Method and apparatus for determining whether a sensor which is responsive to both a reactant and a substance to be reduced by such reactant is responding to either un-reacted portions of the substance or un-reacted portions of the reactant

Abstract

A method wherein a reactant is added to a substance to react with such substance. The product of such reaction along with un-reacted portions of the substance and un-reacted portions of the reactant are directed to a sensor. The sensor produces an output signal in response to detection of both the un-reacted portions of the substance and the un-reacted portions of the reactant. The method includes changing the amount of reactant added to the substance. A measurement is made to determine whether the change in the amount of reactant and the change the output signal are in the same direction or in opposite directions. The changes in reactant and output signal are multiplied an integrated to form a correction on the quantity of reactant to be injected.

What is claimed is:  
     
         1 . A method, comprising: 
 (a) adding a reactant into a substance to react with the substance, the product of such reaction along with un-reacted portions of the substance and un-reacted portions of the reactant being directed to a sensor, such sensor producing an output signal in response to detection of both the un-reacted portions of the substance and the un-reacted portions of the reactant, such method including changing at least one of the amount of reactant added to the substance and the amount of the substance; and    (b) determining from said at least one of the change in the amount of reactant and the change in the amount of the substance, and from the change in the output signal, whether the sensor is responding to the substance or to the reactant.    
     
     
         2 . A method, comprising: 
 (a) adding a reactant into a substance to react with the substance, the product of such reaction along with un-reacted portions of the substance and un-reacted portions of the reactant being directed to a sensor, such sensor producing an output signal in response to detection of both the un-reacted portions of the substance and the un-reacted portions of the reactant, such method including changing the amount of reactant added to the substance; and    (b) determining from the change in the amount of reactant and the change the output signal whether the sensor is responding to the substance or to the reactant.    
     
     
         3 . A sensing system, comprising: 
 (a) a sensor for producing an output signal in response to either a first substance of a reaction or to a second substance of the reaction;    (b) an injector for changing the level of one of the substances in the reaction;    (c) a processor responsive to the output signal for determining whether the sensor is responding to the first substance to the second substance.    
     
     
         4 . A NOx sensing system, comprising: 
 (a) a NOx sensor for producing an output signal in response to NO x  and urea;    (b) a processor responsive to the output signal for determining whether the sensor is responding to NOx or to urea.    
     
     
         5 . A method, comprising: 
 (a) adding a reactant to the substance to react with a substance, the product of such reaction along with un-reacted portions of the substance and un-reacted portions of the reactant being directed to a sensor, such sensor producing an output signal in response to detection of both the un-reacted portions of the substance and the un-reacted portions of the reactant, such method including changing the amount of reactant added to the substance; and    (b) determine whether the change in the amount of reactant and the change the output signal are in the same direction or in opposite directions.    
     
     
         6 . A method for use in reducing a substance with a reactant added to the substance to react with such substance, the product of such reaction along with un-reacted portions of the substance and un-reacted portions of the reactant being directed to a sensor, such sensor producing an output signal in response to detection of both the un-reacted portions of the substance and the un-reacted portions of the reactant, such method comprising: 
 (a) changing the amount of reactant added to the substance;    (b) determining whether the output signal increases or decreases with the changed amount of reactant; and    (c) determining therefrom whether the sensor is responding to the un-reacted reactant or to the un-reacted substance.    
     
     
         7 . A method, comprising: 
 changing an amount of a reactant added to a substance to be reacted , and thereby reduced by, the reactant, the time history of such change in the reactant being represented by:    Û(t)    where t is time;    such reaction taking place in the presence of a catalyst;    wherein un-reacted portions of the reactant and the un-reacted portions of the substance are passed by a sensor, such sensor producing an output signal in response to the un-reacted portions of the reactant or the un-reacted portions of the substance, the change in the output signal from the change in the amount of reactant added to the substance may be represented as:    {circumflex over (V)}(t)    wherein such change takes place over a period of time T, and with a delay between the change in the amount of the reactant, T 0 , to the time the reaction is effected by such change in the amount of reactant being represented by D;    producing a signal, I, to determine whether the output signal increases or decreases with the changed amount of reactant, such signal being produced in accordance with            I   =       ∫   t0     t0   +   D   +     T                 e                 x                 c                  V   ^          (     t   +   D     )              u   ^          (   t   )               t                           determining whether, I>0 or I<0;    concluding that the sensor is responding to the un-reacted reactant if I>0 and concluding that the sensor is responding to the un-reacted substance if I<0.    
     
     
         8 . The method recited in  claim 7  including determining whether I=0, and is so concluding that the injector is faulty.  
     
     
         9 . The method recited in  claim 7  including determining whether V is greater than a calibratable threshold and if so concluded that the catalyst is faulty.