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Legislation aimed at reducing carbon dioxide emissions is forcing significant changes in passenger car engine hardware and lubricants. Reduced viscosity lubricants can reduce friction levels and are therefore helpful to manufacturers seeking legislative compliance. MAHLE and Shell have worked together to determine the crankshaft, bearing and lubricant combination which minimizes friction with an acceptable level of durability. This paper describes the results of our joint simulation studies. MAHLE Engine Systems have developed in-house simulation packages to predict bearing lubrication performance. SABRE-M is a “routine” simulation tool based on the mobility method [1] curve fitting from the finite bearing theory to simulate the hydrodynamic lubrication in steady-state conditions. Whereas, SABRE-TEHL is a specialized simulation package used for performing Thermo-Elasto-Hydrodynamic Lubrication (TEHL) analysis of bearing systems.

Worldwide emissions standards are becoming increasingly rigorous, and this leads to more complex engine demands. Several new PCU (Power Cell Unit) technologies are being applied to cope with these demands. This means engine parameters are changing, e.g. higher EGR (Exhaust Gas Recirculation) rates, higher PCP (Peak Cylinder Pressure), lower viscosity oils, higher oil contamination and soot. Therefore the operating conditions for the bearings have drastically changed, leading to an environment prone to seizure occurrences. There is a clear demand for seizure resistant bearings motivated mainly by the increased engine complexity described above. Therefore for HDD (Heavy Duty Diesel) applications the PCU robustness should not be compromised also in terms of wear and fatigue resistance. The polymeric coating developed by MAHLE was applied over a sputtered layer and has demonstrated to be a suitable solution to attend to the application demands.

The reduction of oil demand for automotive engines has been driven recently by the need to reduce oil pump capacity so that benefits from having a smaller size, including a reduction in power loss and CO₂ emissions. Crankshaft bearings are generally attributed to be the largest consumers, main bearings in particular since the supply pressure in the upper bearing shell oil groove over a large arc (circumferentially) coincides with high average clearance. Measurements of oil flow indicate that the main bearing groove is significant and there is a trade-off between lower oil flow and higher bearing temperatures. All solutions must ensure that the oil supply to the big-end bearings via crank drillings is not compromised. Numerical simulation tools can be used to predict and optimize the total oil flow required by the engine lubrication system. In this work, the Elasto-Hydrodynamics Simulation (EHL) was used to analyze the oil flow required by the crankshaft main bearings.

The coupled EHL analysis of the small-end and the piston-pin boss are carried out using a technique of successive iteration. The pin is free to rotate in both the small-end and the pin-boss. The total frictional torque is used to calculate the angular velocity of the pin. After obtaining a converged solution of pin rotation, a wear simulation is performed by carrying out an additional set of EHL analysis. Results show that the pin rotational velocity is insignificant which suggests that the EHL performance of the small-end is satisfactory. Since it is the friction between small-end bush and the pin that drives the pin to move, less pin rotation is an indication of good lubrication in the small-end interface. Hence, the technique outlined is a useful tool for establishing that the small-end/pin-boss lubrication conditions are sufficient, or when more harsh conditions are encountered, helping to optimize the design.

This paper attempts to address the limitations of quasi-static elastohydrodynamic (EHD) bearing lubrication analysis where the structural inertia of the distributed rod mass is neglected. A procedure is outlined where the big-end bearing distortions due to the structural inertia are pre-calculated using the finite element (FE) method and then included in a subsequent EHD analysis via a dynamic deformation file. The effect on results in terms of oil film thickness and pressure are investigated for a 2.0L gasoline engine. A validation is presented showing good comparison of the EHD bore shape with an instrumented engine test and also a full dynamic FE model. The conclusion is made that distributed inertia effects become significant above 3000rpm and that the outlined method is valid for including such effects.

Use of lighter or compact reciprocating engine components has always been a desirable target for engine designers. Small savings in mass and dimensions here can result in significant benefits such as a reduction in total engine packaging dimensions and weight. A theoretical study of design parameters was carried out using the SABRE software programme developed by Glacier Vandervell Bearings. The results suggested that housing conformability can be favourable when applied to the cap for inertia loads but potentially detrimental when applied to the stem/big end blend. The results of a development and engine testing programme gave total rod weight savings of over 45% as compared to an existing best-in-class design.

For gasoline engines, high speed operation can often be critical for the durability and survival of big-end bearings. When the engine bearings are at the limit of the operating envelope, it is often useful to know the sensitivity of the bearing performance to various options available to the designer. In this paper, a four cylinder big-end bearing operating at 8,000 and 10,000rpm was taken as a reference for demonstrating the calculated changes in bearing performance. The “SABRE” elasto-hydrodynamic software was used for the predictions which included the effect of the “fitting” of the bearing shells and flexibility of the crank and rod.

As engine bearings are subjected to higher loading, the oil film thickness in the loading carrying region becomes thinner and thinner. Under the regime of elastohydrodynamic lubrication (EHL), the differences in the elastic deflection of the bearing/journal along axial direction are shown to have significant influence on the bearing performance. The work reported in this paper made use of SABRE-EHL, a predictive tool developed for the study of automotive engine bearings. The influence of axial profile was firstly investigated by the examination of the operating conditions of both the big-end and main bearings of an modern petrol engine. The investigation was then extended to include a sensitivity study, where different types of axial profile were investigated. The impact of these axial profiles on engine bearing performance was then assessed.

With the continuous demand to squeeze more performance from critical engine components such as crankshaft bearings, design analysis and calculations methods are also required to become more comprehensive. With the advent of Elasto Hydrodynamic Lubrication (EHL) methods, for example, designers could investigate theoretically the effects of housing geometry or stiffness on bearing performance; which was previously not possible with rigid bearing (mobility method) calculations. Traditional methods for EHL analyses of crankshaft bearings normally incorporate the elasticity of the connecting rod or housing but assume that the crankpin is rigid. This paper demonstrates the effects of including the flexibility of the crankshaft journal (up to the adjacent main bearing) for three examples of connecting rod bearings. The examples cover a typical Formula 1 (F1) racing engine at 16000rpm, an automotive gasoline engine at 5500rpm and a 120mm journal diameter diesel engine at 2000rpm.