GEOPOLYTICS AND TRANSPORT - The paradox proposed in the summary is a provocation: the tried and tested induction motors (used for example by Tesla) do not have magnets and those with "brushes", the subject of the article, have existed for some time but now return with important evolutions technological.The mighty BMW iX, for example, uses motors without magnets and Renault also adopts them for the Zoe.In fact, the "fifth generation" of BMW electric motors is also used in the i4, iX3, i7, iX1 and so on, demonstrating how much the Bavarian company believes in this type of engine.One of the main reasons why people try to eliminate permanent magnets from electric motors is that they use Rare Earths, for example neodymium, dysprosium and samarium, which are expensive and come from countries, such as China, considered geopolitically critical.To understand how it is possible to make an electric motor without magnets, let's briefly recall the operating principles of these "electric machines".We know that a magnet has two poles, conventionally called North and South: the same poles repel each other and the opposite ones attract.Therefore, holding a magnet in hand and bringing it closer to another, the latter will move in order to bring the opposite poles closer, moving away the homologous ones.1 _-_ diagram_motore_elettrico_con_motore_avvolto_resize.jpg> In the cross-section of an electric motor with a wound rotor (above) you can see, from the left, the rotor (the windings are not seen), the shaft, the stator, the bearings and the collector rings - slip rings - on which the brushes slide, not visible here.MAGNETIC FIELD WITHOUT MAGNETS - In this way a movement has been created, but it is a one-off: to obtain a continuous one it would take a "rotating magnet", potentially able to rotate another one continuously.It helps that the creation of a magnetic field can also take place by making current flow in a coil of conducting wire: it is an electromagnet and, compared to the permanent magnet, it has the advantage of being able to vary the strength and direction of the magnetic field by varying the intensity and direction of the current.At this point we have the "pieces" we need to build an electric motor.The rotating magnet mentioned above can be obtained with electromagnets / coils powered separately from the individual phases of a three-phase alternating current.These windings are arranged in the stator (the fixed part of the motor) and by “turning them on” in succession we obtain the much desired rotating magnetic field.2 _-_ rotor_motore_zoe_r135_resize.jpg> The rotor of the Zoe engine highlights both the windings and the copper rings of the collector (see text).THE COILS THAT SOLVE - The rotor, that is the "magnet" rotated by the rotating field created by the stator, can be made of permanent magnets - and this is the case of most electric cars in circulation - or also have electromagnets .The latter solution is versatile - remember that electromagnets can modulate the magnetic field - but it requires directing current to the rotor, an organ that can rotate at more than 15,000 revolutions per minute.This has traditionally been done by bringing the ends of the windings on the rotor shaft - in an area called the collector - and making them touch by the brushes, special contacts that carry the current destined for the rotor itself.The brushes crawl on the collector and therefore there is some wear, but at BMW they ensure that they last so long that they do not cause problems during the useful life of the vehicle.Zoe's new engine also uses this pattern.In fact, permanent magnet motors do not need brushes (to the advantage of simplicity and reliability) since the rotor magnetic field is always present: this is why they are defined as brushless.3 _-_ power_unit_bmw-i4-_resize.jpg> In the fifth generation BMW power unit you can clearly see the motor dominated by the inverter;also in evidence the 3 large orange terminals that carry the three-phase current to the stator.THE BRUSHES?LET'S DO WITHOUT IT - A proposal that wants to combine the advantages of the two solutions comes from Mahle, a classic company born with internal combustion engines (its pistons were and are synonymous with high performance) which has also repositioned itself on electric mobility.The current destined for the rotor windings is created by a rotating generator consisting of disks - one fixed and one connected to the rotor - which rotate close together without touching.This is alternating current which is transformed into direct current and then sent to the windings of the rotor, which thus behaves like a permanent magnet.Vitesco Technologies - a spinoff of Continental for components for electric cars - also presented a motor without magnets.In addition to the cost advantages (the materials for a permanent magnet rotor cost from 40 to 80 euros / kg against the 7 euros of those for a wound rotor) and availability, the elimination of permanent magnets offers other benefits.4 _-_ rotore_motore_elettrico_bmw_resize.jpg> The stator of the BMW engine highlights the windings which, powered in succession by three-phase alternating current, create the rotating magnetic field at the basis of the operation of these units.ALMOST ALL GOOD - When an engine of this type is excluded (think of a disengageable four-wheel drive) it has very low resistance while a permanent magnet motor creates energy because the magnetic field is always present: it is as if it were in any case in a slight regenerative braking .Other benefits promised by this architecture are very easy recovery of end-of-life materials, reduced emissions associated with its production and efficiencies of over 95% across the entire range of operating regimes with even higher values ​​at high speed.Obviously, there are some disadvantages: the brush-collector assembly, if present, wears out and must be sealed because the dust generated by wear must not go out or penetrate the motor.Even balancing the rotor is a bit more challenging because it is not easy to make several copper wire windings with identical weight and geometries.In any case, this type of engine seems to be on the crest of the wave: Renault is betting on this scheme for the future and the unit of the Megane E-Tech Electric is also produced in Japan for Nissan.5 _-_ brushes_and_collettore_motore_bmw-i4_resize.jpg> In the center of the photo you can see the 3 dark brushes that carry the current to the collector, the copper-colored ring mounted on the shaft of this BMW electric motor.6 _-_ mahles-innovative-magnet-free-ev-motor-_resize.jpg> The solution chosen by the Mahle component maker to inject current to the rotor windings is quite unusual.The green disk on the right rotates, without touching it, in front of a fixed winding and the alternating current thus created is converted into direct current in the second green disk on the left and then sent to the windings.Electric, richly equipped and well finished, the Mercedes EQA is a crossover that also stands out for its pleasant driving.On the other hand, the trunk is small and the braking is not convincing for its modularity and vigor.The Volkswagen ID.4 is a very well equipped modern power crossover, offering plenty of space and comfort.However, some finishes and the "climate" vents can be improved.The Kia XCeed is a crossover that winks at sportiness.Especially this 1.5 hybrid, which is fast and easy to handle and also consumes little.The trunk is not huge.© 2022 - 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