U.S. Department of Energy - Energy Efficiency and Renewable Energy
Vehicle Technologies Office
To reach the EV Everywhere Grand Challenge goal, the Vehicle Technologies Office (VTO) is supporting research to improve electric motors, with a particular focus on reducing the use of rare earth materials inside the rotor magnet. To learn how electric motors are used in plug-in electric vehicles, visit the Alternative Fuels Data Center page on the basics of hybrid and plug-in electric vehicles.
In an electric drive system, an electric motor converts the stored electrical energy in a battery to mechanical energy. Electric motors consist of a rotor (the moving part of the motor) and a stator (the stationary part of the motor). A permanent magnet motor includes a rotor containing a series of magnets and a current-carrying stator (typically taking the form of an iron ring), separated by an air gap. There are three types of electric motors that can be used in electric vehicle traction drive systems.
- Internal permanent magnet (IPM) motors have high power density and maintain high efficiency over a high percentage of their operating range. Therefore, almost all hybrid and plug-in electric vehicles use rare earth permanent magnets in their traction motors. These motors are relatively expensive due to the cost of the magnets and rotor fabrication. Other challenges to developing IPM motors include the limited availability and high cost of rare earth magnetic materials, thermal management, and packaging. Despite the challenges, the industry anticipates continuing to use IPM motors in the majority of electric drive vehicles over the next decade.
- Induction motors have high starting torque and offer high reliability. Their power density and overall efficiency are lower than that of IPM motors. They are widely available and are common in various industries today. Because this motor technology is mature, it is unlikely research could achieve additional improvements in efficiency, cost, weight, and volume for competitive future electric vehicles. Tesla Motors, a U.S. electric vehicle manufacturer, uses induction motor technology.
- Switched reluctance motors offer a lower cost option that can be easy to manufacture. They also have a rugged structure that can tolerate high temperatures and speeds. However, they produce more noise and vibration than comparable motor designs which is a major challenge. Also, switched reluctance motors are less efficient than other motor types, and require additional sensors and complex motor controllers that increase the overall cost of the electric drive system.
VTO Electric Motor R&D
VTO's primary goal is to decrease the electric motor's cost, volume, and weight while maintaining or increasing performance, efficiency, and reliability. To meet 2022 cost targets, research must reduce the cost of the motor by 50%.
To achieve these goals, VTO and its partners are examining many research avenues: