Vehicular Exhaust Pipe Vacuum Layer Thermal Elongation
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Solution Overview
Problem
The existing vehicular exhaust pipe structures with a vacuum layer between an outer and an inner pipe face issues with heat insulation degradation due to axial thermal elongation differences, leading to compressive loads that cause deformation and potential damage, resulting in heat transfer and vacuum state loss.
Innovation Solution
The use of an inner pipe with a pseudo-cylindrical concave polyhedral shell-shaped part, which has a lower spring constant in axial compression and a higher spring constant in bending, absorbs axial thermal elongation differences while preventing bending deformation, maintaining the vacuum state and heat insulation effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a vacuum layer is formed between the outer pipe and inner pipe for heat insulation, then the temperature decline of exhaust gas is suppressed and condensation is reduced, but a compressive load is applied to the inner pipe due to difference in axial thermal elongation between the pipes
Solution Approach 1:
The inner pipe's cross-sectional shape is changed from circular to pseudo-cylindrical concave polyhedral, which fundamentally alters its mechanical properties. This parameter change reduces the spring constant in axial compression direction, allowing the pipe to flexibly absorb thermal expansion differences without generating excessive compressive loads.
Solution Approach 2:
The pseudo-cylindrical concave polyhedral shell structure provides flexible deformation capability in the axial direction while maintaining structural integrity. This flexible shell design allows the inner pipe to accommodate thermal expansion/contraction cycles without rigid resistance, thereby reducing compressive load accumulation.
2Stability of the object's composition
If the inner pipe is made with lower axial spring constant to absorb thermal elongation, then thermal expansion difference is accommodated, but the pipe becomes more prone to bending deformation and contact with outer pipe
Solution Approach 1:
The cross-sectional shape parameter is specifically designed as pseudo-cylindrical concave polyhedral, which creates anisotropic mechanical properties. The structure exhibits low spring constant in axial compression (good for thermal expansion) while maintaining high spring constant in bending direction (good for structural stability).
Solution Approach 2:
The pseudo-cylindrical concave polyhedral shape introduces geometric asymmetry that selectively affects mechanical response in different directions. The concave polyhedral geometry provides different stiffness characteristics for axial compression versus bending, enabling independent optimization of both properties.
3Reliability
If the inner pipe contacts the outer pipe due to bending deformation, then heat transfer occurs and heat insulation effect is reduced, but using a rigid cylindrical pipe prevents contact while causing damage from compressive load
Solution Approach 1:
By changing the geometric parameters of the inner pipe cross-section to pseudo-cylindrical concave polyhedral form, the structural stiffness distribution is optimized. This parameter optimization allows the pipe to be compliant in axial direction (absorbing thermal stress) while remaining rigid in bending direction (preventing contact with outer pipe).
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
This configuration effectively maintains the heat insulation effect of the vacuum layer, suppresses condensation and water accumulation, and enhances the structural integrity and anti-rust performance of the exhaust pipe, reducing pressure loss and engine output decline.
Implementation Method 1
a decline in the temperature of the exhaust gas that circulates through the inner pipe is suppressed by the heat insulation effect of the vacuum layer
Implementation Method 2
a compressive load is applied to the inner pipe as a result of a difference in axial thermal elongation between the outer pipe and the inner pipe
Implementation Method 3
the bellows pipe being compressively deformed in an axial direction by the compressive load
Data Source
AI summary
A vehicular exhaust pipe structure includes an outer pipe extending along a front-rear direction of a vehicle and an inner pipe disposed inside the outer pipe along an axial direction of the outer pipe. The inner pipe is joined to the outer pipe such that a vacuum layer is formed between the inner pipe and the outer pipe. The inner pipe includes a pseudo-cylindrical concave polyhedral shell-shaped part.