Polymer Rod Retractor Pretensioner Assembly
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Solution Overview
Problem
Conventional seatbelt pretensioners using metallic balls or rack and pinion systems face issues with weight, cost, low resistance conditions, and the need for additional mechanisms to maintain the retractor locked during pretensioning, leading to potential payback and gas leakage.
Innovation Solution
A seatbelt retractor assembly featuring a polymer rod with a non-constant cross-section and a sprocket with vanes, actuated by a gas generator, which becomes locked through plastic deformation and one-way teeth, preventing payback and enhancing sealing in low-resistance conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metallic balls or rack and pinion systems are used for pretensioning, then the pretensioning function is achieved, but the weight and cost increase
Solution Approach 1:
The patent changes the material parameter from metallic balls to a polymer rod, fundamentally altering the physical properties of the driving element. This parameter change reduces weight while maintaining the pretensioning function through plastic deformation of the polymer rod during actuation.
Solution Approach 2:
The polymer rod is designed as a single-use component that deforms plastically during pretensioning and cannot return to its original state. This disposable approach eliminates the need for complex locking mechanisms and reduces overall system weight and cost.
2Reliability
If metallic balls or rack and pinion systems are used for pretensioning, then the pretensioning function is achieved, but the device complexity increases due to synchronizing or clutch features
Solution Approach 1:
The patent extracts and eliminates the complex synchronizing or clutch features from the system by using a polymer rod that directly engages the sprocket. The rod's plastic deformation provides inherent synchronization without requiring additional clutch mechanisms.
Solution Approach 2:
The polymer rod automatically synchronizes with the sprocket through its plastic deformation characteristics during actuation. The system is self-synchronizing without requiring external clutch features or complex control mechanisms.
3Productivity
If driving elements reach end of stroke without substantial resistance, then the stroke is completed, but gas leakage occurs due to reduced backpressure on sealing elements
Solution Approach 1:
The patent changes the resistance characteristic at the end of stroke by using a polymer rod with non-constant cross-section. The varying cross-section creates progressive resistance during actuation, ensuring adequate backpressure is maintained on the sealing element throughout the stroke to prevent gas leakage.
4Reliability
If gas pressure is maintained beyond the amount needed for pretensioning stroke, then the retractor remains locked, but weight and cost increase
Solution Approach 1:
The patent uses a disposable polymer rod that provides mechanical locking through plastic deformation after a single actuation cycle. This eliminates the need for maintaining excessive gas pressure, allowing the gas generator to be sized appropriately for the pretensioning stroke only, reducing overall system weight.
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 reduces weight and cost, ensures effective pretensioning without additional gas pressure, and maintains the seatbelt locked, preventing payback and gas leakage, thereby enhancing occupant restraint during vehicle impacts.
Implementation Method 1
a tube having an arcuate and curved shape having a first end in fluid communication with a gas generator
Implementation Method 2
The polymer rod is plastically deformable. The polymer rod exits the tube, along a perimeter of the sprocket, and toward the curved guide in response to an actuation by the gas generator to rotate the sprocket and spindle
Data Source
AI summary
A pretensioner assembly for motor vehicle belt restraint systems is provided. The pretensioner assembly includes a tube in fluid communication with a gas generator and a polymer rod disposed therein that travels in a first direction in response to actuation of the gas generator. The polymer rod is plastically deformable and engages a sprocket to rotate the sprocket in response to the travel of the rod, where rotation of the sprocket causes pretensioning. The rod has a non-constant cross-section along its length. The rod becomes locked after actuation to prevent travel in an opposite direction. The system further includes a seal member and slug member disposed between the rod and the gas generator, where the seal member is relatively flexible and the slug member is relatively hard.