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

Claim 1

A system for feedback control of the air/fuel ratio of an air-fuel mixture supplied to an internal combustion engine, the control system comprising: an electrically controllable fuel supplying means provided in the intake system of the engine; an air/fuel ratio detector which is disposed in an exhaust passage for the engine and has 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; fuel feed control means for providing a control signal to the fuel supplying means to control the rate of fuel feed to the engine so as to maintain a predetermined air/fuel ratio by utilizing the output of the air/fuel ratio detector as a feedback signal; and a sub-system to supply a heating current to the heater of the air/fuel ratio detector and force 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 to cause 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 comprising operating condition detecting means for producing a command signal while the operation of the fuel feed control means is temporarily discontinued to release the air/fuel ratio from the feedback control and the engine is operated under such a condition as causes a significant lowering of the concentration of oxygen in the exhaust gas, and an electrically controllable switch means for interrupting the supply of said heating current to said heater while the operating condition detecting means produces said command signal, whereby the activity of the solid electrolyte layer in the oxygen-sensitive element decreases while said command signal is produced thereby preventing significant lowering of said reference oxygen partial pressure from a predetermined level by the influence of the lowered oxygen concentration in the exhaust gas.

Claim 2

A system for feedback control of the air/fuel ratio of an air-fuel mixture supplied to an internal combustion engine, the control system comprising: an electrically controllable fuel supplying means provided in the intake system of the engine; an air/fuel ratio detector which is disposed in an exhaust passage for the engine and has 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; fuel feed control means for providing a control signal to the fuel supplying means to control the rate of fuel feed to the engine so as to maintain a predetermined air/fuel ratio by utilizing the output of the air/fuel ratio detector as a feedback signal; and a sub-system to supply a heating current to the heater of the air/fuel ratio detector and force 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 to cause 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 comprising operating condition detecting means for producing a command signal while the operation of the fuel feed control means is temporarily discontinued to release the air/fuel ratio from the feedback control and the engine is operated under such a condition as causes a significant lowering of the concentration of oxygen in the exhaust gas, and an electrically controllable switch means for interrupting the supply of said heating current to said heater while the operating condition detecting means produces said command signal, whereby the activity of the solid electrolyte layer in the oxygen-sensitive element decreases while said command signal is produced thereby preventing significant lowering of said reference oxygen partial pressure from a predetermined level by the influence of the lowered oxygen concentration in the exhaust gas.