Pyrotechnic Actuator Piston Rod Fold for Stroke Limiting
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Solution Overview
Problem
Existing pyrotechnic actuators for raising engine hoods in vehicles are complex and costly to produce, particularly due to the additional effort required for serration and sealant integration, which complicates handling safety and activation without counterforce.
Innovation Solution
A pyrotechnic actuator design featuring a piston rod with a fold on the side away from the ignition unit, where the outer diameter matches the housing inner diameter, and a sealant like an O-ring is placed between the fold and expansion, serving as a stroke limiter and brake without additional structural elements, simplifying production and reducing manufacturing effort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a seal carrier with O-ring is used to seal the piston rod, then sealing reliability is improved, but device complexity increases
Solution Approach 1:
The invention extracts and eliminates the separate seal carrier component from the system. Instead of using a dedicated seal carrier with an O-ring, the piston rod itself is designed with an integrated sealing structure where the O-ring is directly mounted on the piston rod body, simplifying the overall device structure while maintaining sealing functionality.
Solution Approach 2:
The invention merges the sealing function with the piston rod structure. The seal carrier and O-ring assembly is integrated into the piston rod design, combining what were previously separate components (piston rod, seal carrier, O-ring) into a more unified structure that reduces part count and assembly complexity.
2Reliability
If serrations are added to the piston rod for handling safety, then activation safety is improved, but manufacturing complexity increases
Solution Approach 1:
The invention applies local quality by adding serrations only in specific locations on the piston rod where they are most effective for handling safety and preventing unwanted activation. The serrations are concentrated on the outer circumference of the piston rod in the sealing area, providing enhanced grip and safety features only where needed rather than throughout the entire component.
3Length of moving object
If the piston rod is extended further to increase stroke length, then actuator performance is improved, but the risk of piston rod ejection from housing increases
Solution Approach 1:
The invention implements beforehand cushioning by designing the piston rod with a folded-back end section that creates a mechanical stop before the piston rod can be ejected from the housing. This folded structure acts as a pre-planned safety feature that absorbs excess travel and prevents catastrophic ejection, allowing the piston rod to achieve greater extension while maintaining safety.
Solution Approach 2:
The invention applies dynamics by creating a flexible folded section in the piston rod that can dynamically absorb and dissipate energy during extension. The folded structure allows controlled deformation and elastic recovery, providing a dynamic response to excessive extension forces rather than a rigid mechanical stop, thereby preventing ejection while accommodating stroke length increases.
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 design achieves effective stroke limitation and braking without damaging the housing, ensuring reliable operation in unloaded and fire tests, while avoiding the need for additional seal carriers or serrations, thus enhancing production simplicity and cost-effectiveness.
Implementation Method 1
The fold forms a stroke limit for the extension of the piston, but is sufficiently flexible that the piston rod is gently braked
Implementation Method 2
the widened portion is reduced under plastic deformation to the inner diameter of the seal carrier
Implementation Method 3
the piston rod is gently braked without damaging the housing
Data Source
Figure 1
Figure 2
AI summary
A pyrotechnic actuator, such as one used for opening engine hoods, has a housing (11) in which a substantially tubular piston rod (12) is slidably guided. A pyrotechnic ignition unit (17) is provided in a first end region (11a) of the housing (11), and the opposite second end region (11b) has an opening for the piston rod (12). The piston rod (12) has a flare (12e) in the end region (12a) closest to the ignition unit, and according to the invention, the piston rod (12) has a fold (12c) on the side of the flare (12e) facing away from the ignition unit (17). This gently decelerates the piston rod (12) when the fold (12c) strikes the opening in the second end region (11b), while the fold (12c) slightly retracts. To ensure that the fold (12c) bends open but the opening does not widen, the wall thickness of the piston rod (12) should be approximately 80% of the wall thickness of the housing (11).The outer diameter of the piston rod (12) should be approximately 40% larger in the region of the fold (12c) than outside of this region. Such a piston rod (12) can be manufactured very easily by forming the fold (12c) in a preform by means of bulging.