Thermal Switch Bimetallic Disc Thermal Isolation
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Solution Overview
Problem
Existing thermal circuit breakers are prone to undesired triggering due to current heat generation, which can simulate higher temperatures than the actual device temperature, and they often have complex designs that limit their current-carrying capacity and compactness.
Innovation Solution
A thermal circuit breaker design where the current flows through a contact spring with a bimetallic disc arranged at a greater distance, featuring a plunger that lifts the movable contact when the switching temperature is exceeded, and a compact, flat housing with a thermally insulated bimetallic disc to minimize heat impact and enhance current-carrying capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the bimetallic disc carries the movable contact to simplify the structure, then the device complexity is reduced, but the current heat generated in the bimetallic disc causes undesired triggering
Solution Approach 1:
A contact spring is introduced as an intermediary component between the bimetallic disc and the movable contact. The contact spring carries the movable contact and makes contact with the second connecting plate, while the bimetallic disc acts on the contact spring via a plunger. This intermediary structure allows the bimetallic disc to be thermally isolated from the current path, preventing self-heating while maintaining mechanical actuation functionality.
2Volume of moving object
If the bimetallic disc is placed close to the contact spring for compact design, then the device volume is reduced, but the heat from the contact spring affects the bimetallic disc
Solution Approach 1:
The plunger serves as a thermal intermediary that physically separates the bimetallic disc from the contact spring while maintaining mechanical coupling. The plunger is arranged between the first leg of the spring and the bimetallic disc, allowing the bimetallic disc to act on the contact spring without direct thermal contact. This enables compact arrangement while preventing heat transfer to the bimetallic disc.
Solution Approach 2:
The bimetallic disc is extracted from the current-carrying path and positioned outside the insulator body or at a greater distance from the contact spring. By removing the bimetallic disc from the immediate vicinity of the heat-generating contacts, the design eliminates thermal interference while maintaining the switching function through the plunger-mediated mechanical action.
3Device complexity
If the current flows through the bimetallic disc to simplify the circuit, then the device complexity is reduced, but the current-carrying capacity is limited by ohmic heat loss
Solution Approach 1:
The contact spring serves as an intermediary that carries the movable contact and makes electrical contact with the second connecting plate, while the bimetallic disc acts on the contact spring mechanically via the plunger without carrying the current. This separation allows the electrical circuit to be simplified while the bimetallic disc remains thermally isolated, enabling high current-carrying capacity without ohmic heating of the bimetallic 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 solution provides reliable switching behavior with increased current-carrying capacity, reduced heat impact on the bimetallic disc, and a more compact, easier-to-manufacture design that is less affected by ambient temperature changes, suitable for high-power applications.
Implementation Method 1
The switching temperature is specified by a bimetallic disc, which cannot change its shape or curvature continuously, but only abruptly if a temperature change in the bimetallic disc has built up a mechanical minimum stress determined by the shape of the bimetallic disc and its elastic properties
Implementation Method 2
When the switch is closed, the current flows through the contact spring which carries the movable contact on a first leg and makes contact with the second connecting plate with a second leg. In the process, heat is generated in the contact spring
Data Source
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AI summary
The invention relates to a thermal protection switch with a first terminal plate (1) with a fixed contact (2), a second terminal plate (3) which is electrically connected to a movable contact (5), an insulator body from which the two terminal plates (1, 3) protrude, a bimetallic disc (7) which, when a switching temperature is exceeded, breaks a conductive connection between the two terminal plates (1, 3), and a housing (10) into which the insulator body (6a, 6b) is inserted.According to the invention, the movable contact (5) is attached to a first leg (4a) of a spring (4), which contacts the second connecting plate (3) with a second leg (4b), wherein a plunger (8) is arranged between the first leg (4a) of the spring (4) and the bimetallic disc (7), which the bimetallic disc (7) presses against the first leg (4a) when the switching temperature is exceeded, thus lifting the movable contact (5) away from the fixed contact (2).