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From engine to wheels


Generating motion where it is mostly needed, namely in the wheels, would be a rather interesting option. An in-wheel motor could eliminate joints, drive shafts and differential. After many fruitless proposals it is now the turn of Protean, a Sino-American company that seems to be getting serious

Nicodemo Angì

A wheel that directly creates torque, turning into a vehicle itself, has always tickled the imagination of designers, something like a charming Twentieth Century handmade Monowheel. Needless to say, their performance is rather limited: the retarding torque on a device of this kind will send the driver upside down. A much more viable proposition is represented by an in-wheel drive system, with its reliable standard tire, mounted onto a modern car. For dimensional reasons, an in-wheel motor, which fits into a “normal” wheel, can only be electric, but Protean wants to go further: its vision is to produce an in-wheel drive system that can be installed in cars already equipped with a conventional power-train, which can thus be easily transformed into hybrid versions.

The principle of making the creation of electric/hybrid cars “easier” stems from the realization that future emission standards will become increasingly stringent and therefore difficult (and expensive) to be complied with. The need to electrify a vehicle range may soon become essential and will draw considerable interest for solutions such as those currently being researched at Protean. The prospects seem rather favorable: in fact the Chinese Government is aiming to have 5 million ' green ' vehicles on the roads by 2020 and, by the same date, cars will have to consume no more than 5 liters per 100 kilometers. The reference to the Chinese market is not accidental, since the company, with offices in Michigan and an Engineering Center in England, has its manufacturing plants as well as its Development Center in China. Things seem to be going well: last July Protean collected a further 70 million dollars from GO Scale Capital, Zhejiang VIE Science and Technology and Tianjin THSG Corporation, a Private Equity Fund and companies working in automotive components and sustainable technologies respectively; other financing had previously been obtained and last May Protean announced the construction of a production facility in Tianjin, on the Chinese coast, destined to the production of its PD18 model.


All within a standard wheel

That number 18, associated to the Protean Drive acronym, is certainly not accidental, but rather, it reminds us about the main feature of this product: being able to be packed in a standard 18” wheel with its wide outer braking surface that can easily substitute the traditional brake disc.

The large diameter rotor of the Protean engine is covered with permanent magnets which are also the fastening points on the rim. The stator unit, fastened to the suspension, incorporates the coils, wheel bearings and an electronically assisted steering system, divided into several smaller units. If, on the one hand, such tight packing represented a great challenge in design, having to reduce the size of both the inverter and controller, on the other it also made things much simpler with fewer connections required, always with a view to streamlining design and engineering.  In fact, only 2 cables are required to carry the direct current (frequency inverters are integrated), 2 pipes for liquid cooling and a control cable that interfaces with the CAN-Bus, in addition to the pipes for the braking system.

The stator and rotor’s large diameter produces a staggering torque – 650Nm continuous output torque is declared, reaching a peak output torque of 1,000 with 400 volt – with a peak power output of 100hp and continuous output power of 72hp. Even a simple 2WD vehicle can be real fun considering the readiness of the electric motors, the absence of power loss in the transmission chain and the ability to simulate locking differentials of all types. The all-wheel drive, obtainable with 4 Protean units, would be able to effortlessly implement Torque Vectoring and ESP systems. These characteristics could not escape being noticed by the notorious German tuner AMG (signature super sports car from Mercedes) which unveiled a few years ago, a Class E prototype with 4 Protean wheels capable of developing 430 HP and a torque of more than 3,000 Nm!

The power and torque diagram provided by the company is rather interesting: considering that a 225/40 R18 tire has a rolling circumference of 2 meters, 1,200 RPM equal 144 km/h, a speed at which torque is still quite remarkable.

Additionally, an electric vehicle based on these wheels could free a lot of space for passengers and luggage compared to a conventional vehicle, just think of the engine compartment and the space taken up by the transmission:  furthermore, the batteries placed under the floor would further lower the center of gravity, and still take up only a small portion of the freed space. In fact the volume of the Protean unit, given the width of only 11.5 cm and diameter of 42 cm (the volume is about 16 liters, with a claimed weight of 34 kg), looks rather limited.


Adjustments to be reviewed                           

Of course not everything is perfect: for example 18" are not very widespread and, to date, would limit the adoption of Protean wheel to a few models.

Although the weight of the in-wheel drive system is not excessive, it does still have the disadvantage of focusing it into the wheel, increasing the un-sprung weight and therefore being a potential source of damage on uneven surfaces. In other words, the total weight should be similar to that of conventional traction systems, considering the elimination of differential, axle shafts, gearbox and engine in exchange of a battery pack that would still represent a great weight loss in various parts of the car, weight that will be moved to the wheels.  The matter is not one to be underestimated by Protean, which publishes on its website several White Papers on the increase of un-sprung weight and how to implement specific strategies to avoid compromising comfort and road handling. What they suggest is that the response to the strain imposed by different road conditions don't change much, especially at medium and high speeds; on the other hand, at low speeds, a delay in the return of the suspension and a decrease in the resonant frequency of the in-wheel drive system is quite noticeable. Grip and handling and driving comfort are also adversely affected, though Protean is of the opinion that these flaws can be overcome with changes in settings and suspension components. Many of these difficulties may still be overcome with active damping control.

The strains that a wheel unit of this kind will be subjected to cannot be ignored either: continuous vibration, potholes and bumps cause sudden and severe accelerations.

The outlook is still positive and it will be interesting to see on our road vehicles with these promising Protean in-wheel drive units, also to see how these drawbacks have been overcome.

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