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The effect of lubrication on the friction performance in pneumatic clutch actuators
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribologi)
2014 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 309, no 1-2, 166-173 p.Article in journal (Refereed) Published
Abstract [en]

Pneumatic clutch actuators in trucks transform the force applied on the clutch pedal into the force acting on the clutch. The actuator consists of an anodised aluminium cylinder in which a piston, with a rubber lip seal and a PTFE guiding ring mounted on it, slides. The system is lubricated with silicone grease before assembly. Wear of the lip seal will lead to a deteriorated sealing capacity, and ultimately failure.

A test setup is used to evaluate the effect of silicone grease amount on friction performance, PTFE transfer and rubber lip seal wear. Reciprocating sliding and vibration tests were performed. The surfaces of cylinders, guiding rings and lip seals were studied by SEM and ESCA.

The friction level is highly dependent on the amount of grease in the contact area. During sliding, grease is pushed out from or dragged into the contact area, resulting in a fluctuating friction. Furthermore, even with grease lubrication, PTFE transfer to the aluminium surface occurs. A triple transfer from guiding ring, to aluminium surface, to lip seal, to another part of the aluminium surface was observed. Finally, although the unstable lubricating effect, it was found that the grease protects the lip seal from wear.

Place, publisher, year, edition, pages
2014. Vol. 309, no 1-2, 166-173 p.
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-195328DOI: 10.1016/j.wear.2013.11.005ISI: 000331426700021OAI: oai:DiVA.org:uu-195328DiVA: diva2:607711
Available from: 2013-02-25 Created: 2013-02-24 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Tribological Aspects of Pneumatic Clutch Actuators
Open this publication in new window or tab >>Tribological Aspects of Pneumatic Clutch Actuators
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A clutch actuator is used in a vehicle to transmit movement and force from the clutch pedal to the release bearing of the clutch. A pneumatic clutch actuator consists of an anodised aluminium cylinder, inside of which a piston, with a rubber lip seal and a PTFE guiding ring, slides. The system is lubricated with silicone grease before assembly. A commercial clutch actuator of this type, has a service life of 3 million actuations and must function in a wide temperature range, from -40 ºC to 140 ºC.

In this thesis, the complex tribological system of pneumatic clutch actuators has been studied. Field worn actuators have been disassembled and investigated. A laboratory test method has been developed to understand the tribomechanisms present in pneumatic clutch actuators. The test method's capability of simulating the real contact has been verified, by the comparison with studied actuators from the field. The influence of contact parameters: temperature, load, lubrication and particle contamination, has been investigated. In addition, different anodised aluminium surfaces have been studied.

The manufacturing method of the aluminium cylinder influences surface topography and structure of the oxide, resulting in different mechanical and frictional properties.

The wear during tests with only silicone grease is reminiscent, but on a lower scale, to the wear during tests with a mixture of silicone grease and standard dust.

The initially applied amount of silicone grease is not important, the friction seems to depend on the amount of silicone grease that is dragged into or pushed out from the contact area during testing. Silicone grease lubrication reduces wear of the lip seal. However, during some tests, an adhesive layer, composed of  grease residuals and some PTFE, was formed on the lip.

A triple PTFE transfer, from guiding ring to aluminium surface, to lip seal, to aluminium surface, occurred. Such transfer of material from the PTFE guiding ring was detected from the unlubricated tests, and also from the silicone grease lubricated tests, i.e. silicone grease lubrication does not prevent PTFE material transfer.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1021
Keyword
Wear, friction, PTFE transfer, anodised aluminium, NBR rubber lip seal, silicone grease, casting, extrusion
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-195330 (URN)978-91-554-8601-3 (ISBN)
Public defence
2013-04-12, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2013-03-20 Created: 2013-02-24 Last updated: 2013-04-17Bibliographically approved

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Publisher's full texthttp://www.sciencedirect.com/science/article/pii/S0043164813005401

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Riddar, FridaKassman Rudolphi, Åsa

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