Asymmetric Pin Bore Design for Piston Stress Reduction
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Solution Overview
Problem
Pin bosses of pistons in internal combustion engines face reduced service life due to excessive tangential stresses in pin bores, particularly at the zenith and nadir areas, under gas pressure and inertia loading.
Innovation Solution
The pin bores are designed with inner areas farther from the axis than the zenith and closer to the axis than the nadir, with outer areas being transversely oval relative to the piston axis, and inner areas merging continuously into outer areas, reducing tangential stresses by asymmetrically distributing mechanical loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If pin bores are designed with symmetric transverse oval shape, then manufacturing is simple, but tangential stresses at zenith and nadir areas increase reducing service life
Solution Approach 1:
The patent applies asymmetry by designing the pin bore with different radii of curvature at the zenith and nadir areas. The zenith area has a smaller radius of curvature while the nadir area has a larger radius of curvature, creating an asymmetric cross-sectional shape that redistributes tangential stresses to reduce peak stresses and improve piston service life
Solution Approach 2:
The patent applies local quality by varying the geometric properties of the pin bore at different locations. The inner cross-section has different curvature characteristics compared to the outer cross-section, with specific radius ratios optimized for stress distribution. This localized geometric variation allows the pin bore to better withstand localized stress concentrations at critical areas
2Stress or pressure
If pin bore inner areas are closer to the axis, then tangential stresses at zenith are reduced, but piston mass increases
Solution Approach 1:
The patent applies parameter changes by optimizing the radius of curvature at the zenith area to be smaller than at the nadir area. This parameter variation in the geometric configuration allows stress reduction at the zenith while controlling the overall material distribution to minimize mass increase. The specific radius ratio becomes a critical design parameter for achieving the optimal balance
3Stress or pressure
If pin bore has asymmetric inner area design, then stress distribution is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies spheroidality by defining the asymmetric pin bore shape through controlled curvature variations. The use of radius of curvature parameters to describe the zenith and nadir areas provides a mathematically defined curved geometry that achieves asymmetric stress distribution while maintaining manufacturability through standardized curvature control methods
Data Source
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AI summary
The invention relates to pin bosses (1) of a piston (2) for an internal combustion engine, each comprising a pin bore (3) for supporting a piston pin (14). In order to reduce the tangential stresses in the zenith area of the pin bores and thus to extend the service life of the piston, the inner areas (16) of the pin bores (3) as viewed in the direction of the bore axis (13) have areas on both sides of the zenith (4) that have a greater distance from the bore axis (13) than the zenith (4) of the pin bore (3), and the outer areas (17) of the pin bores (3) as viewed in the direction of the bore axis (13) are transversely oval relative to the piston axis (7).