| 摘要 |
<P>PROBLEM TO BE SOLVED: To estimate an accumulation amount of urea crystals accumulated in an exhaust system. <P>SOLUTION: From the exhaust temperature and the addition flow rate of aqueous urea injected into the exhaust upstream side of an SCR (Selective Catalytic Reduction) catalyst, an exhaust emission control device for an engine estimates the per unit-of-time deposition rate for the urea crystals deposited in the exhaust system located further to the exhaust downstream side than the point where the aqueous urea is injected (S2), and estimates an accumulation amount for the urea crystals accumulated in the exhaust system by sequentially adding up the per unit-of-time deposition rate (S3). Furthermore, the device estimates the per unit-of-time desorption amount for the urea crystals which desorb from the exhaust system, according to the exhaust temperature (S4), and sequentially subtracts the desorption amount from the urea crystal accumulation amount, and thus estimates the accumulation amount of the urea crystals remaining in the exhaust system (S5). If the cumulative amount of the urea crystals is equal to or exceeds a specified amount (S6), it is determined that a period for forcibly desorbing the urea crystals accumulated in the exhaust system has begun, thus a warning light is illuminated (S7) and a forcible desorption processing is implemented wherein the exhaust temperature is increased so as to be hotter than the desorption temperature of the urea crystals (S8). <P>COPYRIGHT: (C)2012,JPO&INPIT |
