Thread by @jpr007

"UK-developed magnet-free electric motor ready for the road"

Switched reluctance motors have existed almost as long as the internal combustion engine, but have suffered from weaknesses in performance which have limited their use in electric vehicles
theengineer.co.uk/c2i-2019-magne…

Unlike common DC motor types, in a switched reluctance motor power is delivered to windings in the stator rather than the rotor

This simplifies mechanical design because power does not have to be delivered to a moving part

The rotor is made of a “soft” magnetic material such as laminated steel, with projecting magnetic poles

The stator also has a number of poles

When power is applied to the stator windings, the rotor moves to align the rotor pole with the nearest stator pole

To keep the rotor moving, an electronic control system switches on the windings of successive stator poles ahead of the rotor, so it continues to rotate

However, switched reluctance motors gained a reputation for being noisy

They also suffered from torque ripple – fluctuations in torque as the rotor rotates – which made them unsuitable for traction applications

They required different power electronics to run them compared to permanent magnet machines, which were expensive without economies of scale

AEM’s breakthrough is the subject of a patent and has made it possible to drive the SR motor using the same power electronics as a permanent magnet motor

And although it appears to the power electronics as a standard three-phase motor it is in fact a six-phase design, which reduces the torque ripple and noise problems

The switched-reluctance motor is more sustainable in three ways, says Dr Widmer

First, environmentally, the mining and refining of rare earth elements pose significant problems if not properly managed, and currently emit large quantities of carbon dioxide in the refining process

Second, China controls more than 90% of the world’s supply of rare earth minerals

Third, rare earth elements can be expensive and prices are volatile, particularly given the current US-China trade war

- a motor for a vehicle like the Nissan Leaf needs around 2kg at $100 per kg

"So our motor should provide like-for-like performance with environmental advantages and cost savings,” says Widmer

AEM has also developed a patented manufacturing process that allows aluminium to be used for the windings

Copper has traditionally been used in motors because it is a good conductor and easy to use

Aluminium is not such a good conductor, is less easy to wind and age-hardens in a different way

However, AEM has also developed a patented manufacturing process that allows aluminium to be used for the windings

Aluminium is a tenth of the price of copper and easier to recycle

– because it melts at a lower temperature than steel it can be recovered separately at the end of a motor’s life, whereas copper contaminates the recycled steel

The full article provides much more information for interested parties

It sounds like a good story

- but the results need to be seen on the road

And there are hints of compromises

- so let's see them in practice