Magnetic gear

A magnetic gear , like a conventional mechanical gear , changes the speed of rotation of a rotating shaft .

construction

Schematic sectional view of a magnetic gear

In a mechanical transmission, there are often gears of various sizes that change the rotational speed of the shafts by means of positive locking. In the magnetic gear there are permanent magnets on two different rotors, each mechanically coupled to a shaft. The two rotors have no mechanical contact so that the gearbox produces only low friction losses. The wear is limited to the bearing roller bearings , the noise development is minimal. Since the two shafts do not touch each other as in the case of a gear drive, they do not need to be lubricated , and shaft seals , which lose their tightness after a certain time, can be dispensed with. Magnetic gears are therefore ideal for driving hermetically sealed systems.

advantages

A great advantage of the magnetic gear is that it is not damaged in the event of an overload, but slips until the load decreases and it can re-engage by reducing the drive speed. High speeds can be achieved (approx. 50,000 / min), no lubrication is necessary and there are no jerky accelerations.

disadvantage

Iron losses increase sharply with increasing rotation speed . The iron losses contain the hysteresis losses and the eddy currents induced by the magnets . With low torque and high speed, the efficiency is low.

Types

Torque magnetic gear

There are different types of magnetic gears. Most are designed so that the magnets are on top of the rotating shafts. In this case, the transmission ratio is determined by the magnet pairs of the rapidly rotating shaft divided by the magnet pairs of the slowly rotating shaft.

The ferromagnetic stator is located between the two magnet rotors. The number of iron pieces must either correspond to the difference between the magnet pairs on the slowly turning rotor and the magnet pairs on the fast turning rotor or the sum of the magnet pairs on the two rotors. The latter variant causes both rotors to turn in opposite directions. The two variants mentioned can have the following transmission characteristics:

Slow rotor magnet pairs	Fast rotor magnet pairs	Pieces of iron	Gear ratio	direction
22nd	4th	18th	5.5: 1	equal
22nd	4th	26th	−5.5: 1	opposite

The following formula results in the transmission ratio : ${\displaystyle r}$

${\displaystyle r=\operatorname {sgn}(N_{2}-N_{\text{stahl}})\cdot {\frac {\Omega _{1}}{\Omega _{2}}}=\operatorname {sgn}(N_{2}-N_{\text{stahl}})\cdot {\frac {N_{2}}{N_{1}}}}$

With:

• the sign function sgn
• Ω ₁ as the angular velocity of the fast rotor
• Ω ₂ as the angular velocity of the slow rotor
• N ₁ as the number of magnet pairs of the fast rotor
• N ₂ as the number of magnet pairs of the slow rotor
• N _steel as the number of iron pieces of the stator

Some gearboxes, such as those made by Magnomatics, have the external magnetic circuit as a stator. The inner rotor is thus the fast spinning rotor and the iron bars between the magnets are mechanically coupled to the slower shaft. The formula for determining the gear ratio has to be adapted to this, but the relative speeds of the various parts remain the same.

literature

• Klaus-Jörg Conrad: Basics of construction theory: methods and examples for mechanical engineering and gerontics . 6th edition. Carl Hanser Verlag, 2013, ISBN 978-3-446-43533-9 .

Web links

• Magnetic gear: wear-free solution for high speeds - magnets as dental prostheses. Industrieanzeiger, accessed June 3, 2017 . 

Individual evidence

1. ↑ Peter Trechow: High-speed gear motor prevents wear without lubrication. VDI Nachrichten, November 14, 2014, accessed April 26, 2016 .