A sensor system (1, 1S) including a current DA converter (42) outputting a control current (Ip) of a sensor element (3S), a control unit (4C) generating a control current instruction value (Ipcmd) corresponding to magnitude of the control current and inputting this instruction value to the current DAC, an instruction value sequence generating unit (47) generating, instead of the control current instruction value, an inspection instruction value sequence (RChcmd) in which predetermined inspection current instruction values (Chcmd) inputted to the current DAC are arranged in order and by which failure of the current DAC can be detected, an inspection current detection unit (71) detecting an inspection current value (Ichv) of an inspection current (Ich) outputted from the current DAC, and a failure detection unit (8) detecting failure of the current DAC from an inspection current value sequence (RIchv) in which the inspection current values are arranged in order of detection.

An air-fuel ratio region detection unit, including a first determination voltage higher than a target voltage value indicating the stoichiometric air-fuel ratio, and a second determination voltage lower than the target voltage value, determines that an air-fuel ratio of an engine is within a first rich region when an oxygen sensor output equals or exceeds the first determination voltage, determines that the air-fuel ratio is within a second rich region when the oxygen sensor output equals or exceeds the target voltage value but is lower than the first determination voltage, determines that the air-fuel ratio is within a second lean region when the oxygen sensor output equals or exceeds the second determination voltage but is lower than the target voltage value, and determines that the air-fuel ratio is within a first lean region when the oxygen sensor output is lower than the second determination voltage.

An ECU acquires a fluid temperature, a coolant temperature and a soak time, and determines whether vapors have been produced in a fuel supply device on the basis of a vapor production prediction map. When the ECU determines that vapors have been produced in the fuel supply device, the ECU reduces a feedback gain. Subsequently, the ECU predicts a vapor production time, and, when the ECU determines that a vapor production end time has been reached, executes normal feedback control.

A control apparatus 57 is a 2-input, 2-output integral-type optimal servo system in which intake air amount and intake oxygen concentration are used as control quantities (y1, y2) and the degree of opening of a control valve of an exhaust gas recirculation apparatus and the degree of opening of a control valve of a supercharger equipped with a variable flow rate mechanism are used as manipulated quantities (u1, u2), and includes an output feedback system. The control apparatus (57) is provided with an EGR valve opening degree unit (70) and an opening rate valve of the supercharger. Each of the control units includes a non-interference controller (64) for eliminating interference between the manipulated quantity for the control valve of the exhaust gas recirculation apparatus and the manipulated quantity for the control valve of the supercharger equipped with the variable flow rate mechanism.

An exhaust gas purification system which can suppress a decrease in engine torque during a desulfurization process applied to a NOx storage reduction catalyst. The system includes a NOx storage reduction catalyst in an exhaust pipe of an engine, and a desulfurization process control unit that controls an amount of intake air introduced to the engine to enrich the exhaust gas, and performs a desulfurization process to the NOx storage reduction catalyst. The desulfurization process control unit is configured to gradually reduce an amount of intake air when the desulfurization process is commenced.

An air-fuel ratio region detection unit, including a first determination voltage higher than a target voltage value indicating the stoichiometric air-fuel ratio, and a second determination voltage lower than the target voltage value, determines that an air-fuel ratio of an engine is within a first rich region when an oxygen sensor output equals or exceeds the first determination voltage, determines that the air-fuel ratio is within a second rich region when the oxygen sensor output equals or exceeds the target voltage value but is lower than the first determination voltage, determines that the air-fuel ratio is within a second lean region when the oxygen sensor output equals or exceeds the second determination voltage but is lower than the target voltage value, and determines that the air-fuel ratio is within a first lean region when the oxygen sensor output is lower than the second determination voltage.

Various approaches are described for air-fuel ratio control in an engine. In one example, a method include adjusting fuel injection from an anticipatory controller responsive to exhaust oxygen feedback of an exhaust gas sensor positioned upstream of an exhaust catalyst, the anticipatory controller including a first integral term and a second integral term, the second integral term correcting for past fuel disturbances. In this way, it is possible to provide fast responses to errors via the anticipatory controller, while corrected known past fueling errors, on average, via the second integral term.