FR3115946A1 - Electrical machine rotor with shutter mask in a flux barrier - Google Patents

Abstract

The present invention relates to a rotor of an electric machine, which comprises at least one housing provided with a permanent magnet (7), at least one flux barrier (8). According to the invention, at least one flow barrier (8) comprises an obturation mask (9) which delimits a passage channel (10) for the cooling fluid in the flow barrier (8). Figure 4 to be published

Description

Electrical machine rotor with shutter mask in a flux barrier

The present invention relates to the field of rotating electrical machines, in particular the cooling of rotors of rotating electrical machines.

It relates more particularly to the fluid cooling of a rotor of a synchro-reluctant rotating electric machine, assisted by permanent magnets.

A rotating electrical machine conventionally comprises a fixed part, the stator, and a rotatable part, the rotor, arranged coaxially one inside the other. The rotor is generally housed inside the stator which carries electric windings generating a magnetic field making it possible to drive the rotor in rotation. The rotor is typically formed of a body formed from a stack of laminations, and placed on a rotating shaft. These sheets include housings for permanent magnets or coils forming magnetic poles at the periphery of the rotor. The magnets can appear on the surface of the rotor or be completely integrated within the rotor. A system of bearings and/or bearings is provided between the rotor and the stator to allow their relative movement.

Electrical machines heat up due to electromagnetic losses (Joule effect losses and iron losses) and mechanical losses. This overheating impairs their operation and leads to the degradation of their performance. For example, if the permanent magnets are not cooled, the magnetic flux is less intense, which leads to a loss of torque and therefore a deterioration in the performance of the electrical machine. Irreversible demagnetization of magnets may occur. The winding is also sensitive to temperature rises: the higher the temperature of the winding, the more the electrical conductivity of the copper and the lifetime of the winding are reduced. As the resistance of the copper increases, there is also a loss in efficiency. The various electromagnetic components of a rotating electric machine, as well as certain insulating materials used in the parts of the electric machine, are thus sensitive to the heating produced in operation, and their cooling is essential to dissipate the heat produced, in order to preserve a good output of the machine, to ensure a repeatability of its performances, to lengthen its lifespan and to limit the maintenance. In addition, the rotor is a critical element, as it is thermally isolated from the stator cooling system. It is therefore desirable to provide a cooling system capable of improving the thermal resistance of the electrical machine.

The search for efficient cooling is therefore a major concern for manufacturers and integrators of rotating electrical machines.

Different types of cooling exist, often adapted to the power of the electric machine, among which air cooling systems, generally of lower efficiency and aggressive for the interior of the engine, liquid cooling systems, for example water , in particular used as soon as the losses are significant as in the case of electric traction motors, or by oil. Other helium or liquid nitrogen cooling systems can be used for electrical machinery in power plants. The patent application (FR 3 057 719) describes in particular a cooling system for an electric machine.

Although air cooling is an economically attractive solution, compared to other cooling systems, it generally has lower efficiency, and is therefore often confined to the cooling of low-power electrical machines. This is the case, for example, in traction applications where air cooling is typically used for electric motors with a power close to 140 kW. Beyond that, a liquid cooling system is often implemented.

Different liquid cooling systems have been developed.

There illustrates an embodiment of a liquid cooling system according to the prior art. There illustrates an electric machine 1, formed of a stator 4 and a rotor 6. The rotor 6 comprises a rotor shaft 2 and a stack of laminations 3 forming the body of the rotor. This figure also shows the coil ends 5 of the stator 4. These coil ends can also be cooled. To cool the rotor 6 and the coil heads 5, a cooling system is provided, it is illustrated by the white arrows. For this embodiment, the rotor shaft 2 is machined to form an axial coolant circulation channel. In addition, the coolant leaves the rotor shaft 2 in three places: at the ends of the rotor 6 (outside the body of the rotor) to be directed towards the coil heads 5 and in the center of the rotor, to cross radially the stack of sheets 3 to be directed into the air gap between the rotor 6 and the stator 4. This cooling system has several drawbacks. In fact, the cooling of the rotor is carried out far from the permanent magnets of the rotor (which are placed in the stack of laminations 3), which does not make it possible to limit the effects which may lead to the demagnetization of the permanent magnets. In addition, the coolant circulates in the air gap and outside the body of the rotor, it will therefore create viscous friction between the rotating part and the fixed part, which will cause losses in the operation of the machine. electric. In addition, this solution requires a long and precise machining of the rotor shaft 2.

The aim of the present invention is to achieve efficient cooling of the rotor of an electric machine, by improving the heat exchanges in particular near the permanent magnets in order to avoid the demagnetization of the permanent magnets and to guarantee good performance of the electric machine. . For this, the present invention relates to a rotor of an electrical machine, which comprises at least one housing provided with a permanent magnet, at least one flux barrier. According to the invention, at least one flow barrier comprises an obturation mask which delimits a passage channel for the cooling fluid in the flow barrier. Thus, thanks to the passage of the cooling fluid in the flux barrier, the invention makes it possible to cool the rotor as close as possible to the permanent magnets, without the need to provide specific machining of the rotor.

The present invention relates to an electric machine rotor, in particular a synchronous electric machine assisted by permanent magnets, comprising at least one housing provided with a permanent magnet, at least one housing forming a flux barrier, and means for cooling the rotor by circulation of a cooling fluid within said rotor, in particular a cooling liquid. At least one flow barrier is equipped with an obturation mask made of non-magnetic material which delimits a passage channel for said cooling fluid within said flow barrier, said passage channel being formed at one end of said flow barrier closest to at least one housing provided with a permanent magnet.

According to one embodiment, a section of said passage channel has substantially the shape of a U.

According to one aspect, said cooling means comprise at least one flange at one end of said rotor which directs said cooling fluid into said passage channel.

Advantageously, said flange comprises at least one substantially radial duct.

According to one implementation, said passage channel has an area which represents between 1% and 10% of the area of said flux barrier.

According to one embodiment, said rotor is formed of at least one stack of laminations mounted on a shaft, each lamination being perforated to form said at least one housing provided with a permanent magnet and said at least one flux barrier.

Advantageously, said shutter mask is a one-piece part having substantially the length of at least one stack of laminations, preferably having substantially the length of said rotor.

According to one embodiment, said sealing mask is made of a material chosen from polymers, preferably the material is chosen from: polyethylene terephthalate PET, phenoplasts PF, poly(phenylene sulfide) PPS, and PPA polyphthalamides.

According to one characteristic, said rotor comprises at least one pair of poles, each pole comprises at least one stage comprising a housing provided with a permanent magnet arranged circumferentially and at least two flux barriers arranged on either side of said permanent magnet and oriented towards the periphery of the rotor.

Advantageously, each pole comprises a plurality of stages arranged radially one above the other.

Advantageously, for at least one stage of said pole, said two flux barriers are equipped with a shutter mask.

Preferably, said stage for which said two flux barriers are equipped with an obturation mask is the stage for which said permanent magnet is closest to the center of said rotor.

According to one implementation, said cooling fluid is an oil.

Furthermore, the invention relates to an electric machine, in particular a synchro-reluctant electric machine assisted by permanent magnets, which comprises a stator and a rotor according to one of the preceding characteristics, said rotor being arranged inside said stator.

Other characteristics and advantages of the device according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the appended figures and described below.

List of Figures

There , already described, illustrates a cooling system according to the prior art.

There illustrates a cooling system according to a first embodiment of the invention.

There illustrates a cooling system according to a second embodiment of the invention.

There illustrates a rotor according to one embodiment of the invention.

There illustrates a longitudinal section of a rotor according to one embodiment of the invention.

The present invention relates to a rotor of an electric machine, in particular an electric machine of the synchro-reluctant type assisted by permanent magnets. However, the present invention is suitable for any electric machine comprising at least one permanent magnet inserted in the rotor.

Examples of synchro-reluctant electric machine rotor assisted by permanent magnets are described in particular in the patent applications: FR3035552 (US2018166947), FR3036870 (US2018159387), FR3051296 (US2019149015), FR3071371 (WO2019052828), FR3071360852 (FR307136085 (WO2020020580), FR3084534 (WO2020020581).

According to the invention, the rotor comprises:

• at least one housing for a permanent magnet, which generates a magnetic flux,
• at least one flux barrier, that is to say a perforation which forms a barrier in the circulation of the magnetic flux, such a flux barrier therefore makes it possible to orient within the rotor the magnetic flux generated by the permanent magnets and the stator,
• means for cooling the rotor by circulation of a cooling fluid, preferably a cooling liquid, within the rotor.

In the remainder of the description, only the preferred variant which uses a cooling liquid is described. However, the invention can also be implemented for a gas.

According to the invention, at least one flux barrier is equipped with a shutter mask made of non-magnetic material. The obturation mask delimits a passage channel for the coolant within the flow barrier. Thus, by this design, the coolant passes through at least one flow barrier, which allows this part of the rotor to be cooled. The shutter mask is a part that partially closes the flow barrier, the unclosed part of the flow barrier forms the passage channel for the coolant. In this way, coolant passes through the rotor only by crossing a portion of the flux barrier, thereby controlling the amount and rate of coolant passing through the rotor. Moreover, the shutter mask being made of non-magnetic material, it does not modify the function of the flux barrier. Another advantage of this embodiment is that the cooling system uses already existing machining and does not require modification of the rotor. In addition, this cooling system generates no viscous friction.

In addition, the coolant passage channel is formed at one end of the flux barrier closest to at least one housing provided with a permanent magnet. Thus, the cooling of the permanent magnet is achieved, which makes it possible to limit the temperature rise of the permanent magnet and its possible demagnetization.

According to one embodiment of the invention, the passage channel can have a cross-section having substantially the shape of a U, preferably the edges of the passage channel correspond to the edges of the flow barrier. Thus, the heat exchange surface between the rotor and the coolant is increased, which promotes heat exchange, and therefore the cooling of the permanent magnets.

Alternatively, the passage channel can have other shapes, for example semi-circular, V-shaped, etc.

Preferably, the passage channel may have a shape which corresponds to the edges of the flux barrier closest to the housing provided with the permanent magnet.

According to an implementation of the invention, the passage channel can have an area which represents between 1% and 10%, of the area of the flux barrier. This range of values makes it possible to limit the quantity and flow rate of coolant. Indeed, the shutter mask aims to calibrate the passage section of the cooling fluid in order to adjust the speed of the flow with the aim of maximizing the evacuation of calories via convective transfers, while limiting as much as possible the pressure drops in the circuit.

The cooling liquid can be of any type, for example water, oil or any similar liquid.

At at least one end of the rotor, there may be a flange, which directs the coolant into the passage channel and vice versa (from the passage channel to the rotor shaft). Thus, the coolant can be led from the rotor shaft to the passage channel and vice versa. Such a flange also seals the rotor.

According to a preferred embodiment, a flange can be provided at each end of the rotor, the first flange can make it possible to conduct the cooling liquid from the shaft of the rotor towards the passage channel, and the second flange can make it possible to recover the coolant coming out of the passage channel and leading it to the rotor shaft.

To direct the coolant, the flange may comprise at least one substantially radial duct. Thus, the circulation of the cooling liquid in the passage channel can be done by centrifugation, and the pressure drops are limited.

According to one aspect of the invention, there can be provided in the flange a conduit per flow barrier equipped with a closing mask, so as to direct the coolant in each passage channel of the coolant.

In addition, the flange may include a cooling liquid outlet provided for projecting a portion of the cooling liquid towards the coil heads provided in the stator. Thus, the cooling system allows cooling of the rotor and of the winding heads of the stator, which makes it possible to simplify the cooling system. According to one aspect, the flange can comprise a plurality of coolant outlets, these outlets can be regularly distributed around the periphery of the flange, in order to ensure a homogeneous distribution of the cooling of the coil heads.

According to one embodiment, the rotor can be formed from at least one stack (also called a "stack") of laminations mounted on a shaft, called the rotor shaft. The laminations are made of ferromagnetic material so as to guide the magnetic flux of the permanent magnets and the stator. The sheets are punched to form the at least one housing provided with the permanent magnet and the at least one flux barrier.

For this embodiment, the shutter mask can be a one-piece part having substantially the length (in the axial direction of the rotor) of at least one stack of sheets, preferably having substantially the length of the rotor (in the direction axial). This embodiment allows simplified mounting of the shutter mask.

Alternatively, the shutter mask may have a thickness substantially equal to the thickness of a sheet. Thus, one can provide a blanking mask per sheet.

According to one aspect, the sealing mask can be made of a polymer material, preferably it can be chosen in particular from polyethylene terephthalate PET, phenoplasts PF, poly(phenylene sulfide) PPS, and polyphthalamides PPA. These materials make it possible not to modify the function of the flux barrier and limit the manufacturing cost of the obturation mask.

According to one embodiment of the invention, the cooling means may comprise baffles formed by the shutter mask, in order to increase the turbulence in the circulation of the cooling liquid close to the permanent magnets.

There illustrates, schematically and in a non-limiting way, a first embodiment of a liquid cooling system according to the invention. There illustrates, according to a longitudinal section of the rotor, an electric machine 1, formed of a stator 4 and a rotor 6. The rotor 6 comprises a rotor shaft 2 and a stack of laminations 3 (called the body of the rotor). This figure also shows the coil ends 5 of the stator 4. To cool the rotor 6, a cooling system is provided, it is illustrated by the white arrows. For this embodiment, the rotor shaft 2 is machined to form an axial coolant circulation channel. In addition, the coolant leaves the rotor shaft 2 at the ends of the rotor 6 (and in the body of the rotor) to be directed radially (for example in a flange - not shown), then axially in a passage channel while remaining in the rotor, and finally the coolant is directed radially (eg in a flange – not shown) to the rotor shaft 2.

There illustrates, schematically and in a non-limiting manner, a second embodiment of a liquid cooling system according to the invention. There illustrates, according to a longitudinal section of the rotor, an electric machine 1, formed of a stator 4 and a rotor 6. The rotor 6 comprises a rotor shaft 2 and a stack of laminations 3 (called the body of the rotor). This figure also shows the coil ends 5 of the stator 4. These coil ends can also be cooled. To cool the rotor 6 and the coil heads 5, a cooling system is provided, it is illustrated by the white arrows. For this embodiment, the rotor shaft 2 is machined to form an axial coolant circulation channel. In addition, the coolant leaves the rotor shaft 2 at the ends of the rotor 6 (and in the body of the rotor) to be directed radially (for example in a flange - not shown), then axially in a passage channel while remaining in the rotor, and finally the coolant is directed radially (eg in a flange - not shown) to the rotor shaft 2. In addition, a small part of the coolant is directed to the heads of coils 5, from the flanges.

According to one embodiment, the rotor comprises at least one pair of magnetic poles. A magnetic pole of the rotor comprises at least one permanent magnet oriented along a magnetic direction, and, in a pair of magnetic poles, the permanent magnets are oriented along opposite magnetic directions (for example if in a first pole, the permanent magnet is oriented so that its north polarity faces the rotor periphery, then in the second pole the permanent magnet is oriented so that its south polarity faces the rotor periphery).

Each magnetic pole has at least one stage, which may include a housing provided with a circumferentially disposed permanent magnet (in other words, the permanent magnet is substantially perpendicular to a radius of the rotor), and at least two flux barriers arranged on either side of the housing provided with the permanent magnet. The flux barriers are oriented towards the periphery of the rotor. In other words, a stage can have substantially the shape of a V with a flat bottom, for which the flat bottom is formed by the housing provided with the permanent magnet, and the bars of the V are formed by the flux barriers .

According to one implementation of this embodiment, each magnetic pole may comprise a plurality of stages arranged radially one above the other. In other words, each magnetic pole can comprise several permanent magnets arranged on the same radius of the rotor (in other words the magnets are arranged in a radial direction of the rotor), one above the other, and spaced each other, and each permanent magnet is associated with two flux barriers oriented towards the periphery of the rotor). This implementation makes it possible to increase the magnetic flux of each pole. For example, each magnetic pole can comprise two, three or four floors, or even more.

For this implementation of the rotor, at least one stage of each pole can be equipped with shutter masks. In this case, for at least one stage of each pole, the two flux barriers are equipped with a shutter mask. Thus, the permanent magnet of the considered stage is cooled on two sides, which makes it possible to significantly lower the temperature of the permanent magnet.

According to a first variant embodiment, the stage for which the flux barriers are equipped with an obturation mask is the internal stage, that is to say the stage for which the permanent magnet is most close to the center of the rotor. Indeed, the permanent magnet closest to the center of the rotor is the permanent magnet which is subjected to greater temperatures.

According to a second variant embodiment, the stage for which the flux barriers are equipped with an obturation mask is an external stage, that is to say the stage for which the permanent magnet is closest. from the periphery of the rotor.

According to a third variant embodiment, the stage for which the flow barriers are equipped with a shutter mask is an intermediate stage, that is to say a stage located between the internal stage and the external stage. .

These three alternative embodiments can be combined, and thus several, or even all of the stages can include flow barriers with obturation masks.

For this implementation of the invention, lateral permanent magnets can also be provided in at least one stage. Such a configuration is disclosed in particular in the patent application FR 3094583. For example, the internal stage can comprise a central permanent magnet and two side magnets instead of the flux barriers, an intermediate stage and/or the external stage can include a central permanent magnet, and lateral flux barriers, at least two lateral flux barriers of an intermediate and/or outer stage can be equipped with an obturation mask to form passage channels for the coolant.

According to a preferred embodiment, the rotor may comprise four pairs of poles, each pole comprises three stages (an internal stage, an intermediate stage and an external stage), each stage comprises a circumferential permanent magnet and two flux barriers on either side on the other side of the permanent magnet, the whole having the shape of a V with a flat bottom, and only the flux barriers of the internal stage are equipped with obturation masks. This achievement makes it possible to greatly reduce the temperature of the magnets, and therefore allows gains in motor efficiency, as illustrated in the comparative example below.

Other configurations of the magnetic poles can be envisaged, for example magnets positioned in a V as described in particular in patent application US2017040854, or stages of arcuate shape as described in particular in patent application US2016380492, etc.

There illustrates, schematically and in a non-limiting way, in front view a sheet of a rotor according to a preferred embodiment of the invention. Sheet 3 is perforated in its center for attachment to a rotor shaft 2. Sheet 3 is perforated to form housings for permanent magnets 7, and flux barriers 8. Sheet 3 shown has four pairs of magnetic poles . Each pole has three floors arranged one above the other. Each stage has substantially the shape of a V with a flat bottom, for which the flat bottom is formed by the housing provided with the permanent magnet 7, and the bars of the V are formed by the flux barriers 8. The flux barriers 8 internal (closest to the center of the rotor) include shutter masks 9. The shutter masks 9 partially block the flow barriers 8, to form passage channels 10 of the coolant. The passage channels 10 of the cooling liquid are arranged close to the permanent magnet 7, and have substantially a U-shape.

There illustrates, schematically and in a non-limiting manner, a rotor according to one embodiment of the invention, in cross-sectional view along the direction AA of the . The rotor 6 comprises a rotor shaft 2, seven stacks 11 of sheets, two flanges 12 placed at each end of the rotor. The rotor 6 also comprises an obturation mask 9 which delimits a passage channel 10 in a flow barrier of the rotor 6. The cooling system comprises a channel 15 in the rotor shaft 2, the passage channel 10 in the rotor 6 and a conduit 13 in each flange 12 which connects the channel 15 of the rotor shaft to the passage channel 10 in the rotor. In addition, the cooling system includes an orifice 14 to project part of the cooling liquid towards the coil heads provided in the stator (not shown).

The invention also relates to an electric machine, which comprises a stator and a rotor according to any one of the variants or combinations of variants as described above. The rotor is arranged inside the stator. Conventionally, the stator comprises windings to generate a rotating magnetic field capable of rotating the rotor relative to the stator.

According to one embodiment, the electric machine is a synchro-reluctant machine assisted by permanent magnets.

It goes without saying that the invention is not limited solely to the embodiments of the rotor, described above by way of example, on the contrary it embraces all variant embodiments.

Comparative example

The characteristics and advantages of the rotor according to the invention will appear more clearly on reading the comparative example below.

In this example, the heat exchanges within a rotor of a synchro-reluctant machine, assisted by permanent magnets, are simulated, as illustrated in FIGS. 4 and 5, with a variation in the location of the passage channel in the various flow barriers, at the operating point 14,000 rpm at 50 kW. The rotor is cooled with oil having a temperature of 60°C.

Example n°1 (according to the prior art)

This example corresponds to the electric machine of FIGS. 4 and 5 without a cooling system.

Example n°2 (according to the prior art)

This example corresponds to a cooling system of the electrical machine in accordance with the , with the design of the rotor according to Figures 4 and 5 (without a coolant passage channel in the flow barriers).

Example No. 3 (according to the invention)

This example corresponds to the electric machine of figures 4 and 5 with the passage channel in the flux barriers of the external stage.

Example No. 4 (according to the invention)

This example corresponds to the electric machine of figures 4 and 5 with the passage channel in the flux barriers of the intermediate stage.

Example No. 5 (according to the invention)

This example corresponds to the electrical machine of Figures 4 and 5 with the passage channel in the internal stage flux barriers.

Example No. 6 (according to the invention)

This example corresponds to the electrical machine of Figures 4 and 5 with the passage channel in all the flux barriers (external, intermediate and internal).

After these simulations, the temperatures are compared for the different examples, the results are reported in Table 1:

Example Max rotor temperature (°C) Max magnet temperature (°C) Rotor Gain (°C) Magnet gain (°C) 1 164 180 2 144 161 20 19 3 146 160 18 20 4 125 135 39 45 5 114 127 50 53 6 97 103 67 77

In this table 1, the gain is expressed relative to example no. 1 according to the prior art. It is noted that the invention makes it possible to reduce the temperature of the magnets, whatever the location of the passage channel of the coolant in the flow barriers. We also note that examples 5 and 6 make it possible to minimize the temperatures of the rotor and the magnets by at least 50°C, which allows significant gains in the efficiency of the motor.

Claims (14)

Rotor of an electric machine, in particular a synchronous electric machine assisted by permanent magnets, comprising at least one housing provided with a permanent magnet (7), at least one housing forming a flux barrier (8), and means for cooling the rotor by circulation of a cooling fluid within the said rotor, in particular a cooling liquid, characterized in that at least one flow barrier (8) is equipped with an obturation mask (9) made of non-magnetic material which delimits a passage channel (10) for said cooling fluid within said flow barrier, said passage channel (10) being formed at one end of said flow barrier (8) closest to at least one housing provided of a permanent magnet (7). Rotor according to claim 1, wherein a section of said passage channel (10) is substantially U-shaped. Rotor according to one of the preceding claims, in which the said cooling means comprise at least one flange (12) at one end of the said rotor which directs the said cooling fluid into the said passage channel (10). Rotor according to Claim 3, in which the said flange (12) comprises at least one substantially radial conduit (13). Rotor according to one of the preceding claims, wherein said passage channel (10) has an area which represents between 1% and 10% of the area of said flux barrier (8). Rotor according to one of the preceding claims, in which the said rotor is formed of at least one stack of sheets mounted on a shaft (2), each sheet being perforated to form the said at least one housing provided with a permanent magnet (7) and said at least one flux barrier (8). Rotor according to Claim 6, in which the said shutter mask (9) is a one-piece piece having substantially the length of at least one stack of laminations, preferably having substantially the length of the said rotor. Rotor according to one of the preceding claims, in which the said sealing mask (9) is made of a material chosen from polymers, preferably the material is chosen from: polyethylene terephthalate PET, phenoplasts PF, poly (phenylene sulfide) PPS, and polyphthalamides PPA. Rotor according to one of the preceding claims, in which the said rotor comprises at least one pair of poles, each pole comprises at least one stage comprising a housing provided with a permanent magnet (7) arranged circumferentially and at least two flux barriers arranged (8) on either side of said permanent magnet and oriented towards the periphery of the rotor. A rotor according to claim 9, wherein each pole has a plurality of stages arranged radially one above the other. Rotor according to claim 10, wherein for at least one stage of said pole, said two flux barriers (8) are equipped with an obturation mask (9). Rotor according to claim 11, wherein said stage for which said two flux barriers (8) are equipped with an obturation mask (9) is the stage for which said permanent magnet is closest to the center of said rotor. Rotor according to one of the preceding claims, in which the said cooling fluid is an oil. Electric machine, in particular a synchro-reluctant electric machine assisted by permanent magnets, characterized in that it comprises a stator (4) and a rotor (6) according to one of the preceding claims, the said rotor (6) being arranged at inside said stator (4).