Shear-Pin Inertia Igniter for Compact High-G No-Fire Protection
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Solution Overview
Problem
Existing inertial igniters for thermal batteries in munitions are too large and not suitable for small reserve batteries, particularly those used in miniaturized fuzing and smart munitions, and require significant differences in no-fire and all-fire acceleration levels to ensure safety and reliability, making them unsuitable for high-G setback accelerations.
Innovation Solution
A compact inertial igniter design with a base, striker mass, and a spring mechanism that allows the striker mass to rotate upon fracture of a shearing or tension element during high-G all-fire acceleration, ensuring safe initiation only under specified conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing inertial igniter design is used, then reliable ignition can be achieved, but the igniter becomes too large for small reserve batteries
Solution Approach 1:
The igniter is divided into separate functional components: a base element, a striker mass, a spring element, and a shearing pin. This segmentation allows each component to be optimized independently for its specific function while reducing the overall volume compared to a monolithic design.
Solution Approach 2:
The striker mass is designed to rotate about an axis perpendicular to the direction of acceleration, utilizing rotational motion in a different dimension to achieve the striking action. This dimensional change allows for a more compact arrangement of components and reduces the overall igniter volume.
2Reliability
If existing inertial igniter design is used, then ignition can be triggered, but it requires significant differences in no-fire and all-fire acceleration levels
Solution Approach 1:
The shearing pin is designed with specific geometric parameters (diameter, length, material properties) that allow it to fail at a well-defined acceleration threshold. By carefully selecting these parameters, the igniter can be tuned to respond to a narrow range of acceleration levels, providing clear differentiation between no-fire and all-fire conditions.
Solution Approach 2:
The spring element is pre-loaded to create a mechanical counterforce that must be overcome by the inertial force during acceleration. This substitution of a purely inertial system with a spring-loaded mechanical system allows for more precise control over the acceleration threshold and improves the ability to differentiate between acceleration levels.
3Volume of moving object
If compact igniter design is implemented, then size is reduced, but manufacturing complexity increases
Solution Approach 1:
By segmenting the igniter into distinct components (base element, striker mass, spring element, shearing pin), each part can be manufactured separately using standard processes and then assembled. This reduces the complexity of manufacturing the entire igniter as a single piece while maintaining the compact design benefits.
Solution Approach 2:
Multiple functional elements are combined into a single integrated base element that provides both structural support and mounting surfaces for other components. This merging reduces the total number of parts and simplifies assembly while maintaining the compact volume.
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 design achieves reliable ignition at high-G accelerations while being significantly smaller and less costly, meeting safety and reliability requirements for munitions with reduced height and volume, and avoiding accidental initiation.
Implementation Method 1
a spring element positioned between the striker mass and the shearing pin, the spring element being pre-loaded in compression
Implementation Method 2
a spring element positioned between the striker mass and the shearing pin, the spring element being pre-loaded in compression
Implementation Method 3
a shearing pin fixed to the base element and to the striker mass, the shearing pin having a reduced cross-sectional portion
Data Source
AI summary
An inertial igniter including: a base having a first projection; a striker mass rotatably connected to the base, the base having a second projection aligned with the first projection such that the first and second projections impact when rotated; a member having a first portion engaging with a second portion of the striker mass to restrict rotation of the striker mass unless the predetermined acceleration is experienced; a mass movable from a first position where an acceleration is less than the predetermined acceleration and a second position where the acceleration is greater than the predetermined acceleration, the second position permitting the first and second portions to come out of engagement; a spring biasing the movable mass in the first position; and a shear member permitting impact of the first and second projections when the predetermined acceleration is experienced and the movable mass moves to the second position.