Method and system for compensating nox sensor measurement error

Abstract

Systems and associated methods of treating diesel exhaust in a vehicle are disclosed. An example method includes providing an exhaust aftertreatment device in an exhaust tailpipe, and a first nitrogen oxide (NO x ) sensor upstream of the exhaust aftertreatment device, with the exhaust aftertreatment device configured to reduce NO x present in an exhaust flow through the exhaust aftertreatment device with a treatment fluid applied to the exhaust flow. This example method may also include measuring a concentration of NO x in the exhaust flow with the first sensor, determining an error in the measurement of the NO x concentration, and applying a learning corrective adjustment in a subsequent measurement of the NO x concentration in the exhaust flow in response to that determination. A first magnitude of the learning corrective adjustment may be based at least in part upon a second magnitude of the error in the measurement.

What is claimed is: 
     
         1 . A method of treating diesel exhaust in a vehicle, comprising:
 providing an exhaust aftertreatment device in an exhaust tailpipe, and a first nitrogen oxide (NO x ) sensor upstream of the exhaust aftertreatment device , the exhaust aftertreatment device configured to reduce NO x  present in an exhaust flow through the exhaust aftertreatment device with a treatment fluid applied to the exhaust flow;   measuring a concentration of NO x  in the exhaust flow with the first sensor;   determining an error in the measurement of the NO x  concentration; and   applying a learning corrective adjustment in a subsequent measurement of the NO x  concentration in the exhaust flow in response to the determination in step (c), a first magnitude of the learning corrective adjustment based at least in part upon a second magnitude of the error in the measurement.   
     
     
         2 . The method of  claim 1 , further comprising
 determining that the vehicle is operating in a normal ambient condition;   wherein the error in the measurement of the concentration of NOx is determined n response to the determination that the vehicle is operating in a normal exhaust mode.   
     
     
         3 . The method of  claim 1 , wherein the learning corrective adjustment is applied in step (d) in response to a determination that the second magnitude of the error exceeds a predetermined magnitude. 
     
     
         4 . The method of  claim 1 , wherein the exhaust aftertreatment device is one of a Selective Catalytic Reduction (SCR) device and a Selective Catalytic Reduction on Filter (SCRF) device. 
     
     
         5 . The method of  claim 4 , wherein the exhaust aftertreatment device is configured to reduce at least a portion of the NOx present in the exhaust flow to nitrogen (N 2 ) and water (H 2 O). 
     
     
         6 . The method of  claim 4 , further comprising at least one of a Diesel Oxidation Catalyst (DOC) and a Diesel Particulate Filter (DPF). 
     
     
         7 . The method of  claim 4 , wherein the treatment fluid includes urea. 
     
     
         8 . The method of  claim 1 , wherein the first sensor is positioned downstream of an engine exhaust output. 
     
     
         9 . The method of  claim 1 , further comprising providing a second NO x  sensor positioned downstream of the exhaust aftertreatment device. 
     
     
         10 . The method of  claim 1 , wherein the treatment fluid is supplied by a diesel exhaust fluid dosing system. 
     
     
         11 . The method of  claim 1 , wherein determining the error includes comparing a first integral of the measurement taken with the first sensor with a second integral of a model of expected NOx concentration. 
     
     
         12 . The method of  claim 11 , wherein comparing the first and second integrals including determining a ratio of the first and second integrals. 
     
     
         13 . The method of  claim 12 , further comprising applying a low-pass filter to the ratio of the first and second integrals. 
     
     
         14 . The method of  claim 1 , further comprising determining a dead-band from a variation in at least one of (a) measurement by the first sensor and (b) a. model of expected NOx production based upon one or more engine operating parameters; wherein the learning corrective adjustment is applied in response to a determination that the error in the measurement exceeds the dead-band. 
     
     
         15 . The method of  claim 1 , further comprising modeling an expected NOx concentration from one or more operating parameters of the engine. 
     
     
         16 . A method of treating diesel exhaust in a vehicle, comprising:
 providing an exhaust aftertreatment device in an exhaust tailpipe, and a first nitrogen oxide (NO x ) sensor upstream of the exhaust aftertreatment device, the exhaust aftertreatment device configured to reduce NO x  present in an exhaust flow through the exhaust aftertreatment device with a treatment fluid applied to the exhaust flow;   measuring a concentration of NO x  in the exhaust flow with the first sensor;   determining an error in the measurement of the NO x  concentration, including:
 comparing a first integral of the measurement taken with the first sensor with a second integral of a model NOx reduction by determining a ratio of the first and second integrals; and 
 applying a low-pass filter to the ratio of the first and second integrals; and 
   applying a learning corrective adjustment in a subsequent measurement of the NO x  concentration in the exhaust flow in response to the determination in step (c), a first magnitude of the learning corrective adjustment based at least in part upon a second magnitude of the error in the measurement.   
     
     
         17 . The method of  claim 16 , wherein the learning corrective factor is applied in step (d) in response to a determination that the error exceeds a predetermined magnitude. 
     
     
         18 . A vehicle, comprising:
 an exhaust tailpipe, including:
 an exhaust aftertreatment device configured to reduce nitrogen oxide (NO x ) present in an exhaust flow through the exhaust aftertreatment device with a treatment fluid applied to the exhaust flow; and 
 a first NO x  sensor upstream of the exhaust aftertreatment device, the first NOx sensor configured to measure a concentration of NO x  in the exhaust flow; and 
   a controller communicatively linked to the sensor, the controller configured to determine an error in the measurement of the amount of the NO x  concentration, and apply a corrective factor in a subsequent measurement of the NO x  concentration in the exhaust flow, wherein a first magnitude of the corrective factor is based at least in part upon a second magnitude of the error in the measurement.   
     
     
         19 . The vehicle of  claim 18 , wherein the controller is configured to apply the learning corrective factor in response to a determination that the error exceeds a predetermined magnitude. 
     
     
         20 . The vehicle of  claim 18 , wherein the treatment fluid includes urea.