Alternating CrN and a-C:H:Me Coatings for Piston Ring Wear
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Solution Overview
Problem
Existing DLC coating systems for sliding elements, such as piston rings, are inadequate for diesel or turbocharged Otto engines with iron-based cylinder liners due to limited layer thickness and increased mixed friction, wear, and scuff resistance issues, especially under conditions of insufficient lubrication.
Innovation Solution
A multi-ply coating structure comprising alternating layers of CrN and a-C:H:Me, with a chromium adhesive layer and a metal-free a-C:H outer layer, providing improved wear resistance and friction properties, and allowing for higher overall layer thicknesses by balancing internal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If DLC coating systems are used with thin layers (less than 5 μm), then friction properties are improved due to chemical inactivity and low adhesive tendency, but lifetime and wear resistance are insufficient under high cylinder pressures and mixed friction conditions
Solution Approach 1:
The patent applies a composite coating structure consisting of alternating CrN and DLC layers. The CrN layers provide hardness and wear resistance, while the DLC layers provide low friction and chemical inactivity. This composite structure combines the advantages of both materials to achieve improved lifetime without sacrificing friction properties.
Solution Approach 2:
The coating is segmented into multiple thin alternating layers of CrN and DLC, with each layer being only a few micrometers thick. This segmentation allows the stresses in individual layers to be managed while achieving an overall thicker coating (10-30 μm) that provides sufficient wear resistance and lifetime.
2Duration of action of moving object
If CrN PVD coatings with layer thicknesses of 10 to 30 μm are used, then lifetime is improved, but friction power and wear resistance under insufficient lubrication are impaired
Solution Approach 1:
The patent uses a composite coating where CrN layers (providing wear resistance) and DLC layers (providing low friction) are combined in alternating sequence. This allows the coating to achieve both improved lifetime from the CrN layers and good friction properties from the DLC layers, overcoming the limitations of pure CrN coatings.
3Duration of action of moving object
If thicker DLC layers are applied to improve wear resistance, then lifetime increases, but internal stresses increase leading to coating failure
Solution Approach 1:
The patent segments the thick coating into multiple thin alternating layers of CrN and DLC, each only a few micrometers thick. This segmentation distributes and equalizes the internal stresses throughout the coating structure, preventing stress concentration that would lead to coating failure while still achieving the desired overall thickness for wear resistance.
Solution Approach 2:
The alternating CrN and DLC layers form a composite structure where the different stress characteristics of each material complement each other. The CrN layers, with their lower internal stresses, help equalize the overall stress distribution in the thick coating, enabling stable thick coatings to be achieved.
4Loss of energy
If conventional DLC coating systems are used in diesel or turbocharged Otto engines with iron-based cylinder liners, then friction properties are maintained, but wear resistance and scuff resistance are insufficient due to high cylinder pressures and mixed friction
Solution Approach 1:
The patent employs a composite coating structure with alternating CrN and DLC layers. The CrN layers provide the hardness and wear resistance needed to withstand high cylinder pressures and mixed friction conditions in diesel and turbocharged engines, while the DLC layers maintain the low friction and chemical inactivity properties essential for reliable operation.
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 multi-ply coating significantly enhances the lifetime and reduces wear by over 50% while maintaining good friction properties, even under insufficient lubrication, by combining the advantages of CrN and DLC layers.
Implementation Method 1
PVD coatings, in particular based on CrN
Implementation Method 2
For the adhesion of the CrN layer to the substrate, that is to say the sliding element
Data Source
AI summary
A sliding element, in particular a piston ring, preferably made of cast iron or steel, has a coating which has a plurality of layers of CrN (14) and a-C:H:Me coatings (16) alternately. In a method for coating the sliding element, in particular a piston ring, preferably made of cast iron or steel, a plurality of layers of CrN and a-C:H:Me coatings are applied alternately.