Sensor Element Porous Protective Layer Adhesion
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Solution Overview
Problem
Existing gas sensors with porous protective layers face delamination and detachment issues due to thermal shock, leading to increased gas diffusion resistance and output instability when used in internal combustion engine exhaust applications.
Innovation Solution
A gas sensor configuration featuring a porous leading-end protective layer that extends into the gas inlet and is fixed to the inner wall of the ceramic body, combined with a buffer layer outside the side surfaces, to enhance adhesion and prevent delamination caused by thermal expansion differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous protective layer is provided on the sensor element to protect against thermal shock, then the sensor can withstand thermal expansion differences, but delamination and detachment occur due to repeated thermal shock
Solution Approach 1:
The patent applies preliminary action by forming a protrusion on the sensor element surface before providing the porous protective layer. This protrusion structure is prepared in advance to enhance mechanical interlocking, preventing delamination and detachment when thermal shock occurs during sensor operation.
Solution Approach 2:
The patent utilizes curvature by designing the protrusion with a specific curved shape on the sensor element surface. This curved geometry increases the contact area and mechanical interlocking between the sensor element and the porous protective layer, thereby improving adhesion and preventing delamination under thermal stress.
2Reliability
If the porous protective layer is securely adhered to prevent delamination, then sensor output stability is maintained, but the adhesion strength is insufficient under thermal expansion differences
Solution Approach 1:
The protrusion structure is formed on the sensor element surface before applying the porous protective layer, creating a mechanical interlocking feature that strengthens adhesion from the outset and prevents delamination that would otherwise compromise output stability.
Solution Approach 2:
The curved shape of the protrusion increases the surface area and mechanical interlocking between the sensor element and protective layer, enhancing adhesion strength to maintain sensor output stability under thermal expansion differences.
3Ease of operation
If the protective layer is made porous to allow gas diffusion, then measurement gas can reach the sensor, but diffusion resistance increases and output exceeds predetermined values
Solution Approach 1:
The patent applies local quality by providing the porous protective layer only on specific portions of the sensor element where gas diffusion is needed, while maintaining other areas with different properties. This selective placement ensures adequate gas diffusion to reach the sensor while preventing excessive diffusion that would cause output to exceed predetermined values.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses delamination and detachment of the protective layer, ensuring stable operation and maintaining sensor accuracy over long-term use by securing adhesion and reducing thermal shock effects.
Implementation Method 1
a heater (150) buried in a predetermined range on a side of the one end portion (E1) of the ceramic body (101)
Implementation Method 2
at least one electrochemical pump cell including an outer pump electrode (141) located on an outer surface of the ceramic body (101), an inner pump electrode (142) located to face the at least one internal chamber (102), and a solid electrolyte (101a) located between the outer pump electrode (141) and the inner pump electrode (142), the at least one electrochemical pump cell pumping in and out oxygen between the at least one internal chamber (102) and an outside
Implementation Method 3
a leading-end protective layer (2) being porous, and covering a leading end surface (101e) and four side surfaces of the element base (1) in a predetermined range of the one end portion (E1), wherein the leading-end protective layer (2) has an extension (201a) extending into the gas inlet (105)
Data Source
AI summary
A sensor element includes: an element base including: a ceramic body made of an oxygen-ion conductive solid electrolyte, and having a gas inlet at one end portion thereof; at least one internal chamber located inside the ceramic body, and communicating with the gas inlet under predetermined diffusion resistance; an electrochemical pump cell including an electrode located on an outer surface of the ceramic body, an electrode facing the chamber, and a solid electrolyte located therebetween; and a heater buried in the ceramic body, and an leading-end protective layer being porous, and covering a leading end surface and four side surfaces in a predetermined range of the element base on the one end portion. The leading-end protective layer has an extension extending into the gas inlet, and fixed to an inner wall surface of the ceramic body demarcating the gas inlet.