Selective CrN Coating on Piston Ring Ends to Prevent Flaking
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Solution Overview
Problem
Piston ring coatings in internal combustion engines are prone to flaking and crazing due to harsh engine conditions, which affects their performance and longevity.
Innovation Solution
A piston ring with a rough outer surface texture and a coating of chromium nitride (CrN) or diamond-like carbon (DLC) is used, where the coating is applied only to the textured end sections of the outer surface, distributing stress and retaining oil effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a coating is applied to the piston ring outer surface, then wear resistance and performance are improved, but the coating becomes prone to flaking and crazing under harsh engine conditions
Solution Approach 1:
The patent applies different surface qualities to different regions of the piston ring. The end sections have a rough surface texture while the intermediate section has a smooth surface. The coating is applied selectively to the rough end sections, creating a localized coating application that addresses wear at the ends without causing flaking and crazing across the entire surface. This local differentiation resolves the contradiction by providing wear resistance only where most needed while avoiding the conditions that cause coating degradation.
Solution Approach 2:
The patent prepares the outer surface of the piston ring before applying the coating by creating a rough surface texture on the end sections through machining or other surface treatment methods. This preliminary surface preparation creates a controlled roughness that, when combined with selective coating application, prevents the coating from flaking and crazing while still providing wear resistance. The preliminary action of surface texturing resolves the contradiction by preparing the surface in a way that enables durable coating adhesion.
2Strength
If the entire outer surface is coated, then wear protection is maximized, but manufacturing complexity and cost increase
Solution Approach 1:
The patent implements selective coating application where only the end sections of the outer surface receive the coating, while the intermediate section remains uncoated. This local quality approach provides wear protection at the critical end sections where it is most needed, while avoiding the complexity and cost of coating the entire surface. The selective application process simplifies manufacturing compared to full-surface coating while maintaining adequate wear protection.
Solution Approach 2:
The patent applies coating only to the end sections rather than the entire outer surface, representing a partial action approach. This partial coating provides sufficient wear protection for the critical areas without the complexity and cost of complete surface coating. The end sections are the primary wear zones, so coating only these areas achieves the necessary protection with reduced manufacturing complexity.
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 solution reduces flaking and crazing of the coating, enhancing the piston ring's durability and performance by distributing stress and improving oil retention.
Implementation Method 1
the end sections of the outer surface are rough... distributing stress and retaining oil effectively
Data Source
AI summary
A piston ring with a coated outer surface is provided. The coating is disposed on end sections of the outer surface adjacent a gap. Typically, a middle section of the outer surface located between the end sections is not coated. The coating can be formed of CrN or DLC, and the CrN coating can be applied by physical vapor deposition (PVD). The end sections of the outer surface, upon which the coating is applied, are rough. For example, the outer surface can be blasted or otherwise textured to achieve the rough surface. The rough surface retains oil and distributes stress better than a smooth surface, and thus reduces crazing and flaking of the coating.