Exhaust gas purification system and method

An exhaust gas purification system comprises a particulate filter, a sensor, and a controller. The filter is located in an exhaust passage of the engine and traps particulate in an exhaust gas. The sensor detects the filter differential pressure between an inlet and outlet of particulate filter. The controller controls the regeneration of the particulate filter. An exhaust gas purification system comprises a particulate filter, a sensor, and a controller. The filter is located in an exhaust passage of the engine and traps particulate in an exhaust gas. The sensor detects the filter differential pressure between an inlet and outlet of particulate filter. The controller controls the regeneration of the particulate filter. It is programmed to execute a control for burning particulate accumulated on the particulate filter and thus regenerating a particulate filter, determine whether the regeneration of the particulate filter is completed, detect, in cooperation with the sensor, the filter differential pressure immediately after it is determined that the regeneration of the particulate filter is completed, and estimate an ash accumulation amount based on the detected filter differential pressure. An independent claim is also included for exhaust gas purification comprising executing a control for burning particulate accumulated on the particulate filter to regenerate the particulate filter, determined whether regeneration of the particulate filter is completed, immediately after it is determined that regeneration of the particulate filter is completed, and estimating an ash accumulation amount that is an amount of ash accumulated on the particulate filter based on the detected filter differential pressure.