The engine and gearbox are normally two separate functional units. A new type of motor concept has now been developed at TU Wien that combines the two into a single unit. Instead of a single rotor, four rotors are used, which are mechanically coupled together. The result is a "planetary motor" that is characterized by high power density, energy efficiency, simplicity and reliability. According to TU Wien, the motor, which is unique in the world, will be presented for the first time at this year's Hannover Messe.

"First of all, we considered how to combine several electric motors into one unit," explains Prof. Manfred Schrödl from TU Wien. Each electric motor has a rotor on the inside and electromagnets on the outside. If several motors are arranged next to each other in a geometrically clever way, some sections of the stationary motor parts, the so-called stators, are no longer magnetically necessary. This simplifies the overall structure, which saves space and reduces losses.

"For example, we use four electrical machines with three-strand windings, so we have a total of twelve magnetic coils," explains Schrödl. "However, our arrangement of the machines means that we only need six coils." Two rotors jointly drive a large, internally toothed ring gear; the other two rotors, which rotate in the other direction, drive a slightly smaller, externally toothed wheel. "This creates an image that resembles a single-stage planetary gear," says Schrödl. "That's how the electric planetary motor got its name. The gearbox, which we integrate directly into the motor and its output, is extremely simple, which increases efficiency and reduces manufacturing costs."

The fact that several rotors are involved does not mean that controlling the motor is any more complicated: The planetary motor is controlled and supplied with power from the outside in exactly the same way as a conventional synchronous motor. Another advantage has been built into the planetary motor: It manages without error-prone sensors. Many years ago, Schrödl developed a sensorless motor in which the current position of the rotor no longer has to be measured with special sensors, but is read out via the current-carrying cables. "This sensorless technology has now proven itself in practice thousands of times over," comments the professor.

A planetary motor prototype was produced and extensively measured at TU Wien. "The properties of the new type of machine are exceptionally good," says Manfred Schrödl. "Not only is it extremely compact, but you can also achieve twice the power with the same circumferential speed of the rotors compared to conventional machines."

There are many areas of application for the planetary motor: It could show off its advantages in electric vehicles, and could be used in machine tools as well as lifting and production technology. The planetary motor is particularly suitable for safety-critical and high-performance applications.

Hannover Messe: Hall 6, Stand D18