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Lubricant ageing effects on wet clutch friction characteristics
2008 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Somewhere in the transmission of vehicles today, a wet clutch can often be found. Characteristic of this type of clutch is that they operate under lubricated working conditions. In earlier research, friction characteristics and performance of wet clutches have been well investigated by several authors. Studies have also been made in order to understand the ageing of wet clutches. However, most lifetime studies have been made for systems with paperbased friction discs and systems involving sintered bronze friction discs remain unexplored. Friction discs of sintered bronze is used in the Haldex limited slip coupling (LSC), an all-wheel drive system used in cars from many different manufacturers. In order to get a better understanding of how this system can change over time, the study in this master thesis is focused on how frictional performance is affected by oxidation of lubricant, testrig ageing and additive content. This work has been conducted in cooperation with Haldex Traction in Landskrona and Statoil Lubricants in Nynäshamn. The oxidation effects on friction performance was examined using a modified dry-TOST (Waterless Turbine Oil Oxidation Stability Test) on a fully formulated lubricant. The oxidation time period was divided into five steps from 48 hours to 408h and for each level of oxidation, a friction performance test was run using a pin on disc machine. Also an oil aged in a clutch disc testrig was tested for friction performance. The test is constructed in order to verify that an oil- friction disc combination will last the lifetime of the specific application. Since lubricant additives are vital to the performance of wet clutches the effect of reducing the additive concentration in the oil was also studied, in the range 10 to 100% of the standard additive formulation. Results showed that a general friction increase can be seen for oxidation, additive reduction and testrig ageing. Lubricant aged in testrig shows significantly different friction characteristics with temperature than lubricants aged by dry-TOST implying that dry-TOST alone is not a sufficient method to evaluate lubricant ageing. Further research has to be made in order to understand the ageing of wet clutches. A better understanding of which mechanisms that are responsible for the decomposition of a lubricant in a wet clutch system such as the Haldex LSC is needed. This thesis has focused on lubricant ageing but no attention has been paid to wear and ageing of friction discs. To investigate and relate ageing of lubricant and friction discs is another important task for future research.

Place, publisher, year, edition, pages
Keyword [en]
Physics Chemistry Maths, Wet clutches, friction, oxidation, tribology
Keyword [sv]
Fysik, Kemi, Matematik
URN: urn:nbn:se:ltu:diva-54343ISRN: LTU-EX--08/152--SELocal ID: b4ab72d4-f641-462e-9173-620113cf4a37OAI: diva2:1027724
Subject / course
Student thesis, at least 30 credits
Educational program
Mechanical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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