Automotive electric powertrain whistling and whining: fundamental root cause analysis to novel solutions

The "Road to Zero" strategy is placing the UK at the forefront of designing and manufacturing zero emission vehicles, with the sale of new petrol/diesel cars and vans planned to end by 2040 (perhaps by 2030 according to recent government announcements). The strategy towards cleaner, quieter cities has accelerated the trend in the sales of Electric Vehicles (EVs). Contrary to the prevalent view though, EVs are not silent. Without the effect of masking noise from an internal combustion engine, other sounds radiating from the electric motor and the drivetrain have become more apparent (mainly at medium to high vehicle speeds). This is a major challenge for Automotive OEMs, which need to adapt their Noise, Vibration and Harshness (NVH) design methods to the "new" electric (e-) powertrain environment. Moreover, an optimum balance has to be identified between the vehicle NVH performance (and NVH package weight) and other weight increases due to heavy battery packs needed to increase the driving range.
An important NVH issue in EVs is the tonal e-motor whistling noise (at harmonics of the rotor speed, depending on the number of motor poles). This is generated by the electromagnetic force, which excites the e-motor and the driveline housing. The noise is amplified by the powertrain structure, especially by the stator and its housing. Increased power and e-motor downsizing are key commercial requirements but have adverse effects on whistling noise. In addition to this, e-motor torque variation ripples and introduced misalignments in the system (between the gears, shafts and housing assembly) act as mechanical excitation on the drivetrain, leading to gear meshing oscillations and emitted noise (known as whine NVH). The issue becomes more complex considering the large range of powertrain operating conditions and increased excitation due to high-power motors, which affect the stability of the coupled electromechanical dynamics.
The above e-powertrain NVH landscape requires various interrelated disciplines to be considered under the same framework (electromagnetics, component flexibility, transient dynamics and noise radiation). A coupled whistling and whining fundamental study that leads to root-cause understanding of the involved physics has not yet successfully done.
The proposed research aims to identify the root causes behind the coupling of e-motor whistling and drivetrain whining NVH behaviour in e-powertrains and develop novel design solutions to reduce their severity and avoid costly and difficult remedial NVH measures later in the development process. The research will produce fundamental knowledge in e-powertrain design from the NVH perspective in the following ways: i) novel scientific knowledge will be generated for e-powertrains by analysing the root causes of the coupling between the e-motor and drivetrain transient dynamics that leads to aggressive NVH behaviour (employing 3D e-powertrain models), ii) an accurate and validated methodology for high frequency (above 10 kHz) e-powertrain NVH studies will be developed, iii) new NVH metrics will be set for use in future e-powertrain investigations and iv) novel and fast reduced-order methods will be developed based on the above NVH metrics and the parametric studies of the validated 3D e-powertrain models.
New e-powertrain design methodologies for fast and accurate product development will be developed in this project with strong support of the participating industry partners. Arrival and AVL will integrate the new methods in their design processes and product portfolio (within a 5-year timescale). The project outcomes will be disseminated nationally (and internationally) so that UK automotive manufacturers can directly benefit and the UK maintains its excellence in powertrain technology.