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Electric & Hybrid Vehicle Technology

There are a lot of conventions and naming that is more and more standardized, main categories are HEV and BEV. The main differences for powertrain testing is the electric motor with inverter and battery cooling and sometimes the gearbox.

Electric motor common types are Permanent magnet synchronous motor (PMSM), Induction motor, Switched reluctance motor.  The dominating sound from the electric motor is the magnetic sound, whining noise sometimes called tram noise.  Noise is also important at regeneration (coast down with battery charging).

The inverter use PWM technology to transform high voltage DC battery voltage to 3-phase AC voltage for the motor. Switching frequency and sidebands may be in the audible range.

A gearbox for a BEV has typically 1 gear (and final gear). This means this gear must handle the complete rpm range. Transmission error is important. Some suppliers lack automotive experience.

Water or air cooling/heating are needed for the battery system. The A/C compressor can because of this run during charging.

Contactors are used to be able to fully disconnect the battery system and an impact noise at start-up/shutdown can be disturbing.

Some BEV have range extenders, RE. This is an auxiliary power unit and generator for charging the battery without access to an electrical supply.

Typical challenges within Electric & Hybrid Vehicle technology:
There is still less experience within automotive business for customer expectations. There is also more high frequency sound and a vehicle running only with the electric motor results in less masking effects at low frequencies. This means that other targets on component noise must be changed accordingly.

A BEV requires Electrically driven accessories like A/C compressor instead of belt driven systems for ICE.

Microphones used for Electric & Hybrid driveline testing shall be robust and handle eventual electromagnetic fields. A small size is important for easy positioning when measuring acoustic transfer functions. Free-field or random microphones are most often used and the choice depends on test procedures. Low noise performance and full audible frequency range is also required.

Electric & Hybrid driveline noise

Electrical propulsion is rapidly becoming more or less mandatory to include in every automotive manufacturers vehicle range. The BEV vehicles rely totally on the electric motor while a hybrid will use a combination of electric motor and a traditional combustion engine.
The electric motor means new challenges compared to the combustion engine. The noise level is much lower and this is mostly noticed while driving at low speed. The dominating sound is the magnetic noise which generates a whining noise at high frequencies.
A vehicle running only with the electric motor will also have less masking sound at low frequencies. This means that other noise requirements on for example component noise must be changed accordingly.

The noise during regeneration (battery charging) at coast down is also important.
The inverter use PWM technology to transform high voltage DC battery voltage to 3-phase AC voltage to control the motor rpm.
Switching frequency with sidebands may be in the audible range.
A gearbox for a BEV has typically only 1 gear (and final gear). This means this gear must handle the complete rpm range.

Other new sounds are also introduced, even though belonging more to component noise. Water or air cooling/heating for the batteries. Contactors to connect the high voltage battery creates impact nose at start-up/shutdown.

A BEV requires Electrically driven accessories like A/C compressor instead of belt driven systems for ICE.
The A/C compressor can also run during charging for battery cooling.

Some BEV include range extenders, RE. This is an auxiliary power unit and generator for charging the battery without access to an electrical supply.

Challenges:
• Testing time has to be short since the access to prototypes is limited.
• Instrumentation must be fast and easy in a way to record repeatable results.
• The microphones must be installed to minimize structure borne sound.
• Microphone holders and cables shall not introduce any rattle noise.
• The installation shall be safe for the test engineer during vehicle test.
• Calibration verification must be easy to perform.

The transducers must be able to survive intensive usage, often relocated and perhaps dropped to the floor. Tough environmental conditions is also a part of the everyday testing conditions.

Example:
Vehicle interior magnetic noise and transmission noise is analysed as SPL and electric motor orders. The order level versus background noise, especially above ca 1 kHz is important. The whining can also be analysed by use of some of the methods for tonality.
It is essential to have access to the electric motor specification to know the main magnetic orders.

The inverter noise, switching frequency and sidebands, is analysed with for example FFT maps.

Gearbox whining noise testing is done with similar procedures as for the gearbox for an ICE engine. Tests in drivetrain test rig, sound power and vibrations and vehicle tests on a NVH Chassis dyno.

A range extender has to be analysed as appropriate, depending on type. This component will obviously operate independent of driving speed, which is currently an unusual experience for the driver.

Computer Model validation