Influence Of Gear Speed On Gearing Mixed Thermal Elasto-hydrodynamic Lubrication

The design of gearing contact fatigue strength is currently based on Hertz theory,but this theory is under the condition of smooth surface and lubricating oil environment,which is inconsistent with the actual operating conditions of mixed thermal EHL.Gear speed is one of the most important parameter that affects the lubrication of the gears;therefore many scholars have done this study.However,the existing researches are often based on the hypothesis of smooth tooth surface or tooth surface rough peaks and valleys with cosine(sine)distribution,which have some limitations.The effect of pinion speed on mixed thermal EHL of gear transmission,which based on real rough tooth surface,is necessary.The tooth surface rough outlines,which have transverse stripes,are measured by the profile measurement of gear material disc specimen.Then the function of roughness is formed by Fourier nonlinear transformation.Next this function is superimposed on the equation of film thickness to establish a numerical model of mixed thermal EHL.Based on this model and keeping with the fixed parameters of gear and lubricant parameters to calculate 702 groups numerical of the EHL with the multi-grid method by changing pinion speeds for medium and heavy-duty gear transmissions respectively.Finally quantitative analysis of pinion speed effected on film thickness,oil film ratio and contact stress.The following conclusions can be obtained by analyzing and summarizing the results of this study:(1)Unchanged transmission power and increased pinion speed will increase the average film thickness and reduce the tooth surface pressure,while the fluctuation of the oil film thickness and the tooth surface pressure is gentler and the stress concentration of the subsurface is reduced.(2)Unchanged pinion speed and increased transmission power will increase the tooth surface pressure,while the fluctuation of the tooth surface pressure and the oil film thickness becomes more and more serious,and the stress concentration is more obvious in the contact area.(3)As the pinion speed continues to increase,the corresponding lubrication states change from the mixed elastic flow lubrication state gradually into a full film lubrication state,which means the gear load changes from the tooth surface rough peaks and oil film bearing together to gradually become the full commitment by the lubricating oil film.(4)On the condition of the same speed,the changes in load(power)have little effect on the thickness of the oil film.(5)The contact stress of the gear teeth decreases monotonously with the increase of the gear speed.The contact stress decreases in large amplitude in mixed thermal EHL;but in full film lubrication,the decline trend is relatively slow.In general,industrial gear works mostly in mixed thermal EHL.Therefore,increasing the gear speed can effectively reduce the tooth surface contact stress,thereby improving the industrial gear transmission contact fatigue life.In the end of the text,for nine kinds of working conditions of medium and heavy-duty gear transmissions,quantitative relationships of contact stress with gear speed are established by using the multiple regression theory.The establishment of these formulas has some reference significance for perfecting the contact fatigue strength design of gear transmission.In order to reduce the difficulty of numerical calculation,the model is still based on the hypothesis that one of the tooth surfaces is a smooth tooth surface,which is quite different from the actual situation of the gear transmission,although the actual roughness data is used in this study.