Optimization Design Of Engine Powertrain Mounting System

Automobile NVH characteristic is a comprehensive problem to measure the quality of automobile manufacturing. As an important part of the automotive vibration system, the vibration transmission characteristics of powertrain mounting system has a great influence on vehicle comfort and NVH performance. In this paper, the optimization design of the powertrain mounting system for the assembly of engine is carried out.During the design of automobile engine mounting system, powertrain inertial parameters measurement is a necessary step. The measurements of inertial parameters include centroid, moment of inertia and product of inertia. First, an experimental technique of measuring the inertia parameters of powertrain, based on 3D scanner and three-wire pendulum, is presented. Two standard steel disc was used to calibrate the quality and the pendulum length and obtain measurement accuracy. On the basis of this, the measurement and calculation of the center of mass and inertia parameters of the engine and the gearbox were carried out by the method of split test. The split test of engine and transmission box makes the testing process more flexible. Meanwhile, it reduces the strength requirement of suspension device. Through the integration of the two parameters, the centroid position and the inertia parameters of the power assembly with high precision were obtained.According to the measured power assembly centroid position and inertia parameters, the simulation model of six degree of freedom dynamic assembly is established by using the software ADAMS. Based on the existing parameters of the suspension components, the inherent characteristics of the simulation model and the calculation of the energy coupling are analyzed. According to the results of the analysis, the first-order natural frequency of existing power assembly mounting system is less than the random road excitation frequency, there lies the possibility of resonance with the road excitation force, and the main exciting force in the vertical direction(Z axis) energy distribution rate is low, the energy distribution of y and qy also exist certain coupling. Meanwhile, the dynamic response of the powertrain was simulated in idle mode, the maximum torque condition and the emergency braking condition, and obtains the vibration isolation effect under different conditions.Aiming at the deficiency of the existing suspension system, this paper takes the optimal energy distribution ratio as the goal, and the suspension element three to the principal axis as the design variables. The optimization results show that the percentage of the energy distribution of the optimized energy is improved in different degree, and the energy distribution of the Z axis is increased by 27.3%. Dynamic response shows that the displacement, acceleration and angular displacement amplitude of the center of mass are decreased, and the vibration isolation effect of the dynamic response is improved.According to the requirement of the manufacturer, the strength of right mount bracket of the engine is checked. The modal analysis shows that the first order natural frequency of the suspension bracket is 681.13 Hz, which is greater than the design requirement of the passenger car. The strength analysis shows that the maximum stress of the suspension bracket under the limit condition occurs in the car after the crash, but far less than the yield strength of ductile cast iron QT700-2. In summary, the suspension bracket with a larger design margin. According to the requirement of light weight of the vehicle, the topology optimization of the right mounting bracket was carried out. The optimization results show that, compared with the original support, its weight is reduced by 0.33 kg, and the first order natural frequency is 696.52 Hz, which meets the design requirements of the passenger car mount bracket.