Abstract
Interior noise in a vehicle has a major impact on the subjective perception of comfort. Research and development in the automotive industry have focused on the sound generated in the drivetrain and transferred to the passenger compartment. As in many other fields, the multi body simulation of phenomena is well established in the field of vehicle acoustics. When considering gear whine, the development mechanisms in the transmission, attributed to the varying gear stiffness, on the one hand and the noise transfer to the driver on the other have to be taken into account. A method combining an MBS (multi body system) simulation with experimentally determined transfer functions was developed at the Institute of Automotive Engineering in order to predict the acoustic behaviour of new vehicle-drivetrain configurations before a prototype is created.
The mechanisms causing gear whine are simulated in a multi body system. For the transmission segments of the engaged gear and the axle drive the MBS model shows varying gear stiffness throughout the progress of the engagement. The mechanisms causing gear whine can thus be reproduced. With regard to the mounts of the engine-transmission unit, the points where the body-borne sound is fed to the body are modelled regarding their spatial positions on the one hand while the transfer behaviour of the body-borne sound is considered on the other. The non-linear characteristics of elastomeric and hydro mounts were determined experimentally at the Institute of Automotive Engineering. The mount characteristics up to a frequency of 1000 Hz are represented, taking the dependence of force on travel and speed as well as the axle connections into account. This MBS model had been used to simulate the structure-borne sound occurring at the bodywork’s side of the mounts before it was verified by measurements in the vehicle.
In the second part of the method the structure-borne sound occurring at the bodywork’s side of the mounts is combined with transfer functions in order to predict the whining noise perceived by the driver. The transfer functions specifying the sound progressing from the mounts through the bodywork and the airborne sound propagation in the passenger compartment were determined experimentally for all mounts in all spatial directions. Due to the combination of MBS simulation and experimentally determined transfer functions, the structure borne sound occurring at the mounts can be evaluated regarding the gear whine noise perceived by the driver.
The presented combined method allows the prediction of gear whine for an existing vehicle body considering new engine-transmission configurations without requiring a prototype. If crucial system parameters such as gear stiffness characteristics and non-linear transfer behaviour of the elastomeric / hydro mounts are known, time efficient prediction of noise phenomena and identification of control parameters is possible.
Keywords: Gear Whine, Simulation, MBS, Elastomeric Mounts, Transfer Path