FR2823382A1 - Oil cooling of hybrid vehicle electric propulsion motor, uses restrictors in stator oil channels to improve cooling effect - Google Patents

Abstract

In each of slots (9), the active parts (11a,11b) of a winding (10) are applied against the slot walls and are dimensioned so as to form between them a circulation channel through which a cooling fluid can flow. Cooling fluid obstructers (20) are placed in the channels (14). Electric propulsion motor whose stator (1) has a cooling circuit through which oil passes circulating in stator slots (9) to remove heat generated by the stator winding (10). The bore delimited by the stator is covered by a collar (15) sealing flanges (5,6) of the motor so as to define with them and the motor casing (4) two annular chambers (16,17) in which the cooling fluid bathes the heads of the winding (12a,12b). The chambers are respectively have a supply orifice and an output orifice for the cooling fluid.

Description

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 The present invention relates to an electric motor and more particularly to a cooling system of such a motor.

 An electric motor is usually cooled by air, water or oil.

 Air cooling has the advantage of simplicity and low cost, since it suffices to mount a fan wheel on its shaft to blow air on the coils. However, its efficiency is relatively low, so that it is mainly used in low power electric motors.

 Water cooling is generally based on a circulation of water around the motor housing. It has better thermal efficiency than air cooling, but this efficiency is limited by the multiple thermal resistors interposed between the coolant and the coils. Water can therefore only circulate at a relatively low temperature (for example between 65 C and 70oC). In addition, this type of cooling is relatively bulky.

 In the context of an electric motor, direct oil cooling has an important advantage because of the very good insulating properties of the oil. On the other hand, it is more difficult to implement than cooling with water, since the oil has a high viscosity and a low thermal conductivity so that its capacity as a coolant is low.

 However, since the oil can be brought directly into contact with the coils, it is possible to extract the calories as close as possible to the heat source, so that, ultimately, its overall cooling capacity is better than that of water.

 From document US 5,519,269, it is known to cool an electric motor with oil as

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 coolant. In this case, the winding of the stator of the motor is produced in round wire and the oil is caused to circulate between the wires of the winding in the stator notches.

A ferrule is placed between the stator and the rotor, extending to the end flanges closing the stator casing so that the oil circulates not only in the stator notches but also in the spaces where the coil heads are located.

 If in this arrangement, the oil is effectively brought into direct contact with the winding, this arrangement has the disadvantage that, due to the small space reserved for the oil to circulate between the wires of the winding, the circulation of the oil has a very high pressure drop, especially given its relatively high viscosity. The efficiency of cooling is strongly felt.

 It is also known from document US Pat. No. 5,973,427 to cool an electric motor by circulating water in sheaths which pass through the stator notches between the bundles of wires forming the coils. In this way, the water is isolated from the winding, which from the safety point of view is satisfactory. However, the cooling efficiency in this case is mediocre precisely by the absence of contact between the heat transfer fluid and the coil wires. In addition, this solution is complex, because it requires the insertion of specially designed sealed sheaths in the stator notches as well as the sealed connection of the sheaths at the coil heads.

 The object of the invention is to provide an electric motor comprising a cooling system devoid of the aforementioned drawbacks.

 The invention therefore relates to an electric motor, the stator of which is provided with a cooling circuit traversed by oil as a heat-transfer fluid which circulates in the stator notches to evacuate the

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 heat generated by the stator winding of this motor, the bore delimited by the stator being coated by a ferrule sealingly closing on the puddles of the motor to define therewith and the motor casing two annular chambers in which said fluid heat transfer medium bathes the heads of said winding, said chambers being respectively provided with a supply orifice and a discharge orifice for said heat transfer fluid, characterized in that in each of said notches, the active parts of said winding are applied against the walls of the notch and dimensioned so as to delimit between them a circulation corridor in which flows said heat transfer fluid.

 Thanks to these characteristics, the heat transfer fluid can circulate in a relatively large space which does not impose a high pressure drop on the flow of the heat transfer fluid, even if the latter is oil having a high viscosity.

 According to a particularly advantageous characteristic of the invention, a means of obstructing the circulation of said heat transfer fluid is placed in each of said corridors.

 This characteristic makes it possible to considerably favor the coefficient of heat exchange between the stator winding and the heat-transfer fluid, the latter being forced, to circumvent the obstruction means to follow a more or less tortuous path in the corridors provided between the active parts. of the winding.

 According to other advantageous features of the invention, said obstruction means comprises at least one strip mounted in said corridor over the entire length of the latter and provided with distance by distance of projections extending radially in said corridor while providing in the latter a passage for said heat transfer fluid;

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 said projections have a cross section whose area decreases radially inward relative to the axis of the stator; the cross section of said projection is triangular and one of the angles of this section faces downstream with respect to the flow of said heat transfer fluid; the cross section of said projection is square or circular; the cross section of said projection is rectangular and preferably placed obliquely to the flow of said heat transfer fluid; said strip extends to the flanges of the casing which serve as its longitudinal support; said strip is provided with lateral projections resting on said active parts of the winding to position said strip in the transverse direction in said passage; two strips are mounted in each of said corridors, one at its radially outer end and the other at its radially inner end, said radially extending projections being provided on the faces of said strips facing one another, the lengths of said projections being less than the distance between the two strips; plugs are placed between said flanges and the heads of said coil alternately on either side of this coil to define a meandering path for said heat transfer fluid.

 The subject of the invention is also a propulsion unit for a hybrid motor vehicle comprising a heat engine provided with a cooling circuit, a gearbox and an electric motor mechanically coupled to the gearbox and comprising one or more of the characteristics as defined above

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 above, this propellant assembly being characterized in that the oil circulating in said gearbox is the heat transfer fluid of said electric motor and a circulation circuit of said heat transfer fluid is provided in which said electric motor and said gearbox are inserted series with a circulation pump and one side of a heat exchanger, the other side of the latter being inserted in the cooling circuit of said heat engine.

 Other characteristics and advantages of the present invention will appear during the description which follows, given solely by way of example and made with reference to the appended drawings in which: FIG. 1 is a view in axial half-section, taken along line 1-1 of FIG. 2, of an electric motor provided with a cooling system according to the invention; Figure 2 is a partial sectional view of this engine taken along line II-II of Figure 1; Figure 3 is a perspective view of a possible form of an obstruction means intended to influence the flow of the heat transfer fluid; Figure 4 is a perspective view of another possible form of an obstruction means; Figure 5 is a side elevational view of yet another form of obstruction means; Figure 6 shows a perspective view of this same element; FIG. 7 shows several possible shapes of the teeth of an obstruction means; FIG. 8 shows a partial view, developed in a plane, of the stator of an electric motor according to the invention, as well as a preferred form of circuit for the heat transfer fluid; and Figure 9 is a diagram of an example of a

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 drive line of a hybrid motor vehicle equipped with an electric motor designed according to the invention.

 In Figures 1 and 2, there is partially shown an electric motor provided with a cooling system according to the invention.

 The motor comprises a stator 1 and a rotor 2 fixed on a shaft 3 of axis X-X. The assembly is housed in a casing 4 closed by lateral flanges 5 and 6.

 Conventionally, the stator 1 comprises a stack of sheets 7 forming stator teeth 8 between which are located notches 9 serving to house a winding 10.

 The winding preferably consists of coils wound tooth by tooth, the turns of these coils closing each time around a tooth 8. Each coil thus has two active parts 11a and 11b extending respectively in contiguous notches 9 and two coil heads 12a and 12b (see FIG. 8) located respectively at the ends of the stator stack 7.

 A sheet 13 of insulating material covers the wall of each notch 9 to separate the corresponding coil from the sheets of the stator stack 7.

 In FIG. 2, it can be seen that according to the invention, the active parts 11a and 11b of each coil are placed against the sides of the tooth 8 around which this coil is wound. Therefore, there remains a central corridor 14 in each notch 9 which has in section a trapezoid shape in the embodiment shown.

 Each passage 14 constitutes a passage for the oil used as the heat transfer fluid. It is closed longitudinally by a ferrule 15 inserted in the cylindrical bore formed in the stator stack 7. It is coaxial with the shaft 3 of the motor. This ferrule 15 extends on either side to the flanges 5 and 6 so as to create

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 two annular chambers 16 and 17 in which the coil heads 12a and 12b are located.

 Each of these annular chambers 16 and 17 opens to the outside through a lateral orifice, 18 respectively 19. Fittings not shown are fixed externally on the casing 4 in communication with the orifices 18 and 19 and pipes (not shown here ) bringing the oil from a circulation pump and pumping it towards it after passing through the electric motor.

 In the preferred embodiment of the invention, an obstruction means 20 is placed in each passage 14 of the stator 1. It is formed by at least one strip 21 (FIG. 3) intended to be placed against the bottom of the passage corresponding. This strip has a length such that its ends are in abutment against the respective flanges 5,6 (Figure 1).

 In FIG. 3, the strip 21 has lateral positioning projections 22 in the form of a half-moon provided from distance to distance along its two edges. These projections make it possible to position the strip 21 in the middle of the corridor 14. It also has teeth 23 which extend on one side and which are also provided from distance to distance according to its length. These teeth 23 have a wedge shape and are tapered towards their free end, that is to say that their cross section decreases radially with respect to the axis X-X from the outside to the inside. This section is further dimensioned in such a way that the teeth 23 do not block the passage for the heat transfer fluid in the passage 14. The longitudinal dimension of the teeth 23 is chosen so that their point 24 is supported on the ferrule 15. Thanks to this construction, each strip 21 is locked in position in the corresponding notch 9 and cannot be moved either by vibrations or by the pressure exerted by the heat transfer fluid circulating in the corridor 14.

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FIG. 4 represents a variant 20A of the obstruction means. In this case, the strip 21A proper is slightly wider than the strip 21 and its positioning projections 22A are of smaller lateral dimension than the half-moons of FIG. 3. Here they have a rectangular shape, while the teeth 23 have the same shape as before.

 Figures 5 and 6 show another variant 20B of the obstruction means. In this case, each means comprises two strips 21B-a and 21B-b arranged in opposition in a notch passage 14. The width of the strip 21B-a located radially outwards is adapted to the width at this location of the corridor 14, while that of the strip 21Bb, radially inside has a width adapted to the narrow part of this corridor located near the ferrule 15.

 Each strip 21B-a and 21B-b here also has teeth 23B-a, 23B-b respectively, of radial dimension clearly less than the radial dimension of the corridor 14, but of width which may be that of the corridor at the corresponding place. The heat transfer fluid then flows as shown in FIG. 5.

 Figure 7 shows several examples of sections that can be given to the teeth of the strips 21 and 21A of Figures 3 and 4. This section (25) is triangular in a), the point of the triangle is preferably directed upstream of the flow of heat transfer fluid.

 FIG. 7b shows a flat section 26 placed obliquely with an inverted inclination from one tooth to the other with respect to the direction of flow of the heat transfer fluid.

 Figure 7c shows a rectangular section 27, while in Figure 7d it is circular (28).

 In all the cases represented in FIG. 7, the area of the cross section of the teeth can decrease radially inwards, preferably adapting to the shape of the section of the passage 14.

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 The obstruction means 20, 20A and 20B described above can be manufactured by injection molding of an insulating material compatible in particular with the operating temperature of the engine and the nature of the heat transfer fluid.

 According to another variant of the invention, they can be made in one piece with the protective sheet 13 which lines the wall of each notch 9.

 Although in the simplest embodiment that can be envisaged in the context of the invention, the lanes 14 delimited in the notches 9 between the active parts 11a and 11b of the coils of the winding 10, can be devoid of any means of obstruction of the flow of heat transfer fluid, all forms of obstruction means as described above bring the advantage of creating in each of these corridors a disturbance with respect to an unimpeded flow, which results in a deformation of the fluid vein with possibly the creation of vortices in the flow.

This deformation makes it possible to locally increase the heat exchange coefficient between the winding 10 and the heat transfer fluid. The disruptive degree of the obstruction means must be chosen in such a way that a good compromise is obtained between the importance of the pressure drop which they introduce and this improvement in the heat exchange coefficient. However, it should be noted that the pressure drop can be kept at a relatively low value due to the relatively large dimensions of the passage section of the passage, even if it is obstructed by the teeth of the strips.

 FIG. 8 represents another advantageous variant of the invention aiming to pass the heat-transfer fluid along meanders which make it circulate in opposite directions in groups of neighboring notches 9. These meanders can easily be obtained by placing in the chambers

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 end annulars 16 and 17 of the plugs 29 provided alternately in one chamber and in the other by admitting for example a flow in one direction in two adjacent notches 9 then a flow in the opposite direction in two following notches.

 FIG. 9 schematically shows an example of a hydraulic circuit that can be used for an electric motor designed according to the invention in a hybrid vehicle.

 The supply and discharge connections 18 and 19 of the electric motor 30 are advantageously connected in an oil circuit comprising an oil circulation pump 31 discharging through a line 32 to a filter 33 also connected to a heat exchanger 34 by a pipe 35, the exchanger 34 being in turn connected to the supply connection 18 of the electric motor 30 via a pipe 36.

 On the line 36 is connected in diversion a line 37 which leads to a gearbox 38 mechanically coupled to the electric motor 30. The latter and the gearbox are connected to a tarpaulin 39 respectively by lines 40 and 41.

 In this case, the heat exchanger 34 can be crossed by the cooling water circuit of the heat engine 42 of the vehicle, this circuit comprising a circulation pump 43 and a radiator 44 making it possible to evacuate the calories to the outside. of the vehicle. Conventionally, this cooling water circuit also comprises, in parallel on the radiator 44, a radiator 45 for heating the passenger compartment of the vehicle and a thermostat 46, inserted in series in the circuit.

 In this example, the oil in the gearbox 38 is therefore the heat transfer fluid which allows the heat from the electric motor 30 according to the invention to be removed towards the exchanger 34 which in turn discharges the calories to the circuit of water cooling the engine of the hybrid vehicle.

Claims (14)

 CLAIMS 1. Electric motor whose stator (1) is provided with a cooling circuit traversed by oil as a heat transfer fluid which circulates in the stator notches (9) to evacuate the heat generated by the stator winding (10 ) of this motor, the bore delimited by the stator being coated with a ferrule (15) sealingly closing on the puddles (5,6) of the motor to define therewith and the casing (4) of the motor two annular chambers (16,17) in which said heat transfer fluid bathes the heads of said winding (12a, 12b), said chambers (16,17) being respectively provided with a supply orifice (18) and a orifice delivery (19) of said heat transfer fluid, characterized in that in each of said notches (9), the active parts (11a, llb) of said coil (10) are applied against the walls of the notch and dimensioned so as to delimit therebetween a circulation corridor (14) in which s said coolant flows.  2. Electric motor according to claim 1, characterized in that an obstruction means (20; 20A; 20B) of the circulation of said heat transfer fluid is placed in each of said corridors (14).  3. Electric motor according to claim 2, characterized in that said obstructing means (20; 20A; 20B) comprises at least one strip (21; 21A; 21B-a; 21B-b) mounted in said passage (14) over the entire length thereof and provided with distance by distance from projections (23; 23B-a; 23B-b) extending radially in said corridor while providing in the latter a passage for said heat transfer fluid.  4. Electric motor according to claim 3, characterized in that said projections (23; 23B-a, 23B-b) have a cross section whose area decreases <Desc / Clms Page number 12>  radially inwards with respect to the X-X axis of the stator (1).  5. Electric motor according to claim 4, characterized in that the cross section of said projection is triangular (25) and in that one of the angles of this section is turned downstream relative to the flow of said fluid coolant.  6. Electric motor according to claim 4, characterized in that the cross section of said projection is square or circular.  7. Electric motor according to claim 4, characterized in that the cross section of said projection is rectangular (27).  8. Electric motor according to claim 7, characterized in that said rectangular section (27) is placed obliquely with respect to the flow of said heat transfer fluid.  9. Electric motor according to any one of claims 3 to 8, characterized in that said strip (21; 21A; 21B-a, 21B-b) extends to the flanges (5,6) of the housing (4 ) which serve as its longitudinal support.  10. Electric motor according to any one of claims 1 to 9, characterized in that said strip (21; 21A) is provided with lateral projections (22; 22A) resting on said active parts (lla, llb) of the winding. (10) for positioning said strip in the transverse direction in said corridor (14).  11. Electric motor according to any one of claims 3 to 10, characterized in that two strips (21B-a, 21B-b) are mounted in each of said corridors (14), one at its radially outer end and the 'other at its radially inner end, and in that said radially extending projections (23B-a, 23B-b) are provided on the faces of said strips facing one another. <Desc / Clms Page number 13>  12. Electric motor according to claim 11, characterized in that the lengths of said radially extending projections (23B-a, 23B-b) are less than the distance between the two strips (21B-a, 21B-b).  13. Electric motor according to any one of the preceding claims, characterized in that plugs (29) are placed between said flanges (5,6) and the heads (12a, 12b) of said coil (10) alternately on the side and on the 'other of this winding to define a meandering path for said heat transfer fluid.  14. Propellant assembly for a hybrid motor vehicle comprising a heat engine (38) provided with a cooling circuit, a gearbox (35) mechanically coupled to an electric motor (30) according to any one of the preceding claims, said assembly being characterized in that the oil circulating in said gearbox (35) is the heat transfer fluid of said electric motor and in that a circulation circuit of said heat transfer fluid is provided in which said electric motor is inserted (30) and said gearbox (35) in series with a circulation pump (31) and one of the sides of a heat exchanger (33), the other side of the latter being inserted in the circuit of cooling of said heat engine (38).