Pretensioned Seatbelt RetraCTOR With Independent Coupling
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Solution Overview
Problem
Traditional seatbelt retractors with pretensioners and spools experience ALR zone shifting due to torsion bar yielding under high torque during low-speed impacts, leading to ineffective locking and delayed energy management, which compromises the ability to restrain occupants and child seats.
Innovation Solution
A seatbelt retractor design featuring independent coupling of the pretensioner and locking mechanism, utilizing a torsion bar cam and coupler pawls to manage torque absorption and rotation, allowing the spool to rotate freely during high acceleration events while preventing extraction during low acceleration events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pretensioner and spool are dependently coupled, then the pretensioner can retract the webbing during high acceleration events, but the ALR zone shifts due to torsion bar yielding under high torque during low-speed impacts
Solution Approach 1:
The retractor is divided into two independently coupled systems: a pretensioner system for high acceleration events and a locking mechanism system for low acceleration events. This segmentation prevents the ALR zone from shifting because each system operates independently without interfering with the other's torque transmission path.
Solution Approach 2:
A decoupling mechanism acts as an intermediary between the pretensioner and spool, allowing the pretensioner to engage the spool only during high acceleration events while preventing torque transmission during normal operation. This intermediary prevents the pretensioner from causing ALR zone shifts during low-speed impacts.
2Use of energy by moving object
If the pretensioner and spool are dependently coupled, then torque can be transmitted through the torsion bar, but there is a delay in energy management since the torque from restraining the occupant must overcome the pretensioner energy
Solution Approach 1:
The coupling between the pretensioner and spool is made dynamic rather than static. The decoupling mechanism allows the system to switch between engaged and disengaged states based on acceleration conditions. During high acceleration events, the pretensioner engages to provide immediate torque; during normal operation, it remains disengaged to eliminate delay.
Solution Approach 2:
The system changes the coupling parameter between pretensioner and spool based on acceleration conditions. During high acceleration events, the coupling is engaged to transmit torque; during low acceleration events, the coupling is disengaged to allow immediate torque transmission without overcoming pretensioner energy.
3Reliability
If the locking mechanism prevents spool rotation during low acceleration events, then webbing extraction is prevented, but the spool cannot rotate freely during high acceleration events
Solution Approach 1:
The locking mechanism is designed to be dynamic, automatically engaging during low acceleration events to prevent webbing extraction and disengaging during high acceleration events to allow free spool rotation. This dynamic behavior provides both reliable restraint and adaptability.
Solution Approach 2:
The locking mechanism automatically senses acceleration conditions and adjusts its state accordingly without external control. During low acceleration events, it self-engages to lock the spool; during high acceleration events, it self-disengages to allow the pretensioner to rotate the spool freely.
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
This design prevents ALR zone shifting and enhances energy management by ensuring the spool can rotate freely during high acceleration, effectively restraining occupants and improving safety by mitigating the forces exerted on them during impacts.
Implementation Method 1
The pretensioner includes an explosive charge that rapidly generates gas during a vehicle dynamic event to create pressure to move a piston
Implementation Method 2
The torsion bar is designed to deform torsionally when subjected to a predetermined torque to absorb energy during loading, imparted by the mass of an occupant during acceleration of the vehicle
Implementation Method 3
The locking mechanism may include a locking pawl driven by a force, from a spring or inertia, and having teeth to mesh with teeth of the frame member under low speed impacts
Implementation Method 4
A first end of the torsion bar is coupled to a torsion bar cam and a second end of the torsion bar is connected to a pinion
Data Source
AI summary
Seat belt retractors for spooling seat belts (webbings) include multiple independent torque transmission or absorbing systems. The seatbelt retractor comprises a webbing, a spool, a pinion, a pretensioner, at least one coupler pawl, and a locking mechanism including a lock base and a lock pawl. The at least one coupler pawl is positioned in a cavity in the spool. During a predetermined low acceleration event, the at least one coupler pawl pivots so that a portion of the at least one coupler pawl leaves the cavity and engages the lock base to load the lock base which is then prevented from rotating in a spool extracting direction by the locking pawl. When the pretensioner activates during a predetermined higher acceleration event, the pretensioner rotates the pinion in the webbing retraction direction to rotate the spool in the webbing retraction direction.