Analysis of a Low-Loss Gear Geometry Using a Thermal Elastohydrodynamic Simulation including Mixed Lubrication

Farrenkopf, Felix; Schwarz, Andreas; Lohner, Thomas; Stahl, Karsten

doi:10.3390/lubricants10090200

Cited by 8 publications

(4 citation statements)

References 36 publications

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“…A helical gear setup as described in ref. [16] would be a better option for emulating the reduction gear operation, but unfortunately it was not available. To evaluate the effect of mechanochemical surface finishing, one set of gears was additionally processed applying the Triboconditioning ® CG method.…”

Section: Methodsmentioning

confidence: 99%

The Effects of the Lubricant Properties and Surface Finish Characteristics on the Tribology of High-Speed Gears for EV Transmissions

Zhmud,

Najjari,

Brodmann

2024

Lubricants

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Electric vehicle (EV) transmissions operate at high speeds. High-speed operation puts higher demands on bearings, seals, and gears. Bearings in EV transmissions are prone to electrically induced bearing damage and may exhibit signs of pitting and fluting. Surface-initiated rolling contact fatigue is another common problem gaining increased attention lately. Most EV transmissions require a coupling between an oil-lubricated gearbox to an electrical motor that runs with minimal lubrication at very high rpm. The high mechanical and thermal stresses the seals are exposed to under starved lubrication conditions have a detrimental impact on their service life. Hence, proper lubrication is critical. In general, EV transmission fluids call for a somewhat different spectrum of properties compared to conventional ATFs. Gear tribology simulations open new ways to the design and optimization of lubrication for EV transmissions. Additionally, such simulations can also provide valuable insights into the effects of different oil properties on cooling and lubrication efficiencies, thereby helping in matching the lubricant and hardware characteristics for optimal performance. In the present communication, we demonstrate the effects of different lubricants and surface finishing technologies on the tribology of high-speed gears using tribological tests and advanced thermal elastohydrodynamic (TEHD) simulations. The important roles of lubricity additives and surface finish optimization are highlighted in conjunction with a move towards ultralow viscosity EV transmission fluids.

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Section: Methodsmentioning

confidence: 99%

The Effects of the Lubricant Properties and Surface Finish Characteristics on the Tribology of High-Speed Gears for EV Transmissions

Zhmud,

Najjari,

Brodmann

2024

Lubricants

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“…In this way, in each time step, the contact area in the X-and Y-direction is within ∼ (−1.0, 1.0). A similar strategy was applied in [18].…”

Section: Dimensionless Formulationmentioning

confidence: 99%

Thermal Elastohydrodynamic Analysis of a Worm Gear

et al. 2023

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This study explores the elastohydrodynamic lubrication (EHL) between the contacting tooth flanks of a worm gear with nonconjugate meshing action. The contact is characterized by a slender-like elliptical shape and high sliding. The geometry and contact conditions for the considered worm gear were obtained using tooth contact analysis. Based on that, the complete area of the worm gear contact was analyzed using a validated numerical EHL model considering non-Newtonian, thermal, and transient effects. The geometrical and kinematic design factors that influence EHL film formation in worm gears were identified and are discussed. The results show the specific characteristics of worm gear EHL contacts, such as the very slender contact in the tooth root flank area, which diminishes the effect of the entrainment speed on film thickness. EHL film formation could be supported by increasing conformity between the flanks to make the contact less slender. By comparing the film thickness results against analytically obtained ones, relatively large differences were observed except for one formula for minimum film thickness.

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“…The EHL model with all relevant physics is implemented in a commercial multiphysics software and solved based on the finite element method in a full system approach according to Habchi (2018). For modeling the lubricant properties, the formulated models and the corresponding oil data and parameters are adopted from Farrenkopf et al (2022). For description of the temperature dependency of the viscosity, a model according to Vogel (1921), Fulcher (1925) and Tammann and Hesse (1926) is used.…”

Section: Numerical Modelingmentioning

confidence: 99%

Characteristics in hard conformal EHL line contacts

Schmid

Paschold

Lohner

et al. 2023

ILT

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Purpose Internal gearings are commonly used in transmissions due to their advantages like high-power density. To ensure high efficiency, load-carrying capacity and good noise behavior, a profound knowledge of the local gear mesh is essential. The tooth contact of internal gears relates to a convex and concave surface that form a conformal contact. This is in contrast to external gears, where two convex surfaces form a contraformal contact. This paper aims at a better understanding of conformal contacts under elastohydrodynamic lubrication (EHL) to improve the design of internal gearings. Design/methodology/approach An existing numerical EHL model is used for studying the characteristic properties of a hard conformal EHL line contact. A hard contraformal EHL line contact is studied as reference. Non-Newtonian fluid behavior and thermal effects are considered. By taking into account the local contact conformity and kinematics, the effects and relevance of the curvature of the lubricant gap and micro-slip are analyzed. In a parameter study, scale effects of the contact radii on film thickness, temperature rise and friction are examined. Findings The curvature of the lubricant gap and effects of micro-slip are small in hard conformal EHL line contacts. For high micro-slip, it can be neglected. Hence, the modeling of conformal contacts using an equivalent geometry of the contact problem is reasonable. The parameter study shows beneficial tribological aspects of the conformal contact compared to the contraformal contact. Higher film thickness and lower fluid coefficient of friction are observed for conformal contacts, which can be attributed to lower pressures for the case of the same external normal force, or to a higher contact temperature rise for the case of equivalent contact pressure. Originality/value Despite its widespread existence, the local geometry and kinematics in hard conformal EHL line contacts like in internal gearings have been rarely studied. The findings help for a better understanding of local contact characteristics and its relevance. The quantified scale effects help to improve the efficiency and load-carrying capacity of machine elements with hard conformal EHL contacts, like internal gearings. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2022-0366/

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Analysis of a Low-Loss Gear Geometry Using a Thermal Elastohydrodynamic Simulation including Mixed Lubrication

Cited by 8 publications

References 36 publications

The Effects of the Lubricant Properties and Surface Finish Characteristics on the Tribology of High-Speed Gears for EV Transmissions

The Effects of the Lubricant Properties and Surface Finish Characteristics on the Tribology of High-Speed Gears for EV Transmissions

Thermal Elastohydrodynamic Analysis of a Worm Gear

Characteristics in hard conformal EHL line contacts

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