Exhaust emission purifying apparatus for engine

Abstract

A technology for purifying an exhaust emission from an engine is provided, in which a misjudgment caused by a time lag between the abnormality detection and an abnormality judgment is avoided, in the case where a plurality of abnormalities is judged on the aqueous solution of a reducing agent or the like. After a first abnormality judgment (Femp=1: the time t 2 ) is made, when a second abnormality is detected as a result that the concentration Dn as a state parameter is directly shifted from a first region A to a second region C (the time t 3 ), the first abnormality judgment is maintained for a predetermined period of time PRD after the second abnormality detection.

1 . An exhaust emission purifying apparatus for an engine, operable to add a reducing agent for NO x  to an exhaust gas of the engine thereby reducing the NO x  in the exhaust gas, comprising: 
 a tank for storing the reducing agent to be added to the exhaust gas or a precursor thereof, in an aqueous solution state;    a detecting unit for detecting a predetermined state parameter on the aqueous solution based on a thermal characteristic of the aqueous solution stored in the tank; and    a calculating unit for performing a predetermined calculation on abnormalities of the aqueous solution based on the detected state parameter, wherein    the calculating unit includes: an abnormality detecting section which detects a predetermined abnormality on the aqueous solution when the detected state parameter is within an abnormal region other than a predetermined region defined as a normal region; and an abnormality judging section which makes an abnormality judgment upon an establishment of a predetermined determinate condition after the abnormality is detected,    the abnormality detecting scion detects a first abnormality when the detected state parameter is within a first region in the abnormal region, and also detects a second abnormality when the detected state parameter is within a second region defined as a different region from the first region in the abnormal region, and    the abnormality judging section makes a first abnormality judgment in association with the first abnormality detection, and also makes a second abnormality judgment in association with the second abnormality detection, and after the first abnormality judgment is made, when the second abnormality is detected as a result that the detected state parameter is directly shifted from the first region to the second region, maintains the first abnormality judgment for a predetermined period of time from the detection of the second abnormality concerned.    
   
   
       2 . The apparatus according to  claim 1 , wherein the abnormality detecting section detects, as the first abnormality, one abnormality that is selected from a group containing a residual amount deficiency of the aqueous solution, a dilution of the aqueous solution and a mixing of a different kind of aqueous solution in the tank, based on the detected state parameter, and also detects, as the second abnormality, another one selected from the group.  
   
   
       3 . The apparatus according to  claim 1 , wherein the abnormality judging section performs setting of a counter therein, which is increased by a predetermined value at every time when the first or second abnormality is detected, and makes the first or second abnormality judgment based on a value counted by the counter.  
   
   
       4 . The apparatus according to  claim 3 , wherein the abnormality judging section judges whether or not the aqueous solution is in a stable state in the tank, and varies the predetermined value between a first case where it is judged that the aqueous solution is in the stable state and a second case where it is judged that the aqueous solution is not in the stable state.  
   
   
       5 . The apparatus according to  claim 3 , wherein the abnormality judging section performs setting of the counter on conducting of at least the second abnormality judgment, and makes the second abnormality judgment when the counter reaches a predetermined abnormality judgment value, and 
 the predetermined period of time is determined as being a period of time elapsing from a detection of the second abnormality by the detecting unit until the counter reaches the predetermined abnormality judgment value.    
   
   
       6 . The apparatus according to  claim 1 , wherein the abnormality judging section makes the second abnormality judgment, when the detected state parameter remaining inside the second region becomes a predetermined proportion with respect to a predetermined number of detection of frequencies after the detected state parameter has been shifted to the second region from the outside thereof.  
   
   
       7 . The apparatus according to  claim 1 , wherein the calculating unit generates a signal indicating that the addition of the reducing agent to the exhaust gas should be stopped, when one of the first and second abnormality judgments is made.  
   
   
       8 . The apparatus according to  claim 7 , wherein the calculating unit generates, when one of the first or second abnormality judgments is made, a signal indicating that an amount of NO x  emission from the engine should be reduced to a level below that encountered when one of the first and second abnormality judgments is not made.  
   
   
       9 . The apparatus according to  claim 7 , wherein the calculating unit generates, when one of the first and second abnormality judgments is made, a signal indicating that an output characteristic of the engine should be varied relative to an accelerator control operation from that taken when one of the first and second abnormality judgments is not made, to thereby restrict an output of the engine.  
   
   
       10 . The apparatus according to  claim 7 , wherein the calculating unit further includes an addition control section which controls an adding amount of the reducing agent to the exhaust gas based on the detected state parameter.  
   
   
       11 . The apparatus according to  claim 1 , further comprising a warning unit capable of urging a driver to recognize an occurrence of abnormality when one of the first and second abnormality judgments is made.  
   
   
       12 . The apparatus according to  claim 1 , wherein the state parameter is a concentration of the reducing agent or the precursor thereof contained in the aqueous solution.  
   
   
       13 . The apparatus according to  claim 12 , wherein the detecting unit comprises: a sensor element part arranged inside of the tank; and a circuit section connected to the sensor element part to execute a predetermined calculation to calculate the concentration of the reducing agent or the precursor thereof, wherein 
 the sensor element part includes: a heater; and a temperature sensing element having a property in which an electrical characteristic value thereof is changed according to the temperature, which is directly or indirectly in contact with the aqueous solution and also is heated by the heater, and wherein    the circuit section drives the heater, detects the electrical characteristic value of the heated temperature sensing element, and calculates the concentration of the reducing agent or the precursor thereof based on the detected electrical characteristic value.    
   
   
       14 . The apparatus according to  claim 1 , wherein the reducing agent is ammonia.  
   
   
       15 . An exhaust emission purifying apparatus for an engine, for adding a reducing agent for NO x  to an exhaust gas of the engine to reduce NO x  in the exhaust gas, comprising: 
 a tank for storing the reducing agent to be added to the exhaust gas or a precursor thereof, in an aqueous solution state;    means for detecting a concentration of the reducing agent or the precursor thereof contained in the aqueous solution stored in the tank;    means for detecting a predetermined abnormality on the aqueous solution when the detected concentration is within an abnormal region other than a predetermined region defined as a normal region; and    means for making an abnormality judgment upon the establishment of a predetermined determinate condition after the abnormality is detected, wherein    the means for detecting the predetermined abnormality detects a first abnormality when the detected concentration remains within a first region in the abnormal region, and also detects a second abnormality when the detected concentration remains within a second region defined as a different region from the first region in the abnormal region, and    the means for making an abnormality judgment makes a first abnormality judgment in association with the first abnormality detection, and also makes a second abnormality judgment in association with the second abnormality detection, and after the first abnormality judgment is made, when the second abnormality is detected as a result that the detected concentration is directly shifted from the first region to the second region, maintains the first abnormality judgment for a predetermined period of time from the detection of the second abnormality concerned.