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Investigations for enhanced tribological performance of a hydraulic motor
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A radial piston hydraulic motor has several components that encounter sliding orrolling motion under lubricated conditions. When a hydrostatic, hydrodynamic orelastohydrodynamic oil film separates the interacting surfaces, the wear and frictionare low provided of course the hydraulic fluid is free from the presence ofcontaminants. Mixed lubrication may occur even at relatively high speed when usinglow viscosity fluids and may result in increased friction which adversely affects theoperating efficiency of the hydraulic motor. Additionally, the increased heataccumulation at different interfaces of the motor under extreme operating conditionsinvolving high pressures, high speeds and low viscosities can also lead to unstoppablethermal process resulting in seizure. At low speeds, different tribological pairs operatein boundary lubrication regime and are prone to wear. The associated high friction canalso result in low starting efficiency.The research work reported here has thus focussed on addressing the above mentionedquestions so as to improve understanding of the tribological phenomena and find waysfor improving and alleviating hydraulic motor tribological components.The results have shown that it is possible to reduce both the boundary friction and thelift-off speed through proper choice of surface modification methods and theirapplication on motor components.The running-in aspect is also very important for the satisfactory tribologicalperformance of the motor. An optimal running-in can improve surface roughness andconformity of motor components. The studies have shown that the use of DLC andphosphate coatings can be effective in accomplishing these. It may however also bekept in mind that during the initial sliding (running-in) the machine components aresusceptible to wear and roughening of the surfaces. The conformity and roughness ofthe surfaces of the sliding components are important for the lift-off speed and this alsoinfluences both the seizure resistance and overall efficiency of the motor. Threeprocesses give rise to the occurrence of seizure in a hydraulic motor and these havebeen identified as: friction heat generation during operation in mixed lubricationregime, friction heat generation during operation in full film lubrication regime andentrapment of wear particles between sliding surfaces. The initiation of scuffing on alocal scale has been found to be dependent on interface temperature rather than on thepv-value.There are several polymeric materials that are suitable for journal bearing applicationsin hydraulic motors. The PTFE based polymeric materials have the potential to reducebreak away friction by an order of magnitude. However, after running-in at 100 MPacontact pressure their low coefficients of friction have been found to increase.The simulation of a hybrid journal bearing including influence of surface roughnesshas shown good correlation with practical measurements in component test rig inlubrication regime ranging from full film down to boundary lubrication.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2011.
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Research subject
Machine Elements
URN: urn:nbn:se:ltu:diva-16985Local ID: 106b8fe2-067d-43bb-b5e1-32bb80c9fc84ISBN: 978-91-7439-311-8OAI: diva2:989977
Godkänd; 2011; 20110915 (dannil); DISPUTATION Ämnesområde: Maskinelement/Machine Elements Opponent: Professor Friedrich Franek, Dept Microsystem Technology, Institute of Sensor and Actuator Systems, Vienna University of Technology, Wiener Neustadt, Austria Ordförande: Professor Braham Prakash, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå Tid: Torsdag den 20 oktober 2011, kl 09.30 Plats: E231, Luleå tekniska universitetAvailable from: 2016-09-29 Created: 2016-09-29Bibliographically approved

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