Patent Publication Number: US-2003225493-A1

Title: Method and apparatus for preserving calibration data in a vehicle seat occupant detection system

Description:
TECHNICAL FIELD  
       [0001] The technical field of this invention is a vehicle occupant protection system and particularly an occupant detection system for a vehicle seat.  
       BACKGROUND OF THE INVENTION  
       [0002] Vehicle occupant protection systems are beginning to include occupant detection and characterization systems for helping to decided whether or how to deploy an airbag in a crash event. At least one such system provides an occupant characteristic sensor in a vehicle seat member to determine the weight of a seat occupant. The determination is made by a programmed computer provided in an occupant detection system module, the computer having an input connection from a seat characteristic sensor such as a fluid pressure sensor connected to a fluid filled bladder on the seat pan under the bottom seat cushion member. The output signal from the sensor is compared with calibrated threshold values to characterize a detected seat occupant.  
       [0003] The calibrated threshold values are initially determined in calibration tests of the occupant detection system, which includes the seat cushion member, bladder, sensor and occupant detection system module, and are typically stored in rewritable, non-volatile memory such as EEPROM in the occupant detection system module to allow updating during vehicle operation, service or recalibration. If service of the system requires part replacement, there are typically two alternative replacement modes: (1) replacement of the entire system, including seat member, bladder, sensor and module, or (2) replacement of the module alone. The latter mode of replacement will result in loss of the calibrated threshold values with the discarded module unless additional steps are taken, such as specifically copying these values to the new module or recalibrating the system. But a defect in the replaced module may prevent access to the stored calibrated threshold values; and recalibration requires special equipment not generally available outside manufacturing facilities.  
       SUMMARY OF THE INVENTION  
       [0004] This invention is a method and apparatus for preserving seat calibration data such as the calibrated threshold values in an occupant detection system in an automatic manner, regardless of which replacement mode is performed. The invention provides dedicated memory locations for vehicle identification data and seat calibration data in a first rewritable, non-volatile memory within an occupant detection system module and a second rewritable, non-volatile memory external to the occupant detection system. The second rewritable, non-volatile memory may, in a preferred embodiment, be located within an airbag control module that is separately replaceable in the vehicle with respect to the occupant detection system.  
       [0005] In one aspect of the invention, vehicle identification data is obtained from the vehicle. If the vehicle identification data obtained from the vehicle matches vehicle identification data stored in the first rewritable, non-volatile memory, seat calibration data stored in the first rewritable, non-volatile memory is copied to the second rewritable, non-volatile memory.  
       [0006] In another aspect of the invention, vehicle identification data is obtained from the vehicle. If (a) there is vehicle identification data in the first rewritable, non-volatile memory and (b) the vehicle identification data obtained from the vehicle does not match the vehicle identification data stored in the first rewritable, non-volatile memory and (c) the vehicle identification data obtained from the vehicle matches vehicle identification data stored in the second rewritable, non-volatile memory, then seat calibration data stored in the second rewritable, non-volatile memory and one of the vehicle identification data obtained from the vehicle and the vehicle identification data stored in the second rewritable, non-volatile memory is copied to the first rewritable, non-volatile memory.  
       [0007] In another aspect of the invention, vehicle identification data is obtained from the vehicle. If (a) there is no vehicle identification data stored in the first rewritable, non-volatile memory, and (b) there is seat calibration data stored in the first rewritable, non-volatile memory, then (a) the vehicle identification data obtained from the vehicle is copied to the first rewritable, non-volatile memory and to the second rewritable, non-volatile memory and (b) the seat calibration data in the first rewritable, non-volatile memory is copied to the second rewritable, non-volatile memory.  
       [0008] In yet another aspect of the invention, vehicle identification data is obtained from the vehicle. If (a) there is no vehicle identification data stored in the first rewritable, non-volatile memory and (b) there is no seat calibration data stored in the first rewritable, non-volatile memory and (c) the vehicle identification data obtained from the vehicle matches the vehicle identification data stored in the second rewritable, non-volatile memory, then seat calibration data stored in the second rewritable, non-volatile memory and one of the vehicle identification data obtained from the vehicle and the vehicle identification data stored in the second rewritable, non-volatile memory is copied to the first rewritable, non-volatile memory.  
       [0009] In a preferred embodiment of the invention, the second rewritable, non-volatile memory may be located in an airbag control module separately packaged and replaceable with respect to the occupant detection system. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
     [0011]FIG. 1 is a block diagram of a vehicle passive restraint deployment control system including a seat occupant detection system.  
     [0012]FIG. 2 is a block diagram of a portion of the system of FIG. 1.  
     [0013]FIGS. 3A and 3B together form a state diagram useful in illustrating the operation of system of FIGS. 1 and 2.  
     [0014] FIGS.  5 - 7  are process flow diagrams describing the operation of an occupant detection module within the system of FIGS. 1 and 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0015] A vehicle passive restraint control system comprises an airbag control module (ACM)  10  that receives signals from crash sensors, not shown, and provides deploy signals as required to airbags, not shown. The crash sensors and airbags may be any such articles known in the art for use in vehicle restraint systems. A vehicle seat  14  is provided with a seat cushion member  16 , generally comprising a shaped block of foamed material providing a comfortable seating support, usually covered in a fabric for appearance. A bladder  18  packaged with seat cushion member  16  is typically located under seat cushion member  16  but above a seat pan member, not shown, and is filled with a non-compressible fluid so as to generate a pressure in the fluid in response to the weight of a seat occupant on the seat cushion member. The pressure in the fluid is sensed by a pressure sensor  20  that, together with bladder  18 , forms a seat characteristic sensor apparatus providing an output signal of the weight born by seat cushion member  16 . This output signal is provided to an occupant detection system (ODS) module  12  that includes a computer programmed to determine the occupancy status of the seat according to predetermined, stored calibrated classification thresholds. Additional signals involved in such determination may be provided by, for example, a seat belt tension sensor  22  and/or a switch in a seat belt latch  24 . ACM  10  and ODS module  12  are adapted to communicate with each other over a communication bus  26 , such as a standard vehicle communication bus, which also permits communication with other modules in the vehicle having memory.  
     [0016] Due to variations in seat foam, bladders, sensors and other physical parameters, each system is calibrated after assembly with a particular seat cushion member; and the calibrated threshold values are stored in memory within ODS module  12 . These parameters may be changed by the ODS module during subsequent vehicle operation as characteristics change over time. For example, seat foam material changes its physical characteristics with age and is also subject to changes with environmental parameters. In a calibration process for a particular vehicle seat, one or more objects of predetermined weight and shape are dropped in a predetermined manner onto the installed seat cushion member to generate pressure readings for storage as the calibrated threshold values for determining the boundaries between occupant classifications. For the restraint deployment control to continue to meet its mandated operational standards, these calibrated threshold values must always be present for use; and it is also desired that they be updated as required to compensate for variations in physical and environment seat characteristics over time.  
     [0017]FIG. 2 shows greater detail of modules  10  and  12  in the areas of communication and memory. ACM  10  has a central processing unit (CPU)  30 , input/output (I/O) apparatus  32 , and memory apparatus  34 , which comprises at least RAM and rewritable, non-volatile memory such as EEPROM, a portion (ACM memory  36 ) of the latter being dedicated to vehicle identification data and seat calibration data. ODS module  12  similarly has a central processing unit (CPU)  40 , input/output (I/O) apparatus  42 , and memory apparatus  44 , which comprises at least RAM and rewritable, non-volatile memory such as EEPROM, a portion (ODS memory  46 ) of the latter being dedicated to vehicle identification data and seat calibration data. The seat calibration data in ODS memory  46  is updated as required by CPU  40  in ODS module  12  during vehicle operation; and the updated data is communicated to CPU  30  of airbag control module  10 , which stores it in ACM memory  36 . The communication of seat calibration data from ODS module  12  to ACM  10  occurs at least once each ignition cycle, preferably at power up of the modules; but it may occur during vehicle operation if desired.  
     [0018] As with any system in a vehicle, the occupant detection system is subject to failures of parts requiring repair and/or replacement. In the system of this embodiment, there are two replacement modes for the occupant detection system: (1) the entire system, including seat cushion member  16 , bladder  18 , pressure sensor  20  and ODS module  12 , may be replaced as a unit, or (2) ODS module  12  alone may be replaced. Additionally, the ACM is replaceable separately with respect to any portion of the occupant detection system as part of other repair procedures. In any of these repair procedures, a replacement module will typically not contain the specific seat calibration data of the module being replaced. A procedure for automatically preventing loss of such data is described with respect to the state diagram of FIGS.  3 A- 3 B.  
     [0019] When power is applied to ODS module  12  (and ACM) at the beginning of a vehicle ignition cycle, ODS module  12  enters an initial state  50  and queries the vehicle on bus  26  for vehicle identification data: specifically, the vehicle identification number. This number, which will be called VVIN, will be permanently stored in another module on the vehicle, e.g. the engine control module, that is also connected to bus  26 . In initial state  50 , the number is temporarily stored in ODS module RAM and is compared with vehicle identification data comprising a vehicle identification number SVIN stored in ODS memory  46 , if there is such a stored number. In typical vehicle operation, a number SVIN will be stored and will match VVIN; and the system will proceed to state  52 , in which the ODS module  12  has been identified as being in the correct vehicle. In state  52 , an occupant status flag OCC STATUS is set to CALC VAL, which will cause the occupant detection system in normal operation to calculate the occupant status and pass on the calculated value to ACM  10  for use in determining airbag deployment. In addition, at step  52 , the seat calibration data, comprising calibrated threshold values, in ODS memory  46  is sent over bus  26  to ACM  10  for storage in ACM memory  36 . When this storage is complete, the system enters state  54 ; and the transfer is verified by comparing AVIN, the vehicle identification data just written to and stored in ACM  10 , with SVIN, the vehicle identification data stored in ODS module  12 . If the storage is verified, a copy of the calibrated threshold values for the occupant detection system will be available in ACM memory  36  for copying back into a replacement ODS module  12 . If an error is detected, the system returns to state  52  and repeats the transfer; and this return and repeat will continue to occur until the transfer is verified or for a predetermined maximum number of retries. When either verification or the maximum number of retries has occurred, the system will enter state  56 , the normal operating mode; but an ECU Replacement Fault will be declared if the maximum number of retries resulted in no verification. In the normal operating mode, vehicle operation may proceed, but an ECU Replacement Flag is set to modify vehicle operation in an appropriate manner.  
     [0020] Returning in this description to the initial state  50 , if there is no vehicle identification data SVIN stored in ODS memory  46 , the system enters state  58 , with the recognition that the ODS module has been replaced. In state  58 , the occupant status flag OCC STATUS is reset to IND, which means indeterminate. This indicates that an occupant status value should not be calculated by ODS module  12 , and thus causes, for example, suppression of deployment of the airbag associated with seat  14 , with warning given to the vehicle occupants. The stored seat calibration data in ODS memory  46  is then checked for calibrated threshold values in state  58 . If they are present, it is inferred that an entire calibrated occupant detection system (seat cushion  16 , bladder  18 , pressure sensor  20  and ODS module  12 ) has been replaced in the vehicle (or initially placed in the vehicle with the seat  14  during vehicle assembly). The system thus enters state  60 , in which the vehicle identification number VVIN, which was obtained from the vehicle and stored in RAM in state  50 , is stored in the memories of both ODS module  12  and ACM  10 . If these saves are complete and verified, the system proceeds to state  52  to change the OCC STATUS flag to CALC VAL and copy the seat calibration data in ODS memory  46  to ACM memory  36 . From state  52 , the system then proceeds to state  54  and, if the transfer is verified, to Normal Operating Mode in state  56  as previously described with an original or replacement occupant detection system. But, returning in this description to state  60 , if the copying of vehicle identification data is not complete and verified, the system alternatively enters a faulted system state  66 ; and a FAULT flag is set. The system will not leave faulted system state  66  until it is serviced.  
     [0021] Returning in this description to state  58 , if no calibrated threshold values are found in ODS memory  46 , it means that an ODS module has been replaced without being calibrated to an occupant detection system. This typically means that a new ODS module  12  has been replaced in an existing and calibrated ODS system. The ODS module will thus require storage of both the vehicle identification number VVIN and any calibrated threshold values stored in ACM memory  36 . This will also be required if, in state  50 , it is determined that there is a stored vehicle identification number SVIN in ODS memory  46  but it does not match VVIN obtained from the vehicle. This situation can arise if a replacement ODS module has been removed from an occupant detection system in a different vehicle. In either case, the system enters state  62 , with recognition that the ODS module is in a new vehicle with calibrated threshold values stored in ACM  10 . But no copying of calibrated threshold values from ACM  10  to ODS module  12  is desired unless ACM  10  is verified as being in the correct vehicle. Thus, in state  62 , the system obtains vehicle identification data AVIN from ACM memory  36 . When the data is obtained, the system enters state  64  and validates AVIN against VVIN stored in RAM. If no match is obtained, the system enters the faulted system state  66 . But if a match is obtained in state  64 , ACM is validated as being in the correct vehicle; and the calibrated threshold values therein are considered correct. Thus, the system enters state  70 ; and the calibrated threshold values from ACM memory  36 , as well as either of vehicle identification data AVIN from ACM memory  36  or vehicle identification data VVIN obtained from the vehicle (which have been found identical) are copied to ODS memory  46 . When the storage is complete, the system enters state  72  and the stored data is verified. If verification fails, the storage is retried, up to a predetermined maximum number of times. If the verification succeeds, the system enters state  56 , the normal operating mode. If the verification ultimately fails, the system enters the defaulted system state  66 ; and the ECU Replacement flag is set.  
     [0022] FIGS.  4 - 6  show flow charts illustrating the operation of ODS module  12  in the process of this invention. FIG. 4 shows a routine PRESERVE DATA, which is run at power up of the module, which occurs at the beginning of each vehicle ignition cycle. The routine begins at step  100  by placing a request on the vehicle bus  26  for the vehicle identification data VVIN, which is stored permanently in a vehicle memory such as, typically, the vehicle engine control module, and receiving the requested data. The received vehicle identification data VVIN is held in ODS module RAM. Next, at step  102 , the routine requests vehicle identification data SVIN from memory locations in ODS memory  46  dedicated to that data. If such data are not stored therein, at step  104  the routine calls a routine NEW ODS MODULE, which will be described below. But if the required data is provided, the routine proceeds to step  106 , wherein it compares vehicle identification data SVIN from ODS module EEPROM with vehicle identification data VVIN from the vehicle. If they do not match, at step  108  the routine calls a routine ODS MODULE IN DIFFERENT VEHICLE, which will be described below. But if they do match, it means that the ODS module is in the correct vehicle; and the routine proceeds to step  110 , wherein it obtains seat calibration data such as calibrated threshold values from ODS memory  46  and places this data on bus  26  for copying into ACM memory  36  (or any other rewritable, non-volatile memory not replaced with the occupant detection system). The routine then verifies the data transfer at step  112  by requesting the same data back from ACM memory  36  (or wherever else it is stored) and comparing it with the data in ODS memory  46 . If there is no error, the routine proceeds to NORMAL OPERATING MODE at step  114 , which represents the rest of the operating process of the ODS module during the ignition cycle. If an error occurs, the routine will repeat the copy and verification up to a predetermined number of times. Thus, the routine keeps track of the number of retries in a software counter, not shown; and, in the case of an error determined at step  112 , the routine checks for the maximum retry count at step  116 . If the maximum number has not been reached, the routine increments the retry count and returns to step  110  to try again. When the maximum retry count is detected at step  116 , the routine sets an ECU REPLACEMENT FAULT flag at step  118  and then proceeds to NORMAL OPERATION at  114 . The ECU REPLACEMENT FAULT flag is insufficient to stop operation of the occupant detection system, since ODS memory  46  contains the required calibrated threshold values; but a warning will be provided for service, since the calibrated threshold values in ACM  10  are not verified.  
     [0023] Routine ODS MODULE IN DIFFERENT VEHICLE is described with reference to the flow chart of FIG. 5. It begins at step  120  by placing a request on bus  26  for the seat calibration data and vehicle identification data AVIN stored in ACM memory  36 . When the data is received, the routine proceeds at step  122  to compare the vehicle identification data AVIN from ACM memory  36  with vehicle identification data VVIN from the vehicle. If AVIN matches VVIN, it verifies that ACM  10  is in the proper vehicle. ACM  10  is thus presumed to contain the correct calibrated threshold values for seat  14 , and only ODS module  12  is new to the vehicle. Thus, at step  124 , the routine copies the data received from ACM memory  36 , both the calibrated threshold values and the vehicle identification data, to ODS module  12 . Alternatively to AVIN, the routine could copy VVIN, since the two have been found to match. When this is accomplished, the routine requests verification at step  126  by comparing the calibrated threshold values in ACM memory  36  and ODS memory  46 . If they match (no error), the routine is exited at step  128  to NORMAL OPERATING MODE. If they do not match (error), the routine proceeds to step  130 , in which the routine checks for a maximum retry count. If a maximum retry count is not reached, the routine increments the retry count and returns to step  124  for another attempt at copying and verifying the data. But if the maximum retry count is reached, the routine proceeds to step  132 , wherein the ECU REPLACEMENT FAULT flag is set, and then to step  134 , where further operation of the occupant detection system is halted in a fault condition with the further setting of a FAULT CONDITION flag until required service is performed. Unlike the case at step  112  of FIG. 4, in which the seat calibration data in ODS  12  is known to be correct, in the case of step  126  the correct seat calibration data could not be copied correctly into ODS module  12  from ACM  10 . The occupant detection system cannot be operated correctly without correct seat calibration data in ODS module  12 .  
     [0024] Returning in the description to step  122 , if AVIN does not match VVIN, then neither ACM  10  nor ODS module  12  contains the correct vehicle identification data VVIN. This means that both modules are new to the vehicle and contain no verified seat calibration data. Thus, the occupant detection system cannot be correctly operated; and the routine proceeds to step  132 , wherein the FAULT flag is set, and then to the fault condition at  134 , where further operation is halted until required service is performed.  
     [0025] Routine NEW ODS MODULE is described with reference to the flow chart of FIG. 6. It begins at step  140  by determining if calibrated threshold values are loaded in ODS memory  46 . If not, ODS module  12  is presumed to be new; and the routine is exited at step  142  to routine ODS MODULE IN DIFFERENT VEHICLE for further processing as described above with reference to FIG. 5. It is noted that the routine will reach routine ODS MODULE IN DIFFERENT VEHICLE either from step  106  in FIG. 4, if the vehicle identification SVIN in ODS memory  46  does not match the vehicle identification VVIN obtained from the vehicle itself, or from step  140  in FIG. 6, if there are no calibrated threshold values in ODS memory  46 . In either case, valid seat calibration data for the vehicle in ODS are not found in ODS memory  46 .  
     [0026] Returning to FIG. 6, if ODS memory  46  is found to contain calibrated threshold values at step  140 , the routine proceeds at step  144  to copy vehicle identification data VVIN from RAM to ODS memory  46  of ODS module  12  and to ACM memory  36  of ACM  10 . This data transfer is then verified at step  146  by reading back each value and comparing to VVIN in RAM for a match. If there is no error, the routine is exited at step  146 , through connecting reference point F in FIG. 6 and FIG. 4, to step  110  of FIG. 4. At step  110 , as previously described, the seat calibration data in ODS memory  46  is copied to ACM memory  36 , and the data transfer is verified in steps  112 ,  116  and  118  and the routine exits to NORMAL OPERATING MODE at step  114 , with a Fault flag set at step  118  if an error is detected. Returning in the description to step  146  of NEW ODS MODULE, a detected error leads to a return through step  144  for a retry until a maximum error count is reached, whereupon the ECU REPLACEMENT FAULT flag is set at step  150  and a Fault condition is entered with a setting of the FAULT CONDITION flag at step  152 , whereupon further operation is halted until required service is performed.