Abstract: A filter (41) traps particulate matter contained in the exhaust gas of an engine (1). The filter (41) is regenerated by burning the trapped particulate matter by raising the temperature of the filter (41). When regeneration conditions are satisfied, a controller (31) raises the exhaust gas temperature to a first target exhaust gas temperature via an exhaust gas temperature adjusting mechanism (10) (S39), and burns the trapped particulate matter to regenerate the filter (41). When the engine (1) has rapidly decelerated during regeneration, the controller (31) decreases the exhaust gas temperature to a second target exhaust gas temperature lower than the first target exhaust gas temperature (S44, S45), and increases the exhaust gas flow rate (S52), thereby preventing the filter (41) from exceeding an upper limiting temperature.

Abstract: An exhaust passage (2) of a diesel engine (1) is provided with a filter (41) for trapping particulate matter. Regeneration of the filter (41) is divided into first to third phases. In the first phase the filter temperature is raised to the combustion temperature of the particulate matter in a short period of time through control of the exhaust gas temperature. In the second phase, the oxygen concentration of the exhaust gas is held at a predetermined low level while the filter temperature is maintained so as to prevent excessive combustion of particulate matter. In the third phase, wherein the amount of trapped particulate matter has been reduced, the oxygen concentration of the exhaust gas is held at a predetermined high level while the filter temperature is maintained so as to complete the combustion of the trapped particulate matter.