A Study Of Lubricant Working Condition In The Radial Journal Bearing Based On Ultrasonic Technology

Fluid lubrication film plays a vital role to reduce friction and wear inrelative movement components. When the film between friction pairs is too thin,surface contact would happen,which leadshigh friction and wear. When the lubricant film is too thick,high oil-pumping energy would cost.In order to ensure good lubrication for the moving components and save energy, the thickness of film needs to be controlled effectively. Film thickness measurement is helpful in improving the design of machine elements, and in lubricant condition monitoring. The rupture of lubricant film may lead to the lubricant failure and the componentdestruction, so the measurement of film thickness is very necessary.The use of ultrasound is a non-invasive, safe and portable technique. The ultrasonic equipment is becoming increasingly practical because of the costreduction, and the popularization of pulsing and digitizing equipment. As the ultrasonic wave properties are often dependent on the host medium, ultrasound technology is a very suitable tool to monitor the properties of lubricant films. The technology works by monitoring the portion of a wave reflected back from the lubricant layer. The technology is still in its infancy and has not been widely used due to the lack of calibration, testing and validation.Much work needs to be done for this technology in film thickness measurement.In this paper, high frequency ultrasound is used successfully in measuring the film thickness and the effect of lubricant cavitations in the contact of a radial journal bearing.This paper conducts contributions by simplifying the testing system, decreasing the cost of measurement and enhancing efficiency, the results lay the foundation for on-board measurement of film thickness in a running engine. It also provides the theoretical basis for other furtherresearch, especially inradial journal bearing design and lubricant selection. It is very important that the understanding about the operational regime of the lubricant can promote better decisions of the maintenance period and decrease the financial loss caused by lubricant failure.In this paper, the ultrasonic sensor is mounted inside of the journal and rotating together with axle. The sensor location is decided to suit the measurement of transient film thickness in radial journal bearings. The bear piezoelectric element is chosen according to its position in the radial journal bearing rig and the size of the rig. The frequency is decided based on the distance between the lubricant and the piezoelectric element. A slip ring is used in the circuit to connect the rotating sensor with the stationary power supply. The control software is built by Labview. A spring model is used to calculate the film thickness bythe reflection coefficient. Different testbedsare designed to measure the parameters associated with the spring model. A special test bed is used to study the effect of temperature. The test bed is built and its reliabilityis validated before the measurement. The effect of the load, the rotating speed and the temperature on transient film thickness and cavitations are studied. And, theprognosis for the failure of radial journal bearings is done.The results show that the acoustic technology is very effective and reliable for measuring film thickness. Due to the limitation of ultrasonic wavelength, the film thickness measurement technique, which combines acoustic technology and spring model, is only useful for measuring film thickness in the level of micrometers. With the increase of temperature, the ultrasonic pulse generated by the sensor is decreasing linearly. The increase of load and temperature and the decrease of the rotating speed of radial journal bearing rig may lead to the descent of minimum film thickness and the ascent of the cavitations effect.