Detection device, detection method, and exhaust purification device with detection device

A detection device configured to detect collapse of particulate matter collected in a filter provided in an exhaust system flow path of an internal combustion engine, the detection device comprising:

• a differential pressure acquisition part configured to acquire a differential pressure between an exhaust inlet side and an exhaust outlet side of the filter;
• an electronic control unit (ECU) configured to:
• determine whether water is generated in the exhaust system flow path;
• and
• determine that at least a part of the particulate matter collected in the filter has collapsed when the acquired differential pressure has increased by a predetermined differential pressure or more within a predetermined period or a particulate matter accumulation amount in the filter estimated based on the acquired differential pressure has increased by a predetermined accumulation amount or more within the predetermined period, in a state where:
• the acquired differential pressure is equal to or larger than a predetermined first differential pressure threshold or the particulate matter accumulation amount in the filter estimated based on the differential pressure is equal to or larger than a predetermined first accumulation amount threshold;
• and
• the electronic control unit has determined that water is generated;
• and
• a water temperature acquisition part configured to acquire a water temperature of cooling water of the internal combustion engine,
• wherein the electronic control unit determines that water is generated in the exhaust system flow path in a case where a water temperature decrease amount during a stop period which is obtained by subtracting a restart-time water temperature from a stop-time water temperature is equal to or larger than a predetermined amount, the restart-time water temperature being acquired by the water temperature acquisition part when the internal combustion engine is restarted, and the stop-time water temperature being acquired by the water temperature acquisition part when the internal combustion engine is stopped.