Space-Saving Motor with High Torque Density for Industrial and Transportation Drive Systems

Toshiba has developed a space-saving motor with high torque density (torque per volume) for industrial and transportation drive applications. Generally, torque density can be improved by increasing the number of magnetic poles and magnets, and the motor current. However, the industry has almost reached the limit of its ability to increase torque by increasing the number of magnets and the motor current, due to magnetic saturation of the iron cores and heat generation in the coils. In conventional motors, it is also difficult to increase the number of magnetic poles, considering the complexities of their coil design.

To solve this problem, we have designed a new motor having a simple coil structure to allow a further increase in the number of magnetic poles. The new motor also has low magnetic resistance (which translates into higher magnetic field intensity with the same current). The stator consists of ring coils and U-shaped iron cores surrounding them, making it possible to increase the number of poles simply by increasing the number of U-shaped cores. The rotor has magnets and I-shaped cores on the ring cores. Consequently, N and S poles are formed alternately on the rotor surface, since magnetic flux passes through the ring and I-shaped cores. The motor has three different phases that are axially aligned. Therefore, regardless of the rotational position, the motor can be driven by supplying a three-phase alternating current to the three stator coils. Furthermore, since the rotor and stator cores with low magnetic resistance face each other with only a narrow gap, an intense magnetic field is produced by the motor current.

Structure of high-torque-density motor

The results of a magnetic analysis showed that the new motor has larger torque than a conventional motor under the same volume and electrical input conditions. Our new motor design will make it possible to construct high-torque-density motors of various sizes and realize compact gearless drive systems having a low maintenance cost.