EV Fundamentals: Introduction to EV Motors
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Introduction to EV Motors
06.37
| 00:00 | Motors are at the heart of electric propulsion. |
| 00:02 | Without a lightweight motor that can consistently provide high output torque at both low and high speeds, there's no way that electric vehicles could be a viable alternative to conventional internal combustion engines. |
| 00:13 | Although we mostly take it for granted these days, the development that this technology has seen over the last 10 or so years has been absolutely incredible. |
| 00:20 | We're now at a place where EVs can not only match but easily exceed the power output of conventional internal combustion vehicles. |
| 00:26 | It's actually the batteries that are now the limiting factor of EV performance rather than the motors. |
| 00:31 | For short bursts, the power output levels are nothing short of staggering, with many production EVs offering more than a thousand horsepower. |
| 00:38 | The characteristics of motors used in electric vehicles are very different to your traditional internal combustion engine. |
| 00:43 | While a combustion engine can only operate efficiently within a relatively narrow power band, an electric motor offers near full torque from zero RPM, so that means a clutch or torque converter isn't needed. |
| 00:53 | Modern motors are also able to output a constant peak or near peak power over an extremely wide range of speeds, meaning that a number of different gears that would otherwise be required to keep a combustion engine in the right rev range aren't needed. |
| 01:06 | Often an EV motor will only have one gear reduction, which is used for both forward and reverse, and that results in substantial efficiency, weight, and cost savings for the manufacturer. |
| 01:15 | In this section of the course we're going to explore the capabilities and limitations of modern permanent magnet and induction EV motors, as well as describe some of the more technical aspects that affect their operation and characteristics. |
| 01:28 | To be clear, some of this more in-depth knowledge is a jump up in difficulty, and you certainly don't need to know all of it in order to work on your own EV projects, but the broader the understanding you have of how these devices work and what's going on inside them, the better off you'll be, so I highly recommend sticking with it. |
| 01:42 | Before we get into the technical side though, let's go over some of the basic nomenclatures and functionality of electric motors and their parts so that we're all on the same page. |
| 01:52 | As you may already be aware, motors have a fixed component and a rotating component. |
| 01:56 | The fixed component is called the stator because it stays in place and generally consists of a number of windings that make up an array of north and south poles. |
| 02:04 | Motors will often have multiple pairs of north and south poles and will be designated as having a certain number of poles, or that number divided by two pole pairs. |
| 02:12 | For example, a motor with ten poles has five pole pairs. |
| 02:16 | The rotating part is called the rotor, and depending on the motor type, the rotor may be a metal cage in the case of an induction motor, or a series of magnets, or a combination of iron slots and magnets in the case of an internal permanent magnet motor. |
| 02:29 | There are two primary types of motor layout, radial flux and axial flux. |
| 02:34 | This simply describes the shape of the motor. |
| 02:37 | So radial flux motors is the conventional type you're used to seeing when you think of an electric motor, where the stator windings encase the spinning rotor inside. |
| 02:45 | Both the length and diameter of the rotor influence the torque and power that the radial flux motor can produce, among other things. |
| 02:52 | Additionally, certain motors can be stacked together in line to multiply the torque and power potential. |
| 02:58 | An axial flux motor, on the other hand, has a rotor that looks like a pancake, or you can even imagine it like a Wankel rotary engine. |
| 03:04 | There are three relatively flat components, a stator, the rotor, which is a large thin disc, and in most cases a second stator sandwiching the rotor. |
| 03:11 | Just like a rotary engine, multiple of these components can be then stacked together building up the size and power of the entire motor assembly. |
| 03:19 | So as current is passed through the motor windings, a magnetic field is created. |
| 03:23 | The higher the amplitude of this current, the stronger the magnetic field becomes. |
| 03:27 | And by positioning this magnetic field in the optimal position, which is usually about 90 degrees away from the rotors poles, this rotating magnetic field will pull or push the rotor creating a torque. |
| 03:38 | Different designs of the rotor and stator help increase the efficiency of the motor, with compromises that need to be made to cover the extremely wide range of speeds that an EV motor operates in. |
| 03:48 | Above a certain speed, called base speed or brake speed, the motor is no longer able to output peak torque. |
| 03:54 | The base speed is set by the design of the motor and the available voltage from the battery. |
| 03:59 | Above this base speed, the motor operates in what's called a constant power region, where the torque continues to drop off with increased motor speed, but the total power output stays relatively constant. |
| 04:10 | Below base speed, the torque output is generally a constant or a flat line, which is set by the limits of the inverter or by limits specified by the motor supplier, along with physical limitations such as the magnetics inside the motor themselves. |
| 04:23 | We'll be focusing on the magnetic magic in the inverter section, as there's quite a lot to unpack there, but for now just know that it's the motors job to do the most possible with the current that's passing through its stator. |
| 04:33 | This brings us to the last thing we need to discuss in this module, the final drive. |
| 04:38 | Our rotor is connected to a gear reduction followed by the wheels, either directly or through a differential. |
| 04:43 | There are a number of different layouts here, but most EVs have a single speed gear reduction, as the motor runs at a much higher speed than the wheels. |
| 04:51 | In some instances, a gearbox is in place, especially with hybrids, where the motor is often placed before the transmission. |
| 04:57 | After this gear reduction, there's a differential, typically an open diff, which is then connected to each axle. |
| 05:02 | But as you're probably already very aware, some very high performance EVs have one motor for each wheel, in which case there's a motor and gear reduction connected to only one wheel with no diff needed. |
| 05:12 | This layout allows for torque vectoring, which means the motors can play a role in the handling and dynamics of the vehicle by applying different levels of torque between the left and right wheels. |
| 05:20 | Something to keep in mind with these layouts is that safety is a critical concern. |
| 05:24 | If one motor locks up due to an internal failure, this could result in a vehicle losing control, as it would force the car to turn quite aggressively if there was a large torque difference between the left and right wheels. |
| 05:35 | Alright, so we've covered a lot in this EV motor basics section, so let's run through the main takeaways to recap. |
| 05:40 | Electric motors have come a long way in a very short amount of time, and it's now generally the battery that's a limiting factor in many EVs when it comes to performance. |
| 05:47 | One of the key defining advantages of an electric motor is that near full torque is available from 0 RPM, which means we don't need a clutch or torque converter. |
| 05:54 | Further to that point, thanks to a modern motors ability to output constant peak power above base speed, no gears are typically needed. |
| 06:02 | Often an EV motor will only have one gear reduction, which is used for both forward and reverse, resulting in substantial efficiency, weight, and cost savings. |
| 06:10 | There are two primary types of motor layout, radial flux and axial flux. |
| 06:14 | This refers to the shape of the motor, although they both work in the same basic way and have two main components, a fixed stator and a rotating rotor. |
| 06:21 | Different designs of the rotor and stators result in different levels of efficiency and torque output, and because of the wide range of speeds and voltages that these motors operate in, compromises do need to be made to the target application. |
