تجزیه و تحلیل عملکرد از یاطاقان های ژورنال با استفاده از بازتاب مافوق صوت

One method that shows potential for non-invasive oil film measurement is the use of ultrasonic reflection. In the current work, ultrasonic transducer is coupled to the outside of a bearing and a wave transmitted through the bearing shell. The wave is partially reflected when it strikes an oil film. Experiments were conducted to study ultrasonic reflection coefficient technique in plain journal bearing. Measurements of multiple reflection coefficients were recorded and used to map the viscosity profiles, oil-film thickness and bearing cavitation. In addition, an alternative method using the reflection coefficient phase from film thickness measurement was used for verification. The results revealed that the evaluation of phase method is slightly lower compared to that of the amplitude method. The film thickness profile obtained in the converging region agreed well with classical hydrodynamic predictions.

In journal bearings applications, viscosity is the most important property of the lubricant that affects bearing performance. Measurement of fluid viscosity in bulk is easy with different types of viscometer. Due to the limitation of utilising these devices to measure the lubricant viscosity inside the journal bearing where the lubricant exist in a very thin layer, however, other techniques are required to be applied to measure viscosity inside journal bearings. Ultrasonic approach is a non-conventional approach which is to measure the fluid viscosity. Greenwood and Bamberger [1] reported the use of shear wave reflection at the solid-fluid interface for online measurement of viscosity but the approach has not been extended to measure the viscosity in plain bearings. In recent work, Kasolang and Dwyer-Joyce [2] measured the viscosity in thin layers between parallel plates by using shear reflection coefficient. There have been many studies found in the literature related to ultrasonic reflection coefficient measurement [3], [4], [5] and [6]. They used ultrasonic reflection coefficient technique to conduct tribological studies on coating materials and measurements of their properties. Maintaining an adequate film thickness around the journal circumferences at all times have been the main concern in tribological community [7]. Thin film is produced due to the pressure build-up between the journal and bearing shell. Fluid film bearings rely on the formation of relatively thick film between the journal and the bush, it occurs when opposing bearing surfaces are completely separated by a lubricant film. A number of methods to monitor the performance of plain bearings have been developed in the past and their differences essentially lie in the choice of the monitoring parameter such as lubricant contamination, vibration, temperature, friction and wear [8], [9], [10], [11] and [12]. One method that shows potential control of hydrodynamic journal bearings based on oil-film thickness measurement is suggested by Roy Chowdhury [13]. The proposed method monitors the journal bearing so that an adequate film thickness is maintained at all times as this is desired. However, this technique is useful commonly in industrial applications especially in large installations such as power plants, rolling mills etc. Moreover, the displacement sensor has a much lower accuracy. It can only measure movement of the journal in one direction. It cannot accommodate deflection of the bearing (which occurs in most automotive type journal bearings). Also ultrasound can measure down to smaller film thicknesses (as low as 100 nm)—beyond the resolution of displacement sensors. Chapkov et al. [14] developed a point contact model to predict the film thickness incorporating a shear-thinning rheological model. The model is applicable solely for elastohydrodynamic lubrication in rolling bearings. Glavatskih et al. [15] developed an eddy current transducer with an active compensation for changes in sensor temperature to simultaneous monitoring oil film thickness and temperature in bearings. Of late, techniques for local oil film thickness measurement in bearings suffer from serious drawbacks. According to a comprehensive review done by Dwyer-Joyce [16], one method that shows potential for non-invasive oil film measurement without extensive modification to the components is the use of ultrasonic technique. Thus, in the present study, ultrasonic measurements of multiple reflection coefficients are extended to a practical application in a journal bearing. The reflection data is used threefold; firstly to determine the viscosity, secondly to monitor the film thickness profile; and thirdly to observe the bearing cavitation. Static measurements of shear reflection coefficients are carried out at several locations around the journal bearing. Thereafter, the amplitude reflection coefficient data were converted to viscosity values and compared with an earlier work done by Kasolang et al. [17]. The oil film thickness was determined from both the amplitude and the phase of the reflected signal. These two approaches were then compared with a theoretical solution.

Ultrasonic reflection coefficient means to monitor the thin-film behaviour around the hydrodynamic journal bearing circumference is reported. The results presented in terms of viscosity, film thickness and bearing cavitation based on multiple reflection coefficients. Results reveal that the phase of reflection coefficient can be used to determine the oil film thickness. The phase method is recommended for thinner films with lower Sommerfeld numbers and the amplitude method for thicker films with higher Sommerfeld numbers. The experimental values of amplitude and phase thickness are closer to the predicted values of the theoretical solution in the region from 5 to 15 mi. In general, the ultrasonic method has some significant advantages over electrical and optical based methods. It can be safely said that the amount of understanding and knowledge is still at the early stage and much research is necessary to fully establish the concepts of ultrasonic techniques with various journal bearings parameters. However, in order to qualify as the next generation of ultrasonic technique in journal bearing investigation, many other aspects still need to be examined in detail.