Contactless high-torque magnetic gears with ratios of less than 50:1 with inherent overload capability

A low ratio magnetic gear uses a series of steel pole-pieces to modulate the fields produced by two permanent magnet rotors with different numbers of magnetic poles. The magnet arrays rotate at different speeds with the gear ratio determined by the ratio of magnets in each array. The transfer of motion between input and output shafts is passively achieved using just high power permanent magnets.

A high degree of magnetic coupling between the rotors allows for torque densities comparable with mechanical gears to be realised. Gear ratios of 50:1 down to 1.01:1 with almost zero torque ripple are readily achievable. The low ratio magnetic gear forms an integral component within Magnomatics’ new type of permanent magnet machine, the ultra high torque density pseudo direct drive, PDD®.

Low ratio magnetic gears can be realised in a conventional radial field or in an axial arrangement when a thin “pancake” design is required. Unlike conventional mechanical gears the magnetic gear can be arranged to provide geared linear movement.