Hybrid Inflator Burst Cap Transitional Geometry
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Solution Overview
Problem
Existing burst caps in hybrid inflators require extremely high bursting pressures to open, leading to excessive deformation and material stress, as they need to counteract both the igniter's pressure and the compressed gas tank's filling pressure, which can result in instability and increased manufacturing costs.
Innovation Solution
A self-supporting burst cap design with a transitional portion from the side wall to the bottom, allowing the bottom to rest on the side wall during pressurization, reducing the required bursting pressure and maintaining structural integrity under high filling pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the burst cap is designed to counteract both igniter pressure and compressed gas tank filling pressure, then the burst cap can maintain structural integrity under high filling pressures, but extremely high bursting pressures are required to open the burst cap
Solution Approach 1:
The burst cap is divided into functionally distinct zones: a crown portion that withstands external filling pressure and a skirt portion that is optimized for controlled bursting. The transition zone between these portions creates a geometric discontinuity that concentrates stress during bursting, allowing the cap to maintain integrity under filling pressure while enabling opening at lower bursting pressures.
Solution Approach 2:
Different regions of the burst cap are given different geometric properties tailored to their specific functions. The crown portion has a geometry optimized for withstanding external pressure, while the skirt portion and transition zone have geometries that facilitate controlled bursting at lower pressures. This local differentiation of structural properties resolves the contradiction between maintaining strength and enabling easy opening.
2Reliability
If the burst cap requires extremely high bursting pressures to open, then the burst cap can withstand high filling pressures in the idle mode, but excessive deformation and material stress occur
Solution Approach 1:
By segmenting the burst cap into distinct functional zones with optimized geometries, the structure can reliably withstand filling pressure during idle operation while experiencing minimal deformation during bursting. The transition zone acts as a predetermined failure point that concentrates stress, preventing excessive deformation of the overall structure.
3Ease of manufacture
If the burst cap is designed with continuous constant material thickness, then the manufacturing process is simplified, but the burst cap cannot efficiently differentiate between withstanding filling pressure and enabling controlled bursting
Solution Approach 1:
The burst cap employs local geometric variations in the form of transition zones and geometric discontinuities rather than varying material thickness. This approach maintains manufacturing simplicity while achieving functional differentiation: the crown portion geometry optimizes for pressure resistance, while the skirt portion and transition zone geometries facilitate controlled bursting.
4Strength
If higher bursting pressures are used to open the burst cap, then the burst cap can maintain structural integrity, but the igniter must be more powerful and costly
Solution Approach 1:
Instead of designing the burst cap to require high bursting pressures for structural reasons, the invention inverts the approach by designing the burst cap geometry to enable controlled bursting at lower pressures through transition zones and geometric discontinuities. This inversion allows a simpler, less costly igniter system to effectively open the burst cap while maintaining structural integrity during idle operation.
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 lowers the bursting pressure needed to open the burst cap while maintaining high collapse pressure capabilities, reducing material stress and manufacturing costs by forming a self-supporting structure that does not rely on additional components for support.
Implementation Method 1
a transitional portion from the side wall to the bottom is formed so that when the bottom is pressurized on the outside, a portion of the bottom on the igniter compartment side can rest on a portion of the side wall on the igniter compartment side
Implementation Method 2
maintaining structural integrity under high filling pressures
Implementation Method 3
in the case of operation, being adapted to be destroyed by a bursting pressure on the side of the igniter compartment
Data Source
AI summary
The invention relates to a hybrid inflator (10) including a burst cap (20) including a bottom (21) and a sleeve-like side wall (22), the bottom (21) and the side wall (22) delimiting an igniter compartment (23), and the burst cap (20) in the idle mode being pressurized on the outer peripheral side with compressed gas having a filling pressure (PF) which at a functional maximum temperature of the hybrid inflator (10) has a maximum filling pressure (PFmax), and wherein the burst cap (20) can be destroyed by an igniter compartment side bursting pressure in the case of operation. In accordance with the invention, a transitional portion (24) is formed from the side wall (22) of the burst cap (20) to the bottom (21) so that the igniter compartment side bursting pressure required to destroy the burst cap (20) is lower than the sum of the maximum filling pressure (PFmax) and the filling pressure (PF). The invention further relates to a burst cap, an airbag module, a vehicle safety system as well as a method of manufacturing a burst cap.