Estimation of noise radiation including airborne noise using the in-situ blocked force approach (Third report, experimental verification of the estimation method by application to rattle noise from an electric power steering system)

In the previous reports, a methodology for estimating noise radiation including airborne noise from a mechanical system under the operational condition by component test of a certain active subsystem using the in-situ blocked force approach, which is normally used for estimating only structure borne noise, was proposed and verified by numerical simulations of noise radiation from a cantilever rectangular plate. This paper describes experimental verification of the proposed methodology by application to rattle noise from a column type electric power steering system (EPS) for a vehicle. Therefore an EPS corresponds to the active subsystem and the other parts such as vehicle body correspond to passive subsystems. At first, a method of measuring rattle noise from an EPS under the operational conditions, i.e., running tests with a vehicle, was established. Since it is possible to apply the in-situ blocked force approach also to vehicle running tests and to estimate rattle noise, the measured and estimated rattle noises under an identical operational condition were compared and validity of the proposed methodology was confirmed. Next, a component test bench which enables to reproduce vibration behavior of an EPS under the operational conditions was developed, and rattle noise under an operational condition was estimated by means of the proposed methodology using both vibration accelerations measured with this component test bench and vibro-acoustic transfer functions measured with the vehicle under a static condition. Finally, the proposed methodology was verified by comparing the estimated and measured rattle noises under the operational condition. The proposed methodology is expected to replace time-consuming operational tests of a whole mechanical system to simple component tests of the active subsystem.