Methods and systems are provided for estimating an engine exhaust pressure based on outputs from an exhaust oxygen sensor. In one example, a method may include estimating an exhaust pressure of exhaust gas flowing through an engine exhaust passage based on a difference between a first output of an oxygen sensor disposed in the exhaust passage and a second output of the oxygen sensor and then adjusting engine operation based on the estimated exhaust pressure. As one example, both the first and second outputs may be taken while operating the sensor in a variable voltage mode, after increasing a reference voltage of the oxygen sensor from a lower, first voltage to a higher, second voltage.

This control device for an internal combustion engine is equipped with: an air/fuel ratio sensor provided to the exhaust passage of an internal combustion engine; and an engine control device that controls the internal combustion engine on the basis of the sensor output current of the air/fuel ratio sensor. The air/fuel ratio sensor is equipped with: a gas chamber to be measured, into which exhaust gas flows; a reference cell for which the reference cell output current varies according to the air/fuel ratio of the exhaust gas inside the gas chamber to be measured; and a pump cell that, according to the pump current, pumps oxygen into or out of the exhaust gas in the gas chamber to be measured. The reference cell is configured so that the applied voltage, at which the reference cell output current reaches zero, varies according to the air/fuel ratio of the exhaust gas in the gas chamber to be measured. The applied voltage in the reference cell is fixed at a constant voltage, said constant voltage being set to a voltage different to the voltage at which the reference cell output current reaches zero when the air/fuel ratio of the exhaust gas in the gas chamber to be measured is the stoichiometric air/fuel ratio.

A three-way catalyst, an NSR catalyst, and an SCR catalyst are provided in this order for an exhaust gas passage, wherein the air-fuel ratio (AFR) is set to a first AFR which is a rich AFR before the AFR is switched from a theoretical AFR to a lean AFR, and then the AFR is set to a second AFR which is higher than the first AFR and lower than the theoretical AFR if a NOx occlusion amount is less than a threshold value during a period until an NH.sub.3 adsorption amount of the SCR catalyst becomes a predetermined adsorption amount, while the AFR is set to a third AFR which is higher than the first AFR and lower than the second AFR if the NOx occlusion amount is not less than the threshold value.

An exhaust sensor 1 comprises a sensor cell 51, a voltage application circuit 61, a current detection circuit 62 and a concentration calculating part 80a. The current detection circuit detects a first current flowing through the sensor cell when fuel cut control is being performed in the internal combustion engine and a predetermined voltage is applied from the voltage application circuit to the sensor cell, and detect a second current flowing through the sensor cell when normal control is being performed in the internal combustion engine and the predetermined voltage is applied from the voltage application circuit to the sensor cell. The concentration calculating part is configured to calculate the concentration higher with respect to the second current when the first current is relatively low compared with when the first current is relatively high.

Device and method for correcting an offset in a signal of a first sensor for determining a residual oxygen content in an exhaust gas. A first actual ratio of air and fuel being determined as a function of a first residual oxygen content, a second actual ratio of air and fuel being determined as a function of a second residual oxygen content, a first offset of a first actual ratio relative to a reference ratio being determined for the first actual ratio when the second actual ratio is greater than the reference ratio, a second offset of a first actual ratio relative to the reference ratio being determined for the first actual ratio when the second actual ratio is smaller than the reference ratio, and a deviation being detected between the first offset and the second offset.

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 oxygen sensor that has both an n-type oxygen sensing portion comprising an n-type semiconductor layer and a p-type oxygen sensing portion comprising an p-type semiconductor layer. The n-type sensing portion and the p-type sensing portion share the common electrode. The n-type semiconductor layer and the p-type semiconductor layer attach directly to the common electrode, but are not in physical contact with each other such that a lateral gap exists between the n-type semiconductor layer and the p-type semiconductor layer. The air:fuel ratio for a combustion process may be determined, using the same oxygen sensor, across a range of air:fuel values in both the rich and lean regions; as such, the oxygen sensor may act as a wideband oxygen sensor.

Methods and systems are provided for estimating an engine exhaust pressure based on outputs from an exhaust oxygen sensor. In one example, a method may include estimating an exhaust pressure of exhaust gas flowing through an engine exhaust passage based on a difference between a first output of an oxygen sensor disposed in the exhaust passage and a second output of the oxygen sensor and then adjusting engine operation based on the estimated exhaust pressure. As one example, both the first and second outputs may be taken while operating the sensor in a variable voltage mode, after increasing a reference voltage of the oxygen sensor from a lower, first voltage to a higher, second voltage.

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.

A method of determining an air:fuel ratio based on information from an oxygen sensor exposed to exhaust gases of a combustion process, and related systems. A constant current is supplied to an oxygen sensor that has both an n-type sensing circuit and a p-type sensing circuit that share a common electrode. The currents in the respective sensing circuits is determined and a temperature value representative of a temperature of the oxygen sensor is determined. Then, an air:fuel ratio is determined based on the determined currents and the temperature value. The combustion process may then be controlled based on the air:fuel ratio. The air:fuel ratio may be determined, using the same oxygen sensor, across a range of air:fuel values in both the rich and lean regions; as such, the oxygen sensor may act as a wideband oxygen sensor.