Low-pressure cooling circuit

Abstract

The invention relates to an expansion vessel (150) for an axial flow electric motor cooling circuit, comprising: - a container (151) adapted to hold a coolant, - a deformable membrane (152) that delimits two compartments (158, 159) in the container and is adapted to conform to the shape of the surface of the coolant contained in one of said compartments, and - a pressure regulation means (153) for a second of said compartments. Figure for the abstract: Fig. 2

Description

Title of the invention: Low pressure cooling circuit Technical field of the invention

[0001] The present invention relates generally to the cooling of electrical or thermal machines.

[0002] It relates more particularly to an expansion tank for a cooling circuit, comprising a container adapted to contain a cooling liquid.

[0003] The invention finds a particularly advantageous application in the cooling of electrical machines, and in particular in that of axial flux electrical machines.

[0004] It also relates to an engine group comprising an electric motor and a cooling circuit for the electric motor, the inlet and outlet of which are connected to the electric motor and which comprises a coolant pump, a heat exchanger, and an expansion tank. State of the art

[0005] An electric or hybrid motor vehicle has an electric machine for its propulsion.

[0006] For example, the electrical machine may be of the axial flux type and comprise a casing which houses a disc-shaped rotor flanked by one or two stators.

[0007] Each stator comprises a disc-shaped frame on one face of which teeth rise, and coils of electrical wires wound around the teeth.

[0008] During operation, such an electric motor emits a lot of heat, which needs to be evacuated.

[0009] It is then known from document FR2823382 to use oil to cool the motor by circulating it between the motor coils (in spaces called "stator slots"). This solution is quite effective since the oil has dielectric properties and can therefore come into direct contact with the coils to cool them.

[0010] Due to the increase in its temperature during operation of the electric motor, the oil, which is not compressible, increases in volume. It is then known to use an expansion tank to absorb the differences in oil volume when the temperature of the electric motor varies.

[0011] Such an expansion vessel generally comprises a rigid container, closed by a cap equipped with a pressure relief valve, allowing the air contained in the vessel to be evacuated when its pressure exceeds a threshold, and a vacuum valve allowing air to enter the vessel when the pressure therein is below another threshold.

[0012] The pressure in such a vessel can then vary between the two thresholds, so that the pressure of the coolant in the circuit also varies.

[0013] The disadvantage is that it is then difficult to find a solution which, when the pressure increases, guarantees good sealing in the electric motor (to prevent the oil from escaping from the intended path) and a homogeneous flow rate through the different stator notches (to obtain homogeneous cooling of the different coils of the motor). Presentation of the invention

[0014] In order to overcome the aforementioned drawback of the state of the art, the present invention proposes a solution in which the pressure of the coolant remains low, which reduces sealing problems.

[0015] More particularly, the invention proposes an expansion vessel as defined in the introduction, in which a deformable membrane is provided which is adapted to match the shape of the surface of the cooling liquid.

[0016] This deformable membrane separates the coolant from the outside air.

[0017] It is designed to deform in such a way as to absorb on its own the variations of volume of coolant in the cooling circuit.

[0018] It is further designed to deform without requiring a significant increase in coolant pressure.

[0019] Thus, thanks to the invention, the oil pressure at the expansion tank remains substantially equal to atmospheric pressure. However, the pressure at each point of the cooling circuit depends on this pressure. Consequently, the pressure of the coolant at any point of the electric motor remains limited and does not vary from one instant to the next. As a result, the sealing of the cooling circuit is easier to guarantee.

[0020] Other advantageous and non-limiting characteristics of the expansion vessel according to the invention, taken individually or in all technically possible combinations, are the following: - said deformable membrane delimits two compartments in the container, including a compartment adapted to contain the cooling liquid, and a compartment which has a vent opening; - said membrane is elastically stretchable; - said membrane is made of a flexible material and has folds or undulations.

[0021] The invention also relates to an engine group as defined in the introduction, the expansion tank of which is as mentioned above.

[0022] Advantageous and non-limiting characteristics of the engine group in accordance with the invention, taken individually or in all technically possible combinations, are as follows: - the electric motor comprises a casing, a rotor and a stator which is equipped with coils delimiting stator notches between them; - the casing delimits an annular collector whose inlet is connected to the outlet of the cooling circuit and which opens into each of the stator notches via separate openings; - the coolant undergoes a pressure drop between the outlet of the annular collector and the outlet of said openings which is strictly greater than that undergone by the coolant during its passage through the stator notches; - the coolant undergoes a pressure drop between the outlet of the annular collector and the outlet of said openings which is strictly greater than that undergone by the coolant between the outlet of the openings and the inlet of the cooling circuit; - separation means are provided to isolate the cooling liquid circulation paths between each opening and each stator notch; - a baffle is provided between each opening and each stator notch, forcing the coolant to change direction at least twice; - the coolant is an oil.

[0023] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Detailed description of the invention

[0024] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0025] In the attached drawings:

[0026] [Fig-1] is a schematic view of a motor group according to the invention;

[0027] [Fig.2] is a schematic view of the expansion tank of the engine group of [Fig.l];

[0028] [Fig.3] is a schematic view of the electric motor of the motor group of [Fig.l] ; And

[0029] [Fig.4] is a graph illustrating the variation in pressure of the coolant along the cooling circuit and the electric motor of the power unit of [Fig.l].

[0030] In [Fig.l], a motor group 10 is shown which comprises an electric motor 200 and a cooling circuit 100 of the electric motor 200.

[0031] The cooling circuit 100 mainly comprises a pump 110 and a heat exchanger 120 which are connected in series with the electric motor 200 by means of pipes, as well as an expansion tank 150 which is connected to one of the aforementioned pipes.

[0032] The pump 110 could take various forms. Here it is a gear type pump, the inlet of which is directly connected to the electric motor 200 by a first pipe 131 and the outlet of which is directly connected to the heat exchanger 120 by a second pipe 132.

[0033] The heat exchanger 120 has an outlet directly connected to the electric motor 200 by a third pipe 133. It could be an air or water exchanger, in which the cooling of the coolant circulating in the cooling circuit 100 would therefore be done by air or by water.

[0034] This heat exchanger 120 and the pump 110 being well known to those skilled in the art, they will not be described further here.

[0035] The expansion tank 150 is connected by a fourth pipe 134 to the first pipe 131.

[0036] An embodiment of this expansion vessel 150 is more precisely represented in [Fig.2].

[0037] In this embodiment, the expansion tank 150 comprises a container 151 of any shape, for example parallelepiped, adapted to receive coolant. This container 151 is for example made of plastic, in a single piece or in several elements assembled together.

[0038] It is watertight, except at its openings 153, 154 described below.

[0039] This container 151 internally houses a deformable membrane 152 which delimits two compartments 158, 159 in the container 151, separated in a sealed manner.

[0040] One of these compartments, called the lower compartment 158, is designed to receive only coolant. It has an opening 154 on the edge of which the fourth pipe 154 is connected.

[0041] The other of these compartments, called upper compartment 159, is designed to be filled with air.

[0042] The deformable membrane 152 then serves as an interface between the cooling liquid and the air.

[0043] It is therefore solid (i.e. without a hole) and is attached in a sealed manner over its entire periphery to the internal face of the container 151.

[0044] This membrane is described as “deformable” in the sense that it does not prevent the filling or emptying of the lower compartment 158. More precisely here, during operation of the electric motor 200 at full load, when the coolant increases in volume until it reaches a maximum volume, the deformable membrane 152 is designed to deform sufficiently so that the coolant pressure does not vary or varies only slightly (less than 0.1 bar).

[0045] In practice, it could be provided that the membrane is stretchable, like a balloon that is inflated.

[0046] But here, as shown in [Fig.2], the deformable membrane 152 is rather flexible and it has an irregular shape, with folds or undulations, which allows it to match the shape of the surface of the cooling liquid, whatever the volume of liquid contained in the first compartment 158.

[0047] It could thus, for example, be a membrane made of plastic or rubber material, which would perfectly fit (with a minimum of folds) the shape of the top of the container 151 if the latter were filled.

[0048] A means 153 for regulating the air pressure in the upper compartment 159 is provided to ensure that the pressure of the air contained therein does not vary or varies little (by less than 0.1 bar).

[0049] In practice, this means of regulation is a simple vent opening 153 which, when the level of coolant rises in the container 151, allows the air contained in the upper compartment 159 to escape so that its pressure remains equal to atmospheric pressure.

[0050] At this stage, it may be noted that the filling of the cooling circuit 100 may be done via a plug provided not in the expansion tank, but at a distance from it. At the start of filling, it will be necessary to ensure that the lower compartment 158 ​​does not contain any air and then that it does not fill with air. For this, it will be possible, for example, to put the upper compartment 159 under air pressure.

[0051] The electric motor 200 to be cooled is preferably an axial flux type motor.

[0052] A part of this engine is shown in [Fig.3].

[0053] This electric motor 200 conventionally comprises a motor shaft, a casing 231, one or preferably two stators 201 fixed to the casing, and a disc-shaped rotor, which is located between the stators and which is fixed to the motor shaft. This configuration makes it possible, when the stators are supplied with electric current, to rotate the motor shaft around an axis of rotation.

[0054] In the remainder of this presentation, we will only be interested in one of the stators (the two stators being identical or similar).

[0055] As shown in [Fig. 3], this stator 201 comprises a disc-shaped flange 202 centered on the axis of rotation, which is pierced in its center by a central opening 204 for the passage of the motor shaft. It is also pierced on its periphery by openings 203 for fixing the flange to the casing 231.

[0056] The flange 202 thus has a substantially circular peripheral edge, and two flat faces. One of these faces, the one facing the rotor, carries teeth 205 (or “plots”) projecting from the flange 202.

[0057] These teeth 205, here 13 in number, are distributed all around the central opening 204.

[0058] They have cross-sections to the axis of rotation in the overall shape of isosceles trapezoids.

[0059] They are designed to allow the winding of a conductive electric wire around each of them, so as to form coils 220. Once supplied with electric current, these coils 220 make it possible to generate a magnetic field oriented parallel to the axis of rotation, so as to force the rotor to turn around this axis.

[0060] The coils 220 wound on neighboring teeth 205 are located at a reduced but non-zero distance from each other, and they therefore delimit between them a space hereinafter called “stator notch 210”. These stator notches 210 extend in length along a radial axis relative to the axis of rotation, and they have substantially identical sections (apart from manufacturing dispersions).

[0061] The aforementioned cooling circuit 100 is then designed to cool the coolant before passing it through the stator 201 of the electric motor 200, via these stator notches 210.

[0062] The cooling liquid then used is preferably oil, which makes it possible to pass this liquid against the coils 220 of electric wire without fear of electrical problems.

[0063] The casing 231 of the electric motor 200 then has an inlet 232 connected to the third conduit 133, and an outlet connected to the first conduit 131.

[0064] As explained above, this casing 231 delimits a chamber for receiving the rotor and the stators. For this purpose, it comprises a side wall substantially of revolution around the axis of rotation.

[0065] This side wall is partly hollow, so as to internally delimit a toric space, called oil collector 230, into which the oil inlet 232 opens and which makes it possible to distribute the oil towards each of the stator notches 210.

[0066] This oil collector 230 preferably has a symmetry of revolution around the axis of rotation.

[0067] The section of this oil collector could be substantially round or square. However, for reasons of space (the thickness of the side wall of the casing being limited), it will rather be flattened in shape (rectangular or oval).

[0068] Because this oil collector 230 is defined inside the side wall of the casing 131, which may for example be made from a casting, the pressure prevailing there does not pose any difficulty with regard to its sealing.

[0069] The oil collector 230 is connected to the stator slots 210 via ou- openings (not visible) provided in the casing 231 and via openings 211 (visible in [Fig.3]) which are made in the flange 202 of the stator 201 and the number of which is equal to the number of teeth 205.

[0070] The oil, when it emerges from these openings 211, is in a space which extends around the outer periphery of the coils 220 and which is delimited, on one side, by these coils, and, on the other, by the casing 231 (or by a sealing wall).

[0071] Means are then provided for separating this space into as many angular sectors as there are coils 220. These means are here formed by separating partitions 206.

[0072] Thanks to these partitions, each stator notch 210 is supplied with oil via its own opening 211.

[0073] Each opening 211 has a reduced size, which has the function of creating a high pressure drop on the circulation of the oil.

[0074] This pressure drop created by the opening 211 can be supplemented by a reduction in the cross-section of the passage (called the nozzle orifice) of the fluid made in the passage portion between the outlet of the collector and the opening 211. The advantage of this solution is not to reduce the diameter of the opening 211 too much, because the smaller this diameter, the higher the speed of the fluid at the outlet of the opening 211. An overspeed (greater than 3 m / s) can cause damage to the coils which have a fragile varnish layer for their electrical insulation.

[0075] Thanks to the architecture used, the oil flow rates in the different stator notches 210 are substantially identical.

[0076] The cross-section of these openings is for example between 4 and 20 mm2, while that of the oil collector is between 50 and 200 mm2.

[0077] This pressure drop also has the effect of reducing the oil pressure in the stator notches 210, so that it is easier to make these notches watertight.

[0078] Due to manufacturing variations, it happens that the sections of the stator notches 210 are not all exactly identical.

[0079] The openings 211 and the separating partitions 206 are then arranged relative to the inlets of the stator notches 210 so as to form baffles 212 between each opening 211 and each notch inlet, forcing the oil to change direction twice. These baffles 212 then make it possible to participate in the homogenization of the oil flow between the different stator notches 210, and therefore to ensure homogeneous cooling of the different coils 220.

[0080] The oil, when it comes out of these stator notches 210, ends up in a space delimited between the coils 220 and the motor shaft (or between sealing walls). It can then come out through a single outlet 219 of large section, connected to the cooling circuit 210.

[0081] It thus has a larger space at its exit from the notches than that which it had to pass through the stator notches 210. Once it has exited the stator notches 210, it then undergoes a reduced pressure loss.

[0082] In [Fig.4], the variations in the pressure P of the oil when it circulates along the cooling circuit 100 and in the electric motor 200 are shown.

[0083] In this graph, the abscissa axis L represents the curvilinear abscissa of the path taken by the oil, and the ordinate axis P represents the oil pressure.

[0084] At the abscissa point L0, which corresponds to the junction point of the first and fourth pipes 131, 134 (denoted Z0 in [Fig.l]), the oil pressure is equal to the atmospheric pressure PO thanks to the particular architecture of the expansion tank 150.

[0085] From the abscissa point L1, which corresponds to the inlet of the pump 110, the oil pressure increases progressively until reaching a pressure P2 at the outlet of the pump (at the abscissa L2).

[0086] When the oil passes through the heat exchanger 120 (between the abscissa points L2 and L3), the pressure P gradually decreases.

[0087] When it enters the electric motor 200, the oil still has a high pressure P3.

[0088] Due to the reduced section of the openings 211 provided in the stator 201 (possibly supplemented by adjustments), the oil will undergo a significant pressure loss, so that its pressure at the inlet of the stator notches 210 (at the abscissa point L4) will have decreased significantly until reaching a pressure P4. As explained above, this significant drop in pressure will ensure that the oil flow rate is substantially the same in all the stator notches 210. This will also make it easier to guarantee the tightness of the oil passage in the motor.

[0089] The pressure P4 being then reduced, the passage of the oil in the notches will generate a lower pressure loss than that generated by the openings 211 (and possible adjustments), so that at the outlet of the notches (abscissa L5), the pressure P5 is such that:

[0090] [Math.l] P4-P5 < P3 - P4

[0091] As explained above, the outlet of the notches is designed to generate minimal pressure losses, so that at the outlet opening 219 (abscissa L6), the pressure P6 is almost equal to atmospheric pressure.

[0092] Preferably, we can then write:

[0093] [Math.2] P4-P6 <P3-P4

[0094] The present invention is in no way limited to the embodiment described and re presented, but those skilled in the art will be able to make any variation in accordance with the invention.

[0095] The different variants described below may, as far as possible, be combined with each other.

[0096] According to a first variant, the expansion vessel could comprise a bowl-shaped container, closed on top by the deformable membrane. The deformable membrane would then no longer be in a closed enclosure, but would be in direct contact with the outside.

[0097] According to a second variant, the container of the expansion tank could be formed by the deformable membrane itself, which would then be in the form of an inflatable balloon attached to the chassis of the vehicle.

[0098] According to a third variant, the electric motor could be, not axial flux, but radial flux. Indeed, such a motor comprises coils of electric wire wound around radial axes, which delimit between them notches through which it is possible to pass a cooling liquid.

[0099] According to a fourth variant, the cooling liquid could be, not oil, but water. In this variant, it will then be necessary to provide means for sealingly isolating the water from the electrical coils.

[0100] According to a fifth variant, the cooling circuit could be equipped with a degassing vessel making it possible to purge the cooling liquid of its air bubbles.

[0101] This degassing vessel may possibly be equipped with a cap to allow the cooling circuit to be filled with oil.

[0102] For example, the degassing vessel may have an oil inlet and outlet, and be connected to the cooling circuit 100 in parallel with the electric motor 200 (with the inlet connected to the third pipe 133 and the outlet connected to the first pipe 131).

Claims

Claims

1. Expansion tank (150) for a cooling circuit (100) comprising a container (151) adapted to contain a cooling liquid, characterized in that it comprises a deformable membrane (152) which is adapted to match the shape of the surface of the cooling liquid.

2. Expansion vessel (150) according to the preceding claim, wherein said deformable membrane (152) delimits two compartments (158, 159) in the container (151), including a compartment (158) adapted to contain the coolant, and a compartment (159) which has an opening (153) for venting.

3. An expansion vessel (150) according to any preceding claim, wherein said membrane (152) is elastically stretchable.

4. Expansion vessel (150) according to one of the preceding claims, wherein said membrane (152) is made of a flexible material and has folds or undulations.

5. Engine group (10) comprising an electric motor (200) and a cooling circuit (100) of the electric motor (200), the inlet and outlet of which are connected to the electric motor (200), said cooling circuit (100) comprising: - a coolant pump (110), - a heat exchanger (120), and - an expansion tank (150), characterized in that the expansion tank (150) is in accordance with one of the preceding claims.

6. Motor group (10) according to claim 5, in which the electric motor (200) comprises a casing (231), a rotor and a stator (201) which is equipped with coils (220) delimiting between them stator notches (210), in which the casing (231) delimits an annular collector (230) which is connected at the inlet to the outlet of the cooling circuit (100) and which opens into each of the stator notches (210) via separate openings (211).

7. Engine group (10) according to claim 6, in which the coolant undergoes between the outlet of the annular collector (230) and the outlet of said openings (211) a pressure drop which is strictly greater than that undergone by the coolant during its passage in the stator notches (210), and which is preferably slightly greater than that experienced by the coolant between the outlet of the openings (211) and the inlet of the cooling circuit (100).

8. Motor unit (10) according to claim 6 or 7, in which separation means (206) are provided for isolating cooling liquid circulation paths between each opening (211) and each stator notch (210).

9. Engine unit (10) according to one of claims 6 to 8, in which a baffle (212) is provided between each opening (211) and each stator notch (210), forcing the coolant to change direction at least twice.

10. Engine unit (10) according to one of claims 5 to 9, in which the coolant is an oil.

Images