Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-05-13
2004-07-13
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S052000, C310S054000, C310S208000, C310S254100
Reexamination Certificate
active
06762520
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a reluctance electric machine comprising
a stator part with stator teeth of magnetically conductive material that are provided with coil windings;
and a rotor part arranged coaxially with respect to the stator part and located opposite the stator part so as to leave free an air gap therebetween,
the rotor part having a number discrete poles of magnetically conductive material that project in the direction towards the stator part.
Reluctance electric machines differ from other electric machines in that they have no electromagnetic or permanent-magnetic excitation part. Reluctance electric machines operate by using the effect of magnetic attraction of magnetically conducting parts under the influence of magnetic flux flowing through are same. Both the stator and the rotor have distinctive magnetically conductive poles. The coil windings have current flowing therethrough such that they attract an adjacent rotor pole each. The current in the stator pole has to be turned off again at the proper time after attraction of the respective rotor pole, in order to release the rotor pole in running direction. For, if the coil current would continue to flow (irrespective of the direction of flow), continued attraction by the stator pole, i.e. a retroactive force, would result that would prevent further rotation of the rotor.
It is thus in the nature of reluctance electric machines that these are exploited basically half of the time only. This is why reluctance electric machines—assuming otherwise identical design parameters—normally achieve only about half of the torque values or power values in comparison with other electric motors.
SUMMARY OF THE INVENTION
It is the object of the invention to improve a reluctance electric machine of the type indicated at the outset towards higher values as regards permanent torque and permanent power.
To meet this object, the reluctance electric machine according to the invention is characterized in that cooling with channelled coolant flow is provided at least for partial sections of the coil windings of the stator part.
Preferably, the coil windings are provided with an enclosure each. As an alternative, there are preferably several coil windings commonly provided with an enclosure each. In accordance with a particularly preferred embodiment, the stator part is provided with an enclosure in its entirety. In all of the cases mentioned, there may be provided, for the space enclosed by the enclosure, one or more coolant supplies and one or more coolant discharges.
As regards the term “projecting, discrete poles” in feature (c) of claim 1, it is to be pointed out furthermore that the portions between the discrete poles may also be filled with a non-magnetic material so that the rotor part is virtually smooth on the air gap side.
The invention teaches to make the cooling of the stator part considerably more efficient than with known reluctance electric machines. The electric machine thus can be subjected to considerably higher loads—permanently and not only for short periods, as before.
The statements further below will make clear that the channelling of the coolant flow according to the invention, in practical application, mostly has the effect that the stator part of the reluctance electric machine is provided with a sealing layer on the side facing the air gap. The result of the sealing layer is that the distance between the stator poles and the rotor poles across the air gap is greater than without provision of a sealing layer. This means—with otherwise unchanged design parameters—a reduction of the magnetic flux between the respective pair of stator pole and rotor pole in consideration and thus a deterioration of the magnetic conditions of the electric machine. With the corresponding designs of the reluctance electric machine according to the invention, which have a sealing layer, this disadvantage is deliberately tolerated; according to the invention, the considerably more efficient cooling achieves a greater advantage than the deterioration of the magnetic conditions due to additional material in the air gap.
These restrictions are not applicable when the stator poles, by way of suitable enclosures, have individually associated cooling spaces or cooling channels that cover only the end face portions and do not project into the air gap.
Known reluctance electric machines also have already made use of cooling means. Known concretely are the non-specific blowing of air through the entire electric machine (stator part, air gap, rotor part) or as cooling on the stator part side directed away from the air gap. In contrast thereto, the reluctance electric machine according to the invention employs direct or quasi-direct cooling of those portions where the heat losses arise in the first place. A first major portion of generation of heat losses are the coil windings (often referred to as “copper losses”; these are caused mainly by the passage of current). According to the invention, the coil windings are cooled directly by cooling medium flowing therealong. Even if the coil windings are cooled only in the spaces between the stator teeth or only in the spaces on the face side of the stator teeth (and not in both spaces), very efficient cooling is achieved since the material of the coil windings, which has good current conducting properties, also provides for good conduction of the heat losses to the portions cooled concretely. Another major place of generation of heat losses are the stator teeth (often referred to as “iron losses” in simplified manner; these losses are caused mainly by the continuous alternation between magnetization and demagnetization or remagnetization of the stator teeth). The described cooling operation by flow of cooling medium through spaces accommodating coil windings of the stator part, at the same time constitutes cooling of the stator teeth since—at least with many design types of the coil windings—the cooling medium flows in the spaces mentioned so as to reach the stator teeth and since the coil windings establishing physical contact with the stator teeth dissipate heat from the stator teeth by thermal conduction. Furthermore, the cooling medium usually flows along the stator back between the stator teeth; the stator back receives heat from the stator teeth by thermal conduction.
A preferred development of the invention provides that the stator teeth have internal flow passages for cooling medium. This provides for direct, particularly efficient internal cooling of the stator teeth. Furthermore, it is pointed out as preferred possibility according to the invention to provide in addition to, or instead of, the described internal cooling of the stator teeth, internal flow passages for cooling medium in the region of the stator part which are set back from the stator teeth.
It is expressly pointed out that the term “reluctance electric machine” used in the present application comprises both electric motors (conversion of electric energy to mechanical energy) as well as current generators (conversion of mechanical energy to electric energy). In addition thereto, it is expressly pointed out that the term “stator part” is not supposed to mean that the stator part cogently is to be non-moving, and that the term “rotor part” is not supposed to mean that the rotor part cogently is supposed to be a rotatable part of the electric machine. Rather, it is easily possible to provide the stator part (i.e. the part of the electric machine provided with coil windings) as rotating machine part and the rotor part as stationary, non-moving machine part. The inverse design, however, is usually more favorable since the current windings having current supplied thereto and, in case of the generator, discharged therefrom, are located on a stationary machine part, whereby sliding contacts are avoided. In addition thereto, the possible embodiment is to be mentioned that both the stator part and the rotor part rotate at different speeds and/or different directions of rotation, in particular when they are con
Ehrhart Peter
Heidelberg Goetz
Elkassabgi Heba
Kaminski Jeffri A.
Kinberg Robert
Magnet-Motor Gesellschaft fur Magnetmotorische Technik mbH
Mullins Burton S.
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