Exhaust gas purification apparatus

An exhaust gas purification apparatus including:

• a reducing catalytic converter disposed in an exhaust system of an engine, for reducing and purifying nitrogen oxide in the exhaust gas using a reducing agent;
• a reducing agent tank in which the reducing agent is stored;
• a reducing agent supply unit, which sucks up reducing agent from the reducing agent tank and mixes it with high pressure air for delivery;
• and an injection nozzle capable of injecting the reducing agent which is mixed with high pressure air, into an exhaust gas moving upstream side of the reducing catalytic converter in an exhaust gas passage of the exhaust system,
• wherein the apparatus comprises a clogging detection unit configured to detect clogging of the injection nozzle based on each detection output of a pressure of the high-pressure air introduced into the reducing agent supply unit, and a temperature of the injection nozzle,
• wherein the clogging detection unit comprises:
• a first comparator configured to compare a pressure of the high pressure air introduced into the reducing agent supply unit with a predetermined threshold value;
• a second comparator configured to compare a temperature of the injection nozzle with a predetermined threshold value;
• a logic circuit capable of performing a logical AND operation on outputs from each of the comparators;
• and
• a determination section that determines clogging of the injection nozzle based on an output from the logic circuit when the pressure of the high-pressure air and the temperature of the injection nozzle both exceed the threshold values, respectively, and outputs a signal indicating an occurrence of clogging.