Martensitic Piston Ring with Localized Nitriding and Ion Plated Coating
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Solution Overview
Problem
Piston rings in high-speed diesel engines experience catastrophic failures due to cracks initiated at the upper and lower chamfers, leading to engine disassembly, as existing nitrided stainless steel rings with PVD coatings fail to provide sufficient strength and durability under severe operational conditions.
Innovation Solution
A piston ring made from martensitic stainless steel with upper, lower, and internal faces nitrided and an external face coated with chromium nitride using the ion plating process, where the nitrided portions have a reduced hardness to prevent crack propagation, and the external face and chamfers are coated with a layer of chromium nitride to enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the entire piston ring is nitrided and coated with PVD, then hardness and wear resistance are improved, but crack propagation resistance deteriorates
Solution Approach 1:
The patent applies nitriding only to specific regions of the piston ring (external face and chamfers) while leaving other regions (internal face, groove area) un-nitrided. This localized treatment provides hardness and wear resistance where contact with the cylinder wall occurs, while avoiding the brittleness that would cause crack propagation in fully nitrided rings.
Solution Approach 2:
The piston ring is divided into different treatment zones: nitrided regions (external face and chamfers) for wear resistance, and non-nitrided regions (internal face and groove area) for maintaining toughness and crack resistance. This segmentation allows each region to have properties optimized for its specific functional requirements.
2Reliability
If chromium nitride coating is applied by PVD process, then low sliding friction and high spalling resistance are achieved, but manufacturing cost increases
Solution Approach 1:
The chromium nitride coating is applied only to the external face and chamfers of the piston ring where contact with the cylinder wall occurs, rather than coating the entire ring. This localized coating approach reduces material costs and manufacturing complexity while maintaining friction and spalling resistance in the critical contact zones.
3Reliability
If nitrided portions have reduced hardness, then crack propagation is prevented, but wear resistance decreases
Solution Approach 1:
The nitrided portions (external face and chamfers) maintain high hardness for wear resistance, while the non-nitrided portions (internal face and groove area) provide toughness and crack resistance. The selective nitriding ensures that hardness is preserved only in regions subject to wear, while other regions maintain ductility to prevent crack propagation.
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 effectively prevents catastrophic cracks and maintains competitive manufacturing costs, ensuring the piston ring's durability and strength under high-pressure and high-rotational-speed conditions in diesel engines.
Implementation Method 1
provided with at least one layer of coating applied by the process of ion plating
Implementation Method 2
having the upper, lower and internal faces nitrided
Data Source
AI summary
A piston ring for a piston of an internal combustion engine may include a body composed of a ferrous material. The body may have an upper portion, a lower portion opposed to the upper portion, an internal portion configured to face towards a piston groove and an external portion opposed to the internal portion. An upper chamfer may be disposed between the upper portion and the external portion. A lower chamfer may be disposed between the lower portion and the external portion. The upper portion, the lower portion and the internal portion may each have a nitrided layer. The external portion, the upper chamfer and the lower chamfer may include at least one ion plated coating layer. The nitrided portion in at least a superficial layer may have a hardness of 700 HV or less.