DLC Piston Ring Coating With Graded sp2 Ratio for Bore Protection
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Solution Overview
Problem
DLC coatings for piston rings face challenges in maintaining wear resistance and low attacking properties on cylinder bore sliding surfaces, especially in environments with deteriorated engine lubricating oil where abrasive wear is prevalent.
Innovation Solution
A DLC coating with a specific sp2 component ratio of 0.5 to 0.85, coating hardness of 12 GPa to 26 GPa, Young's modulus of 250 GPa or less, and controlled macroparticle density, applied with an underlayer containing Ti, Cr, or Si, to enhance adhesion and reduce surface irregularities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sp2 ratio in the DLC coating is increased to improve flexibility and cushioning effect, then the coating becomes more resistant to cracking and peeling, but the hardness and wear resistance of the coating decreases
Solution Approach 1:
The patent applies a graded composition structure where the sp2 ratio varies through the coating thickness. The inner surface side has lower sp2 ratio (higher hardness) while the outer surface side has higher sp2 ratio (higher flexibility). This local quality variation allows the coating to simultaneously achieve wear resistance at the interface and flexibility at the surface, resolving the contradiction between hardness and peeling resistance.
Solution Approach 2:
The patent changes the compositional parameter (sp2 ratio) continuously or stepwise through the coating thickness. By controlling the sp2 ratio gradient, the coating transitions from a hard, wear-resistant inner layer to a flexible, cushioning outer layer, thereby achieving both wear resistance and peeling resistance without sacrificing either property.
2Strength
If the DLC coating is made harder to improve wear resistance, then the coating becomes more resistant to abrasive wear, but the coating becomes more prone to cracking and peeling under load
Solution Approach 1:
The patent creates a non-uniform coating structure where the inner portion adjacent to the base material has higher sp3 content (higher hardness) for wear resistance, while the outer portion has higher sp2 content (higher flexibility) for stress absorption. This local quality differentiation allows the coating to resist both wear and peeling simultaneously.
Solution Approach 2:
The DLC coating is structured as a composite material with varying carbon bonding configurations (sp2 and sp3 phases) distributed through the thickness. This composite structure combines the advantages of hard sp3-bonded regions (wear resistance) and flexible sp2-bonded regions (crack resistance), resolving the contradiction between wear resistance and coating integrity.
3Reliability
If the coating is made more flexible to reduce cracking, then the coating can better absorb sliding stresses, but the wear resistance and hardness of the coating decreases
Solution Approach 1:
The patent implements a graded structure where flexibility (sp2 ratio) increases from the inner surface toward the outer surface. The inner layer maintains high hardness for wear resistance, while the outer layer provides flexibility for stress absorption. This local quality gradient resolves the contradiction between flexibility and hardness.
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 provides excellent wear resistance and low attacking properties on cylinder bore sliding surfaces, reducing abrasive wear and peeling, while maintaining a smooth sliding surface.
Implementation Method 1
the sp2 component ratio, as measured by TEM-EELS using a transmission electron microscope (TEM) in combination with electron energy loss spectroscopy (EELS)
Implementation Method 2
as well as a coating hardness of 12 GPa to 26 GPa and a Young's modulus of 250 GPa or less as measured by a nanoindentation method
Data Source
AI summary
The present invention addresses the problem of providing a piston ring covered with a DLC coating that has excellent wear resistance and shows a low attacking property on a cylinder bore sliding surface. The problem is solved by a piston ring which is used in the presence of an engine lubricating oil and includes a DLC coating on an outer peripheral sliding surface. The DLC coating has an sp2 component ratio of 0.5 to 0.85 as determined from a TEM-EELS spectrum obtained by a combination of a transmission electron microscope (TEM) and electron energy loss spectroscopy (EELS), as well as a coating hardness of 12 GPa to 26 GPa and a Young's modulus of 250 GPa or less as measured by a nanoindentation method.