Propellant Cage Spiral Spring for Airbag Inflator Gas Flow

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Solution Overview

Problem

Existing propellant cages for tubular inflators in airbag modules face inefficiencies in gas flow, ignition, and manufacturing complexity, with sharp edges potentially harming propellant pellets and requiring numerous additional components for fixation.

Innovation Solution

A propellant cage designed as a spiral spring with a smaller gas inlet cross-section and larger outlet cross-section, featuring a funnel-shaped portion to stabilize shock waves and a packing element with a spiral spring configuration to reduce component count and enhance ignition efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If radial through-holes are used for both ignition gas inlet and propellant gas outlet, then the structure is simplified, but ignition efficiency is reduced

Engineering Contradiction:

Improvestructure complexityVSAvoidignition efficiency

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The gas flow path is segmented into separate inlet and outlet openings. The ignition gas inlet opening is positioned at the axial end facing the igniter unit, while the propellant gas outlet opening is at the axially opposed end. This segmentation allows optimized gas flow paths for different functions, improving ignition efficiency while maintaining structural simplicity through the spiral spring design.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The spiral spring structure acts as an intermediary element that facilitates controlled gas flow. The winding structure provides a pathway for ignition gas to reach propellant pellets while directing propellant gas toward the outlet. This intermediary structure resolves the contradiction by enabling functional separation without requiring complex additional components.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If sharp edges are present on the propellant cage, then manufacturing is simplified, but propellant pellets are harmed

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidpropellant pellet damage

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The propellant cage is designed as a spiral spring with inherently curved and rounded geometry. The spiral windings provide smooth surfaces without sharp edges, eliminating the harmful effect on propellant pellets. This curved design is achieved through standard spiral spring manufacturing processes, maintaining ease of manufacture while removing the harmful sharp edges through geometric transformation.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Stability of the object's composition

If multiple components are used for fixation, then assembly stability is improved, but device complexity increases

Engineering Contradiction:

Improveassembly stabilityVSAvoidcomponent quantity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The propellant cage spiral spring integrates multiple functions into a single component: it provides structural support, contains the propellant bed, facilitates gas flow, and ensures stable assembly through its geometric configuration. The spiral spring's inherent elasticity and geometry provide self-stabilizing features, eliminating the need for separate fixation components and reducing overall device complexity while maintaining assembly stability.

Inventive Principle:

Principle #5Merging (Combining)

4Stability of the object's composition

If the gas inlet cross-section is smaller than the outlet cross-section, then shock wave stability is improved, but gas flow resistance increases

Engineering Contradiction:

Improveshock wave stabilityVSAvoidgas flow resistance

Core Design Contradiction:

Stability of the object's compositionVSLoss of energy

Solution Approach 1:

The cross-sectional area parameter of the propellant cage is varied along its length, with the gas inlet cross-section being smaller than the outlet cross-section. This parameter change creates a diffuser effect that stabilizes the shock wave by gradually expanding the gas flow path. The spiral spring geometry naturally provides this area variation, and the open winding structure minimizes flow resistance, resolving the contradiction between shock wave stability and gas flow efficiency.

Inventive Principle:

Principle #35Parameter changes

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 spiral spring design simplifies manufacturing, reduces sharp edges, improves gas flow efficiency, and maintains shock wave stability, while the packing element minimizes required components and ensures proper ignition, enhancing the overall performance and safety of the tubular inflator.

Implementation Method 1

The propellant cage serves for forwarding a shock wave which is generated in the area of the gas inlet opening. The shock wave is formed by excess pressure forming within an ignition chamber when the igniter unit is ignited.

Methodology Applied

Scientific EffectShock wave: Shock Wave

Data Source

PatentUS11046283B2Propellant cage and packing element for a tubular inflator

Publication Date: 2021.06.29 TRW AIRBAG SYSTEMS GMBH

AI summary

A propellant cage (10) for a tubular inflator (100), especially for a tubular inflator (100) of an airbag module, for forming a propellant chamber (14) and a flow passage (15) of the tubular inflator (100). The propellant cage (10) is in the form of a propellant cage spiral spring (11) having a gas inlet-side end (12) and a gas outlet-side end (13), the gas inlet-side end (12) having a smaller cross-section than the gas outlet-side end (13).