Patent ID: 7258771
Filing Date: 2007-08-21
Classification: G01N

Abstract:
1. An air/fuel ratio detection apparatus comprising: a heater portion that has an elongate cylindrical shape and heats by applying electricity to the heater portion from an outside source; a solid electrolyte layer formed on and surrounding an outer periphery of the heater portion, the solid electrolyte layer being activated by heat from the heater portion to conduct oxygen ions through the solid electrolyte layer; first and second electrodes that are in contact with an outer periphery of the solid electrolyte layer and are disposed away from each other such that a pumping voltage supplied from an outside source is applied by the first and second electrodes to the solid electrolyte layer, the first and second electrodes being disposed away from each other by a first distance; a reference electrode for outputting an air/fuel ratio detection signal in relation to one of the first and second electrodes, the reference electrode being formed on the an outer periphery of the solid electrolyte layer and being disposed away from the first and second electrodes; and a diffusion layer made of a porous material, the diffusion layer being formed on and surrounding a periphery of the solid electrolyte layer to cover the first and second electrodes and the reference electrode wherein the first electrode is disposed closer to the reference electrode than the second electrode, wherein the first electrode and the reference electrode are disposed away from each other by a second distance that is greater than the first distance, and wherein the diffusion layer comprises: a first diffusion layer surrounding the periphery of the solid electrolyte layer, said layer forming a sintered assembly with the heater portion and the solid electrolyte layer; and a second diffusion layer for adjusting a gas diffusion resistance of each of the first and second electrodes relative to an exhaust gas, the second diffusion layer being formed on periphery of the first diffusion layer and being characterized by the structure of a sprayed material, wherein the first diffusion layer is made of an aluminum oxide material or an aluminum oxide material comprising zirconia, and wherein the second diffusion layer is made of an aluminum oxide material comprising magnesium oxide.