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Friction, wear and surface damage mechanisms of 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)
2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 305, no 1-2, 36-44 p.Article in journal (Refereed) Published
Abstract [en]

Wear and surface degradation mechanisms of a pneumatic clutch actuator have been studied. The applied test method simulates the sliding contact of an anodised aluminium surface against a rubber lip seal and a PTFE guiding ring. The influences of contact load, temperature and particle contamination on wear mechanisms and friction were investigated. A controlled amount of lubrication was applied; both pure silicone grease and silicone grease mixed with standard dust particles were used.

The wear occurring at the tests with only silicone grease is similar, but on a lower scale, to the wear at the tests with a mixture of silicone grease and standard dust. The polishing of the anodised aluminium is increased with increasing temperature or increasing load. The wear of the anodised aluminium surface is more prominent when sliding against the PTFE guiding ring than when sliding against the lip seal. The wear of the guiding ring increases with increasing load or increasing temperature. The lip seal is worn but at 140 °C (with silicone grease or with a mixture of silicone grease and standard dust) or at increased load (with a mixture of silicone grease and standard dust) a thick layer of adhered material is formed.

Place, publisher, year, edition, pages
2013. Vol. 305, no 1-2, 36-44 p.
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-195327DOI: 10.1016/j.wear.2013.05.006ISI: 000341961800005OAI: oai:DiVA.org:uu-195327DiVA: diva2:607548
Available from: 2013-02-24 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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Riddar, FridaKassman Rudolphi, Åsa

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