ACOUSTIC NOISE AND VIBRATIONS OF ELECTRIC POWERTRAINS Focus on electromagnetically-excited NVH for automotive applications and EV/HEV Part 3 Review of electrical systems in electric powertrains and specificities of electromagnetically-excited NVH LE BESNERAIS Jean contact@eomys.com Note: this presentation is based on extracts of EOMYS technical training https://eomys.com/services/article/formations?lang=en EOMYS ENGINEERING 2013- www.eomys.com 1
REVIEW OF ELECTRICAL SYSTEMS IN EV / HEV SPECIFITIES OF NVH OF EV / HEV EOMYS ENGINEERING 2013- www.eomys.com 2
Review of electrical actuators in ICE vehicles 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- [R2] A conventional ICE cars can already contain up to 100 electric motors EOMYS ENGINEERING 2013- www.eomys.com 3
Main architectures of HEV [B47] Parallel HEV (ex: Honda Accord) Series HEV (ex: Chevy Volt) Series/Parallel HEV (ex: Toyota Prius) EOMYS ENGINEERING 2013- www.eomys.com 4
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 EOMYS ENGINEERING 2013- www.eomys.com 5
Review of power electronics in HEV/EV 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 / inductors HF transformer DC-DC converter Mains DC to ESS Charging Filter capacitors 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 EOMYS ENGINEERING 2013- www.eomys.com 6
Example of Honda Accord power converter unit [B42] EOMYS ENGINEERING 2013- www.eomys.com 7
Electromagnetic NVH sources in cars Static components Charging Parking Traction Braking Inductors & capacitors Rectifier Inverter Inductors & capacitors Rectifier Rotating components Comfort actuators Starter motor Steering motor Parking brake motor Comfort actuators Electric motor Cooling motors Alternator (ICE) Comfort actuators Electric motor / generator Cooling motors Alternator (ICE) Comfort actuators EOMYS ENGINEERING 2013- www.eomys.com 8
Rotor unbalance in HEV Mechanical imbalance of the rotor creates dynamic eccentricity, enriching magnetic force spectrum both in frequency (sidebands) and space domaines (modulation of wavenumbers with +/-1) Dynamic eccentricity transforms pulsing forces in unbalanced magnetic forces, generating shaft bending vibrations and structure borne noise Couple imbalance occurs when 2 equal masses are placed symmetrically (static balance but dynamic unbalance) Couple imbalance is found frequently in EV/HEV when rotor is connected to imbalanced powertrain components [R1] EOMYS ENGINEERING 2013- www.eomys.com 9 [R1] [R1]
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/closing timing, 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] EOMYS ENGINEERING 2013- www.eomys.com 10
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 EOMYS ENGINEERING 2013- www.eomys.com 11
Psychoacoustics of electromagnetically-excited noise [R5] 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 ICE EV No hearing experience of drivers to electrical noise Specific features: harmonic excitation / high pitch / high tonality / PWM EOMYS ENGINEERING 2013- www.eomys.com 12 [R9] Interior noise at full load, 2 nd gear
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 survey for annoyance judgement, pleasantness judgement, detectability and sound design [R11] Residential background Shopping background Busy background [R13] [R10] EOMYS ENGINEERING 2013- www.eomys.com 13 [R8]