1,720,998 research outputs found
EHL-squeeze at pin-pulley interface in CVTs: Influence of lubricant rheology
No full textIn this paper we analyze the influence of fluid rheology on the strongly non-stationary squeeze process of an oil film sandwiched between the chain-pin and pulley in continuously variable transmission. As recently demonstrated [Carbone G, Scaraggi M, Soria L. The lubrication regime at pin-pulley interface in chain CVT transmissions. ASME Journal of Mechanical Design 2009;131(1)], the spatial pressure distribution is characterized by a non-central annular pressure peak, which first appears in the external region of the contact region and moves toward the center of the pin with rapidly decreasing speed. In this paper we show that the non-Newtonian viscoelastic rheology of the lubricant plays a crucial role in determining the actual value of pressure peaks and leads to a strong reduction of such pressure spikes in comparison to a perfect Newtonian lubricant. Even more, if the threshold value of shear stress τl, which characterizes the transition from Newtonian to non-Newtonian behavior of the lubricant, is sufficiently small the annular pressure peak may even disappear. In this case the squeeze process occurs faster, the film thickness distribution is reduced and the lubricant may not be able to avoid direct asperity contact between the two approaching surface
Transition from elastohydrodynamic to mixed lubrication in highly loaded squeeze contacts
No full text
Mixed Lubrication in High Loaded Squeeze Contact
No full textWe analyze the influence of surfaces roughness on the strongly non-stationary squeeze process of an oil film sandwiched between the chain-pin and the pulley in continuously variable transmissions. As recently demonstrated for a Newtonian oil in the elasto-hydrodynamic conditions [G. Carbone, M. Scaraggi, L. Soria, ASME Journal of Mechanical Design, 131 (1), 2009], the spatial fluid pressure distribution is characterized by a non-central annular peak, which firstly appears in the outer region of the contact domain and moves toward the center of the pin with rapidly decreasing speed. In particular, an high-viscosity oil central dimple is generated, which is able to keep separated the solid surfaces, avoiding direct metal-metal interactions for typical pin-pulley travelling time of 0.01s. In this work we include in the lubrication model the interactions between asperities of randomly rough surfaces, adopting as solid contact model the Persson's mean field contact theory. We show that the coupling between oil rheology and surface roughness determines a wide range of lubrication conditions for high-pressure squeeze contacts. In particular we find that increasing the surface roughness anticipates the transition time at which the lubrication regime changes from a fully lubricated to a mixed lubricated regime. The knowledge of such peculiar behaviour is of fundamental importance to determine the pin-pulley frictional and wear properties
Elastic contact of rough surfaces: A simple criterion to make 2D isotropic roughness equivalent to 1D one
No full textWe analyze the periodic contact between an elastic half-space and two types of rough substrates: (i) a perfect isotropically rough rigid substrate (2D isotropic roughness), and (ii) a perfect anisotropically rough rigid substrate, i.e. a substrate with roughness in only one direction (1D roughness). The analysis is carried out with the aid of proprietary codes, that we have developed (both in real and Fourier space) to deal with this type of contacts. Of course, 1D contacts differ from 2D isotropic contacts. However, our results and theoretical arguments suggest a possible criterion to make 2D contacts equivalent to 1D ones from the point of view of contact area and separation calculations. The rule consists in replacing the 2D power spectral density (PSD) of the isotropic surface into an equivalent 1D PSD. Interestingly the transformation rule does not depend on the statistical properties of the surface roughness, hence seems to have a universal character for isotropic surfaces. © 2012 Elsevier B.V
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