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This paper discussed the sound quality which assumed important factor in the development of outboard engines in the 183 to 257 kW class in the future. Many kinds of industrial product development dealt with sound quality, and there were many examples using sound quality index adapted customer requirements or products usage. In case of outboard engine development, there were examples of noise reduction and compliance with noise regulations, but there was almost no example of sound quality development. This research proceeded a questionnaire survey of 90 boat owners who were listening to several cruising engine sounds in main market, US. From this result, authors discussed customer trend and extracted 3 sound quality indexes, luxury, deep and sporty, which were demanded in our target class. Next step was that authors made simulation sounds referring 3 sound quality indexes to verify customer’s trend.

In order to efficiently enhance engine sound quality under acceleration, the authors have developed an evaluation method for primary judgment of the sound quality of engine combustion noise at the stage of advanced engine development before the prototype vehicle is built. This method is an application of an existing method for evaluating the sound quality of engine combustion noise in vehicle interiors to the evaluation of noise and vibration at an engine acoustic test bench. In this method, it is necessary to consider the air-borne and the structure-borne components separately. The analysis procedure for the air-borne component is as follows. First, the sound pressure at a point 1 m away from the engine and the in-cylinder pressure of each cylinder are measured simultaneously in a semi-anechoic engine dynamometer test chamber. Next, the signal correlated with engine combustion is extracted from the measured sound pressure using the time domain combustion noise separation method.

This report will introduce a new engine sound design concept and propose a design process. In sound design for automotive development of popular vehicles, it is common to seek to enhance the state of the existing marketed vehicle in order to meet further demands from customers. For standout models such as sports vehicles and flagship vehicles, sound design commonly reflects the sound ideals of the manufacturer’s branding or engineers. Each case has common point that the sound direction is determined by itself clearly. However, in this way, it is difficult to create abstract concept sound. Because it is no direction for the sound. Therefore, this paper examines ways to achieve a new sound that satisfies a sound concept based on an unprecedented abstract concept “wood”. The reason why sound concept is “wood”, it is the difficult to make as a new engine sound and good study to reveal usefulness of new sound design process.

This paper summarizes the piston pin noise mechanism and show the way to reduce noise level of semi-floating system. A mechanism of piston pin noise of semi-floating system was clarified by measurement of piston and piston pin behavior and visualization of engine oil mist around piston and piston pin. Piston and piston pin behavior was measured by accelerometer and eddy current type gap sensor with linkage system at the actual engine running condition. Engine oil behavior was visualized and measured its flow vector by Particle Tracking Velocimetry (PTV). For PTV, engine oil mist particle image was taken by high speed camera with fiber scope attached to linkage system. From themeasurement, it was cleared that engine oil doesn't reach to piston hole from undersurface of piston land and come rushing out from piston broach via groove. The result shows that lacking of engine oil between piston and piston pin makes noise larger.

Crank rumble is an amplitude-modulation of engine noise perceived inside a car. It is common under full load acceleration but not under part load acceleration, so could cause concern. Honda and Ricardo carried out a program of work to research methods to reduce the perceived (subjective) level of crank rumble inside a vehicle under part load acceleration. Transfer Path Analysis (TPA) is a method of predicting vehicle interior noise by separating sources (the engine) and transfer paths (the vehicle body). TPA was applied in the time domain to allow subjective assessment of the different contributors to the interior sound quality. Subjective assessment was performed by a panel of listeners, to avoid bias caused by individual opinions. This approach identified key contributors to the perceived crank rumble, and allowed targets to be set. Computer Aided Engineering (CAE) was used to study a range of modifications to the engine.