System for Controlling Urea Injection Quantity of Vehicle and Method Thereof

Abstract

In a vehicle that is equipped with a selective catalytic reduction (SCR) device, the ammonia consumption amount is accurately predicted in the SCR catalytic convertor based on the ammonia amount consumed by NOx, and the absorbed ammonia amount is controlled to improve the purification performance of the NOx and responsiveness to a rapid variation of driving conditions such that the purification efficiency is enhanced. A method for controlling the urea injection amount of a vehicle may include calculating an entire consumption amount of ammonia that is necessary in an SCR catalytic convertor by applying an ammonia amount consumed by the NOx exhaust amount, an absorbed ammonia amount, an ammonia reaction ratio, an absorbed HC amount, and an deterioration, calculating a necessary urea amount by calculating a necessary ammonia amount corresponding to the calculated entire ammonia consumption amount, and injecting the necessary urea amount when the temperature of the SCR catalytic convertor is in a predetermined range.

1 . A urea injection amount control apparatus of a vehicle, comprising;
 an engine;   an SCR catalytic convertor that is configured to purify NOx through a reduction reaction of the NOx and NH3 that is included in exhaust gas;   a dosing module that is configured to inject a urea solution at the front of the SCR catalytic convertor; and   a control portion that is configured to estimate a necessary ammonia amount by predicting an entire ammonia consumption amount that is necessary in the SCR catalytic convertor so as to estimate an injection amount of a urea according to the necessary ammonia amount.   
   
   
       2 . The urea injection amount control apparatus of  claim 1 , wherein the control portion applies an ammonia amount consumed by the NOx, an absorbed ammonia amount, an ammonia reaction rate, an absorbed HC amount, and an deterioration according to exposure time to a predetermined temperature so as to predict the entire necessary ammonia consumption amount, and controls an absorbed ammonia amount according to the predicted entire necessary ammonia consumption amount. 
   
   
       3 . The urea injection amount control apparatus of  claim 2 , wherein the control portion applies a function of “NOx exhaust amount×stoichiometric ratio (NH 3 /NOx)×the ammonia reaction rate” to estimate the ammonia amount consumed by the NOx. 
   
   
       4 . The urea injection amount control apparatus of  claim 2 , wherein the control portion applies a function of “a present absorbed ammonia amount+an ammonia inflow amount−an ammonia amount consumed by the NOx (a reacted ammonia amount+a detached ammonia amount)” to estimate the absorbed ammonia amount. 
   
   
       5 . The urea injection amount control apparatus of  claim 2 , wherein the control portion divides a reacted amount of an ammonia into a reacted amount with the NOx and a reacted amount with oxygen, and applies a NOx purification ratio, in which a specific gravity of a reaction route is applied according to a variation of an exhaust condition and the stoichiometric ratio to estimate the reacted amount with the NOx. 
   
   
       6 . A method for controlling the urea injection amount of a vehicle, comprising:
 calculating an entire consumption amount of an ammonia that is necessary in an SCR catalytic convertor by applying an ammonia consumption amount according to a NOx exhaust amount, an absorbed ammonia amount, an ammonia reaction rate, an absorbed HC amount, and an deterioration;   calculating a necessary urea amount by calculating a necessary ammonia amount corresponding to the calculated entire ammonia consumption amount; and   injecting the necessary urea amount when a temperature of the SCR catalytic convertor is in a predetermined range.   
   
   
       7 . The method of  claim 6 , wherein the ammonia reaction rate includes a reaction rate with NOx and a reaction rate with oxygen. 
   
   
       8 . The method of  claim 6 , wherein the absorbed ammonia amount is “an accumulatively absorbed amount that is absorbed in the SCR catalytic convertor plus a new inflow amount minus a reacted amount and a detached amount.”