Pyrotechnic Cut-Off Device Sealing and Centering
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Solution Overview
Problem
Existing pyrotechnic cut-off devices are unreliable at high voltages and have increased breaking times, necessitating a more reliable and economical design for efficient current interruption.
Innovation Solution
A pyrotechnic cut-off device featuring a pyrotechnic initiator, a conductive portion, and a movable piston with sealing portions that create a surface seal to separate terminals, allowing for efficient current interruption with a Morse taper fit and varying material hardness for enhanced sealing and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If known pyrotechnic cutting devices are used to interrupt high-voltage circuits, then the device structure is simple, but the reliability decreases and interruption time increases
Solution Approach 1:
The conductive portion is segmented into multiple sections with defined breaking points, allowing controlled fracture into separate segments when the piston moves. This segmentation enables reliable current interruption by ensuring complete separation of conductive paths, while the predetermined breaking points reduce the time needed for effective disconnection.
Solution Approach 2:
The piston is pre-positioned in a first position where the conductive portion is held in place before interruption. Upon activation, the piston moves to a second position that pre-determines the breaking location and creates immediate sealing contact. This preliminary positioning reduces interruption time by eliminating the need for searching or adjusting the breaking point during the interruption process.
2Reliability
If the piston is fitted into the cavity without centering features, then the device is easier to manufacture, but the piston movement and seal maintenance are compromised
Solution Approach 1:
The piston and cavity feature asymmetric tapered surfaces (Morse taper) that provide self-centering functionality. The narrowing cross-section of the piston relative to the cavity, with angled contact surfaces, creates a geometric constraint that automatically centers the piston during assembly and operation. This asymmetric design maintains reliable sealing contact without requiring additional active centering mechanisms, balancing manufacturing simplicity with functional reliability.
3Reliability
If the sealing portions have parallel surfaces, then the manufacturing is simpler, but the seal effectiveness and current interruption are reduced
Solution Approach 1:
The sealing portions utilize asymmetric tapered surfaces instead of parallel planes. The first and second sealing portions have narrowing cross-sections with angled surfaces that create a wedge-shaped sealing interface. This asymmetric geometry concentrates contact pressure at the sealing interface, improving current interruption effectiveness by ensuring complete electrical isolation, while the self-aligning nature of the taper reduces the need for complex adjustment mechanisms.
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 device achieves a low characteristic cut-off time of 50 µs to 150 µs, improving reliability and sealing by centering the piston and maintaining a seal, even at high voltages.
Implementation Method 1
a pyrotechnic initiator configured, when triggered, to move a piston with a raised surface towards a conductive bar to be severed
Implementation Method 2
the first sealing portion of the piston and the second sealing portion, defined by the cavity wall, can cooperate in the piston's second position to create a surface seal on both sides of the conductive portion
Implementation Method 3
the narrowing of the sealing portions allows the piston to be fitted into the cavity in a manner similar to a Morse taper or spigot joint. This centering of the piston within the cavity prevents movement once it is in the second position
Implementation Method 4
the conductive portion can be broken by impact with the piston during the transition from the first to the second position. Specifically, the conductive portion can be broken into three parts, one of which is driven by the piston
Data Source
Figure 1~2
Figure 3~4
Figure 5a~5b
AI summary
The invention relates to a pyrotechnic cut-off device (100) comprising: a pyrotechnic initiator (20), a conductive portion (40) and a movable piston (30), the piston being able to move in a cavity (14) in a movement direction (A) following the activation of the pyrotechnic initiator between a first position allowing the current to flow in the conductive portion and a second position allowing the current to be cut-off, characterised in that the piston (30) defines a first sealing portion (33) having a narrowing cross-section in the movement direction (A), and in that the cavity (14) has a wall defining a second sealing portion (14b), which extends on either side of the conductive portion (40) and which has a narrowing cross-section in the movement direction (A), the first sealing portion (33) being in contact with the second sealing portion (14b) along a contact surface extending on either side of the conductive portion (40) when the piston is in the second position.