Snap-Action Disc Rotation for Switch Contact Resistance
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Solution Overview
Problem
The service life of temperature-dependent switches is limited due to high contact resistance between stationary contacts and the current transmission element, which increases with the number of switching operations, limiting their usage in high-current applications.
Innovation Solution
Introducing unevenness on the edge of the snap-action disc and/or its bearing surface, allowing the snap-action disc to rotate slightly with each switching operation, distributing contact resistance over multiple points and increasing the service life without altering the thermal and mechanical properties of the snap disks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the switch is used for high-current applications with frequent switching operations, then the operating current capability is improved, but the contact resistance increases rapidly limiting service life
Solution Approach 1:
The contact surface of the current transmission element is segmented into multiple contact points around its circumference. The unevenness on the snap-action disc edge creates multiple discrete contact locations, so that wear and contact resistance increase are distributed across these segments rather than concentrated at a single point, extending the service life under high-current conditions
Solution Approach 2:
An asymmetric unevenness is introduced on the edge of the snap-action disc, creating a non-uniform contact profile. This asymmetric feature causes the contact point to shift with each switching operation, preventing continuous wear at the same location and reducing the rate of contact resistance increase while maintaining high current carrying capability
2Reliability
If the contact pressure is increased to reduce contact resistance, then the electrical connection is improved, but the mechanical stress on the snap-action disc increases
Solution Approach 1:
The unevenness on the snap-action disc edge creates localized contact zones with optimized pressure distribution. Instead of uniform contact across the entire edge, the contact pressure is concentrated at specific local points determined by the unevenness profile, achieving low contact resistance without requiring excessive overall mechanical stress on the snap-action disc
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 rotation of the snap-action disc slows the increase in contact resistance, extending the service life of the switch while maintaining the switching behavior and thermal properties, allowing for more switching operations before reaching impermissible contact resistance values.
Implementation Method 1
The temperature-dependent switching mechanism has a bimetal snap-action disk, which is circular in plan view... depending on the temperature, on a contact surface formed by the shoulder of the lower part or the edge of the spring snap-action disc, thereby allowing the contact bridge to rest against the two stationary contacts
Implementation Method 2
a spring snap-action disk, which is circular in plan view, through which a pin, which carries the contact bridge, passes centrally
Data Source
Figure 1
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AI summary
The temperature-dependent switch (10) comprises a housing (12) comprising a temperature-dependent switching mechanism (11). A ring (17) is arranged between upper and lower portions of the housing. The stationary contacts (31,32) are provided at the inner side (37) of upper portion of housing and are connected to external terminals (35,36). Two circular snap discs (21,22) are provided on the switching mechanism and are supported by a shoulder (28). The uneven portions are provided at edges (19,27) of circular snap discs respectively.