Electric vehicles are on the increase – just about every major manufacturer is promising a full-electric model by 2020 – but how exactly do they work?
For all the awesomeness of a howling V8, it has to be admitted that an internal combustion engine isn’t the most elegant or efficient way to generate power. Although modern engines are far more sophisticated and efficient than powerplants from a few decades ago, they are still based on an old technology that has survived not necessarily because it’s the best solution possible, but because fossil fuels have (at least until now) been abundant and cheap. The fact of the matter is, engines that run on fossil fuels are inherently complicated, messy and inefficient, with a lot of generated energy going to waste through things like heat. Compared to traditional cars, electric vehicles are actually quite simple. In terms of the drivetrain, an electric car essentially consists of three things.
1. Power storage unit The first thing an electric vehicle requires is some kind of power storage unit. With a full-electric vehicle, it’s usually a large battery. When it comes to making an electric vehicle a viable replacement for a traditional car, this is undoubtedly the most problematic component. It goes without saying that you need a pretty big battery to power a 2 000kg car successfully, especially if you want it to be able to keep the vehicle going for a few hundred kilometres between charges. Batteries are heavy, bulky and not yet capable of providing the same sort of range you’d get from a full tank of petrol. But things are changing. The lithium-ion technology that is the basis of these batteries is improving all the time. The batteries are becoming lighter, smaller and more powerful. When Tesla launched its Roadster six years ago, the maximum range was about 320km.
Thanks to an improved battery pack, which Tesla unveiled late last year, the range you can expect from the average Tesla is now about 500km. That’s pretty impressive, but according to Tesla CEO Elon Musk, taking things to the next level won’t be easy. Musk says that his company has now basically achieved the maximum efficiency you can expect from these batteries in terms of energy density. To go beyond the current limit, Tesla will need to figure out a way to somehow alter the essential chemistry of its batteries by using better materials or a better cell design. Short of doing that, it’ll need to make bigger and bulkier battery packs, which will have a negative impact on practicality and performance.
2. Control unit The second crucial drivetrain component of an electric vehicle is a control unit. From the battery, power flows to a controller, which, as its name suggests, controls this power and makes it usable. The control unit will modulate the power and keep it even, ensuring a smooth ride and providing the right amount of power when you need it. In this way, it acts as a sort of gateway to the electric motor. Without it, maximum power will constantly be sent to the motor, which will make the car just about impossible to use. The control unit interacts with components like the brake pedal and accelerator, and provides you with a driving experience that’s similar to what you’d get from a traditional vehicle with an internal combustion engine. The control unit also does other things. For example, it can act as a converter, transforming power from one type to another (DC to AC power, for instance), and it could also increase or decrease amperage. The control unit is essentially the ‘brain’ of the drivetrain, and is responsible for taking the stored energy and converting it in whatever way necessary to provide forward motion.
3. Electric motor The motor, quite obviously, is what makes an electric vehicle go. At the moment there are essentially two kinds of motors in use. The first is the DC brushless electric motor, which consists of two or more permanent magnets that generate a DC magnetic field. You’ve probably heard that an electric car offers you peak torque from standstill. That’s a feature of a DC series motor, not necessarily every electric motor. This feature makes it popular, but the motor does have some drawbacks. A DC motor doesn’t do well when you need a constant speed under a constantly varying load. Translation? It can’t handle hilly terrain.
A DC series motor has to be run under a load, otherwise it turns with too much force. You need to manage the load and keep it constant. That’s easy on flat terrain but not when you’re dealing with loads of hills. To counteract this, you need to manage the magnitude and polarity of the magnetic field through an inverter (control unit). Without this, a DC motor is useless as far as powering a vehicle is concerned, since it has a one-speed all-or-nothing power delivery. The second type of motor often used is the AC induction motor, which was originally invented by Nikola Tesla. No magnets are used here. Instead, currents flowing through stacked steel laminations generate a magnetic field. This kind of motor is more complicated (and therefore more expensive), but it has the advantage of delivering a torque curve that’s similar to what you get from a traditional engine.
The electrified future
Fundamentally, the technology that under-lies electric vehicles is fairly simple. It already exists and companies like Tesla are using it to produce vehicles that can be used on a daily basis. But long-term success will lie in improving efficiency and packaging things more effectively. In that sense, an electric vehicle has more in common with an iPhone or MacBook than a traditional car. As with a phone or laptop, success in the realm of electric vehicles will mean improving battery life while making components smaller and sleeker.
Text: GG van Rooyen