Vehicle Seat Reclining Device Lock Tooth Weak Point Design
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Solution Overview
Problem
Conventional vehicle seat reclining devices face instability and breakage under large loads due to uneven distribution of forces and lack of stabilization in the engagement between the external and internal gears, particularly when a belt anchor is positioned at the seat back, leading to increased inertia forces during collisions.
Innovation Solution
A vehicle seat reclining device with a lock tooth having an arc-shaped bearing surface and a weak portion, supported by a shaft portion and guide projections, which allows controlled rotation and engagement with the internal gear, and a cam mechanism to enhance engagement strength and stability by breaking at a predetermined weak point under excessive load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the lock tooth is supported by the shaft portion and guide portions with a clearance arrangement, then the device allows controlled rotation and engagement, but under large rotational forces the bearing portion is pressed against the shaft portion causing the lock tooth to ride on the circular surface, which applies bending force and causes unstable engagement strength
Solution Approach 1:
The lock tooth is segmented into two functional parts: a bearing portion with arc-shaped bearing surface that contacts the shaft portion, and an engagement portion with external gear that meshes with the internal gear. This segmentation allows the bearing portion to handle rotational forces through controlled riding on the shaft's circular surface, while the engagement portion maintains stable gear engagement, resolving the contradiction between controlled rotation and engagement stability.
Solution Approach 2:
The shaft portion is designed with a circular cross-section and the bearing portion of the lock tooth has an arc-shaped bearing surface that matches this curvature. This spherical/curved geometry enables the bearing portion to smoothly ride on the shaft's circular surface during rotation, distributing forces evenly and maintaining stable engagement between the gear portions while allowing controlled rotational movement.
2Adaptability or versatility
If a belt anchor is provided at the seat back, then the seat back can support seat belt loads, but during vehicle collision large inertia forces are transmitted to the seat back through the seat belt, requiring the reclining device to withstand further large loads
Solution Approach 1:
The lock tooth is designed to dynamically adapt its engagement state with the internal gear based on applied loads. Under normal conditions, the cam maintains engagement between the external and internal gears. Under excessive collision loads, the weak portion breaks, allowing the lock tooth to disengage and rotate freely, preventing catastrophic failure while maintaining strength under normal operational loads.
Solution Approach 2:
The weak portion is pre-designed as a sacrificial element that breaks under excessive load to cushion and protect the rest of the structure from catastrophic failure. This beforehand cushioning allows the device to withstand large collision forces by controlled failure of a non-critical component, preserving the overall structural integrity and safety.
3Reliability
If the external gear and internal gear are engaged to maintain angular position, then the seat back angular position is maintained, but under excessive load the engagement may break, compromising reliability
Solution Approach 1:
The gear engagement system is designed to dynamically respond to load conditions. The cam mechanism actively maintains engagement between the external and internal gears during normal operation, ensuring stable angular position maintenance. Under excessive collision loads, the system transitions to a disengaged state through weak portion failure, preventing catastrophic damage while maintaining reliability during normal use.
Solution Approach 2:
The weak portion serves as a pre-designed failure point that protects the gear engagement system from catastrophic failure under excessive loads. By sacrificing this non-critical component, the system cushions against extreme forces and prevents damage to the critical gear engagement mechanisms, ensuring they remain intact for normal operational reliability.
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 stabilizes the engagement between the external and internal gears, preventing breakage and maintaining the seat's angular position under large loads, thereby enhancing the durability and reliability of the reclining mechanism.
Implementation Method 1
a cam pushing the lock tooth to engage the external gear with the internal gear
Implementation Method 2
the lock tooth having a bearing portion which has an arc shaped bearing surface; a shaft portion integrally formed with the base member, the shaft portion having an inner-periphery guiding surface, on which the bearing surface of the lock tooth slides in contact with the inner-periphery guiding surface of the shaft portion
Implementation Method 3
an internal gear being formed on an inner peripheral surface of the rotating member; a lock tooth having an external gear, which is engageable with the internal gear of the rotating member
Data Source
AI summary
A seat reclining device is comprised of a base member connected to one of a seat back and a seat cushion; a rotating member connected to the other of the seat back and the seat cushion; a lock tooth having an external gear engageable with the internal gear of the rotating member; a shaft portion having an inner-periphery guiding surface for swinging the lock tooth on the shaft portion; and a weak portion formed at an end portion of the lock tooth opposite to the external gear across the shaft portion.