Permanent magnet for electromagnetic device and method of making

#The invention relates generally to permanent magnet materials, methods of making permanent magnet materials, and electromagnetic devices including permanent magnet materials.

#Many types of electromechanical energy converters such as motors, generators, and actuators use permanent magnets to create an open circuit flux density which interacts with a field created by an electric circuit to provide torque. To a large extent, the size and efficiency of a converter of a given power rating is determined by the “energy density” of the magnet in the device. The higher the open circuit air gap flux density produced by the magnet, the more torque that can be produced per unit weight and the higher the motor efficiency for a given power input. Open circuit flux is determined by the strength of the magnet and the effective length of the air gap. The stronger the magnet and the smaller the effective air gap, the more efficient and smaller the machine.

#As a practical matter, cost savings can be achieved by making the magnets as thin as feasible while providing a sufficient thickness to prevent demagnetization from armature reaction flux density. As compared with thicker magnets, thinner magnets require less space. However, the permanent magnets are typically designed to be thick so as to avoid experiencing an operating point that might result in demagnetization. For example, magnet thicknesses for 373 Watt (one-half horse power) motors typically range from about 2.54 millimeters (about 0.1 inches) to about 7.62 millimeters (about 0.3 inches).

#These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

#FIG. 1 is a sectional schematic view of an electromechanical energy converter comprising a permanent magnet according to one embodiment of the present invention.

#FIG. 2 is another sectional schematic view of an electromechanical energy converter comprising a permanent magnet according to another embodiment of the present invention.

#Commonly assigned Benz et al., U.S. Pat. No. 6,120,620, describes a permanent magnet having substantially stable magnetic properties and having as the active magnetic component a sintered product of compacted iron-boron-rare earth intermetallic powders. The sintered product has pores which are substantially non-interconnecting, a density of at least 87 percent of theoretical and a composition consisting essentially of, in atomic percent, about 13 to about 19 percent rare earth elements, about 4 to about 20 percent boron, and about 61 to about 83 percent of iron with or without impurities; where the rare earth content is greater than 50 percent praseodymium with an effective amount of a light rare earth selected from the group consisting of cerium, lanthanum, yttrium and mixtures thereof, and balance neodymium.

#It has been discovered that magnetic properties of particulate obtained from the permanent magnet material of aforementioned U.S. Pat. No. 6,120,620 have a significantly higher than expected intrinsic coercive force (Hci) as compared with the permanent magnet material of aforementioned U.S. Pat. No. 6,120,620 and as compared with other commercially available magnetic particulate. Thus permanent magnets in applications such as rotational electromechanical energy converters (motors and generators, for example) and translational electromechanical energy converters (actuators, for example) can be made thinner than in conventional embodiments with a resulting decrease in magnet and air gap length which decreases the cost and size of a motor.

#Furthermore, as compared with sintered permanent magnets, permanent magnets bound with a binder (molded magnets) have several other advantages including, for example, simpler and less expensive fabrication techniques, ease of integration with other molding operations, and, depending upon the binder, intrinsic protection of the magnetic material from corrosive conditions. Sintered magnets are brittle and therefore are difficult to fabricate into complex shapes and cannot be made with thicknesses much less than about 4.57 millimeters (about 0.18 inches).