| Automobile transmission manufacturing error and assembly error lead to the gear meshing backlash and the fluctuation of the driving gear speed can cause the driving gear and driven gear out of the engagement,which may result in gear rattle noise.Noise and vibration caused by gear rattle transmit into vehicle body through acoustic radiation and structural vibration.And it will affect the vehicle ride comfort.Therefore,controlling gear rattle noise is one of the important issues during the transmission design process.The topic was based on an engineering project and the target was to evaluate and diagnose the transmission gear rattle of a MPV vehicle.The main research contents and conclusions are as follows:(1)A MPV vehicle transmission gear rattle noise and vibration characteristics were analyzed based on experiment and subjective evaluation to explore the condition when the gear rattle happened.It is found that transmission gear rattle noise is low in second shift WOT condition as engine speed range is 1950 r/min to 2050 r/min.Besides,transmission gear rattle noise is loud in third shift WOT condition as engine speed range is 1600r/min to 1800r/min and it disappears when the speed exceed 1900r/min.(2)The conditions,excitation,transmission path and characteristics of gear rattle were analyzed and a model of single gear pair was established to study the relationship between rattle force power and rattle noise.It is found that the power of the rattle force causes the change of driven gear kinetic energy and the absolute value of the power is positively correlated with the gear rattle noise.Besides,the results show that gear rattle noise become louder with the increasing of the speed fluctuation and the moment of inertia of the driven gear.And when the backlash was increased,gear rattle firstly become louder and then become weaker.(3)The MPV vehicle transmission system model was built.In addition,modeling method of engine torque characteristics,clutch torsional vibration characteristics and dynamic characteristics of other key components were developed in the thesis.Based on the second order component of flywheel and gear angle acceleration,the simulation results were compared with the experimental data.And it is found that the model can be used to analyze the dynamic characteristics of gears.Then displacement between driving gears and driven gears,angular acceleration of driven gears and loose gears meshing force in third WOT condition were analyzed by the transmission model simulation.It is found that gear rattle noise is loudest in third WOT condition as the engine speed range is 1600r/min to 1800r/min.(4)The process of gear rattle was analyzed from the perspective of conservation of energy and a gear rattle evaluation method called "energy fluctuation index" was proposed.The principle of energy fluctuation index is to compute the absolute value of elastic potential energy variation of the gear system.Besides,threshold value of gear rattle noise was ascertained and energy fluctuation index was used to evaluate gear rattle noise in second WOT condition and fourth WOT condition.And results were in good agreement with the actual situation.(5)Energy fluctuation index was used to analyze relative gear rattle strength of different gear pairs and gears causing gear rattle noise are diagnosed.In addition,the optimization scheme was developed.It is found that gear rattle noise was mainly caused by fifth gear pairs and third gear pairs in second WOT condition and gear rattle noise was mainly caused by fifth gear pairs and second gear pairs in third WOT condition.The innovation of subject:(1)A single gear pair model was built to study the relationship between the power of rattle force and gear rattle noise.It is found that kinetic energy of driven gear is affected by rattle force and there is a positive correlation between the power of rattle force and gear rattle noise.This conclusion lays the foundation for the study of gear rattle based on energy methods.In addition,the influence of the fluctuation of the speed,the inertia of the driven gear and the backlash on the gear rattle noise is analyzed,which provides a reference for the percussion optimization scheme.(2)This thesis analyzed gear rattle process from the perspective of energy conservation and proposed an evaluation method called "energy fluctuation index",which is used to evaluate gear rattle noise by calculating the absolute value of elastic potential energy variation of the gear system.Besides,threshold value of gear rattle noise was ascertained and the effect of energy fluctuation index was tested by experiment and subjective evaluation.The evaluation and diagnosis method of gear rattle proposed in this thesis was different from previous index which rely on gear rattle force,driven gear angle acceleration and other kinematic parameters.And energy fluctuation index overcome pervious indicators' shortcomings that are unable to evaluate gear rattle noise of Multi-gear pairs.Energy fluctuation index is important for solving engineering problems. |
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