Seatbelt Control Device Dynamic Force Limiter Threshold
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Solution Overview
Problem
Existing seatbelt control technologies fail to appropriately adjust the load of the force limiter mechanism during collisions with varying deceleration patterns, leading to inadequate protection in cases where deceleration changes over time, such as collisions with objects having a soft leading end followed by a hard portion, as the load cannot be switched from low to high even if deceleration increases after an initial period.
Innovation Solution
A seatbelt control device with a pre-tensioner section and a force limiter section, controlled by a controller that activates the pre-tensioner based on collision detection and adjusts the force limiter load based on collision velocity, setting a second threshold to ensure a higher load is applied if deceleration exceeds the threshold within a predetermined period, thereby addressing low impact intensity collisions by correlating collision energy with collision velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the force limiter mechanism is set to a low load by igniting the Micro Gas Generator (MGG), then the seatbelt tension is reduced for comfort in low-severity collisions, but the load cannot be switched to a high load even if deceleration increases after the time period A has elapsed
Solution Approach 1:
The force limiter mechanism is designed with dynamic load switching capability, allowing the load to be changed from low to high based on real-time deceleration monitoring. The controller continuously monitors deceleration and switches the force limiter load mode when deceleration exceeds the second threshold after the time period A, enabling the system to adapt to changing collision conditions rather than being fixed at one load level.
Solution Approach 2:
The system implements feedback control by continuously monitoring deceleration and using this information to adjust the force limiter load. The controller receives deceleration signals and switches the force limiter between low-load and high-load modes based on whether the deceleration exceeds the second threshold during the monitoring period, creating a closed-loop control system that responds to actual collision conditions.
2Reliability
If the second threshold is set high to avoid false activation, then the force limiter remains at low load for comfort, but appropriate protection is not provided when collision energy is actually high
Solution Approach 1:
The system uses two different thresholds for different purposes: the first threshold for initial collision detection and the second threshold (set higher than the first) for determining force limiter load mode. This parameter differentiation allows the system to distinguish between minor deceleration fluctuations and genuine high-energy collisions, enabling reliable false activation prevention while ensuring appropriate protection when needed.
3Object-affected harmful factors
If the force limiter mechanism is set to a high load, then appropriate protection is provided for high-energy collisions, but excessive load is applied in low-severity collisions causing unnecessary discomfort
Solution Approach 1:
The control system is divided into distinct operational phases: an initial phase (time period A) where the first threshold is used for collision detection, and a subsequent phase where the second threshold is used for force limiter load determination. This segmentation allows the system to initially respond to any collision and then refine its response based on sustained deceleration levels, providing appropriate load levels for different collision severities.
Data Source
AI summary
A seatbelt retractor device includes a pre-tensioner section, and a force limiter section that can change a magnitude of a load at which to start reducing tension of the retracted seatbelt. A seatbelt control ECU activates the pre-tensioner section when a deceleration G detected by a floor sensor exceeds a first threshold, and acquires a collision velocity from a radar device and sets a second threshold value to a lower value the greater the collision velocity. The seatbelt control ECU controls the starting load for tension reduction by the force limiter section to be a high load when the deceleration G has exceeded the second threshold within a determination time period after activation of the pre-tensioner section, and controls the starting load for tension reduction to be a low load when which the deceleration G has not exceeded the second threshold within the determination time period.