Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-05-15
2001-02-27
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S168000
Reexamination Certificate
active
06194805
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a reluctance motor electric machine.
The references DE 42 12 547 C2, U.S. Pat. No. 5,266,859, and WO 92/10022 have disclosed electric machines of this kind, which can be operated as reluctance motors. Each electric machine having a respective stator with an essentially annular yoke body, stator pole teeth extending radially inward from this yoke body, and excitation coils associated with the stator pole teeth. Each electric machine having a rotor which is supported so that the rotor can rotate around a rotor axis and has rotor pole teeth that are directed radially outward, which temporarily form pairs with respective stator pole teeth that coincide with them, enclosing an air gap between these respective teeth. There is a minimal reluctance in a pair that is aligned in this manner.
In the reluctance motor according to DE 42 12 547 C2, the rotor has four rotor pole teeth aligned crosswise and the stator has six stator pole teeth aligned at regular angular intervals, wherein the stator pole teeth are each enclosed by an excitation coil winding. By means of its FIG. 1, DE 42 12 547 C2 shows that two respective rotor pole teeth and two stator pole teeth coincide at the same time, which produces simultaneous tensile forces directed radially inward on diametrically opposed stator pole teeth, which leads to an elastic, elliptical deformation of the for example circular ring-shaped yoke body that connects the stator pole teeth to one another. After the excitation coils which produce these tensile forces are switched off and after the disappearance of the magnetic field in these stator pole teeth, the yoke body springs back into its original shape and even beyond this. With rotation of the rotor around one revolution, the yoke body is elliptically deformed six times. The elliptical deformations and their frequency produce annoying noise, which according to the teaching of DE 42 12 547 C2 can be counteracted by reinforcing the yoke body in a manner described in conjunction with
FIG. 2
of this reference so that the yoke body is delimited hexagonally on the outside. A reinforcement of this kind increases the natural oscillation frequency of the yoke body or the stator so that with a constant excitation frequency or constant motor speed, the excited oscillation amplitudes are smaller, with the desired result that less noise is generated.
The reluctance motor according to U.S. Pat. No. 5,266,859 likewise has four rotor pole teeth and six stator pole teeth as well as a circular ring-shaped yoke body from which the stator pole teeth protrude radially inward. In order to reduce operating noise, stamped plates, which constitute the rotor and the stator, are twisted like screws in relation to one another and are combined into packets, by means of which the elastic deformations of plates of the stator and/or rotor take place in a time-delayed fashion and there is also a reduction in noise.
The reluctance motor according to WO 92/10022 has a stator with a circular, annular yoke body and ten stator pole teeth leading inward from the yoke body at regular angular intervals. A rotor of this reluctance motor has eight rotor pole teeth and every two of these neighboring rotor pole teeth are combined into pairs which have an angular spacing that corresponds to that of the stator pole teeth. During operation of this reluctance motor, in rotational positions of the rotor which cause minimal reluctance, four air gaps are magnetically flowed through, wherein stator pole teeth disposed diagonally opposite from each other are loaded radially inward in pairs and the yoke ring of the stator therefore receives an essentially elliptical elastic deformation which also causes the generation of noise. The existence of four recurring air gaps is required for a torque delivery of the rotor.
SUMMARY OF THE INVENTION
The electric machine, in particular a reluctance motor, has the advantage that forces directed radially inward by stator pole teeth, which act on the yoke body, instead of producing an essentially elliptical deformation of the yoke ring in accordance with the prior art, now produce a deformation with a shape that is similar to a triangle, but which has sharply rounded curved regions in lieu of corners. It is clear that the yoke body, through the action of stator pole tooth forces, has three sharply curved zones and three less curved zones in the vicinity of the air gaps. Correspondingly, the yoke body or the stator behaves in a more rigid manner and with comparable dimensions, has an oscillation behavior with a higher natural frequency. This has the advantage of resulting in a greater distance between an electromagnetically induced predetermined excitation frequency and the natural resonance of the stator, which leads to the fact that an oscillation excitation by way of electromagnetic forces is less effective and causes less noise.
Less radial spring deflection of the yoke ring also results in less air gap change and therefore smaller high frequency fluctuations of forces acting on the rotor in the circumference direction and therefore smaller high frequency fluctuations of torques.
Advantageous improvements of the electric machine, in particular a reluctance motor, are possible by means of the measures taken hereinafter.
The improvement has the advantage that magnetic forces acting on the two rotor pole teeth with the smaller cross sections are essentially half as great as the force that comes from the stator pole tooth with the greatest cross section. In other words: magnetic flux through a wide stator pole tooth is divided in the yoke body into two fluxes travelling essentially in a mirror inverted fashion relative to one another, which, by means of the stator pole teeth with the smaller cross sections, and thereby with essentially the same flux density as in the large stator tooth cross section, travel to the air gap and the through this air gap into the rotor and finally through another air gap to the above-mentioned stator pole tooth with the large cross section. This is an advantageous electromagnetic utilization of the electric machine according to the invention with the advantage of a favorable torque delivery of this electric machine.
The feature combinations disclosed concretely indicate five different exemplary embodiments. From these five exemplary embodiments, one skilled in the art of drive technology can, for example, choose between embodiments to be operated in three-phase or exemplary embodiments to be operated in four-phase. It is known that the cost of electronic switching is cheaper for three-phase operation than it is for four-phase operation. On the other hand, though, a more uniform production of torque can be expected from operation with four phases.
REFERENCES:
patent: 5168190 (1992-12-01), Bahn
patent: 5652493 (1997-07-01), Hendershot, Jr.
patent: 5737164 (1998-04-01), Ferreira et al.
patent: 5866964 (1999-02-01), Li
patent: 6028385 (2000-02-01), Pengov et al.
patent: 6051903 (2000-04-01), Pengov
patent: 11-346464 (1999-12-01), None
Heese Thomas
Heidrich Markus
Greigg Edwin E.
Greigg Ronald E.
Nguyen Tran
Robert & Bosch GmbH
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