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Vehicles with electrified powertrains are being introduced at an increasing pace. On the level of interior sound, one is often inclined to assume that NVH problems in EV have disappeared together with the combustion engine. Three observations demonstrate that this is not the case. First of all, only the dominant engine sound disappears, not the noise from tire, wind or auxiliaries, which consequently become increasingly audible due to the removal of the broadband engine masking sound. Secondly, new noise sources like tonal sounds from the electro-mechanical drive systems emerge and often have, despite their low overall noise levels, a high annoyance rating. Thirdly, the fact that engine/exhaust sounds are often used to contribute to the “character” of the vehicle leads to an open question how to realize an appealing brand sound with EV. Hybrid vehicles are furthermore characterized by mode-switching effects, with impact on both continuity feeling and sound consistency problems.

The noise radiated by an ICE engine results from a mixture of various complex sources such as combustion, injection, piston slap, turbocharger, etc. Some of these have been categorized as combustion related noise and others as mechanical noise. Of great concern is the assessment of combustion noise which, under some operating conditions, is likely to predominate over the other sources of noise. The residual noise, produced by various other sources, is commonly referred to as mechanical noise. Being able to extract combustion and mechanical noise is of prime interest in the development phase of the engine and also for diagnostic purposes. This paper presents the application of combustion mechanical noise separation techniques on a V8 engine. Three techniques, namely the multi regression analysis, the classical Wiener filter and the cyclostationary (synchronous) Wiener filter, have been investigated.

The current trend toward hybrid and electric automotive powertrains increases the complexity of the vehicle development and integration work for the NVH engineers. For example, considering that the combustion noise is reduced or absent, secondary noise sources like drivetrain, auxiliary systems, road and wind noise become of relevance in terms of vehicle noise comfort. This trend combined with the shortening of vehicle development cycle, the increased number of vehicle variants and an increasingly competitive marketing landscape, force engineers to front-load their design choices to the early stages of the development process using advanced engineering analysis tools. In this context, innovative technologies such as Virtual Prototype Assembly (VPA) and NVH simulator provide the right support to the engineer’s needs when developing the vehicles of the future.

Certification of vehicle noise emissions for passenger vehicles, motorcycles and light trucks is achieved by measuring external sound levels according to procedures defined by international standards such as ISO362. The current procedure based on a pass-by test during wide-open throttle acceleration is believed far from actual urban traffic conditions. Hence a new standard pass-by noise certification is being evaluated for implementation. It will put testing departments through their paces with requirements for additional testing under multiple ‘real world’ conditions. The new standard, together with the fact that most governments are imposing lower noise emission levels, make that most of the current models do not meet the new levels which will be imposed in the future. Therefor automotive manufacturers are looking for new tools which are giving them a better insight in the Pass-by Noise contributors.

This paper presents a new time-domain source contribution analysis method for in-room pass-by noise. The core of the method is a frequency-domain ASQ model (Airborne Source Quantification) representing each noise generating component (engine, exhaust, left and right tyres, etc.) by a number of acoustic sources. The ASQ model requires the measurement of local FRF's and acoustic noise transfer functions to identify the operational loads from nearby pressure indicator responses and propagate the loads to the various target microphones on the sides of the vehicle. Once a good ASQ model is obtained, FIR filters are constructed, allowing a time-domain synthesis of the various source contributions to each target microphone. The synthesized target response signals are finally recombined into a pass-by sound by taking into account the speed profile of the vehicle.

The Transfer Path Analysis method is at the core of the Source-Transfer-Receiver approach to address noise and vibration problems. While originally developed for analyzing structure-borne noise transmission, its application range has been extended to airborne noise. Various frequency and time domain approaches have been developed with a focus of supporting specific design engineering problems. One such application is the source contribution analysis in the context of vehicle pass-by-noise. The upcoming changes in the pass-by noise regulation will not only require more complex tests in different conditions but most importantly, the new directive will force car manufacturers to further reduce the emitted noise levels of their vehicles.