The Design And The Analysis Of NVH Performance Of Powertrain For Rear-drive Car

NVH performance of vehicles is one of a basic and most important performance of vehicles. As an important part of the car, the drive trian system’s NVH performance largely determine the vehicle’s comfort. So it is significant to match the car engine and drive train. The main task of this paper is based on the selected 486 Q engine, designing a rear-wheel drive SUV power train which is used in city roads, and evaluating NVH performance of the drive train.This paper first carried out the numerical calculation formula of power performance evaluation(each gear maximum power factor, maximum gradeability, maximum speed and acceleration time) and fuel economy evaluation, and then calculated the gear reduction ratios of different transmission gears with Matlab programming.Next,each transmission’s power and fuel economy parameters were calculated separately based on these ratios. Finally, by comparing the power performance and fuel economy performance of the four-speed to the eight-speed transmission, the five-speed transmission is selected as the final optimization goal.Secondly,the paper did a brief introduction of genetic algorithms, analyzing the optimized objective function, constraints and selection of calculation variables by Matlab programming.GA toolbox of Matlab was applied to optimize the transmission ratios. In order to make the multi-objective function to reflect the importance of each goal reasonably, weighting processing was used and units were unified.In this step,first, power performance and fuel economy were optimized separately. After obtaining the weighted minimum, the multi-objective function was optimized by GA toolbox to gain better effect.Furthermore, according to the optimized parameters of transmission ratio, the parameter values of the drive train components were calculated. Duing to the actual situation,do a match seclection for some parts.Then we used CATIA to model these components,which is based on the calculated parameters,determining material and calculating the centroid of the components,etc. The actual operation on the part of the subject-independent member made a simplification. These three-dimensional models then were assembled into the clutch, transmission, drive shaft,and rear axle.At last, this four parts were assembled to the whole drive.Finally, imported all the three-dimensional models of transmission components into Hyper Mesh software, mesh them separately, and check out the mesh quality. The three-dimensional torsional vibration models were established by making all the components in a whole part according to the actual installation state. Added the middle constraints the drive shaft of the transmission system, analysis the driveline torsional vibration modal successfully. The results turned out that the third natural frequency of the system does not meet the goal, so this paper designed a dynamic vibration absorber, reached the target that the third torsional natural frequency of the frequency should be met.The results of this paper is meaningful to the design and analysis of the powertrain in rear wheel drive car.