Magnetic gear

The magnetic gear resembles in part, the traditional mechanical gear. All cogs of each gear component of magnetic gears act as a magnet with periodic alternation of opposite magnetic poles on mating surfaces. Gear components are mounted with a "cushioned" backlash capability similar to other mechanical gearings with no cushioning effect. Although they can exert as much force as a traditional gear, such gears work without touching and so are immune to wear of mating surfaces, have very low noise and can slip without damage making them very reliable. They can be used in configurations that are not possible for gears that must be physically touching and can operate with a barrier completely separating the driving force from the load. The magnetically coupled gear can transmit force into a hermetically sealed enclosure without using a radial shaft seal, which may leak. Hermetically sealed processes are not contaminated or chemically affected by the magnetic gear. This can be an advantage in explosive or otherwise hazardous environments where leaks constitute a real danger.

Advantages of Magnetic gears over mechanical gears include:

  1. Leak proof mechanical coupling
  2. Shear / Overload proof mechanical coupling
  3. Wear is limited to bearings not mating contact surfaces of gears
  4. Interchangeable ratios either electronically or mechanically in minutes not hours.

The magnetic gear is a magnetic coupling device that renders a mechanical ratio between two magnetically coupled devices such that:

  1. They have a ratio of rotation or translational movement between input and output which may be unity in the case of a pure magnetic coupling or one of many gear ratios in a magnetic gearbox.
  2. They have a torque or traction limiting factor based on the magnetic coupling force.
  3. They have no physical contact between the main driving and driven elements.

A magnetic gear is composed of magnets of the type permanent, electromagnetic or otherwise magnetically induced fields. It consists of two or more elements that are usually rotating but can be linear or curve linear in nature.

The classical gear is defined as a ratio of pole pairs. Where the Pole pairs are magnets N-S and S-N in nature. For the ratio to be affected there must be at least two elements. with Magnetic pole pair pieces.

Such devices were invented Armstrong, C. G., 1901, “Power Transmitting Device”, U.S. Pat. No. 0,687,292[1] and developed further from the 1940s[2][3]

Modes of gearing

There are 4 basic modes of magnetic gearing.

First-order device

A defined ratio of magnets on one driving element and one driven element. This mode One device such as Patented by Andrew French of MGT Australia near Port Stephens NSW and Hungarian Arpad Kasler with his Magnemot can be implemented at angles, and through walls. MGT devices are claimed to be 99.9 % efficient which translated to near zero maintenance and roughly a 22% reduction in power losses.

Second-order device

Generally a rotational device. A ratio of magnetic pole pairs, where the least number rotates at a higher rate than the higher number pole pair. An intermediate ferromagnetic pole "stator" is usually held stationary and used to effect the concentration of the magnetic lines of force between the high speed rotor and the low speed rotor. The ratio of High speed to Low Speed is the number of magnetic pole pairs on the high speed rotor to the number of magnetic pole pairs on the low speed rotor. This implies an even number of magnets on both rotors. The Ferromagnetic stator has two alternative solutions. The first being the sum of the number of pole pairs of the two rotors, giving the opposite direction of rotation, and the second having pole pieces numbering the difference between the pole pairs of the rotors, which results in the direction of rotation being the same.

Low Speed Magnets Low Speed Pairs High Speed Magnets High Speed Pairs Iron Stator Pieces Gear Ratio Direction
20 10 14 7 17 10:7 Opposite to input
20 10 14 7 3 10:7 Same as input

Third-order device

Generally a rotational device, where a mode 2 device is modified to have external field coil(s), thus effecting a variable transmission or variable ratio magnetic gear. This type of gear consumes approximately 25% of its input power in the process. This renders the variable magnetic gearbox to less than 75% efficiency. However the lower maintenance and the torque limiting characteristics may find suitability in some applications.

Fourth-order device

The mode 4 (Four) device is a modification to the Mode 3 device having a Low torque variable speed Mechanical input, a High Torque Mechanical Input, and a High Torque Mechanical output. As with the Mode 3 Device it consumes approximately 25% of the energy to supply the variable input, however if the variable input is held stationary the device functions as a Mode 2 Device. Such a device can be termed a torque multiplier.

References

  1. ↑ http://www.google.com/patents/US687292
  2. ↑ http://www.google.com/patents/US3382386
  3. ↑ http://www.google.com/patents/US7438035

External References

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