What are the conditions for ecu to implement air-fuel ratio feedback control?

In the process of engine open-loop control, ECU only determines the fuel injection quantity according to signals such as rotational speed, intake air volume, intake pressure and coolant temperature. The air-fuel ratio of a car is controlled by the throttle, the pedal controls the throttle, and the fuel injector controls the fuel intake. It is the control principle of gasoline vehicle to detect the proportion with oxygen sensor and control the oil intake of nozzle by computer.

In order to meet the increasingly stringent emission regulations, the most effective method is to use the catalytic purification efficiency of three-way catalytic converter for exhaust gas. Modern electronically controlled gasoline engines realize closed-loop control of air-fuel ratio under most working conditions.

Feedback control principle

In the process of air-fuel ratio feedback control, the change relationship between air-fuel ratio, voltage signal output by oxygen sensor and air-fuel ratio feedback control signal.

Assuming that the actual air-fuel ratio of the mixture is slightly less than 14.7 at the beginning, the oxygen sensor outputs a high-level signal, and the ECU reduces the basic fuel injection duration according to the high-level signal of the oxygen sensor, so that the actual fuel injection duration is shortened and the fuel injection quantity is reduced, and the correction process is carried out in a way of fast first and then slow.