Analysis On Torsional Vibration Characteristics Of Passenger Vehicle Power Transmission System During Various Operating Process

Automobile power transmission system composes of engine,transmission,drive shaft,driving axle and wheels,which is a shafting system with specific natural frequencies and modes.The studying and improving of the power transmission system torsional vibration characteristics under different working conditions are significant to promote vehicles’ NVH performance and lengthen the service life of related parts.The main contents of this paper are as follows:(1)Based on the lumped parameter modeling method,a model of passenger vehicles in third gear was established use LMS Virtual.lab Motion in which the simplified crank connecting rod mechanisms are driven by time-varying cylinder pressure obtained by experiments.Some factors such as crankshaft non-constant moments of inertia,nonlinear stiffness of clutch,backlash and time-varying meshing stiffness of gear pairs were considered in this model.Then natural frequencies and modes of the power transmission system are calculated and analyzed.(2)The full throttle acceleration condition of a passenger vehicle was simulated by LMS Virtual.lab Motion and the maximum relative error of flywheel rotation rate between experiments and simulation is 4.8%.Aimed to validate the model,the 2nd order vibration of angular acceleration of experiments and simulation at flywheel,input shaft and output shaft were compared.Analyzed the torsional vibration response of system and found that the 3rd resonance phenomenon occurs at the engine speed of 2500~2700rpm with the transmission input shaft’s maximum angular acceleration up to 1650rad/s2.Then investigated the method of improve the power transmission system torsional vibration characteristics based on system natural vibration analysis and found the inertia distribution between flywheel and clutch driven plate and the stiffness of clutch torsion shock absorber have a large effect on the 3rd natural vibration.(3)Simulating the transient state of the throttle tip-in/out in third gear by united simulation with LMS Virtual.lab Motion and SIMULINK,the maximum relative error of flywheel rotation rate between simulation and experiments is 2.35%.Observed rotation rate curve of experiments and simulation at tip-in and tip-out respectively and found that there is large fluctuations both flywheel and input shaft rotation rate curve at the moment of engine torque change suddenly,and the input shaft rotation rate changes more rapid than flywheel.In both of acceleration and deceleration phase,the frequency of rotation rate fluctuation both experiments and the simulation are close to the 1st order natural frequency 5.71 Hz of the transmission system.The simulation results show that the clutch torsion shock absorber with smaller stiffness can effectively improve the transient performance of power transmission system.(4)Equipping dual mass flywheel for the passenger vehicle.The comparative results between experiments and simulation indicates that for the full-throttle acceleration in third gear,the resonance phenomenon is avoided in the whole accelerating process,and the maximum acceleration fluctuation amplitude of input shaft reduces to 313.6rad/s2.For the throttle tip-in/out process in third gear,the simulation result shows the maximum amplitude of the flywheel rotation rate fluctuation at tip-out reduces from 61 rpm to 47 rpm,and maximum amplitude of the input shaft rotation rate fluctuation at tip-out reduces from 58 rpm to 20 rpm with the drastic change in ration rate curve is completely eliminated.The maximum amplitude of the flywheel rotation rate fluctuation at tip-in reduces from 49 rpm to 28 rpm,and the maximum fluctuation amplitude of the input shaft rotation rate at tip-in drastically reduces from 42 rpm to 15 rpm with drastic change in ration rate curve almost completely disappear.