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For electric vehicles, road noise, together with wind noise, is the most important contributor for vehicle interior noise. Road noise is very dependent on the NVH behavior of axle system including wheels and tires. Axle system is part of vehicle platform which should be compatible with different body variants. Therefore, il is important to characterize the NVH performance of an axle system independently of car body structure, so that the design the axle can be optimized at the early stage according to the global requirements of all the related vehicles. The best way to characterize the NVH performance of an axle system is to measure the blocked forces on an appropriate test rig. However, the measurement of blocked forces from an axle system requires very stiff boundary conditions which is difficult to achieve in practice. For axles with rigid mountings, it is nearly impossible to measure the blocked forces on test rig.

In this article, NVH performance of fully electric vehicles and some key technologies for NVH improvement are presented. A focus is made on a global NVH simulation methodology able to take into account the electromagnetic excitation sources and all the powertrain structure. Examples of simulation results are shown which allow us not only to predict the NVH performance, but also to understand better the fundamental NVH behavior of an electric motor. In an electric motor, the most important NVH phenomenon is the whistling noise, which is caused by the electromagnetic forces and amplified by the powertrain structure. With the current NVH simulation technology, e-motor whistling noise levels can be accurately simulated up to 4500 Hz. The improvement of e-motor whistling noise can be achieved both by reduction of the electromagnetic forces at the source and by optimization of powertrain structure.

Currently, new technologies in automotive industry are mainly driven by CO2 regulation and fuel economy. For most of the OEMs, the priority is to optimize internal combustion engines, make light-weighting and develop hybrid vehicles or fully electric vehicles. In this context, it is difficult and expensive trying to reach absolute silence in the cars. A good NVH strategy for non-specialist OEMs will be to keep the noise to an acceptable level and make it as homogenous as possible. This article presents several NVH guidelines for the powertrain in order to achieve homogenous noise in the cars. Firstly, master the level of powertrain vibration and maintain it at a suitable level. Secondly, eliminate abnormal noises which are unpleasant and disturbing, such as transient Diesel clatter noise. Thirdly, reduce the levels of emerging noises from powertrain components, such as turbo charger whistling so that they can be masked by background noise.

The recent use of electric motors for vehicle propulsion has stimulated the development of numerical methodologies to predict their noise and vibration behavior. These simulations generally use models based on an ideal electric motor. But sometimes acceleration and noise measurements on electric motors show unexpected harmonics that can generate acoustic issues. These harmonics are mainly due to the deviation of the manufactured parts from the nominal dimensions of the ideal machine. The rotor eccentricities are one of these deviations with an impact on acoustics of electric motors. Thus, the measurement of the rotor eccentricity becomes relevant to understand the phenomenon, quantify the deviation and then to use this data as an input in the numerical models. An innovative measurement method of rotor eccentricities using fiber optic displacement sensors is proposed.

The vehicle pass-by noise regulation will change in the near future and noise limits will be lowered significantly. This evolution will require improvement of engine's sound radiation. On the other hand, under the current pressure for fuel economy, future engines will be more and more lightened, and this will have negative impact on engine's sound emission. Therefore, the requirements related to the new pass-by noise regulation should be taken into account in the design of new powertrains, and in some cases, innovative solutions must be developed in order to improve the level of noise of the engine while reducing the masse of the engine. One effective way is to optimize the design of some key engine parts, such as crankshaft and engine bottom structure. Original approaches had been conducted and showed how much these engine parts can affect powertrain radiated noise, and in addition to find a quantitative relationship between crankshaft stiffness and powertrain radiated noise.

The Euro 6 emission standard requires a strong reduction of NOx and soot emissions for future Diesel engines. One of the ways to reach the Euro 6 standard for new Diesel engines is to adopt the low NOx combustion concept with new injection strategy, but this kind of combustion can give higher combustion noise and worse stability in transient conditions. This paper describes some of the new methodologies developed by Renault for controlling and optimizing Diesel combustion noise, particularly for engines with low NOx combustion modes. In steady working conditions, it was found that a homogeneous combustion mode gave high level of combustion excitation particularly in the 1000 Hz octave band. Thus improvement should be made in the engine structural attenuation (SA) in this frequency range in order to limit engine noise deterioration. This requires not only the technical solutions for improving the structural attenuation, but also reliable methods for measuring engine SA.

For a considerable time now, the reduction of noise and vibration is one of the priorities of Renault for its Diesel engines. For example, the target for the latest 2.0 L Diesel engine was to be in the top class category in terms of the noise and vibration. In order to reach this target, combustion noise has been improved at each stage of engine development process, and special methodologies have been developed either for combustion noise characterization or for combustion noise optimization. This paper describes some of the methodologies developed in Renault and illustrates some examples of results obtained. For measuring combustion noise in chambers, the combustion Noisemeter has been improved by introducing realistic engine structure attenuation. By comparison with other standard tools, it has been shown that the improved Noisemeter gives the best results with respect to the engine radiating noise, as well as to the subjective perception.

This paper describes the results of a study carried out in Renault about the effects of variation of flywheel bending stiffness on powertrain vibrations in the range of acceleration noise (250 Hz and 500 Hz octave bands). The flywheels used covered a wide range of stiffness, from a standard rigid flywheel to a very flexible one. On the one hand, NVH tests have been carried out on a Diesel common rail injection engine with 4 flywheels of different bending stiffness, from a rigid flywheel to a flexible one. On the other hand, simulations have been carried out by Excite on a whole Diesel powertrain model. Both test and calculation results have shown that the vibrations at powertrain mounting points in the 250 Hz octave band decrease continuously with the reduction of flywheel bending stiffness, and there is a nearly linear relationship between the vibration amplitudes and the first bending frequency of the cranktrain.