Abstract:
Testing of temperature sensors ( 28, 30, 32 ) in an emission control system, such as in an exhaust system ( 10 ) of a diesel engine, serves to condition further component and/or system testing by determining that sufficient sensor cooling has occurred and that no sensor is “stuck within range” using a strategy ( 50 ).

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to emission control systems of internal combustion engines, more particularly diesel engines that have exhaust gas treatment devices for treating exhaust gases passing through their exhaust systems. The invention further relates to a system and method for verifying the functionality of certain sensors associated with emission control devices, more especially temperature sensors associated with exhaust gas treatment devices, prior to subsequent diagnostic testing.  
       BACKGROUND OF THE INVENTION  
       [0002]     A known system for treating exhaust gas passing through an exhaust system of a diesel engine comprises a diesel oxidation catalyst (DOC) upstream of a diesel particulate filter (DPF). The combination of these two exhaust gas treatment devices traps diesel particulate matter (DPM) and promotes chemical reactions in exhaust gas as it flows through the exhaust system from the engine, thereby preventing significant amounts of pollutants such as hydrocarbons, carbon monoxide, soot, SOF, and ash, from entering the atmosphere.  
         [0003]     Certain sensors are associated with exhaust gas treatment devices like DOC&#39;s and DPF&#39;s in diesel engine exhaust systems. The sensors provide certain information for control and/or diagnostic purposes. The information may also be used for verifying compliance with relevant regulations. Such verification may require that the functionality of the sensors themselves be verified before further evaluation of the functionality of the exhaust gas treatment system.  
         [0004]     Certain government regulations that are anticipated to become applicable to certain motor vehicle engines require certain diagnostic testing of emission control systems. A specific document entitled “Engine Manufacturer Diagnostic System Requirements For 2007 And Subsequent Model-Year Heavy-Duty Engines (EMD)” sets forth certain requirements for assuring functionality of diesel engine exhaust gas treatment systems. Functionality of the sensors associated with the exhaust gas treatment systems needs also to be assured.  
         [0005]     Functionality testing of certain sensors is best performed when they are “cold”. To confirm that they are indeed “cold”, it has been proposed to use a timer to time the amount of time that an engine has been shut off since it last was running and to allow further testing only after a certain amount of time has elapsed on the timer.  
         [0006]     Such a timer, which is typically implemented in the engine control system, requires power in order to run while the engine is shut off. Some existing engine control systems that are otherwise entirely suitable for use with exhaust gas treatment systems that are subject to the future regulation may not however possess features and the necessary hardware (“keep alive memory” or KAM for example) that allow for measuring engine off time.  
         [0007]     Accordingly, a system and method that can verify sensor functionality without having to draw power from a vehicle battery or battery bank for measuring engine off time would be advantageous for those engines.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is directed toward such a system and method.  
         [0009]     Sensor functionality is verified in several ways in the disclosed embodiment of the invention. Failure to verify sensor functionality in any of those ways disallows further diagnostic testing until subsequent sensor functionality testing verifies sensor functionality.  
         [0010]     One generic aspect of the present invention, which is used to determine if a sensor is “stuck within range”, relates to a method for conditioning performance of an emission control system test comprising processing temperature data from spaced apart locations along a flow path containing one or more emission control devices to develop a first set of data values each representing a respective temperature difference between a respective pair of locations.  
         [0011]     The first set of data values is processed to develop a second set of data values each representing the difference between a respective pair of data values of the first set. Each data value of the second set and a respective reference value are processed to develop a third set of data values. Performance of the test is conditioned on the third set of data values.  
         [0012]     Another generic aspect, that determines if at least one sensor has cooled down sufficiently for enabling sensor functionality to be verified, relates to a method for conditioning performance of an emission control system test by processing temperature data from spaced apart locations along a flow path containing one or more emission control devices to develop a first set of data values each representing a respective temperature at a respective location.  
         [0013]     The first set of data values and a second set of data values representing respective highest temperatures measured earlier at the respective locations while flow was occurring through the flow path are processed to develop data values representing the difference between each data value of the first set and a respective data value of the second set. Performance of the test is conditioned on the difference between at least one of the data values of the first set and the respective data value of the second set being more than a respective defined difference.  
         [0014]     The invention also relates to an internal combustion engine comprising an emission control system comprising temperature sensors disposed at spaced apart locations along a flow path containing one or more emission control devices providing a first set of data values each representing a respective temperature difference between a respective pair of locations.  
         [0015]     A further aspect involves a processor processing the first set of data values to develop a second set of data values each representing the difference between a respective pair of data values of the first set, processing each data value of the second set and a respective reference value to develop a third set of data values, and conditioning performance of the test on the third set of data values.  
         [0016]     A still further aspect involves the processor processing the first set of data values and a second set of data values representing respective highest temperatures measured earlier at the respective locations while flow was occurring through the flow path to develop data values representing the difference between each data value of the first set and a respective data value of the second set, and for conditioning performance of the test on the difference between at least one of the data values of the first set and the respective data value of the second set being more than a respective defined difference.  
         [0017]     The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a general schematic diagram of a portion of an exemplary diesel engine exhaust system with which the present invention can be practiced.  
         [0019]      FIGS. 2A and 2B  taken together comprise a software strategy diagram embodying principles of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]      FIG. 1  shows a diesel engine exhaust system  10  comprising branches  12 ,  14  from exhaust manifolds to successive turbine stages  16 ,  18  a two-stage turbocharger. Downstream of stage  18  in succession are a diesel oxidation catalyst (DOC)  20 , a diesel particulate filter (DPF)  22 , and a muffler  24 .  
         [0021]     When the engine is running to power a motor vehicle, exhaust gas exits engine combustion chambers to enter the exhaust manifolds and pass through branches  12 ,  14  where the flows merge to pass through the turbines stages and then DOC  20 , DPF  22 , and muffler  24  before passing to atmosphere through an exhaust pipe.  
         [0022]     Although none are shown, it is possible that an exhaust system could have one or more valves associated with devices in the exhaust system in various ways. A by-pass valve shunting an exhaust system device and an engine exhaust brake would be examples.  
         [0023]     A differential pressure sensor  26  is associated with DPF  22  to measure pressure drop through DPF  22 . A DOC inlet temperature sensor  28  is disposed to measure temperature at the inlet of DOC  20 . A DPF inlet temperature sensor  30  is disposed to measure temperature at the inlet of DPF  22 . A DPF outlet temperature sensor  32  is disposed to measure temperature at the outlet of DPF  22 .  
         [0024]     These four sensors provide data to a processor-based engine control system (ECS)  34  that processes data from various sources to develop various control data for controlling various aspects of engine operation, including performing certain diagnostic testing.  
         [0025]     The inventive method is implemented in control system  34  by the strategy shown in diagram  50  of  FIGS. 2A and 2B  as an algorithm that is repeatedly executed as the engine operates. The algorithm comprises processing data from temperature sensors  28 ,  30 , and  32  upon the ignition switch being turned on after the engine has been off to ascertain if the exhaust system has cooled sufficiently to allow “cold” testing of the sensors for verifying sensor functionality prior to further diagnostic testing. Hence, the inventive method may be considered to have several aspects, one of which is verifying functionality of the sensors themselves, and conditioning further diagnostic tests on verification of sensor functionality.  
         [0026]     At power up, each sensor  28 ,  30 ,  32  is read by ECS  34  to develop a respective data value for a respective parameter TEG_MES_PCAT_UP[0], TEG_MES_PCAT_DOWN[0], TAC_MES[0] representing the temperature sensed at the respective sensor location in exhaust system  10 . Further processing of each parameter by the algorithm is controlled by a respective switch function  52 ,  54 ,  56  with which a respective store  58 ,  60 ,  62  is associated as shown.  
         [0027]     With each switch function  52 ,  54 ,  56  in its OFF state, no further processing of the temperature data occurs. When each switch function  52 ,  54 ,  56  switches to its ON state, further processing of temperature data occurs. Switching from OFF state to ON state occurs when conditions monitored by an AND logic function have been satisfied. Two NOR logic functions  66 ,  68  collectively form a single NOR logic function that assures that no relevant error flags identified by the various inputs to the NOR logic functions have been set. A comparison function  70  assures a slight delay time after the ignition switch has been turned on to allow any transients associated with power up to dissipate.  
         [0028]     With switch functions  52 ,  54 ,  56  ON, data values for TEG_MES_PCAT_UP[0], TEG_MES_PCAT_DOWN[0], TAC_MES[0] are processed respectively by respective comparison functions  72 ,  74 ,  76 . Each function  72 ,  74 ,  76  compares the data value for the respective stored sensor temperature with a data value for respective reference temperature C_T_HOT_DOC, C_T_HOT_DPF_IN, C_T_HOT_DPF_OUT. The purpose of these comparisons is to condition further performance of the sensor functionality test on any one of the sensors  72 ,  74 ,  76  indicating that it is sufficiently “cold” for a meaningful test to proceed. That a sensor is sufficiently “cold” is determined by monitoring results of the comparison functions by a NAND logic function  78 . The state of NAND logic function  78  and that of AND logic function  64  determine the state of an AND logic function  80 .  
         [0029]     With switch functions  52 ,  54 ,  56  ON, stored data values for TEG_MES_PCAT_UP[0], TEG_MES_PCAT_DOWN[0], TAC_MES[0] are also processed by respective subtraction functions  82 ,  84 ,  86 . Function  82  subtracts the data value representing the temperature of sensor  30  from the data value representing the temperature of sensor  28 . Function  84  subtracts the data value representing the temperature of sensor  32  from the data value representing the temperature of sensor  30 . Function  86  subtracts the data value representing the temperature of sensor  28  from the data value representing the temperature of sensor  32 .  
         [0030]     Next a respective absolute value function  88 ,  90 ,  92  processes the data value representing the respective difference calculated by the respective function  82 ,  84 ,  86  to yield a respective magnitude of the respective difference. The data value representing that respective magnitude is then processed by a respective comparison function  94 ,  96 ,  98 .  
         [0031]     Comparison function  94  compares the magnitude of the temperature difference between sensors  28  and  30  with a defined minimum value represented by parameter C_MIN_DIFF — 1. Comparison function  96  compares the magnitude of the temperature difference between sensors  30  and  32  with a defined minimum value represented by parameter C_MIN_DIFF — 2. Comparison function  98  compares the magnitude of the temperature difference between sensors  28  and  32  with a defined minimum value represented by parameter C_MIN_DIFF — 3.  
         [0032]      FIG. 2B  shows that the results of those three comparisons are further monitored by respective AND logic functions  100 ,  102 ,  104 . The state of AND logic function  80  is also monitored by each AND logic function  100 ,  102 ,  104 . The state of each AND logic function  100 ,  102 ,  104  is identified by a respective parameter ERR_SYM_DPF_T_IN, ERR_SYM_DPF_T_OUT, ERR_SYM_DOC_T_IN, and those parameters determine the state of a NOR logic function  106 .  
         [0033]      FIG. 2A  shows still further processing of stored data values for TEG_MES_PCAT_UP[0], TEG_MES_PCAT_DOWN[0], TAC_MES[0] by respective subtraction functions  108 ,  110 ,  112 . Functions  108 ,  110 ,  112  subtract the respective stored data values for TEG_MES_PCAT_UP[0], TEG_MES_PCAT_DOWN[0], TAC_MES[0] from respective data values for parameters DOC_T_IN_OLD_MEM[MEM], DPF_T_IN_OLD_MEM[MEM], and DPF_T_OUT_OLD_MEM[MEM].  
         [0034]     The data values representing those differences are then processed by respective comparison functions  114 ,  116 ,  118 . Comparison function  114  compares the difference between the data value for DOC_T_IN_OLD_MEM[MEM] and that for the stored value of TEG_MES_PCAT_UP[0]. Comparison function  116  compares the difference between the data value for DPF_T_IN_OLD_MEM[MEM] and that for the stored value of TEG_MES_PCAT_DOWN[0]. Comparison function  118  compares the difference between the data value for DPF_T_OUT_OLD_MEM[MEM] and that for the stored value of TAC_MES[0].  
         [0035]     The results of those three comparisons control the state of an OR logic function  120 . The state of OR logic function  120  and that of NOR logic function  106  determine the state of an AND logic function  122 . The latter sets a latch function  124  when both OR logic function  120  and NOR logic function  106  assume logic “1” states.  
         [0036]     Latch function  124  is reset by a comparison function  126  with which a store  128  is associated as shown. Resetting occurs by the action of turning the ignition switch from OFF to ON. The parameter LV_IGK is a logic signal that assumes a “0” value when the ignition switch is off, and a “1” value when the ignition switch is on. When the value for LV_IGK changes, store  128  stores the value that existed immediately prior to the change. Hence, the act of switching the ignition switch from OFF to ON causes comparison function  126  to switch the data value to latch function  124  to a “1” thereby resetting latch function  124  to “0”. The latter can be set only by AND logic function  122  switching a logic “1” to the latch function. That can occur only when NOR logic function  106  and OR logic function  120  are both in the logic “1” state.  
         [0037]     A parameter LV_ENG_OFF_OK represents the state of latch function  124 . When LV_ENG_OFF_OK switches from a “0” to a “1”, the “1” signals that conditions precedent to performance of other diagnostic testing exist, thereby allowing such other testing to proceed. The switching of LV_ENG_OFF_OK from a “0” to a “1” is also one of two inputs to an AND logic function  132 . The other input is the inverse of a parameter LV_ES, the inversion being provided by an inversion function  130 .  
         [0038]     AND logic function  132  serves to enable values for parameters DOC_T_IN_OLD_MEM[MEM], DPF_T_IN OLD _MEM[MEM], and DPF_T_OUT_OLD_MEM[MEM] to be updated as the engine continues to run, if they require updating in order to log the maximum temperature measured. The updating occurs via respective switch functions  134 ,  136 ,  138  that are switched ON when AND logic function  132  is placed in the logic “1” state.  
         [0039]     A respective maximum value function  140 ,  144 ,  148  provides an updated value for the respective parameter DOC_T_IN_OLD_MEM[MEM], DOC_T_IN_OLD_MEM[MEM], and DPF_T_OUT_OLD_MEM[MEM] when switch functions  134 ,  136 ,  138  are ON. Each maximum value function determines the greater of one of two inputs to it. The current sensor temperature data TEG_MES_PCAT_UP[0], TEG_MES_PCAT_DOWN[0], and TEG_MES[0] are one of the inputs to the respective functions  140 ,  144 ,  148 . The other input to each function  140 ,  144 ,  148  is from a corresponding store  142 ,  146 ,  150 .  
         [0040]     Each store  142 ,  146 ,  150  stores the result of each function  140 ,  144 ,  148  so that the maximum temperature measured while the engine is running will be the data value stored in memory for the respective parameter DOC_T_IN_OLD_MEM[MEM], DOC_T_IN_OLD_MEM[MEM], and DOC_T_OUT_OLD_MEM[MEM], to be used by functions  108 ,  110 ,  112  the next time that the engine is started after having been shut off.  
         [0041]     When the engine is stopped, the parameter LV_ES causes the state of AND logic function  132  to switch to “0”, thereby causing switch functions  134 ,  136 ,  138  to switch to OFF. The stores  142 ,  146 , and  150  are also set to zero at key off.  
         [0042]     From the foregoing description, the reader can now appreciate that the inventive method conditions performance of further diagnostic testing of the emission control system at engine start up on verification of at least one of the sensors being sufficiently “cold” and there being no sensor that is “stuck within range”. A properly functioning sensor will closely follow temperature changes over the relevant temperature range to provide a reasonably accurate temperature measurement at the sensor location. Hence, they are expected to cool down in similar ways once the engine is shut off although there respective temperature ranges may be somewhat different due to their different locations in the exhaust system.  
         [0043]     That at least one sensor has cooled down sufficiently is determined at engine start up by functions  72 ,  74 ,  76 . That no sensor is stuck within range is determined by AND logic functions  100 ,  102 ,  104 . If one sensor is stuck within range, it will be identified by one of the parameters ERR_SYM_DPF_T_IN, ERR_SYM_DPF_T_OUT, ERR_SYM_DOC_T_IN. By sensing temperature at engine start up, it is unnecessary to measure the time that the engine was off, thereby avoiding electric current consumption while the engine was off, and also certain hardware modifications to existing engine control systems.  
         [0044]     While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.