Performance-Match Of Hydraulic Mount For Light Vehicle Cab

As long as the domestic and foreign laws for NVH are stricter, and the consumer are increasingly concerned about the driving comfortableness day by day, How to reduce vibration and noise in cab has become a hot research issues. There are two main incents for the vibration of the cab-the road and the engine. The cab mount is the most important vibration-isolating system. So, for improving the ride comfortableness, we must do more and more research about the cab mount. Compared with the traditional rubber cab mount, hydraulic mount has better characteristics which can play a better role to reduce the vibration and noise. There are so many people researching the hydraulic mount for engine, but few for vehicle cab. In this paper, the methods of nonlinear finite element analysis as well as the technology of elastic multi-body dynamics are used for the research of vehicle cab's hydraulic mount. The methods of finite element analysis were developing recent years along with the developing of computer technology. By the methods we can study the vehicle cab's hydraulic mount more direct-viewing, and we can instruct trial manufacturing and designing more directly. So, it can shorten the development cycle, reduce development costs greatly. According to the research and development process proposed by this dissertation, the study of vehicle cab's hydraulic mount is done step by step. The methods we used include fluid-structure interaction, elastic multi-body dynamics, finite element modal analysis of cab and testing, acoustic- structure interaction and so on.This dissertation studies the performance-match of the vehicle cab's hydraulic mount using the methods which combine the finite element analysis (FEA) and trials. There are 6 main parts in the dissertation.The first part summarizes the current status of the research on performance-match of the vehicle cab's hydraulic mount and the studying based on finite element analysis. The kinds of vehicle cab's mount were introduced. The advantages of the hydraulic mount, the theory and technical requirements of vibration isolation, as well as the advantages of hydraulic mount studying using FEA methods are presented. Finally, the main contents and the significance of this dissertation are presented.The main rubber spring and the liquid part of the hydraulic mount are established in part two based on the theory and methods of FEA fluid-structure interaction. When establishing the main rubber spring, the tests date to characterize the rubber material constants as well as the hyperelastic material stability is discussed. The rubber material of mount is analyzed based on different forms of strain energy potentials using finite element analysis software. The method of using test data, material stability, and minimum mean square error to calibrate material coefficients is obtained. In the dynamic analysis, especially high frequency excitation analysis, the velocity of liquid is fast and the Reynolds number of fluid is high. With the presence of small hole and high speed flow, a turbulent flow condition is likely exist in fluid. In order to simulate the dynamic characteristics of hydraulic mount in high frequency excitation, we use K-Epsilon RNG turbulence model as liquid material parameters. The dynamic stiffness and loss angle of hydraulic mount are presented via finite element model. The simulations of static and dynamic characteristics agree well with corresponding test results.The main structure parameters affecting the dynamic characteristics of the hydraulic mount are analyzed by the finite element model in part 3. The parameters include rubber spring static stiffness, equivalent piston area of main rubber spring, volume stiffness of the Lower Cavity, inertia-track parameters, compensation hole, rubber membrane of upper cavity, the liquid viscosity, and the structure of restrictor plate. The influence and sensitivity of these parameters to the dynamic characteristics of hydraulic mount are presented. According to studies, the author proposes the method of hydraulic mount performance-match based on the NVH of overall cab. The design requirements of the main components of hydraulic mount are discussed and studied.The Finite element model of the cab Body-in-White (BIW) is established based on the 3-D CAD model by software Hypermesh. Welding connections among parts of body and frame are simulated by the rigid element connection. Bolt-connections are simulated by the beam element connection. The modals between the frequencies of 0～100 Hz are analyzed by the method of Lanczos. The trial for modal is done using the equipments of LMS data acquisition system, MB vibrator, and acceleration sensors. Measuring point arrangement in the trial is base on finite element model. This arrangement can improve test accuracy and reduce test cost. Adding door and window glass, as well as lumped mass for simulating the interior parts, the FEA model of whole cab is established based on the BIW model. The quality of finite element model is close to the real vehicle cab. So the FEA model of whole cab is correct.The FEA model is imported into multi-body dynamics analysis software in the form of MNF. The hydraulic mount module is appended at the cab mount points. With the mean square root of cab seat acceleration as evaluation indicator, the parameter optimizing and matching of the hydraulic mount dynamic stiff and loss angle are carried out. More reasonable hydraulic mount is designed based on the optimizing result and the studying of parameters affecting to dynamic characteristics. The FEA model of cavity acoustics in the cab is established based on the structure and the modal analysis of the cavity acoustics is done. An acoustic- structure interaction model of the cab is established combined the structure model and the cavity acoustics model. Sound pressure response of the node nearby the driver left ear is carried out based on the loading spectrum obtained in the road test. The sound pressure value unit is transformed as the decibel. The computed result indicated that the improved hydraulic mount can reduce the cab internal noise more effectively.In part 6, the hydraulic mount trial-manufacture is done according to the optimizing structure, as well as the road trail for validating the new hydraulic mount. The mould design and the key points of assembly process are stated. There are four conditions in the trial. The vibration isolation rate and vibration acceleration on the driver seat track are measured. The result of the trial indicates that the hydraulic mount improvement is effective. In this dissertation, the in-depth and detail study on performance-match of hydraulic mount for light vehicle cab is conducted with the methods of combining FEA and trials. The study is significance for improving the independent development capabilities of the light vehicle cab's hydraulic mount, enhancing the hydraulic mount performance of our country.