Ceramic Adhesive Seal for Exhaust Gas Sensor Leakage
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Solution Overview
Problem
Existing exhaust sensors face contamination issues due to gas leakage between the exhaust gas and the air reference channel, which current sealing methods, such as compacted talc powder and glass seals, fail to adequately prevent, leading to detrimental effects on sensor output.
Innovation Solution
The integration of a ceramic adhesive structure, comprising one or multiple layers with a coefficient of thermal expansion matching the materials it bonds to, is applied to the sensing element, insulator, and metal shell to effectively seal potential leak paths and prevent gas contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compacted talc powder or glass seal is used to seal between exhaust gas and air reference, then sealing function is provided, but gas leakage occurs leading to air reference contamination
Solution Approach 1:
The patent uses a composite sealing structure combining ceramic adhesive material with metal and ceramic components. The ceramic adhesive is applied between the metal shell and ceramic insulator/sensing element, creating a multi-material seal that prevents gas leakage more effectively than single-material seals like talc powder or glass alone.
Solution Approach 2:
The ceramic adhesive material is specifically selected to have a coefficient of thermal expansion (CTE) matching that of the ceramic insulator and sensing element. This parameter matching prevents thermal stress and seal failure during temperature cycling, ensuring reliable sealing under exhaust gas temperature conditions.
2Object-affected harmful factors
If ceramic adhesive structure with matched CTE is used, then gas leakage is reduced and air reference remains uncontaminated, but manufacturing complexity increases due to multiple adhesive layers and CTE matching requirements
Solution Approach 1:
The ceramic adhesive is applied selectively only at the critical sealing interfaces between the metal shell and ceramic components, rather than throughout the entire assembly. This localized application provides sealing where needed while minimizing additional complexity in non-critical areas.
Solution Approach 2:
The ceramic adhesive acts as an intermediary material that bonds the metal shell to the ceramic insulator and sensing element. This intermediary layer accommodates differences in thermal expansion between metal and ceramic, preventing seal failure while maintaining a relatively simple overall structure.
3Strength
If multiple ceramic adhesive layers are used, then seal robustness is improved, but manufacturing time and process complexity increase
Solution Approach 1:
The seal is divided into multiple ceramic adhesive layers applied at different interfaces: one layer between the metal shell and ceramic insulator, and another layer between the metal shell and sensing element. This segmentation provides comprehensive sealing at each interface while allowing independent optimization of each layer.
Solution Approach 2:
The ceramic adhesive layers are applied and cured during the assembly process before final sensor operation. This preliminary sealing action ensures that all potential leakage paths are closed before the sensor is put into service, preventing contamination from the outset.
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 ceramic adhesive structure significantly reduces gas leakage, ensuring the air reference remains uncontaminated and enhancing the reliability of exhaust sensor output by forming a robust seal between the exhaust gas and the air reference channel.
Implementation Method 1
a cured ceramic adhesive structure that is bonded to the insulator and the metal shell, to the insulator and the sensing element, and/or to the sensing element and the metal shell
Implementation Method 2
a ceramic adhesive layer has a coefficient of thermal expansion (CTE) that is close to the CTE of each material to which the ceramic layer is bonded
Data Source
AI summary
A gas sensor includes a sensing element formed on a ceramic substrate, an insulator surrounding at least a portion of the sensing element, and a metal shell surrounding at least a portion of the sensing element. The gas sensor further includes a cured ceramic adhesive structure bonded to the insulator and the sensing element, to the insulator and the metal shell, or to the sensing element and the metal shell. The ceramic adhesive structure is disposed so as to mitigate gas leakage through the gas sensor.