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  • 1.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    How a small change in surface roughness dramatically changes the transition to full-film lubrication in EHL2019Conference paper (Refereed)
    Abstract [en]

    To improve the efficiency in non-conformal type of machine elements, it is of crucial importance to gain knowledge about the underlying mechanism that governs the formation of an elastohydrodynamic (EHD) oil film. This study was set out to explore the dependency of surface roughness and operating conditions on the transition to full film elastohydrodynamic lubrication (EHL). A ball-on-disc device, arranged for monitoring electrical contact resistance (ECR), was operated under a wide variety of heavily loaded rolling/sliding conditions. To reduce complexity in the film formation process, any tribo-chemical effects were minimized by the selection of a neat synthetic lubricant. Two types of tests were set-up to examine, in particularly, the role of load and slide-to-roll ratio (SRR) on the EHD film formation. In the first, the contact was mapped over the speed and SRR parameter space to capture the transition from EHL to mixed lubrication when starting in EHL. The contact was then operated under different loads to reveal the EHL transitions dependency to variations in Hertzian contact pressure. In the second set of tests, the contact was initiated in mixed lubrication, and film formation was monitored until surfaces achieved lift-off for EHL by adequate surface modification due to running-in. Subsequently, special emphasis was set out to investigate what transformations those surfaces had to undergo in order for EHL lift-off to take place.

  • 2.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Improved performance by ionic additives in hydrocarbon base fluids for mixed-rolling/sliding contacts2018Conference paper (Refereed)
  • 3.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lubricant Film Formation in Rough EHL Contacts2020Conference paper (Refereed)
    Abstract [en]

    Conference: 22nd International Colloquium Tribology, Technical Academy Esslingen, 28–30 January 2020, Stuttgart / Ostfildern, Germany

    Main subject: Fundamentals of Tribology

    Title: Lubricant film formation in rough EHL contacts

    Author(s): Jonny Hansen1,2, Marcus Björling1, Roland Larsson1

    Affiliation: 1) Machine Elements, Luleå University of Technology, Luleå, Sweden

    2) Gear Technology, Transmission Development, Scania CV AB, Södertälje, Sweden

     

    Abstract:

    Downsizing of machine elements and thinner lubricating oils, with simultaneous improved power density, is an on-going pursuit in automotive industry and lubrication science. The outcome is shifting the performance of e.g. gear contacts to operate under more severe lubricating regimes. In extension, this sets the role of surface finish in the view of increased importance since roughness amplitude in combination with thin films generally is considered to activate surface degradation mechanisms such as wear, fatigue, and ultimately machine failure. Thus, in order to meet the present demands, it is of critical importance to better understand the interplay between surface roughness and elastohydrodynamic oil film (EHL) formation.

    Recently, our research [1] has shown that the default model [2] for estimation of lubrication quality strongly deviates from the supposed proportional relationship between film thickness and composite surface roughness (). Thus, with the present approach, false assumptions about lubrication quality are possible. An adequately run-inned surface may operate under elasto-hydrodynamic performance even at such conditions when  suggests substantial contact interference. The latter suggest that the more detrimental opposite situation also would be possible under a certain surface roughness configuration. This research was therefore set out as part of a long term goal of improving the present engineering design tool so that better and more safe estimates of the lubrication quality can be made.

    This work explores the mechanisms involved in the formation of an elasto-hydrodynamic (EHD) oil film under heavily loaded mixed rolling/sliding operation of circular contacts. A WAM ball-on-disc machine was operated under conditions representative for those found in heavy duty transmission assemblies. Specimens were prepared with isotropic engineering surface finishes to capture the effect of roughness amplitude on the contacts capability to form a protective EHD film. Electrical contact resistance (ECR) and the coefficient of friction was monitored during running-in tests to reveal how surface roughness affects the number of cycles to EHL lift-off, and the associated response to friction. Specific emphasis was set out to investigate what changes surface topographies must undergo in order to reach a steady state in EHL when starting in mixed lubrication. A surface-re-location technique was developed to enable for detailed examination of the most active sites that typically involve the most prominent asperity features. Surface analysis was conducted with the aim of clarifying the importance to lubrication quality of parameters from all families, i.e. spatial, feature and hybrid parameters in addition to the present approach that only accounts for the surfaces height by root-mean-square-average (RMS/). A strong correlation between friction change and the modification of surface topography was found as the contact went through the running-in process for EHL lift-off. Additionally, it was observed that surface roughness still significantly affect the coefficient of friction at EHL steady state operation.

     

    [1]      Hansen J, Björling M, Larsson R. Mapping of the lubrication regimes in rough surface EHL contacts. Tribol Int 2018. doi:10.1016/j.triboint.2018.11.015.

    [2]      ISO/TR 15144-1:2014. Calculation of micropitting load capacity of cylindrical spur and helical gears. Geneva: n.d.

  • 4.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Gear Technology, Transmission Development, Scania CV AB, Södertälje.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mapping of the lubrication regimes in rough surface EHL contacts2019In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 131, p. 637-651Article in journal (Refereed)
    Abstract [en]

    Understanding film formation in rough surface elastohydrodynamically lubricated (EHL) contacts have been an ongoing pursuit in lubrication science for more than half a century. This study furthers that quest by establishing a single combined friction and electrical contact resistance map that forms a clear and comprehensive overview of the lubrication performance. A ball-on-disc machine was operated under a wide variety of heavily loaded rolling/sliding contact conditions. Results show that while sweeping the contact over the SRR- and entrainment speed-domain, the primary sweep direction significantly affects running-in and consequently the transition from full-film to the mixed lubrication regime. Such knowledge sheds new light into the mechanisms that governs EHL film formation and the concurrent interplay with the mixed lubricated friction coefficient.

  • 5.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the full film to mixed lubrication transition in rolling/sliding non-conformal contacts2018Conference paper (Refereed)
    Abstract [en]

    Lower weight components and thinner lubricating oils, with simultaneous improved power density, is an on-going pursuit in industry and lubrication science. The outcome is shifting the tribological performance towards more severe lubricating regimes. This in turn sets new levels of demands for knowledge about the complex and concurrent interaction between engineering surfaces and lubricants. An emerging need is therefore to make use of the enhancing properties of tribo-improvers, thus to gain knowledge of their working mechanism is consequently of uttermost importance. This study was set out to investigate the tribofilm formation induced by different degrees of surface roughness. A ball on disc device was operated under heavily loaded rolling/sliding conditions at elevated temperature to simulate gear like conditions. The tribological performance is ultimately evaluated in terms friction and wear with special emphasis on the development and mechanism of additive derived tribofilms.

  • 6.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the surface lift-off transition in rough surface EHL contacts2019Conference paper (Refereed)
    Abstract [en]

    The pumping and churning losses in transmission assemblies are minimized when gears are operated in low viscosity lubricants. Therefore, in order to improve gear efficiency, it is of crucial importance to gain knowledge about the underlying mechanism that governs elastohydrodynamic (EHL) contacts ability to form a separating oil film. This study was set out to explore the necessary requirements for EHL contacts to achieve a state of full film separation. A ball on disc device, arranged for electrical contact resistance (ECR) measurement, was operated under a wide variety of heavily loaded rolling/sliding conditions. Friction and ECR-signal were simultaneously monitored to capture the contact performance until surfaces achieved lift-off by adequate surface modification due to running-in. Special emphasis was set on post-test surface analysis to reveal whether any surface roughness parameter could provide insights in the pre-requisite for surface lift to take place.

  • 7.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Small changes in surface roughness can make a dramatic difference!2019Conference paper (Refereed)
  • 8.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Transmission Development, Scania CV AB, Södertälje, Sweden.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Topography transformations due to running-in of rolling-sliding non-conformal contacts2020In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 144, article id 106126Article in journal (Refereed)
    Abstract [en]

    A ball-on-disc machine was operated under conditions relevant to heavily loaded gears. Various levels of isotropic surface finishes were evaluated to reveal the influence on elasto-hydrodynamic lubrication (EHL). Stribeck tests were conducted for insight about roughness effects in all regimes, whereas lift-off tests were conducted to investigate the influence on running-in. A 3D surface re-location approach was developed to enable studies of the topography on exactly the same area before and after test. This helps to find asperity level details about how topographies must transform to allow a shift from the mixed- and boundary lubrication regimes, into the full film micro-EHL regime. The micro-conformity was highlighted to play a key-role for EHL lift-off that precedes the completion of running-in.

  • 9.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Gear Technology, Transmission Development, Scania CV AB, Södertälje.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Performance and mechanisms of silicate tribofilm in heavily loaded rolling/sliding non-conformal contacts2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 123, p. 130-141Article in journal (Refereed)
    Abstract [en]

    Lubricant performance is vital as heavy-duty gear manufacturers increase power density in their efforts towards increased efficiency. In this work, a recently developed ionic liquid is introduced as a multifunction additive for use in hydrocarbon base fluid. A ball-on-disc tribological test machine was used to evaluate friction and wear in heavily loaded mixed rolling/sliding conditions. The novel multifunctional additive is benchmarked against conventional axle-gear oil additives, and results shows excellent tribological performance in terms of friction and wear. Post-test surface analysis of the wear scars revealed a silicate based tribofilm derived from the novel ionic additive, contrary to conventional phosphorous and/or sulfur based. The silicate tribofilm is correlated to a significantly increased wear resistance and vastly improved running-in performance.

  • 10.
    Hansen, Jonny
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gear contact simulation on asperity level2015Conference paper (Refereed)
    Abstract [en]

    Gears used in gearboxes and those used in rear axles are subject to constantly increasing demands for reliability, performance and efficiency. To meet the requirements of the future market computer aided engineering, CAE, is becoming more and more vital in order to understand the onset and cause to failure and to optimize for best possible performance. The aim of this master thesis was to pave the way for numerical modelling as a complement to testing and to give insight in how the problem of simulating gears with oil and surface roughness incorporated can be addressed. Moreover, as part of this, the work was to be conducted in order to give insight in possibilities as well as shortcomings with present tools. Therefore a numerical tool which is capable of indicating the load carried by the asperities and the separating lubricant film during the event of a gear mesh has been developed. Several contact mechanics codes and different EHL formulas has been studied in order to provide alternative foundations to the gear simulation model. The model accounts for real surface topographies, different oil formulations as well as operational conditions and gear designs. Results show that the model visually correlates to test gears subjected to similar conditions in terms of critical areas on the gear flank. Even though validation is required to reveal model accuracy, at present, the model can be utilized to indicate how different conditions affect the asperity and lubricant load share and thus what combination that is most beneficial in terms of better performance and prolonged service life. In addition, a local scale asperity simulation where single asperities have been subjected to numerous collisions has also been developed. Results show that there is very promising potential in terms of future development as the model comprises the ability to potentially capture the initial state on the formation and development of a micropit.

  • 11.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hansen, Jonny
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the Effects of Two-Sided Roughness in Rolling-Sliding EHL Contacts.2020Conference paper (Refereed)
1 - 11 of 11
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