Pre-tensioner Piston Locking via Acceleration Thresholds
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Solution Overview
Problem
Existing pre-tensioner arrangements for motor vehicle safety devices often require replacement after undesired activation, leading to costly replacements due to the difficulty in resetting the system.
Innovation Solution
A pre-tensioner arrangement with a piston member, connecting member, and locking means that locks the piston member when subjected to acceleration exceeding a predetermined level, and retaining means that prevents locking during lower accelerations, allowing for easy resetting and avoiding undesired locking during pre-impact braking events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If locking means are added to prevent undesired activation, then reliability is improved, but device complexity increases
Solution Approach 1:
The locking means and retaining means are integrated into the existing piston member and cylinder chamber structure. The locking body utilizes the same acceleration forces that affect the piston member, combining the locking function with the existing mechanical components rather than adding entirely separate systems.
Solution Approach 2:
The locking mechanism responds to changes in acceleration parameters. When acceleration exceeds a predetermined level in the direction opposite to retraction, the locking body is forced against the locking surface, changing the state from unlocked to locked automatically based on the physical parameter of acceleration.
2Reliability
If the piston member is made lockable to prevent undesired movement, then reliability is improved, but ease of operation worsens due to difficulty in resetting
Solution Approach 1:
The retaining means utilizes pressure as a controlling parameter. By applying pressure to the cylinder chamber, the piston member can be displaced to a position where the locking body is prevented from engaging with the locking surface, enabling resetting without requiring mechanical disassembly or complex operations.
Solution Approach 2:
The retaining means acts as an intermediary mechanism between the operator's resetting action and the locking body. It mediates the resetting process by controlling whether the locking body can engage with the locking surface, allowing easy resetting while maintaining reliable locking when needed.
3Reliability
If the pre-tensioner arrangement is designed to lock during high acceleration events, then reliability is improved, but ease of operation worsens due to inability to reset during normal operations like pre-impact braking
Solution Approach 1:
The system uses acceleration level as a discriminating parameter. The locking means responds only when acceleration exceeds a predetermined threshold level in the direction opposite to retraction. During pre-impact braking, acceleration in the opposite direction does not trigger locking, allowing normal resetting operations to continue while maintaining protection against undesired activation during actual crashes.
Solution Approach 2:
The locking and retaining functions are activated under different local conditions (different acceleration directions and magnitudes). The locking body and locking surface are positioned and dimensioned to engage only under specific high-acceleration crash conditions, while the retaining means prevents engagement under normal operating conditions like pre-impact braking.
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 easy and smooth resetting of the pre-tensioner arrangement, reducing the need for replacements and ensuring the safety device remains functional during pre-impact braking events by avoiding undesired locking.
Implementation Method 1
a piston member arranged in a cylinder chamber, said piston member being displaceable in a retraction direction by a pressure applied to a first part of said cylinder chamber through an inlet
Implementation Method 2
locking means for locking the piston member, wherein said locking means being arranged to lock the piston member when the piston member is subjected to an acceleration in a direction opposite to said retraction direction, said acceleration exceeding a predetermined acceleration level
Implementation Method 3
retaining means arranged in the cylinder chamber for preventing said piston member from being locked when the piston member is subjected to an acceleration in a direction opposite to said retraction direction, said acceleration being below said predetermined acceleration level
Data Source
Figure 1
Figure 2a~2c
Figure 3a~3c
AI summary
A pre-tensioner arrangement (1), for use in a motor vehicle safety device, comprises a piston member (9) arranged in a cylinder chamber (13), said piston member (9) being displaceable in a retraction direction by a pressure applied to a first part (13a) of said cylinder chamber (13) through an inlet (15), a connecting member (5) connected to the piston member (9) and connectable to a part (3) of the motor vehicle safety device for pretensioning the motor vehicle safety device, and locking means (25, 27, 29) for locking the piston member (9). The locking means (25, 27, 29) being arranged to lock the piston member (9) when the piston member (9) is subjected to an acceleration in a direction opposite to said retraction direction, said acceleration exceeding a predetermined acceleration level, and retaining means (11) arranged in the cylinder chamber (13) for preventing said piston member (9) from being locked when the piston member (9) is subjected to an acceleration in a direction opposite to said retraction direction, said acceleration being below said predetermined acceleration level.