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  • 1.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    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.
    The influence of DLC coating on EHL friction coefficient2012In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 47, no 2, p. 285-294Article in journal (Refereed)
    Abstract [en]

    High hardness, high elastic modulus, low friction characteristics, high wear and corrosion resistance, chemical inertness, and thermal stability are factors that make diamond-like carbon (DLC) coatings the subject of many studies. For the same reasons they also seem suitable for use in, amongst others, machine components and cutting tools. While most studies in the literature focus on the influence of coatings on wear and friction in boundary lubrication and pure sliding contacts, few studies can be found concerning rolling and sliding elastohydrodynamic lubrication (EHL) friction, especially in the mixed and full film regime. In this article tests are carried out in a Wedeven Associates Machine tribotester where an uncoated ball and disc pair is compared to the case of coated ball against uncoated disc, coated disc against uncoated ball, and coated disc against coated ball. The tests are conducted at two different temperatures and over a broad range of slide-to-roll ratios and entrainment speeds. The results are presented as friction maps as introduced in previous work (Björling et al. in J Eng Tribol 225(7):671, 2011). Furthermore a numerical simulation model is developed to investigate if there is a possibility that the hard, thin DLC coating is affecting the friction coefficient in an EHL contact due to thermal effects caused by the different thermal properties of the coating compared to the substrate. The experimental results show a reduction in friction coefficient in the full film regime when DLC-coated surfaces are used. The biggest reduction is found when both surfaces are coated, followed by the case when either ball or disc is coated. The thermal simulation model shows a substantial increase of the lubricant film temperature compared to uncoated surfaces when both surfaces are coated with DLC. The reduction in friction coefficient when coating either only the ball or the disc are almost the same, lower than when coating both the surfaces but still higher than the uncoated case. The findings above indicate that it is reasonable to conclude that thermal effects are a likely cause for the decrease in coefficient of friction when operating under full film conditions, and in the mixed lubrication regime when DLC-coated surfaces are used

  • 2.
    Cha, Matthew
    et al.
    Kungliga tekniska högskolan, KTH.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Glavatskih, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of pad compliance on nonlinear dynamic characteristics of tilting pad journal bearings2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 57, p. 46-53Article in journal (Refereed)
    Abstract [en]

    The effect of padcompliance on the dynamic response of tiltingpadjournalbearings is investigated. Padcompliance is varied by changing pivot geometry and Young’s modulus of pad backing and pad liner. Two pad support configurations are considered: one that allows only circumferential tilt and another one that allows both circumferential and axial tilts. Journal orbits, oil film pressure and oil film thickness are compared and discussed. It is shown that higher pad backing compliance significantly increases the journal orbit size and results in an increase in oil film pressure while oil film thickness is decreased. With a compliant liner, oil film pressure is decreased while oil film thickness is increased. Tapers at the pad edges are essential to increase the global minimum oil film thickness in compliant liner bearings.

  • 3.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Simulation of tribology in hydraulic motors2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Tribology is the science of friction, lubrication and wear. A tribological interface is composed of two contacting surfaces in relative motion. The radial piston hydraulic motor includes a lot of tribological interfaces. The interfaces are made up of the contacts between the moving parts in the motor that transform energy in the form of hydraulic flow into motion of the output shaft. Many of them are highly loaded due to the large forces that must be transmitted to produce the required torque. The performance in view of efficiency of the hydraulic motor depends strongly on the tribological properties in these interfaces. In industry today, there is a general strive towards better efficiency to minimize impact on the environment by lowering energy consumption. This puts a lot of focus on tribology, especially in applications like the hydraulic motor whose purpose is to convert energy into some desired motion. Indeed, minimizing the losses/friction in the tribological interfaces leads to less energy needed to produce the desired motion. Another aspect of tribology is wear in the interfaces which can affect durability or toughness of the motor. At present, design and optimization of tribological interfaces is mostly done by trial and error experimental work and testing. This will always be needed but if more of the testing can be done using computer based computational models a more cost effective and faster design process could be achieved. A computational model would also lead to better understanding of tribological processes present in the simulated application due to the possibility to investigate properties that are very hard to measure. The work in this thesis involves development of computer based computational models for simulation of the tribology in hydraulic motors. The model is validated through comparison with experiments. Furthermore it is shown that modelling can be used to analyze tribology in the hydraulic motor and consequently can be used as a design tool for improving efficiency.

  • 4.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Simulering av smörjfilmsuppbyggnad i glidlager2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 129-Conference paper (Other academic)
  • 5. Isaksson, Patrik
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effects of simplified energy equation to the solution of temperature in conformal contacts2009Conference paper (Refereed)
  • 6. Isaksson, Patrik
    et al.
    Nilsson, Daniel
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elasto-hydrodynamic simulation of complex geometries in hydraulic motors2008In: Proceedings of NORDTRIB 2008, 13th Nordic Symposium on Tribology: Scandic Rosendahl Hotel, Tampere, Finland, June 10 - 13, 2008 / [ed] Jaakko Kleemola; Arto Lehtovaara, Tampere: Tampere University of Technology, 2008Conference paper (Refereed)
    Abstract [en]

    As many other machines, the radial piston hydraulic motor contains a lot of tribological interfaces. One important area is the piston assembly and the journal bearing contact between the piston and cam roller. There exists good models to describe the performance of simpler geometries such as journal bearings, but when put into a system or when having a more complex geometry, the models do not apply very well. To be able to predict the tribological performance of such components, it is important to have a model that is able to include the real geometry and the properties of the system. A simulation model of the piston assembly in Hägglunds Compact hydraulic motor was built using FE software which made it easy to include the complex geometries. The model includes the deformation of the piston. The hydrodynamics is solved by using Reynolds equation. Density/pressure and viscosity/pressure dependency for the oil are included. The whole model was solved with the built in solvers in the software. Simulation results such as friction, hydrodynamic pressure and oil leakage was compared with test results. Good agreement between simulation and tests shows that this kind of model can be a useful tool in development and optimization of tribological systems.

  • 7. Isaksson, Patrik
    et al.
    Nilsson, Daniel
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elasto-hydrodynamic simulation of complex geometries in hydraulic motors2009In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 42, no 10, p. 1418-1423Article in journal (Refereed)
    Abstract [en]

    As many other machines, the radial piston hydraulic motor contains a lot of tribological interfaces. One important area is the piston assembly and the journal bearing contact between the piston and cam roller. There exists good models to describe the performance of simpler geometries such as journal bearings, but when put into a system or when having a more complex geometry, the models do not apply very well. To be able to predict the tribological performance of such components, it is important to have a model that is able to include the real geometry and the properties of the system.A simulation model of the piston assembly in Hägglunds Compact hydraulic motor was built using FE software which made it easy to include the complex geometries. The model includes the deformation of the piston. The hydrodynamics is solved by using Reynolds equation.Density/pressure and viscosity/pressure dependency for the oil are included.Simulation results such as friction, hydrodynamic pressure and oil leakage was compared with test results. Good agreement between simulation and tests shows that this kind of model can be a useful tool in development and optimization of tribological systems.

  • 8.
    Isaksson, Patrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Nilsson, Daniel
    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.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence of surface roughness on friction in a flexible hybrid bearing2011In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, no J10, p. 975-985Article in journal (Refereed)
    Abstract [en]

    The effect of surface roughness on friction in all lubrication regimes is studied for a flexible hybrid bearing of a radial piston hydraulic motor. The effect is studied by performing experiments in a specially designed test rig and numerical simulations of the real measured surface topographies of the bearings. The simulations are performed with a two-scale model where surface roughness is treated on a local asperity level by homogenized flow factors and a global scale where the bearing structure is included. Three bearings with different surface topographies are included in the study and both experimentally measured and simulated friction are analysed for each of them. Comparison of friction predicted by the model and experimentally measured friction is performed and it reveals that the model is a valuable tool for analysing the effect of surface roughness in this type of bearing

  • 9.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Simulations of lubricated interfaces: a way to obtain efficient machines2010Conference paper (Other academic)
  • 10. Nilsson, Daniel
    et al.
    Isaksson, Patrik
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effects of area ratio and nature of surfaces on scuffing in lubricated contacts2008Conference paper (Other academic)
  • 11.
    Nilsson, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effects of area ratio and nature of surfaces on scuffing in lubricated contacts2009In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 223, no 3, p. 445-455Article in journal (Refereed)
    Abstract [en]

    Heavily loaded moving machine components encounter severe tribological problems. Typical examples include piston and cylinder contacts in a hydraulic motor. Piston and cylinder bore contacts invariably operate in boundary lubrication regime and the risk for seizure of these contacts is high particularly when lubricated with low-viscosity lubricants. The piston assembly in a radial piston hydraulic motor has conformal (area) contact. In this work, these contacts have been simulated in the laboratory by using a thrust washer test configuration. The influence of area ratio, nature of contacting surfaces, and speed on scuffing has been investigated by using a factorial design of experiments approach. The influence of area ratio on wear at lower speed has also been studied. The results have revealed that the surface power, or μpv-value, at scuffing varies by 3-4 times when the area ratio was increased from 8 to 72 per cent. The running-in wear tests have shown that running-in of the upper and lower specimens also varies with the area ratio. During the first 30 s the upper specimen is polished with low area ratio, whereas the lower specimen is polished with high area ratio. The surface temperature was estimated by using finite-element calculation and it was found to be similar prior to scuffing for both 8 and 72 per cent area ratios at 1.7 m/s sliding speed. The comparison of the results with the actual motor tests shows that an area ratio of 24 per cent seems to simulate the piston-cylinder contact better.

  • 12.
    Söderfjäll, Markus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    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.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Spencer, Andrew
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The effect of 3D deformations of a cylinder liner on the tribological performance of a piston ring-cylinder liner system.2013Conference paper (Refereed)
  • 13.
    Söderfjäll, Markus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Spencer, Andrew
    Scania CV AB, Södertälje.
    Almqvist, Andreas
    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.
    The effect of three-dimensional deformations of a cylinder liner on the tribological performance of a piston ring–cylinder liner system2014In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, no 10, p. 1080-1087Article in journal (Refereed)
    Abstract [en]

    This paper describes a numerical simulation model for prediction of the tribological effects of an oil control ring running against an out-of-round cylinder liner in a heavy duty diesel engine. The model considers the full three-dimensional geometry of the oil control ring and includes the effect of both surface roughness and global deformation. Results that test the model’s ability to do this under stationary conditions are presented. Furthermore, stationary results for prediction of the friction reduction possible by reduced ring tension in combination with reduced out-of-roundness are given. The model predicts the friction for the oil control ring at mid-stroke to be 78% larger in an out-of-round cylinder liner compared to a perfectly cylindrical one.

1 - 13 of 13
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