《A Method for the Measurement of Hydrodynamic Oil Films Using Ultrasonic Reflection》.pdf

Tribology Letters, Vol. 17, No. 2, August 2004 ( 2004) 337 A method for the measurement of hydrodynamic oil films using ultrasonic reflection R.S. Dwyer-Joycea, , P. Harpera and B.W. Drinkwaterb aDepartment of Mechanical Engineering, Mappin Street, University of Sheffield, Sheffield S1 3JD, UK bDepartment of Mechanical Engineering, University Walk, University of Bristol, Bristol BS8 1TR, UK Received 23 November, 2003; accepted 23 January, 2004 The measurement of the thickness of an oil film in a lubricated component is essential information for performance moni- toring and control. In this work, a new method for oil film thickness measurement, based on the reflection of ultrasound, is evaluated for use in fluid film journal bearing applications. An ultrasonic wave will be partially reflected when it strikes a thin layer between two solid media. The proportion of the wave reflected depends on the thickness of the layer and its acoustic properties. A simple quasi-static spring model shows how the reflection depends on the stiffness of the layer alone. This method has been first evaluated using flat plates separated by a film of oil, and then used in the measurement of oil films in a hydrody- namic journal bearing. A transducer is mounted on the outside of the journal and a pulse propagated through the shell. The pulse is reflected back at the oil film and received by the same transducer. The amplitude of the reflected wave is processed in the frequency domain. The spring model is then used to determine the oil film stiffn