Sensor is used test engine combustion exhaust oxygen is surplus information, namely, oxygen content, and the oxygen content into voltage signal transmission to the engine computer, make the engine can realize take the excess air factor as the goal of the closed loop control; To ensure the three-way catalytic converter to exhaust the hydrocarbon (HC) and carbon monoxide (CO) and nitrogen oxides (NOX) three kinds of pollutants have the biggest transformation efficiency, the greatest degree on the transformation of the discharge of pollutants and purification.