Compression Piston Ring Coating Layout Against Joint Spalling
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Solution Overview
Problem
Compression piston rings with PVD or CVD layers face layer spalling due to exposure to hot combustion gases, particularly at the joint area, leading to potential damage and wear.
Innovation Solution
A piston ring design where a TaC layer covers at least 95% of the circumferential sections but is layer-free in a defined area near the joint, maintaining equal radial wall thickness across coated and uncoated sections, thereby isolating the wear-resistant TaC layer from direct thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piston ring running surface is provided with a PVD or CVD layer for wear protection, then the wear resistance is improved, but the layer is exposed to hot combustion gases through the gap which causes chipping and layer spalling
Solution Approach 1:
The piston ring circumference is divided into two distinct zones: a coated zone (95-98% of circumference) providing wear protection, and an uncoated gap zone (2-5% of circumference) isolating the coating from combustion gases. This segmentation allows the wear-resistant TaC layer to be applied while preventing direct exposure to thermal stress through the gap area.
Solution Approach 2:
Different circumferential regions of the piston ring are given different properties: the running surface area receives a hard TaC coating for wear resistance, while the gap area remains uncoated to prevent thermal stress exposure. The radial wall thickness is adjusted locally in the gap area to maintain structural integrity despite the missing coating.
2Strength
If the radial wall thickness is increased in the gap area to compensate for missing coating, then the structural integrity is improved, but the manufacturing complexity increases
Solution Approach 1:
The piston ring blank is pre-formed with a non-uniform radial wall thickness distribution before coating application, with the gap area having greater thickness. This preliminary action ensures that after the coating is applied to 95-98% of the circumference, the final product achieves uniform effective thickness and structural integrity without requiring post-coating machining or complex assembly.
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
This design prevents chipping and reduces the risk of layer spalling by spatially separating the TaC layer from hot combustion gases, ensuring prolonged durability and reduced wear.
Implementation Method 1
at least the running surface is provided with a single PVD or CVD layer
Implementation Method 2
at least the running surface is provided with a single PVD or CVD layer
Data Source
Figure 1~3
AI summary
The invention relates to a piston ring, in particular a compression piston ring, containing a running surface, upper and lower face regions, an inner peripheral surface, and a joint, at least the running surface being provided with at least one wear-resistant PVD or CVD layer, wherein the PVD or CVD layer extends with a predeterminable layer thickness over a peripheral length of more than 95%, but less than 100%, of the piston ring, and defined peripheral portions in the region of the joint are not provided with this layer.