Friction and Wear in Automotive Journal Bearings Operating in Today’s Severe Conditions

Abstract

A current trend in the transport sector seeks to increase the vehicle efficiency and to cut fuel consumption which leads to new technologies and advancements in modern and future combustion engines. Some of these technical progresses lead to highly stressed engine parts and new challenges arise, particularly for journal bearings. The increasing thermal and mechanical load caused by downsized and turbocharged engines, friction reduction by employing low-viscosity lubricants and other emission reduction measures-for utilizing stop-start systems-put additional stress on the crankshaft journal bearings. This contribution focuses on highly stressed journal bearings which operate in the boundary, mixed and hydrodynamic lubrication regime. Therefore, measurements on a journal bearing test-rig are performed which allow an extensive verification of the numerical investigation. For the numerical analysis of friction and wear, a mixed elasto-hydrodynamic simulation approach is developed, which considers the elastic deformation of the contacting components, the complex rheological behaviour of the lubricant and metal-metal contact if the lubricant is unable to separate the contacting surfaces. Both the rheological data and the surface roughness parameters are obtained from measurements. The current challenges are studied in four application-oriented examples and the influencing parameters on a reliable friction and wear prediction are explored.

Piston-Pin Rotation and Lubrication

“…Accurately simulating the large range of operating conditions of journal bearings that extend from fully hydrodynamic lubrication to severe mixed lubrication involves many factors. As it is not possible to discuss these in deserved detail here, the authors refer to the original works [16,17], where the specific points are not only discussed in depth, but which also contain the relevant references to previous works. In the following, only a brief discussion of the key points and related references is given for this reason.…”

“…From these results [28], a very simple equivalent-bearing temperature relation was derived for the isothermal EHD-simulation that is consequently able to predict the journal bearing friction losses very accurately for a large range of different lubricants, journal speeds, and loads, as was shown in direct comparison to experimental data (see in particular, [23,24]). A complete and exhaustive discussion of these points is given in two open-access published book chapters [16,17] (the cited book chapters can be downloaded for free at [1]).…”

“…All variants are summarized in Table 3. To describe the physical properties of the lubricant realistically, an extensive rheological model is employed for the description of the 5W30 lubricant (as described by Table 2) in the simulation [16,17].…”

Investigations of the Friction Losses of Different Engine Concepts. Part 1: A Combined Approach for Applying Subassembly-Resolved Friction Loss Analysis on a Modern Passenger-Car Diesel Engine

“…Also, the investigation of friction reduction potentials using low viscosity lubricants as well as the resulting possible risks due to increased mixed lubrication regimes have been conducted in the past using the developed simulation methodology [28,29]. In the following, a short summary is reproduced here for brevity, and for a rather complete overview, we refer to References [30][31][32]. To calculate the journal-bearing friction losses of the engine using the developed simulation approach, a engine model based on the MBS (Multi-body system) AVL Excite Power Unit (AVL EXCITE Power Unit Version 2017.1, AVL List GmbH, Advanced Simulation Technology, Hans-List-Platz 1, 8020 Graz, Austria, www.avl.com.)…”

Friction Reduction Tested for a Downsized Diesel Engine with Low-Viscosity Lubricants Including a Novel Polyalkylene Glycol

“…It is made available specifically for use in combustion engines and features a very high viscosity index (VI) without the necessity to add VI-improving additives. VI-improvers can cause a significant non-Newtonian behaviour [21][22][23][24] of the lubricant. Therefore, a lubricant without these is expected to maintain its high viscosity also in the presence of locally high shear rates, which is an advantage for highly loaded contacts.…”