A loud silence: how vehicle NVH can hinder electric car adoption

As the race to commercialize the electric car continues, issues surrounding vehicle NVH and its impact on passenger comfort is proving to be one of the disadvantages of electric vehicles.

Although fraught with challenges, building the electric vehicle is leading to new vehicle concepts and forcing engineers to rethink how transportation vehicles are developed, which include e-motor design, battery packing and electrical systems.

While some engineers focus on ways to make the exterior of a vehicle auditorily pleasing and not make our city streets sound like a Las Vegas casino, others struggle for ways to make the interior cabin pleasant. For decades, the purr of an engine has hidden a variety of displeasing noises, but with electric vehicles and their near-silent powertrains, these annoying sounds are front and center, and they must be addressed.

As consumers started purchasing and driving electric vehicles, it soon became clear there was a noise issue that significantly hindered passenger cabin comfort.

Even if it’s not very noisy, it’s still present and it’s important to have the tools to make the right decisions and solve the problems as early as possible.

Electrifying systems and attributes can lead to unforeseen vehicle NVH issues. There is not a single source; noise comes from a myriad of places:

• Powertrain
• HVAC
• Sound system
• Brake squeal
• Wind noise
• Road noise

Each application carries a whole host of noises that need managing. The powertrain, for instance, has the following sources to consider:

• Noise directly from the engine
• Noise transmitted from the engine into the car structure through vibration
• Noise coming from driveline
• Auxiliary noise from alternators or pumps

Electric vehicles offer much lower powertrain noise levels than their conventional vehicle counterparts, but that doesn’t mean they are quiet. Electric vehicles are lighter by design to help improve driving range and, for example, with no internal combustion engine roaring from under the hood, engineers shed weight by using thinner panels and fewer sound-deadening components.

The lack of an engine humming makes auxiliary noise from the electronics, wind, road and other elements more prominent. The high frequency internal aspects, also known as the ‘peep’ noises, are particularly intrusive even at the lowest levels. The high-pitched whistling of the wind makes driving sound like someone’s ears the day after a loud rock concert.

Where’s the ambiance?

Drivers and riders inside a vehicle with an internal combustion engine have a consistent humming relieving them of the lower volume noise such as wind, road, the sounds from the HVAC and even the windshield wipers swiping rain away.

Unlike the noise of an airplane, an electric vehicle doesn’t have the broad range of noises jumbled together to create a soothing sound. A single tone can be annoying, in fact, according to a survey conducted by the Journal of the Acoustical Society of America; the high-frequency, tonal e-car sound without additional sound was considered “horrible.”

Solving the complex problem of the once-hidden noises to ameliorate passenger comfort is critical. The challenges are cumbersome with each solution often resulting in a new challenge. For instance:

• Reducing the HVAC noise, battery life could be negatively impacted and, thus, decrease the vehicle’s range.
• Thinner panels may reduce weight but it leads to a more prevalent, higher frequency and tonal noise from electric motor, gearbox and inverter.

Engineers must address the physics to optimize acoustics and change or minimize the perceived noise. For electric car technology, this equates to reducing sounds or providing an artificial noise to prevent passengers from noticing the noises they may never have known were there in the first place.

Testing before prototyping

The key is in using an integrated platform that combines all the physics involved. Engineers can use multi-physics tools and applications to address specific focused technologies. What is needed now as we have so many physics involved, is a platform that enables a single engineer to address multi-physics. Combining physics is one aspect, but likely multiple engineers, designers and other experts have their hands in the development process, therefore, data and resource management is critical. Without integration, the process slows and engineers working on a single physics aspect will lack communication.

Interior noise comes from a variety of places: road, tires, and smaller systems. The answer seems to lay in active noise control, or fake noise patterns, being injected into the cabin. Engineers and designers must put their attention on the location and frequency of the speakers. Before, speaker location was based on multimedia, but now vehicle NVH countermeasures are shifting this priority.

OEMs are already considering white noise through the car’s speakers to combat the unfamiliar sounds plaguing the interior of the vehicle. This means NVH engineers must also apply sound system engineering. Implementing updates means engineers will have to consider the unintended consequences, especially when the changes can impact battery life.

Using acoustic simulation and 3D software, engineers can analyze and optimize powertrain noise, interior and exterior acoustics and system and subsystem levels. Tools exist to model the speaker in such ways that include directivity, the car interior, frequency level and trim materials so engineers can figure out how to reduce noise before an actual prototype exists.

Conclusion

The two main challenges for the electric vehicle developer will be proper branding and meeting regulations.

Branding. Simply put, if the driver of the electric vehicle is not comfortable, bringing the vehicle to mass market will prove monumentally difficult. By not solving these issues, electric vehicle manufacturers will face a branding problem — annoying sounds can easily be equated to poor design.

Regulations. With more stringent policies coming into place in varying regions, automakers will have to prove their vehicle meets these standards before introducing their vehicle into the market.

Building a smaller, lighter and quieter electric engine may mean developing from a non-traditional design. The foundation of the vehicles themselves may entirely different construction to ensure passenger comfort, customer acceptance and regional approval. Simulation meets these challenges head on by avoiding costly prototyping and reducing development time. It’s imperative that OEMs and suppliers have the tools to make the good decision on design or risk losing the race if drivers find the disadvantages of electric vehicles too great.