Pellet Thermal Fuse Insulation Structure for High-Temperature Cutoff
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Solution Overview
Problem
Conventional temperature-sensitive pellet-type thermal fuses face limitations in maintaining insulation performance and withstand voltage, particularly at high temperatures, due to the reliance on sealing resin for insulation, which is insufficient in ensuring reliable electrical disconnection during overheating events.
Innovation Solution
Incorporating an insulating tube and multi-layered sealing resins with different properties to enhance electrical insulation and heat resistance, while maintaining mechanical strength, in the narrowest insulation distance between the tubular case and the first lead, thereby improving the thermal fuse's reliability and insulation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sealing resin is used for insulation between the tubular case and the first lead, then the device structure is simple and manufacturing is easy, but the insulation performance and withstand voltage are insufficient at high temperatures
Solution Approach 1:
The patent uses a composite insulating structure combining an insulating tube (made of ceramic, glass, or heat-resistant plastic) with multi-layered sealing resins. The insulating tube provides primary insulation with high temperature resistance, while the sealing resins fill gaps and provide secondary insulation. This composite approach overcomes the limitations of using sealing resin alone, achieving both high insulation performance at elevated temperatures and ease of manufacture through modular assembly.
Solution Approach 2:
The insulating tube acts as an intermediary component between the tubular case and the first lead. Instead of relying solely on sealing resin to provide insulation, the insulating tube is inserted into the narrowest insulation distance region to serve as a dedicated insulating barrier. This intermediary structure specifically addresses the insulation deficiency at high temperatures while maintaining the simplicity of the overall device structure.
2Strength
If the end portion of the opening is made narrower by swaging to fix the insulating lid body, then the mechanical strength and fixation are improved, but the insulation distance between the tubular case and the first lead is reduced
Solution Approach 1:
The insulating tube serves as an intermediary component placed in the narrowest insulation distance region between the tubular case and the first lead. By inserting this dedicated insulating structure, the patent compensates for the reduced insulation distance caused by the swaged end portion, ensuring adequate insulation performance is maintained even where the geometry is most constrained.
Solution Approach 2:
The patent applies local quality enhancement by placing the insulating tube specifically in the narrowest insulation distance region rather than uniformly increasing insulation throughout. This targeted approach maintains the mechanical strength benefits of the swaged end portion while locally compensating for the reduced insulation distance where it is most critical.
3Device complexity
If single-layer sealing resin is used, then the device complexity is low and manufacturing is simple, but the insulation performance and heat resistance are insufficient
Solution Approach 1:
The patent employs multi-layered sealing resins with different properties applied in sequence on the insulating tube and tubular case. Each layer provides complementary insulation and sealing functions, with the first sealing resin providing base insulation and subsequent layers enhancing heat resistance and gap filling. This multi-layer composite approach improves insulation performance without significantly increasing device complexity, as the layers are applied in a systematic manufacturing process.
Solution Approach 2:
The sealing insulation is segmented into multiple functional layers rather than using a single homogeneous material. The first sealing resin layer provides primary sealing and insulation, while additional layers provide enhanced heat resistance and fill gaps. This segmentation allows each layer to be optimized for specific functions while maintaining overall structural simplicity and ease of manufacturing through sequential application.
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 ensures more reliable electrical disconnection during fuse operation and improved insulation performance at high temperatures, extending the creepage distance and maintaining mechanical strength, thus preventing overheating damage.
Implementation Method 1
the temperature-sensitive pellet melts or softens, whereby the movable contact is separated from the first lead with the urging force, thereby breaking the circuit
Implementation Method 2
The tubular case, the first lead, and the insulating lid body are sealed with a sealing resin
Data Source
AI summary
Provided is a temperature-sensitive pellet-type thermal fuse having excellent reliability including an insulation property after having operated. The fuse includes, in a tubular case with high electrical conductivity and high thermal conductivity, at least a temperature-sensitive pellet being capable of melting and softening at a specific temperature, a strong compression spring pressing the temperature-sensitive pellet, an insulating lid body closing an end portion of an opening of the tubular case, a weak compression spring being in contact with the insulating lid body, a first lead having an inner end penetrating the insulating lid body as a stationary contact, and a movable contact electrically connected to the first lead and the tubular case, and further includes a second lead disposed at an end of the tubular case.