Experimental And Mechanism Research On Random Oil Film Cavitation Noise In Dynamically Loaded Journal Bearings

Aiming at the problem that a small number of high-power vehicle engines discovered by Ford Motor Company may produce random noises which are similar to typewriter noises when running at neutral idle speed,firstly,the random cavitation noise of parallel plate squeeze oil film is experimental and theoretical researched based on the dynamic load effect which has the important impact on cavitation in this paper.Besides,the random cavitation noise of the dynamic journal bearing considering the shear effect is studyed.The main research contents and results are as follows:The parallel plate squeeze oil film noise testing apparatus that can realize the simultaneous acquisition of sound pressure,displacement,vibration,force and images of cavitation is used to study the influence of signal waveform,oil level height,inclination angle between two plates,oscialltory frequency,lubricant viscosity and temperature on the cavitation noise.At the same time,in order to reduce the cavitation noise of parallel plate squeeze oil film,based on the noise reduction effect of the carbon black(77.24 %),the effect of the porous aluminosilicate and the non-oil-soluble phosphor on the cavitation noise is studied.The results show that they also have the effect of reducing the cavitation noise of parallel plate squeeze oil film due to their porous particle structure similar to that of carbon black particle,with an average noise reduction rate of 82.06 % and 75.86 %.And when they are mixed with equal mass,the composite additive obtained has a better noise reduction effect,with an average noise reduction rate of 90.01 %.In view of the phenomena observed in the experiments,the hypothesis of uniform distribution of cavitation nuclei in the oil film is proposed,and the spherical bubble dynamics equation is introduced.According to the actual situation of the oil film in two parallel plates,it was limited to visible columnar cavitation.On this basis,the ReynoldsRayleight-Plesset-Scriven model(RRPS model)which coupled bubble dynamics and hydrodynamic lubrication theory is proposed for the parallel plate squeeze oil film.By comparing the calculated results with model and experimental results in literature,it is found that RRPS model can accurately predict the pressure change of oil film in oscialltory parallel plate.The RRPS model is verified again by the collected images of cavitation in experiments.The experimental results show that RRPS model can predict the generation,development and the maximum area of cavitation in oil film accurately.Based on it,the influence of surface dilatational viscosity,initial cavitation nuclei radius and the number of bubbles per unit volume on the pressure and cavitation area are analyzed.The results show that increasing the lubricant surface dilatational viscosity and reducing the initial cavitation nuclei radius can significantly increase the maximum tensile stress that the oil film can withstand and delay the generation time of cavitation.The number of bubbles per unit volume has no significant effect on the film pressure but larger number of bubbles per unit volume will accelerate the collapse speed of the cavitation.According to the force of the parallel plates in squeeze oil film,a kinetic equation of the upper plate during the squeezing process is established.Aiming at the randomness of the oil film cavitation noise,the Rosin-Rammer distribution function is used to obtain the distribution of the cavitation nuclei radius by statistical methods.The consistency of the distribution of probability model and the images of cavitation verify the correctness of the probability model.On this basis,the influence of temperature and solid powder additives on cavitation nuclei radius of the squeezed oil film is explored,and the distribution function under this working condition is fitted.Finally,the volume change of cavitation calculated by the RRPS model is combined with the Lighthill equation to calculate the sound pressure of the oil film cavitation noise.The RRPS model of the journal bearing under static load condition is established by considering the shear effect and squeeze effect at the same time.The effects of surface dilatational viscosity,initial cavitation nuclei radius and number of cavitation nuclei per unit volume on the pressure distribution,cavitation distribution,load and deflection angle of the journal bearing under static load conditions are respectively explored.On this basis,the kinetic equation of shaft is established according to the dynamic load,the axis trajectory of the journal bearing under dynamic load is solved,and the influence of different working conditions is compared and analyzed.The results show that increasing the squeeze force and spindle speed will increase the vibration amplitude of the shaft in the horizontal and vertical directions;increasing the surface dilatational viscosity and reducing the initial cavitation nuclei radius will increase the swing range of the shaft in the horizontal position and have little effect on the amplitude in the vertical direction;changing the initial volume fraction has little effect on the movement of the axis.Finally,a dynamically loaded journal bearing oil film noise test machine is designed and built to verify the accuracy of the RRPS model for journal bearing under static and dynamic load conditions by experiments.On this basis,the random oil film cavitation noise under the combined action of the shearing effect and the squeezing effect was successfully reproduced.The influence of experimental conditions on the cavitation noise in dynamically loaded journal bearing is explored.The results show that when the oscillatory frequency is 10 Hz,the oil film cavitation noise is the most severe.Besides,using square wave excitation,increasing the spindle speed and the eccentricity between the shaft and bearings will also increase the intensity of oil film cavitation noise.The influence of the carbon black and compound additives on the cavitation noise in dynamically loaded journal bearing is explored,respec.The results show that they still have the suppression effect on the cavitation noise compared with the lubricant without additives.At the same time,the noise reduction effect of compound additives is better.