Seat Belt Retractor With Switchable Multi-Stage Force Limiting
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Solution Overview
Problem
Existing belt retractors for motor vehicle seatbelts lack sufficient force-limiting levels during relative rotation between the belt shaft and the locked profile head.
Innovation Solution
A belt retractor with a second force-limiting device that is initially decoupled, allowing force-limited relative rotation without its involvement, and can be coupled via a pyrotechnic drive to add additional force-limiting levels, doubling the achievable force-limiting stages with a multi-stage first force-limiting device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multi-stage first force-limiting device with two torsion bars is used, then two force-limiting levels can be set, but the number of force-limiting levels is insufficient for enhanced safety requirements
Solution Approach 1:
The force-limiting function is segmented into two independent devices: a first force-limiting device with two torsion bars (providing two force levels) and a second force-limiting device with one torsion bar (providing one additional force level). When combined, these segments create four distinct force-limiting levels without requiring a single complex multi-stage mechanism, thus resolving the contradiction between adaptability and device complexity.
2Adaptability or versatility
If the second force-limiting device is actively decoupled from the first force-limiting device, then three force-limiting levels can be set, but the coupling mechanism adds structural complexity
Solution Approach 1:
The second force-limiting device is designed to be actively decoupled from the first force-limiting device through a pyrotechnic drive. This extraction principle allows the second device to be removed from the force transmission path when not needed, enabling three force-limiting levels while minimizing the complexity of the coupling mechanism by using a simple pyrotechnic separation system rather than a complex mechanical coupling.
3Extent of automation
If a pyrotechnic drive is used to couple the second force-limiting device, then electronic activation is enabled, but the system requires additional activation control mechanisms
Solution Approach 1:
The mechanical coupling between the first and second force-limiting devices is replaced with a pyrotechnic drive system that can be activated electronically. This substitution eliminates the need for complex mechanical coupling mechanisms and enables electronic activation control, resolving the contradiction between automation extent and device complexity by using chemical energy conversion (pyrotechnic) instead of mechanical linkage.
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 provides four distinct force-limiting levels, enhancing the safety and functionality of the belt retractor by incorporating a second force-limiting device that can be activated electronically, improving the force-limiting capabilities beyond traditional two-stage systems.
Implementation Method 1
a drive, which can be activated electronically, for example, is provided, by means of which a coupling of the second force-limiting device is possible... In this case, it is proposed in particular that the drive is a pyrotechnic drive, by means of which a transfer of the belt retractor from the initial state to a coupled state can be triggered
Data Source
AI summary
The invention relates to a belt retractor for a seatbelt of a motor vehicle, comprising a belt shaft which is rotatably mounted in a housing frame, a profile head which can be locked with respect to the housing frame, a multi-stage first force-limiting device, wherein the first force-limiting device is coupled to the profile head and to the belt shaft, wherein the first force-limiting device allows a force-limited relative rotation of the belt shaft with respect to the locked profile head, and comprising at least one second force-limiting device, wherein, in an initial state, the second force-limiting device is decoupled, so that the force-limited relative rotation of the belt shaft with respect to the locked profile head takes place without a force-limited involvement of the second force-limiting device.