Piston Engine Fastening Screw Shank Asymmetry
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Solution Overview
Problem
Vibration of fastening screws in piston engines leads to damage due to mismatched natural frequencies with engine excitation frequencies, causing structural stress and potential failure.
Innovation Solution
Designing fastening screws with a shank cross-sectional shape that deviates from a circle, specifically with varying shapes such as oval, quadrangular, triangular, or pentagonal, to alter the natural frequency, reducing vibration and associated damage by optimizing bending stiffness in different directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fastening screw has a circular cross-sectional shank, then the manufacturing is simple and uniform, but the natural frequency matches the engine excitation frequency causing vibration and damage
Solution Approach 1:
The patent applies asymmetry by changing the shank cross-sectional shape from a symmetric circular form to an asymmetric non-circular form (such as oval, triangular, or polygonal sections). This asymmetric geometry modifies the moment of inertia and bending stiffness characteristics, thereby shifting the natural frequency of the fastening screw away from the engine's excitation frequency range, reducing resonance vibrations and improving reliability.
Solution Approach 2:
The patent applies local quality by modifying only the cross-sectional shape of the shank while keeping other parts of the fastening screw (threads, head, material composition) unchanged. This localized modification targets specifically the vibrational characteristics without affecting the fastening function, threading engagement, or overall structural integrity.
2Reliability
If the shank cross-sectional area is reduced to alter natural frequency, then vibration is reduced, but the strength and load-bearing capacity decrease
Solution Approach 1:
The asymmetric non-circular cross-section is designed to optimize the distribution of material around the neutral axis, maintaining or enhancing the moment of inertia in critical directions. This allows the shank to resist bending moments more effectively while having reduced mass compared to a circular section, thereby lowering natural frequency without sacrificing strength.
Solution Approach 2:
The patent changes the geometric parameters of the shank cross-section (shape, dimensions, orientation) to simultaneously achieve two objectives: reducing the overall cross-sectional area to lower mass and natural frequency, while optimizing the moment of inertia distribution to maintain or improve bending strength. Specific parameters such as the oval ratio, polygon side lengths, and section thickness are carefully controlled.
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 modified cross-sectional shape of the fastening screws aligns their natural frequency with or diverges from typical engine excitation frequencies, minimizing vibration and damage, thereby enhancing the durability and reliability of the engine components.
Implementation Method 1
the natural frequency of the fastening screw may be made unequal to, i.e. higher and/or lower than, the excitation frequencies occurring in a piston engine
Implementation Method 2
the vibration of the fastening screw is small and thus also the damages caused by the vibration are minor
Data Source
Figure 1
Figure 2a~2d
Figure 3a~3b
AI summary
A fastening screw (1) comprising two end sections (2), at least one of which is provided with threads, and a shank (3) between the end sections (2). The cross-sectional shape of the shank (3) deviates from a circle.