Prediction of sound pressure level for a dual-stage hydromechanical transmission

Hydromechanical continuously variable transmissions are frequently used in high power applications, including agricultural vehicles, buses and heavy vehicles. These offer several operative advantages such as improved driving comfort, better operational management and less fuel consumption if appropriately managed. However, the acoustic impact that they generate in the environment, which should be checked in the early stages of the project, is often neglected. This paper studies the noise emitted by a drive train for urban buses, which comprises a natural gas engine and a hydromechanical input coupled dual-stage transmission. The aim of this study is the evaluation of the noise emitted by the transmission compared with that emitted by the engine, which is considered the main noise source in the vehicle. The study was carried out by means of a model of the entire vehicle that was implemented in an Amesim environment. The mechanical model was integrated with the acoustic models of the engine and of the transmission. The results show that the transmission, despite its two hydraulic machines, produces a sound pressure level lower by about 2 to 15 dBA than that of the engine, whereas its contribution to the total pressure level does not exceed 1 dBA.