Patent Application Shows Dedicated Electric Motorcycle Braking System That’s Wear-Free and Similar to Trains
September 12, 2024
One of the strongest arguments of those who propose electric vehicles is the fact that they require less maintenance than an endothermic one and this, let’s face it, is intriguing even for those who hate battery-powered vehicles. But how would their perception change if they did not require any maintenance at all? A project for a braking system that BMW is working on and for which the German company has requested a quote goes in this direction. According to what was also reported by Cycle World, it would be a system that uses electromagnetism and is not an absolute novelty even if it certainly would be on a two-wheeled vehicle. So let’s try to better understand how it works.
Once upon a time we would have said “it goes like a train!”, in the near future we might find ourselves saying “it stops like a train!”. If normal disc brakes disperse the kinetic energy accumulated by the movement of the motorcycle by transforming it into heat by exploiting the friction between discs and pads, in most electric motorcycles regenerative braking systems are able to recover part of that energy by transforming the engine into a real generator, a sort of giant dynamo that returns part of the energy consumed to bring the motorcycle up to speed to the battery. Clearly this is already a significant step forward in terms of efficiency. However, it is not free from limitations. For example, if the battery is already charged it is not able to accept further energy and therefore must be dissipated anyway, but not only that. This is one of the reasons why a similar system cannot be used as the only braking system and even the electric motorcycle needs conventional brakes.
The diagram filed by BMW to illustrate the eddy current braking system
BMW’s patent instead proposes to use eddy currents, also called Foucault or Eddy currents (from the English term used to indicate vortices). These currents are induced in conductive metal masses immersed in a magnetic field. The variation in magnetic flux that is obtained with the movement generates these currents that were discovered by the French physicist in 1851. If friction brakes (i.e. those we are used to) apply a force between two parts in relative motion (i.e. between them), magnetic brakes that use eddy currents slow down thanks to electromagnetic induction. The slowing force therefore occurs without there being any contact between the parts and is due to the transformation of the induced currents into heat. To get to the point we started from: since there is no contact and therefore no friction, the magnetic brake is free from wear. This type of brake, already used on some electric trains, is then distinguished between electromagnetic or permanent magnet. As you can imagine, in the first case a source of energy is required to brake and this is the type of brake that interests us at this moment.
Operating diagram of an eddy current brake
When a conductor (such as a coil of copper wire, as in a generator) is moved through a magnetic field, an electric current is generated. In an eddy current braking system, this conductor is a block of conductive material, essentially the brake disc, and the current generated by its passage through the magnetic field has no outlet. Instead, it is spun like a vortex inside the brake disc, heating it. By using electromagnets mounted near the brake disc to generate the magnetic field, the magnetic field can be turned on or off and its intensity can be modulated, to control braking. This, in a nutshell, is the basic concept used by BMW for this very promising patent, which would lead to the elimination not only of wear but also of the need for a mechanical brake, because even if the battery were too charged to accept the electrical energy from regenerative braking, the current could be directed to the electromagnets to dissipate it as heat.
Rotating magnetic brake used on the 700 Series Shinkansen
The advantage of this type of brake would not only be the absence of wear, there would be at least another not insignificant one: the speed of action. Contrary to what we might hypothesize, this eddy current brake would require significantly shorter reaction times than a conventional brake. With a disc brake we know that there is a short interval of time from when we pull the lever to when the pressure of the liquid pushes the pistons and therefore these press on the pad which in turn “bites” the disc. Then there is another period of time between this phenomenon and that of the wheel stopping on the asphalt. Eddy current brakes do not have this delay and can go instantly from zero to maximum braking force.
In the BMW patent, however, we also see a conventional brake as a support. The reason? Because otherwise, when the bike is off, we would not be able to brake. Therefore, to be honest, we cannot say that this system is totally and absolutely maintenance-free, even if, presumably, using the conventional brake only when maneuvering with the bike off, you can understand that the pads can last as long as the bike.
What do you think? Would you trust a magnetic brake? Let us know in the comments.
