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This paper deals with the results of an investigation of moulded cases such as acoustic deflectors housing noisy equipment of the vehicle. The main advantage of the deflector is to decrease the level of noise, but the phenomenon of self-excitation is important, too, because it becomes a new source of noise. Readjustment of the vibration modes spectrum is possible by creating special structural variations, which increase the internal dissipation of energy of the vibrations in the deflector material. This approach is related to the introduction of design variables, the kind of material or to the choice of the points of fixation. The principal indication of a vibration mode of such a structure as a deflector is the number of nodal points. This characteristic gives the possibility to select several groups of modes, which are effective from the viewpoint of decreasing vibration amplitudes. Other possibilities are related to the means of active vibroinsulation.

This paper summarizes the results that were obtained from investigations of vibrations of cover- and box-shaped elements that cover assemblies of automobiles and are intended to diminish noise. The problem is that the elements in hand can appear to be the additional source of vibrations. For the elements fastened on the automobile body, the conditions for vibration excitation and recommendations for design are made more precise, at the same time keeping in mind that the main function of mentioned elements is not the reduction of noise. Our approach consists of three main directions: modifying properties of material, changing structure of elements and recommendations for choosing the preparation of its fixation points.

Vibration of an exhaust tube with a non-linear fixing construction is analyzed. Numerical and laser holography investigation methods are used for the determination of vibration processes happening nearby the cylinder fixing areas. Obviously, the analyzed non-linear system can produce complex reactions even to harmonic excitations. The knowledge about such zones of “wrong” dynamic behavior may help to eliminate and reduce higher noise levels and extend the lifetime of the construction.

The dynamics of the vehicle is strongly dependent from the quality and interaction between its subsystems. The quality of assembly and mounting of bearings can effect the characteristics of the system, especially its dynamical properties. The assembly process of bearing joints requires rather high pressing forces. At the same time the accuracy of the assembled components must be controlled with extreme precision. Rather small deviations from the predefined limits can cause quite severe complications, - such as necessity of maintenance, or just problems with dynamical response of the subsystem, especially under heavier dynamic loads. The goal of the study was to evaluate the status of bearing joints assembly, and to optimize the process of mechanical integration. The control of the mounting forces was altered introducing the high frequency vibration excitation. The resulting effect decreased friction and static load forces in the joint under the assembly.