I am increasingly interested in the concept of wheel hub motor technologies to move into the future of electric vehicles. There are a number of reasons I find wheel hub technology interesting: (1) integration with existing vehicles; (2) direct application of rotational acceleration to the wheel; (3) elimination of drivetrain and engine weight. There are some drawbacks as well. For example, the unsprung mass – the amount of weight that needs to be “supported” (really, pushed down) by the car’s shocks or struts – is increased. Also, taking mass away from the front of the vehicle can have some unintended consequences.
Adding electric power to existing vehicles, increasing power and reducing tail pipe emissions at the same time, is what really has me most interested in this technology. Perhaps the market for hybrid or electric vehicles will surge but how long would it take? Does everybody want one? What if you were able to select hybrid as a factory option on any Toyota, for example. Suddenly it’s not just the Prius or a sprinkle of other vehicles but a whole line that you can choose from. In my case, I continue to lust after a particular car, the GT-86, also branded as a Scion FR-S.
This vehicle has two problems in my mind: (1) it doesn’t have good torque, and (2) it is a gas burner. – For a sporty car, it gets good gas mileage (30 mpg) but that isn’t helpful in stop-start traffic. If I could purchase a factory or aftermarket electric package for the car then I’d be elated because it would help provide more consistent torque and would let me recover some of the energy lost when braking, and I wouldn’t have range anxiety. Given the number of people who tinker and tune cars, particularly this one, it would not be entirely absurd to consider this (just a little bit).
Wheel hubs potentially can allow you to add the entire motor assembly as a bolt on package. There are multiple researchers and manufacturers working on this technology. You can learn more about it here (Protean), here (MTSU), here (Schrieffer-Ford), here (Michelin) and here (Toyota). – I am sure there are others working on it as well. In fact, it is not a new technology at all. – The concept is relatively simple and a diagram is shown below. A magnetic force is induced, creating rotational motion, by pulsing electric coils in the stator to push magnets embedded in the rotor. This technique has been used in a number of electric drives (both big and small) and amusingly is applied as a sort of wheel hub in most radio controlled toy trucks.
There is a reason that toy cars don’t have one engine with a transmission, driveshaft, differential, etc. That is because it is unnecessarily complicated and easy to break and because small DC electric motors are relatively inexpensive. Much of the power of a traditional combustion engine is wasted just moving parts inside the engine (62%) but the remaining power is further eroded by losses along the drivetrain (another 5.6%).
This may not sound like much but a significant portion of weight is removed by eliminating the drivetrain as well, increasing overall gas-mileage. Still, amongst other downsides such as placing the motor close to road debris, the oft-heard cry is the impact of these motors on road handling. – This is where I get very excited!
As mentioned at the top of this article, unsprung mass is the amount of weight that isn’t supported by the car’s shocks or struts. This weight is typically associated with the brakes and wheels (rims, nuts, tires) which generally comes to about 30 lbs. Hub motors can increase this to 100 lbs. or more. What can be done? Road handling issues can be solved either by reducing the wheel motor weight or by using technology invented by none other than BOSE. After his recent passing, I began reading up on BOSE’s passion and work. His impact on car audio is well known but few know of his work on suspension technology. Rather than describe it in words, I invite the reader to view this cheesy but impressive video demonstration of the BOSE suspension technology.
The active management technology of BOSE could arguably do a better job of keeping the wheels in contact with the road WITH a wheel motor than a traditionally sprung system can with traditional wheels today. Problem, meet solution. This would probably require a fairly radical redesign of a car’s suspension system and may prove difficult to offer as an aftermarket solution (combined with a wheel motor), thus making it difficult to imagine every making its way into my forlorn sporty vehicle dream but it offers creative solutions in vehicles built from the ground up with this tech.
By taking traditional engines out of (typically) the front of our cars, we reduce the giant mass of metal sitting in front of the car’s occupants. This is a good thing and a bad thing. It (along with removing the drivetrain) lightens up the vehicle. It frees up space for storage. It even may offer increased battery space, but it also removes a fair amount of inertia that sits between the driver and any vehicle or object that may come in to contact with the car. I’m not sure I’d feel 100% comfortable with a battery in front of the car but in an accident, mass matters.
So, in the end of this mini-research endeavor I find that the aftermarket motor may not happen, particularly because the FR-S is a rear wheel drive machine and the wheel motors would need to be placed on the front wheels, which (arguably) are the most important wheels. I have discovered that there are some cool opportunities for this technology and look forward to seeing it developed. You can learn some more about this topic and find other people’s opinions by visiting some links below: