System for feedback control of air/fuel ratio in IC engine with means to control supply of current to oxygen sensor

A system for feedback control of the air/fuel mixture ratio for an internal combustion engine, the control system comprising:

• an electrically controllable fuel supply means provided in the intake system of the engine;
• an air/fuel ratio detector disposed in an exhaust passage of the engine and having an oxygen-sensitive element of a concentration cell type comprising a substrate, a microscopically porous reference electrode layer formed on the substrate, a microscopically porous layer of an oxygen ion conductive solid electrolyte formed on the substrate so as to cover the reference electrode layer substantially entirely and a microscopically porous measurement electrode layer formed on the solid electrolyte layer and an electric heater;
• control means for providing a control signal to the fuel supply means to control the rate of fuel feed to the engine to maintain a predetermined air/fuel ratio by utilizing an output voltage of the air/fuel ratio detector as a feedback signal;
• and
• a sub-system for supplying a heating current to the heater of the air/fuel ratio detector and for causing a DC current of a predetermined intensity to flow through the solid electrolyte layer of the oxygen-sensitive element from the reference electrode layer toward the measurement electrode layer resulting in a migration of oxygen ions through the solid electrolyte layer from the measurement electrode layer toward the reference electrode layer to thereby establish a reference oxygen partial pressure at the interface between the reference electrode layer and the solid electrolyte layer,
• said sub-system further comprising temperature detection means for detecting the temperature of the oxygen-sensitive element as an indication of the internal resistance between the reference and measurement electrode layers of the oxygen-sensitive element and for providing a command signal while the detected temperature is below a predetermined temperature and current regulation means for decreasing the intensity of the DC current flowing through the solid electrolyte layer from said predetermined intensity by a definite value while the temperature detection means provides the command signal, whereby the basic level of the output voltage of the oxygen-sensitive element is precluded from undesirably rising while said internal resistance is excessively high.