Magnetic bearing and an assembly comprising a stator portion and a rotor portion suspended via such a bearing

A magnetic bearing enabling a solid body having a center of gravity O to rotate about a fixed axis z, the bearing having a circularly-symmetrical fixed portion, and a circularly-symmetrical moving portion, and including a passive magnetic abutment composed of a fixed element secured to said fixed portion, and of a moving element secured to said moving portion, said magnetic bearing further including a passive magnetic centering bearing which is coaxial with said passive abutment, and which is composed of a fixed element secured to said fixed portion, and of a moving element secured to said moving portion, said passive abutment externally surrounding said passive centering bearing, said passive abutment having axial stiffness k.sub.ab, radial stiffness k.sub.rb, a mean radius R.sub.mb, and ran inside radius R.sub.ib, and said passive centering bearing having axial stiffness k.sub.ac, radial stiffness k.sub.rc, a mean radius R.sub.mc, and an outside radius R.sub.ec, an air gap e separating the fixed element of said abutment from the moving element thereof and separating the fixed element of said centering bearing from the moving element thereof, these parameters being chosen so as to satisfy the following three relationships simultaneously:

• 1) .vertline.k.sub.rc .vertline.>.vertline.k.sub.rb .vertline.
• 2) R.sub.mb >R.sub.mc ##EQU4## 3) R.sub.ib -R.sub.ec .gtoreq.3e;
• thereby providing stability about 4 degrees of freedom, namely;
• translation along axes Ox and Oy orthogonal to fixed axis Oz, and rotations .theta..sub.x and .theta..sub.y, about axes Ox and Oy, respectively.