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Turmoil in electric vehicle motors

The folks at IDTechEx recently completed a research report on the motors likely to be used in upcoming generations of electric vehicles. They shared some of the findings, more of which can be found in "Electric Motors for Electric Vehicles 2012-2022."

They say the market is going to move away from the relatively small brushless dc motors now used to power golf carts and vehicles of a similar size, and toward much bigger motors that will likely use different technology. In that regard, they say their survey of 123 manufacturers shows far too few making asynchronous or switched reluctance synchronous motors and larger, high power, motors with strong traction. And there are far too many making traction motors with brushes.

In short, they say, this is an industry structured for the past headed toward a nasty surprise when the future comes. Most motor makers, they say, aren't talking to the vehicle manufacturers that will spend the most to buy traction motors in the years to come.

IDTechEx also says it is a mistake to think easy money comes from pursuing the fearsomely competitive electric car market where 90% of vehicle makers are headed for insolvency. In China alone, they say, there are over 100 manufacturers of electric cars and none are successful.

Today, most vehicle motors are permanent magnet synchronous versions, notably brushless dc driven by a trapezoidal waveform, and permanent magnet ac driven with a sinusoidal waveform. About half the money spent on traction motors for EVs goes into small vehicles such as mobility scooters and power chairs for the disabled. Mobile robots in the home and pedestrian-operated golf caddies are both popular in Japan. Other small vehicles include stair walkers, motorised lifters, sea scooters that pull scuba divers, all Terrain Vehicles (ATVs), go-karts and so forth. It turns out that 92% of electric vehicle traction motors are currently needed for those small vehicles and they therefore sell substantially on price.

But there are big changes coming. Those small EV motors will become just 25% of the electric vehicle motor market value in 2022 as big vehicles increasingly become EVs. For example, the value of the market for military electric vehicles will rise by a factor of over 20 as military forces buy battlefield hybrids rather than just small pure electric runabouts.

Similarly, says IDTechEx, the market for electric motors in buses should rise by a factor of seven as China, in particular, buys huge numbers of large hybrid buses as part of its national transportation plan. Such developments turn the world of traction motors on its head.

The electric motors required for the bulk of the market by value are becoming much higher in power and torque. For example, a motor for an Autonomous Underwater Vehicle (AUV) -- like a torpedo but making its own decisions -- can push 400 kW. Motors for large forklifts or buses typically deliver 250 to 350 kW but cars typically need up to 70 kW. A low-cost electric bicycle, in contrast, merely needs 0.25 kW.

At the high end, torque from traction motors can hit 6,000 Nm yet many two wheelers and mobility vehicles for the disabled need only 0.2 to 0.5 Nm. In the high end, the asynchronous motor is gaining share because its performance has improved and the cost of the control electronics has come down. This category includes forklifts and mobile cranes and here IDTechEx finds that 89% use asynchronous (ac induction) motors. The firm's analysis of 212 electric vehicles, past, present and planned, shows that around 63% of military vehicles and 52% of large buses could make use of asynchronous motors. Toyota, world leader in electric vehicles by a big margin, is using asynchronous motors for its forklifts and buses and has now developed them for possible use on its cars, which currently use permanent magnet motors.

Many experts believe asynchronous motors will sweep the board at 5 kW and upwards. That is tantamount to saying that they will take over 70% of the traction motor market value because there are even 5-kW motors in golf cars and the smallest leisure boats. But IDTechEx says it is important to observe the rapid improvements in synchronous motors which include a taming of noise and vibration. In the larger electric vehicles performance matters more than cost. Besides, asynchronous motors use a lot of expensive copper and control circuitry. All in all, the firm says, winners in future traction motor markets will win on performance more than price.

But there are many problems still to solve. For example, Boeing has a contract to develop a UAV that can stay aloft for five years. It has subcontracted Newcastle University in the UK to create a traction motor with a much improved power-to-weight ratio to make the UAV possible. NASA's dream of small aircraft taking off purely under the power from in-wheel motors may call for new motor designs, as will the thunderbolt of power from regenerative braking of landing airliners. The planes will become electric vehicles while on the ground.

IDTechEx thinks only 2.5% of electric vehicles by land, water and air will have multiple traction motors in 2022. That may mean only 5.6% of traction motors sold will be for multi-motor vehicles -- mainly in-wheel motors for land vehicles. That is big enough for two or three suppliers to make enduringly profitable, substantial businesses out of supplying them but it is not a primary route to leadership in the overall traction motor business, the firm says.

While there are a few asynchronous in-wheel motors, nearly all of the sales of in-wheel motors concern the usually smaller synchronous versions, already a huge success in e-bikes which sell by the tens of millions. Here a warning comes for Mitsubishi deciding not to use its in-wheel motors in its best-selling MiEV pure electric car because of cost. Currently, says IDTechEx, you cannot have several in-wheel motors for the price of one conventional unit. While in-wheel motor manufacturers hope they'll get a price premium because they eliminate the need for a transmission and differential, there are still problems to be tackled. Ride problems with unsprung motor weight are still a concern, as are worries at Fiat, for example, about wheels jamming.

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