| 摘要 |
In a treatment for regenerating the purification capability of an exhaust emission control system, a technique for improving exhaust emission more positively is provided by supplying a reducing agent to the exhaust emission control system and allowing part of exhaust to bypass the exhaust emission control system. When an addition synchronous bypass control is carried out in which an reducing agent is added when an NSR is subject to NOx reduction treatment and the volume of exhaust passing through a bypass pipe out of exhaust passing an exhaust pipe is increased to thereby decrease the volume of exhaust passing through the NSR, a judgment is made (S106) as to which is larger a reduction in volume of Nox exhausted (S105) due to an increase in conversion efficiency of the NSR as the result of the addition synchronous bypass control carried out or an increase in volume of Nox exhausted (S103) due to an increase in exhaust passing through the bypass pipe. When a reduction in volume of NOx exhausted due to an increase in conversion efficiency of the NSR is judged to be larger than an increase in volume of Nox exhausted due to an increase in exhaust passing through the bypass pipe, the addition synchronous bypass control is executed (107).
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