参考：The Economist July 13th Science & Technology
In the motor industry, opinion is divided as to whether the conventional propulsive system, namely drivetrains, or in-wheel propulsive systems, which separate the concentrated driving system into several parts directly connected with wheels whose numbers are usually four for cars and trunks, should be employed for a possible burst of commercial opportunities of electric vehicles (EVs). At present, drivetrains are generally applied in products thanks to the abundant experiences in practice, but the author of the article in the latest The Economist believes that the time of in-wheel solutions may, at last, have come. By the way, to the best of my knowledge, it is the first time that the specific field, machine industry, as a part of the commerce. is focused on and discussed in this prestigious journal.
However, it should be clarified firstly that the in-wheel propulsive systems share nearly the same history of drivetrains if you don't date the latter back to carriages. In 1900, a pioneer, Ferdinand Porsche, presented a vehicle with a pair of electric motors incorporated into the front wheels, respectively, for driving, which caused a sensation at the Paris World Fair. The main goal of this proposing was to dispense with cumbersome belts and chains, which were quite weak at that age. The following history was well-known: the EVs were rapidly out of road after peaking at 70% in the 1910s. But despite the fact that EVs are now returning to the road quickly the idea of using in-wheel motors has failed to follow suit. In reports, only a few suppliers, like Michelin from France, NSK in Japan and Protean (UK&China) have developed modern versions of in-wheel drives, but these have yet to make it into commercial models. In other words, the drivetrains solution remains dominant for EVs when many firms, including some startups, are desperately wishing to break the ground in this field.
The reasons for this reluctance are complex. Technically, even the advanced design of motors is still not able to fulfill all the requirements as industrial products equipped in an EV because of the high standard in many aspects, including but not limited to torque density, robustness, and vibration. Besides, as exposed to the elements other than being snug inside a vehicle's body, motor systems have to face complicated conditions and phenomenon and therefore must be simultaneously protected against damage from road debris and the risks of sudden vibration and of shorting out when accidentally soaked in water. In the view of the vehicle technology, using in-wheel solution increases the unsprung weight of a vehicle, though the total weight may be reduced, resulting in a bumpy ride and poor handling. For industrial production, the problems are even massive. Lacking practical experiences desperately raises concerns about the new technology in safety, because the industrial adventure for household products is a thing of the past, which means that the attempts may be nipped in the bud to ensure the benefits unless enough tests are carried out for verification.
Fortunately, adventurous scientists, engineers, and businessmen have never given up to make inroads on advanced in-wheel propulsive systems. As reported in The Economists, Indigo Technologies of Cambridge, founded by a professor of MIT, has developed a new system as a module that incorporates brakes, steering, a motor, and an active suspension to overcome the unsprung-weight problem. In the design of motors, low rated voltage, 48V precisely, is selected for the electrical problem, though paving the way for thermal and mechanical difficulties. On the contrary, both the propulsive system and the vehicle see reduced weight because of the elimination of driveshafts, transmissions and other weighty components. High efficiency may be achieved during the duty circle and a smaller battery system can be topped up more effectively while can be recharged faster.
As the edges and drawbacks of in-wheel motors are all clear, a compromise is finally required to see if the synthetic benefits cover the conventional solutions, living up to expectations. Hopefully, as the machine industry has been changed beyond recognition in recent years, in-wheel systems can become competitive alternatives to the mainstream, because technology can only be promoted in the rat race, especially for the EV industry which seems here to stay but still cannot be proved as state-of-the-art to turn motoring upside and down.
Though sale figures of EVs remain fantastic in 2019 when combustion-engined vehicles see a significant decrease, the risks of this new industry, or reborn industry more precisely, are buried because the increase is brought by regulation, other than attractive products, which may be neither real nor graduate. The "real" here means that the sales are represented of commercial demands when the effect of governmental regulation is taken apart. It is true that financial subsidy and policy regulations can effectively promote the development simultaneously, but not standing since subsidy can only be regarded as a tool of redistribution with a proportion of consuming. The only way the validate the value of an industry is its commercial benefits, just like a firm has to pave the way for profits. When EVs finally become all the rage and give way to gas-powered competitors, it will start the age of EVs or even electrified transportation. But before that time, large varieties of research and work are required, and hopefully, the progress will be beyond our's wildest dreams.