Abstract
Vehicles should provide a comfortable circumstance for passengers during driving. The noise from the transmission case is one of the causes of discomfort. The transmission is composed of gears, shafts, bearing and cases. When transmission activity occurs, noise is transferred to passengers through the transmission case. Design of the transmission case is performed in order to reduce the transmission noise. Acoustic analysis is carried out and structural optimization is utilized for the design to reduce the noise. The boundary element method (BEM) has been utilized for acoustic analysis. However, it is difficult to utilize the boundary element method in structural optimization because the cost to calculate the sensitivity information is fairly expensive in the optimization process. Instead, the finite element method (FEM) is employed for calculating the radiation noise of the transmission. The radiation noise is considered as the total noise from the transmission. The radiation noise is calculated at the outside of the transmission case and it can be expressed indirectly by multiplication of the velocity in the normal direction of the finite elements, the radiation efficiency and the acoustic impedance. The high frequencies are dominant for the transmission noise and the radiation efficiency is 1 at the high frequency range. Since acoustic impedance is a constant value, the noise is the same as the absolute value of the velocity. The velocity of each finite element is calculated from modal analysis and the noise is the sum of the velocities at all elements which yield noise. In structural optimization, the design variables are the thicknesses of the groups of the transmission cases, the objective function is the mass of the structure and a constraint is defined on the noise. An alternative formulation is made by exchanging the objective and constraint functions. The optimization results are discussed in terms of practical application.
Keywords: Acoustic power, Transmission case, Superelement, Size optimization