Seat Belt Retractor Layout for Stable Pretensioning and Force Limiting
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Solution Overview
Problem
Existing safety belt retractors with pretensioning functions can provide excessive force, leading to over-restraint of vehicle occupants, and have complex structures with high assembly requirements, where the pretensioning force must be overcome before the force limiter activates, resulting in uncertain shoulder forces during emergencies.
Innovation Solution
A safety belt retractor with a compact structure incorporating a belt reel, a force-limiting member that fails at a predetermined load threshold, and a pretensioner drive wheel coupled via the force-limiting member, ensuring the pretensioning function does not interfere with the force-limiting function, featuring a direct rotation-fixed connection between the drive wheel and the belt reel, and optionally a stop member for additional stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pretensioner is added to provide pretensioning force, then the pretensioning function is improved, but the structure becomes more complex and assembly requirements increase
Solution Approach 1:
The patent combines the pretensioner and force limiter into a single integrated assembly where the drive wheel of the pretensioner is directly connected to the force-limiting member. This merging eliminates the need for separate mounting structures and reduces the number of parts, thereby improving the pretensioning function while reducing structural complexity
Solution Approach 2:
The force-limiting member serves dual functions: it transmits the pretensioning force from the drive wheel to the belt reel, and simultaneously limits the maximum force applied to the occupant. This multi-functionality reduces the need for additional components, simplifying the overall structure while maintaining reliable pretensioning and force-limiting functions
2Reliability
If a force limiter is arranged separately from the pretensioner, then the force-limiting function is independent, but the number of parts increases and assembly becomes more difficult
Solution Approach 1:
The force limiter is integrated with the pretensioner by directly connecting the drive wheel to the force-limiting member, eliminating separate mounting operations. This reduces the number of assembly steps and improves manufacturing ease while maintaining independent force-limiting functionality
Solution Approach 2:
The force-limiting member is pre-configured with the drive wheel in a predetermined spatial relationship during manufacturing. This preliminary arrangement of components allows for simpler final assembly, as the critical alignment between the force limiter and pretensioner is already established
3Force
If the pretensioning force is high, then the pretensioning effect is improved, but excessive force may cause injury to the occupant
Solution Approach 1:
The force-limiting member is pre-configured with a predetermined failure load that is set below the level that would cause occupant injury. When the pretensioning force reaches this predetermined threshold, the force-limiting member fails or yields, automatically limiting the force transmitted to the occupant. This preliminary design ensures that even high pretensioning forces cannot exceed safe limits
Solution Approach 2:
The force-limiting member acts as a built-in safety mechanism that activates before excessive force can be transmitted to the occupant. By designing the force-limiting member with a specific load threshold, the system provides beforehand protection against over-restraint, ensuring that the pretensioning force is automatically capped at a safe level
Data Source
AI summary
The present invention relates to a safety belt retractor, comprising a frame (1), a belt reel (3), which is rotatably supported in the frame (1) and is configured for winding a webbing (2), a force-limiting member (4), which fails when a predetermined load threshold is exceeded, and a pretensioner (10) having a drive wheel (6) coupled with the belt reel (3) via the force-limiting member (4), wherein the drive wheel is drivable to rotate the belt reel (3) in a winding direction of the webbing, so as to pretension the webbing. The drive wheel (6) is directly rotation-fixedly connected with the force-limiting member (4) at a first side facing the belt reel (3), wherein the drive wheel (6) is rotatably supported relative to the belt reel (3) except for a rotation-fixed connection. The safety belt retractor further comprises a lockable stop wheel (9), wherein the drive wheel (6) is directly rotation-fixedly connected with the stop wheel (9) at a second side facing away from the belt reel (3). The safety belt retractor has a compact structure and a stable force-limiting function.