Two-Stage Expansion Valve Spool Assembly for Brazing Tolerance
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Solution Overview
Problem
The manufacturing process of known two-stage proportional control valves, such as MSEVs, is complex and costly due to the need for final machining steps after brazing fluid inlet and outlet connector tubes and capillary tubes, which can cause spool bore distortion, leading to tolerance issues and lengthy manufacturing times.
Innovation Solution
The improved two-stage proportional control valve design allows for the spool assembly to be machined and assembled before brazing, with a spool and sleeve configuration that maintains dimensional tolerance and enables independent testing and assembly, reducing the impact of brazing heat on machining precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If final machining steps are performed after brazing, then dimensional tolerance of spool bore is maintained, but manufacturing time increases and process complexity increases
Solution Approach 1:
The spool bore is machined to final dimensions before the brazing operation. By performing the critical machining operation in advance, the bore is protected from heat-induced distortion. The sequence is reversed from conventional practice: components are assembled and brazed first, then the spool bore is machined to precise tolerances as a final step, ensuring dimensional accuracy without requiring post-brazing machining.
2Productivity
If spool bore is machined before brazing, then manufacturing time is reduced, but spool bore distortion occurs and dimensional tolerance is lost
Solution Approach 1:
The spool bore machining is performed as a preliminary action before brazing, but with the understanding that it will be followed by a final precision machining step after brazing. This allows the bulk material removal to occur early, reducing total manufacturing time, while the critical final dimensional control is performed after heat exposure to ensure tolerance compliance.
3Ease of manufacture
If components are brazed before final machining, then assembly fixtures are simplified, but spool bore becomes out of tolerance due to heat distortion
Solution Approach 1:
Components are brazed in a preliminary assembly before final spool bore machining. This preliminary brazing allows for simplified fixtures during assembly, while the critical final machining operation is performed after brazing to compensate for any heat-induced distortions and ensure the spool bore meets dimensional tolerances.
4Reliability
If spool assembly is made independent for testing, then quality control is improved, but device complexity increases
Solution Approach 1:
The spool assembly is segmented as a separate, independently testable component. The spool, sleeve, and associated features are manufactured and assembled as a distinct module that can be tested for dimensional tolerance and functionality before being integrated into the complete valve assembly. This segmentation enables quality control at an intermediate stage without significantly increasing overall device complexity.
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 design simplifies the manufacturing process, reduces costs, and maintains precise dimensional tolerances, allowing for easier assembly and testing of the spool assembly, thereby improving the efficiency and cost-effectiveness of valve production.
Implementation Method 1
the microvalve modulates to change a pressure differential across the second stage spool valve. The spool valve will move to balance the pressure differential
Implementation Method 2
the brazing operation may cause the machined spool bore to become out of tolerance if the brazing operation is performed after the spool bore has been machined
Data Source
AI summary
A two-stage proportional control valve configured for use in a fluid system includes a valve body having a longitudinally extending valve body bore formed therethrough. A first stage microvalve is mounted within the valve body bore, and a second stage spool assembly is mounted within the valve body bore downstream of the microvalve. The second stage spool assembly includes a sleeve and a spool slidably mounted within the sleeve.