ARRANGEMENT AND METHOD FOR COOLING AN ELECTRIC MACHINE

ARRANGEMENT AND METHOD FOR COOLING AN ELECTRIC MACHINE

FIELD OF THE INVENTION

[0001 ] The invention relates to an arrangement and a method for cooling an electric machine.

BACKGROUND OF THE INVENTION

Electric machines, such as motors or generators, may be cooled by means of one or more blowers blowing a cooling agent into an electric machine or sucking a cooling agent therefrom. This enables a cooling agent circulation to be achieved around the electric machine and/or therethrough. The cooling agent may be air, for instance.

A cooling blower may be implemented as a separate blower such that the blower comprises a motor of its own for driving the blower. Typically, such a separate blower is electrically driven and thus also requires a power supply of its own. A problem with the use of a separate blower is that if the power supply to the separate blower is interrupted, the cooling of the electric machine is also interrupted even if the electric machine itself does not necessarily stop. This may cause the electric machine to become overheated. Further, the separate blower and possible control units associated therewith may require a relatively large space.

Another alternative for implementing a cooling blower for an electric machine is to use a cooling blower connected to an axle of the electric machine. In such a case, while rotating, the electric machine at the same time also drives the cooling blower connected to the axle, which means that the cooling is in operation whenever the electric machine rotates. Typically, a cooling blower connected to the axle of an electric machine requires less space than a separate blower. Further, a cooling blower connected to an axle does not necessarily require separate bearing, for instance.

An example of a commonly used cooling blower connected to the axle of an electric machine is an axial blower which has a propeller type blade and which moves a cooling agent in a direction parallel to an axle around which the blower blade rotates. JP 2007089255 discloses another example of a cooling blower connected to the axle of an electric machine, the cooling blower in this case being a centrifugal blower. The centrifugal blower moves a cooling agent by means of centrifugal force radially with respect to a rotation axle of a blade wheel of the blower. A problem with the above-described cooling blowers connected to an axle is that they do not necessarily enable a sufficient pressure and/or flow of a cooling agent to be achieved, at low rotation speeds in particular.

BRIEF DESCRIPTION OF THE INVENTION

An object of the invention is to provide an apparatus so as to enable the above-mentioned problem to be solved or at least alleviated. The object of the invention is achieved by an arrangement and a method which are characterized by what is disclosed in independent claims 1 and 10. Preferred embodiments of the invention are disclosed in the dependent claims.

The idea underlying the invention is that a cooling blower to be connected to an axle of an electric machine is a side channel blower.

An advantage of the solution according to the invention is that the solution enables a good cooling agent pressure generation and/or flow to be achieved already at a relatively low rotation speed. Further, the side channel blower can be made compact in structure.

BRIEF DESCRIPTION OF THE FIGURES

The invention is now described in closer detail in connection with the preferred embodiments and with reference to the accompanying drawings, in which:

Figure 1 shows an example of an arrangement for cooling an electric machine;

Figure 2 shows an example of an arrangement for cooling an electric machine;

Figure 3 shows an example of an arrangement for cooling an electric machine;

Figure 4 shows an example of a side channel blower;

Figure 5 shows an example of a side channel blower;

Figure 6 shows an example of a side channel blower;

Figure 7 shows an example of a rotor of a side channel blower;

Figure 8 shows an example of a part of a stator of a side channel blower; and

Figure 9 shows an example of a side channel blower. DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows an example of an arrangement according to an embodiment. Figure 1 is a sectional view showing one half of the arrangement perpendicularly to an axle 1 1 . It should be noted that the figure only shows elements relevant to the understanding of the invention. The arrangement of Figure 1 comprises an electric machine 10 which may be a motor or a generator, for instance. Further, the electric machine 10 may be a synchronous machine or an asynchronous machine. The electric machine 10 comprises an axle 1 1 and a rotor 12 fastened thereto. Preferably, ends of the axle 1 1 are provided with bearings 15, enabling rotation of the axle 1 1 and the rotor 12. The electric motor 10 further comprises a stator 13 which is preferably fastened to a stator frame 14. The arrangement of Figure 1 further comprises a side channel blower 20. The side channel blower 20 comprises a stator 23 which is preferably fastened to the stator frame 14 of the electric machine 10, and a rotor 24 which is connected to the axle 1 1 of the electric machine 10 and thus rotates along with the axle 1 1 of the electric machine 10. The side channel blower 20 further comprises at least one cooling agent inlet opening 21 and at least one cooling agent outlet opening 22. The side channel blower 20 may comprise two or more cooling agent inlet openings 21 and two or more cooling agent outlet openings 22. The number of inlet openings 21 and outlet openings 22 may be for instance 2, 3, 4, 5, 6, 7, 8 or 9 or more. Preferably, the number of both inlet openings 21 and outlet openings 22 is the same. By increasing the number of inlet openings 21 and outlet openings 22 of the side channel blower 20, cooling agent generation of the side channel blower 20 may be increased but, correspondingly, cooling agent pressure generation decreases. Preferably, the number of inlet openings 21 and outlet openings 22 is selected each time according to the properties of an electric machine 10 being cooled and the operating conditions so as to enable the cooling of the electric machine 10 to be optimized. Similarly, the size and design of the inlet openings 21 and the outlet openings 22 may vary without this having any bearing on the basic idea of the invention.

The operation of the exemplary arrangement of Figure 1 is based on a closed cooling agent circulation, whereby the arrangement comprises at least one channel for conveying a cooling agent being discharged from the electric machine 10 back to the electric machine. In the example of Figure 1 , such a channel is formed inside an outer cover 17 of the electric ma- chine. When the electric machine 10, and thus the side channel blower 20, are in operation, the side channel blower 20 sucks the cooling agent from the electric machine 10 into one or more inlet openings 21 and further blows the cooling agent out of one or more outlet openings 22. The cooling agent circulation is designated by arrows in the figure. In the example of Figure 1 , the arrangement also comprises at least one heat exchanger 18 for cooling a cooling agent when the cooling agent circulates through the heat exchanger 18. In the example of Figure 1 , the cooling agent passes through an air opening between the rotor 12 and the stator 13 of the electric machine 10 and/or through a rotor air duct 16, for instance. The cooling agent may be e.g. a gaseous cooling agent, such as air, or a cooling agent of another type. However, the type of the cooling agent has is irrelevant to the basic idea of the invention.

Figure 2 shows an example of an arrangement according to an embodiment. The arrangement of Figure 2 substantially corresponds to the example shown in Figure 1 but the arrangement of Figure 2 is based on an open cooling agent circulation. In the exemplary arrangement of Figure 2, the cooling agent circulated through the electric machine 10 is blown via one or more outlet openings 22 of the side channel blower 20 into a space surrounding the electric machine 10. Similarly, the cooling agent is sucked into the electric machine 10 from the surrounding space.

It is to be noted that in the exemplary arrangements of Figures 1 and 2, the direction of the cooling agent circulation could also be opposite, in which case the side channel blower 20 would blow the cooling agent into the electric machine 10 rather than suck the cooling agent out of the electric machine 10. Also, more than one side channel blower 20 could be provided.

Figure 3 shows an example of an arrangement according to an embodiment. The arrangement of Figure 3 otherwise corresponds to the example shown in Figure 2 but the exemplary arrangement shown in Figure 3 comprises two side channel blowers 20, and the design of the inlet openings 21 and the outlet openings 22 of the side channel blowers 20 differs from the examples of Figures 1 and 2. Furthermore, in the example of Figure 3 the side channel blowers 20 blow the cooling agent into the electric machine 10 in a manner shown by the arrows, symmetrically from both ends of the electric machine 10. It is to be noted that in the exemplary arrangement of Figure 3, the direction of the cooling agent circulation could also be opposite. Also, only one side channel blower 20 could be provided in one or the other end of the electric machine 10.

Figures 4 and 5 show an example of a side channel blower 20, as viewed from different directions. The design of the cooling agent inlet openings 21 and the cooling agent outlet openings 22 of the side channel blower 20 of the example of Figures 4 and 5 substantially corresponds to the examples shown in Figures 1 and 2. In the example of Figures 4 and 5, the number of inlet openings 21 and outlet openings 22 is four but the number of openings could also be greater or smaller than this. A middle part of the rotor 24 of the side channel blower 20 shown in Figure 4 is fastened to the axle 1 1 (not shown in the figure) of the electric machine to be cooled.

Figure 6 is a partial sectional view of a side channel blower

20 similar to that shown in Figures 4 and 5, wherein a quarter of the stator 23 is missing in order to show the structure of the rotor 24. The stator 23 of the side channel blower is a substantially hollow annular casing inside which an annular side channel typical of side channel blowers is formed which runs along a side of the rotor 24 and opens up in the direction of the rotor 24. In other words, in the side channel blower 20 a side channel runs in a side direction (in the direction of the rotation axle of the rotor 24) substantially immediately adjacent to the rotor 24. Each cooling agent inlet opening 21 and each cooling agent outlet opening 22 of the side channel blower 20 open up into this side channel. In the example of Figure 6, where the number of inlet openings

21 and outlet openings 22 is four, the side channel is correspondingly divided into four sections by wall parts 25 between the sections such that each side channel section is provided with one inlet opening 21 and one outlet opening 22. The side channel may thus comprise two or more sections separated from one another, in which case preferably at least one cooling agent inlet opening and at least one cooling agent outlet opening open up into each side channel section. The side channel may also consist of only one section provided with one inlet opening 21 and one outlet opening 22. In such a case, the side channel preferably travels an almost 360° circle from the inlet opening 21 to the outlet opening 22, a separating wall part 25 being provided therebetween to cut the side channel.

Figure 7 shows an example of a rotor 24 of a side channel blower 20. The rotor 24 comprises a number of blades which, as the rotor 24 rotates, cause a cooling agent flow from an inlet opening 21 and into an outlet opening 22. It is to be noted that the number and design of the blades of the rotor 24 may differ from the example of Figure 7 without this having any bearing on the basic idea of the invention.

Figure 8 shows an example of a part of a stator 23 of a side channel blower 20. The example of Figure 8 corresponds to one quarter of the stator 23 of the side channel blower 20 shown in Figures 4 to 8, i.e. a whole stator 23 is formed by four interconnected pieces shown in Figure 8. Figure 8 shows the hollow structure of the stator 23 and a side channel formed therein, the cooling agent inlet opening 21 and the cooling agent outlet opening 22 opening up into this side channel. Thus, one quarter of the total length of the side channel of a side channel blower 20 similar to that shown in Figures 4 to 6 is formed inside the part of the stator 23 shown in Figure 8.

Figure 9 shows an example of a side channel blower 20 according to an embodiment. The side channel blower 20 of Figure 9 otherwise corresponds to the examples shown in Figures 4 to 6 but the example shown in Figure 9 comprises five inlet openings 21 and outlet openings 22 and the design of the openings differs from the examples of Figures 4 to 6. The example of Figure 9 thus substantially corresponds to the side channel blowers 20 comprised by the arrangement of Figure 3. The number of inlet openings 21 and outlet openings 22 may differ from that shown in the figure.

It will be apparent to a person skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above but may vary within the scope of the claims.