Reversible Force Limiting Device for Belt Retractor Oscillation
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Solution Overview
Problem
Belt retractors with force limiting devices often experience abrupt drops in restraining force during transitions from high to low levels, causing unwanted oscillations in the elastically biased belt system, which are undesirable for optimal occupant restraint.
Innovation Solution
A reversible force limiting device with a reversing mechanism that includes a deformation element, which temporarily increases the restraining force by performing additional work, acting as a damping mechanism to quickly reach and maintain a lower force level by plastic deformation of a blocking element, triggered by an actuator-driven retaining element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the force limiting device reverses from a higher restraining force level to a lower restraining force level, then the vehicle occupant is relieved corresponding to his/her weight, but the abrupt drop of force excites the elastically biased belt system to oscillate
Solution Approach 1:
The reversing means performs a significant work share during reversing that is added to the performance of the force limiting element, temporarily increasing the restraining force to compensate for the upcoming drop. This preliminary anti-action counteracts the oscillation tendency before it fully develops, preventing the abrupt force drop from exciting the belt system.
Solution Approach 2:
The deformation element is pre-positioned in the force limiting device to provide cushioning during the reversing process. When reversing occurs, the deformation element deforms (preferably plastically) to absorb energy and dampen the oscillations that would otherwise be excited by the abrupt force level change, providing beforehand cushioning for the transition.
2Stability of the object's composition
If the reversing means performs a significant work share during reversing, then the oscillation is damped and the lower force level is maintained, but the device complexity increases
Solution Approach 1:
The reversing means is integrated into the existing force limiting device structure, combining the reversing function with the force limiting elements. The deformation element is incorporated within the flux of the force limiting device, merging multiple functions (force limitation, reversing, and damping) into a unified structure rather than adding separate independent components.
Solution Approach 2:
The deformation element serves multiple functions: it acts as part of the force limiting mechanism, provides the reversing work share, and simultaneously functions as a damping element to reduce oscillations. This multi-functionality reduces the need for separate dedicated components for each function, thereby limiting the increase in device complexity.
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 effectively dampens oscillations by compensating for the 'switching jump' and maintaining the lower force level, reducing amplitude and ensuring a smoother transition, thus providing improved occupant restraint.
Implementation Method 1
the reversing means includes a deformation element which is preferably plastically deformed upon reversing
Implementation Method 2
the additional performance of the reversing means completely or at least to the effect that the amplitude of a possible subsequent oscillation is considerably reduced
Data Source
AI summary
A force limiting device for a belt retractor is reversible from a higher restraining force level to a lower restraining force level by means of a reversing means during a force limiting phase, wherein the second restraining force level is largely determined by a performance of at least one force limiting element. The reversing means is arranged so that it accomplishes a significant work share upon reversing which is added to the performance of the force limiting element and thus temporarily increases the restraining force of the force limiting device. In this manner undershooting of the characteristic line of the force limiting device upon reversing to the lower restraining force level is compensated.