Passive magnetic bearings and thrust bearings

A PMP passive magnetic bearing operates only through the permanent forces of interaction between its fixed and rotating parts. These forces can be created :

• or by the attraction between opposing soft-iron parts, polarized by magnetic flux;

• or by direct attraction or repulsion between permanent magnets.

The first principle is used in variable-reluctance passive magnetic bearings; the second in permanent-magnet bearings.

Whatever the system, the function of these passive bearings is either to center an axis (exactly like a ball bearing), or to control translation along the axis. In the first case, the bearing is called a magnetic centering bearing, and in the other, a magnetic thrust bearing. Both are magnetic bearings. We'll use the term "magnetic bearing" for everything that applies to both, and "magnetic thrust bearing" or "magnetic centering bearing" for everything that applies to both.

Passive bearings are sometimes used to control linear displacements. As there are very few applications for these passive linear bearings, we will only look at rotary bearings: centering and thrust bearings.

The calculation of these bearings is the subject of various analytical or numerical methods of calculating forces and stiffnesses.

These magnetic bearings are only magnetic suspension components. To create a complete magnetic suspension, they must be correctly combined with active magnetic bearings.

A partial magnetic suspension of passive bearings can also be combined with a mechanical centering or stop system.