The effect of skew angle in thermoelastohydrodynamic spinning contacts
Abstract
Studies on the dynamical behaviour of rolling element bearings show that the position as well as the loading of the flange roller-end contact depends on the momentum created on the roller track cause by local friction variability. This situation is characterized by a skew angle. The investigations described in this paper intend to propose a better understanding of the physical phenomena occurring in spinning contacts under skewing. Experimental investigation is done in a unique test rig called TRIBOGYR, dedicated to large size-contacts with spinning kinematics, which allows both film thickness and friction measurement. In the meantime, a numerical analysis is lead, based on a Finite Element software, aiming to take into account the multiphysics aspect of this thermoelastohydrodynamic contact. Longitudinal and transverse friction as well as power losses are both measured and computed as a function of the kinematics conditions imposed to the contact. When the skew increases, the transverse power losses increases due to the new orientation of the velocity field over the contact surfaces. The overall magnitude of the velocity field increases to match the kinematics imposed by the skew and as a consequence temperature elevation occurs. The shearing induced by the transverse component of the velocity impacts the viscosity and thus the longitudinal slide power losses as well as the spin power losses. Variations of viscosity are explained by both shear and thermal thinning. When the skew angle is large enough, both experimental and numerical analysis show the formation of a dimple (local increase of film thickness inside the contact area) caused by a viscosity gradient due to high shear in the transverse direction.