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INTERNAL PUBLIC SECRET CONFIDENTIAL
NVH of Electric Vehicles
Juan J García.
9/11/2020
INTERNAL PUBLIC SECRET CONFIDENTIAL
What characterises electric powertrain sound , sound quality and
how can it be described with acoustic metrics?
Contents:
INTERNAL PUBLIC SECRET CONFIDENTIAL
Comparison of Energy Efficiency of powertrains
INTERNAL PUBLIC SECRET CONFIDENTIAL
New components to take into account
INTERNAL PUBLIC SECRET CONFIDENTIAL
EV Powertrain configuration
INTERNAL PUBLIC SECRET CONFIDENTIAL
Drive Control System – Architecture for one EM
INTERNAL PUBLIC SECRET CONFIDENTIAL
EV Global arquitecture
INTERNAL PUBLIC SECRET CONFIDENTIAL
Types of electric machines
INTERNAL PUBLIC SECRET CONFIDENTIAL
Properties of electric machines
Maximum torque available at start-up
Can be designed with any shape or size
• Several possibilities to design stator and rotor for the same technology
High power density
High efficiency
• Several operating points with an efficiency higher than 90%
INTERNAL PUBLIC SECRET CONFIDENTIAL
Masker
Masked high
frequency
region
The hidden ‘electric’ sounds
40 dB
60 dB
80 dB
Masker
level
INTERNAL PUBLIC SECRET CONFIDENTIAL
Noise and vibration of electric motors
Although electric powertrain is quieter that internal
combustion engines (ICE), the sound character is
different and not more acceptable.
The noise signature from an electric traction motor is
characterised by speed-dependent high frequency
tonal components form the dominating electromagnetic
harmonics covering a wide r.p.m range
With a relative low levels of broad band masking noise
from tyres and wind, the tonal components can be
accented in a large frequency range and contribute to
perceived annoyance in the car
Good coupling
for bending
waves
generation on
stator surface
Segment of a PMSM with surface mounted
permanent magnet with radial and tangential
components of the electro-magnetic field
INTERNAL PUBLIC SECRET CONFIDENTIAL
Noise and vibration of electric motors
Concept Observation Interpretation
ODS allows the definition of
the circumferential order that
dominates the radiation
efficiency.
INTERNAL PUBLIC SECRET CONFIDENTIAL
ICE
EM
A new soundscape…
Relative distribution of excitation orders:
ICE v.s EM
INTERNAL PUBLIC SECRET CONFIDENTIAL
ICE v.s. EV noise and vibration: Observations
ICE
EM
INTERNAL PUBLIC SECRET CONFIDENTIAL
Inverter noise
The conversion of DC to AC voltage takes place in the inverter by pulse-width
modulation (PWM)
In order to produce a sinusoidal-like output voltage with a certain frequency to the electric
motor, a switching-frequency is required to control the duration of the pulsed voltage
The output voltage from the inverter contains the fundamental frequency component
distorted with the switching frequency and respective harmonics.
During run-ups, the switching frequency component induces adjacent side bands.
Pulse width modulation speed control works by driving the motor with a series of “ON-
OFF” pulses and varying the duty cycle, the fraction of time that the output voltage is “ON”
compared to when it is “OFF”, of the pulses while keeping the frequency constant.
INTERNAL PUBLIC SECRET CONFIDENTIAL
Inverter + magnetic motor noise
Pulse-width modulation (PWM) frequency lines including side-bands
and magnetic harmonics during motor run-up of an electric vehicle.
Stator housing radial
velociy
v
INTERNAL PUBLIC SECRET CONFIDENTIAL
WOT: 0-100 km/h
Volvo C3: 82 kW
1000 – 9000 Hz
200 – 2000 Hz
Sound quality evaluation in EV
INTERNAL PUBLIC SECRET CONFIDENTIAL
High tonal levels for frequencies > 1kHz, the results in higher perceived
annoyance, sharpness, aggressiveness and a low sound quality.
Increasing levels of high of frequency (1kHz-9kHz) tonal components and
decreasing mid frequency tonal components (200Hz-2kHz) from electric
motor and transmission gives high rankings on sharpness, annoyance,
toughness and powerfulness
Lowering the same high frequency components improves sound acceptability
Sound quality evaluation in EV
INTERNAL PUBLIC SECRET CONFIDENTIAL
101
102
103
104
105
101
102
103
104
Center frequency (Hz)
Crit
ical
ban
d w
idth
The bandwidth of the critical bands are similar to 1/3 octave
bands, but in contrast they do not have fixed frequency limits
Bark 1
Bark 24
Sound quality evaluation in EV: Critical bands
INTERNAL PUBLIC SECRET CONFIDENTIAL
Prominence ratio is calculated from the sound pressure level of the critical band of
the tone and the adjacent critical bands.
The critical band is the frequency range of a noise, centred at the frequency of a
tone, which effectively can mask the same tone
For the calculation of the PR, the critical band containing the tone or tones is
compared to the adjacent two critical bands:
𝑃𝑅 (𝑑𝐵) = 10 log10
𝐿𝐵
𝐿𝐴 + 𝐿𝑐 2
Sound quality evaluation in EV: Prominence ratio
INTERNAL PUBLIC SECRET CONFIDENTIAL
In steady state and acceleration conditions the psycho-acoustic metrics
prominence ratio (PR) , which quantifies the tones levels relative to the
adjacent background noise is well correlated to sound quality in EV
PR ≤ 2dB, the perceived annoyance was similar and independent on
frequency range
Increased PR-level (PR ≥ 3) provides high probability of detecting the
tones and increases the perceived annoyance, particularly for tones
above 2.5 kHz
Sound quality evaluation in EV : Some criteria
INTERNAL PUBLIC SECRET CONFIDENTIAL
02000
40006000
800010000
0
5
10
0
0.2
0.4
0.6
0.8
1
Frequency (Hz)PR - value (dB)
Audib
le
Poor order
evolution
Good order
evolution
Application: projection of order evolution on the PR-f plane
Order
projection
Order Audibility
PR-f plane
INTERNAL PUBLIC SECRET CONFIDENTIAL
0.9
0.7
0.5
0.3
Low audibility
Mid audibility
High audibility Run-up
order Seady state
order
𝑡𝑖 𝑡𝑓
Application: projection of order evolution on the PR-f plane
INTERNAL PUBLIC SECRET CONFIDENTIAL
With the absence of acoustic emissions from an operating internal combustion
engine, the presence of high pitched tonal components from the electric
traction motor can be pronounced in many driving conditions
There is a robust relationship between the psychoacoustic metric PR and the
threshold of detecting the tones and the perceived annoyance, for both
constant speed and acceleration of EV
The perceived noise annoyance in EV is low for tonal noise with PR ≤2 dB.
With higher audibility (PR≥3dB), the perceived annoyance is significantly
increased above 5 kHz compared to frequencies below 800 Hz (constant speed
and acceleration)
Conclusions
INTERNAL PUBLIC SECRET CONFIDENTIAL
Thank you for your attention
INTERNAL PUBLIC SECRET CONFIDENTIAL
Second Public Technical Course: Fundamentals of Electric Vehicle NVH
Time Title
09:00 - 10:00 NVH of Electric Vehicles
10:00 - 11:00 Target setting for Electric Vehicles NVH
11:00 - 11:15 Coffee
11:15 - 12:15 Effect of motor controller on Electric Vehicles NVH
12:15 - 13:00 Effect of driveline design on Electric Vehicles NVH
13:00 - 14:00 Lunch
14:00 - 15:00 Early Damage Detection of electric motors based on modal energy vibration
15:00 - 15:15 Coffee
15:15 - 16:30 NVH objectives for powertrain in-vehicle integration: experimental and simulation approach
16:30 - 17:00 Close
PBNv2 - AIT & IDIADA Technical and Complementary Training & Course