Design Method And Experimental Study Of Three-Cylinder Engine Mounting System

At present,the market share of three-cylinder engine is increasing,but its inherent imbalance is not conducive to the comfort of passengers inside the car.Consumers are increasingly demanding the comfort of their cars,and OEMs and component suppliers pay special attention to the NVH performance of their vehicles.Powertrain mount is a important part of a car.It not only has the function of supporting the powertrain and controlling its displacement,but also reduces the vibration and noise of the powertrain to the cab.Therefore,the good design of the powertrain mounting system can improve NVH performance of the car.In this paper,the three-cylinder engine mounting system is researched.Firstly,the excitation force of the three-cylinder engine is qualitatively analyzed,which shows that the three-cylinder engine has poor balance.Then a powertrain mounting system with 6 Degree of Freedoms（DOFs）is proposed.According to the order and magnitude of the exciting force received in each direction of the three-cylinder engine block,the natural frequency distribution and decoupling rate requirements of the mounting system are set.Mount stiffness is used as a variable to optimize the natural frequency and decoupling rate of the system so that it is within the ideal interval.Considering displacement limitation function of mounting system,the inflection point of the mount nonlinear section is designed,and calculated displacement of powertrain’s centroid under 28 general case,which meet the design requirements.In addition to the matching of powertrain mounting system,mount part performance can not be ignored.So the modal and intensity of engine mount bracket are analyzed by finite element method.Six typical and six extrem conditions are as input for engine mount bracket intensity analysis.The results show natural frequency of the bracket is far above the minimum requirement,and the maximum principal stress and Mises stress of the bracket are far below safety stress,so the bracket meets the design requirements.In order to know the exact contribution of each direction of the mount to the vibration and noise in the vehicle,the transfer path analysis test of the powertrain mounting system is carried out to determine the dominant mount direction that affects the vibration and noise inside the vehicle.And stiffness of these mounts directions are adjusted.The powertrain mounting system rigid mode and steering wheel mode are tested and anlyzed.The results show that the natural frequency distribution of the mounting system is reasonable,but the steering wheel mode is coupled with the engine excitation.Evaluation criteria for powertrain mounting system NVH performance while the vehicle under different condition is developed.And the mounts isolation rates,cab vibration and noise while the vehicle under 3^rd WOT,idling and key on/off condition are tested.The test data indicates the vehicle’s NVH performance met the project targets.