AIR-FUEL RATIO CONTROL DEVICE, AIR-FUEL RATIO CONTROL METHOD, AND EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To provide air-fuel ratio control device, in which oxygen concentration in exhaust is correctly measured, and in which purification ability of a three-way catalyst to harmful components in exhaust is maximized.

SOLUTION: This device is provided with an oxygen sensor to output a binary signal to indicate if the oxygen concentration in the exhaust exceeds a prescribed threshold value or not, and a control device to output a signal for controlling an air-fuel ratio based on the binary signal. The catalyst device is installed in a muffler comprising at least two expansion chambers of a first expansion chamber to receive an exhaust pipe from the internal combustion engine and a second expansion chamber separated from the first expansion chamber. An exhaust gas passage is formed between the first expansion chamber and the second expansion chamber. The oxygen sensor to detect the oxygen concentration in the exhaust is installed close to an exhaust inflow port to the catalyst device in the first expansion chamber in the muffler. The control device adjusts the oxygen concentration in the exhaust to the prescribed threshold value to change the air-fuel ratio between a rich state and a lean state.

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