초록 ▼

In an addition-amount controller for an exhaust gas purifying agent to be used for an exhaust emission control system, a catalyst has properties of storing NH3 and further decreasing the critical reaction temperature as an amount of NH3 storage at the catalyst is increased. In the addition-amount co

In an addition-amount controller for an exhaust gas purifying agent to be used for an exhaust emission control system, a catalyst has properties of storing NH3 and further decreasing the critical reaction temperature as an amount of NH3 storage at the catalyst is increased. In the addition-amount controller, a present NH3 storage amount that is a storage amount of NH3 of the catalyst is detected at a detection time, the NH3 storage amount of the catalyst is changed by controlling an addition amount by an addition valve, and the NH3 storage amount of the catalyst is controlled to a target NH3 storage amount based on the detected present NH3 storage amount.

대표청구항 ▼

1. An addition-amount controller for an exhaust gas purifying agent, the controller for use with an exhaust emission control system including a catalyst for promoting a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit, and an a

1. An addition-amount controller for an exhaust gas purifying agent, the controller for use with an exhaust emission control system including a catalyst for promoting a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit, and an addition valve for adding an additive of NH3 or an additive serving as a generating source of the NH3 to the catalyst itself or the exhaust gas on an upstream side with respect to the catalyst, the additive being adapted to purify NOx in exhaust gas by the exhaust gas purification reaction on the catalyst, the addition-amount controller being adapted to control an amount of addition by the addition valve, the catalyst having properties of storing NH3 and further decreasing the critical reaction temperature as the amount of NH3 storage is increased, the addition-amount controller comprising: an electronic control unit including instructions which when implemented by the electronic control unit provides at least functionality comprising: obtaining a present NH3 storage amount that is a storage amount of NH3 of the catalyst at a detection time;changing the NH3 storage amount of the catalyst by controlling the addition amount by the addition valve;controlling the NH3 storage amount of the catalyst to a target NH3 storage amount, based on the obtained present NH3 storage amount;detecting a limit NH3 storage amount that is able to be stored in the catalyst, based on the temperature of the catalyst or a value equivalent to the temperature of the catalyst;setting a variable range of the target NH3 storage amount using the detected limit NH3 storage amount as an upper limit; andselecting one mode to be executed based on satisfaction of an execution condition for each mode, from among a plurality of control modes, the control modes including a purification control mode in which the addition amount by the addition valve is determined according to a predetermined parameter associated with an amount of NOx in the exhaust gas, and a storage control mode in which the addition amount by the addition valve is set to be larger than that in the purification control mode;executing the control of the addition amount by the addition valve based on a difference between the present NH3 storage amount and the target NH3 storage amount when the storage control mode is selected;executing the control of the addition amount by the addition valve based on the predetermined parameter associated with the amount of NOx in the exhaust gas, without using the present NH3 storage amount and the target NH3 storage amount, when the purification control mode is selected;the target NH3 storage amount being variable in the set variable range with the limit NH3 storage amount as the upper limit;determining a required NH3 storage amount based on the critical reaction temperature;comparing the limit NH3 storage amount with the required NH3 storage amount determined based on the critical reaction temperature; andsetting the target NH3 storage amount based on the comparison including setting the required NH3 storage amount as the target NH3 storage amount if the required NH3 storage amount is smaller than the limit NH3 storage amount in said comparing, and setting the limit NH3 storage amount as the target NH3 storage amount if the required NH3 storage amount is not smaller than the limit NH3 storage amount in the comparison. 2. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein detecting the limit NH3 storage amount as the value equivalent to the temperature of the catalyst is based on a temperature of exhaust gas on a downstream side with respect to the catalyst. 3. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein controlling the NH3 storage amount of the catalyst to the target NH3 storage amount is performed by covering a shortfall of the NH3 storage amount corresponding to a difference between the target NH3 storage amount and the present NH3 storage amount. 4. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein controlling the storage amount control comprises repeatedly executing the control of the NH3 storage amount while a predetermined condition is satisfied. 5. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein the functionality further comprises determining whether the NH3 storage amount of the catalyst is larger than a predetermined amount, wherein a satisfaction requirement of an execution condition of the storage control mode includes a determination that the NH3 storage amount of the catalyst is not larger than the predetermined amount. 6. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein the functionality further comprises determining whether NH3 is able to be stored in the catalyst, wherein a satisfaction requirement of an execution condition of the storage control mode includes a determination that NH3 is able to be stored. 7. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein the functionality further comprises determining whether the temperature of the catalyst is lower than a predetermined temperature, wherein a satisfaction requirement of the execution condition of the storage control mode includes a determination that the temperature of the catalyst is lower than the predetermined temperature. 8. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein the exhaust emission control system is adapted to purify the exhaust gas emitted from an internal combustion engine, and wherein obtaining the storage amount of NH3 includes determining an amount of increase or decrease in the NH3 storage amount of the catalyst of each time based on a difference between the NH3 amount supplied to the catalyst and an amount of consumption of NH3 on the catalyst, while subsequently summing the amounts of increase or decrease of the respective times, so as to detect the present NH3 storage amount. 9. The addition-amount controller for an exhaust gas purifying agent according to claim 8, wherein the functionality further comprises determining the amount of consumption of NH3 on the catalyst based on a predetermined parameter associated with an operating condition of the internal combustion engine. 10. An exhaust emission control system comprising: the addition-amount controller as in claim 8;the catalyst and the addition valve; anda urea water supply device for supplying the urea aqueous solution to the addition valve. 11. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein the functionality further comprises determining the target NH3 storage amount based on a boundary value at which the critical reaction temperature is not decreased even by increasing the NH3 storage amount of the catalyst. 12. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein the addition valve is adapted to inject and add a urea aqueous solution as the additive to the exhaust gas on an upstream side with respect to the catalyst. 13. The addition-amount controller for an exhaust gas purifying agent according to claim 1, wherein the target NH3 storage amount is variable in the variable range that is changed in accordance with a temperature of the catalyst. 14. A method of controlling an addition-amount controller for an exhaust gas purifying agent for use with an exhaust emission control system including a catalyst for promoting a specific exhaust gas purification reaction in a temperature range having a critical reaction temperature as a lower limit, and an addition valve for adding an additive of NH3 or an additive serving as a generating source of the NH3 to the catalyst itself or the exhaust gas on an upstream side with respect to the catalyst, the additive being adapted to purify NOx in exhaust gas by the exhaust gas purification reaction on the catalyst, the addition-amount controller being adapted to control an amount of addition by the addition valve, the catalyst having properties of storing NH3 and further decreasing the critical reaction temperature as the amount of NH3 storage is increased, the method comprising: obtaining a present NH3 storage amount that is a storage amount of NH3 of the catalyst at a detection time;changing the NH3 storage amount of the catalyst by controlling the addition amount by the addition valve;controlling the NH3 storage amount of the catalyst to a target NH3 storage amount, based on the obtained present NH3 storage amount;detecting a limit NH3 storage amount that is able to be stored in the catalyst, based on the temperature of the catalyst or a value equivalent to the temperature of the catalyst;setting a variable range of the target NH3 storage amount using the detected limit NH3 storage amount as an upper limit;selecting, using a computer processor, one mode to be executed based on satisfaction of an execution condition for each mode, from among a plurality of control modes, the control modes including a purification control mode in which the addition amount by the addition valve is determined according to a predetermined parameter associated with an amount of NOx in the exhaust gas, and a storage control mode in which the addition amount by the addition valve is set to be larger than that in the purification control mode;executing control of the addition amount by the addition valve, based on a difference between the present NH3 storage amount and the target NH3 storage amount when the storage control mode is selected;executing control of the addition amount by the addition valve, based on the predetermined parameter associated with the amount of NOx in the exhaust gas, without using the present NH3 storage amount and the target NH3 storage amount, when the purification control mode is selected;determining a required NH3 storage amount based on the critical reaction temperature;comparing the limit NH3 storage amount with the required NH3 storage amount which is determined based on the critical reaction temperature; andsetting the target NH3 storage amount based on said comparing;wherein the target NH3 storage amount is variable in the set variable range with the limit NH3 storage amount as the upper limit; andwherein the required NH3 storage amount is set as the target NH3 storage amount if the required NH3 storage amount is smaller than the limit NH3 storage amount in said comparing, and wherein the limit NH3 storage amount is set as the target NH3 storage amount if the required NH3 storage amount is not smaller than the limit NH3 storage amount in the comparing.