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The automotive industry continues to develop new powertrain and vehicle technologies aimed at reducing overall vehicle-level fuel consumption. Specifically, the use of innovative drivetrain technologies including conventional and electrified propulsion systems is expected to play an increasingly important role in helping OEMs meet fleet CO2 reduction targets for 2025 and beyond. NVH development for vehicles with electrified powertrains introduces new challenges, which need to be understood and solved. The electrified vehicle space spans variants from micro and mild hybrids all the way through plug-in hybrids and fully electric vehicles. In addition to conventional NVH development methodologies, active sound design (ASD) can play a crucial role to enhance the interior sound perception of such vehicles and hence, improve customer acceptance of new technologies. This paper will begin with an introduction to the NVH challenges posed by electrified vehicles.

In modern vehicle acoustics, Active Sound Design (ASD) is a popular method to enhance the interior sound perception of a vehicle. In vehicles with a traditional internal combustion engine, the load dependency of the sound can be increased to give a positive dynamic feedback. Irritating small band resonances can be attenuated by boosting the surrounding frequency content, and downsized-engines with a small number of cylinders can be made to sound like the larger ones from former days. However, once a characteristic sound is designed for a specific vehicle, it is a tedious process to transfer this lead-sound to derivatives (e.g. same model but different exhaust system). So far, sound designers must adapt the ASD dataset manually - usually this takes several loops of measuring the vehicles interior sound on a track and adjusting the ASD settings back in the office.

The most appreciated driving characteristics of electric vehicles are the quietness and spontaneous torque rise of the powertrain. The application of range extenders (REX) with internal combustion engines (ICE) to increase the driving range is a favourable solution regarding costs and weight, especially in comparison with larger battery capacities. However, the NVH integration of a REX is challenging, if the generally silent driving characteristics of electric vehicles shall remain preserved. This paper analyses key NVH aspects for a REX design and integration to fulfil the high expectations regarding noise and vibration comfort in an electric vehicle environment. The ICE for a REX is typically dimensioned for lower power outputs, incorporating a low number of cylinder units, which is even more challenging concerning the NVH integration. It will be explained that sophisticated, innovative technologies are required on component and vehicle side to ensure best possible NVH comfort.

The automotive industry continues to develop new powertrain and vehicle technologies aimed at reducing overall vehicle-level fuel consumption. Specifically, the use of electrified propulsion systems is expected to play an increasingly important role in helping OEM’s meet fleet CO2 reduction targets for 2025 and beyond. This will also include a strong growth in the global demand for electric drive units (EDUs). The change from conventional vehicles to vehicles propelled by EDUs leads to a reduction in overall vehicle exterior and interior noise levels, especially during low-speed vehicle operation. Despite the overall noise levels being low, the NVH behavior of such vehicles can be objectionable due to the presence of tonal noise coming from electric machines and geartrain components as well as relatively high shares of road/wind noise. In order to ensure customer acceptance of electrically propelled vehicles, it is imperative that these NVH challenges are understood and solved.

The automotive industry continues to develop new powertrain and vehicle technologies aimed at reducing overall vehicle-level fuel consumption. Specifically, the use of electrified propulsion systems is expected to play an increasingly important role in helping OEM’s meet fleet CO2 reduction targets for 2025 and beyond. Electric and hybrid electric vehicles do not typically utilize IC engines for low-speed operation. Under these low-speed operating conditions, the vehicles are much quieter than conventional IC engine-powered vehicles, making their approach difficult to detect by pedestrians. To mitigate this safety concern, many manufacturers have synthesized noise (using exterior speakers) to increase detection distance. Further, the US National Highway Traffic Safety Administration (NHTSA) has provided recommendations pursuant to the Pedestrian Safety Enhancement Act (PSEA) of 2010 for such exterior noise signatures to ensure detectability.

In order to minimize the development and production costs in the automotive industry, despite steadily increasing variety of models and applications offered by the OEMs, the pressure on standardization of components and production processes is increasing continuously. As a direct consequence, modular engine families are already established with high degrees of common parts and kits as well as standardized interfaces for all vehicle platforms by most manufacturers these days. At the same time, the world adopted and announced massive legal demands concerning the reduction of CO2 emissions for the entire vehicle fleet. In addition to the optimization of the combustion process, the exhaust gas aftertreatment and thermal management, the use of improved and more resilient materials for higher reduction of mechanical friction leads to a significant amount of the realized lowering in fuel consumption respective CO2 emissions.

Besides an excellent driving performance and power output the reduction of CO2 emission is one of the main driver for the increasing distribution of modern diesel engines. Downsizing/downspeeding, friction reduction, new combustion processes and light weight engine architecture describe additional improvement potentials. Nevertheless, these development trends have a significant influence on the noise and vibration behavior of diesel engines. Therefore measures are also necessary to compensate these acoustic disadvantages. Within this publication the most important and efficient countermeasures are described and assessed. Combustion is still one of the dominant noise sources of a modern diesel engine. Diesel knocking is annoying and the combustion noise level is typically higher than for gasoline engines.

In the future, computer-based development tools will lead to a significant reduction in the duration of the development period for both powertrains and vehicles as well as ensure a dramatic increase in product quality. Today, CAE tools support the development process beginning with concept design and ending in series production. This paper presents today's state-of-the-art CAE capabilities in the simulation of the dynamic and acoustic behavior of Powertrain components. The paper focuses on the interaction of the excitation mechanisms and noise transmission. Modern CAE tools allow the analysis, assessment and target-oriented acoustic optimization of the powertrains and powertrain components.

Combustion noise plays a considerable role in the acoustic tuning of gasoline and diesel engines. Even though noise levels of modern diesel engines reach extremely low values, they are still higher than those of conventional gasoline engines. On the other hand, new combustion procedures designed to improve fuel consumption lead to elevated combustion noise excitations as in case of today's direct injecting gasoline engines whose vibration excitation and airborne noise emissions are slightly increased during stratified operation. The partly conflicting development goals resulting from this can only be realized by integrating the NVH specialists' expertise into every development step from concept to SOP.

Geartrain-related noise has become a more dominant noise concern mainly due to the increasing demand for high-pressure injection systems. Engine geartrain noise is mainly caused by torque fluctuations of the crankshaft and the injection system, both leading to tooth impacts between the gears of the geartrain. Gear impacts can generate dominant NVH problems due to the high frequency content of the gear impact forces, although their amplitudes are much lower than those of the combustion forces. If the natural frequencies of the surrounding structure are met, an intensive radiation of the surrounding structure is caused. FEV has developed a simulation method for the analysis of geartrain dynamics aimed at identifying and optimizing potential noise sources. This simulation method is an essential tool for the development process of a technical product. It realizes a minimum effort to set up the model at reduced calculation time.