This paper intends to present a novel full-vehicle numerical approach for in-wheel and on-board motor Battery Electric Vehicle (BEV) powertrain architectures, which overcomes the electrical and mechanical deficits widely present in the current literature. Namely, neglecting of the interaction between mechanical and electrical phenomena and its impact on the vehicle dynamic performance.

A co-simulation approach is employed: whereas the mechanical systems and their interactions are simulated with Adams Car, the electrical phenomena are solved by MATLAB/Simulink. The investigation is conducted over a full throttle maneuver by monitoring a set of performance indicators.

The in-wheel motor powertrain configuration adds new advantages to the use of electric motors over traditional internal combustion engine architectures. Novel control techniques take advantage of low response times and complete independence among the devices so to allow faster and more precise actions. Nevertheless, technological drawbacks impose uncertainty on its large-scale adoption.

In comparison with the on-board configuration, it presents lower efficiency throughout the operating conditions map. Due to smaller size, the in-wheel architectures present higher Joule losses in the motor armature windings and additional conduction and switching losses in the inverters.

On the other hand, smaller motors often have high rated speed. The application of field weakening techniques, which fairly worsens the motor efficiency, can become less frequent by choosing an adequate transmission ratio for the single-speed gearbox.

For longitudinal performance and this specific set of motors, the rapid power delivery penalizes the in-wheel configuration by an earlier BMS intervention so to keep the currents in the motor armature windings under the rated threshold. A similar trigger might happen later to the on-board configuration.

 Although, in the presented simulations, there is no evidence that the vehicle performance was curbed by the power delivery by the battery pack, frequently in real cases the device is not able to deliver the power requested by the motors. Such disadvantage is commonly mitigated using hybrid energy storage systems.

In this paper, the choice of the individual powertrain devices is limited by the available public information on websites and catalogues of OEMs and automakers. This way, it is not possible to optimize the overall powertrain design, which harms the comparison between the two configurations. For instance, not only the in-wheel and on-board models do not have the same rated power, but the motors are not able to take advantage of the battery pack energy in the same way. For a hypothetical fixed DC bus voltage, the on-board model can receive more electrical power due to its higher rated current. In this case, the use of a DC/DC converter in the in-wheel configuration should be considered.

Ultimately, the present work intends to introduce the interaction between the electrical and mechanical phenomena and to give more details about the overall impact on the longitudinal vehicle dynamics. Further developments might include the modelling processes of the single-speed gearboxes and sensitivity analyses over the main parameters that affect the simulation results.


Dynamic Performance Comparison Between In-Wheel and On-Board Motor Battery Electric Vehicles

Division / Sponsors: 
Design Engineering Division and Computers & Information In Engineering Division


Paper Proceedings: https://asmedigitalcollection.asme.org/IDETC-CIE/IDETC-CIE2020/volume/83907

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