Research Progress on Friction Reduction and Wear Resistance Characteristics of Cam-tappet Friction Pair

SHI Boxing; CHEN Wengang; CHEN Keyue; ZHONG Yinkun; LI Guifen

doi:10.16490/j.cnki.issn.1001-3660.2026.05.002

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Surface Technology ›› 2026, Vol. 55 ›› Issue (5) : 22-42. DOI: 10.16490/j.cnki.issn.1001-3660.2026.05.002

Friction, Wear and Lubrication

Research Progress on Friction Reduction and Wear Resistance Characteristics of Cam-tappet Friction Pair

SHI Boxing^1,2, CHEN Wengang^1,2,*, CHEN Keyue^1,2, ZHONG Yinkun^1,2, LI Guifen^1,2

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Abstract

As a core component of the valve train in internal combustion engines (ICEs), the cam-tappet friction pair undertakes the critical function of converting the rotational motion of the camshaft into the linear reciprocating motion of the valves. However, this friction pair accounts for over 70% of the total frictional losses in the entire valve mechanism, directly constraining engine efficiency, reliability, and service life. Against the backdrop of continuously growing global energy demands and increasingly stringent greenhouse gas emission regulations, optimizing the tribological performance of the cam-tappet friction pair has become an urgent research focus. This paper systematically reviews the latest research progress in four key areas: material selection, simulation technology, surface modification, and lubricating oil additives. In terms of materials, the development of cam-tappet materials has consistently advanced alongside the ICE technology, evolving from traditional carbon steels, gray cast iron, and alloy cast iron to modern alloy structural steels and advanced ceramic materials. Traditional materials offer advantages such as low cost and mature processing technologies, but possess from limited hardness and wear resistance. Alloy structural steels, after heat treatment, achieve a favorable balance between hardness and toughness, making them the mainstream choice in current applications. Ceramic materials demonstrate exceptional wear resistance and high-temperature stability, but their inherent brittleness and high manufacturing costs hinder their widespread industrial adoption. Recent research, through the addition of sintering aids like TiC₀.₅N₀.₅ or nanowires, combined with spark plasma sintering (SPS) technology, has effectively improved the processability and mechanical properties of ceramic materials, laying a foundation for their future application. Simulation has become a powerful tool for optimizing the tribological performance of cam-tappet pairs, serving as a "virtual test bench" to reveal lubrication mechanisms and guide experimental design. Numerical simulation methods, including fluid-solid coupling and finite element analysis, have been widely applied to optimize surface texture parameters and analyze oil film behaviors. Researchers can use MATLAB to simulate surface textures and determine optimal parameter ranges under different load conditions. Using COMSOL for fluid-solid coupling simulations of triangular textures on GCr15 steel surfaces has confirmed that the hydrodynamic pressure effects generated by textures can significantly reduce friction. These simulation studies not only enhance the reliability of experimental results but also shorten the R&D cycle by providing precise theoretical guidance. Surface modification technologies are crucial for improving the tribological performance of cam-tappet pairs and are mainly categorized into four types: laser surface texturing, solid lubricant coatings, ion implantation, and composite surface modification. Laser surface texturing creates micro-dimples or grooves on the material surface, enabling lubricant storage, wear debris capture, and hydrodynamic pressure effects under lubricated conditions. However, single texture technologies are prone to damage under high loads. Solid lubricant coatings, particularly diamond-like carbon films deposited via physical vapor deposition, exhibit low friction coefficients and high wear resistance, but suffer from poor substrate adhesion and susceptibility to delamination. Ion implantation (e.g., Ce, N, Ti ions) enhances surface hardness and wear resistance by altering the chemical composition and microstructure of the material surface, while multi-ion implantation (e.g., N+B) can achieve synergistic enhancement effects. Composite surface modification, which combines two or more single technologies (e.g., texture+coating, texture+nitriding, multi-layer coatings), effectively overcomes the limitations of individual methods. Through synergistic effects such as enhanced coating adhesion, improved load-bearing capacity, and extended service life, it achieves superior tribological performance. Lubricating oil additives play a key role in reducing friction and wear at the cam-tappet interface. Traditional additives like molybdenum dithiocarbamateand zinc dialkyldithiophosphate improve lubrication efficiency and anti-scuffing performance, but pose environmental concerns. Emerging environmentally friendly additives, including bio-based additives (e.g., modified biodiesel, ginger oil) and nano-composite additives, not only effectively reduce friction and wear but also minimize environmental impacts, aligning with the green manufacturing trend. Lubricant performance is also influenced by factors such as viscosity, temperature, and compatibility with surface textures, highlighting the necessity for integrated optimization of lubricants and surface engineering. Finally, an outlook is provided on the future research directions for cam-tappet tribological performance.

Key words

cam-tappet / simulation / surface modification / friction reduction and wear resistance / friction coefficient / lubricating oil additives

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SHI Boxing, CHEN Wengang, CHEN Keyue, ZHONG Yinkun, LI Guifen. Research Progress on Friction Reduction and Wear Resistance Characteristics of Cam-tappet Friction Pair[J]. Surface Technology. 2026, 55(5): 22-42

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Funding

The National Natural Science Foundation of China (52465023); Scientific Research Fund Project of Yunnan Provincial Department of Education (2025Y0872); Academician Dongyang Li Workstation in Yunnan Province (202305AF150019); Yunnan Provincial Agricultural Joint Key Project (202301BD070001-001)