TEHL Simulation on the Influence of Lubricants on the Frictional Losses of DLC Coated Gears

Ziegltrum, A.; Lohner, Thomas; Stahl, Karsten

doi:10.3390/lubricants6010017

Cited by 25 publications

(23 citation statements)

References 30 publications

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“…The present author provided an alternative hypothesis where the friction reduction is explained by thermal softening of the lubricant as a result of thermal insulation [8][9][10] due to the low thermal conductivity of DLC coatings. This has been further validated numerically [14][15][16][17] and experimentally by other authors [18].…”

Section: Introductionsupporting

confidence: 54%

DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication

Björling

Shi

2019

Tribol Lett

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Low friction is one of the most important parameters for the development of machine components and machines with high efficiency. Many of the common machine components of today such as gears, rolling element bearings and cam-followers are defined by their non-conformal contacts leading to high-contact pressures, typically 1-4 GPa. The lubrication of such contacts is usually called elastohydrodynamic lubrication (EHL). Diamond-like carbon (DLC) coatings and glycerol have individually been shown to produce low friction in boundary, mixed and full film lubrication. A few studies have been conducted using both glycerol and DLC-coated surfaces to achieve even lower friction in pure sliding boundary-lubricated contacts. However, the literature is lacking studies of how the combination of glycerol and DLC performs in non-conformal rolling/sliding contacts where many common machine components operate. Such a study is presented in this article where a ball-on-disc test rig is used to investigate the performance of the combination of DLC and glycerol at pressures up to 1.95 GPa at various entrainment speeds and slide-to-roll ratios. The investigation shows that the DLC-glycerol combination provides very low friction values, in some cases, below the superlubricity threshold of 0.01, possibly shown for the first time at such high pressure in a non-conformal rolling/sliding contact. The low friction mechanism in full film lubrication is a combination of the low pressure-viscosity and high temperature-viscosity sensitivity of glycerol in combination with thermal insulation of the DLC coating and is presented as thermally assisted liquid superlubricity.

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Section: Introductionsupporting

confidence: 54%

DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication

Björling

Shi

2019

Tribol Lett

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“…For the latter, the fluid temperature was shifted towards the coated surface. Using TEHL simulations of spur gears, Ziegltrum et al [42] showed a similar trend in frictional behavior for different lubricants (mineral, polyalphaolefin, and polyglycol oil) due to the thermal insulation effects of the amorphous carbon coating. However, the degree of friction reduction varied between 14% and 28%, depending on the lubricant properties.…”

Section: Introductionmentioning

confidence: 87%

On Friction Reduction by Surface Modifications in the TEHL Cam/Tappet-Contact-Experimental and Numerical Studies

2019

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The overall energy efficiency of machine elements and engine components could be improved by using new technologies such as surface modifications. In the literature, surface engineering approaches like micro-texturing and the application of diamond-like carbon (DLC) coatings were frequently studied separately, with focus on a specific model contact and lubrication conditions. The contribution of the current study is to elucidate and compare the underlying friction reduction mechanisms of the aforementioned surface modifications in an application-orientated manner. The study applied the operating conditions of the thermo-elastohydrodynamically lubricated (TEHL) cam/tappet-contact of the valve train. Therefore, tribological cam/bucket tappet component Stribeck tests were used to determine the friction behavior of ultrashort pulse laser fabricated microtextures and PVD/PECVD deposited silicon-doped amorphous carbon coatings. Moreover, advanced surface characterization methods, as well as numerical TEHL tribo-simulations, were utilized to explore the mechanisms responsible for the observed tribological effects. The results showed that the DLC-coating could reduce the solid and fluid friction force in a wide range of lubrication regimes. Conversely, micro-texturing may reduce solid friction while increasing the fraction of fluid friction.

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“…This effect seems to be due to the lapping effect of the DLC coating [19]. A friction reduction mechanism has also been reported that is attributed to wall slip [19], caused by a decline in lubricant viscosity accompanying a localized temperature increase owing to the low thermal conductivity of the DLC coating [20,21] and by the effects of functional groups on the DLC coating surface. The friction reduction mechanism will continue to be studied in future work.…”

mentioning

confidence: 91%

Excellent Seizure and Friction Properties Achieved with a Combination of an a-C:H:Si DLC-Coated Journal and an Aluminum Alloy Plain Bearing

et al. 2021

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Friction occurring between the crank journal and main bearings accounts for a large share of the mechanical losses of automotive engines. The effects of higher in-cylinder pressures and narrower bearings have raised the specific load applied to bearings, making it essential to secure sufficient seizure resistance as well. For the purpose of meeting both requirements, we have endeavored to reduce friction and improve seizure resistance by applying a diamond-like carbon (DLC) coating to the crank journal. In the present study, a bearing tester was used that has received international standard certification from the International Organization for Standardization for reproducing the sliding behavior occurring between the crank journal and main bearings in actual engines. Test results indicated that a silicon-containing hydrogenated amorphous carbon (a-C:H:Si) DLC-coated journal showed a definite friction reduction and a marked improvement in seizure resistance. An acoustic emission (AE) analysis revealed that an adhesion-induced AE peak observed for a steel journal was not seen for the DLC-coated journal. Additionally, tin and aluminum elements in the bearing material that were transferred to and observed on the sliding surface of the steel journal were not seen on the DLC-coated journal. Accordingly, the low affinity of the DLC coating with these metal elements presumably led to the clear friction reduction and superior seizure resistance displayed by the DLC coating.

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TEHL Simulation on the Influence of Lubricants on the Frictional Losses of DLC Coated Gears

Cited by 25 publications

References 30 publications

DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication

DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication

On Friction Reduction by Surface Modifications in the TEHL Cam/Tappet-Contact-Experimental and Numerical Studies

Excellent Seizure and Friction Properties Achieved with a Combination of an a-C:H:Si DLC-Coated Journal and an Aluminum Alloy Plain Bearing

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