| The aero-gear transmission system is the critical component of the aero-engine power transmission,and its working reliability has an essential influence on the function and performance of the aero-engine.Aero-gear transmission systems already feature high-speed and lightweight structures(flexibility).Using traditional gear dynamics modeling methods for analysis leads to significant discrepancies between simulation results and measured results.System dynamics modeling and accurate prediction of vibration response have been a puzzle for gear transmission design,which has long plagued the innovative development of China’s aviation gear transmission.The thesis focuses on the fundamental research on the high-speed and flexible gear dynamics modeling method and techniques in aerospace parallel shaft systems,proposing solutions for the construction of element models of high-speed ball bearings,thin-walled gears,thin-walled hollow shafts,flexible meshing pairs and their complex coupling with the vibration response of gear systems based on the finite element method,rotor dynamics and gear dynamics theories.Experimental verification is performed on the aerogear transmission test rig.The main research contents and conclusions are as follows:1)The new method for dynamics modeling of the gear system considering high-speed operating conditions and structural flexibility is investigated.Bearing models in conventional gear dynamics ignore nonlinear characteristics and centrifugal forces.This dissertation establishes the non-linear bearing force model based on Hertzian contact theory that considers load,bearing clearance,rolling body rotation,and centrifugal force.For the rigid gear body assumption,rigid disc meshing,and shaft beam element assumption in the traditional gear dynamics model,the vibration characteristics analysis model of the high-speed and lightweight gear system is established based on finite element shell theory,rotor dynamics theory,and gear dynamics theory,considering the gyroscopic effect of high-speed conditions,gear body flexibility,thin-walled hollow shaft flexibility and the meshing action based on flexible wheel body.The super element of the gear,thin-walled hollow shaft,and housing are established based on the dynamic substructure method to improve the computational efficiency,reducing the degrees of freedom of the vibration characteristic analysis model.It provides a theoretical basis for subsequent research on the effects of vibration characteristics analysis.2)The non-linear bearing model taking into account load,bearing clearance,rolling body rotation,and the centrifugal force is introduced into the gear dynamics model.The effect of non-linearity of high-speed deep groove ball bearing and centrifugal force on the vibration characteristics of spur gear systems is investigated.The advantages of considering the bearing non-linearity are illustrated by comparison with the conventional gear dynamics model.The results show that when the bearing energy in the resonant frequency energy distribution is relatively low(3.8% in the case of this dissertation),the resonant frequency and vibration response obtained using the conventional bearing model and the non-linear bearing model are the same.On the contrary,when the bearing energy in the resonance frequency energy distribution is higher(52.1% in this dissertation),the bearing non-linear characteristics have a significant impact on the resonance frequency of the gear system.The second-order resonance frequency is reduced by 9.9%,at which time the conventional bearing model will lead to a large predicted resonance frequency.After considering the centrifugal force,the root mean square value of dynamic transmission error and bearing vibration displacement gradually increase upwards as the speed increases.The phenomenon cannot be observed with the conventional bearing model.3)Based on the proposed modeling approach,the dynamic model is built considering the flexibility of the wheel body.The effects of the flexible body on the vibration characteristics of the spur gear,helical gear,and herringbone gear system are investigated.The advantages of the model considering gear flexibility are illustrated by comparing it with the conventional gear dynamics model.In the spur gear system,the resonant speeds of the two models are essentially the same in the low-speed range(0-8275 rpm in the case of this dissertation).However,the rigid wheel body assumption in the conventional gear dynamics model leads to a large predicted higher-order resonant speed.The error is 18.54% in the case of this dissertation.It indicates that the traditional model is only suitable for analyzing low-speed gearing systems.In helical gear systems,the conventional gear dynamics model loses information on the vibration pattern associated with the gear.So,it cannot analyze the transverse vibration of the helical gear.The bending-torsional vibration can be obtained.In contrast,the vibration model that considers the gear flexibility predicts a vibration response that can include the transverse vibration of thin-walled gears.Similarly,in the herringbone gear system,conventional gear dynamics models are unable to analyze the transverse vibration of thin-walled herringbone gear under asymmetric error excitation due to the assumption of a rigid wheel body.The comparative results show that the gear dynamics model taking into account the flexible gear is necessary to analyze the vibration characteristics of highspeed and flexible gear systems.4)The dynamics model considering the flexibility of the thin-walled hollow shaft is developed based on the proposed new modeling approach.The effects of the thin-walled hollow shaft on the vibration characteristics of the spur gear system are investigated.Compared with the conventional gear dynamics model,the advantages of a gear dynamics model considering the thin-walled hollow shaft are described.The beam element assumption in the traditional gear dynamics model leads to bias in predicted higher-order resonant frequency results(the error is 19.9% in this dissertation).But the predicted lower-order resonant frequencies are consistent with the flexible model.The different dynamic response curves predicted by the two models for gear trains operating at speeds above8000 rpm indicate that the traditional gear dynamics model is suitable for analyzing gear trains at low operating speeds.The dynamic response results for different diameter-to-thickness ratios show that thin-walled hollow shafts have a noticeable contribution to the vibration in the highspeed region of the gear train.Simplifying the thin-walled hollow shaft to a beam model results in the absence of high-speed resonant frequencies.5)This dissertation validates the theoretical model based on lowspeed and high-speed gearboxes.The validity of the non-linear model of bearings was completed on the low-speed test rig.After considering the bearing non-linearity,the calculated vibration acceleration results are in better agreement with the experimental results.The predicted resonance speed is closer to the test value.The high-speed gearbox is modeled on an aero-engine accessory drive system,retaining the characteristics of highspeed operating conditions and flexible structure.Therefore,the dynamics model considering the flexible body was validated on the high-speed test rig.The error between the single-axis free mode calculated by the flexible model and the experimental test results is within 5%.In contrast,the errors calculated by the conventional model are greater,in the range of 34.72% to 67.13%.From the comparative results of the box vibration acceleration,the resonant speed predicted by the flexible model is consistent with the experimental results,while the results predicted by the conventional model are on the large side and the error is 27.3%.The work in the thesis advances the solution to the problem of accurate dynamics modeling in the aerospace gear system considering high-speed operating conditions and flexible structures.The proposed high-speed flexible gear dynamics model can be more precise in analyzing and calculating the vibration response of aerospace high-speed lightweight gear systems.The research provides a theoretical basis and support for modeling and analysis methods for high-performance design and vibration and noise reduction of aerospace gear drives.196 Figures,38 Tables,177 References... |
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