Cylinder Liner Nitrided Layer Pit Control
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Solution Overview
Problem
In internal combustion engines, cylinder liners with nitrided layers face issues of irregularly occurring minute concave sections (pits) on the inner periphery, leading to increased oil consumption and scuffing risks due to uneven surface roughness and graphite exposure, which complicates achieving optimal lubrication and friction reduction.
Innovation Solution
A cylinder liner with a metal structure featuring dispersed flaky graphite in a cast iron matrix, where some graphite is exposed on the surface and covered by the matrix, and a controlled cross-hatching angle, combined with a nitrided layer and nitrogen diffusion layer, to minimize pit formation and optimize surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If finishing honing is performed to form a cross hatching section on the inner periphery, then lubricating environment is improved, but irregular pits with depth of 1.5 μm or more occur
Solution Approach 1:
The patent changes the surface roughness parameters by controlling the honing process to achieve Rz ≤ 4.0 μm and Rmax ≤ 6.0 μm, which reduces pit formation while maintaining cross hatching for lubrication. This parameter optimization resolves the contradiction between improving lubrication and maintaining surface uniformity.
Solution Approach 2:
The patent applies preliminary nitriding treatment before finishing honing to strengthen the surface layer. This preliminary action prevents excessive material removal during honing that would create deep pits, while still allowing cross hatching to be formed for proper lubrication.
2Loss of energy
If open graphite ratio is increased to reduce friction, then oil consumption increases due to pit formation
Solution Approach 1:
The patent optimizes the open graphite ratio to be 5% or more but controls the surface roughness parameters (Rz ≤ 4.0 μm, Rmax ≤ 6.0 μm) to prevent excessive pit formation. This balanced parameter control allows graphite exposure for friction reduction while limiting oil reservoir formation that would increase consumption.
Solution Approach 2:
The patent uses partial exposure of graphite (not complete exposure) by controlling the open graphite ratio and surface roughness. This partial action provides sufficient friction reduction benefit while avoiding the excessive oil consumption that would result from complete graphite exposure and deep pit formation.
3Strength
If nitrided layer is formed to improve abrasion resistance, then surface roughness becomes uneven causing scuffing
Solution Approach 1:
The patent applies nitriding as a preliminary treatment before finishing honing. This preliminary nitriding strengthens the surface for abrasion resistance, and the subsequent finishing honing process smooths the nitrided surface to remove unevenness that would cause scuffing, while maintaining cross hatching for lubrication.
Solution Approach 2:
The patent controls the surface roughness parameters after nitriding and finishing honing to achieve Rz ≤ 4.0 μm and Rmax ≤ 6.0 μm. This parameter control ensures the nitrided layer provides abrasion resistance while the controlled roughness prevents scuffing by eliminating excessive surface unevenness.
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 reduces oil consumption and friction while minimizing the risk of scuffing by controlling graphite exposure and surface roughness, enhancing the engine's performance and compliance with environmental regulations.
Implementation Method 1
a structure in which a cylinder liner formed of cast iron is fitted thereinto... soft nitriding is applied to form a compound layer on the entire surface... a cylinder liner having a nitrided layer on an inner periphery
Implementation Method 2
a cross hatching section is formed through finishing honing... after finishing an inner surface of a cylinder liner formed of cast iron to be processed to a surface roughness of 2 to 6 μ with oil pockets everywhere by honing
Implementation Method 3
a metal structure in which flaky free graphite is dispersed and crystallized in a cast iron matrix
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4B
AI summary
A cylinder liner of the present invention is a cylinder liner mounted on a cylinder block and formed of flaky graphite cast iron, at least a nitrided layer is provided on an inner periphery of the cylinder liner, and a cross hatching section is formed on the inner periphery, a roughness curve of the inner periphery has a plateau honing shape, a ten-point average roughness Rz of the inner periphery pursuant to JIS B0601:1982 is 4.0 µm or less, and an average value of an area ratio of pits generated in the inner periphery is 8% or less.