Webbing Take-up Device Asymmetric Teeth Coupling
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Solution Overview
Problem
Existing webbing take-up devices face challenges in reducing size and weight while maintaining excellent coupling strength between the pawl member and the ring portion, which is crucial for efficient load transmission.
Innovation Solution
The design incorporates a load transmission mechanism with a ring portion and a pawl member, where one has a lower material strength than the other, and the teeth are designed such that the tips of the higher material strength member engage with the bottoms of the lower material strength member, maximizing the shear area for enhanced coupling strength, allowing for reduced size and weight while maintaining required strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the size and weight of structural members of the load transmission mechanism are reduced, then the overall size and weight of the webbing take-up device are reduced, but the coupling strength between the pawl member and the ring portion deteriorates
Solution Approach 1:
The patent applies local quality by creating an asymmetric tooth configuration where the tooth heights of the pawl member and ring portion are deliberately made different. Specifically, the tooth heights of the pawl member are set to be lower than those of the ring portion, creating a localized geometric feature that ensures the tips of the ring portion teeth engage with the bottoms of the pawl member teeth. This local geometric differentiation maximizes the shear area at the engagement interface, thereby maintaining coupling strength while allowing overall size reduction.
Solution Approach 2:
The patent employs parameter changes by modifying the tooth height parameters of the pawl member and ring portion. By setting the tooth height of the pawl member (Hp) lower than that of the ring portion (Hr), and controlling the pitch circle diameter ratio, the engagement geometry is optimized to maximize shear area. This parameter optimization allows the coupling strength to be maintained or even enhanced while reducing the overall size and weight of the components.
2Weight of stationary object
If the tooth size is minimized to reduce weight, then the device weight is reduced, but the shear area for load transmission is insufficient
Solution Approach 1:
The patent applies asymmetry by deliberately designing the tooth heights of the pawl member and ring portion to be different. The tooth heights of the pawl member are set lower than those of the ring portion, creating an asymmetric engagement geometry. This asymmetry ensures that during meshing, the tips of the ring portion teeth engage with the bottoms of the pawl member teeth, maximizing the shear area. This asymmetric design allows minimal tooth sizes for weight reduction while ensuring sufficient shear area for reliable load transmission.
Data Source
AI summary
A webbing take-up device that is both capable of promoting reductions in size and weight and capable of excellently maintaining coupling strength between a pawl member and a ring portion. A clutch plate and a lock ring of this webbing take-up device are coupled by plural teeth provided at the clutch plate meshing with plural teeth provided at the lock ring. This lock ring is specified to have a lower material strength than the clutch plate. A tooth height H2 of the plural teeth of the lock ring is specified to be lower than a tooth height of the plural teeth of the clutch plate. Thus, when the lock ring and the clutch plate mesh, tooth tips of the plural teeth of the clutch plate come into contact with tooth bottoms of the plural teeth of the lock ring.