Kazuto Sakai

Principle of the variable-magnetic-force memory motor

Electrical appliances and electric vehicles (EV) require reduction of electrical consumption. Then, we have developed a novel permanent magnet motor for energy saving. In this paper, we propose the novel motor that can change magnetic flux by a new method magnetizing a permanent magnet and clarify the principle and unique characteristics. Furthermore, the results of analysis and experiments prove that the novel motor can change the flux of permanent magnet on load and has realization for a variable speed drive with high performance.

High efficiency and high performance motor for energy saving in systems

Recently, increasing importance has been placed on energy saving in various systems. This has created a need for a motor with high efficiency that is capable of operation over a wide range of speeds. The authors have developed a novel permanent magnet reluctance motor (PRM) that has permanent magnets embedded in the isotropic rotor to increase the power density and the power factor. The PRM produces reluctance torque and torque by permanent magnet (PM) flux. The reluctance torque is 1 to 1.5 times larger than the PM torque. It is clarified that the PRM operates at a wide variable-speed range (1:5) and at high efficiency (92-97%). With an output power of 8 to 250 kW, the motor is suitable for application to electric vehicles, railway systems and elevator systems.

Structure and characteristics of new high speed machines with two or three rotor discs

The authors describe the basic structure, analysis, and characteristics of newly developed super-high-speed machines which rotate at 20000 RPM. These machines are of axial-type field with high-energy permanent magnets (NdFeB). The stator has two or three discs sandwiched by the mold coils. Many cylindrical magnets are embedded in the duralumin discs (nonmagnetic material) of the rotor. This construction makes it possible to make a considerably light rotor which can withstand large centrifugal force at high speed. Little armature reaction, little cogging torque, and large power are thus realized.<<ETX>>

Development and characteristics of servomotor for use under high temperature and radiation flux conditions

Recently, robots have been required to inspect the insides of nuclear reactors under high temperature and radiation flux conditions. In a FBR (fast breeder reactor), the viewing system of the robot is particularly important because the reactor vessel of the FBR is filled with opaque liquid sodium. To drive this robot, servomotors must meet special requirements. At temperatures above 220°C, the integrity of organic materials cannot be maintained for long periods. In addition, the air-gap length of the motor varies, because metals expand at high temperatures. Thus, the characteristics of induction motors with an air-gap length of 0.2–0.4 mm may vary. Furthermore, the rotor may come into contact with the stator. In this paper, a newly developed permanent magnet motor which can withstand high temperatures and radiation is presented, and the characteristics of the rotor at high temperatures are discussed. Coils for winding ceramic magnetic wires are installed in the stator and Sm2Co17 permanent magnets are embedded in the rotor yoke. This motor is suitable for use at up to 400°C due to the use of inorganic materials in it. In addition, the permanent magnet motor can incorporate a long air-gap length, which has little effect on the characteristics of the motor. The test results show that the motor has excellent characteristics at high temperature.