Performance Match Of Key Rubber Isolators For Ligh Bus

Coincident with the development of automotive industry and people's living standards, the NVH (Noise, Vibration and Harshness) performance of automobile is more and more popular. Vibration reduces the service life of automotive and and its noise pollutes the environment, which is bad for people's physical and moral integrity. The vibration isolators between the assemblies and components could reduce vehicle vibration and noise effectively. Powertrain mount, exhaust pipe hanger and body mount can attenuate the vibration and shock arising from engine and road, and decrease the vibration transmission to frame. A reasonable match of these isolators may enhance the ride comfort greatly. Therfore, it's necessary to study the match of powertrain mount, exhaust pipe hanger and body mount.The multi-body dynamics and finite element methods was utilized to establish the rigid-elastic coupling model of full vehicle including powertrain mount, exhaust pipe hanger and body mount in this dissertation, which was validated by the experiment test. Then the match of rubber isolators in the full vehicle model was study from the following aspects: single type isolators'match and integration design of all isolators. During the research process, the isolators' stiffness ratio of compression to shear was controlled closely combining with engineering practice while the robust optimization of the rubber isolators was carried out for the uncertainty of the isolators'stiffness.In the study of powrtrain mount, the powertrain mount system was optimized based on the traditional six DOF model of powertrain mount system and the mount system under the full vehicle model respectively, and the results demonstrate that the latter could obtain a better effect. There are many different objectives for powertrain mount optimization, the kinetic energy decoupling method and dynamic response method was taken simultaneously to optimize the traditional powertrain mount system in the thesis. Both of the optimized results were simulated in the full vehicle model to compare the vehicle interior vibration. It's concluded that the mount of dynamic response method causes a smaller vibration in the driver's seat rail and the dynamic reaction force in the powertrain mount is better. To have a further research on the the relationship between the vehicle interior vibration and the kinetic energy of powertrain mount system, the vibrations of driver's seat rail, the second seat rail, the fourth seat rail and the last seat rail in the same automotive with different mounts were tested and the results demonstrate that the powertrain mount system with good decoupling level has a worse vibration. The kinetic energy of powertrain mount system can to some extent reduce the vehicle vibration, but it's usually not the best solution. For a more accurate data of vehicle vibration, the powertrain mount system in a full vehicle model was optimized from the standpoint of energy to cut down the vibration power of the powertrain resulting from the mount supporting position to the frame.As for the match of exhaust pipe hanger, calculating modal analysis and experiment modal analysis of the exhaust system were carried out. The result of the experiment modal analysis was utilized to validate the finite element model of exhaust system, and then hanger position of the exhaust pipe was optimized to find the location with minimum ADDOFD (average driving degree of freedom displacement) in the calibrated model, which could decrease the exhaust system vibration transmission to the frame. The stiffness of exhaust pipe hanger affects the dynamic performance of exhaust system. Altering the stiffness of the hanger could change the natural frequencies of exhaust system which should keep far away from the engine excitation frequency of idle speed and economy speed to reduce the vehicle vibration. Meanwhile the hanger vibration of the exhaust pipe was tested and analyzed. Then exhaust pipe hangers were optimized in a full vehicle model which contained the flexible exhaust system, the vibration acceleration acted as the objective, and at the same time only two types of hanger were used in the four hanger location to save the enterprise cost.With reference to the study of body mount, the vibration of driver's seat rail, the second seat rail, the fourth seat rail and the last seat rail was tested, and the results show that the vehicle interior vibration is related with engine, drive shaft and wheel. In the dissertation, the contribution of stiffness of each body mount to the vehicle interior vibration was studied and the body mount system model with elastic connection and bolt connection was established. When determining the the design variables limit of body mount, vehicle handling and stability was taken into consideration and then the body mount system was optimized.In respect of integrated design for rubber isolators, the interaction of powertrain mount, exhaust pipe hanger and body mount was taken into account, and all the isolators were optimized at one time. Before the optimization, the orthogonal experimental design of all the isolators was taken to determine the sensitivity of each isolator. Then on the premise that powertrain mount, exhaust pipe hanger and body mount had achieved optimal performance of vibration isolation respectively, the stiffnesses of rubber isolators were optimized integratively with vehicle vibration served as the optimization objective. As a rule actual stiffness of the isolators fluctuate around the target stiffness in a plus or minus 10% range, therefore robust optimization was performed for the isolator and the solution process of optimization was improved to heighten the efficiency of roubust optimization in the dissertation.In the process of vehicle research and development, it can accelerate the development to combine the simulation method with experiment mehtod and establishing a full vehicle model could predict the vibration performance of the automotive more accurately. When matching the rubber isolators of the automotive, comprehensive factors should be taken into account, such as isolators'installation space, machining technics, production cost and so on. The powertrain mount system under the full vehicle model was optimized with the input vibration power at the location of the powertrain mount acted as the objective, and this method could reduce the vehicle vibration effectively, which has good correlations with the traditional objective in the thesis. The body mount system model with elastic connection and bolt connection was established, which could give a reference to other similar body mount system. Rubber isolation of the automobile has a mutual influence, and the integrated design of them was studied. In addition, the robust optimization was carried out according to the engineering practice. Considering the stiffness's uncertainty of rubber isolators is beneficial to the stability of objective in the design phase, which makes the products achieve the desired performance better.