Modeling And Optimization On Gearrattle Problem Of Unloaded Gear Pairs At The Transmission During Vehicle Marching

The gear rattle problem of unloaded gear is a common NVH problem.The main reason for this problem is the imbalance torque excitation of the engine,which affected the meshing motion of the unloaded gear pair.Because of the high cost of gear manufacturing,it is difficult to solve this problem by adjusted transmission itself in the practical engineering.The other way to solve this problem is by analysised the torsional vibration of the vehicle transmission system.In this paper,both simulation calculation and experimental research were used to solve the gear rattle problem of unloaded gear in the transmission.First of all,the theory and method of data acquisition and processing and the test method for vehicle accelerated noise road test were analyzed.The acceleration sensor,microphone and speed sensor needed for test were selected and arranged.At the same time,the mechanism of the torsional vibration of the engine was analyzed,and the characteristics of the order component of the inertia force,the inertia moment and the gas moment were pointed out.According to the test method,a preliminary test data of a vehicle with the problem of accelerated noise was obtained.It was found that the sound pressure value near the transmission and the angular acceleration of the input shaft of the transmission appeared bulge near the 1900 rpm speed.And the sound pressure signal had a remarkable characteristic of the wide frequency band,which is the special phenomenon of gear rattle.It is explained that the resonance phenomenon of the driveline system caused the gear rattle problem.Then a six degrees of freedom dynamic model of the driveline system was built,which considered the nonlinear characteristics of the clutch stiffness and damping and the meshing clearance between the geared gears in the transmission,and gived the calculation method of clutch multistage torsional stiffness,clutch multistage damping torque and transmission torque of gear pairs.the dynamic model was calculated and solved by used state equation and four order Runge Kutta method.The natural frequencies and corresponding main modes of the model were calculated.It was found that the third order natural frequency was in the frequency range of the second order excitation of the engine.And the dynamic response of the model was calculated.It was found that the angular acceleration of the input shaft of the transmission also appeared bulge near the 1800 rpm in the error range of speed.The second order excitation of the engine was enlarged and passed to the transmission input shaft,then the relative displacement between the unloaded gear pairs was fluctuated on the left and right sides of the backlash,and the gear rattle phenomenon occured.The results of dynamic response calculation verified the correctness of the dynamic model.On this basis,The change of the input shaft angle acceleration and the gear rattle condition of the transmission were researched by analysised moment of inertia of flywheel side,moment of inertia of clutch hub,moment of unload gear in the transmission,third torsional stiffness of clutch,third hysteresis of clutch,damping torque of transmission unload gear and back lash of gear pair these 7 model parameters varied in a certain range.The simulation results showed that the input shaft angular acceleration can be attenuated by adjusted these parameters.The change rule of the gear rattle intensity and the input shaft angular acceleration of the transmission was in overall agreement,only the adjustment of backlash was different,input shaft angle acceleration was increased by increased backlash,but the gear rattle intensity becamed weakened to single side rattle.According to the result of parametric analysis,the weighted angular acceleration of the input shaft of the transmission is taken as the optimization target,and the design parameters of the clutch were optimized.Based on the optimization result,the new clutch were made,and the vehicle accelerated noise road test was carried out again.The testing data of the input shaft angle acceleration,the acceleration of the gearbox and the sound pressure of transmission side are compared.The test result showed that the resonance phenomenon of the driveline system near the 1900 rpm speed was suppressed.Also the bulge of input shaft angle acceleration and the sound pressure of transmission side were disappeared,and the wide band characteristics of the sound pressure signal disappeared too.This proved that the input shaft angle acceleration and the gear rattle condition of the transmission can be restrained by increasing third hysteresis of clutch and adjusting the third torsional stiffness of clutch properly.At the same time,it is proved that the calculation and test method of this paper is of guiding significance for solving the problem of unloaded gear rattle during vehicle marching.