Patent Description:
The present invention relates to a stator with bar winding and fluid cooling for a rotary electric machine.

Patent Application <CIT> discloses a stator of a rotary electric machine provided with a rigid bar winding (so-called "hairpins"). In winding a stator by means of rigid bars, a series of rigid bars are used, which are initially shaped into a "U" and are then axially inserted into the stator slots, forming an inlet side, wherein the cusps of the U-shaped rigid bars are arranged, and an outlet side, wherein the end portions of the legs (i.e. the straight portions) of the U-shaped rigid bars are arranged. Once the rigid bars have been inserted into the stator slots, the legs on the outlet side are bent and then the free ends of the legs are connected to each other by means of welding to form the electrical paths of the stator winding.

To adequately cool a stator with a rigid bar winding, it is known to create a series of axial cooling channels, through which a cooling fluid (typically mineral oil) is circulated. It has been proposed both to create the axial cooling channels through the magnetic core and to create the axial cooling channels through the slots where the conductor bars are arranged. In particular, the solution that involves creating axial cooling channels through the slots where the conductor bars are arranged allows to obtain a high cooling efficiency (since most of the heat is generated inside the conductor bars), but, on the other hand, it hinders the fill factor of the slots (since a relevant part of the slot volume must be allocated to the cooling channels) and has a very complex winding design.

Patent Application <CIT> discloses an electric machine comprising: a pack of metal sheets, at least one conductor element which is arranged in at least one slot of the pack of steel plates and has a cross-section with at least one rounded corner, and at least one cooling channel which is directly delimited by the rounded corner of the conductor element.

Patent Application <CIT> discloses a winding system wherein at least one pair of adjacent coils are spaced from each other so as to provide at least one channel for the passage of a cooling fluid.

The object of the present invention is to provide a stator with bar winding and fluid cooling for a rotary electric machine, which stator winding allows to obtain a high cooling efficiency while not excessively hindering the slot fill factor, and that is also easy and quick to manufacture.

According to the present invention, a stator with bar winding and fluid cooling is provided for a rotary electric machine as defined in independent claim <NUM>. A methoed for manufacturing the stator is defined in independent claim <NUM>.

The present invention will now be described with reference to the attached drawings, which show a non-limiting embodiment thereof, wherein:.

In <FIG>, a stator of a synchronous and rotary electric machine of the reversible type (i.e. which can operate both as an electric motor absorbing electric power and generating a drive torque, and as an electric generator absorbing mechanical power and generating electric power) is overall indicated by <NUM>. The stator <NUM> has a cylindrical tubular shape and is arranged around a permanent magnet rotor to enclose the rotor itself therein.

The stator <NUM> comprises a magnetic core <NUM> (better shown in <FIG>) which is made up of a series of steel plates tightened in a pack and has a centrally drilled tubular shape. The magnetic core <NUM> is longitudinally (axially) crossed by thirty-six slots <NUM> (better shown in <FIG>) which are evenly distributed along the inner side of the magnetic core <NUM> and accommodate a three-phase stator winding <NUM>; according to other embodiments not shown, the number of slots <NUM> could be different (e.g. there could be forty-eight or seventy-two slots <NUM>).

As shown in <FIG>, the three-phase stator winding <NUM> comprises a series of rigid U-shaped bars <NUM>, each comprising two legs <NUM> connected by a cusp <NUM> (as further shown in <FIG>); the two legs <NUM> of a same bar <NUM> constitute two corresponding active conductors of the stator winding <NUM>.

As shown in <FIG>, the U-shaped bars <NUM> are inserted through the slots <NUM> defining an inlet side <NUM>, where the cusps <NUM> of the U-shaped bars <NUM> are arranged, and an outlet side <NUM>, where the end portions of the legs <NUM> of the U-shaped bars <NUM> are arranged. The two heads of the stator winding <NUM> are arranged at the two sides <NUM> and <NUM> of the stator winding <NUM>: one head consists of the cusps <NUM> of the bars <NUM> (at the inlet side <NUM>) while the other head consists of the end portions of the legs <NUM> of the bars <NUM> (at the inlet side <NUM>).

In the embodiment shown in the attached Figures, eight legs <NUM> (i.e. eight conductors of the stator winding <NUM>) belonging to eight corresponding U-shaped rigid bars <NUM> are arranged in each slot <NUM> (as better shown in <FIG>). The ends of the legs <NUM> of the U-shaped bars <NUM> are electrically connected (welded) to each other to form the electrical paths of the stator winding <NUM>.

As shown in <FIG>, there is provided a plurality of cooling channels <NUM> which can, in use, be flown through by a cooling fluid (generally mineral oil), and which are obtained within the slots <NUM> between the bars <NUM> of the stator winding <NUM>. In particular, a plurality of covering elements <NUM> is provided, each of which is made of an electrically insulating plastic material, which engages, without clearance, a corresponding slot <NUM> on all sides of the slot <NUM>, and centrally has a cavity <NUM> wherein a series of corresponding bars <NUM> are arranged and wherein the cooling channels <NUM> are obtained.

According to a preferred embodiment, the plastic material constituting the covering elements <NUM> is electrically insulating and, as far as possible, thermally conductive so as to also promote the cooling of the magnetic core <NUM> (wherein some heat generation due to eddy currents and magnetic hysteresis occurs); for example, the plastic material constituting the covering elements <NUM> preferably has a thermal conductivity greater than <NUM> W/m K.

Each covering element <NUM>, being electrically insulating, replaces the insulating paper which is normally placed inside the slots <NUM> to separate the bars <NUM> from the metal of the magnetic core <NUM>; consequently, the covering elements <NUM> do not constitute an additional component with respect to a standard stator as they replace the insulating paper which is normally placed inside the slots <NUM>.

Each covering element <NUM> has two major side walls <NUM> that are opposed and are radially oriented and two minor head walls <NUM> that are opposed and are circumferentially oriented, connect the two major side walls <NUM> to each other and have an extension that is lower than an extension of the major side walls <NUM>.

Each cooling channel <NUM> is delimited by walls <NUM> and/or <NUM> of a corresponding covering element <NUM> and by at least one corresponding bar <NUM>; in particular, in each slot <NUM> two end cooling channels <NUM> are provided which are arranged at the sides of the bars <NUM> (thus delimited radially on one side by a bar <NUM> and on the opposite side by a smaller end wall <NUM> of the covering element <NUM>) and central cooling channels <NUM> arranged between the bars <NUM> (thus delimited radially by two bars <NUM> on both sides).

Each covering element <NUM> has seats <NUM> (four seats <NUM> in particular), each of which is configured to accommodate a pair of corresponding bars <NUM> arranged in contact with each other. According to a different embodiment not shown, each seat <NUM> is configured to accommodate a single bar <NUM> or three or four bars arranged in contact with each other. Accordingly, in each covering element <NUM>, the cooling channels <NUM> are arranged next to the seats <NUM> where the bars <NUM> are arranged and are directly delimited by the bars <NUM> (i.e. at least one wall of each cooling channel <NUM> consists of a bar <NUM>).

According to a preferred embodiment shown in the attached figures, each major side wall <NUM> has axial ribs <NUM>, each of which delimits a corresponding seat <NUM>; that is, each seat <NUM> is delimited by two radially staggered axial ribs <NUM>.

Each slot <NUM> has a through opening <NUM> facing a central axis; the through openings <NUM> have an important function, as they serve to "magnetically insulate" the teeth of the magnetic core <NUM> in such a way that they "force" the magnetic flow generated by the bars <NUM> to affect the rotor instead of only closing in the magnetic core <NUM> of the stator <NUM>. According to a preferred embodiment shown in the accompanying figures, each covering element <NUM> has a protuberance <NUM> which engages the through opening <NUM> of the corresponding slot <NUM> without clearance; that is, each protuberance <NUM> completely fills the through opening <NUM> of the corresponding slot <NUM>.

The stator <NUM> comprises two annular cooling manifolds <NUM> and <NUM> (shown in <FIG> and <FIG>) which are arranged at opposite ends of the magnetic core <NUM> and into which the cooling channels <NUM> flow. The cooling manifold <NUM> forms the cooling fluid supply to the cooling channels <NUM> and is connected with a cooling fluid inlet <NUM> in the stator <NUM> (shown in <FIG>). The cooling manifold <NUM> constitutes the return of the cooling fluid from the cooling channels <NUM> and is connected with a cooling fluid outlet <NUM> in the stator <NUM> (shown in <FIG>). As mentioned above, the stator winding <NUM> has two heads and the two heads are accommodated in the cooling manifolds <NUM> and <NUM> in such a way that they are cooled by the cooling fluid circulating in the cooling manifolds <NUM> and <NUM>.

As shown in <FIG> and <FIG>, the stator <NUM> comprises a casing <NUM> which contains the magnetic core <NUM> and externally delimits the two cooling manifolds <NUM> and <NUM>. In addition, the stator <NUM> comprises two annular containing bodies <NUM>, each of which internally delimits a corresponding cooling manifold and is made of plastic.

According to the invention, as shown in the attached figures (and better visible in <FIG> and <FIG>), the stator <NUM> comprises two annular connection bodies <NUM>, which are arranged at the two opposite ends of the magnetic core <NUM>, are connected without interruptions to the covering elements <NUM> with which they form a single, indivisible assembly, and form a base for the containing bodies <NUM>. In particular, the containing bodies <NUM> can be welded to the annular connection bodies <NUM> to create a tight fit that prevents leakage of the cooling fluid. In other words, each connection body <NUM> connects together (on a respective side of the magnetic core <NUM>) all the covering elements <NUM> that are present in the slots <NUM>.

According to the invention, manufacturing the stator <NUM> involves injection moulding the plastic material into the grooves <NUM> of the magnetic core <NUM> in order to make the covering elements <NUM> and preferably also the two connection bodies <NUM> (the two connection bodies <NUM> are thereby connected without interruptions to the covering elements <NUM> with which they form a single and indivisible assembly). In other words, the covering elements <NUM> (together with the two connection bodies <NUM>) are co-injected into the magnetic core <NUM> before the bars <NUM> are inserted into the slots <NUM> of the magnetic core <NUM>. Once the covering elements <NUM> have been manufactured by injection moulding, the bars <NUM> are inserted into the covering elements <NUM> which internally cover the slots <NUM>.

The herein described embodiments can combine one another without departing from the scope of protection of the present invention defined in the independent claims.

The above-described stator <NUM> has many advantages.

Firstly, the above-described stator <NUM> allows to obtain high cooling efficiency due to the fact that the cooling channels <NUM> are directly delimited by the bars <NUM> and thus remove heat directly from where it is generated.

Furthermore, the above-described stator <NUM> has a good filling coefficient of the slots <NUM>, as some of the walls of the cooling channels <NUM> consist of the bars <NUM> and are therefore made without adding additional components that would take space inside the slots <NUM>, reducing the filling coefficient of the slots <NUM>.

In addition, the above-described stator <NUM> is easy and quick to manufacture, as all the covering elements <NUM> can be made together quickly by being co-injected in the magnetic core <NUM>.

Claim 1:
A stator (<NUM>) for a rotary electric machine (<NUM>) and comprising:
a magnetic core (<NUM>) axially crossed by a plurality of slots (<NUM>);
a stator winding (<NUM>) comprising a plurality of bars (<NUM>), which are arranged inside the slots (<NUM>);
a plurality of cooling channels (<NUM>), which, in use, can be flown through by a cooling fluid and are obtained inside the slots (<NUM>) between the bars (<NUM>) of the stator winding (<NUM>); and
a plurality of covering elements (<NUM>), each of which is made of an electrically insulating plastic material, engages a corresponding slot (<NUM>), without clearance, on all sides of the slot (<NUM>) and has, at the centre, a cavity (<NUM>) where a series of corresponding bars (<NUM>) are arranged and the cooling channels (<NUM>) are obtained;
wherein each covering element (<NUM>) has two major side walls (<NUM>) that are opposed and radially oriented and two opposite minor head walls (<NUM>) connect the two major side walls (<NUM>) to each other and have an extension lower than an extension of the major side walls (<NUM>); and
wherein each cooling channel (<NUM>) is delimited by walls (<NUM>, <NUM>) of a corresponding covering element (<NUM>) and by at least one corresponding bar (<NUM>);
the stator (<NUM>) is characterized in that:
each covering element (<NUM>) has seats (<NUM>), each of which consists of two facing and opposite recesses cut into the two major side walls (<NUM>) of the covering element (<NUM>) and is configured to accommodate therein, without clearance, the ends of at least one corresponding bar (<NUM>);
the cooling channels (<NUM>) are arranged next to the seats (<NUM>) where the bars (<NUM>) are arranged;
two annular cooling manifolds (<NUM>, <NUM>) are provided which are arranged at opposite ends of the magnetic core (<NUM>) and into which the cooling channels (<NUM>) flow;
two annular containing bodies (<NUM>) are provided, each of which internally delimits a corresponding cooling manifold and is made of plastic material; and
two annular connection bodies (<NUM>) are provided, which are arranged at the two opposite ends of the magnetic core (<NUM>), are connected without interruptions to all the covering elements (<NUM>) with which they form a single, indivisible assembly, and thus connect all the covering elements (<NUM>) together, and form a support base for the containing bodies (<NUM>) .