Research On Torsional Vibration Characteristics Of Lock-up Torque Converter Transmission System Of Loader

As one of the most commonly employed types of engineering vehicle,the transmission system affects the service performance and operation efficiency of the whole machine.At present,the hydromechanical transmission system is the most widely developed transmission system in loaders in China.The fuel economy and transmission efficiency of loader transmission system can be improved by employing lock-up technology in hydrodynamic torque converter.The loader transmission system is a multi-degree of freedom nonlinear system.When the excitation frequency from the power source is close to or equal to the natural frequency of the transmission system,torsional vibration or resonance will occur in the transmission system of the loader.Furthermore,resonance will shorten the life of the transmission system components,which will force the parts and components to break seriously,and also affect the working comfort of the driver.A large number of studies have been carried out on torsional vibration of vehicle transmission system in China,and some experience has been accumulated.However,there are relatively few studies on the torsional vibration of the transmission system of the engineering machinery,especially the loader with a lock-up torque converter transmission system.Therefore,it is necessary to carry out relevant research to reduce the occurrence of torsional vibration,improve the service life of loader parts and components,reduce maintenance costs,and improve the driving environment of drivers.In this paper,the torsional vibration of an 8t loader equipped with lock-up torque converter transmission system in an enterprise is studied.The physical and simulation models of hydrodynamic torque converter before lock-up,lock-up process and transmission system after lock-up are established respectively.The torsional vibration of each advancing gear is analyzed,and the specific research work and related conclusions are as follows.(1)The torsional vibration theory of loader hydrodynamic transmission system is analyzed.The simple harmonic analysis of loader engine is carried out,and the comprehensive excitation torque is decomposed into simple harmonic excitation torque components under different frequency functions.It lays a foundation for the torsional vibration analysis of hydrodynamic transmission systems.(2)Aiming at the flexible transmission of hydrodynamic torque converter,the variable damping and variable stiffness model is established.The ralitionship that the damping and stiffness of torque converter varied with speed ratio and pump rotational speed is deduced,and the torsional vibration analysis method based on variable damping and variable stiffness of hydrodynamic torque converter is given.The lumped mass method is used to analyze the moment of inertia,equivalent damping and equivalent stiffness of the shaft system of hydrodynamic transmission system.The physical and simulation models of hydrodynamic working condition、the locking process and the locked condition of the torque converter lock-up clutch are analyzed and established.(3)Based on the variable stiffness and damping model of the hydrodynamic torque converter,a method for determining the process equivalent damping stiffness is proposed.Based on AMESim platform,the torsional vibration analysis of loader locking hydrodynamic torque converter transmission system under hydrodynamic condition,locking process condition and after locking condition is carried out respectively.The analysis results show that under hydrodynamic conditions,through the damping effect of the variable damping and stiffness model of the hydrodynamic torque converter,the resonance amplitude at the resonance frequency is low.On the contrary,assuming the hydrodynamic torque converter as a fixed damping stiffness model,the resonance amplitude at the output shaft of the transmission is large,and the variable damping and stiffness model of the hydrodynamic torque converter is more realistic.Under the working condition of locking process,the damping effect of torque converter is gradually weakened,the effect of torsional damper is enhanced,and the system is in the mixed state of hydrodynamic transmission and mechanical friction transmission.Since both the torque converter and the torsional damper have the function of vibration reduction,the torsional vibration of the transmission system behind the hydrodynamic torque converter and the torsional damper is reduced,and the dangerous section of torsional vibration is mainly concentrated in front of the hydrodynamic torque converter and the torsional damper.In the working condition after locking,due to the loss of the vibration damping and isolation function of the hydrodynamic torque converter,compared with the torsional vibration working condition of the transmission system before and during the locking of the hydrodynamic torque converter,the resonance amplitude of the transmission system at a certain natural frequency after the locking of the hydrodynamic torque converter is significantly increased,and the number of dangerous sections is increased.(4)To verify the torsional vibration simulation analysis results of the lock-up torque converter transmission system,an experimental study of an 8t loader equipped with the lock-up torque converter was carried out.Comparing the simulation results with the test,the torsional vibration prediction accuracy of the engine flywheel and the input shaft of transmission with the variable damping variable stiffness model is higher than the fixed damping stiffness model.The simulation results and test data are compared under each gear of locking process condition and post locking condition,and the effectiveness and correctness of the simulation model and the simulation results are verified.