Motors in electric cars: light, powerful and maintenance-free

The electric motors that propel modern electric cars are surprisingly simple in construction. That gives electric cars a lot of advantages. See how the electric motors work and what’s interesting about them.

8. 11. 2024 eMobility

The history of electric motors is as long as that of internal combustion engines. You might even be surprised to learn that in the early days of motoring there was even a time when electric motors dominated car propulsion. As such, the electric motor has been a long and well-known device in the industry, but even today it is still evolving. Having said that, the basic technical principles remain largely unchanged. The electric motor is a highly efficient device, outperforming internal combustion engines in this respect. While the very best internal combustion engines today have a maximum efficiency of around 40%, electric motors typically achieve double that figure. As a result, they are able to make optimum use of the energy for powering the vehicle.

Simple design

The high efficiency of electric motors is due to the principle governing their operation. There are many types of electric motors, but the basic principle is very similar for all types. An electric motor has a stator (the static part that does not move) and a rotor, the rotating part that is used to transmit the driving force. The stator is usually the outer part of the electric motor, the rotor the inner part. The rotation is caused by changes in the electromagnetic field caused by the passage of electric current.

Cross-section of an electromotor

There are two types of electric motors largely used in electric vehicles today. Each has its own advantages, and disadvantages, so they are used in different ways. The two are synchronous and asynchronous electric motors. The latter always use alternating current to create driving force, so an electric vehicle must always be equipped with an inverter, as the battery is the source of DC electric current.

Why this difference in the motors used? The reason is simple. A permanent-magnet synchronous electric motor generally achieves greater efficiency over a wide range of revolutions (i.e. car speed). An asynchronous electric motor is ideal with respect to the required peak power and overall drive efficiency. Technically, the difference between them is that the synchronous motor has the same rotor revolution speed with the stator electric field and uses permanent magnets in the MEB platform cars, while the asynchronous motor has a different (lower) rotor speed. Asynchronous motors don’t use permanent magnets, have minimal losses and so do not increase the car’s power consumption when not used for traction.

There are a number of other benefits for electric car users. These include a flat floor for the car’s occupants due to the way the electric motor is incorporated into the car’s structure. With a suitable design, this is possible thanks to the absence of an exhaust system and, in the case of all-wheel drive, the absence of a cardan shaft because there is an electric motor on each axle. The transmission systems also take up much less space. “MEB-platform electric motors use a simple reduction gearbox,” Oldřich Vyziblo points out.

In the Enyaq, the driver selects the recuperation intensity by means of stalks beneath the steering wheel.

Another practical advantage of electric motors is recuperation. Electric motors in electric cars can also function like an electricity generator during braking. This not only saves the car’s brakes from wear, but also returns some of the energy to the batteries, something a traditional internal combustion engine car (without a hybrid powertrain) can’t do.

If designed well, electric motors can also be environmentally friendly. For example, parts made from an aluminium mixture can be reused for new parts as part of the recycling process. Copper motor windings are also recycled.

A robot places an electric car’s battery on the chassis.

The current goal in the development of electric motors for cars is to reduce the use of synchronous electric motors’ permanent magnets with precious metal content. One example of this kind of device is a motor that replaces the expensive permanent magnets with standard copper windings similar to stator windings. Known as a synchronous motor with excitation. This type of motor is commonly used in industry, and its use in cars is driven by the optimum price-to-performance ratio. On the minus side, it is not as compact and places higher demands on the power control electronics. “The aim is to reduce the quantity of rare and precious metals contained in the magnets or to do without them altogether,” concludes Jiří Šlechta.