Thermally Responsive Switch Using Cadmiumless Contacts
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Solution Overview
Problem
Thermally responsive switches using cadmium-based contacts face challenges in maintaining durability and current cutoff performance while being compact enough for hermetic compressor housings, as cadmium use is limited and silver-cadmium oxide contacts have reduced durability and current cutoff performance when replaced.
Innovation Solution
A thermally responsive switch using cadmiumless silver-tin oxide-indium oxide contacts within a hermetically sealed container filled with helium gas at specific pressures, optimizing contact design and internal pressure to enhance durability and current cutoff performance without increasing size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If silver-cadmium oxide contacts are replaced with cadmiumless contacts, then environmental compliance is improved, but current cutoff performance and durability are reduced by half
Solution Approach 1:
The patent changes the material parameters of the contacts from silver-cadmium oxide to silver-tin oxide-indium oxide, and adjusts the gas pressure parameter to 0.05-0.15 MPa to achieve equivalent current cutoff performance without cadmium
Solution Approach 2:
The patent uses a composite contact material system consisting of silver, tin oxide, and indium oxide in specific proportions to replace the cadmium-based contact material, achieving both environmental compliance and electrical performance
2Reliability
If contact size is increased to improve current cutoff performance, then durability is improved, but device size increases making it difficult to mount in hermetic housing
Solution Approach 1:
The patent optimizes the gas pressure parameter to 0.05-0.15 MPa and adjusts contact material composition to achieve high current cutoff performance with standard-sized contacts, avoiding the need to increase contact dimensions
3Force
If thermally responsive plate size is increased to increase separating force, then contact separation performance is improved, but device size increases
Solution Approach 1:
The patent adjusts the gas pressure parameter and contact material properties to enhance the effectiveness of the thermally responsive plate's separating force, achieving adequate contact separation with a compact plate design
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 a compact thermally responsive switch with improved durability and current cutoff performance, equivalent to cadmium-based systems, by using silver-tin oxide-indium oxide contacts and helium gas filling, which reduces arc damage and extends the number of switching operations.
Implementation Method 1
The thermally responsive plate reverses a direction of curvature at a predetermined temperature
Implementation Method 2
When current having such a large inductivity is cut off by the opening of contacts, arc is generated between the contacts, whereupon contact surfaces are damaged by heat due to arc
Data Source
AI summary
A thermally responsive switch includes a hermetically sealed container including a metal housing and a header plate, at least one conductive terminal pin hermetically fixed in a through hole, a fixed contact fixed-to the terminal pin in the container, a thermally responsive plate having one end connected via a support to an inner surface of the container and reversing a curvature direction at a predetermined temperature, and at least one movable contact electrically conductively secured to the other end of the thermally responsive plate. Each contact includes a silver-tin oxide-indium oxide system contact. The container is filled with a gas containing helium ranging from 50% to 95% so that an internal pressure of the container ranges from 0.3 to 0.6 atmosphere at room temperature.