US 4,304,652 AGranted

Device for detection of air/fuel ratio from oxygen partial pressure in exhaust gas

AssigneeNissan Motor Co., Ltd.

InventorsMasao Chiba, Takeshi Fujishiro

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Abstract

A device having a probe of the oxygen concentration cell type to be disposed in a combustion gas to detect actual air/fuel ratio values of an air-fuel mixture subjected to combustion. The probe has a gas impermeable layer of a solid electrolyte such as zirconia, a porous reference electrode layer made of a catalytic material such as platinum and formed on the solid electrolyte layer, a porous gas-diffusion layer covering the reference electrode layer and a porous and noncatalytic measurement electrode layer formed on the solid electrolyte layer so as to be spaced from the reference electrode layer. A DC power supply is connected to the probe to force a constant current of an adequate intensity to flow through the solid electrolyte layer between the two electrode layers. Depending on the direction of the current flow, an output voltage of this device becomes indicative of air/fuel ratio values above or below the stoichiometric air/fuel ratio.

A device to detect an actual air/fuel ratio of an air-fuel mixture subjected to combustion in a combustor based on the magnitude of an oxygen partial pressure in a combustion gas which is exhausted from the combustor and which contains combustible substances, the device comprising:

(i) an oxygen sensing element which is to be disposed in the combustion gas and comprises:
(a) an oxgyen ion conductive solid electrolyte layer having a dense and gas impermeable structure,
(b) a gas permeable porous first electrode layer which is formed on said solid electrolyte layer and comprised of a conducting and catalytic material which catalyzes oxidation reactions of combustible substances contained in the combustion gas,
(c) a porous gas-diffusion layer formed on said first electrode layer, and
(d) a gas permeable porous second electrode layer which is formed on said solid electrolyte layer so as to be spaced from said first electrode layer and made of a conducting material which does not catalyze said oxidation reactions;
(ii) DC power supply means electrically connected to said first and second electrode layers of said oxygen sensing element for forcing a constant DC current to flow through said solid electrolyte layer between said first and second electrode layers, the intensity and the direction of flow of said constant current being determined such that an output voltage developed across said first and second electrode layers varies in dependence on the air/fuel ratio of an air-fuel mixture, from which the combustion gas is produced, when the air/fuel ratio varies on one side of the stoichiometric air/fuel ratio of said air-fuel mixture but remains substantially constantly at a maximal level when the air/fuel ratio varies on the other side of the stoichiometric ratio;
and
(iii) voltage-measuring means, electrically connected to said first and second electrode layers in parallel to said DC power supply means, for measuring the voltage produced across said first and second electrodes.

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Abstract

Claims17