52 PRODUCT PROFILE
Predicting the acoustic
signature of EVs
Electrified powertrains are gaining market share, but their quiet propulsion can make
previously masked noises more noticeable. A multiphysics workflow developed by
MSC Software can validate EV powertrain designs to help create a quiet driving experience
VehicleDynamicsInternational.com •November/December 2019
FIGURE 1 (ABOVE):
Electric vehicles
reduce CO2
emissions
FIGURE 2 (BELOW):
Traditional workflow
for gear-reducer
noise prediction
With the emergence of HEVs the
automotive industry is also facing new
NVH challenges. The removal of both
engine and transmission will make
the vehicle a lot quieter, compared
with conventional ICE cars. However,
previously hidden noise sources such
as HVAC and tyre/road interaction
will become more noticeable, which
will potentially annoy customers. New
noises will also originate from the EV
powertrains, including the electric
motor and gear reduction systems.
It is challenging to predict these
new types of noise accurately
because they are usually generated
at a high frequency level, while other
non-traditional powertrain physics
components such as electromagnetics
need to be captured during computer
engineering simulation analyses.
Workflow solution: EV powertrain
acoustic analysis
EV powertrains usually consist of an
electric motor and a gear reduction
system. In order to predict the noise
generated by the entire electric
powertrain accurately, dynamics
performance and acoustic behaviour
need to be studied together for both
the electric motor and the gear reducer.
Gear rattle and gear whine noises are
the result of specific forces being applied
››Since 2010 the global electric
vehicle (EV) market has been
growing rapidly. Different EV
technologies have been introduced,
including hybrid electric vehicles (HEVs),
plug-in hybrid electric vehicles (PHEVs),
battery electric vehicles (BEVs) and
fuel cell vehicles (FCVs). According to
projections, BEV and PHEV will be the
dominant technologies in the coming
years, with a larger proportion of BEVs
in the field. In other words, we will face
a complete change of landscape in the
way passenger cars will be powered,
with a removal of internal combustion
engine (ICE) technologies.
To understand this growth, one
needs to look at government and
state regulations. Indeed, all major
automotive markets in the world have
emissions regulations in place aiming
at reducing CO2 emissions and improving
vehicle fuel economy. Taking a closer
look at the European CO2 regulations for
instance, 2020 will see the introduction
of a new C02 emissions target, together
with an excess emissions premium being
applied to manufacturers that fail to
meet it. This new regulation will actually
demand a 27% emissions reduction from
all OEMs, which will be achievable only
by changing the technology that powers
passenger cars and by moving to the
electrification of powertrains (Figure 1).
on the gear mechanism. While rattling
is an impact-induced noise generated
by the unloaded gear pairs, whining can
stem from different factors including a
change in tooth stiffness, tooth surface
imperfections, or transmission errors
resulting from the tooth deformation.
In order to capture these physics
behaviours in a systems model, engineers
need the correct tool to predict dynamic
loads generation, structural vibration
and the acoustic radiation of the gear
mechanism. The traditional engineering
simulation workflow (Figure 2) for such
analysis involves a sequential application
of a multi-body dynamics (MBD) tool,
a finite element analysis (FEA) tool,
and finally acoustic software, which
could be fairly time consuming,
especially when dealing with multiple
changes in the design.
A co-simulation methodology
developed at MSC Software allows
engineers to perform modelling within
an MBD interface (Adams) to get initial
results and impressions of the acoustic
behaviour without needing to manually
export the results into acoustics
software. Typical acoustic results are
computed in the background via an
acoustics solver (Actran) and displayed
in the MBD interface, including the
acoustic pressure evolution at selected
positions and the creation of audible
acoustic wave files for listening to the
/VehicleDynamicsInternational.com