Effects of Automotive Megatrends on NVH

Noise Vibration Harshness

10. October 2018 | Engineering Service

Several trends in the automotive industry, driven by social and political changes, as well as new technology possibilities, will cause fundamental changes for future vehicles and will strongly effect vehicle NVH requirements. Four megatrends are summarized by the acronym CASE: Connected, Autonomous, Shared and Electric.
It’s been scientifically proven that human-made carbon dioxide (CO2) emissions contributes to global warming, and since then, strategies to reduce traffic-related CO2-emissions have been a major factor in (conventional) powertrain and vehicle development.

For some years, downsizing combustion engines to reduce fuel consumption was an important field of development, driving and fueling a number of research activities. Recently, electrification of the powertrain has become the strongest trend with regard to CO2-emmission reduction. Hybridization in varying degrees is already widespread in the automotive market. For the European market, FEV expects a major shift towards plug-in-vehicles, with a final distribution mainly dependent on customer preferences.

A second trend that is already visible is the increasing degree of shared mobility. Recently, companies with a strong commercial focus have explored the field of shared mobility with enormous growth rates. With regard to ongoing urbanization and the population increase, the demand for public and shared mobility can be expected to increase at the cost of motorized individual traffic.
Two more megatrends can be identified in the automotive world and are largely linked to each other: connected vehicles and autonomous driving. FEV expects the first fully autonomous cars in ~2027, with an expected market share of about 12% in 2030. Fully autonomously driving vehicles can be expected to develop a very different environment from conventional vehicles. Connecting vehicles to each other, the road and the world is not only a prerequisite to enabling autonomous driving, it will also provide drivers and passengers various information. This, too, will have an impact on the NVH properties demanded from the vehicle.

>> Customers have certain expectations concerning brand sound and the sound character

The new trends in automotive industry raise many questions for current and future development: How will the car of tomorrow look? What will it be able to do and how will it sound? What will the interior look and feel like? To which extend can personal taste be addressed when cars are no longer personal property, but have largely become shared goods? What kind of environment will the automotive industry create inside of an autonomously driving car and which role does NVH play in this environment? How much and which information will be provided acoustically, and how? For many of these questions, there are answers and for some of them, none. However, FEV would like to offer some ideas and encourage you to develop some of your own.

Shared

Different car manufacturers and models distinguish themselves from others through various attributes. Besides rather objective properties like weight, power, fuel consumption, size or price, soft skills, such as exterior and interior design, and NVH are more important selling points. FEV uses evaluation criteria to describe a vehicle’s NVH characteristic. Two very important parameters of these are applied to describe a vehicle’s NVH: comfort and dynamic. These parameters are determined by jury evaluations or are calculated from objective sound characteristics. Generally, vehicles that are more dynamic tend to be observed less pleasant.

If vehicles of the future are shared between many users, not just by one, how should the vehicle be positioned on a map that shows comfort and dynamic ratings? A potential scenario is that future shared vehicles are tuned to the current customer’s taste by active sound design, which may mean adding driving situation related noise shares by the HiFi-system, as seen in Figure 1.

Fig. 1: Target variants for positioning of Dynamic/Comfort-Ratings and possibility for tuning through Active Sound Design

The current vehicle user would be identified by his or her chip-card, which also stores their personal NVH preferences. The systems in the vehicle, which take active influence on the interior noise, are then controlled by user preferences.

Connected

Connected vehicles will have increasingly more access to various types of information. Some of this information will be used solely by the vehicle itself, and some of the information will be forwarded to driver and/or passengers. Such information will be presented visually, aurally or for example by movements of the seat or other features. However, this is largely the situation today. Thus, the increased connectivity is expected to influence tomorrow’s vehicles’ NVH rather indirectly by enabling other technologies like autonomous driving.

Electrification

The electrification of automobile propulsion is probably the most advanced of the trends considered here. Electrified vehicles, whether hybrid or fully electric, have been successfully introduced in series production by many OEMs.
Different subject areas arise when NVH of electrified vehicles is considered (Figure 2).

Fig. 2: NVH phenomena of electrified vehicles

Safety: Some countries already prescribe an additional vehicle warning noise for pedestrian safety. The challenge is not to lose the advantage of traffic noise reduction with quieter electric vehicles by deliberately created irritating warning noises. In addition, the warning noise should not be perceived by the driver or passenger. Therefore, a good isolation between the loudspeaker and interior must be implemented.

Irritating interior noise: Although electric vehicles are often considerably quieter than comparable vehicles with combustion engines, the interior noise is marked by high-frequency noise components, which typically are subjectively perceived as irritating and unpleasant. Tonal noise components are especially critical.

Masking: Moreover, disturbing noise is no longer masked by combustion engine noise. That means, noise from the drivetrain itself, as well as unpleasant noise shares from other vehicle systems, come into the fore. Due to the missing noise from the ICE, road and wind noise will become more apparent. This frequency dependent background noise is used to define target lines for other noise shares from e-motors or transmissions.

Sound character/brand sound: The automotive industry has experience in designing the interior sound of vehicles with combustion engines. In addition, customers have certain expectations concerning brand sound and the sound character regarding comfort and dynamic. Quiet electric vehicles offer new creative prospects, which must be filled by responsible engineers. More frequently, synthetic sound is used to give the driver load feedback and thus create a dynamic sound impression.
Amongst other trends in automotive industry, vehicle electrification offers interesting possibilities:

  • Autonomous: Option to create more quiet and comfortable interior noise, and less vibration as it is expected from a driver not concentrating on driving
  • Shared: Quiet electric vehicles offer more options to create customized interior noise for the specific user by active sound design
  • Connected: The sounds, which inform the driver about the surroundings, can be created more discreet due to less masking noise of the drivetrain

Autonomous

Autonomous vehicles offer the chance to use travel time for other things, which can be for occupational or recreational purpose. It is expected, that highly automated and connected vehicle concepts will enter the markets in the next ten to 15 years. Vehicles with different degrees of autonomous driving functionalities will be introduced step by step.

The transition from user driven to autonomously driving vehicles will have a strong effect on user expectations and thus on the vehicle requirements. The user of a fully autonomous vehicle does not actively take part in the traffic events; he is out of the control loop. His situation is similar to a passenger in a train or a person in the backseat of a chauffeur driven vehicle, but very different from the driver of a conventional vehicle. His main interest will likely be that the driving events do not disturb his activities like talking, reading, talking on the phone, watching movies or working on a laptop. Maybe the only wanted disturbance is information from the vehicle, such as when the estimated arrival time is changing. Considering this, it can be expected that all comfort oriented vehicle features will become more important, whereas other features like acceleration performance or engine power will become less important. Interior noise and vibrations (N&V) are main influencing factors for a comfortable impression of the surrounding, thus all comfort criteria of interior N&V will likely have a higher weight in the vehicle requirement book. The dynamic and sporty oriented noise features will not be needed, as the user will perceive them as interference.
A user surveillance confirmed this general evaluation. Together with experts for the different components and features of vehicle and powertrain, the relevance of different vehicle specifics of an automated vehicles in relation to a conventional vehicle is derived (Figure 3). For the rating of the vehicle specifics, two very different fields of vehicle application are distinguished: a specialized “City Pod” vehicle is purely designed for mobility within a city anda “Highway Pod” is designed for long distance travel. In such a future mobility concept, vehicle hubs can be assumed, where the passenger changes from city-pod to highway-pod and vice versa.

Fig. 3: Change in relevance for vehicle specifics in dependence of use case

According to this assessment, engine features, such as nominal power and torque will become less important, especially for the city-pod. Low-end torque and responsiveness will become less important especially for the highway-pod. Comfort-related NVH features, such as jerkiness of start, interior vibration, high frequency quality of interior noise and low- and high-speed boom are expected to be significantly more relevant for automated vehicles. Again, the importance of the NVH criteria differs according to the vehicle use case, with the behavior at vehicle start clearly more important for the city-pod, and high-speed behavior more relevant for the highway-pod.

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