Optimum Design Of The Engine Mounting System

The standard of living is getting better and better with the development of economy,and automobile plays an important part in people's life. People attach more and more importance to the capabilities of the car,especially the ride comfort,and it is one of the indexes of the vibration isolation performance to value the ride comfort. Powertrain is one of the main vibration sources of the car,and its vibration which transfers to the car body through the mount system not only arouses the vibration of the body,but also influences its quality and dependability when working. How to design a good engine-mount system which can effectively isolate the vibration of the engine from the rest part of the car and improve the ride comfort capability has became an important problem of car design. In the paper,in order to improve the vibration isolation performance of the powertrain,the engine-mount system of N300 which is belonged to a certain automotive factory is optimized and designed. The main works we do are as follows:1. After referring many professional literatures about the engine-mount system,the present conditions including the mount components and the mount technologies are summarized.2. The engine-mount system is simply summarized including the requests of the mount in design,the placement form,the number andthe position,the calculation reference frame and so on,and it is convenient for optimizing and designing the engine-mount system.3. The one-dimensional and the three-dimensional mechanical model of the rubber mount are set up;Then the six-Degree-of Freedom model of the engine-mount system is also set up. The methods about intrinsic characteristic analysis , energy coupling analysis , static characteristic analysis,dynamic characteristic analysis are illustrated,and the analysis programmes are compiled.4. The methods which are used to measure the mass,centroid, inertia of the powertrain,the position,stiffness,angle of the mount are illustrated,and the initializations are given correspondently. Then the performances of the N300 are analyzed using the parameters which are measured. The analysis results show that:the vertical distortion and the lateral distortion of the front mounts are serious;The vertical displacement of the powertrain is also serious;The lateral frequency and the vertical frequency of the engine-mount system are too low;The energy descoupling degrees of other directions are not good except the portrait, and the pitch direction and the yaw direction are seriously coupled with each other. The lateral direction and the vertical direction,the list and the yaw are also coupling in a certain extent. So it is necessary to optimize and design the original system to improve the vibration isolation performance of the engine-mount system.5. The mathematical models which are often used in optimizing and designing the engine-mount system are summarized. In the paper,in order to solve those problems which are found out in the performances analysis of the engine-mount system,the optimization model is carried out,and the objective function is compose ofdecoupling the model kinetic energy of each mode and matching the vertical frequency rationally. Due to the optimization,the lateral frequency and the vertical frequency are both increased, and the vertical frequency keeps away from the vibration frequency of the car body in the vertical direction;The energy descoupling degree of each direction is improved except the portrait ,especially the pitch direction and the yaw direction ; The displacement and the force of the powertrain in the vertical direction are both minished;Although the roll angle of the engine-mount system when it is vibrating is bigger than before,it is rational,and the speed of vibration reaching to a constant is faster.It is obvious that the vibration isolation performance of the engine-mount system is improved.