Sensor element of gas sensor

Abstract

The invention provides a sensor element of a gas sensor. This sensor element comprises a distal end protection layer that is a porous layer provided on an outer peripheral part of a prescribed range from the end of an element substrate of the sensor element on the side where a detection unit is provided. The distal end protection layer comprises: first distal end protection layers that are provided on two main surfaces of the element substrate; a second distal end protection layer that is provided so as to cover the end and four lateral surfaces of the element substrate, including the two main surfaces on which the first distal end protection layers are formed; and a third distal end protection layer that is provided so as to cover the second distal end protection layer and has a lower porosity than the second distal end protection layer. The first distal end protection layers have a porosity of at least 40%. Given lengths of extension, in the longitudinal direction of the element substrate and starting from the end face of the element substrate, of the first distal end protection layers, second distal end protection layer, and third distal end protection layer of L1, L2, and L3, respectively, L1 >= L2 and L1 >= L3.

Description

technical field [0001] The invention relates to a sensor element of a gas sensor, in particular to a surface protection layer thereof. Background technique [0002] Conventionally, as a gas sensor for knowing the concentration of a desired gas component contained in a gas to be measured such as exhaust gas from an internal combustion engine, a gas sensor having a material made of zirconia (ZrO 2 ) and other solid electrolytes with oxygen ion conductivity, and has a sensor element with several electrodes on the surface and inside. As such a sensor element, it is well known that it has a long plate-like element shape, and a protective layer (porous protective layer) formed of a porous body ( See, for example, Patent Document 1). [0003] The purpose of providing the protective layer on the surface of the sensor element is to ensure the water immersion resistance of the sensor element when the gas sensor is used. Specifically, the purpose is to prevent water immersion cracki...

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Problems solved by technology

[0004] However, when such a protective layer is provided for the purpose of improving thermal shock resistance, the heat capacity of the sensor element as a whole increases, and the binding force on the sensor element increases.

This results in deterioration of the rapid temperature rise of the sensor element

In addition, depending on the environment in which the gas sensor is used, the protective film may detach from the sensor element due to vibrations generated in the environment. Therefore, it is also necessary to ensure the adhesion of the protective layer

[0005] In addition, in the case where water that adheres to and condenses on the protective layer when using a gas sensor remains in the protective layer after use, the water evaporates as the temperature of the sensor element rises at the start of use again, thereby generating volume in the protective layer. Swells, so the protective layer sometimes peels off

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