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Research Papers: Elastohydrodynamic Lubrication

# A Theoretical Tribological Comparison Between Soft and Hard Coatings of Spur Gear Pairs

[+] Author and Article Information
Huaiju Liu

State Key Laboratory of Mechanical
Transmissions,
Chongqing University,
Chongqing 400044, China
e-mail: huaijuliu@cqu.edu.cn

Caichao Zhu, Zhanjiang Wang, Ye Zhou, Yuanyuan Zhang

State Key Laboratory of Mechanical
Transmissions,
Chongqing University,
Chongqing 400044, China

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received February 25, 2016; final manuscript received October 14, 2016; published online March 17, 2017. Assoc. Editor: Jordan Liu.

J. Tribol 139(3), 031503 (Mar 17, 2017) (13 pages) Paper No: TRIB-16-1065; doi: 10.1115/1.4035028 History: Received February 25, 2016; Revised October 14, 2017

## Abstract

A thermal elastohydrodynamic lubrication (TEHL) model is developed for a coated spur gear pair to investigate the effect of soft coatings and hard coatings on the tribological behavior of such a gear pair during meshing. The coating properties, i.e., the ratio of the Young's modulus between the coating and the substrate, and the coating thickness, are represented in the calculation of the elastic deformation. Discrete convolution, fast Fourier transform (DC-FFT) is utilized for the fast calculation of the surface deformation. The variation of the radius of curvature, the rolling speed, the slide-to-roll ratio, and the tooth load along the line of action (LOA) during meshing is taken into account and the transient squeeze effect is considered in the Reynolds equation. Energy equations of the solids and the oil film are derived. The temperature field and the pressure field are solved iteratively. The tribological behavior is evaluated in terms of the minimum film thickness, the maximum pressure, the temperature rise, the coefficient of friction, and the frictional power loss of the tooth contact during meshing. The results show discrepancies between the soft coating results and hard coating results.

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## Figures

Fig. 1

The spur gear pair contact and a simulated coated line contact problem

Fig. 2

The calculation flowchart of the numerical model

Fig. 3

Variation of the tooth load, the radius, the rolling speed, and the slide-to-roll ratio during meshing

Fig. 4

Distribution of the pressure during meshing under the three coating conditions

Fig. 5

Distribution of the film shear stress τ during meshing under the three coating conditions

Fig. 6

Variation of the minimum film thickness, maximum pressure, coefficient of friction, and the maximum film temperature during meshing under three coating cases

Fig. 7

Effect of the modulus ratio on the minimum film thickness and the maximum pressure under thermal and isothermal conditions

Fig. 8

Effect of modulus ratio on hmin under various working conditions

Fig. 9

Effect of the modulus ratio on the mean coefficient of friction and the maximum film temperature

Fig. 10

Comparison of the instantaneous coefficient of friction between the engage-in point and the pitch point

Fig. 11

Comparison of the instantaneous film maximum temperature between the engage-in point and the pitch point

Fig. 12

Effect of the coating thickness on the minimum film thickness and the maximum pressure with hard or soft coating

Fig. 13

Effect of the coating thickness on the mean coefficient of friction and the maximum film temperature with hard or soft coating

Fig. 14

Effect of the coating thickness on the mean frictional power loss and the maximum oil film shear stress with hard or soft coating

Fig. 15

Variation of the minimum film thickness, the maximum pressure, and the maximum temperature as the coating properties change

Fig. 16

Variation of the mean coefficient of friction, the mean frictional power loss, and the maximum film shear stress τmax as the coating properties change

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