Seatbelt Retractor Load Limiting With Elastic Arm Release
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Solution Overview
Problem
Existing seatbelt retractor systems do not effectively manage the load applied to the chest of an occupant during vehicle impacts, as they lack a mechanism to control the extension of the seatbelt webbing beyond a certain load threshold.
Innovation Solution
A seatbelt retractor system that includes a frame, a spool, a ring, and a locking device with an arm that is elastically bendable. When the rotational force exceeds a certain threshold, the arm disengages from its recess, allowing a discrete amount of webbing extension while resisting further rotation, thus limiting the load on the occupant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the locking device locks the spool to prevent webbing extension, then the occupant is protected from excessive chest compression, but the seatbelt cannot accommodate controlled webbing extension when force exceeds the load-limiting threshold
Solution Approach 1:
The locking device transitions from a static locked state to a dynamic unlocked state when the rotational force exceeds the load-limiting threshold. The arm moves from engaging the recess to disengaging, allowing the system to adapt its locking behavior based on the applied load, thereby providing both chest compression protection and load threshold adaptation.
Solution Approach 2:
The system changes the locking parameter (engaged/disengaged state) based on the rotational force parameter. When the rotational force exceeds the load-limiting threshold, the arm disengages from the recess, changing the system state from locked to unlocked, allowing controlled webbing extension while maintaining protection below the threshold.
2Reliability
If the arm is made rigid to maintain locking engagement, then the locking device remains reliably engaged, but the arm cannot disengage to allow controlled webbing extension when force exceeds the threshold
Solution Approach 1:
The arm has different local qualities: it is rigid in its engagement with the recess to maintain reliable locking, but it is designed to be elastically bendable at specific locations to allow controlled disengagement when the rotational force exceeds the load-limiting threshold. This local differentiation of rigidity enables both reliable locking and controlled operation.
Solution Approach 2:
The elastic bendability of the arm acts as a cushioning mechanism that allows controlled disengagement before complete failure or excessive force is applied. The arm flexes to permit the spool to rotate and webbing to extend, cushioning the transition from locked to unlocked state and preventing abrupt or uncontrolled movement.
3Adaptability or versatility
If the arm is made elastically bendable to allow disengagement, then controlled webbing extension is permitted, but the locking engagement becomes less reliable under normal operating forces
Solution Approach 1:
The arm is pre-loaded in a biased position that maintains reliable engagement with the recess under normal operating forces. This preliminary positioning ensures that the locking engagement remains stable during typical seatbelt use, while still allowing disengagement when the rotational force exceeds the load-limiting threshold.
Solution Approach 2:
The system merges the rigid locking function with the elastic disengagement function in a single integrated arm component. The arm combines both the locking engagement capability and the controlled disengagement capability, eliminating the need for separate mechanisms and ensuring that the same component that provides reliable locking also enables controlled webbing extension when needed.
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 system effectively limits chest compression by allowing controlled extension of the seatbelt webbing during high forces, while maintaining the ability to reset and reuse the retractor after the force subsides.
Implementation Method 1
the arm is elastically bendable relative to the ring and the frame when rotational force on the ring relative to the frame about the rotational axis exceeds a non-zero threshold
Implementation Method 2
the arm locks the ring relative to the frame about the rotational axis when rotational force on the ring relative to the frame about the rotational axis is below the non-zero threshold
Data Source
AI summary
A seatbelt retractor includes a frame and a spool rotatably supported by the frame. A ring is coaxial with the spool on a rotational axis and is selectively lockable with the spool. A locking device is operatively coupled between the spool and the ring to rotationally engage the spool with the ring in a locked position and rotationally disengage the spool from the ring in an unlocked position. One of the ring or the frame defines a recess and an arm is fixed to and extends from the other of the ring or the frame into the recess. When the locking device is in the locked position, the arm is elastically bendable relative to the ring and the frame when rotational force on the ring relative to the frame about the rotational axis exceeds a non-zero threshold to allow rotation of the ring relative to the frame.