【作者】

Martin Offenbecher

【摘要】

该论文已在赫尔辛基举行的第28届CIMAC大会上发表，论文的版权归CIMAC所有。ABSTRACT Since many years the reduction of emissions has been one of the major drivers of combustion engine design. After the implementation of Euro 6, IMO Tier III and various other local emission standards, now the focus lies on fuel efficiency and reduction of CO2 emissions. In the recent years, the engine operation conditions have been studied intensively and start-stop operation has been widely introduced to passenger car engines to further contribute to a further reduction of fuel consumption. This trend is now rolled out to larger engines and subject of further studies. However, CO2 emissions and fuel efficiency are linked and directly influenced by the internal friction of the combustion engine. Among other, a major part of this internal friction is coming from the crank train system, with all its mechanical and tribo-chemical interactions. Additionally to the engine operating conditions like full load, idle and start-stop, there are several factors influencing the internal friction of this tribo-system. Design factors like the number and width of bearings have a major influence on the potential reduction of friction. However, also the used lubricant viscosity and its interaction with the bearing surface influence the total friction of the crank train. The current trend towards reduced oil viscosity is reducing the hydrodynamic friction significantly, but also leads to an increasing share of mixed friction running conditions. These changed operating conditions may result in extreme cases in increased friction instead of a friction reduction, and together with the above described trend and more startstop cycles it may also result in a reduced bearing life. In order to fulfill the demands of the latest emission legislations there is a trend to low SAPS lubricant formulations (LowSAPS: lubricants containing low levels of sulphated ash, phosphorus and sulphur). The combination of the two trends in lubricant formulation, low SAPS and low viscosity, additionally seems to reduce the tribologic robustness of a journal bearing system. For a holistic picture on the potential of friction reduction in the crank train is not enough to look only on changing crank train design, operation conditions and oil viscosity. Additionally there will be a deeper focus on tribologic effects on friction reduction and lifetime of components. In this paper the amount of potential friction reduction based on simulation as a function of different operating conditions will be estimated. In the well-known ring-on disc tribotest set-up the mixed friction behavior of several bearing surfaces, like AlSn sputter bearings, polymer coated bearings and AlSn bimetal bearings and their tribo-chemical interactions with latest generation low viscosity, low SAPS lubricants will be compared. Additionally, we will introduce a new test set-up to show the tribologic interactions between bearing materials and lubricants also in the hydrodynamic regime. This new test set-up is an excellent complement to a deeper understanding of the tribo-chemical interactions of the crank train system, allowing the holistic estimation of the friction reduction potential of low viscosity, low SAPS oils together with lifetime estimations of the bearings. Finally, a new robust, start-stop capable low friction bearing material, which is able to maintain excellent bearing lifetime also under severe lubricant conditions will be introduced.

【会议名称】

第28届CIMAC会议

【会议地点】

芬兰 赫尔辛基

【下载次数】

3

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