Method for estimating exhaust gas state of engine, method for determining abnormality of catalyst, and catalyst abnormality determination device for an engine

Abstract

A method that includes estimating an ammonia adsorption amount of a NOx selective reduction catalyst; detecting a catalytic temperature of the catalyst; and estimating a slip amount of ammonia that is an amount of ammonia discharged into a portion of an exhaust passage on a downstream side of the catalyst based on the estimated ammonia adsorption amount and the detected catalytic temperature, and for a same catalytic temperature, the slip amount of ammonia is estimated to be larger when the estimated ammonia adsorption amount is a first value than when the estimated ammonia adsorption amount is a second value smaller than the first value, and for a same estimated ammonia adsorption amount, the slip amount of ammonia is estimated to be larger when the detected catalytic temperature is a third value than when the detected catalytic temperature is fourth value smaller than the third value.

1 . A method, comprising:
 estimating an ammonia adsorption amount of a NOx selective reduction catalyst, the NOx selective reduction catalyst being provided in an exhaust passage of an engine, the NOx selective reduction catalyst reducing NOx in an exhaust gas by using a supplied reducing agent, ammonia or a precursor of the ammonia being supplied as the reducing agent to the NOx selective reduction catalyst by a reducing agent supplier;   detecting a catalytic temperature of the NOx selective reduction catalyst; and   estimating, using processing circuitry, a slip amount of ammonia that is an amount of ammonia discharged into a portion of the exhaust passage on a downstream side of the NOx selective reduction catalyst based on the estimated ammonia adsorption amount and the detected catalytic temperature, wherein   in the estimating of the slip amount of ammonia, for a same catalytic temperature, the slip amount of ammonia is estimated to be larger in a case where the estimated ammonia adsorption amount is a first value than in a case where the estimated ammonia adsorption amount is a second value that is smaller than the first value, and   in the estimating of the slip amount of ammonia, for a same estimated ammonia adsorption amount, the slip amount of ammonia is estimated to be larger in a case where the detected catalytic temperature is a third value than in a case where the detected catalytic temperature is a fourth value that is smaller than the third value.   
     
     
         2 . The method according to  claim 1 , wherein
 in the estimating of the slip amount of ammonia, for a same catalytic temperature, an increase in the estimated slip amount of ammonia with respect to an increase in the estimated ammonia adsorption amount is larger in the case where the estimated ammonia adsorption amount is the first value than in the case where the estimated ammonia adsorption amount is the second value.   
     
     
         3 . The method according to  claim 1 , wherein
 in the estimating of the slip amount of ammonia, for a same estimated ammonia adsorption amount, an increase in the estimated slip amount of ammonia with respect to an increase in the detected catalytic temperature is larger in the case where the detected catalytic temperature is the third value than in the case where the detected catalytic temperature is the fourth value.   
     
     
         4 . The method according to  claim 1 , further comprising:
 estimating an amount of ammonia that is discharged from a NOx storage catalyst into the exhaust gas when NOx stored in the NOx storage catalyst is reduced by a NOx catalyst regeneration controller of the engine, wherein   in the estimating of the ammonia adsorption amount, the ammonia adsorption amount of the NOx selective reduction catalyst is estimated based on the amount of ammonia or an amount of a precursor of ammonia that is supplied by the reducing agent supplier and the amount of ammonia that is estimated in the estimating of the amount of ammonia that is discharged from the NOx storage catalyst.   
     
     
         5 . The method according to  claim 4 , wherein
 the NOx storage catalyst is disposed in a portion of the exhaust passage on an upstream side of the NOx selective reduction catalyst, capable of storing NOx in the exhaust gas, and capable of reducing stored NOx, and   the NOx catalyst regeneration controller is configured to bring an air-fuel ratio of the exhaust gas to an air-fuel ratio near a stoichiometric air-fuel ratio or a richer air-fuel ratio than the stoichiometric air-fuel ratio in order to reduce NOx stored in the NOx storage catalyst.   
     
     
         6 . The method according to  claim 1 , further comprising:
 controlling an abnormality determination of the NOx selective reduction catalyst based on the estimated slip amount of ammonia.   
     
     
         7 . The method according to  claim 1 , wherein
 the engine comprises a NOx sensor that is disposed in the portion of the exhaust passage on the downstream side of the NOx selective reduction catalyst, an output value of the NOx sensor varying in accordance with an amount of NOx and the amount of ammonia in the exhaust gas, and   the method further comprises:   performing the abnormality determination on whether the NOx selective reduction catalyst is abnormal based on the output value of the NOx sensor; and   restricting the abnormality determination in a case where the estimated slip amount of ammonia is equal to or larger than a specified slip amount.   
     
     
         8 . The method according to  claim 1 , wherein
 the estimating of the slip amount of ammonia estimates larger slip amount of ammonia as the estimated ammonia adsorption amount approaches adsorption limit of the NOx selective reduction catalyst.   
     
     
         9 . The method according to  claim 1 , wherein
 the estimating of the slip amount of ammonia estimates the slip amount of ammonia such that, for the estimated slip amount of ammonia under a same catalytic temperature that is equal to or higher than a specified temperature, an increase in the slip amount of ammonia with respect to an increase in the estimated ammonia adsorption amount is larger in a case where the estimated ammonia adsorption amount is equal to or larger than one-third of an adsorption limit of the NOx selective reduction catalyst than in a case where the estimated ammonia adsorption amount is smaller than one-third of the adsorption limit.   
     
     
         10 . The method according to  claim 9 , wherein
 the specified temperature is a temperature near a lower limit of a temperature range where a NOx purification rate of the NOx selective reduction catalyst is equal to or higher than a specified purification rate.   
     
     
         11 . The method according to  claim 1 , wherein
 in the estimating of the slip amount of ammonia, the ammonia adsorption amount, with which the slip of ammonia starts occurring, is estimated to be smaller as the catalytic temperature is increased.   
     
     
         12 . The method according to  claim 1 , wherein
 in the estimating of the slip amount of ammonia, the slip amount of ammonia is multiplied by a correction coefficient based on a concentration of ammonia in the exhaust gas.   
     
     
         13 . The method according to  claim 12 , wherein
 the correction coefficient is set to 1 in a case where the concentration of ammonia is located at a middle value between a highest concentration of ammonia that the engine possibly acquires and 0,   the correction coefficient is reduced from 1 in a case where the concentration of ammonia is higher than the middle value,   the correction coefficient is increased from 1 in a case where the concentration of ammonia is lower than the middle value, and   the correction coefficient varies within a range that is larger than 0 and smaller than 2.   
     
     
         14 . The method according to  claim 1 , further comprising:
 calculating a NOx purification rate of the NOx selective reduction catalyst;   determining whether the NOx purification rate is lower than a specified purification rate; and   determining whether the estimated slip amount of ammonia is less than a specified slip amount in a case where the NOx purification rate is determined to be lower than the specified purification rate.   
     
     
         15 . The method according to  claim 14 , further comprising:
 adding 1 to a failure account in a case where the estimated slip amount of ammonia is determined to be less than the specified slip amount; and   outputting a warning in a case where it is determined that the failure count is equal to or larger than a specified value.   
     
     
         16 . The method according to  claim 1 , further comprising:
 controlling an amount of the reducing agent supplied to the NOx selective reduction catalyst based on the estimated slip amount of ammonia.   
     
     
         17 . The method according to  claim 1 , further comprising:
 calculating a NOx purification rate of the NOx selective reduction catalyst based on the estimated slip amount of ammonia.   
     
     
         18 . The method according to  claim 1 , further comprising:
 storing, in a memory, a map that represents a relationship between the ammonia adsorption amount, the slip amount of ammonia, and the catalytic temperature; and   estimating the slip amount of ammonia using the map.   
     
     
         19 . A non-transitory computer readable medium including executable instructions, which when executed by a computer cause the computer to execute a method, the method comprising:
 estimating an ammonia adsorption amount of a NOx selective reduction catalyst, the NOx selective reduction catalyst being provided in an exhaust passage of an engine, the NOx selective reduction catalyst reducing NOx in an exhaust gas by using a supplied reducing agent, ammonia or a precursor of the ammonia being supplied as the reducing agent to the NOx selective reduction catalyst by a reducing agent supplier;   detecting a catalytic temperature of the NOx selective reduction catalyst; and   estimating a slip amount of ammonia that is an amount of ammonia discharged into a portion of the exhaust passage on a downstream side of the NOx selective reduction catalyst based on the estimated ammonia adsorption amount and the detected catalytic temperature, wherein   in the estimating of the slip amount of ammonia, for a same catalytic temperature, the slip amount of ammonia is estimated to be larger in a case where the estimated ammonia adsorption amount is a first value than in a case where the estimated ammonia adsorption amount is a second value that is smaller than the first value, and   in the estimating of the slip amount of ammonia, for a same estimated ammonia adsorption amount, the slip amount of ammonia is estimated to be larger in a case where the detected catalytic temperature is a third value than in a case where the detected catalytic temperature is a fourth value that is smaller than the third value.   
     
     
         20 . A device, comprising:
 a catalytic temperature detector configured to detect a temperature of a NOx selective reduction catalyst, the NOx selective reduction catalyst being provided in an exhaust passage of an engine, the NOx selective reduction catalyst reducing NOx in an exhaust gas by using a supplied reducing agent, ammonia or a precursor of the ammonia being supplied as the reducing agent to the NOx selective reduction catalyst by a reducing agent supplier;   a NOx sensor that is disposed in the portion of the exhaust passage on the downstream side of the NOx selective reduction catalyst, an output value of the Nox sensor varying in accordance with an amount of NOx and an amount of ammonia in the exhaust gas; and   processing circuitry configured to
 estimate an ammonia adsorption amount of the NOx selective reduction catalyst; 
 estimate a slip amount of ammonia that is an amount of ammonia discharged into a portion of the exhaust passage on a downstream side of the NOx selective reduction catalyst based on the estimated ammonia adsorption amount and the detected catalytic temperature; 
 perform an abnormality determination on whether the NOx selective reduction catalyst is abnormal based on the output value of the NOx sensor; and 
 restrict the abnormality determination in a case where the estimated slip amount of ammonia is equal to or larger than a specified slip amount, wherein 
   in the estimating of the slip amount of ammonia, for a same catalytic temperature, the slip amount of ammonia is estimated to be larger in a case where the estimated ammonia adsorption amount is a first value than in a case where the estimated ammonia adsorption amount is a second value that is smaller than the first value, and   in the estimating of the slip amount of ammonia, for a same estimated ammonia adsorption amount, the slip amount of ammonia is estimated to be larger in a case where the detected catalytic temperature is a third value than in a case where the detected catalytic temperature is a fourth value that is smaller than the third value.