EXHAUST GAS CLEANING SYSTEM

An exhaust gas purifying system causes less torque fluctuation and is capable of preventing the occurrence of white smoke in a regeneration control operation for regenerating a continuous regeneration DPF 3. When the continuous regeneration DPF 3 with an oxidation catalyst 3Aa on the upstream side of a filter 3Ab is controlled to regenerate, an exhaust throttle valve 31 provided in an exhaust passage 2 is closed and a delay multi-step injection control is performed to increase the temperature of the exhaust gas if an exhaust temperature T1 at the inlet of the oxidation catalyst 3Aa is less than the activation temperature Ta of the oxidation catalyst. After the exhaust temperature T1 at the inlet of the oxidation catalyst 3Aa has risen to the activation temperature Ta of the oxidation catalyst or higher, the exhaust throttle valve 31 is opened in a stepwise or continuous manner so that the exhaust temperature T2 at the inlet of the filter 3Ab rises to a lower limit temperature of PM forced combustion Tb1 or higher.