Abstract: The present invention provides a hydrogen sensor including a concentration cell holding a solid electrolyte having proton conductivity. The solid electrolyte is mainly formed of &agr; alumina in which oxide of alkaline earth metal is doped. The hydrogen sensor can measure a hydrogen concentration of measuring objects. For example, it is possible to measure a hydrogen concentration of high temperature gas or molten metal such as copper alloy, cast iron, carbon steel, and alloy steel.

Abstract: Disclosed is an apparatus for detecting deterioration of a catalyst of an internal combustion engine having a plurality of cylinder banks in such a manner that the deterioration of the catalyst can be assuredly discriminated regardless of the presence of deviation of a control phase with respect to each cylinder bank. The influence of change of the air/fuel ratio can be eliminated considerably by reducing the air/fuel ratio correction coefficient for a right bank, or by also using the correction coefficient for the left bank as that for the right bank to cause the phases of them to be synchronized with each other, or by dither-controlling the right bank. Therefore, the change of the air/fuel ratio with respect to the left bank can be assuredly detected while necessitating one sub air/fuel ratio sensor.

Abstract: Deterioration of a catalyst of a catalytic converter of an internal combustion engine is detected, during negative feedback control of the air-fuel ratio based on an output signal from at least one of a pair of O.sub.2 sensors disposed respectively upstream and downstream from the catalyst in the exhaust system. Detection is executed after changing the feedback period, which is the period of alternation of a feedback correction coefficient used to control the fuel injection quantity, with the change in period being such as to provide improved accuracy of detection of catalyst deterioration. The change may consist of a single step change, in which the feedback period is set to a specific predetermined value at which the output signal amplitude from the downstream sensor, or the phase difference between the two sensor output signals, should be within predetermined limits if the catalyst is in satisfactory condition.

Abstract: An apparatus for detecting a purification factor of a catalyst for purifying an exhaust gas of an internal combustion engine comprises a catalyst disposed in an exhaust system of the internal combustion engine for purifying an exhaust gas, first and second air-fuel ratio sensors disposed upstream and downstream of the catalyst for detecting air-fuel ratios, respectively, a response delay time difference detecting device for detecting differences in response delay time between the first and second air-fuel ratio sensors in respective different operation states of the engine, a purification factor detecting device for detecting a purification factor of the catalyst on the basis of a deviation between the first and second response delay time differences detected in respective different operation states of the engine.

Abstract: According to the present invention, in a system wherein O.sub.2 sensors are disposed on upstream and downstream sides, respectively, of a catalytic converter, and an air-fuel ratio coefficient for the amount of fuel to be injected is determined on the basis of an output of the upstream-side O.sub.2 sensor, the deterioration of the upstream-side O.sub.2 sensor. More particularly, a delay is added to the output of the upstream-side O.sub.2 sensor in accordance with an output signal provided from the downstream-side O.sub.2 sensor, then an air-fuel ratio F/B control is performed in accordance with the delayed output, and when the F/B control period has become longer than a predetermined value, it is judged that the upstream-side O.sub.2 is deteriorated. As a result, not only the deterioration of response characteristic but also the deterioration caused by the Z characteristic center can be detected because it appears as a change of the F/B control period.

Abstract: A relation with output characteristic of an oxygen density sensor corresponding to a deviation of an air fuel ratio of a mixed gas supplied actually to an internal combustion engine from a desired air fuel ratio is stored beforehand in an air fuel ratio controller of the present invention. Then, the air fuel ratio deviation is computed correspondingly to an actual output of the oxygen density sensor according to the stored relation, and an air fuel ratio controlled variable is corrected according to the computed air fuel ratio deviation, thereby controlling the air fuel ratio to the desired air fuel ratio.

Abstract: In an apparatus for controlling an air-fuel ratio in an internal combustion engine, a main air-fuel ratio sensor having an element temperature strongly affected by the temperature thereof, a sub air-fuel ration sensor having an element temperature weakly affected by the temperature thereof, and a heater associated with the main air-fuel ratio sensor are provided. The resistance value or electric power of the heater is controlled in accordance with the output of the sub air-fuel ratio sensor.