A thermal resistances-based approach for thermal-elastohydrodynamic calculations in point contacts

Abstract

This article presents a thermal resistances-based approach for solving the thermal-elastohydrodynamic lubrication problem in point contact, taking the lubricant rheology into account. The friction coefficient in the contact is estimated, along with the distribution of both film thickness and temperature. A commercial tribometer is used in order to measure the friction coefficient at a ball-on-disc point contact lubricated with a polyalphaolefin base. These data and other experimental results available in the bibliography are compared to those obtained by using the proposed methodology, and thermal effects are analysed. The new approach shows good accuracy for predicting the friction coefficient and requires less computational cost than full thermal-elastohydrodynamic simulations.

An Analytical Approach for Predicting EHL Friction: Usefulness and Limitations

“…These expressions are derived from the results in reference [57] and they are valid for the whole range of surface velocities. The second increment can be found by considering that in EHL the main mechanism of heat transfer from the lubricant to the surfaces is conduction in the direction normal to the surfaces [5,15]. Thus, a simple heat balance provides the approximate equations that are also included in Table 4 [13,14].…”

“…All tests were performed with a polyalphaolefin (PAO-6) at a bath temperature of 80 • C under fully-flooded conditions. For this lubricant, some viscous properties are given in reference [15]: η 0 = 7.36 mPa•s, α* = 9.0 GPa −1 at 80 • C; and η 0 = 4.78 mPa•s, α* = 8.2 GPa −1 at 100 • C. In addition, according to references [13,14,59], the following values of the powerlaw exponent, shear modulus and thermal conductivity at 80 • C can be taken for the PAO-6: n = 0.81, G = 0.1 MPa and K L = 0.15 W/(mK).…”

“…The authors have also previously developed simplified models for EHL [13][14][15], by means of a completely analytical process of deduction of the friction equations. The methodology includes estimates of the film thickness, the rheology of the lubricant and the temperature of the film according to commonly accepted expressions, which are routinely used under typical EHL operating conditions [16][17][18][19].…”

Los cojinetes de fricción, arquetipo del progreso histórico de la Tribología

“…Por otra parte, la disipación viscosa puede causar un aumento considerable de la temperatura del cojinete [40], lo que hace necesario estudiar los efectos termohidrodinámicos. Esto puede realizarse resolviendo directamente la ecuación de la energía o, equivalentemente, aplicando un elegante método propuesto por Wilson [51,52], el cual está basado en un modelo de resistencias térmicas. El enfoque de Wilson consiste en analizar un elemento diferencial de lubricante entre las superficies en contacto.…”

Individual and combined effects of introducing DLC coating and textured surfaces in lubricated contacts

“…On the other hand, if we assume that all the heat generated in the lubricant is conducted to the contacting surfaces [35], a heat balance for point contact [28] gives the increase of lubricant temperature due to viscous heating…”