Movable Wall Gas Generator for Vehicle Restraint Systems
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Solution Overview
Problem
Gas generators for vehicle occupant restraint systems face issues with 'jamming' and after-burning due to gas accumulation and compacting of pyrotechnic solid propellant tablets, leading to slower burning and unpredictable pressure curves, which existing solutions attempt to address with stable filter-like spacers that can be constricted by pressure.
Innovation Solution
A movable wall part is introduced into the combustion chamber that penetrates deeper into the propellant bed, creating a gas-directing channel and offering less resistance to gas flow, allowing ignition from a different side and controlling burning through geometric shape, with at least 50% of the combustion chamber's envelope consisting of through-flow openings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a filter-like spacer is incorporated between the combustion chamber wall and propellant bed to prevent jamming, then gas outflow is improved, but the spacer may be constricted or closed by pressure and requires stable construction that increases device complexity
Solution Approach 1:
The wall part is designed to be movable rather than stationary, allowing it to dynamically respond to gas pressure by moving into the propellant bed. This dynamic behavior prevents jamming without requiring a complex stable construction, as the movable wall part automatically adjusts its position based on operating conditions.
Solution Approach 2:
The movable wall part acts as an intermediary element between the combustion chamber wall and the propellant bed. It mediates the interaction by creating a gas-directing channel that facilitates gas flow while preventing direct contact and potential jamming between the propellant bed and the combustion chamber wall.
2Ease of manufacture
If the propellant bed is ignited from one side, then ignition is simple, but gas accumulation occurs and burning speed decreases
Solution Approach 1:
The movable wall part segments the combustion chamber into different regions, creating a gas-directing channel that divides the gas flow path. This segmentation allows gas to reach different parts of the propellant bed more effectively, improving burning speed while maintaining simple one-side ignition.
Solution Approach 2:
The movable wall part introduces a new spatial dimension for gas flow by creating a channel that extends into the propellant bed. This dimensional change allows gas to penetrate deeper into the propellant bed, improving burning speed without complicating the ignition system.
3Productivity
If the wall part moves into the propellant bed, then jamming is prevented and ignition is improved, but the wall part must withstand significant gas pressure
Solution Approach 1:
The wall part is designed to move dynamically in response to gas pressure rather than resisting it statically. By moving into the propellant bed with the gas flow, the wall part reduces the pressure differential across its structure, minimizing structural stress while maintaining ignition efficiency.
Solution Approach 2:
The gas pressure that would normally stress the wall part is converted into a beneficial force that drives the wall part into the propellant bed. This movement creates the gas-directing channel and improves ignition, transforming the potentially harmful pressure into a useful driving force.
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
This design reduces jamming and ensures rapid ignition, allowing for reproducible outflow parameters and a more compact gas generator, as the movable wall part minimizes flow resistance and facilitates efficient gas flow through the propellant bed.
Implementation Method 1
When it is activated electrically, the igniter generates hot gas and particles which ignite the pyrotechnic charge in the combustion chamber
Implementation Method 2
the wall part being arranged in the combustion chamber, which is moved by a gas stream generated on activation of the gas generator into the region of the propellant bed which is not yet ignited
Implementation Method 3
By the movement in the direction of flow, the wall part offers a small resistance to the gas flow
Data Source
AI summary
A gas generator, particularly for a vehicle occupant restraint system, has at least one igniter (12), a pyrotechnic solid propellant bed (22), a combustion chamber (20) containing the propellant bed (22) and at least one wall part (24), the wall part (24) being arranged in the combustion chamber (20), which is moved by a gas stream generated on activation of the gas generator into the region of the propellant bed (22) which is not yet ignited, and in its interior (25) defines a gas-directing channel reaching into the propellant bed (22).