Optimization of Bushing Stiffness Using Numerical Approximation Model to Improve Automotive NVH Performance

Paper #:
  • 2017-01-1804

  • 2017-06-05
An efficient method to determine bush stiffness of passenger cars for satisfying requirement of noise and vibration is developed. In general, a passenger vehicle includes various types of bush to connect systems and control forces (loads) transferred between systems which affect characteristics of noise and vibration of the vehicle. Noise and vibration of a vehicle are mainly caused by forces from power train (engine and transmission) and road excitation. While a vehicle is in operation, road excitation is applied to the vehicle through bushes. If a bush transfers less force to the body structure, levels of noise and vibration will be decreased. In other words, it is necessary to well determine characteristics of bushes when developing passenger vehicles. Bush stiffness is one of key factors to affect the performance of noise and vibration of the vehicle. In the development process of a vehicle, bush stiffness is decided in the early stage and it is not validated until test is performed. If the performance is not satisfied in the test, another tests need to be conducted by changing bushes, which requires additional costs. In general, several test runs are performed to fix bushes which satisfy the requirement. In addition, setting the bush stiffness is complicated since there is typically a conflict between requirements of the bush stiffness induced from diverse vehicle performance, such as ride, handling, noise, and vibration. Therefore, in the early design process, validation of bush stiffness is desirable to save cost of development and ensure the performance of the vehicle. In this paper, optimization method is applied to improve the performance of noise for a four door sedan. For the analysis, a finite element model of the vehicle is employed in which the total number of degree of freedoms is almost 26 million. In the model, bush is modeled as linear spring with stiffness and damping in all the directions. Commercial solver NASTRAN is utilized for the analysis. For the optimization, a numerical approximation model describing the relation between bush stiffness and road noise is first constructed based on a Taylor series expansion. The expansion is obtained up to second order to consider effects of interaction between bush stiffness. Coefficients of the expansion are calculated by the finite difference method. Road noise analysis (considering only structure-borne noise) for the full vehicle model is conducted and coefficients of the numerical model are obtained. Then, optimization is preceded using the algorithm (active-set method) offered by MATLAB. Next, optimized bush stiffness to satisfy target performance is obtained using the approximation model. It is found that bush stiffness is well optimized while improving the noise.
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