Exhaust purifying apparatus for an internal combustion engine and a failure prevention method therefor

An exhaust purifying apparatus of an internal combustion engine, comprising:

• an exhaust throttle valve provided in an exhaust passage of the internal combustion engine, so as to be able to be closed to close the exhaust passage;
• a relief passage provided communicating with the exhaust passage and bypassing said exhaust throttle valve;
• a relief valve provided in said relief passage so as to be able to be closed to close said relief passage, and arranged to be open to open said relief passage when receiving an increased pressure in the exhaust passage that is closed with closure of said exhaust throttle valve;
• deceleration determining means for determining whether the internal combustion engine is during deceleration;
• and
• a relief-valve forcibly operating means for closing said exhaust throttle valve to open said relief valve when it is determined by said deceleration determining means that the internal combustion engine is during deceleration.