Particulate matter sensor and exhaust gas purification apparatus

A particulate matter sensor comprising:

• a first detection filter provided in an exhaust gas flow passage and capable of collecting particle matter;
• a second detection filter provided on a downstream side of the first detection filter in the exhaust gas flow passage and capable of collecting the particle matter;
• a first differential pressure detection unit configured to detect a first differential pressure between pressures of an upstream side and the downstream side of the first detection filter;
• a second differential pressure detection unit configured to detect a second differential pressure between pressures of an upstream side and a downstream side of the second detection filter;
• and
• a particle matter amount detection unit configured to detect an amount of particle matter based on a detection result of the first differential pressure detection unit and a detection result of the second differential pressure detection unit, wherein
• the particle matter amount detection unit comprises:
• a first differential pressure initial value estimation unit configured to, based on an initial ratio between the first differential pressure and the second differential pressure and based on the second differential pressure detected by the second differential pressure detection unit, estimate an initial value of the first differential pressure in same conditions where the second differential pressure is detected by the second differential pressure detection unit;
• and
• a ratio calculation unit configured to calculate a ratio between the initial value of the first differential pressure estimated by the first differential pressure initial value estimation unit and the first differential pressure detected by the first differential pressure detection unit, wherein
• the particle matter amount detection unit is configured to detect the amount of particle matter based on the ratio calculated by the ratio calculation unit.