Research On The Key Technology Of Automotive Powertrain Mounting System

Engine is one of the main source of automotive vibration, and mounting system is an important design to prevent the vibration transferring from engine to the frame and body. The reasonably designed automotive powertrain mounting system can significantly reduce the vibration of the automotive powertrain and body, and improve vehicle’s NVH (Noise, Vibration and Harshness) properties, which has become a key problem during the process of the development of the vehicle’s high speed and light weight.The powertrain mounting system research involves the study of different fields, mainly including the mounting element modeling, powertrain mounting system operation mode analysis and recognition, as well as mounting system modeling and optimization design.Rubber engine mount is not an ideal viscoelastic element, and has the nonlinear dynamic characteristics.This paper introduces in detail the basic theories and characteristics of the complex stiffness of rubber mounting model, Kelvin-Viogt model, three parameters model and the BERG model. BERG model is applied to construct the model of a engineering vehicle’s mounting. The dynamic performance tests for mounting in different amplitude are studied by using elastomer dynamic testing equipment. Based on the experimental data of different conditions, The fmincon-the constrained nonlinear multivariable optimization function in MATLAB-is used to recognize the suspension parameters of BERG model. The experiment and simulation results show that there is close relationship between frequency and amplitude of the vibration, and the simulation calculation result is consistent with the experimental result. The dynamic stiffness relative error is less than1%, and the damping coefficient of relative error is less than10%. The BERG model can reflect the nonlinear property in the rubber mounting’s dynamic characteristics, and can be applied to the optimization design of the powertrain mounting system.As for the inline four cylinder engine of180°uniform layout crank angle, the main incentive component is two order reciprocating inertia force and moment of the cylinder combustion. An engine mount system dynamic model with six degrees of freedom has been established. By four pole parameters method, the transmission rate formula of the elastic mounting support is deduced. The mounting vibration spectrum is calculated and the calculated results coincide with the measured data, so it is verified that the model and the calculation method is effective.The elastic effect of engine mounting support is one of the main reasons for the high rise of the vibration transmissibility curves and the poor isolation performance in high frequency range.The mounting vibration isolation performance is tested on a domestic car. The mount engine side and the frame side vibration parameters are measured under four engine’s conditions (idling,1500rpm、2500rpm and3000rpm). The mounting system vibration decay rate are analysed under different conditions. The main direction of vibration suspension elastic response was simulated and the calculated results coincide with the measured data. According to the nonlinear characteristics of rubber suspension stiffness, Based on the Newmark numerical integral method, the displacement calculation in the powertrain mounting system is presented. The vibration displacement in the directions of the elastic spindle is calculated and tested in the condition of three-gear sharp acceleration.The three kinds of operational modal tests (starting, idling and revving up) are done on a SUV vehicle’s powertrain mounting system. For the mounting system with the heavy damping and close modal property, the PRLSCF or PolyMAX technology is employed in the modal parameter identification. As the engine power source does not have zero mean and white noise characteristics, the modal assurance criterion (MAC), modal phase linear (MPC), average phase offset (MPD) and other confidence index are employed in the modal verification, and a credible modal parameters and the system working mode have been obtained. Operational modal parameters are relative to the operating condition of the engine and the operational modal frequency is higher than the calculated modal frequency. Multiple operational modal tests can more accurately identify the modal parameters, which is consistent with the mounting component parameter design.Based on orthogonal experiments, sensitivity analysis of an engine mounting system is made to show the influence of the mounting coordinates on the six-order natural frequency and the influence of the mounting stiffness on the vibration decoupling rate. The robust optimization methods based on the sensitivity analysis of the engine mounting system is put forward and the optimization result has good robustness. In the paper, the global best and personal best of particle swarm algorithm are selected by the grey relational analysis. Furthermore, the grey particle swarm robust algorithm is presented for multi-objective models solution in the robust optimization design, and the algorithm is employed in the optimization design of the engine mounting system. It has been verified that the conflicts between optimization objects can be coordinated, the satisfactory synthetic effects can be found, and the reliability of the optimized mounting parameters can be obtained by using the algorithm.