Load-Limiting Retractortorsion Bar Segmentation
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Solution Overview
Problem
Existing seat belt retractor systems fail to effectively limit chest deflection during collisions for occupants of varying sizes, as they do not adequately adjust load limiting features to accommodate different force exertions.
Innovation Solution
The retractor system incorporates a torsion bar and torsion tube that deform progressively to limit webbing extension, allowing for two load-limiting phases: one for smaller occupants and another for larger ones, by using a locking mechanism and ratchet system to manage the deformation of these components based on force thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single threshold torsion bar is used for load limiting, then the device complexity is low, but the adaptability to occupants of different sizes is insufficient
Solution Approach 1:
The single torsion bar is segmented into two functional phases: a first load-limiting phase with a lower threshold force and a second load-limiting phase with a higher threshold force. This segmentation allows the retractor to adapt to different occupant sizes by providing appropriate load limiting at different force levels, resolving the contradiction between maintaining low device complexity and achieving adaptability to various occupants.
2Object-affected harmful factors
If the torsion bar yields at a known threshold force, then the force imparted to the occupant is limited, but the chest deflection is not adequately reduced for all occupant sizes
Solution Approach 1:
The retractor transitions from a static single-threshold system to a dynamic two-phase system where the load-limiting threshold changes based on the force exerted. The first phase yields at a lower threshold force for smaller occupants, while the second phase engages at a higher threshold force for larger occupants. This dynamic adjustment optimizes chest deflection reduction across different occupant sizes.
3Adaptability or versatility
If the spool applies a twisting force to the torsion bar during collision, then the webbing extension is controlled, but the system cannot adequately respond to varying forces from different occupant sizes
Solution Approach 1:
The twisting force mechanism is segmented into two distinct phases: a first phase where the torsion bar yields at a lower threshold and a second phase where it yields at a higher threshold. This segmentation enables the system to respond appropriately to varying forces from different occupant sizes without requiring a completely separate system for each occupant type, thus managing complexity while improving adaptability.
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 solution effectively reduces chest deflection by allowing additional webbing extension only when necessary, thereby distributing force more evenly across occupants of different sizes, enhancing safety during collisions.
Implementation Method 1
The torsion bar yields, that is, deforms, at a known threshold force
Implementation Method 2
both the torsion bar 34 and the torsion tube 36 deform relative to the spool 32
Data Source
AI summary
A retractor includes a spool, a torsion bar and a torsion tube rotationally fixed to the spool, and a locking member aligned with the torsion bar. The torsion bar and the torsion tube extend coaxially from the spool to respective first ends, and the torsion bar has a key. The locking member is movable from an unlocked position rotationally disengaged with the torsion bar to a locked position wherein the key rotationally fixes the locking member to the first end of the torsion bar. When the locking member is in the unlocked position, the torsion bar may be plastically deformed to limit the load applied by webbing against an occupant. If sufficient force is applied to the webbing, the locking member moves to the locked position in which both torsion bar and the torsion tube are locked together and, in tandem, limit the load applied by the webbing.