Exhaust-emission control device for a combustion engine

摘要

An NOx catalyst, a broad-band air/fuel ratio sensor and an NOx gas sensor are arranged in an exhaust duct. A quantity of oxygen contained in the exhaust gas is detected by the air/fuel sensor. In response to the data obtained on the quantities of oxygen, an air/fuel ratio in the gas containing the mixture of fuel and air is adjusted in such a way that the combustion of a combusion engine takes place in a lean condition. An NOx gas quantity contained in the exhaust gas is detected by the NOx gas sensor. In response to the data on the quantities of NOx detected, a desired value for the air/fuel ratio is adjusted in accordance with the quantity of NOx after its reduction.