P) is a calibrated gain or weight associated with the Pth sensor position. So long as P is less than the total number pmax of sensor positions for the bladder  12 , as determined at block  258 , the block  260  is executed to increment P, whereafter blocks  256  and  258  are re-executed. When block  258  is answered in the affirmative, the block  262  calculates RAW_COMPOSITE_PRESSURE by dividing the weighted sum COMPOSITE_PRESSURE by Pmax, and the block  264  low-pass filters the result using a filter gain Kpc to form the filtered pressure FILT_PRESSURE. 
     Referring to FIG. 6, determining the suppression status generally involves compensating FILT_PRESSURE based on POS_COMP_FACTOR, and comparing the result to various predetermined thresholds. Initially, the blocks  266  and  268  are executed to determine if there has been a driver-override of the occupant sensing system or if system initialization has not been completed. In either case, the block  284  is executed to set STATUS to INDETERMINATE, and the routine is exited. Usually, however, blocks  266  and  268  will be answered in the negative, and the block  270  is executed to compute a compensated pressure COMP_PRESSURE according to the product of FILT_PRESSURE and POS_COMP_FACTOR. If COMP_PRESSURE is less than or equal to a predetermined low threshold Kempty indicative of an unoccupied seat, the blocks  272  and  274  detect the condition and set STATUS to EMPTY, completing the routine. If COMP_PRESSURE exceeds Kempty, but is less than or equal to a predetermined threshold Kadult indicative of child occupant (a occupant smaller than a 5 th  percentile adult female, for example), the blocks  276  and  278  detect the condition and set STATUS to SUPPRESS. If COMP_PRESSURE exceeds Kadult but is less than an unrealistically high threshold Khigh_pr, the blocks  280  and  282  detect the condition and set STATUS to ALLOW. If COMP_PRESSURE exceeds Khigh_pr, a reliable indication of occupant position cannot be obtained, and the block  284  is executed to set STATUS to INDETERMINATE. Although not shown, the routine will preferably include a degree of hysteresis to prevent STATUS from toggling between two different states; once STATUS stabilizes in a given state, the hysteresis values can be increased to reduce sensitivity to road noise, occupant movement, and so on. 
     In summary, the system of this invention provides inexpensive and reliable determination of whether deployment of an inflatable restraint should be allowed or suppressed based on both occupant weight and position on a vehicle seat. While described in reference to the illustrated embodiment, it is expected that various modifications will occur to persons skilled in the art. For example, this invention is not limited to a particular bladder configuration, and may be used to determine if deployment of other restraints such as side air bags should allowed or suppressed. Accordingly, it should be understood that occupant detection systems incorporating these and other modifications may fall within the scope of this invention, which is defined by the appended claims.