Have you ever wondered what the future holds for electric vehicle propulsion?
Well, let me tell you, it's all about the axial flux motor! Forget about those old radial flux motors, axial flux is the future! So, what exactly is an axial flux motor? It's a type of 200-year-old electric motor where the magnetic fields are aligned with the axis of the motor, hence the name. Yes, you heard that right, it's a 200-year-old technology that is making waves in the modern world. And let me tell you, these bad boys are becoming the standard for electric vehicles and even aviation.
It's all about that high torque-to-weight ratio, which is perfect for aircraft companies like Rolls Royce and Magnex, which are currently deep in research and development on these motors. But here's the thing: axial flux motors aren't exactly new.
In fact, the genius Michael Faraday actually developed the first ever electrical generator, which was an axial flux type. Unfortunately, it never quite took off back then. But now, it's having its time in the sun! Now, I know what you're thinking: how does it actually work?
Well, get ready as we explore the amazing world of axial flux motors. Nikola Tesla already had this technology patented back in 1889, so why haven't we seen more of them? Well, let's just say that the radial flux motors had their time in the spotlight. They were simple to design and build, and they worked pretty well. But now, with the rise of electric vehicles and the constant need for more power and efficiency, axial flux motors are back in the game. Think of axial flux motors as the turbocharged cousins of radial flux motors. In a radial flux motor, the magnetic flux is perpendicular to the axis of rotation. In an axial flux motor, the magnetic flux lines are parallel to the axis of rotation.
But how does it actually work? So, the axial flux motor operates based on the interaction between permanent magnets and electromagnets. When coils are energized, they become electromagnets. The most common design of axial flux motors has fixed coils and freely rotating permanent magnets. The motor's coil arrangement can be seen here(Axial flux ). When a direct current supply is given to one of the coils, it gets energized and becomes an electromagnet. And when that happens, the s pole of the rotor is attracted to the stator's opposite end pole, while the like poles repel. The tangential component of these two forces makes the rotor rotate.
Now, you might be thinking, "Wait, what if the rotor stops at perfect alignment?" Well, that's where the rotor's speed and inertia come into play. It travels ahead of the perfect alignment angle, and during that time, the next coil gets energized. And because of the same forces of attraction and repulsion, the rotor then reaches the next coil. It's all pretty fascinating, isn't it? And the best part is that axial flux motors are just getting started. With electric mobility and aviation on the rise, it's clear that these motors are the way to go.
Now, if you're used to the traditional radial flux BLDC motors, you might be wondering what the big deal is about this Axial Flux motor. Well, let me tell you, this baby has a different geometry from the radial machines that you're used to. Here's the lowdown: while radial motors have a rotor made of permanent magnets located inside a stator, the stator of an Axial Flux motor contains a support known as a yoke, which is outfitted with "teeth" containing electromagnetic coils. These teeth function as alternating magnetic poles that interact with the rotor's magnetic poles, resulting in the motor's torque.
But, wait! There's more. You see, in this operation, two coils are always dead, which drastically reduces the motor's power output. But here's the trick to overcoming this problem: we simply have to pass the opposite-polarity current through the second coil. It's like a game of magnet chess, and we're winning! To ease our understanding, let's focus just on the nearest pairs of magnets. You can see that on the stator side, two south poles are together. The combined effect of these two poles produces a net tangential force, which means that the combined effect produces more torque and power output from the rotor. This process also ensures that the motor has a constant torque output, which is music to our ears.
Now, you might be wondering: how will we decide which coil to energize to get continuous rotation? Well, we use a smart electronic controller. The sensor determines the rotor's position, and based on this information, the controller decides which coil to energize. It's like the motor has a brain of its own! And, while theoretically, rectangular pulses like this produce a constant torque output for the axial motors, in practice, when you suddenly switch on or off a phase current, ripples will be produced in the other two phases. And you don't want ripples in your motor.
So, what's the best solution to overcome this issue?
Well, it's simple: gradually kill or raise the phase current, resulting in a pattern like this. Although axial flux motor geometry has been around for a while, it was never really commercially viable. But now, thanks to Soft Magnetic Composite (SMC) materials exclusive to powder metal, designers are able to exploit this topology's advantages and drive the future of electric motors!
What makes axial flux motors so exciting, you ask? Well, for starters, they have a high power density, which means they can produce more torque than their radial counterparts. And who doesn't love torque? I mean, it's the reason why we get goosebumps when we hear the engine of a muscle car revving up. Axial flux motors also have a simplified high-current BLDC motor winding design and a shorter magnetic path. These motors are more efficient, which is great for the environment and your wallet!
Now, let's compare the axial flux motor with the most commonly used motor, the radial flux induction motor. The first thing that sets these two apart is the flux flow path in the machines. If you compare the magnetic flux patterns of both motors, you'll notice that the axial motor's flux flow path is much denser and shorter than the induction motor's. And this is a big deal. Although the radial design has been the standard for decades, axial and TFM motors offer distinct features and performance advantages that make them the preferred choice for modernizing your automotive or industrial applications.
Let's take a motor for a wheel hub, for example. What's the most important thing you want it to do? Produce lots of torque, right? Well, axial and transverse motor designs can have rotating member located on their outer diameter, which means they create higher torque while reducing their motor footprint. It's like having your cake and eating it too! An axial flux motor also has a higher power density, which means it develops 30–40% more torque than a similar-sized radial motor. And as if that wasn't enough, it also has better cooling. Axial flux motors are the way of the future.
As mentioned earlier, in a radial flux motor, the magnetic flux moves from one tooth to the stator, then back to the next tooth, and finally to the magnets. It's like taking the long way around to get to your destination. On the other hand, an axial flux motor takes a much more efficient approach. It has a magnetic flux path that goes from one magnet, through the core, and then to another magnet.
It's like taking a shortcut and getting there faster. Speaking of speed, let's talk about McLaren, the company that's synonymous with speed and power.
They've been making cars for over 60 years, and they sure know a thing or two about going fast. So, when it came to making their new car, the McLaren Artura, they knew they had to go electric. But there was a catch—electric motors are heavy, and McLaren didn't want to compromise on the weight of their car. I mean, who wants a 3,500-pound supercar, right? So, what did they do?
They went on a tear, eliminating as much mass as possible from the front to the back of the car. They touched every system—from the chassis to the powertrain, the suspension, and even the seats. And the results? Well, the Artura weighs only about 100 more pounds than the 570S it replaces in the marque's lineup. And what makes the Artura even more special is its 94-horsepower axial-flux electric motor and 7.4 kWh of batteries.
It's like the car has been injected with steroids but in a good way. But wait, there's more! We also have transverse flux motors (TFM motors), which take a completely different stator winding design approach. Instead of copper wire around the stator teeth or pole, it has coils that are circumferentially around the axis of rotation. This design enables the magnetic flux to flow in three dimensions, where it crosses axially through the stator, circumferentially through the rotor, and radially through the gap between them. The result?
You get increased low-speed torque, efficiency, and even power for specific energy inputs and motor sizes. This design is uniquely suited for surface-mounted permanent magnet motors (SMCs), and with their lower inherent core losses, there are decreased cooling requirements for this style of motor. But have you wondered how some of these lightweight motors are perfect for electric airplanes, where every ounce counts?
Rolls-Royce has developed the Ion Bird craft, which uses three axial flux motors by YASA, powered by 6,000 lithium-ion batteries, and a smart electronics controller with an incredible efficiency level promise of more than 96 percent! And the best part? With their compact size, axial flux motors can even become a good choice for electric cars.
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