Force Limiter Bell-Crank Lever Mechanism
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Solution Overview
Problem
Existing energy-absorbing force limiters in seat-belt systems face challenges in varying the level of energy absorption based on occupant weight and position, with control loops being slow and inefficient, especially in rapid accident scenarios.
Innovation Solution
An energy-absorbing force limiter with adjustable control elements that respond to real-time signals for desired resistance, incorporating mechanisms like friction, hydraulic, or deformation effects, with sensors to adjust coefficients and apply precise forces to manage movement resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a control loop is used to adjust the frictional force in the force limiter, then the movement-resisting effect can be controlled, but the control is slow and cannot respond quickly enough in real accident situations
Solution Approach 1:
The patent replaces the electronic control loop with a mechanical control system using a bell-crank lever mechanism. The lever mechanically links the reel's rotational movement to the friction element's position, providing instantaneous mechanical response without electronic delays. The bell-crank lever translates rotational motion into linear motion to adjust the friction force in real-time during acceleration events.
Solution Approach 2:
The force limiter system is self-regulating through the mechanical bell-crank lever that automatically adjusts the friction force based on the reel's rotational position. The system uses its own operational parameters (reel rotation) to control the friction element, eliminating the need for external sensors, controllers, and power sources that would slow down the response.
2Loss of energy
If friction is used to provide movement-resisting effect, then energy absorption is achieved, but the frictional force varies with temperature making precise control difficult
Solution Approach 1:
The patent employs a dynamic friction control mechanism where the friction force is continuously adjusted during operation. The bell-crank lever mechanism dynamically changes the friction element's position and contact pressure based on the reel's rotational speed and position, allowing the system to adapt to varying operating conditions and maintain reliable energy absorption throughout the acceleration event.
Solution Approach 2:
The system changes the friction parameter dynamically during operation. By mechanically linking the reel rotation to the friction element positioning, the friction force is automatically adjusted as a function of the reel's rotational position and speed. This parameter change ensures that the friction force remains appropriate throughout the varying conditions of the acceleration event, compensating for temperature effects.
3Reliability
If metal element deformation is used for energy absorption, then the operating characteristic is predictable, but it is not easy to vary the energy absorption level based on occupant weight or position
Solution Approach 1:
The patent creates a dynamic friction-based force limiter where the friction force can be varied during operation through the bell-crank lever mechanism. Unlike static metal deformation elements, this mechanical system allows the friction force to change dynamically based on reel rotation, enabling adaptation to different occupant weights and positions while maintaining predictable operation through controlled mechanical leverage.
Solution Approach 2:
The friction-based mechanism with mechanical control serves multiple functions: it provides predictable energy absorption through controlled friction, allows variation of the force level through the bell-crank lever ratio, and can adapt to different operating conditions. This multi-functional approach replaces the single-function metal deformation element with a versatile system that handles both predictability and adaptability requirements.
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
Enables rapid and precise energy absorption tailored to occupant-specific parameters, reducing injury risk by providing optimal movement resistance during accidents.
Implementation Method 1
a frictional effect can be applied to parts of the spool by expanding a series of piezo-electric plates which form a stack of plates. A control signal is supplied to expand the piezo-electric plates, and thus the frictional force, and the movement-resisting effect, can be controlled.
Implementation Method 2
friction is used to provide the movement-resisting effect and to absorb energy
Data Source
AI summary
An energy-absorbing force limiter for a safety device comprises a first component (5) and a second component (2), such as a seat-belt, that is moveable relative to the first component (5). The force limiter provides an energy-absorbing movement-resisting effect, for example by means of a frictional brake (4, 5), to resist movement of the second component relative to the first. An adjustable control element (6) actuates the brake. The magnitude of the frictional effect is a function of the degree of adjustment of the control element and at least one parameter, such as temperature, which influences the coefficient of friction. The control mechanism (9) adjusts the adjustable control element (6) to control the magnitude of the movement-resisting effect in response to a signal (12) representative of the desired resistance to movement together with a signal (10, 11) representative of that at least one parameter.