Optimizing NVH for EVs
This article first appeared in Automotive Engineering – October 2019.
Unique acoustic and harmonic challenges require an integrated approach to simulation and analysis. An expert at Adaptive Corp. explains.
Despite global sales market share stuck at single-digit levels, electric vehicles (EVs) are steadily filling the development pipelines at major OEMs. And as engineers are acutely aware, EVs bring a paradigm shift in the noise, vibration and harshness (NVG) arena. Their harmonic spectra are dramatically different than those of even the smoothest, most refined combustion-engine vehicles and hybrids.
EVs are anything but silent, however. They’ve got their own acoustic challenges, experts assert. Traction motors can be relatively quiet (in terms of tonal harmonic noise) in the low and mid frequencies, but unmasked gear whine and various sounds in the propulsion system are far more noticeable and potentially annoying. There’s also the relative cacophony of the tire noise, HVAC fans and compressor cycling. Even electrical switching and the muffled gurgle of battery coolant can be heard in some EVs while at rest.
While the industry is likely years away from customers complaining of EV cabin noise, leading practitioners in the NVH-reduction field are already working on up-front solutions. One of them is Adaptive Corp., a specialist in simulation, structural analysis and product lifecycle management for automotive, aerospace and other industries. Optimizing designs for improved performance (including NVH, weight, cost, durability) is Adaptive’s specialty, according to customers with whom Automotive Engineering spoke. The NVH science behind EVs and hybrids is increasingly a focus of Adaptive’s services, explained Wayne Tanner, the company’s chief operating officer.
“It’s true that we have to ‘up our game’ with EVs,” Tanner told AE. “We’re hearing this from all our customers who are in the EV supply chain, such as those who make tires and suppliers of motors. We’re looking at components and subsystems that were never before considered to make the vehicle quieter.”
Easing the development crunch
The industry’s move to electric propulsion is driving new business across the engineering-solutions sector. Tanner, who is responsible for all his company’s activities related to simulation and analysis, notes that the industry trend is toward clean-sheet vehicle platforms dedicated to battery-electric propulsion. OEMs such as Tesla and Volkswagen – the latter’s dedicated and modular MEB platform to be shared by Ford on some models – are committed to this strategy that optimizes structural stiffness (with its related NVH benefits) and other attributes.
“The time-to-market is increasingly short, which is why product-development teams need simulation to do their fast, quick iterations,” Tanner said, “and to make accurate predictions before they build prototypes and test vehicles.”
The aim is to avoid the dramatic and often eleventh-hour ‘band-aiding’ of vehicle structures. Such activities include costly material replacements and noise-path mitigation by adding heavy NVH countermeasures, in order to meet production deadlines. “That’s certainly something that we can help with if we’re brought into the development process sooner, farther upstream,” Tanner noted. Engineers sometimes don’t think of components and subsystems as a system until they’re actually put together, he observed.
“Some customers, because they’re moving so fast, can’t find time to do a simulation upfront – then they discover the need for add-on countermeasures at a late hour,” he said.
Tanner has worked in simulation for over 20 years in various disciplines including design optimization, load development, weld fatigue and dynamics. He and other NVH experts assert that the sooner system-level and full-vehicle models can be developed in any vehicle program, the more effectively predictions can actually improve those designs to reduce NVH, rather than being band-aids in the end.
Inside the toolbox
For its simulation platform, Adaptive partners with Dassault Systèmes, whose 3DEXPERIENCE is rated by users as state of the art in comprehensive NVH simulation toolsets. “The advantage of (3DEXPERIENCE) is, it gives us a single data model that can contain CAD and simulation data,” Tanner said. “We connect that to systems engineering to drive requirements all the way from start to finish, to manage the workflow. Some of the tools we have at our disposal aren’t fully integrated into the platform, but we’re able to put everything together and manage that data. This allows our customers to access a single data source.”
Tanner offered a peek inside Adaptive’s extensive sim toolbox. On the aerodynamics /CFD side is PowerFLOW; on the acoustics side is another Dassault tool called Wave6 that’s used to project an acoustic signature. On the mechanical side, Adaptive engineers use Simpack, which helps them develop all the mechanical vibrations needed for a given analysis. There are also electromagnetic tools.
“We connect all these tools into a single workflow – to drive mechanical and/or aerodynamic vibrations into the acoustic field, for example – on the 3DEXPERIENCE platform,” he said. Once an OEM is ready to begin road and/or dynamometer testing, they employ Adaptive to validate and correlate from the company’s virtual model into production models.
Another weapon in the arsenal is True-Load from Wolfstar Technologies. It leverages finite-element models to determine the optimum location for strain gauges on unmodified physical parts then generates load-scaling functions. The company claims typical strain correlation within 2% of measured values. Output feeds directly into True-QSE events, described by Tanner as “a powerful post-processing tool” that supports rapid virtual iteration.
“It allows us to take that test mule and put information-gathering tools on it, whether it be strain gauges or accelerometers, capture real-time load and vibration data from that system, and correlate it to our FE models,” Tanner explained. “We use that to drive our simulation – and to predict more that may happen.”
NVH simulation and analysis is “at the beginning of the power of what we can do,” Tanner said. “The tools are becoming more inter-connected and fully integrated, allowing us to run seamlessly from CAD to simulation to structural analysis to acoustics to vibration. The workflow is increasingly faster, enabling us to run multiple simulations in a single day. It used to take weeks.”