Dynamic And NVH Performance Study Of Gear Drives In Continuously Variable Transmission

With the deterioration of the natural environment,the energy crisis and the implementation of dual-point policy,it is particularly important to further improve the fuel economy of vehicles.Continuously Variable Transmission(CVT)is an ideal vehicle transmission device which enables the engine,motor and other power sources to work at the optimal operating point,thus improving the vehicle fuel economy.As a part of the vehicle transmission system,CVT is driven by metal belt to achieve variable speed function.It has certain uniqueness in structure,but also has a series of common transmission components such as gear pairs.However,NVH problems such as howling noise exist in both reverse and forward in the CVT,which seriously affect the comfort of the vehicle and reduce the overall quality of the product.Many efforts have been put on the analysis of the vibration and noise of the gear system,however,the influence of metal belt,gear installation mode and time-varying torque caused by the working principle of CVT on the gear transmission system has not been analyzed in detail.Therefore,this paper focuses on the improvement of the NVH performance of CVT transmission system.Relying on the special national science and technology cooperation project and the national natural science foundation project,this paper studies the dynamics and NVH performance of the gear transmission of the metal belt CVT.The noise source of CVT is identified and analyzed in detail through theoretical analysis and experimental verification and the performance of CVT and the whole vehicle NVH is improved through the corresponding optimization method.The main work in this paper is as follows:(1)The main source of the roaring in gear drives was identified by theoretical and experimental means.The vibration acceleration and noise experiments under various forward and reverse gear working conditions were carried out.Based on order tracking,analysis the roaring in the process of forward and reverse gear,and research the dynamic characteristic of the gear drive in CVT.(2)Considering the effect of belt tension,the parameter of gear pair are optimized and verified by experiments.The dynamic model of the CVT drive system was established in Romax software.The force condition of the gear system due the metal belt are analyzed the certified through mesh spot test.These proved the correctness of the dynamic model.Secondly,the genetic algorithm is used to optimize the microscopic modification parameters of the studied gear pair to determine the optimal value.It was found that the forward noise value of the modified gearbox was reduced and the NVH problem of the gearbox was improved to a certain extent.(3)In order to further study the noise problem of forward noise suppression,especially the CVT vibration noise problem under different working conditions,the nonlinear dynamic model was established by taking the gear pair as the research object.Aiming at the time-varying torque in the variable speed process,the TVMS of the gear pair with different input torque is analyzed by combining the slicing method and the regression approximate formula method.Then,the vehicle dynamics model is established,and the correctness of the model is verified by experiments.Finally,based on the vehicle model,the non-linear dynamic characteristics under different input torque are researched based on the dynamic model.(4)In order to solve the problem of reversing roaring,the effect of two-stage planetary system on the performance of gearbox NVH was studied.Firstly,the nonlinear dynamic modeling of this gear drive used to reverse in CVT was established,and the TVMS of this gear pair was obtained by the computing method proposed above.Meanwhile,the time-varying meshing stiffness and nonlinear dynamic characteristics of gear pairs with different input torque were obtained to study the influence of input torque on the dynamic characteristics of gear drive and the NVH performance of CVT.(5)Considering the assembly mode of spline,to analysis the dynamic of gearspline system and the NVH performance of CVT.Firstly,a finite element model is established to obtain the TVMS of the forward noise source gear pair.Then,the dynamic model is established to analyze the effects of different assembly modes and different interference amounts on the nonlinear dynamic characteristics of the gear pair.Finally,the result of the simulation based on the dynamic model and the experiments are compared to verified the correctness of the dynamic model and analysis result.In general,combined with kinetic analysis and experimental verification,the cause of the howling noise and its influence on the NVH performance in the reverse and forward of the CVT transmission system were studied.To improve the vibration and noise characteristics of CVT and the Overall NVH performance of the transmission system,an optimization method of reduceing the vibration and noise of the CVT transmission system was proposed.The analytical and optimization methods proposed in this paper could be used in the development of the CVT transmission system,which would further improve the performance of the independent domestic CVT transmission system.