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The small size and flexibility of connection enable a variety of new
concepts for positioning the electric machine in the vehicle and
thus enabling new vehicle architectures. For example, a central
arrangement, comparable with today’s combustion engines, is
possible, as is distribution of the propulsion power between two
smaller motors on the front and rear axles, or even four wheel-hub
motors in the wheels of the vehicle (example: Active Wheel from
Michelin, Fraunhofer or MIT, see Fig. below).
Fig. 12: Wheel hub drive: Historical look back and current concepts
13 Authors’ own illustration
Wheel-hub motors offer numerous advantages, such as selective
wheel activation for supplemental functions (e.g. torque vectoring
or ESP without complex auxiliary systems), good weight distribution,
extensive freedom for automobile designs and divided brake ener-
gy recovery on all four wheels. But there are still some challenges;
e.g. relative to the issues of unsuspended mass, particularly in the
high-speed range, that must be resolved. It is also expected that
wheel hub motors will be more expensive overall and they require
greater effort to ensure safety and service life. In addition, cabling
is more complex if the power electronics remain situated in the ve-
hicle chassis, and there is high mechanical stress for the machine.