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ACOUSTIC NOISE AND VIBRATIONS OF ELECTRIC POWERTRAINS
Focus on electromagnetically-excited NVH for automotive applications and EV/HEV
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LE BESNERAIS Jean
Note: this presentation is based on extracts of EOMYS technical traininghttps://eomys.com/services/article/formations?lang=en
Part 3 Review of electrical systems in electric powertrains and specificities of electromagnetically-excited NVH
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REVIEW OF ELECTRICAL SYSTEMS IN EV / HEV SPECIFITIES OF NVH OF EV / HEV
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Review of electrical actuators in ICE vehicles
• A conventional ICE cars can already contain up to 100 electric motors
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•Electrically assisted steering, clutch control•Electric turbochargers•Electric motors to open and close hoods and trunks•
•Electric motor to open gas cap cover• -by- -by-
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Main architectures of HEV [B47]
Series/Parallel HEV (ex: Toyota Prius)
Parallel HEV (ex: Honda Accord) Series HEV (ex: Chevy Volt)
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Review of passive components in electric traction chains
• Energy storage • Transformers• Inductors (input filter inductors, power-factor-correction chokes)• Capacitors (DC link filter, DC-DC converters)• Cables
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Review of power electronics in HEV/EV
• Switching frequency of most converters goes up to 20 kHz, but switching is lowered under light-load and no-load to reduce switching losses and switching frequency
• Buck-boost converter include a capacitor and an inductor
Name Function Operation mode Components
3-phase DC-AC inverter / rectifier
ESS HV to AC voltage to power electric motors in traction, the opposite in braking
Traction / Braking DC link capacitor
AC-DC rectifier Mains AC 50/60 Hz to ESS Charging Filter capacitors
DC-DC converter ESS HV to onboard LV conversion (ex from 400 V to 12V) = buck/boost converter
Traction / Braking / Parking
Capacitors / inductorsHF transformer
DC-DC converter Mains DC to ESS Charging Filter capacitors
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Electromagnetic NVH sources in cars
Charging Parking Traction Braking
Static components Inductors & capacitorsRectifier
Inverter Inductors & capacitorsRectifier
Rotating components Comfort actuators Starter motorSteering motorParking brake motorComfort actuators
Electric motorCooling motorsAlternator (ICE)Comfort actuators
Electric motor / generatorCooling motorsAlternator (ICE)Comfort actuators
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Rotor unbalance in HEV
• Mechanical imbalance of the rotor creates dynamic eccentricity, enriching magnetic force spectrumboth in frequency (sidebands) and space domaines (modulation of wavenumbers with +/-1)
• Dynamic eccentricity transforms pulsing forces in unbalanced magnetic forces, generating shaftbending vibrations and structure borne noise
• Couple imbalance occurs when 2 equal masses are placed symmetrically (static balance but dynamicunbalance)
• Couple imbalance is found frequently in EV/HEV when rotor is connected to imbalanced powertraincomponents [R1]
[R1][R1]
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Start-up & shut-down noise of ICE in HEV
• ICE start-up & shup down vibration is a significant contributor to overall vehicle vibration
• Special noise reduction techniques can be applied at neutral or park mode on conventional ICE
• However in HEV, ICE start-up does not always occur at neutral or park mode, it depends of many factors (e.g. state of charge of battery, driver torque demand)
• Dedicated noise reduction techniques are implemented on ignition timing, valve opening/closingtiming, piston stop position etc. [R1]
• In HEV special noise & vibration control techniques are based on compensating ICE torque pulsation during starts using fast response characteristics of the electric motor to mechanical torque ripples[R1]
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Some specificities of electric vehicles NVH
• Rubber isolation in more effective on high frequency vibration of electric motors compared to ICE, acoustic absorption materials are also more effective
• New balance between electric motor noise, tire/road noise and wind aerodynamic noise
• Modified moments of inertia & eigen-frequencies in the powertrain, lower torque ripple on the shaft line compared to ICE
• Importance of mass/stiffness of batteries in EV lighter body structure
• High directivity, highly integrated components (ex: L, C, generator + motor), high sensitivity to temperature
• Low reproductibility: +/- 10 dB in electric motor or passive components manufactured according to same specification
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Psychoacoustics of electromagnetically-excited noise
• Psychoacoustics of electrical machines is still an active research field
• Below 50 km/h, HEV/EV are considered too quiet from pedestrian/cyclists/visually-impaired point of view (addition of warning sound in some cases)
• In HEV/EV there is no longer masking noise of diesel engine, road noise & powertrain noise are more noticeable
• No hearing experience of drivers to electrical noise
• Specific features: harmonic excitation / high pitch / high tonality / PWM
[R5]
[R9]
ICE EV
Interior noise at full load, 2nd gear
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Psychoacoustics of electromagnetically-excited noise
• Objective psychoacoustic metrics often used in EV/HEV: loudness (sound intensity), roughness and fluctuation strength (frequency modulation), tonality, Tone-to-Noise and Prominence Ratios (tonal metrics), sharpness (sound timbre and energy at high frequency), Articulation Index (tone detectability) [R8]
• Subjective psychoacoustic evaluation: hearing tests and subjects surveyfor annoyance judgement, pleasantness judgement, detectability and sound design
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[R10]
Residential background Shopping background Busy background
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