Abstract: In a gas sensor determining a NOx concentration in a measurement gas based on a pump current flowing between a NOx measurement electrode and an outer pump electrode, the outer pump electrode has catalytic activity inactivated for HC and CO, so that a sensor element further includes a HC sensor part having a mixed potential cell constituted by the outer pump electrode, a reference electrode, and a solid electrolyte between these electrodes, and a HC mode for determining a HC concentration in the measurement gas based on a potential difference between the outer pump electrode and the reference electrode when the sensor element is heated to a temperature which is 400° C. or higher and 650° C. or lower and a NOx mode for determining a NOx concentration in the measurement gas based on the pump current can selectively be performed based on the temperature of the sensor element.

Abstract: A gas sensor that is unlikely to have Au evaporation from an external electrode even when used under a high temperature atmosphere is provided. The gas sensor includes a sensor element mainly made of an oxygen-ion conductive solid electrolyte; an external electrode provided on the sensor element and containing a Pt—Au alloy; and an electrode evaporation preventing film provided on the sensor element while being insulated from the sensor element and separated from the external electrode, and made of Au or a Pt—Au alloy having an Au composition ratio not smaller than an Au composition ratio of the Pt—Au alloy contained in the external electrode. A protection cover is provided so that at least part of the sensor element, at which the external electrode and the electrode evaporation preventing film is positioned, is inside the protection cover, and so that a measurement gas is introduced inside the protection cover.

Abstract: A gas sensor in which an electrode is prevented from being poisoned is provided. A mixed-potential type gas sensor includes a sensor element composed a solid electrolyte. The sensor element includes: a measurement gas introduction space having an open end at a distal end and extending in a longitudinal direction; a sensing electrode provided on an inner side of the measurement gas introduction space; and a heater configured to heat the sensor element. The concentration of the gas component is determined based on a potential difference between the sensing electrode and a reference electrode, while the heater heats the sensor element so that a place having a temperature higher than the temperature of the sensing electrode and the melting point of a poisoning substance exists between the open end and the sensing electrode and the temperature decreases toward the sensing electrode.

Abstract: A system for diagnosing the degree of deterioration of a catalyst disposed in an exhaust path of an internal combustion engine and oxidizes or adsorbs a target gas in an exhaust gas, includes a temperature sensor measuring a temperature of the exhaust gas at the upstream from a catalyst in an exhaust path and a gas sensor detecting a target gas at the downstream of the exhaust path and outputting an output value in accordance with a concentration of the target gas, wherein a control element is configured to diagnose the degree of deterioration in the catalyst, based on at least the output value in the gas sensor, the temperature of the catalyst identified based on a measurement value in the temperature sensor, and the threshold value at the temperature of the catalyst.

Abstract: A mixed-potential type gas sensor capable of preferably determining the concentration of THC including a kind of gas having a large C number is provided. A sensor element composed of an oxygen-ion conductive solid electrolyte is provided with, on its surface, a sensing electrode formed of a cermet of Pt, Au, and an oxygen-ion conductive solid electrolyte, and includes a reference electrode and a porous surface protective layer that covers at least said sensing electrode. An Au abundance ratio on a surface of noble metal particles forming the sensing electrode is 0.3 or more. The surface protective layer has a porosity of 28% to 40%, a thickness of 10 to 50 ?m, and an area ratio of a coarse pore having a pore size of 1 ?m or larger of 50% or more; or has a porosity of 28% to 40% and a thickness of 10 to 35 ?m.

Abstract: Provided is a method for diagnosing whether an oxidation catalyst has degraded, based on an output value from one diagnostic sensor with higher accuracy. When a ratio of nitrogen monoxide that is oxidized by a catalyst and discharged downstream of the catalyst as nitrogen dioxide, with respect to nitrogen monoxide contained in an exhaust gas supplied upstream of the catalyst in an exhaust path is defined as a NO conversion rate, a diagnostic sensor configured to output an electromotive force corresponding to the NO conversion rate as a diagnostic output is provided downstream of the catalyst in the exhaust path, and whether the catalyst has degraded beyond an acceptable limit is diagnosed by comparing the diagnostic output with a threshold value predetermined depending on a temperature of the catalyst.

Abstract: Provided is a method for accurately diagnosing a degree of degradation of an oxidation catalyst. A target gas detecting element configured to output an electromotive force corresponding to a concentration of a target gas is provided downstream of a catalyst in an exhaust path of an internal combustion engine. A sum of change amounts of an electromotive force in a time-variable profile thereof after the introduction of a gas atmosphere for diagnosis into the catalyst is set as a diagnosis index value. The gas atmosphere has been intentionally created in the engine and includes a target gas having a concentration higher than the concentration of a target gas during a steady operation state of the engine. The index value is then compared with a threshold corresponding to the temperature of the catalyst to diagnosis whether degradation exceeding an acceptable degree has occurred in the catalyst.

Abstract: Provided is a method for accurately diagnosing a degree of degradation of an oxidation catalyst. A target gas detecting element configured to output an electromotive force corresponding to a concentration of a target gas is provided downstream of a catalyst in an exhaust path of an internal combustion engine. A maximum change amount of an electromotive force after the introduction of a gas atmosphere for diagnosis into the catalyst is set as a diagnosis index value. The gas atmosphere has been intentionally created in the engine and includes a target gas having a concentration higher than the concentration of a target gas in a steady operation state of the engine. The index value is then compared with a threshold corresponding to the temperature of the catalyst to diagnosis whether degradation exceeding an acceptable degree has occurred in the catalyst.

Abstract: Provided is a gas sensor which is capable of preferably sensing an ammonia gas, and has excellent durability. A mixed-potential gas sensor includes a sensor element composed of an oxygen-ion conductive solid electrolyte, and a heater provided inside the element. The sensor element includes on a surface thereof a sensing electrode formed of a cermet including Pt, Au and an oxygen-ion conductive solid electrolyte, and also includes a reference electrode formed of a cermet of Pt and an oxygen-ion conductive solid electrolyte, and a porous electrode protective layer whose porosity is 5 to 40% covering at least the sensing electrode. The Au abundance ratio in a surface of noble metal particles forming the sensing electrode is 0.4 or more. The concentration of an ammonia gas is determined on the basis of a potential difference occurring between the sensing electrode and the reference electrode when the sensor element is disposed in a measurement gas and heated to 400° C. to 800° C.

Abstract: Provided is a gas sensor capable of accurately obtaining a hydrocarbon gas concentration even if a measurement gas contains water vapor. A main pumping cell adjusts an oxygen partial pressure of a first internal space such that a hydrocarbon gas in a measurement gas is not substantially burned in the first internal space. An auxiliary pumping cell adjusts an oxygen partial pressure of a second internal space such that inflammable gas components except for hydrocarbon are selectively burned. Then, a measuring pumping cell supplies oxygen to a surface of a measuring electrode. As a result, hydrocarbon existing in the measurement gas being in contact with the measuring electrode is all burned on the surface of the measuring electrode and, based on the magnitude of a current flowing between the measuring electrode and a main pumping electrode at that time, identifies a concentration of a hydrocarbon gas component existing in the measurement gas.

Abstract: A gas sensor capable of measuring a high concentration range is provided. A sensing electrode provided in a sensor element of a mixed-potential gas sensor for measuring the concentration of a predetermined component in a measurement gas is formed of a cermet including a noble metal and an oxygen-ion conductive solid electrolyte. The noble metal includes Pt and Au. A Au abundance ratio, which is an area ratio of a portion covered with Au to a portion at which Pt is exposed in a surface of noble metal particles forming the sensing electrode, is 0.1 or more and less than 0.3.

Abstract: A mixed-potential gas sensor for measuring a concentration of a predetermined gas component of a measurement gas includes sensing electrodes mainly made of an oxygen-ion conductive solid electrolyte and located on a surface of a sensor element, and at least one reference electrode including a cermet including Pt and an oxygen-ion conductive solid electrolyte. The sensing electrodes each include a cermet including a noble metal and an oxygen-ion conductive solid electrolyte. The noble metal includes Pt and Au. A Au abundance ratio, which is an area ratio of a portion covered with the Au to a portion at which the Pt is exposed in a surface of noble metal particles forming each of the sensing electrodes, differs among the sensing electrodes. The gas sensor determines a concentration of the predetermined gas component based on a potential difference between each of the sensing electrodes and the at least one reference electrode.

Abstract: A gas sensor with excellent detection sensitivity is provided. A sensing electrode, which is provided in a mixed-potential gas sensor for measuring a concentration of a predetermined gas component of a measurement gas to sense the predetermined gas component, is formed of a cermet of a noble metal and an oxygen-ion conductive solid electrolyte. The noble metal includes Pt and Au. A range of at least 1.5 nm from a surface of a noble metal particle included in the sensing electrode is a Au enriched region having a Au concentration of 10% or more.

Abstract: Provided is a method for recovering output of a gas sensor in shorter time. The method includes: determining a recovering temperature T1 and a recovering time ??1 based on a condition setting range where a high recovery rate is expected; and recovering the output based on T1 and ??1, wherein in the recovering, a duty ratio for a heater is instantly increased to value D1 higher than a value in a normal driving mode when the recovering starts, D1 is maintained up to T1, and PID control is performed by reducing the duty ratio to value D2 to maintain T1. After an elapse of ??1, the duty ratio is reduced to value D3. When the temperature of the element reaches a value 1 to 1.2 times as high as the temperature in the normal drive mode, the duty ratio is instantly changed to value D0 in the normal drive mode.

Abstract: Provided is a gas sensor capable of accurately obtaining a hydrocarbon gas concentration even if a measurement gas contains water vapor. A main pumping cell adjusts an oxygen partial pressure of a first internal space such that a hydrocarbon gas in a measurement gas is not substantially burned in the first internal space. An auxiliary pumping cell adjusts an oxygen partial pressure of a second internal space such that inflammable gas components except for hydrocarbon are selectively burned. Then, the measurement gas is introduced into a third internal space through a third diffusion control part. With oxygen concentration equilibrium kept in the third internal space, hydrocarbon existing in the measurement gas that has reached the third internal space is all burned. Then, the concentration of the hydrocarbon gas component existing in the measurement gas is identified based on the magnitude of a current flowing between the measuring electrode and the main pumping electrode at that time.

Abstract: A method for diagnosing the degree of deterioration of a catalyst disposed in an exhaust path of an internal combustion engine and oxidizes or adsorbs a target gas, including at least one of a hydrocarbon gas and a carbon monoxide gas, in an exhaust gas from the internal combustion engine, is adapted to determine whether deterioration exceeding an acceptable level of a catalyst occurs or not by comparing, at any timing when the internal combustion engine is in a state of a steady operation, the concentration of a target gas detected downstream from the catalyst in the exhaust path with a threshold value of the concentration of a target gas corresponding to the temperature of a catalyst at the timing which is previously defined according to an allowable range of an index value representing the degree of oxidation or adsorption at the catalyst corresponding to the temperature of a catalyst at the timing.

Abstract: A system for diagnosing the degree of deterioration of a catalyst disposed in an exhaust path of an internal combustion engine and oxidizes or adsorbs a target gas in an exhaust gas, includes a temperature sensor measuring a temperature of the exhaust gas at the upstream from a catalyst in an exhaust path and a gas sensor detecting a target gas at the downstream of the exhaust path and outputting an output value in accordance with a concentration of the target gas, wherein a control element is configured to diagnose the degree of deterioration in the catalyst, based on at least the output value in the gas sensor, the temperature of the catalyst identified based on a measurement value in the temperature sensor, and the threshold value at the temperature of the catalyst.

Abstract: A method for diagnosing the degree of deterioration of a catalyst disposed in an exhaust path of an internal combustion engine and oxidizes or adsorbs a target gas, including at least one of a hydrocarbon gas and a carbon monoxide gas in an exhaust gas from the internal combustion engine, is adapted to determine whether deterioration exceeding an acceptable level of a catalyst occurs or not by comparing the concentration of a target gas detected downstream from the catalyst in the exhaust path when a diagnosis-gas atmosphere containing a target gas higher in concentration than a target gas during a steady-operation state of the internal combustion engine is intentionally produced and introduced into the catalyst with a threshold value corresponding to the temperature of a catalyst at the timing which the diagnosis-gas atmosphere is introduced.

Abstract: Provided is a gas sensor having excellent detection sensitivity and responsiveness. In a sensor element, 3.5?D2/D1?6 is satisfied, where D1 is a value of a diffusion resistance of a measurement gas via a main gas distribution part extending from an outside edge position of a first gas inlet to the second internal space, and D2 is a value of a diffusion resistance of a measurement gas flowing via a second gas inlet that causes the outside and the second internal space to communicate with each other. The concentration of a predetermined gas component contained in the measurement gas through the second gas inlet is determined on the basis of a potential difference between the sensing electrode and a reference electrode, while pumping oxygen in or out for the measurement gas via the main gas distribution part such that the oxygen concentration of the second internal space is maintained at 1 vol % or more.

Abstract: A sensing electrode for sensing a predetermined gas component of a measurement gas, which is provided in a mixed-potential gas sensor that measures the concentration of the predetermined gas, component, is formed of a cermet containing a noble metal and an oxygen-ion conductive solid electrolyte. The noble metal comprises Pt and Au. An Au abundance ratio, which is an area ratio of a portion covered with Au to a portion at which Pt is exposed in a surface of noble metal particles forming the sensing electrode, is 0.3 or more.