EXHAUST GAS PURIFYING DEVICE

摘要

PROBLEM TO BE SOLVED: To exhibit catalytic capacity to maximum and to efficiently purify NOx in a wide temp. range by controlling a reducing agent concn. in the exhaust gas flowing into the catalyst may be temporarily increased based on a detected temp. of a catalyst for purifying exhaust gas with a proper frequency that its NOx reduction capacity becomes maximum. SOLUTION: The catalyst 2 containing at least rhodium is arranged on an exhaust gas passage of an engine 1 and a temp. sensor 3 is arranged on the upstream side of the catalyst and also the feed rate of a hydrocarbon feed unit 6 is controlled variably by a control device 7 based on a detected signal of the temp. sensor 3. That is, the control device 7 reads the real catalyst temp. and judges whether the hydrocarbon may be fed or not from a table stored at a ROM 77. When the control device judges to start feeding, the hydrocarbon feed unit 6 is driven through a hydrocarbon feed unit driving part 73. The activity of the rhodium catalyst 2 is improved and the NOx is efficiently reduced and purified to N2 by executing such a feed back control.