Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-03-15
2004-05-25
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06740993
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application, Ser. No. 101 12 532.1, filed Mar. 15, 2001, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates, in general, to an air-cooled electric machine, and more particularly to an air-cooled electric rotary machine of a type having a stator with a laminated stator core having axial ends terminating in winding end portions, and a rotor spaced from the stator at formation of an air gap therebetween.
German Pat. No. 672,623 describes a cooling arrangement for closed electric machines, in particular three-phase motors. Disposed inside the closed machine are two fans for generating a flow of cooling air which is re-cooled by closed channels, or groups of channels, disposed on the outer surface area of the machine and circulated by a stream of coolant to define an outer coolant flow. At the axial ends, an inner coolant flow is routed by deflection walls through a looped path from one longitudinal channel or channel group in opposite direction to the following longitudinal channel or channel group.
This cooling arrangement suffers shortcomings because it requires the provision of two fans, one for each axial end of the stator core, in order to implement the looped deflection of the air stream. The use of two fans heightens the probability of a breakdown of the cooling action, and higher production costs are incurred compared to a system that would employ only one fan. Moreover, the presence of two separate cooling systems is also disadvantageous because heat has to be transferred from the inner cooling system to the outer cooling system. In accordance with the given thermal transmission coefficient, the cooling action is decreased by the cooling on the machine. The overall construction of the closed electric machine does not allow modular and variable constructions and thus is difficult to manufacture in various designs. This is true especially for types of machines that have different lengths, because separate constructions of cooling arrangements are required for each type, i.e. the construction of the machine requires a particular configuration of the cooling arrangement.
It would therefore be desirable and advantageous to provide an improved air-cooled electric rotary machine which obviates prior art shortcomings and which is so configured as to be applicable for different types of machines, in particular as far a machine length is concerned, while yet establishing a reliable and effective cooling action in a cost-efficient manner.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an air-cooled electric rotary machine, includes a stator including a stator having a stator core formed of laminations and having axial ends terminating in winding end portions, a rotor spaced from the stator at formation of an air gap therebetween, plural air channels, separated from one another and extending within and/or on the stator core, for allowing an air stream in complementary flow directions, a looped air stream conduction established by a directional deflection of the air stream at the winding end portions, and a single fan for cooling the stator by forcing the air stream to flow through the cooling channels and the looped air stream conduction.
The present invention resolves prior art problems by so structuring the electric rotary machine that only a single fan can be used for conduction of a sufficient air stream for cooling at least the laminated stator core. The air stream is conducted in separate cooling channels which can be formed in and/or on the stator core. Cooling channels provided in the stator core can be suitably formed, for example, by individually stamping the individual metal sheets of the stator core. The looped deflection of the air stream at the axial ends of the stator core allows an air stream in complementary flow directions. The looped air conduction is characterized by two factors. On the one hand, the air stream is guided about the winding end portions at the axial ends of the stator core, thereby following a circular, almost closed path and as a result assuming a looped configuration, and on the other hand the looped conduction of the air stream is established by separate cooling channels because of the necessity to reverse the flow direction by 180°.
When the stator core is cooled by only one air stream in only one direction, the temperature difference between air temperature and temperature of the stator core decreases as the air stream travels in the cooling channel. This cooling effect, which differs substantially and is dependent on the entry point of the cooling air, is counteracted when feeding air through separate cooling channels of the stator core. A temperature equalization is realized between the separate cooling channels in the stator at any location with respect to the longitudinal axis. When, for example, referring to the location on the stator core, which is characterized by the initial air entry into a cooling channel of the stator core, on the one hand, but also in a neighboring, separate cooling channel by the exit of the cooling air stream, on the other hand, a temperature equalization is realized there. The equalization is provided at this location—in this area—by air which has cooled a winding end portion, on the one hand, and has flowed already through two winding end portions and in addition has passed twice cooling channels in the stator core. As a consequence, a mean cooling action is established for each axial area of the stator core.
The fan for generating the air stream may be configured as an internal machine-own fan. This is advantageous in conjunction with complete systems. The machine-own fan may be positioned on one side of the axial ends of the stator core behind the end winding portions and constitutes the starting point for the air stream being forced through the machine. In the description, the term “machine-own fan” will denote merely the fact that the fan is part of or incorporated in the electric rotary machine. Hereby, it is, of course, conceivable to position the fan also on different locations of the machine. The air streams should then be so conducted as to establish a flow in a manner according to the invention.
In particular, when larger air-cooled electric rotary machines are involved or even groups of electric rotary machines, the air cooling of the electric rotary machine may also be implemented by an external fan, i.e. a fan that is positioned outside the electric rotary machine. The air stream produced by the external fan has at least one entry into the coolant system of the electric rotary machine. The utilization of an external fan has the advantage to allow the application of a single fan for different electric rotary machines or for different units to be cooled. An external fan, which is not part of the electric rotary machine, can also be more easily replaced. Two types of external fans can be referred to here by way of example. When the fan should not be positioned on the shaft of the electric rotary machine, it is possible to place the fan on the housing of the electric rotary machine. When ventilating several electric rotary machines with one fan, air channels are provided which distribute and feed the air to the individual electric rotary machines.
Regardless whether an internal fan or an external fan is involved, at least one exit zone is provided for the air stream. The looped conduction of the air stream at the end faces of the stator core is established by measures that effect a routing of at least a portion of the air stream radially through the winding end portions. Examples of such measures includes the provision of cap-like formed parts, air guides or air baffles, which may interact separately or in concert with a motor housing. Depending on the configuration of the winding end portions, the radial air conduction on the end faces of the stator core may be implemented by different configurations. Cast win
Greubel Klaus
Hellmann Heinrich
Schueller Uwe
Feiereisen Henry M.
Mullins Burton
Siemens Aktiengesellschaft
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