An exhaust gas purification device for an engine

摘要

An exhaust gas purification device, for an engine (1) having an exhaust passage (16), said device comprising a catalyst (17) arranged in the exhaust passage (16) for purifying NOx with a reducing agent. A purification ratio of the NOx by said catalyst (17) becomes more than a predetermined ratio when a temperature of said catalyst (17) is within a predetermined temperature range. A predetermined amount of a reducing agent is fed to said catalyst (17). An amount of the reducing agent to be fed is increased with respect to the predetermined amount when a temperature of an upstream end (20) of the catalyst (17) is lower than a lowest value of the predetermined temperature range and a temperature of a downstream end (24) of the catalyst (17) is higher than the lowest value.