Twin Shoulder Strap Harness RetraCTOR With Intermediate Shaft Load Distribution
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Solution Overview
Problem
Existing twin shoulder strap retractor assemblies fail to dynamically distribute load evenly between the straps, leading to reduced effectiveness in restraining occupants during off-center vehicle impacts, where one strap bears the majority of the load.
Innovation Solution
A retractor assembly with a load distribution mechanism featuring an intermediate shaft, webbing spools, and torsion bars, along with locking and load regulation mechanisms, dynamically distributes load between the shoulder straps by controlling webbing pay-out and applying pre-tensioning, load-limiting, and active seatbelt control functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a twin shoulder strap harness is used to increase webbing area and reduce chest deflection, then chest deflection is reduced, but load distribution between straps becomes uneven during off-center impacts
Solution Approach 1:
The patent introduces an intermediate shaft as a mediator between the two webbing spools. This intermediate shaft mechanically couples the spools together, enabling automatic load distribution through torsional flexibility without requiring complex electronic sensors or control systems. The intermediate shaft acts as a passive intermediary that equalizes load distribution through mechanical means during off-center impacts.
Solution Approach 2:
The patent employs torsion bars with specific torsional stiffness parameters to control the rotational resistance of the intermediate shaft. By carefully selecting the torsional stiffness parameter, the system achieves optimal load distribution between the two shoulder straps while maintaining the ability to adapt to different impact scenarios. The torsional parameter allows the system to transition between rigid and flexible states as needed.
2Reliability
If a load distribution mechanism with intermediate shaft and webbing spools is implemented, then load distribution between straps is improved, but device complexity increases
Solution Approach 1:
The patent divides the retractor assembly into modular segments: two independent webbing spools, each with its own retractor mechanism, coupled through a central intermediate shaft. This segmentation allows each component to be optimized independently while maintaining overall system simplicity. The modular design facilitates easier manufacturing, assembly, and maintenance compared to a fully integrated single-spool design.
Solution Approach 2:
The load distribution mechanism operates autonomously without requiring external control systems. The torsion bars and intermediate shaft automatically sense and respond to load imbalances through passive mechanical means. When one shoulder strap experiences higher load, the intermediate shaft naturally rotates to allow more webbing payout from that side, self-regulating the load distribution without electronic sensors or actuators.
3Ease of operation
If webbing spools are rotatably mounted to provide free movement under normal conditions, then occupant comfort is improved, but emergency locking response time may be delayed
Solution Approach 1:
The patent implements dynamic characteristics in the webbing spool system, allowing the spools to rotate freely under normal conditions for occupant comfort while incorporating inertial locking mechanisms that automatically engage during emergency deceleration. The system transitions from a static locked state to a dynamic free-rotation state and back again, adapting its mechanical properties based on the operational phase. The torsion bars also provide dynamic flexibility during impact, allowing controlled rotation before the locking mechanism fully engages.
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 solution ensures even load distribution between the shoulder straps, enhancing occupant restraint and reducing chest deflection during impacts, thereby improving safety and compliance with stringent safety regulations.
Implementation Method 1
Each said first load-limiter comprising a torsion bar in the driveline between the respective webbing spool and the intermediate shaft
Implementation Method 2
A spring cassette applies a biasing force to rotate the webbing spool in the webbing retraction direction
Implementation Method 3
A locking mechanism prevents relative rotation between the webbing spool and the intermediate shaft in an emergency situation
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
A retractor assembly (30) for a twin shoulder strap automotive seat harness has a load distribution mechanism (42) with an intermediate shaft (44). First and second webbing spool sub-assemblies (48a, 48b) are located on either side of the mechanism. Each sub-assembly includes a rotatable webbing spool (50a, 50b) drivingly coupled to the intermediate shaft (44) through respective load limiters (54). At least one webbing spool is selectively coupled to the intermediate shaft by a locking mechanism (60). The load distribution assembly has a load regulator (46) operative on the intermediate shaft (44) to apply pre-tensioning and/or further load-limiting and/or webbing pay-out limiting and/or active seatbelt control. The first load-limiters (54) dynamically distribute the load between both shoulder straps (32a, 32b) in an impact, whilst the load distribution mechanism (42) equally distributes the load from the load regulator to each webbing spool sub-assembly.