Development of Intake Sound Control Technique for Sports-Type Motorcycles

Engine sound is one of the most important factors when selecting a motorcycle from various models. Therefore, it is necessary to create an appealing sound in the rider's ears in addition to complying with noise regulations. In this paper, how we control intake sound is described through the study of a sports-type motorcycle with an inline 4 cylinder engine. To control intake sound, both intake pressure pulsations generated by the engine and acoustic transfer characteristics of the intake system are important. It is shown by unsteady-state one-dimensional computational fluid dynamics analysis that specifications of the exhaust system affect intake pressure pulsations across the valve overlap period. Therefore, to emphasize high order components of the engine revolutions in the intake sound, for example, modifying the layout of the exhaust muffler is effective. Next, acoustic transfer characteristics from the air cleaner box to the rider's ears of the motorcycle are investigated by acoustic tests based on the reciprocity principle. We try tuning these acoustic transfer characteristics by controlling resonance in the air cleaner box by means of finite element analysis. And, it is illustrated experimentally that the sound in the rider's ears is created as intended by modifying the air cleaner box. As a result, it is shown that intake sound can be designed effectively by the proposed method.