Webbing Take-Up Device Extension Rib Absorbs Cam Rotation Variation
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Solution Overview
Problem
Existing webbing take-up devices face challenges in accurately switching between ELR and ALR states due to rotation variation of the cam member, especially when the speed reduction ratio is set to a small value, leading to potential misengagement of the ALR pawl with the lock mechanism.
Innovation Solution
The webbing take-up device incorporates a switching cam connected via a speed reduction mechanism, a control disk, a pressing portion, and an extension portion to absorb rotation variation, ensuring accurate switching between ELR and ALR states by preventing the ALR pawl from climbing over the lock mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the speed reduction ratio of the speed reduction mechanism is set to a small value, then the accuracy for switching timing from ELR to ALR state is improved, but the rotation variation of the cam member increases due to assembly variation and component variation
Solution Approach 1:
The extension portion is designed to extend in the take-up direction from the pressing portion, creating a buffer zone that absorbs rotation variations of the switching cam beforehand. This prevents the ALR pawl from climbing over the pressing portion due to rotation variations, while maintaining accurate switching timing when the cam rotates in the pull-out direction.
2Reliability
If the speed reduction ratio of the speed reduction mechanism is set to a large value, then the rotation variation of the cam member is reduced, but the switching timing from ELR to ALR state becomes unclear
Solution Approach 1:
The extension portion provides dynamic absorption of rotation variations in both directions. When the cam rotates in the pull-out direction, the pressing portion maintains contact with the holding portion for accurate switching. When the cam rotates in the take-up direction, the extension portion absorbs variations, allowing the system to tolerate larger speed reduction ratios while maintaining reliability.
Data Source
AI summary
An extension rib extends from a pressing portion in the take-up direction of an ALR cam and is formed to be able to abut with an ALR pawl. Accordingly, when the ALR cam excessively rotates in the pull-out direction with respect to a set position in a maximal pulled-out state, the ALR pawl abuts the extension rib. Accordingly, it is possible to suppress a state in which the ALR pawl climbs over the pressing portion and engages with a V-gear. Namely, even if a rotation variation of the ALR cam becomes large by setting a speed reduction ratio of speed reduction mechanism to a small value, it is possible to absorb such variation by the extension rib. Thus, it is possible to absorb rotation variation of the ALR cam while improving accuracy of switching timing from the ELR (or ALR) state to the ALR (or ELR) state.