Refrigerant Block Fitting Fastener Design for Thermal Cycle Compliance
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Solution Overview
Problem
Refrigerant block fitting assemblies in vehicle air conditioning systems face issues with thermal expansion gradients, leading to reduced clamping force and potential leaks due to dissimilar materials used for block fittings and fasteners, which are not designed to thermally expand or contract effectively.
Innovation Solution
A block fitting assembly with a fastener design that includes a non-threaded portion adjacent to a threaded portion, allowing for increased free length or a necked portion with a reduced outer diameter, enabling thermal expansion and contraction while maintaining a desired clamping force, thereby addressing the thermal expansion mismatch between different components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If threaded fasteners are used to couple block fittings, then the blocks are securely fastened together, but the fasteners cannot thermally expand or contract effectively due to thread constraints, leading to reduced clamping force
Solution Approach 1:
The fastener is segmented into two distinct portions: a threaded portion for securing the connection and a non-threaded portion that provides thermal expansion capability. This segmentation allows each portion to fulfill its specific function independently, resolving the contradiction between secure fastening and thermal adaptability.
Solution Approach 2:
Different portions of the fastener have different structural qualities - the threaded portion provides mechanical engagement and clamping force, while the non-threaded portion provides thermal expansion freedom. This local differentiation of properties allows the fastener to simultaneously achieve both secure fastening and thermal adaptability.
2Adaptability or versatility
If dissimilar materials are used for block fittings and fasteners, then the assembly can be optimized for different functions, but thermal expansion rates differ between components, causing clamping force reduction
Solution Approach 1:
The invention changes the structural parameter of the fastener by introducing a non-threaded portion with different thermal expansion characteristics than the threaded portion. This parameter change allows the fastener system to accommodate differential thermal expansion between dissimilar materials while maintaining clamping force.
3Strength
If the fastener is fully threaded, then the connection is mechanically strong, but the fastener lacks flexibility to accommodate thermal load cycling
Solution Approach 1:
The fastener is divided into threaded and non-threaded segments, where the threaded segment provides connection strength and the non-threaded segment provides thermal cycle durability through flexible expansion and contraction.
Solution Approach 2:
The non-threaded portion introduces dynamic flexibility to the otherwise static threaded connection, allowing the fastener to adapt to thermal load cycling while maintaining structural integrity through the threaded portions.
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 provides compliance and flexibility to the fastening assembly during thermal load cycling, ensuring a consistent clamping force and reducing the likelihood of refrigerant leaks by allowing the fastener to expand and contract, thus meeting the stringent testing requirements.
Implementation Method 1
allowing for increased free length or a necked portion with a reduced outer diameter, enabling thermal expansion and contraction
Data Source
AI summary
A block fitting assembly comprises a first block having a first fastener aperture formed therethrough, a second block having a second fastener aperture formed therethrough in axial alignment with the first fastener aperture, and a fastener extending through the first fastener aperture and the second fastener aperture to couple the first block to the second block. The block fitting assembly includes a thermal expansion compliancy feature in the form of at least one of an inner surface of the second block defining the second fastener aperture including an axially extending non-threaded portion adjacent a threaded portion thereof or the fastener including a necked portion having a smaller outer diameter than a minor thread diameter of a threaded portion of the fastener.