A motor is the soul of an EV. Where gas-powered cars use an internal combustion engine as their powerhouse, an EV replaces it with an electric motor. Several types of motors are used in electric vehicles today. The choice of the motor can go a long way in the powertrain design of an EV.
The type of electric motor decides the efficiency, peak output power, torque, and plenty of other variable factors. Each type of electric motor used in EVs has its ups and downsides. It is entirely dependent upon the manufacturer to choose a motor that best suits their vehicle.
Electric motors can be classified with respect to many things, such as AC or DC input and synchronous or asynchronous. But largely, the types of motors used in EVs are these:
Let’s discuss the pros and cons of each of these motors for an EV.
All Types of EV Motors
1. DC Brushed Motor
During the initial days of EVs, brushed DC motors were used to energize the powertrains. However, soon the shortcoming of the DC brushed motors became apparent, and they were replaced with other modern motors. A brushed DC motor uses brushes made out of carbon, copper, or graphite. The brushes and commutators are in direct contact with each other.
The combo of brush and commutator acts as a nexus between the external power source and armature. An electric current is applied to the stator magnets, and rotor coils turn due to the resulting magnetic field. DC brushed motors are good for high torque applications, but they have poor power density and limited top speed due to high friction between brushes and commutators.
2. DC Brushless Motor
A brushless DC motor was an advancement on the brushed motors. Instead of brushes, they use an electronic controller to switch DC current to the motor windings. They resolve the problem of worn-out brushes while improving the efficiency of the powertrain. Due to these benefits, almost all modern-day hybrid cars use brushless DC motors.
Brushless DC motors are a popular choice among many automakers because they require the least maintenance. There are two main types of brushless DC motors. The out-runner type has an internal stator whereas an external rotor. They can be mounted directly onto the wheel. The in-runner are like conventional motors with internal rotor and external stator.
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3. Asynchronous Induction Motor
In asynchronous induction motors, the speed of the rotor is less than the speed of the induced revolving field. The work begins when a 3-phase AC supply is connected to the stator winding. It creates a magnetic field that interacts with the static rotor conductors. This induces a current in these rotors. The induced current and revolving field interact to produce unidirectional torque.
There are issues like low initial torque and complex circuits with the Asynchronous induction motors. But it has high efficiency and excellent speed regulation. In addition, AC induction motors have a longer lifespan as compared to other motors. These are the reasons why General Motor EV-1 and 1st generation Tesla Roadster used asynchronous induction motors.
4. Current Excited AC Synchronous Motor
The most recent example of the current excited AC synchronous motor in an EV is the new BMW i4 and iX. BMW surprised everyone by opting for a brushed current excited synchronous AC motor. However, this has allowed these cars to reduce dependency on permanent magnets. Plus, you can vary the strength of the magnetic field of the rotor to optimize peak power output.
The working principle of a current-excited AC synchronous motor is that it uses energized copper lobes instead of permanent magnets to create an electromagnetic force. The copper lobes are powered using DC battery power. This is an efficient motor design, but there are concerns about the wearing of spring-loaded brushes on the rotor’s shaft. Their longevity yet remains to be seen.
5. Switched Reluctance Motor
Switched reluctance motors are not new to the world of electronics. However, their use for automotive applications dates back only a few years. Switched reluctance motors provide many benefits over other types of electric motors. They have a high starting torque, better reliability, wide speed range, inherent fault-tolerance capability, and high motor-drive efficiency, and on top of that, the overall cost of the system is also reduced.
The working of a switched reluctance motor is rather complicated. An SRM has coils around the stator windings, whereas the rotor has no attached magnets. When electrical power is applied to the stator winding, the rotor’s magnetic reluctance creates a pull. This pull tends to align the rotor pole against the nearest stator pole. Think of it as a big Ferris wheel. The weight of people sitting in each cabin pulls them down only if they are being pulled by force around the wheel.
6. Permanent Magnet AC Motor
The working of a permanent magnet motor is quite similar to the brushless DC motor. It has permanent magnets on the rotor. Unlike the switched reluctance and current-excited motors, no power is needed to create the rotor’s magnetic field. This is why a permanent magnet motor is quite efficient at low speeds. They offer higher efficiency and, in turn, a longer range and better performance than all other types of electric motors.
These are the reasons why a permanent magnet motor is probably the most commonly used type of motor in electric vehicles today. Despite higher initial costs, a permanent magnet motor is used in the drivetrain of popular EVs such as Ford Focus, Nissan Leaf, BMW i3, Chevy Bolt, Ford Mustang Mach-E, vehicles made on the Ultium platform, and almost all models of Tesla.
Final Word, Types of Motors Used in EV
These are the major types of motors used in EVs today. Brushed DC motors might be the least favorite of all, whereas induction and permanent magnet motors are in high demand. They offer better efficiency and hence higher output power leading to better performance and a long range. If you want to learn more about the internal components of EV, please follow our blog. You will find interesting articles there!
