Thermal Protector Bimetal Inversion Area Positioning
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Solution Overview
Problem
Conventional thermal protectors often incorrectly shut down due to Joule heating, causing unnecessary operations at lower ambient temperatures, as the bimetal element is influenced by heat generated within the protector itself, leading to frequent false triggering.
Innovation Solution
A thermal protector design where the bimetal element is positioned such that its inversion area does not overlap with the conduction path, minimizing the impact of Joule heating, with a movable plate and bimetal element configuration that allows for precise control of contact pressure and heat management, ensuring the bimetal element is not inverted at lower temperatures than intended.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the bimetal element is positioned to overlap with the conduction path area, then the thermal protector can be compactly designed, but the bimetal element is exposed to Joule heating causing false triggering at lower temperatures
Solution Approach 1:
The patent positions the bimetal element's inversion area to overlap with only 1/3 or less of the conduction path area, strategically utilizing spatial arrangement in three-dimensional space. This dimensional positioning allows the bimetal element to be close enough for compact design while avoiding direct exposure to the majority of Joule heating in the conduction path, thus resolving the contradiction between compact size and shutdown accuracy.
2Device complexity
If the bimetal element forms a conduction path, then the structure is simplified, but Joule heating in the bimetal element causes premature inversion and shutdown
Solution Approach 1:
The patent extracts the harmful function of Joule heating from the bimetal element by making it non-conductive or minimizing its conduction path. The bimetal element is designed to not form a significant conduction path, thereby removing the source of self-heating that causes premature inversion. This allows the bimetal element to respond only to ambient temperature changes rather than being influenced by its own resistive heating.
3Device complexity
If the entire inversion area of the bimetal element is positioned over conduction areas, then the device structure is simplified, but radiation and convection heating causes frequent operation at lower temperatures
Solution Approach 1:
The patent applies local quality by creating a non-uniform spatial relationship between the bimetal element and conduction paths. Specifically, the inversion area is positioned to overlap with only 1/3 or less of the conduction path area, creating zones of different thermal exposure. This localized spatial arrangement reduces the overall thermal coupling between conduction paths and the bimetal element, thereby reducing radiation and convection heating effects while maintaining structural simplicity.
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 stabilizes current conduction by preventing false triggering, allowing the thermal protector to operate reliably at normal temperatures without being activated by internal heat generation, thus ensuring accurate shutdown only at prescribed high temperatures.
Implementation Method 1
the bimetal element is operated by not only ambient temperature but also the influence of Joule heating generated by the bimetal element itself
Implementation Method 2
a bimetal element which is inverted in the direction of bending backward at prescribed temperature to switch on/off the pair of fixed contacts
Implementation Method 3
The movable plate is disposed in the direction where its one end side reverse to the other end side provided with the movable contact is getting away from the fixed contacts and the terminal
Data Source
AI summary
Various embodiments include a thermal protector, including the rear end of a movable plate fixed to one end of a resin base and a pair of terminals for connection with an external circuit fixed to the other end thereof. Fixed contacts are formed on the fixed portions of the terminals, and the movable contact of the movable plate is disposed opposed to the fixed contacts. A bimetal element engaged with the center of the movable plate is set to project upward at normal temperature, thus bringing the movable contact into pressure contact with the fixed contacts with prescribed contact pressure. The bimetal element consists of an inversion area wherein the inversion area has no portion overlapping the conduction path area of load current.