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This paper focuses on psychoacoustical experiments for the assessment of roughness by using vehicle interior noise. The experimental design is carried out carefully to derive reliable data for further analysis with objective parameters. Apart from the acoustical properties of the recording/playback system the different meanings of the word roughness are taken into account, because each person has its own interpretation of ‘roughness’ differing between the phenomenons of roughness, r-roughness, rumble, harshness, fluctuation strength, etc.. An important preparation for psychoacoustical experiments is a clear definition of the sound attribute under investigation by using typical examples. Furthermore, accidental influences of other psychoacoustical parameters like the influence of loudness have to be avoided.

The exterior and interior noise level of passenger cars has been reduced in the past to a large extent by legislation and on the demand of the car purchasers. One important marketing aspect today is the possibility to enjoy driving, which is determined by the noise quality and not the noise level inside passenger cars. However the interior noise quality of today's passenger cars does not always satisfy the people affected. In the development process of a vehicle, the noise quality is determined on a subjective basis by test drivers. A great deal of experience and time is required for the subjective assessment and for the further definition of strategies and their application to meet sound engineering targets for noise quality. This paper reports on the result of a R&D program to develop a software based Noise Quality Map with which the interior noise quality of passenger cars can be determined on an objective basis by measurement in real-time.

Noise legislation and subjective customer demands set future standards for noise and vibration control in all types of vehicles, from small passenger cars to heavy trucks. To obtain the required improvements, it is necessary - particularly for vehicles with diesel engines - to deal with all parameters which effect vehicle interior and exterior noise. For optimisation of total vehicle noise-vibration-harshness (NVH) the interaction of the power unit and other noise sources with the power unit mounting system, the vehicle chassis structural response and the vehicle local transmission losses have to be taken into account. It is then possible to design appropriate measures not only to meet certain noise levels, but most importantly to achieve, in parallel, a high quality subjective interior noise character over the complete operating range. In this paper the procedure adopted for optimising the NVH of a production off-road vehicle equipped with a DI-TCI diesel engine will be reported.

Future noise regulations for trucks require a 1 m engine noise level of 95 dBA or below at rated speed and load. To achieve this goal, noise reductions at source - lowering the excitation forces and the structure response - or secondary measures such as engine mounted shielding or encapsulation have proved to be effective. Since encapsulation technology is already well advanced, although rarely applied by vehicle manufacturers, the reduction of noise at source has become an important technique. In this paper it will be reported that the required noise level of 95 dBA can be achieved by the combined effect of reducing combustion excitation, optimising the engine structural response and using low noise materials for noisy engine parts. For all three subjects different approaches for noise reduction and their effect on overall engine noise, performance and reliability will be discussed in detail.

An efficient method for the reduction of vehicle noise is to close the engine compartment in a soundtight manner. By this means, the sound radiation from the power unit, which has main influence on the vehicle's exterior noise, can be reduced in an economic way. Furthermore, the increased suppression on the impulsive high frequency noise is subjectively recognized as an additional advantage. However, a large scale use of an encapsulation demands for proper cooling of the engine and, with respect to interior noise, a deterioration of passenger comfort must be avoided. In two different vehicles three kinds of engine enclosures have been tested. It is demonstrated that thermal problems within the enclosure can be avoided by an appropriate design. In addition, with some development of the cooling system, sufficient cooling rate can be provided.