EXHAUST PURIFICATION DEVICE FOR ENGINE

摘要

From the exhaust temperature and the addition flow rate of aqueous urea injected into the exhaust upstream side of an SCR converter, the disclosed device can estimate the per unit-of-time deposition rate for urea crystals deposited in an exhaust system located further to the exhaust downstream side than the point where the aqueous urea is injected, and can estimate an accumulation amount for the urea crystals accumulated in the exhaust system by sequentially adding up the per unit-of-time deposition rate. Furthermore, the device estimates the per unit-of-time disengagement amount for the urea crystals which disengage from the exhaust system, according to the exhaust temperature, and sequentially subtracts the disengagement amount from the urea crystal accumulation amount, and thus estimates the accumulation amount of the urea crystals remaining in the exhaust system. Then, if the cumulative amount of the urea crystals is equal to or exceeds a specified amount, it is determined that a period for forcibly disengaging the urea crystals accumulated in the exhaust system has begun, thus a warning light is illuminated and a forcible disengagement processing is implemented wherein the exhaust temperature is increased so as to be hotter than the disengagement temperature of the urea crystals.