Magnetic thrust bearing with permanent bias flux

DETAILED DESCRIPTION OF THE INVENTION Turning to the drawings wherein like characters designate identical or corresponding parts, FIG.
6 shows a preferred configuration of the magnetic thrust bearing 10.
A thrust disk 111 is attached to the shaft 112 and is acted upon by a lower yoke ring 113 and an upper yoke ring 114.
A single coil 115 provides the control flux 122.
An upper permanent magnet ring 116 provides the upper bias flux 118 and the lower permanent ring 117 provides the lower bias flux 119.
The magnets 116 and 117 as well as the yokes 113 and 114 could be made as only a segment and not a complete ring.
However, this would cause eddy currents in the thrust disk 111 during rotation so it is not desirable for rotating shaft applications.
The control flux 122 and bias fluxes 118 and 119 have substantially non-coincident paths but do share the same paths through the pole rings 120 and 121 and in the airgaps to the thrust disk 111.
By superposition, as shown in FIG.
6, the control and upper bias flux 122, 118 subtract and the control and lower bias flux 122, 119 add.
The result is a net force downward on the thrust disk 111.
Reversing the current in the control coil 115, results in a net force upward.
Because of the bias fluxes 118 and 119, the force generated is linear with the current in control coil 115.
The force is also greatly amplified.
The invention uses small airgaps in the bias flux paths and in the control flux path.
The low permeability permanent magnets are also not included in the electromagnetic flux path 122.
Therefore, the bearing achieves maximum efficiency of force to applied control current.
The bearing 110 works according to the following non-dimensionalized example.
If the bias flux is 12 and a control flux of 8 is applied, the flux in the upper steel pole and airgap would be 20 and the flux in the lower steel pole and airgap would be 4.
The force is proportion to the square of the flux density.
Therefore the upward force exerted on the thrust disk would be (20 2-4 2) or 384