| 1. |
- Calderon Salmeron, Gabriel, 1990-, et al.
(author)
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Bearing frictional performance of a grease thickened with recycled polypropylene
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Other publication (other academic/artistic)abstract
- In our previous publication, we showed that grease thickened with polypropylene could be a potential contributor to electric motor efficiency by reducing the bearing energy consumption by 22% in comparison to the most common type of grease: lithium grease. This work studies the feasibility of using polypropylene grease, with recycled polymer material as part of its thickener, in rolling element bearings operating under conditions typical of an electric motor. The frictional performance of a bearing lubricated with the recycled polymer grease was evaluated in deep groove ball bearings operating for 385-hour experiments under a wide range of speeds (up to 10,000 rpm). Friction torque results were complemented with rheological tests of the greases before and after the tests. The recycled polypropylene grease denoted significant rheological changes after the bearing tests. Such rheological changes were reflected in the higher energy dissipation in comparison to a reference polypropylene grease. However, the grease with recycled polypropylene led to a lower energy dissipation than a reference lithium complex grease. This represents a milestone in the development of greases with recycled materials in the grease thickener and shows the potential of using this grease in a real application.
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| 2. |
- Calderon Salmeron, Gabriel, 1990-, et al.
(author)
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Greases for electric vehicle motors : thickener effect and energy saving potential
- 2022
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In: Tribology International. - : Elsevier Ltd. - 0301-679X .- 1879-2464. ; 167, s. 107400-107400
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Journal article (peer-reviewed)abstract
- Electric vehicle motors in e-drivetrain are equipped with grease-lubricated bearings operating at both low and high speeds with frequent speed changes. The grease-bearing system must secure a long lifespan and low frictional torque to improve efficiency and sustainability. The present paper focuses on the influence of two types of thickener, lithium complex and polypropylene, on the grease lubrication performance under conditions typical for e-motors. The comparison of both thickeners is performed in terms of friction torque and energy consumption in eight long-duration experiments (337 hr). The results show that the polypropylene thickener provides 21.5% lower energy consumption compared to the lithium complex. Changes in grease rheology and degradation in the tests are analysed and correlated with the grease lubrication performance.
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| 3. |
- Calderon Salmeron, Gabriel, 1990-, et al.
(author)
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Greases for electric vehicle motors: Bearing friction torque under driving cycle conditions and the thickener effect on oil release
- 2024
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In: Tribology International. - : Elsevier Ltd. - 0301-679X .- 1879-2464. ; 198
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Journal article (peer-reviewed)abstract
- Performance of Lithium Complex (LiX), Polyurea (PU), and Polypropylene (PP) greases in SKF6208 bearings subjected to driving cycle conditions for 28 days (equivalent to 23,000 km of electric vehicle operation) was studied by continuously measuring bearing friction torque and temperature. The energy dissipation was correlated to the differences in oil bleeding and rheology for the three greases. Evolution of the friction torque, friction torque hysteresis, and changes in grease rheology were dominated by the oil release property. The latter was determined by the thickener system and its particular response to the conditions imposed by the driving cycle. A quantitative estimate of the carbon footprint from using these greases to lubricate bearings under driving cycle conditions is also presented.
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| 4. |
- Calderon Salmeron, Gabriel, et al.
(author)
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Greases for electric vehicles: a drastic reduction of bearing friction torque by a non-halogenated ionic liquid additive
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Other publication (other academic/artistic)abstract
- Due to their advanced tribological and electric properties, ionic liquids (ILs) are seen as potential lubricant additives in emerging green technologies. To verify their potential in complex machinery, an evaluation of tribological performance at the component and machine level is necessary. This work presents the effect of using a non-halogenated ionic liquid as a grease additive in bearings operating under driving cycle conditions. These harsh conditions are designed to be analogous to what a grease-bearing system must endure in an electric vehicle motor. One-month experiments, equivalent to 23,000 km of vehicle operation, were used to evaluate grease additive performance. Our results reveal that the addition of the ionic liquid resulted in a high-impact improvement, reducing bearing friction losses by up to 45%. Grease rheology and surface wetting measurements indicate that the sharp drop in friction torque is related to a complex balance of factors that results in a limited amount of highly effective lubricant products at the contact inlets (optimum degree of starvation).
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| 5. |
- Calderon Salmeron, Gabriel, et al.
(author)
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Influence of the running-in speed profile on ageing of lithium-complex and polyurea greases in rolling bearings
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Other publication (other academic/artistic)abstract
- The churning phase of a grease-lubricated rolling bearing significantly impacts the ageing of the grease, affecting both bearing performance and service life. The knowledge about the influence of the running-in procedure on grease ageing is limited. In this paper, we studied grease ageing in a ball-bearing running-in process with two additive-free greases made with the same base oil but different thickeners: lithium-complex and polyurea. Rheological characterization of the used greases was performed after two different 48-hour running-in speed profiles. Both procedures employed a step-wise running-in process, either increasing or decreasing speed, while maintaining the same total duration and using the same speeds. The results reveal that grease ageing in the bulk and near the raceway varies significantly depending on the speed profile used and the level of ageing induced by the speed profiles is thickener-dependent. The PU grease exhibits more severe ageing when subjected to a running-in profile with sudden high speeds (decreasing speed profile). Conversely, the LiX grease is more susceptible to ageing during a running-in profile with increasing speeds. The implications of the applicability of these speed profiles in industrial and research applications are also discussed.
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| 6. |
- Calderon Salmeron, Gabriel, 1990-
(author)
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Reduced friction by ionic technology : Grease lubrication of bearings for e-motors
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Reducing the environmental impact of machinery relies on all machinery components operating more efficiently. Rolling element bearings are an indispensable part of all modern machinery, enabling and facilitating machine operation. Greases, an often overlooked machine component, are an essential part of rolling bearings and have the greatest scope for improving the bearing efficiency. Thus, studying the mechanisms of friction generation and energy loss originating from the grease and all of its components in a grease-lubricated bearing is fundamental for further improving their efficiency. This is a challenging task since only fully formulated commercial greases are often available, making it difficult to study in isolation the contribution of each individual component to the friction process. The complexity of studying grease lubrication increases further due to the intricacy of measuring friction within the bearing. Robust methodologies and standards for measuring grease efficiency within a rolling element bearing are scarce and must be developed.This doctoral thesis investigated the effect of different grease components, such as different grease thickeners and a non-halogenated ionic liquid grease additive, on the frictional performance of rolling bearings operating under conditions typical of those encountered in electric motors. This required that a new and robust experimental set-up was designed with the purpose of continuously measuring friction torques from a rolling element for prolonged periods. An evaluation of the role of each of the grease components in the process of friction generation thus became possible. First, the effect of the running-in procedure on the grease ageing was studied. Imposing an increasing speed profile appeared to induce a mild ageing on the greases. In the second and third studies, the effect of different thickeners on the lubrication performance during the bleeding phase was studied under steady-state conditions. Compared to lithium-complex grease, polypropylene grease reduced the energy consumption of the grease-lubricated bearing. A modified polypropylene grease, with recycled polypropylene in the thickener, was also tested. The experiments with the recycled polypropylene grease finished successfully with no traces of bearing damage and friction torque values lying between the lithium complex and polypropylene greases. This represented a milestone in the development of greases with recycled materials. In a fourth study, the effects of three different grease thickeners (lithium complex, polyurea (diurea) and polypropylene) were evaluated on lubrication performance and energy-saving potential during prolonged conditions of transient and variable speeds, typical for electric motors of battery electric vehicles. From the analysis of the resulting friction torques, it was concluded that the thickener influences the friction torque through the process of dynamic bleeding and that friction torques under both steady-state and transient speed conditions were predominantly controlled by rolling friction. In the fifth study, the addition of a non-halogenated ionic liquid to a LiX grease resulted in a drastic 45% reduction of energy dissipation. The feasibility and potential of using this novel grease under e-motor conditions were discussed. Finally, the overall environmental footprint (kg CO2-eq) of a grease-lubricated bearing system was estimated (production of grease and bearing together with energy consumption over a typical service life). Reducing friction torques and their corresponding energy losses through a better design of individual grease formulations appears to ensure that the greatest impact on CO2-eq released can be obtained.
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| 7. |
- de la Presilla, Roman José, et al.
(author)
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Grease lubricity in the fretting contact : Are ionic liquids the solution?
- 2023
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In: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 185, s. 108509-
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Journal article (peer-reviewed)abstract
- A statistical, energy-based approach is employed to experimentally characterize the ability of different greases to reduce friction when a point contact is subjected to repeated reciprocal displacements of smaller magnitude than the contact diameter. This approach allows the assessment of lubricant fretting performance with respect to its ability to remain within the contact and also its boundary lubrication properties. The results indicate that composition-dependent boundary lubrication properties of greases loaded with non-halogenated ionic liquids containing bis(oxalato)borate ([BOB]) and bis(mandelato)borate ([BMB]) anions can result in no detectable wear and low friction, even under conditions of moderately high pressures and where the original contact area is never fully uncovered. This discovery paves the way for the development of anti-fretting ionic greases.
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| 8. |
- Engman, Cecilia, 1974, et al.
(author)
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Probing the influence on folding behavior of structurally conserved core residues in P. aeruginosa apo-azurin.
- 2004
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In: Protein Science. ; 13:10, s. 2706-2715
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Journal article (peer-reviewed)abstract
- The effects on folding kinetics and equilibrium stability of core mutations in the apo-mutant C112S of azurin from Pseudomonas aeruginosa were studied. A number of conserved residues within the cupredoxin family were recognized by sequential alignment as constituting a common hydrophobic core: I7, F15, L33, W48, F110, L50, V95, and V31. Of these, I7, V31, L33, and L50 were mutated for the purpose of obtaining information on the transition state and a potential folding nucleus. In addition, residue V5 in the immediate vicinity of the common core, as well as T52, separate from the core, were mutated as controls. All mutants exhibited a nonlinear dependence of activation free energy of folding on denaturant concentration, although the refolding kinetics of the V31A/C112S mutant indicated that the V31A mutation destabilizes the transition state enough to allow folding via a parallel transition state ensemble. Phi-values could be calculated for three of the six mutants, V31A/C112S, L33A/C112S, and L50A/C112S, and the fractional values of 0.63, 0.33, and 0.50 (respectively) obtained at 0.5 M GdmCl suggest that these residues are important for stabilizing the transition state. Furthermore, a linear dependence of ln k(obs)(H2O) on DeltaG(U-N)(H2O) of the core mutations and the putative involvement of ground-state effects suggest the presence of native-like residual interactions in the denatured state that bias this ensemble toward a folding-competent state.
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| 9. |
- Farré-Lladós, Josep, et al.
(author)
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On the Flow Dynamics of Polymer Greases
- 2022
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In: Lubricants. - : MDPI. - 2075-4442. ; 10:4
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Journal article (peer-reviewed)abstract
- In this paper, the flow dynamics of polymer greases was investigated using micro-particle image velocimetry. Polymer greases have a different thickener structure, compared to widely used lithium-based greases, and they have the well-known ability to release oil. How these properties affect grease deformation and its ability to flow is investigated and compared to the corresponding behavior of a lithium complex grease with the same consistency. Two main tests were carried out, where velocity profiles in a straight channel were measured and analyzed, and velocity evolution during the transition period from a no-flow to a fully-established flow was measured, respectively. It was found that the polymer grease flow dynamics is different from that of the lithium grease. This indicates that the internal structure of the grease and the grease ability to bleed oil have a strong influence on the deformation on a global scale, which in turn entails other lubricating abilities for the two grease types.
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| 10. |
- Glavatskih, Sergei, et al.
(author)
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Grease design strategies for electric vehicles
- 2024
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In: Electric Vehicle Tribology. - : Elsevier BV. ; , s. 225-247
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Book chapter (other academic/artistic)abstract
- With a rapid shift in our society to e-mobility, novel grease formulations for machine efficiency, reliability, and availability are even more important than ever. Greases are expected to provide low friction and noise while extending the machine service life. Whether the grease should be electrically conductive or not remains a subject of debate. The chapter discusses grease architecture and how to tune it in view of the latest and upcoming specification requirements. Selection strategies for base oils, thickeners, and additives are discussed. Integrating these components in the final formulation is a delicate process of balancing required properties that can be contradictory. Grease testing methods are addressed reflecting the need for complementary characterization of grease energy efficiency, conductivity, and protection against fretting. The arguments are made in connection to the representative transmission components.
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