Clutch actuators are used in trucks to convert the travel and the force applied by the driver to the clutch. A pneumatic actuator consists of a piston that slides inside a cylinder in an axial back- and forward motion. The pneumatic cylinder is sealed off by a lip seal of rubber that is mounted, together with a guiding ring of PTFE, on the piston. The system is lubricated with silicon grease before assembly. Wear of the lip seal will lead to a deteriorated sealing capacity, i.e. leakage and ultimately failure. Aluminium clutch actuators that have been employed in trucks, have been investigated. The surfaces of the inside of the aluminium cylinders, of the lip seals and of the guiding rings have been studied by SEM and optical microscopy. For most of the actuators no significant wear was revealed. However, one actuator, with leakage problems, was severely worn. An extensive amount of scratches was seen on the cylinder surface, the thickness of the guiding ring had decreased and large parts were missing from the lip seal. A possible explanation is that particles have entered the system thus altering the contact conditions. The particles become embedded in the lip seal and guiding ring, and scratched the cylinder surface. The then rougher cylinder surface will cause wear of lip seal and guiding ring upon further sliding. When the wear debris reaches a high enough amount they will obstruct the lubrication, and the guiding ring will be worn by adhesion and the lip seal by roll formation. A test setup was developed to investigate how particles present in the system affect the wear. A part of the piston, with lip seal and guiding ring mounted on it, slides against a part of the aluminium cylinder in a back- and forward motion. After tests lubricated with silicon grease the aluminium surfaces displayed no wear. If dust particles were added the situation changed. Distinct scratches were visible on the aluminium surface and embedded particles could be seen in the guiding ring and the lip seal. These tests provide results in good agreement with the wear revealed in the investigations of used actuators and support the theory that wear is caused by particles entering the system.


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    Titel :

    On the wear of pneumatic clutch actuators


    Beteiligte:
    Riddar, F. (Autor:in) / Rudolphi, Kassman A. (Autor:in) / Hogmark, S. (Autor:in)


    Erscheinungsdatum :

    2008


    Format / Umfang :

    19 Seiten, 16 Bilder, 3 Tabellen, 8 Quellen



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Datenträger


    Sprache :

    Englisch




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