Electrical machine

#The present invention relates to an electrical machine having a stationary main element as stator and a rotating main element as rotor, of which one is produced from SMC material.

#Magnetic conductive members of stators or rotors of electrical machines will, in the near future, be increasingly made of SMC material (soft magnetic powder iron composite), and will replace laminated core assemblies or laminated cores, since, from a manufacturing technology point of view, they are much more simple to produce. The SMC material is pressed into the desired shape using a pressing mold, and is then heat treated at a relatively low temperature, so that the necessary insulating layers between the powder particles are not destroyed.

#In one known multipolar stator made of SMC material for an internal-rotor machine (PCT International Publication No. 99/50949) the outer-lying magnetic yoke is composed of a number of yoke segments corresponding to the number of poles of the stator poles. Each yoke segment carries in one piece a stator pole having a pole core and a pole shoe bordering the pole core at the latter's remote end. Each yoke segment along with pole core and pole shoe is produced from SMC material by pressing and heat treating. The pole cores are rounded off at their axial ends or have an oval profile, so that, as a result of the removal of sharp edges at the pole cores, only a thin insulating layer has to be applied, onto which the pole winding may then be wound. The individual pole windings of the stator winding are wound directly onto the pole cores, using the usual machine-based winding technology. After winding the pole windings, the individual yoke segments are set next to one another in the circumferential direction and are fixedly connected to one another.

#FIG. 1 shows a perspective view of an external-rotor motor.

#FIG. 2 shows an exploded view of the external-rotor motor in FIG. 1.

#FIG. 3 shows an exploded view of an external-rotor motor according to a further exemplary embodiment.

#FIGS. 1 and 2 show a brushless, eight pole external-rotor DC motor having a stator 11 and a rotor 12 that concentrically surrounds stator 11 in a perspective or an exploded representation. Stator 11 and rotor 12 represent the so-called main elements of the motor. Rotor 12 has the usual construction and has a solid or laminated outer ring 13, that bears eight permanent magnet segments 14 on its inner surface facing stator 11, which are situated offset by equal circumferential angles, and are polarized alternately in opposite direction. Stator 11 has a ring-shaped magnetic yoke 15 and twelve teeth or poles 16 in total, which project radially outwards from magnetic yoke 15, and are situated offset by equal circumferential angles with respect to one another at magnetic yoke 15, and in one piece with it.

#Each pole 16 has a pole core 161 and a pole shoe 162, which is situated in one piece with pole core 161 at the end of pole core 161 facing away from the yoke. Pole shoes 162 have an axial length corresponding to the axial width of permanent magnet segments 14, and protrude on all sides beyond pole cores 161, which, on the one hand, has the effect of a flux concentration in pole cores 161, and, on the other hand, is used for supporting a pole winding wound on pole core 161. All poles 16 are covered by a pole winding not shown in FIGS. 1 and 2, which is designed as a concentrated ring coil.

#As may be seen in the exploded representation of the motor in FIG. 2, stator 11 is composed of two axially adjoining modules 17, 18 that are rigidly connected to each other. Each module 17, 18 has a ring-shaped yoke part 151, 152, closed on itself, of magnetic yoke 15, having in each case six of the in total twelve poles 16. Corresponding to the division of poles 16 into the two yoke parts 151, 152, at each yoke part 151 or 152, poles 16, in turn, are offset by equal circumferential angles to one another, the angle of staggering being twice as great as the angle of staggering between poles 16 in stator 11 in FIG. 1. Pole shoes 162 of poles 16 are aligned asymmetrically to pole cores 161, and axially protrude beyond the one end face of yoke part 151 or 152. Modules 17, 18 are made of SMC material (soft magnetic powder iron composite), SMC iron powder being pressed in a press form into the shape of modules 17, 18 that are to be seen in FIG. 2, and is subsequently exposed for 30 min to a temperature of ca. 500° C. Since the two modules 17, 18 have identical shapes, they may be produced using the same mold, so that there results a large quantity of modules 17, 18 that is favorable for manufacturing. Now, a pole winding is wound on all poles 16, because of doubly enlarged distance between adjacent poles 16, the usual winding techniques on the usual winding machines may be used without a problem