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It has been required recently that diesel engines for passenger cars meet various requirements, such as low noise, low fuel consumption, low emissions and high power. The key to improve the noise is to reduce a combustion noise known as “Diesel knock noise”. Conventional approaches to reduce the diesel knock are decreasing combustion excitation force due to pilot/pre fuel injection, adding ribs to engine blocks or improving noise transfer characteristics by using insulation covers. However, these approaches have negative effects, such as deterioration in fuel economy and increase in cost/weight. Therefore, modification of engine structures is required to reduce it. We analyzed noise transfer paths from a piston, a connecting rod, a crank shaft to an engine block and vibration behavior during engine operation experimentally, and identified that piston resonance was a noise source.

Conventionally, the effort of gear whine reduction has focused on minimizing the transmission error generated in automobile transmission. In mean time, as demands on gear whine reduction increased, the need of controlling noise transfer path was arisen because transmission error turns into interior noise in those paths [1-2]. In this paper, we provide experimental technologies to clarify the noise transfer path which dominants high frequency gear whine from experimental point of view.

Some of the frequencies of transmission gear whine noise reach up to several kHz. High-frequency gear whine noise is mostly transmitted by air (airborne); therefore, it is critical to reduce transmission radiation noise. This paper presents how to solve the problem of high-frequency noise in the range of 2.0 - 4.1kHz by experiment using Inverse Boundary Element Method (IBEM) and by computer simulation using Boundary Element Method (BEM).

The effort of gear noise reduction has traditionally focused on minimizing transmission error. On the other hand, gears vibration characteristics are also known to influence gear noise strongly. With the thin helical gears, therefore, the entire gear noise mechanism is clarified quantitatively by experimental analysis, and a dominant factor is specified. The analysis has shown that meshing force is the most significant factor. Thus, innovative gear structure has been devised, which aggressively controls meshing force characteristics like a dynamic vibration reducer. Redesigned gears have successfully improved gear noise. These experimental technologies and design methods can be applied to general gear noise problem in order to conduct optimization.

In order to minimize power train length, it is required for transmission components to layout compact. The requirement results in thinner and larger transfer gears, which are disadvantageous for gear noise. On the other hand, improvement of gear accuracy and/or vehicle interior noise increases sensitivity to manufacturing variation. It tends to appear noisiness by transmission unit variation. To prevent such gear noise problem, we made detailed investigation by both several tests and simulation, i.e. noise measurement, shaker test, running gear vibration measurement and FE Model analysis. This paper describes the experimental analysis of gear noise generation mechanism of transmission with thin and large diameter gear and its prediction method. It was found that gear web out-of-plane vibration modes are closely related to vibration transfer to the mission case. Planarly non-symmetric modes have dominant effect for case dynamic excitation by gear engagement.