In-Wheel Motors: How to Roll with Direct Drive

The wheel may date from as long ago as 3500 BC, with the development of a wheel used in pottery making in Mesopotamia.  But the wheel as a transportation device came some 300 years later, after humans met the challenge of fitting a cylinder that could rotate freely, to an axle, a stationary, stable platform, without friction and without falling off.

Fast forward to the early 21st century, and the still-evolving idea of wheels that are driven directly from electric motors incorporated into the hub itself (in-wheel motors are also known as wheel hub motors, wheel motors, wheel hub drive, and hub motors).

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In fact, in-wheel motors have their own fairly lengthy modern history.  According to Wikipedia, Wellington Adams of St. Louis, Missouri was awarded a U.S. patent for the first wheel motor concept in 1884. Ferdinand Porsche, who developed his first cars as electric vehicles, raced the electric wheel hub motor in 1897 in Vienna, Austria, and the pioneering Lohne-Porsche, fitted with one wheel motor in each of the front wheels, appeared at the 1900 Paris World Exhibition, with 300 subsequently produced.

So, why is the in-wheel motor not the standard in auto technology today?


The growth in power (if not efficiency) of the gasoline engine eclipsed the power of the electric wheel hub motor and became the norm, which is where things largely stand today. (In-wheel motors are widely used in electric bikes and industrial assembly lines, among other applications.)



In-wheel motors are a drive system that replaces the gas engine (or the electric motor in the case of a traditional EV) with motors located in the hubs of the wheels themselves, and that drive the wheels directly, through extremely small drive shafts. This means no engine and no transmission (and no transmission ‘bump’ on the interior floor) or other related components. The drive power being located that close to the wheels means greater mechanical efficiency. In city driving for example, an internal combustion engine can run at only 20% efficiency, because of mechanical energy lost getting the power to the wheels. An in-wheel electric motor in a comparable situation may operate at about 90% efficiency. Some EV vehicle in-wheel designs have regenerative braking that captures some of its own kinetic energy while braking and sends it back to charge the battery.  The in-wheel active suspension system is electrically-operated.  It can react in just 3/1000ths of a second to correct pitching and rolling motions automatically.

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The direct power the motors generate varies depending on manufacturer and the motors’ size.  For example, a Ford F 150 truck displayed at a SEMA show several years ago, was modified by removing its V8 engine and adding four in-wheel electric motors. Each of the motors could deliver over 100 hp each, a total of 400 hp from the group. Vehicles can utilize two or four motors in the in-wheel configuration.

Because in-wheel motors drive the left and right wheels by separate motors, left and right torque can be controlled independently, meaning better (more precise) accelerator responsiveness, the wheels moving more intuitively in sync with the way the driver prefers.

But there is the factor of unsprung weight, a topic we deal with often at Yes, you would lose the engine weight (around 400-700 pounds, depending on make and displacement), but upping the unsprung weight of each wheel by around 50 pounds adversely affects handling and ride. The wheels are less responsive to road conditions, when accelerating and cornering, and especially at fast speeds over bumps, and those vibrations are transmitted to the chassis instead of being absorbed.  There are also the issues of ‘multiple prime movers’ (at least two; four in a 4-wheel drive car) in this system, a power distribution complexity that affects torque; and the fact that electric motors inside the wheel require electrical connections, thus increasing risk of fire.

So, are IWMs a production-ready technology poised to take off? Innovative technological solutions are under development, so the potential is clearly present.





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