| Gear system plays an irreplaceable role in aerospace,machinery,shipbuilding and other industries.From single-stage to multi-stage gear transmission system,its dynamic research and lubrication design are becoming more and more complex.Under the lubrication condition,the oil film with certain thickness and stiffness is formed on the tooth surface due to the action of entrainment speed and load.Its function is to reduce the friction and wear of the gear and mitigate the impact.Its stiffness is combined with the stiffness of dry friction contact of the gear teeth,forming one of the excitation of the vibration of the gear transmission system.Under different working conditions,oil film stiffness excitation and system vibration response have important laws,which provide important theoretical reference for gear system optimization design,lubrication design and vibration and noise reduction.In this paper,the two-stage fixed axis gearbox in the experimental platform is taken as the research object,and the gear oil film excitation is considered and analyzed emphatically,and the parametric model of gear lubrication and gear dynamics is constructed.The lubrication characteristics,natural frequency,vibration mode and dynamic load of the system are studied by numerical solution.The main contents of this paper are as follows:(1)Based on the theory of Line Contact Elastohydrodynamic Lubrication,the elastohydrodynamic lubrication equations suitable for the object in this paper are derived,and the Newton iteration method is used to obtain the oil film thickness and pressure distribution.Numerical analysis shows that lubrication should be taken into account at the alternation of single and double teeth,and the setting of initial viscosity has little effect on the formation of film pressure and film thickness.(2)Based on gear meshing theory,the time-varying parameters such as curvature radius,entrainment speed and load are obtained.According to the definition of oil film stiffness,the time-varying oil film stiffness of gear is obtained.The important elements of global stiffness matrix are supplemented for the later system dynamics analysis.The results show that with the change of speed and load,the oil film stiffness presents a certain rule.(3)Based on the elastohydrodynamic lubrication theory of smooth tooth surface,the lubrication characteristics,natural frequency and vibration mode of gear system under different speeds and loads are discussed.The simulation results show that when considering the gear lubrication effect,the comprehensive stiffness of the system gear decreases,which leads to different amplitude reduction of natural frequency,among which the 11 th order effect is the most prominent;in the resonance speed region,the change of natural frequency is relatively slow,and the larger the resonance speed is,the weaker the change is.The results show that the composite stiffness of the superposed gear decreases,the bending order of the transmission shaft increases,the vibration of the system intensifies,and the dynamic characteristics are more sensitive.(4)Based on the rough tooth surface,the influence of oil film stiffness on the dynamic characteristics of the system under different working conditions is explored.The simulation results show that the transverse tooth surface roughness has the effect of pump blade,which is conducive to the formation of oil film thickness;but the peak value of oil film pressure is very large,which is easy to cause dry contact and lead to tooth surface fatigue failure.Considering the superposition of oil film,the amplitude of gear dynamic load is weakened,the frequency component of vibration response is reduced,and the vibration effect of the second gear pair on the first gear pair is weakened.Compared with the second gear pair,the lubrication condition of the first gear pair is more favorable. |
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