Automotive Engineering - June 2023 - 21

COVER STORY
Lexus's first EV, the 2023 RZ, features comprehensive lower
body NVH acoustic 'masking'.
Evolving simulation
Govindswamy noted that higher-end EVs that are
more refined typically " do a very good job " at reducing
the road and wind noise entering the cabin - but
sometimes at the expense of exposing the higherfrequency
whine of the high-rpm electric machine and
geartrain. Power inverters also exhibit high-frequency
noise in the range of 10,000 Hz.
Three main sources of EDU noise include electromagnetic
noise from the motor itself that radiates off
the unit's housing; geartrain noise, and overall mechanical
noise from bearings, fluids and rotating systems.
Defining the noise sources, their transmission
paths, and establishing acceptable levels, is almost a
clinical process for NVH engineers. FEV, for example,
employs simulation-based processes that develop
EDUs to meet customer acoustic targets.
" We use a combination of what we call 'multibody
systems simulation' [a dynamic system-level analysis of
how interconnected multiple moving parts interact with
each other] and finite-element analysis, which consider
the electromagnetic forces as well as the geartrain forces,
then predicts what the noise levels are. " FEV is continuously
improving the fidelity and accuracy of its predictions
to ensure it can meet customer targets. " When
AUTOMOTIVE ENGINEERING
we come into the test cell with the first prototype, we're not too far off
from where we need to be, " Govindswamy said.
Simulation is evolving and continues to improve, but it's still a work
in progress in terms of correlation, experts assert. " We rely a lot on
simulation, but I think many new companies [automotive startups]
rely on it too much, " Saha opined. " They're not verifying the simulated
results until very late in development, or their simulation predictions
may not be totally correct. We've seen examples of predictions
being adjusted based on what the measurements were telling. I
can't understand how they get to their target. "
He noted that while the established OEMs who are moving into
EVs also are using predictive sim, " they have a much stronger measurement
background " and verify their predictions much sooner in
the development process.
Lightweighting and simulation
The alarming mass of lithium-ion battery packs in electric trucks,
large utilities and high-performance EVs has led body engineers to
offset that weight with lightweighting material solutions that, in
some cases, have caused NVH issues at the cabin level.
" In the interest of lightweighting we're seeing steel and other metals
being replaced by polymeric materials, and barrier decouplers being
replaced by dissipative systems, " noted Saha. " There are vibracoustic
issues associated with lighter weight body panels. Passengers want a
quieter cabin, while the engineering team is focused on mass efficiency.
June 2023 21
LEXUS
Automotive Engineering - June 2023

Table of Contents for the Digital Edition of Automotive Engineering - June 2023
