Patent ID: 9334822
Filing Date: 2016-05-10
CPC Classification: B01D,F01N,F02D,Y02T

Claim Text:
1. A purification apparatus of an exhaust gas of an engine, comprising: a catalyst having an oxygen holding capacity with which oxygen in the exhaust gas discharged from the engine is held or released in accordance with an air fuel ratio in the exhaust gas, an upstream air fuel ratio sensor adapted to detect an air fuel ratio of the exhaust gas in an upstream side of the catalyst, and a downstream air fuel ratio sensor adapted to detect an air fuel ratio of the exhaust gas in a downstream side of the catalyst, and comprising further: an engine controller configured to: calculate, when the downstream air fuel ratio sensor judges a rich side of a theoretical air fuel ratio, wherein a value in a lean side of the theoretical air fuel ratio is taken as an initial target air fuel ratio, a first target air fuel ratio, which is an air fuel ratio between the initial target air fuel ratio and the theoretical air fuel ratio, directing toward a richer side from the initial target air fuel ratio to the theoretical air fuel ratio based on a first target catalyst's oxygen holding amount and a first estimated catalyst's oxygen holding amount, correct a fuel supply amount to the engine thereby obtaining the first target air fuel ratio, calculate, when a target air fuel ratio is the first target air fuel ratio, the first estimated catalyst's oxygen holding amount based on an air fuel ratio that is detected by the upstream air fuel ratio sensor and the theoretical air fuel ratio, continue calculation of the first target air fuel ratio and the first estimated catalyst's oxygen holding amount until the first estimated catalyst's oxygen holding amount reaches the first target catalyst's oxygen holding amount, calculate, after the first estimated catalyst's oxygen holding amount reaches the first target catalyst's oxygen holding amount, wherein a value in a rich side of the theoretical air fuel ratio is taken as a final target air fuel ratio, a second target air fuel ratio, which is an air fuel ratio between the theoretical air fuel ratio and the final target air fuel ratio, directing toward a richer side from the theoretical air fuel ratio to the final target air fuel ratio based on a second target catalyst's oxygen holding amount and a second estimated catalyst's oxygen holding amount, correct a fuel supply amount to the engine thereby obtaining the second target air fuel ratio, calculate, when the target air fuel ratio is the second target air fuel ratio, the second estimated catalyst's oxygen holding amount based on an air fuel ratio that is detected by the upstream air fuel ratio sensor and the theoretical air fuel ratio, and continue calculations of the second target air fuel ratio and of the second estimated catalyst's oxygen holding amount until the second estimated catalyst's oxygen holding amount reaches the second target catalyst's oxygen holding amount.