subject: Switched Reluctance Motor is improved to successfully eliminate the need of the rare earth-contained motors [print this page] The rare earth issue has been closed up recently in Japan.
Over 90% of the rare earths currently used in Japan is imported from China. Recently, the collision accident between the Chinese fishing boat and the Japanese patrol boat occurred.As the result of the collision accident, the Chinese government took an action to try to stop the export of the rare earths to Japan. Fortunately, the export prohibition was not exercised. It is generally said that the export prohibition of the rare earths to Japan, if exercised, will not decisively damage the Japanese industries when viewed in a medium- and long-range perspective.
As is known, the rare earths are contained in the permanent magnet of the motor. The motors are used for driving the vehicles such as electric vehicles, hybrid vehicles and fuel cell vehicles.It is clear that those vehicles will rapidly increase in terms of number in near future.
Interior permanent magnet synchronous motors (IPMSM) are mainly and currently used for the driving sources of those vehicles. The IPMSM is a synchronous motor in which permanent magnets are placed in the rotor. The motor has many advantages of high torque, large adjustable range of motor speed, high energy-conservation and high efficiency. Its disadvantage is that the permanent magnet used contains rare earths.
A synchronous motor called a switched reluctance motor (SRM) has bee known. The SRM does not use the permanent magnet, that is, the rare earth. The SRM rotates the rotor by utilizing reluctance differences between the rotor and the stator of the motor cause to rotate the rotor. The SRM has advantages of simple structure, excellent heat resistance and high rigidity. The SRM is inferior to the IPMSM in that the torque and energy utilization efficiency are poor. Where the SRM is designed to produce the performance comparable with that of the IPMSM, its size is too large to mount it on the vehicle.
Recently, the SRM was improved to have the performances comparable with those of the incumbent IPMSM. Some characteristics of the improved SRM exceeded those of the IPMSM. The improved SRM (prototype) has the specifications: max. torque = 400 Nm, torque density = 45Nm/l, efficiency = 83%, and size being vehicle-mountable.
Researchers focused their creative efforts on the motor structure and selection of the materials to be used, and found the best combinations of them.
