In order to develop a 1 ton truck rear wheel air suspension module, this study designed and manufactured a Z-type spring and air suspension module test jig to optimize the design and reliability of the Z-type spring and vibration-free air suspension module, which are core parts, and to secure the reliability of the developed parts. We were able to achieve the technology development goal of this thesis by making a prototype and conducting a test evaluation at an external test and research institute to perform the vibration endurance test aimed in this study.

In commercial vehicles. the pulsation noise when the power steering operating is the major item to make the complain for users. If this noise have related to vibration characteristics in steering system's parts or assembly, it makes the problem in vehicle quality. Recently, the users demand the high quality in commercial vehicles, and we must identified the relevance between the pulsation noise and the vibration characteristics. After the identification, we can design the power steering system for satisfaction the user’s needs. Finally, the identification of relevance in pulsation noise for analysing the vibration characteristics will be suggested advanced power steering system.

There are many causes of interior noise in commercial vehicles. The one of them is power steering noise and this study try to reduce the power steering noise by theoretical consideration. The interior noise was tested for the real truck and analysed the frequency. For reducing the interior noise, the spiral tube was adapted and modified the structure in the steering system. The spiral tube system was analysed and made the formula to calculate the reducing frequency. And the effective frequency for reducing the interior noise was calculated by changing the length of tube. Finally, we found the possibility between thoeretical results and real interior noise by comparing the frequency results. The second, the experimental consideration will be worked in power steering system. Finally, the optimal design result will be suggested for reduce the noise.

There are many different causes of air drum brake judder noise in commercial vehicles. This study set out to identify those causes from the perspective of brake structure, not taking the environment into account. For that purpose, the investigator measured vibrations and noises in case of brake judder noise and analyzed their causes. The structural vibrations of the brake were analyzed to identify the causes with an experimental method involving O.D.S. (Operational Deflection Shape) analysis and model testing. In an effort to find directions for improvement with an analytical method, the investigator modeled the brake system in an analytical manner, correlated it with the experiment results, and tested directions for improvement in an analytical fashion. The structural rigidity of the brake that had been tested analytically was increased so that the generation frequency and structural vibration frequency of brake judder noises would not be contiguous. The parts of high structural rigidity were tested for brake judder noises with a model test and vehicle test.

For the purpose of finding out the acoustical characteristics of exterior materials in bridge, analytical studies are performed with boundary elements method by using the commercial program SYSNOISE. Before analysis, to figure out material property, it was conducted experiments of absorption coefficient for absorptive material. And prediction of pressure were conducted I GIRDER type (before & after installation of absorption panel ) and BOX GIRDER type (before & after installation of absorption panel) The results show that when the absorption panel is installed, environment around bridge can help reduce traffic noise. It was proved to be the effective noise reduction counter-plan for a traffic noise in the bridges.