Air/fuel ratio control device for internal-combustion engine

摘要

An internal-combustion engine of the invention includes a catalyst which has an oxidizing ability and is provided in an exhaust passage, wherein an air/fuel ratio of an air/fuel mixture is controlled so that the air/fuel ratio leaner than a theoretical air/fuel ratio and the air/fuel ratio richer than the theoretical air/fuel ratio are alternated with a predetermined amplitude with respect to a target air/fuel ratio. On the assumption that the temperature of the catalyst is referred to as a catalyst temperature, an amplitude set according to the catalyst temperature is adopted as the predetermined amplitude, and the amplitude set when the catalyst temperature is higher than a predetermined temperature is smaller than the amplitude set when the catalyst temperature is lower than the predetermined temperature.

主权项

1. An air/fuel ratio control device for an internal-combustion engine comprising:
a catalyst which has an oxidizing ability and is provided in an exhaust passage; and an electronic control unit configured to control an air/fuel ratio of an air/fuel mixture formed in a combustion chamber of the internal combustion engine such that (i) when the air/fuel ratio of the air/fuel mixture is richer than a target air/fuel ratio, the air/fuel ratio of the air/fuel mixture is controlled to become leaner than the target air/fuel ratio by a predetermined degree and leaner than a theoretical air/fuel ratio, and (ii) when the air/fuel ratio of the air/fuel mixture is leaner than the target air/fuel ratio. the air/fuel ratio of the air/fuel mixture is controlled to become richer than the target air/fuel ratio by the predetermined degree and richer than the theoretical air/fuel ratio, thereby controlling the air/fuel ratio of the air/fuel mixture so that the air/fuel ratio leaner than the theoretical air/fuel ratio and the air/fuel ratio richer than the theoretical air/fuel ratio are alternated with a predetermined amplitude with respect to the target air/fuel ratio, wherein the electronic control unit adopts, as the predetermined amplitude, an amplitude set according to (a) an air intake amount which is an amount of air suctioned to the combustion chamber or (b) a catalyst temperature which is a temperature of the catalyst, the amplitude set according to the air intake amount when the air intake amount is larger than a predetermined amount is smaller than the amplitude set according to the air intake amount when the air intake amount is smaller than the predetermined amount, the amplitude set according to the catalyst temperature when the catalyst temperature is higher than a predetermined temperature is smaller than the amplitude set according to the catalyst temperature when the catalyst temperature is lower than the predetermined temperature, the amplitude set according to the air intake amount is adopted as the predetermined amplitude when the amplitude set according to the air intake amount is smaller than the amplitude set according to the catalyst temperature, and the amplitude set according to the catalyst temperature is adopted as the predetermined amplitude when the amplitude set according to the air intake amount is larger than the amplitude set according to the catalyst temperature.