How does an electric motor work? 10 questions and answers

How does an electric motor work? 10 questions and answers

Just what is the principle that electric cars work on? How do they behave differently from internal combustion engine cars? How reliable are they? ŠKODA’s experts have come up with clear and easily understandable answers to all of your burning questions.

17. 5. 2018 eMobility

The Electrical Age has dawned. Electric cars will soon become part and parcel of our everyday lives. ŠKODA itself will have 10 electric models by 2025. And yet the way they work remains much of a mystery for many drivers. Electric cars exude the exotic, appearing to be complex, perplexing, and technologically distant, when in fact they are simpler than internal combustion engine cars in many respects.


1. How does an electric motor differ from an internal combustion engine?

The principle of energy conversion to mechanical movement is completely different. While an internal combustion engine relies on thermodynamics to burn fuel, electric motors make this conversion by harnessing the electromagnetic forces generated when an electric current passes through a magnetic field. An internal combustion engine has a crank mechanism (cylinders, pistons, valves, crankshaft, etc.), whereas nothing more than a stator and rotor (and their mutual interaction) are at the heart of electric motors used to propel vehicles. What’s more, this electric motor can act as a generator so, when you brake or decelerate, the energy can be channelled back to the battery, thus recharging it.


2. How does an electric motor behave differently from a combustion engine?

The power bands and torques of each of these engines are entirely different. While the power and torque of an internal combustion engine increase with the RPM until they top out, in an electric motor maximum torque is delivered from almost zero revolutions and decreases as it reaches the highest RPM. In practice, this means that an electric car has greatest traction at the start, and therefore relatively high dynamics. In addition, an electric motor’s very wide operating RPM range means that it doesn’t need a multi-speed transmission with a clutch, so your average electric car can get by with a single gear – or a reduction drive – from standstill to top speed.


3. How is the power of an electric car calculated?

Calculating power is not as simple as it is for conventional cars. In an electric car, the total power is not based only on what the powertrain supplies, but is also affected by the battery power. As this is always a value determined by the entire drive system, the drive can even be designed so that, for example, its technical basis is the same for a variety of power versions, and the ultimate power of the car depends solely on how it is combined with differently sized batteries.


4. And how is consumption measured?

In electric cars, consumption indicates the energy consumed in kilowatt-hours per 100 kilometres of travel (kWh/100 km). In the instrument cluster, as in conventional cars, you can see information on both the instantaneous and average consumption. On top of this, it also displays the amount of regenerated energy sent back to the batteries.


5. How about the servicing and life of electric motors?

Since the main, and in fact the only, moving part of an electric motor is the rotor, servicing requirements are minimal in comparison to a combustion engine. There is no need for any oil changes or fuel and air filter replacement. These tend to be high-revving machines, so they need to be well designed (especially the bearings), but, in general, electric drive requires less maintenance than a conventional engine.


6. Which wheels does the electric motor provide drive to?

In principle, the motor can be mounted on either the front or rear axle. Generally, though, it’s better for an electric car to have rear-wheel drive, as this enables the electric motor to transfer its powerful torque to the road surface better and more efficiently. Fully electric all-wheel drive can be installed quite simply by adding a second electric motor to the front axle.


7. Do all electric cars have the same type of motor?

In the same way that different types of internal combustion engines have evolved, there are multiple options and variations when it comes to electric motors, too. The type always depends on the characteristics required of the car. Stepping into a little more detail, three-phase synchronous motors, often with permanent magnets, are the most widespread, along with asynchronous motors or their variations. An integral part of these motors is usually a power electronics unit, which can be either directly integrated into the motor or fitted separately and then coupled with the motor via three strong phase conductors.


8. Is there a difference between the electric motors in plug-in hybrids and in pure electric cars?

Yes. In the design of a purely electric car, it is assumed that there will be no other type of drive in the car, so this doesn’t need to be taken into account. Consequently, the motor can be optimally primed for the required torque and power, RPM, and vehicle options. The hybrid engine design, on the other hand, must also take into account the characteristics of the internal combustion engine that is to partner the electric motor, focusing on mechanical connection possibilities, operating temperatures, RPM, and the power band. The drive control system is also more complex. The car must be able to move purely electrically, with a combustion engine, or in combined mode, and always with optimal energy use.


9. Is it true that electric vehicles existed more than a century ago?

The first attempts to build an electric car date back to 1835 (48 years before the first petrol engine was built) and were made – independently of each other – in Italy and the Netherlands. Figures such as Ferdinand Porsche and the Czech inventor František Křižík were working on the design of electric vehicles at the turn of the 20th century (Křižík even unveiled a LAURIN & KLEMENT car at this time). In 1900, more electric vehicles were driven in the US than internal combustion engine cars, and the first car to break through 100 km/h was electrically powered. However, these cars drew on heavy lead batteries and had a short range. The arrival of serial car production and the mass use of combustion engines with a more convenient range sidetracked the application of electric drive for many years.


10. Why are electric motors being developed again today?

The modern eMobility boom is being driven not only by the need to reduce local exhaust and CO2 emissions, but also by the rapid development and availability of new technologies. Modern lithium-based batteries are much better at storing and releasing the necessary amount of power. They have their own control electronics, they communicate with the car’s entire system, and their further development is progressing in earnest. Likewise, today’s semiconductor components can transmit much larger currents with minimal loss and can be used to control and regulate powerful electric motors efficiently. The increased availability of green energy from renewable sources and plans to develop charging station infrastructure have also played a role in the recent promotion of eMobility.


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