Restraint Pretensioner Deceleration Ramp Mechanism
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Solution Overview
Problem
Existing restraint pretensioners suffer from bounce back issues after activation, which can interfere with the operation of interconnected inertial reels and lead to potential injuries due to excessive body displacement during adverse events in vehicles.
Innovation Solution
The pretensioner incorporates a deceleration ramp to gradually stop the rack at the end of its stroke, secured by a shear pin and featuring a compact design with a perpendicular initiator, eliminating bounce back and ensuring safe operation by preventing rack re-engagement with the pinion gear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pretensioner uses a rack and pinion mechanism to tighten the restraint webbing, then the occupant is secured firmly against the seatbelt, but the rack may bounce back after reaching the end of its stroke and re-engage with the pinion gear, interfering with the proper operation of the inertial reel
Solution Approach 1:
A deceleration ramp is introduced as an intermediary component between the rack and the pinion gear. The ramp gradually decelerates the rack as it approaches the end of its stroke, preventing the rack from bouncing back and re-engaging with the pinion gear, thus eliminating the harmful bounce back effect while maintaining the tightening function
Solution Approach 2:
The deceleration ramp provides beforehand cushioning by gradually reducing the rack's velocity before it reaches the end of its stroke. This pre-cushioning approach prevents the rack from having excessive kinetic energy that would cause bounce back, ensuring reliable operation of the inertial reel without interference
2Speed
If the rack is allowed to move freely to tighten the webbing quickly, then the pretensioning action is fast and effective, but the rack may overshoot and bounce back, causing interference with the pinion gear
Solution Approach 1:
The deceleration ramp dynamically adjusts the rack's motion characteristics. During most of the stroke, the rack moves freely at high speed for effective pretensioning. As the rack approaches the end of its stroke, the ramp gradually increases resistance to slow the rack down, preventing overshoot and bounce back while maintaining overall speed and effectiveness
Data Source
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AI summary
Disclosed is a pretensioner for an occupant restraint. The pretensioner is designed to be used in conjunction with an inertial reel that locks the occupant restraint when detecting an adverse event. The pretensioner acts to remove slack in the webbing of the restraint and thereby safely secure the occupant once the reel is locked. The pretensioner described herein includes a rack that is initially held in place by a shear pin. Upon being activated, the rack is forced to a fully extended orientation, whereby the shear pin is severed. A deceleration ramp in included beneath the rack to slowly bring the rack to a stop at the end of the stroke.