Patent Description:
In electric machines, such as electrical motors in electric or hybrid vehicles, thermal capacity of rotor magnets and stator winding affects available output power of the electric nachines. The rotor magnets typically have a thermal limit of <NUM> and when temperature increases further, demagnetization occurs which reduce performance or the machine. The stator winding which consists of multiple copper wires is insulated with a material which has a temperature limit of approximately <NUM> and if the temperature increases further, thermal fatigue cracks can occur which can cause shortcuts and terminate the electric machine.

The rotor and the stator windings need to be cooled in order to improve performance of the electric machine. This cooling is commonly performed using a liquid medium such as oil of water, resulting in a more complex and expensive cooling mechanism.

<CIT> discloses an electrical machine comprising a rotor having blo-ing structures for moving gaseous cooling fluid when the rotor is rotating, and a stator having cooling channels for conducting cooling liquid. The stator further comprises heat exchange structures for transferring heat from the gaseous cooling fluid to the cooling liquid, and the electrical machine further comprises guide structures for directing the gaseous cooling fluid moved by the rotor to the heat exchange structures and/or from the heat exchange structures back to the blowing structures of the rotor.

<CIT> discloses a gas turbine engine for aircraft. A generator, which undertakes to supply energy for auxiliary devices, is spaced between a compressor and a turbine. A heat exchanger which surrounds the generator housing, and through which compressor air and fuel flow, is pro-vided for cooling the generator. The compressor air which is cooled by the fuel is supplied to the rotor of the generator, and possibly to a hearing of the rotor shaft.

<CIT> discloses a permanent magnet electric machine including a rotor having a plurality of permanent magnets and a stator in magnetic communication with the rotor and positioned defining a radial air gap between the rotor and the stator. A housing is configured to seal the rotor and the stator from an outside environ-ment. A pumping element is configured to urge a closed loop airflow across the plurality of permanent magnets to remove thermal energy therefrom, and a plurality of cooling channels are located in the housing and are configured to transfer thermal energy from the stator to a flow of fluid coolant through the plurality of cooling channels. A heat exchanger is located in thermal communication with the plurality of cooling channels to transfer thermal energy from the airflow to the fluid coolant.

<CIT> discloses a generator and cooling mechanism. The generator includes a rotor comprising a shaft with a skewed alignment of magnets on a ring, a stator of toothed laminations with coils wound around the teeth, and a housing with cooling chambers. The housing has annular sub-chambers arranged successively along the length of the generator in such a way that cooling fluid must flow to the opposite side of the generator to pass into the next chamber.

<CIT> discloses a rotor of a rotating electrical machine including: a magnet; and a rotor yoke including at least a first core block and a second core block formed by stacking steel plates, each of the steel plates includes an opening portion serving as a coolant flow path, the opening portion positioned on an outermost diameter side includes an outer-diameter-side inner wall portion with a predetermined width in a circum-ferential direction and located on an imaginary circle centered on an axis of the rotor, the second core block is arranged adjacent to the first core block while the second core block is rotated by a predetermined angle with respect to the first core block, and the predetermined width is a length at which the outer-diameter-side inner wall portions of the opening portions of the first core block and the second core block overlap each other when seen from the axial direction.

<CIT> discloses a cooling system for a water jacket style generator to improve the iron core and coil temperature of a rotor.

An objective is to solve, or at least mitigate, this problem and thus provide an improved rotor air cooling system.

This objective is attained in an aspect by a rotor air cooling system of claim <NUM>.

<FIG> schematically illustrates a rotor air cooling system <NUM> in a side sectional view according to an embodiment.

The system <NUM> comprises a rotor <NUM> contained in an inner housing <NUM>. The inner housing is configured to be inserted into an outer housing <NUM>. A cover <NUM> attached to the inner housing <NUM> ensures that the inner housing <NUM> and the outer housing <NUM> become enclosed spaces upon the inner housing <NUM> being inserted into the outer housing <NUM>. The rotor <NUM> comprises a rotor shaft 11a penetrating the inner and outer housing <NUM>, <NUM> and a main rotor body 11b, commonly referred to as a rotor stack, being encapsulated in the inner housing <NUM> and surrounding the shaft 11a. The rotor shaft 11a is coupled to the inner housing <NUM> and the outer housing <NUM> via rotor bearings. As will be illustrated in more detail in the following, the main rotor body 11b comprises axially oriented cavities 11c where air will pass through the main rotor body 11b as it rotates. The direction of the rotor cooling air flow is indicated by means of arrows in <FIG>.

Hence, air will axially enter the rotor stack 11b in an inlet end, pass through the cavities 11c of the main rotor body 11b, and then exit the main rotor body 11b at an outlet end. In order to avoid the rotor <NUM> being overheated, the rotor <NUM> must be cooled, which is typically undertaken using for instance a liquid cooling medium such as oil or water being applied to the rotor as previously discussed.

In this embodiment, a water jacket <NUM> is arranged in the relatively tight space between the outer housing <NUM> and the inner housing <NUM>. A first flange <NUM> and a second flange <NUM> is arranged to radially protrude from an exterior side of the inner housing <NUM> and extend around a periphery of the inner housing <NUM> to abut an interior side of the outer housing <NUM> (or vice versa), thereby forming a casing surrounding the inner housing <NUM> where water can be accommodated, thereby creating the water jacket <NUM>. Cold water will thus be applied in the casing formed by the inner housing <NUM>, the outer housing <NUM> and the two radially protruding flanges <NUM>, <NUM>, thereby forming the water jacket <NUM> which will cool the inner housing <NUM>.

Fixedly arranged to an interior side of the inner housing <NUM> is also a stator <NUM> comprising stator windings <NUM>.

Further, a heat exchanger <NUM> may in an embodiment be arranged in an enclosed space <NUM> at an exterior side of the outer housing <NUM> for dissipating heat from the heated rotor cooling air having passed through the main rotor body 11b and exiting at its outlet end. The space <NUM> may be enclosed with a metal plate acting as a lid <NUM>. It may be envisaged that the heat exchanger <NUM> is integrated with the outer housing <NUM> as will be illustrated in the following. It is envisaged that the system <NUM> may comprise a plurality of heat exchangers utilized to cool air circulating in the system.

A number of configurations are envisaged for the heat exchanger <NUM>; it may be integrated with or attached to the outer housing <NUM>. Alternatively, the heat exchanger <NUM> may be part of or attached to the inner housing <NUM> or even arranged externally from the inner and outer housing and connected to the system <NUM> via closed air channels.

The inner housing <NUM> comprises an air outlet <NUM> aligned with an air outlet <NUM> of the outer housing <NUM> to enable fluid communication between the outlet end of the main rotor body 11b and an inlet of the heat exchanger <NUM>.

As further can be seen, the outer housing <NUM> comprises an air inlet <NUM> where air will enter into the inner housing <NUM> from an open backend <NUM> of the inner housing <NUM> to enable fluid communication between an outlet end of the heat exchanger <NUM> and an inlet end of the main rotor body 11b.

Thus, with the created fluid communication between the heat exchanger <NUM> and the interior of the inner housing <NUM>, the air exiting the main rotor body 11b is radially guided (due to direction of air flow through the system <NUM>) to pass via the respective air outlet <NUM>, <NUM> of the inner and outer housing <NUM>, <NUM> through the heat exchanger <NUM> where heat is dissipated from the air before the air is being radially guided via the air inlet <NUM> of the outer housing <NUM> and the open backend <NUM> of the inner housing <NUM> to the air inlet of the main rotor body 11b for recirculation of the cooled air through the cavities 11c of the main rotor body 11b.

Again with reference to <FIG>, to conclude, cooled air axially enters the rotor stack 11b at its inlet end and passes through the cavities 11c of the rotor stack 11b. Hence, this cooled air cools the rotor <NUM>, i.e. the rotor shaft 11a as well as the rotor stack 11b. Further advantageous is that the cooled air entering the inner housing <NUM> also will cool the stator <NUM> and its windings <NUM>.

Upon exiting at the outlet end of the rotor stack 11b, the warmed-up air will rise and thus be radially guided in the inner housing <NUM> towards the air outlets <NUM>, <NUM> of the inner and outer housing <NUM>, <NUM> via which the warmed-up air enters the enclosed space <NUM> and is cooled off by the heat exchanger <NUM>. Further, the cold water of the water jacket <NUM> surrounding the inner housing <NUM> will cool the circulated air. it is noted that the water jacket <NUM> servers as a general cooling element for various components of the system, such as the heat exchanger <NUM>, the stator <NUM>, the rotor <NUM>, etc..

The air being cooled off passing through the heat exchanger <NUM> will reach an outlet end of the heat exchanger <NUM> and enter the inner housing <NUM> in a radial direction via the air inlet <NUM> of the outer housing <NUM> and the open backend <NUM> of the inner housing <NUM> before again being recirculated through the cavities 11c of the main rotor body 11b in order to advantageously cool the rotor <NUM> as well as the stator <NUM> and its windings <NUM>.

Advantageously, an effective rotor cooling system is thus attained using air instead of liquid, such as water or oil. This provides for a more inexpensive and non-complex cooling system <NUM>. Further, the handling is far messier when using liquid instead of air.

<FIG> illustrates a perspective exterior view of the air rotor cooling system <NUM> where for illustrative purposes the inner housing <NUM> has not been inserted int the outer housing <NUM>.

As can be seen, the inner housing <NUM> comprises an air outlet <NUM>. Further, the first flange <NUM> and second flange <NUM> are shown, which protrudes radially from the inner housing <NUM> - more so than the other three flanges - in order to abut the inner surface of the outer housing to create the water jacket (not shown in <FIG>) upon the inner housing <NUM> being inserted into the outer housing <NUM> as indicated with the arrow. The water jacket will extend axially between the first flange <NUM> and the second flange <NUM> and typically surround the inner housing <NUM> when the system <NUM> is in operation. The three flanges in between the enclosing flanges <NUM>, <NUM> serves as a spiral-shaped rib <NUM> extending along a length of the exterior side for guiding the water accommodated in the casing when the inner housing <NUM> is inserted into the outer housing <NUM>.

When the inner housing <NUM> is inserted into the outer housing <NUM>, the cover <NUM> enclosing the inner housing <NUM> will further close the outer housing <NUM>. Moreover, the air outlet <NUM> of the inner housing <NUM> will be aligned with the air outlet <NUM> of the outer housing <NUM>, while the air inlet <NUM> of the outer housing <NUM> will be in fluid communication with the open backend <NUM> of the inner housing.

In the embodiment shown in <FIG>, the lid <NUM> of <FIG> has been removed to show the heat exchanger <NUM> being integrated with the outer housing, though which the rotor cooling air passes from the air inlet <NUM> to the air outlet <NUM> and is recirculated in the inner housing <NUM>. During operation, the lid <NUM> of <FIG> is attached to the outer housing <NUM> to create the enclosed space for the heat exchanger <NUM>. As can be seen, the heat exchanger <NUM> is in this exemplifying embodiment arranged with wave-shaped cooling fins. However, any appropriate cooling fin shape may be envisaged; such as for instance rectangular fins, offset strip fins, triangular fins, etc..

The cavities 11c extending through the main rotor body 11b from the inlet end to the outlet end, via which the rotor cooling air passes, may extend in an axial direction of the rotor <NUM>, i.e.in parallel with the rotor shaft 11a. However, in an embodiment, the cavities 11c extend slightly helically trough the main rotor body 11b in relation to the rotor shaft 11a.

<FIG> illustrates a rotor <NUM> in a perspective view according to such an embodiment. Hence, the main rotor body 11b is arranged around the rotor shaft 11a. The main rotor body 11b comprises cavities 11c where air will pass through the rotor body 11b from the inlet side to the outlet side as illustrated with arrows. In this embodiment, the cavities 11c are arranged to extend helically from the inlet end of the main rotor body 11b to the outlet end of the main rotor body 11b with respect with respect to the rotor shaft 11a.

In an embodiment, the helix angle of the helically shaped cavities 11c extending through the main rotor body 11b is about <NUM>-<NUM>°, such as <NUM>-<NUM>°. Advantageously, the helically shaped cavities 11c results in greater air velocities through the main rotor body 11b, and thus a higher air circulation velocity in the system, which effectively improves transfer of heat from the rotor and stator in the system.

With reference to <FIG>, in practice, the main rotor body 11b is formed by individual circular metal discs <NUM>-<NUM> (in practice tens or even hundreds of discs may be utilized depending on the size of the rotor) axially arranged along the rotor shaft 11a and abutting a preceding disc to form the main rotor body 11b, each having through-holes 30a-30b, 31a-31b, 32a-32b distributed around the disc (<NUM> holes in the example of <FIG> and <FIG> in the example of <FIG>) where the number of holes correspond to the number of cavities 11c in the main rotor body 11b. The through-holes are illustrated as having pentagonal shape in the Figures. However, the trough-holes may alternatively be circular, triangular, mushroom-shaped, etc., or have any appropriate shape. Further, any appropriate number of through-holes can be utilized depending on the particular implementation. As is understood, the discs are tightly abutted to form a compact set of discs. The through-holes may further be arranged with cooling fins to increase the heat exchange. This may for instance be attained by arranging inner walls of the through-holes with small tooth-shaped cooling fin members.

The discs <NUM>-<NUM> are thus "stacked" one after another along the rotor shaft 11a, which explains why the main rotor body 11b commonly is referred to as the "rotor stack".

In order to attain axial cavities 11c through the main rotor body 11b, i.e. cavities 11c extending in parallel with the rotor shaft 11a, the discs <NUM>-<NUM> are arranged axially one after another along the rotor shaft 11a to form the main rotor body 11b, the holes of one disc <NUM> being aligned with the holes of a following disc <NUM> until all discs have been arranged around the shaft.

However, as shown in the embodiment of <FIG>, each disc is rotationally offset around the rotor shaft with respect to the preceding disc thereby creating cavities extending helically through the main rotor body.

Thus, after having arranged the first disc <NUM> around the rotor shaft (the shaft not being shown in <FIG>), the second disc <NUM> is arranged around the rotor shaft and slightly rotationally offset with respect to the first disc <NUM>, in this example in a counter-clockwise direction. As a result, the through-holes 31a, 31b of the second disc <NUM> is rotationally offset with respect to the corresponding through holes 30a, 30b of the preceding first disc <NUM>. Thereafter, the third disc <NUM> is arranged around the rotor shaft and slightly rotationally offset with respect to the second disc <NUM> (in the same rotational direction as the previous discs) causing the through-holes 32a, 32b of the third disc <NUM> to become rotationally offset with respect in relation to the corresponding through holes 31a, 31b of the preceding second disc <NUM>, and so on.

Advantageously, this rotational offset of the discs <NUM>-<NUM> causes the cavities 11c created by the through-holes to extend helically with respect to the rotor shaft 11a.

<FIG> illustrates a further embodiment, where an axial input endplate <NUM> is arranged around the rotor shaft 11a at the inlet end of the main rotor body 11b. Through-holes of axial input endplate <NUM> is aligned with the through holes at the inlet end of the main rotor body 11b forming the cavities 11c. Hence, the axial input endplate <NUM> acts as an axial fan for increasing the flow of cooled air through the main rotor body 11b.

The axial input endplate <NUM> has at least two advantages; firstly, it is used to balance the discs <NUM>-<NUM> of the main rotor body. That is, it can be pressed against the inlet end of the main rotor body 11b to have the discs <NUM>-<NUM> tightly abut each other along the rotor shaft 11a. Secondly, the axial input endplate <NUM> - being an axial fan - guides the air having been cooled off by the heat exchanger into the main rotor body 11b axially, creating a high pressure zone at the inlet side of the main rotor body 11b, which will push air into the cavities 11c.

<FIG> illustrates a further embodiment, where an impeller <NUM> is arranged around the rotor shaft 11a at an outlet end of the main rotor body 11b. the blades of the impeller <NUM> will advantageously facilitate the guiding of the rotor cooling air in a radially direction towards the heat exchanger (not shown in <FIG>). The impeller <NUM> distributes the air radially creating a low pressure zone at the outlet side of the main rotor body 11b, which will draw pull air out of the cavities 11c. It is noted that the use of the impeller <NUM> does not require that the axial input endplate <NUM> also is utilized. Typically, the impeller <NUM> is in practice arragned around the rotor shaft 11a such that the impeller abuts the outlet end of the main rotor body 11b.

Claim 1:
A rotor air cooling system (<NUM>), comprising:
an outer housing (<NUM>);
an inner housing (<NUM>) configured to be inserted into the outer housing (<NUM>), the inner housing (<NUM>) comprising an open backend (<NUM>) and further a cover (<NUM>) arranged to enclose the inner housing (<NUM>) and the outer housing (<NUM>) upon the inner housing (<NUM>) being inserted into the outer housing (<NUM>);
a stator (<NUM>) attached to an interior side of the inner housing (<NUM>);
a main rotor body (11b) comprised in the inner housing (<NUM>), the main rotor body (11b) being arranged around a rotor shaft (11a) arranged to extend through the inner housing (<NUM>) and the outer housing (<NUM>), wherein cooling air axially enters the main rotor body (11b) in an inlet end via the open backend (<NUM>) of the inner housing (<NUM>), passes through cavities (11c) of the main rotor body (11b), and exits the main rotor body (11b) in an outlet end;
a water jacket (<NUM>) arranged between the inner housing (<NUM>) and the outer housing (<NUM>), the water jacket (<NUM>) being formed by an exterior side of the inner housing (<NUM>) being arranged with a radially protruding first flange (<NUM>) and a radially protruding second flange (<NUM>) around the exterior side, the first and second flange (<NUM>, <NUM>) being arranged to abut an interior side of the outer housing (<NUM>), thereby forming a casing surrounding the inner housing (<NUM>) where water can be accommodated;
a heat exchanger (<NUM>) for dissipating heat from the cooling air exiting the main rotor body (11b), the heat exchanger (<NUM>) being integrated with the outer housing (<NUM>); wherein
the air exiting the main rotor body (11b) is radially guided, via an air outlet (<NUM>) of the inner housing (<NUM>) being aligned with an air outlet (<NUM>) of the outer housing (<NUM>), through the heat exchanger (<NUM>) before being arranged to be radially guided via an air inlet (<NUM>) of the outer housing (<NUM>) being in fluid communication with the open backend (<NUM>) of the inner housing (<NUM>) to the air inlet of the main rotor body (11b) for recirculation of the cooled air through the main rotor body (11b), the rotor air cooling system (<NUM>) further comprising:
an impeller (<NUM>) arranged around the rotor shaft (11a) at an outlet end of the main rotor body (11b) to facilitate radial guiding of the cooling air exiting the main rotor body (11b) at the outlet end.