Exhaust Pipe Sensor Mounting with Stainless Steel Boss
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Solution Overview
Problem
When using low specific gravity materials like titanium for exhaust pipes in vehicles, the high-temperature strength issues lead to potential loosening of components, such as air-fuel ratio sensors, due to the difficulty in welding dissimilar metals and the exposure of screw portions to high-temperature gases.
Innovation Solution
A mounting structure that incorporates an intermediate member made of higher high-temperature strength material, such as stainless steel, between the component and the exhaust pipe, with a pouch-like screw hole design and multiple bolt fastenings, along with sealing members to prevent torque down and ensure secure attachment and sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If titanium or titanium alloy is used for the exhaust pipe and boss to achieve weight saving, then the specific gravity is reduced, but the high-temperature strength is insufficient causing screw portion softening and torque down
Solution Approach 1:
The exhaust pipe is constructed using composite materials: the main body is made of lightweight titanium or titanium alloy, while the boss is made of stainless steel with high high-temperature strength. This composite structure allows the screw portions to maintain structural integrity at high temperatures while the overall exhaust pipe achieves weight reduction through the use of low-specific-gravity titanium material.
2Ease of manufacture
If titanium or titanium alloy is used for the boss to match the exhaust pipe material, then welding difficulty is avoided, but the screw portion exposed to high-temperature gas softens and loosens
Solution Approach 1:
The boss is made of stainless steel while the exhaust pipe is made of titanium or titanium alloy, creating a dissimilar metal composite structure. This approach prioritizes the high-temperature strength requirement for the screw portion over welding ease, accepting that dissimilar metal welding procedures will be used to connect the stainless steel boss to the titanium exhaust pipe.
Solution Approach 2:
Different material properties are applied to different parts of the structure: the boss is made of high-temperature strength material (stainless steel) where thermal resistance is critical, while the exhaust pipe body uses lightweight material (titanium). This local differentiation of material quality ensures each component performs optimally in its specific functional environment.
3Reliability
If stainless steel is used for the boss to ensure high-temperature strength, then torque down is prevented, but weight saving is reduced compared to using titanium throughout
Solution Approach 1:
The exhaust pipe assembly uses a composite material strategy where only the boss (a relatively small component) is made of heavy stainless steel to provide high-temperature strength, while the majority of the exhaust pipe structure remains lightweight titanium. This localized use of high-strength material minimizes the weight penalty while ensuring the critical screw portions maintain reliability.
Solution Approach 2:
High-density, high-strength stainless steel is applied locally only to the boss where high-temperature strength is critical for preventing screw softening, while the rest of the exhaust pipe structure uses low-density titanium for weight saving. This spatial differentiation of material density optimizes the trade-off between weight and reliability.
Data Source
AI summary
When an exhaust gas sensor is mounted to an exhaust pipe into which exhaust gas from an engine is introduced, an intermediate member is made to intervene between the exhaust gas sensor and a boss provided in an exhaust manifold, the intermediate member being fastened to the boss by bolts and the exhaust gas sensor being screwed into a screw hole formed in the intermediate member, so that a sensor portion at a front end of the exhaust gas sensor is inserted into the inside of the exhaust pipe. Though the screw hole formed in the intermediate member is to be exposed to high-temperature gas of the exhaust manifold, stainless steel, whose high-temperature strength is high, being used for the intermediate member, a female screw of the screw hole is hard to be softened and an occurrence of torque down can be suppressed.