Recently engine sound quality is becoming more noticeable as noise level in a vehicle passenger compartment has been decreasing. It is necessary to reduce such discomforting noise as rumbling noise in order to improve engine sound quality.
This paper describes the experimental study to find out causes of rumbling noise in an engine structure and several investigations to reduce rumbling noise. Some new approaches have been introduced to evaluate the influence of an combustion impact, the movement of a crankshaft, timing of rumbling noise and so on. The result shows that the primary cause of rumbling noise is the movement of a crankshaft due to the impact of combustion and next is the vibration characteristics of the engine-transmission assembly (power plant).
Finally superior engine sound quality is achieved by increasing counterweights and stiffness of a crankshaft and also by optimizing the spark advance and improving vibration characteristics of various engine parts.