Method and apparatus for obtaining a control variable for the closed-loop control of the fuel-air ratio in the operating mixture of internal combustion engines

A method for obtaining a control variable for a closed-loop control device for the closed-loop control of the fuel-air ratio of the operating mixture in internal combustion engines utilizing an exhaust gas threshold-current sensor exposed to the exhaust gas flow and a control device for adjusting the fuel-air ratio of the operating mixture, said sensor operating on the principle of oxygen ion conduction when exposed to voltage and having a body made of fixed electrolyte material which conducts oxygen ions and furnishes a control signal corresponding to the oxygen content in the exhaust gas, wherein the threshold current of the sensor, defined by the diffusion speed of the measured gas, is a standard for the oxygen content in the exhaust gas, the method comprising the steps of:

• generating a voltage difference signal which corresponds to the change in the air number .lambda. of the operating mixture when there is a change in the operational state of the engine;
• generating a reference measurement voltage signal;
• adding the generated voltage difference signal and the generated reference measurement voltage signal;
• and
• applying the added generated voltage difference signal and the generated reference measurement voltage signal to the exhaust gas threshold-current sensor and measuring the resultant current through the exhaust gas threshold-current sensor, said resultant current serving as a standard for the percentage oxygen content in the closed-loop control circuit with the oxygen content which is to be maintained;
• whereby the closed-loop control device corrects the fuel-air ratio accordingly.