Automotive Engineering - August 2022 - 18

NVH FEATURE
EVs drive
NVH material
innovations
NVH analysis is steadily
incorporating more virtual
tools and processes as EV
development takes off.
Skateboard platforms, high-frequency motor noise push lower dB thresholds
and new countermeasure solutions.
by Lindsay Brooke
T
he definition of a 'quiet' vehicle, as determined by the occupants'
ears, is changing radically, as electric motors replace the
internal-combustion engine. And electric vehicles are changing
the technologies used to reduce, and eliminate, NVH - noise,
vibration and harshness. Removing the piston engine, with its exhaust,
intake and valvetrain/injector noises, unmasks a plethora of
cabin sounds that occupants never heard before.
" ICEs generate at least 20 dB more noise at the cabin level, " noted
Vahid Mortazavian, Ph.D, global CAE leader at Ascend Performance
Materials, in a presentation at the 2022 SPE Automotive conference.
Tire and road noise become more prevalent in an EV. Even the heater
fan is louder without engine noise to mask it. But EVs generate their
own noises, including high-frequency buzz from the electric motor.
These are among the new challenges facing development engineers
and NVH specialists.
" Reducing and eliminating cabin noise in electric vehicles is now a
significant focus for the OEMs, " noted Arnold Braun, a veteran polyurethane
systems engineer at Dow. Another challenge for the NVH
analysis and materials communities is the speed in which EVs are
being designed. " Everybody's in a race and have reduced their design
cycles, " added his colleague Selamawit Belli, Dow's automotive
acoustics strategic manager, in an interview with SAE Media.
Dampening demand
Braun and Belli noted the dramatic change in vehicle architectures,
with the " skateboard " layout for EVs emerging as preeminent, presents
new challenges and opportunities for NVH engineers, as well as
18 August 2022
for their company's widely-used Betafoam product
line. In an EV, with the flat floorpan and battery pack
underneath, " we're now looking at body structures
that have stiffer and stronger rocker systems than
those in ICE vehicles, " Braun explained. " We face the
question of how to apply our NVH treatments into
those areas so that the strength is retained along with
the acoustic performance. "
The water-blown polyurethane-based Betafoam is a
family of two-component acoustic foam technologies
featuring a >4000% expansion rate. When robotically
injected into vehicle body cavities, the foam (both openand
closed-cell types) creates an effective, three-dimensional
acoustic seal, according to Braun. Betafoam solutions
have been industry workhorses in reducing tire/
road noise - a longstanding cabin noise source for all
vehicles - through the wheelhouse. It's also being employed
on recent EV platforms to block electric motor
frequencies (a new EV acoustics bogey) in an impressive
dynamic range from 500 Hz to 10,000 Hz.
In their quest for cabin quiet, OEMs now are pushing
suppliers for solutions with vibration dampening as
well as sound-absorption qualities. " A lot of the new
EV structures the OEMs are showing us have a closed
plenum in the cowl section of the body. And we see
growing interest in cast parts, not the welded sheetmetal
fabrications used today, " Braun noted. " There
may not be areas where you can apply acoustic foams
AUTOMOTIVE ENGINEERING
DOW
Automotive Engineering - August 2022

Table of Contents for the Digital Edition of Automotive Engineering - August 2022
