Katrien Wyckaert

Operational analysis, transfer path analysis, modal analysis: tools to understand road noise problems in cars

This paper discusses a road noise analysis application on a passenger car. It involves a study of the interior noise in the car, which is explained in function of the energy transfer paths from the suspension into the car body. For this, multiple reference transfer path analysis is used. A link is made between specific characteristics of this energy transfer and the operational analysis of the measurements on the suspension during road tests, as well as the acoustical modes of the cavity. The operational data are correlated with modal analysis results on the suspension, explaining certain problems occurring during running condition.

Modular Vehicle Noise and Vibration Development

Fundamentally, vehicles are assemblies of subsystems or modules: engine, tyres, dashboard, steering system, body structure, wheel suspensions, etc. These modules are developed in parallel at multiple locations and often for more than one vehicle. On top of this, the integration of modules in a complete vehicle is also becoming a parallel rather than sequential development activity. This has a strong impact on vehicle NVH development. The noise and vibration (NVH) quality of a vehicle will become apparent not too long before its planned production start, on the first fully trimmed and equipped prototype vehicles. Under normal costs and product release pressure, this does not leave much scope for further NVH development. The obtainable NVH quality therefore relies strongly on the specification and assessment process of the subsystems as well as on the early part of the integration process. Recent improvements of substructuring and transfer path analysis techniques can contribute significantly to the reliability and practicality of modular NVH assessment and development. This does not only cover the individual subsystem design, but also the assessment of proposed packaging and subsystem interfacing solutions. The accuracy of modular NVH assessment is improved by these techniques in two ways: 1. Top-down; from vehicle behaviour to required subsystem behaviour and parameters. The transfer path analysis techniques for airborne and structure borne effects can be used in many situations to derive adequate subsystem NVH requirements from complete vehicle NVH requirements; 2. Bottom-up; estimating the vehicle NVH response from subsystem tests and numerical models. Modal based synthesis and frequency response function based synthesis can be used to build assemblies of subsystems. In situations where the subsystems dynamics and/or acoustics are strongly coupled, individual subsystem requirements (top-down) will not necessarily ensure a good assembled system behaviour. Substructuring can produce estimations of the NVH properties by combining data from existing and newly proposed subsystem solutions. The paper will give an overview of the methods and some test-based case examples are used to clarify the procedure. (A) For the covering abstract see ITRD E113232.