Low Noise and Less Vibrations achieve Highest Comfort

“A car is a technical means that takes people from A to B.” Certainly a powerful statement in the very beginning of the vehicle era.  But time has changed, and so does the role of vehicles in our society. Users, vehicles and their environment are increasingly connected. The trend towards the increased electrification of vehicle powertrains is now firmly established. Whether through hybridization or substitution with pure battery-electric architectures. It is more and more necessary to question former methods and tools.

Passenger comfort challenges automotive OEMs

The trend towards automated driving today and autonomous driving in the future forces vehicle manufacturers to dive deep into the newly redefined attribute “passenger comfort”. What does passenger comfort in terms of noise, vibration, harshness (NVH) mean in the upcoming time when using cars as a new opportunity to work/relax/entertain?

Driven by growing customer expectations, interior noise has become a crucial vehicle comfort attribute. Vehicle sound is a complex issue, which decisively affects the well-being of humans. Depending on driving conditions, different noise sources such as powertrain, tires or exterior aerodynamics rule the overall acoustic comfort fingerprint of a vehicle.

On top of this, squeak, buzz and rattle noises, whose noise generation mechanisms do not necessarily correlate with the vehicle operating conditions, represent an annoying disturbance. As cars are in general becoming more silent, this gives the raise to noises such as squeak in dashboard or rattling of an internal locking mechanism inside a seatbelt retractor.

The human ear can capture a broad range of frequencies. While there are reliable vehicle acoustic models dedicated for low frequencies, the mid- and high frequency modelling still rely on simplified statistical approaches and hence represents an unresolved research niche. This particularly holds for electrified vehicles exhibiting high frequency tonal components due to the electric machine and its control components.

Generating the right sound

But not only reducing noise has become important – in psychoacoustics it’s all about generating the right sound. There are many open questions about the impact of noise to humans. Therefore, psychoacoustic models are being developed to find out what is relevant to optimize the acoustic environment. In addition, legal requirements such as warning sounds must be considered. This also plays a relevant role as a differentiator to brand sound.

Vehicle efficiency and acoustic comfort

Lightweight design substantially contributes to higher vehicle efficiency. Unfortunately, these measures often also imply worsening of sound insulation properties. Understanding of complex structure and airborne noise transfer paths in a vehicle and the way how to reduce them is hence of vital importance. Description and characterization of damping materials can greatly support this challenging task by adopting a targeted application of these noise control treatments.

The electrification of the modern powertrain – both in hybrid and full electric vehicles – also requires comprehensive investigation of phenomena in noise and vibration generation, their transfer and the impact evoked at passengers.

Safety first!

Reaching the targets for functional performance attributes such as safety or efficiency are the upmost priority in vehicle development process. Therefore, areas such as acoustics are often considered as subordinate. Furthermore, detailed numerical NVH models and, in particular, representative material properties are typically available at a later stage of vehicle development process. NVH issues, which emerge in a pre-final stage due to the lack of NVH models are hence difficult to solve, as the major design has been already frozen and the space for potential mitigation is correspondingly limited. As a consequence, quick fix workarounds are very expensive.

More detailed numerical models and in particular hybrid experimental-computational methods could hence greatly enhance the vehicle NVH design process. A close link between high-fidelity system simulation models and real-life testing is necessary to master the challenges such as growing complexity. This leads to more insight into noise generation and simulation results directly on testbeds will bring more clearness into powertrain and subsequently a shorter test cycle.