Piston Ring Groove Asymmetric Radius Design
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Solution Overview
Problem
Piston ring grooves in internal combustion engines face a challenge in balancing structural strength with the need for optimal gas pressure transmission and sealing, as the shape of the grooves affects both structural integrity and the efficiency of gas pressure transfer to the piston rings, which are primarily pressed against the cylinder wall by gas pressure.
Innovation Solution
The piston ring groove design features a lower flank with a larger radius of curvature merging into the groove base to reduce stress and avoid crack formation, while the upper flank has a smaller radius of curvature, creating a conical area that widens towards the piston axis, allowing for efficient gas pressure transmission and minimizing dead volume behind the piston ring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the ring groove shape is optimized for structural strength, then the piston body strength is improved, but the gas pressure transmission to the piston ring is delayed
Solution Approach 1:
The groove bottom is designed with different radii of curvature in different regions: a larger radius (0.15-0.30 times the groove width) in the lower region for structural strength, and a smaller radius (0.05-0.15 times the groove width) in the upper region for rapid gas pressure transmission. This local differentiation resolves the contradiction by optimizing each region for its primary function.
Solution Approach 2:
The groove bottom transitions from a symmetric shape to an asymmetric shape with the larger radius extending beyond the groove centerline toward the piston crown. This asymmetric configuration allows the groove to withstand bending stresses better while creating a smaller dead volume for faster gas pressure action on the piston ring.
2Reliability
If the ring groove shape is optimized for gas pressure transmission, then the sealing effect is improved, but the structural strength of the piston is reduced
Solution Approach 1:
The upper region of the groove bottom has a smaller radius of curvature that extends closer to the piston ring, creating a smaller dead volume for rapid gas pressure transmission and improved sealing. The lower region has a larger radius for structural strength, with the transition zone designed to avoid stress concentrations.
3Ease of manufacture
If a uniform radius of curvature is used in the ring groove, then the manufacturing is simplified, but stress peaks occur at the groove transitions
Solution Approach 1:
Instead of a uniform radius, the groove bottom uses two different radii of curvature in different regions. The larger radius in the lower region and smaller radius in the upper region are both within manufacturable ranges, and the smooth transition between them eliminates stress peaks while maintaining manufacturing feasibility.
4Object-generated harmful factors
If the dead volume behind the piston ring is reduced, then hydrocarbon emissions are reduced, but the piston ring may press into the groove rounding
Solution Approach 1:
The smaller radius of curvature in the upper region of the groove bottom reduces the dead volume to minimize hydrocarbon emissions, while the larger radius in the lower region provides structural support to prevent piston ring pressing into the groove. The transition zone smoothly connects these two regions.
Data Source
Figure 1~2
AI summary
The invention relates to a piston with a piston ring groove, in particular a compression groove, on the outer circumference of a piston for internal combustion engines. The groove comprises a groove bottom extending between opposite groove flanks, and the groove bottom merges into the lower groove flank (away from the piston bottom) with the large radius of curvature and merges into the upper groove flank (close to the piston bottom) with a small radius of curvature.