Piston Pin Bore Ovality for Combustion Engine Stress Reduction
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Solution Overview
Problem
Existing piston pin bearing designs in internal combustion engines fail to adequately reduce mechanical stresses and extend piston lifetime, as they do not effectively manage deformation and stress concentrations, leading to crack formation in the combustion bowl edge and base due to increasing ignition pressures.
Innovation Solution
A pin bore shape with high ovality on one side, specifically in the equator-zenith-equator pin boss region, and a circular-cylindrical shape in the equator-nadir-equator region, where the mantle line is inclined to maximize stress distribution and minimize tangential stresses, thereby reducing bending and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional pin bore shapes (oval or bent mantle line) are used, then the piston can withstand initial stress and deformation, but cracks form in the combustion bowl edge and base after hundreds of hours due to increasing ignition pressures
Solution Approach 1:
The pin bore is designed with different geometries in different regions: the equator-zenith-equator region has high ovality with an inclined mantle line to reduce tangential stresses at the combustion bowl edge, while the equator-nadir-equator region has circular-cylindrical shape to minimize play between piston pin and pin boss. This localized differentiation allows each region to address specific stress issues.
Solution Approach 2:
The pin bore exhibits asymmetric geometry where the ovality is concentrated only in the upper equator-zenith-equator pin boss region, while the lower equator-nadir-equator region remains circular-cylindrical. This asymmetric design optimizes stress distribution by applying ovality where it most effectively reduces tangential stresses at the combustion bowl edge.
2Ease of operation
If high ovality is configured in the pin bore to increase resistance to seizing and reduce noise, then play between piston pin and pin boss is reduced, but tangential stresses increase at the combustion bowl edge and base
Solution Approach 1:
High ovality is localized only in the equator-zenith-equator pin boss region where it most effectively reduces tangential stresses at the combustion bowl edge, while the equator-nadir-equator region maintains circular-cylindrical geometry to minimize play and noise without adding unnecessary stress.
Solution Approach 2:
The mantle line in the zenith region is configured with a specific curvature and inclination angle (5° to 15°) relative to the pin boss axis, creating an optimized oval shape that distributes stresses more favorably and reduces tangential stresses at critical points while maintaining noise reduction benefits.
3Ease of manufacture
If the mantle line runs parallel to the pin bore axis to simplify manufacturing, then manufacturing is easier, but stress distribution is not optimized and tangential stresses remain high at critical points
Solution Approach 1:
The mantle line is configured with a controlled inclination angle (5° to 15°) relative to the pin boss axis in the zenith region, creating a curved, inclined path that optimizes stress distribution and reduces tangential stresses at the combustion bowl edge while remaining manufacturable through conventional processes.
Data Source
AI summary
The invention relates to a piston pin bearing of an internal combustion engine, in which a cylindrical piston pin is mounted. The aim of the invention is to create a hub bore shape that is improved compared to prior art in order to significantly reduce mechanical stress in the piston and thus extend the service life of the piston. Furthermore, the shape is to prevent noise from being generated in the piston pin bearing. The aims are achieved by the fact that the surface line of the highly oval outer surface, which runs in the zenith of the hub, extends at an angle to the hub axis from a radially outward point to a radially inward point on the piston side such that the greatest degree of ovalness defined by the oval diameter thereof is created at the respective inner ends of the hub bores and does not exceed a predefined value of the oval diameter.