Piston Ring DLC Coating Residual Stress Gradient
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Solution Overview
Problem
Existing piston rings in internal combustion engines face challenges in maintaining favorable friction characteristics over their lifespan due to issues like lubrication deficiencies and wear, leading to increased fuel consumption and carbon dioxide emissions.
Innovation Solution
A DLC (Diamond-Like Carbon) coating with a gradient of residual stresses is applied to the piston rings, featuring a negative residual stress gradient near the base material for adhesion, a positive gradient on the outer surface for running-in, and alternating stresses in the middle region to prevent cracking, allowing for a thick and durable coating with improved friction and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thick DLC coating is applied to improve wear resistance and friction properties, then the coating's durability and protection capability are improved, but the coating becomes more brittle and prone to adhesion failure
Solution Approach 1:
The patent applies a non-uniform residual stress distribution within the coating thickness, creating different stress states at different depths. The surface region has compressive residual stresses for wear resistance, while the transition region has tensile residual stresses that reduce brittleness and improve adhesion to the substrate, allowing thick coatings without adhesion failure
Solution Approach 2:
The patent changes the residual stress parameter as a function of coating depth, creating a gradient from compressive at the surface to tensile in the transition region. This parameter variation allows the coating to simultaneously achieve high wear resistance and maintained adhesion stability throughout its thickness
2Stability of the object's composition
If the residual stress in the DLC coating is reduced to improve adhesion, then the coating's bonding to the base material is improved, but the coating's resistance to plastic deformation and wear protection is reduced
Solution Approach 1:
The patent creates different functional zones within the coating: a surface zone with compressive residual stresses for wear protection, and a transition zone with tensile residual stresses for adhesion. This local differentiation allows each region to optimize its function without compromising the other
Solution Approach 2:
The coating is functionally segmented into distinct regions with different stress states - the surface region handles wear protection while the transition region handles adhesion. This segmentation allows independent optimization of wear resistance and adhesion properties
3Device complexity
If a uniform residual stress distribution is maintained throughout the coating, then the coating structure is simpler, but the coating cannot simultaneously achieve good adhesion and wear resistance
Solution Approach 1:
Rather than uniform stress distribution, the patent implements locally differentiated stress states - compressive at the surface for friction resistance and tensile in the transition zone for adhesion. This local quality variation enables simultaneous optimization of both properties
4Duration of action of stationary object
If the DLC coating thickness is increased to extend service life, then the coating's wear resistance is improved, but the coating becomes more prone to cracking and adhesion failure
Solution Approach 1:
The patent changes the residual stress parameter through the coating thickness, creating a gradient that transitions from compressive to tensile stresses. This parameter change enables thick coatings to maintain reliability by reducing brittleness in the transition region while preserving wear resistance at the surface
Solution Approach 2:
Different regions of the thick coating serve different functions: the surface region provides wear resistance while the transition region provides structural integrity and adhesion. This local quality differentiation allows the coating to achieve extended service life without sacrificing reliability
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 DLC coating with a stress gradient provides excellent friction properties and extended lifespan by preventing wear and adhesion issues, maintaining favorable running-in characteristics and reducing fuel consumption while minimizing carbon dioxide emissions.
Implementation Method 1
a DLC coating of the ta-C type which has changing residual stresses over its thickness. In other words, at least one residual stress gradient is formed over the thickness of the coating
Implementation Method 2
This type of layer provides on the one hand good friction characteristics
Data Source
AI summary
The invention relates to a gliding element of an internal combustion engine, especially a piston ring, having a DLC coating of the ta-C type which has at least one residual stress gradient.