Fusible Element Thermal Safety Device for High Current

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Solution Overview

Problem

Existing thermal safety devices are not suitable for high currents and have limited reliability under harsh conditions due to material stresses and lack of buffer volumes, which can lead to temperature rises and potential fires in applications like automotive systems.

Innovation Solution

A thermal safety device with a fusible element that melts to disconnect electrical circuits, featuring a layered construction with a capillary coating and epoxy resin encapsulation, ensuring rapid pressure rise and reliable disconnection without free buffer volumes, and using stable flux for long-term activation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a fusible element is used in thermal safety devices, then the device can disconnect electrical circuits under thermal stress, but the device cannot handle high currents due to material stresses and lack of buffer volumes

Engineering Contradiction:

Improvereliability under thermal and mechanical stressVSAvoidcurrent capacity

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent changes the physical parameters of the fusible element by providing it with a buffer volume that allows for thermal expansion and material displacement during melting. This parameter change enables the element to handle high currents while maintaining reliability under thermal stress, as the buffer volume accommodates the material's expansion without causing premature failure or short circuits.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If solder and connection points are permanently subjected to material stresses, then the electrical connection is maintained, but the service life and reliability are limited under harsh ambient conditions

Engineering Contradiction:

Improveelectrical connection stabilityVSAvoidservice life under thermal cycling

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent applies beforehand cushioning by providing a buffer volume around the fusible element that anticipates and accommodates thermal expansion and material stress during operation. This cushioning space prevents excessive stress from being transmitted to the solder and connection points during thermal cycling, thereby extending service life and maintaining reliability under harsh ambient conditions.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Volume of moving object

If a small mass of fusible element is used, then the device can be compact, but it is not suitable for high currents since only a small mass is available to carry the current

Engineering Contradiction:

Improvedevice sizeVSAvoidcurrent carrying capacity

Core Design Contradiction:

Volume of moving objectVSPower

Solution Approach 1:

The patent applies the nesting principle by placing the fusible element within a buffer volume that is itself enclosed by the housing. This nested structure allows the fusible element to have sufficient mass for high current applications while keeping the overall device compact. The buffer volume is efficiently utilized space that accommodates the fusible element's operational requirements without increasing the external dimensions of the device.

Inventive Principle:

Principle #7Nested doll (Nesting)

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 reliable disconnection of high current electrical circuits under thermal and mechanical stress, preventing fatal temperature rises and ensuring safety without the limitations of existing technologies.

Implementation Method 1

a fusible element (10), which melts on attainment of a certain temperature

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 2

By virtue of the encapsulation of the fusible element no buffer volume is provided between the fusible element and the encasement for the purpose of accommodating the fluid fusible element. Within the fusible safety device the fusible element is completely surrounded by directly adjoining components... As a result of the pressure rise the fusible element is displaced such that the electrical connection between the terminals is disconnected.

Methodology Applied

Scientific EffectPressure rise: Pressure Increase

Implementation Method 3

DE 10 2007 014 338 A1 describes a thermal safety device in the form of a circuit structure, in particular in the form of a stamped grid or a printed circult board, which has a fusible element and effects the disconnection of the electrical connection by virtue of the surface tension.

Methodology Applied

Scientific EffectCapillary action: Capillary Action

Data Source

PatentUS9899171B2Thermal safety device

Publication Date: 2018.02.20 VISHAY BCCOMPONENTS BEYSCHLAG GMBH

AI summary

In order to provide a method for isolating a circuit and a thermal link, wherein the link has a very low resistance and is suitable for high currents, in particular very high short load currents, and also has a high degree of reliability, in particular under difficult conditions, such as thermal and mechanical loading which lasts for a relatively long time, for example, the invention proposes that, during the phase transition of the material of the fusible element (10) from the solid to the liquid state, the volume of the fusible element (10) increases and the pressure increases and, owing to the increase in volume and the increase in pressure, the fusible element (10) is dislodged so as to break the electrical connection.