Seatbelt Pretensioner Friction Load Limiting Mechanism
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Solution Overview
Problem
Conventional seatbelt pretensioners do not effectively limit excessive tension in safety belts during a crash, which can lead to passenger injury due to rapid increases in belt tension.
Innovation Solution
A pretensioner system incorporating an external cylinder, internal cylinder, piston, retracting member, gas generator, and one-way restriction device, which applies tension to the seatbelt and limits it to a predetermined load by allowing the piston to move in one direction while restricting reverse movement, thus preventing excessive tension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional pretensioner is used to apply tension to the seatbelt, then the seatbelt tension increases rapidly to restrain the passenger, but the tension exceeds the load limit and causes passenger injury
Solution Approach 1:
The patent changes the mechanical parameter of the system by introducing a friction-based load limiting mechanism. The friction force between the inner cylinder and outer cylinder is designed to match the load limit, automatically regulating the tension force to prevent excessive values while maintaining effective restraint.
Solution Approach 2:
The inner cylinder acts as an intermediary element between the piston and the seatbelt. It transmits the pulling force from the piston while simultaneously limiting the maximum tension through friction with the outer cylinder, thus mediating between the high force generation and the load limit requirement.
2Object-affected harmful factors
If friction force between the inner cylinder and outer cylinder is set to limit the load, then excessive tension is prevented, but the pretensioner cannot effectively apply sufficient tension to restrain the passenger
Solution Approach 1:
The system uses friction as a controllable parameter to limit force. By designing the friction force between the cylinders to equal the load limit, the system automatically regulates tension without requiring complex control mechanisms, resolving the contradiction between force application and force limitation.
3Device complexity
If the piston is allowed to move freely in both directions, then the mechanism is simple, but the piston cannot maintain tension or prevent reverse movement during crash
Solution Approach 1:
The system transitions from a static restriction approach to a dynamic friction-based approach. The friction between the inner and outer cylinders provides automatic, adaptive resistance that allows piston movement during pretensioning while preventing reverse movement during crash, eliminating the need for complex mechanical one-way valves or locks.
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 system effectively maintains seatbelt tension at or below a load limit, preventing passenger injury by controlling the force transferred during a crash, as illustrated by the comparison of tension development in conventional and load-limited pretensioners.
Implementation Method 1
a gas generator configured to supply gas to the inside of the external cylinder to move the piston in a direction of pulling the retracting member
Implementation Method 2
Frictional force between the outer surface of the internal cylinder and the inner surface of the external cylinder may be set to be at or below a load limit of the belt
Data Source
AI summary
Disclosed are a pretensioner and a safety belt assembly including the same. The pretensioner includes an internal cylinder movably installed within an external cylinder with an outer surface thereof in contact with an inner surface of the external cylinder, a piston installed in the internal cylinder, a retracting member configured with one side connected to the piston and the other side configured to extend from the external cylinder and connected to a belt fastening a passenger, a gas generator configured to supply gas to the inside of the external cylinder to move the piston in a direction of pulling the retracting member, and a one-way restriction device configured to allow the piston to move with respect to the internal cylinder when the piston moves in the direction of pulling the retracting member and to restrict the piston to be within the internal cylinder when the piston moves in reverse direction.