Exhaust purifier of an internal combustion engine

Abstract

An exhaust purifier purifies an exhaust gas of an internal combustion engine used in an exhaust purification system that has an addition unit and a catalyst. The addition unit, disposed in an exhaust pipe of the exhaust purification system, adds an additive agent to the exhaust pipe, and the catalyst, disposed on a downstream side of the addition unit in the exhaust pipe, purifies the exhaust gas with the additive agent added by the addition unit and stored therein. The exhaust purifier determines a total amount of the additive agent to be added, and calculates an exhaust flow velocity of the exhaust gas. The purifier controls the addition unit to enable the additive agent to be added to the exhaust pipe by the total amount determined, such that the purifier controls the addition unit to decrease a per-unit-time addition amount of the additive agent as the exhaust flow velocity decreases.

What is claimed is: 
     
         1 . An exhaust purifier for purifying an exhaust gas of an internal combustion engine used in an exhaust purification system that has an addition unit and a catalyst, wherein the addition unit, disposed in an exhaust pipe of the exhaust purification system, adds a predetermined additive agent to the exhaust pipe, and the catalyst, disposed on a downstream side of the addition unit in the exhaust pipe, purifies the exhaust gas with the additive agent added by the addition unit and stored therein, the exhaust purifier comprising:
 an addition amount determination unit determining a total amount of the additive agent to add from the addition unit;   an addition control unit controlling the addition unit to enable the additive agent to be added to the exhaust pipe by the total amount determined by the addition amount determination unit; and   a flow velocity calculation unit calculating an exhaust flow velocity of the exhaust gas, wherein   the addition control unit controls the addition unit to decrease a per-unit-time addition amount of the additive agent as the exhaust flow velocity calculated by the flow velocity calculation unit decreases.   
     
     
         2 . The exhaust purifier of  claim 1 , wherein
 the addition control unit adds the total amount of the additive agent in the exhaust pipe at one time.   
     
     
         3 . The exhaust purifier of  claim 1 , wherein
 the addition control unit adds the total amount of the additive agent in the exhaust pipe according to a division number that defines a number of times the additive agent is added, and   the addition control unit increases the division number as the exhaust flow velocity decreases to lower the per-unit-time addition amount of the additive agent.   
     
     
         4 . The exhaust purifier of  claim 1 , wherein
 the addition control unit adds the additive agent to the exhaust pipe according to a duty-control of the addition unit, and   the addition control unit decreases a driving duty as the exhaust flow velocity decreases to lower the per-unit-time addition amount of the additive agent.   
     
     
         5 . The exhaust purifier of  claim 1 , wherein
 the addition control unit adds the additive agent to the exhaust pipe according to a frequency-control of the addition unit, the frequency-control drives the addition unit periodically for a predetermined period, and   the addition control unit increases the predetermined period as the exhaust flow velocity decreases to lower the per-unit-time addition amount of the additive agent.   
     
     
         6 . The exhaust purifier of  claim 1 , the addition amount determination unit further comprising:
 a temperature acquisition unit acquiring a temperature of the catalyst;   a first calculation unit calculating a target storage amount indicating an amount of the additive agent stored in the catalyst as a temperature-dependent amount according to the temperature acquired by the temperature acquisition unit;   a second calculation unit calculating an estimated storage amount indicating an amount of the additive agent currently stored in the catalyst; and   a third calculation unit calculating a deviation between the target storage amount from the first calculation unit and the estimated storage amount from the second calculation unit, wherein   the addition amount determination unit determines the total amount of the additive agent to be added to the catalyst based on the deviation from the third calculation unit.   
     
     
         7 . The exhaust purifier of  claim 6 , wherein
 the first calculation unit calculates the target storage amount as an amount that is smaller than a maximum storable amount of the additive agent in the catalyst at the acquired temperature.   
     
     
         8 . The exhaust purifier of  claim 1 , wherein
 the flow velocity calculation unit calculates the exhaust flow velocity as a space velocity of the exhaust gas in the catalyst.   
     
     
         9 . The exhaust purifier of  claim 1 , wherein
 the addition unit adds urea aqueous solution as the additive agent,   the catalyst stores ammonia after converting the urea aqueous solution to ammonia, and is a NOx selective reduction catalyst that chemically reduces NOx in the exhaust gas by using the stored ammonia in the catalyst.