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Vehicle manufacturers throughout the world are facing increasingly stringent noise legislation which demands highly refined vehicles and powertrains for compliance. Further to the demanding legislative requirements, an increase in customer awareness regarding high ride comfort has forced additional refinement as regards competitive sound level and sound quality. In the commercial vehicle market this trend in increased customer awareness is growing ever more apparent, although the expectations regarding noise are, for some applications, justifiably lower than in the passenger car market. Further to legislative compliance and a competitive noise level in dB(A), noise quality issues are increasingly being addressed to satisfy customer demand. In the passenger car market customer awareness regarding noise has increased to such an extent that in order to satisfy customer expectations engineering desirable sound has become an integral requirement.

Despite the increasingly stringent emissions legislation, users and owners of commercial diesel vehicles are continually demanding that each new engine generation is more economical than the previous one. This is especially important for commercial vehicles where the majority of engines are in the 1-2ltr./cyl. class. The demands are being reflected in new engine designs with lower friction and improved structural stiffness, together with fuel systems having increased pressure capability, higher spill rates, injection rate shaping and advanced control features. These fuel system requirements have led to a variety of new fuel injection systems and in the search for increased injection pressure these fuel systems have placed greater demands on the engine, especially in areas such as the cylinder head and fuel system drive, sometimes with adverse effects on the combustion and fuel injection system induced mechanical noise.

Noise legislations and the increasing customer demands determine the NVH-development of modern commercial vehicles. In this paper suitable engineering approaches will be discussed. In order to meet the very stringent legislative requirements of the EEC and some other countries refinement of all vehicle noise sources is required. Cost-effective solutions, however, can only be found with low-noise powertrains, thus being able to avoid excessive noise packages on the vehicle. There is increasing demand, because modular systems should be ready to power a variety of different trucks and busses and allow for easy servicability. With this focus on powertrain noise, the paper discusses and outlines the technological developments required to achieve sufficient noise reduction which aims towards a 1m engine noise level of 93 dBA measured in an acoustic test cell under rated conditions.