The motor is the source of power for an electric vehicle. It determines top speed, acceleration, hill climbing ability, power consumption and vehicle performance. In this article, Gurusharan Dhillon (Director of eMobility at Customised Energy Solutions) explains the characteristics and the major components of different kinds of motors used in electric vehicles.
Three Important points to consider when finalising the choice of Electric Motor are:
- Vehicle characteristics
Vehicle weight, overload, and aerodynamics help determine the speed, torque and power requirements of the electric motor.
- Driving cycle
Driving cycle consideration of various factors like traffic density, terrain, temperature, etc, influence the size of the battery pack and choice of powertrain.
- Maximum speed
To factor in motor speed, the maximum speed of the vehicle needs to be considered. How long speed need to be sustained, differential ratio, and wheel radius also influence motor selection.
Specific consideration factors for selecting the most suitable Electric Motor are:
|Power to Weight Ratio|
Higher Power to Weight ratio provides higher speed and acceleration
|Power Density||Higher Power density helps minimize space utilisation (compactness) for highest possible power output|
|Efficiency||Higher motor efficiency means less energy losses and more usable mechanical energy|
|Peak Power Output||The maximum power that the Motor can sustain for short duration|
Electric vehicle performance directly depends on the performance of the Electric Motor. The performance of the motor is determined by Torque-Speed and Power-Speed characteristics of the traction motor.
Selecting the proper output characteristic of an EV motor is a challenge because it is necessary to find the balance between acceleration performance and wide speed range in the constant power region. The constant torque operating region is important at low speeds to provide a good start and up-hill drive. The constant power region determines the maximum speed on a flat surface.
Major components of electric motor
The rotor is the moving part which turns the shaft that delivers mechanical power. The rotor is supported by bearings which support it to turn on its axis, the windings form magnetic poles when energized with current. The stator is the stationary part.
Types of motors in EVs
Mounting position of the motor
Reduction of rare earth materials
In electric motors, magnets are used to generate rotation using electrical current passing through loops of wire. These magnets are typically made with rare-earth materials such as neodymium and dysprosium, which have a very geographically constrained supply chain. China accounts for the vast majority of rare-earth production worldwide, leading to huge price volatility.
Apart from cost and availability problems, these materials also evoke important environmental, political and ethical issues regarding their extraction, trade and disposal.
Motor designs that avoid the use of rare earth elements are being developed, requiring higher levels of optimisation of the motor with the controller.
Recent developments include spoke rotor PMSM that uses ferrite magnets with a similar or better power density than an equivalent induction motor. Other innovations include utilizing wound rotor configuration to replace magnets with copper windings, aluminium rotor induction motors and switched reluctance motors which require no magnets or copper in the rotors.
Synchronous Reluctance Motors (SynRM)
The main characteristics of synchronous reluctance motors are high efficiency at synchronous speed without using rare earth permanent magnets. There is no concern about demagnetisation, so these are inherently more reliable than permanent magnet motors.
The main advantage of synchronous reluctance motors is negligible rotor losses. Reduced heat in synchronous reluctance motors improves torque and power densities allowing them to be sized smaller for a given rating. These motors are also quiet due to low torque ripple and vibration levels.
Efficiency is a critical factor in electric motors, and future developments are likely to focus on increasing efficiency further. This could involve the use of new materials, improved design, and more advanced control algorithms.
Integration with IoT
Higher integration with IoT systems, allowing for remote monitoring, control, and optimization.
There is a movement toward non-traditional designs because of increased demands for:
- Higher torque density
- More efficient cooling (motor)
- Reduced size of the motor
- Optimized or reduced use of copper wire and magnet material.
References and further reads:
About the author
Gurusharan Dhillon is an automotive professional with 30+ years of expertise in Strategy, Operations, Sales, and Marketing. He currently serves as the Director of eMobility at Customised Energy Solutions. With a focus on the electric mobility sector, Dhillon specializes in Powertrain, Battery Technology, Charging Infrastructure, and emerging technologies. He has worked with leading automotive OEMs like Toyota, Nissan, Honda, and Hyundai.
Customized Energy Solutions closely works with several leading Motor manufacturers and OEMs to support in design and recommendation of best-suited motors delivering optimum performance for your Powertrain applications.
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