Thermal analysis of elastohydrodynamic contacts

Tribology as the science of lubrication, friction and wear represents an interdisciplinary research field on different scales. Highly loaded lubricated rolling-sliding contacts of machine elements such as gears or roller bearings are important tribosystems and are classified as thermal elastohydrodynamically lubricated (TEHL) contacts due to their major physical basis. Besides the fluid film formed between the rolling elements and stresses in lubricant and materials, the local temperature strongly determines power losses and lifetime as a result of friction. As TEHL contacts and their thermal response are very small in space and time, this work focuses on the numerical investigation of influencing factors and effects of local temperature as a thermodynamic state variable and as a result of heat generation and heat flux. A comprehensive calculation study on the basic influences of lubricant and material properties as well as on selected model and gear contacts shows general correlations between operating conditions and lubricant and material properties in TEHL contacts. For example, flank areas of gears with negative specific sliding feature highest surface temperatures due to inhibited advective heat transfer within pinion or wheel. A detailed analysis of heat generation and heat flux contribute to the establishment of a thermal network for TEHL contacts based on thermal resistances gained from TEHL calculations. This thermal network can contribute to an efficient and accurate representation of local temperature and can be included in thermal networks of gearboxes.