Electric machine and electric axle drive train

Abstract

Electric machine (1), in particular for a drive train (2) of a motor vehicle (3), comprising a stator (4) and a rotor (5) rotatable relative to the stator (4), wherein the stator (4) and / or rotor (5) are connected to a first cooling circuit (7) through which a cooling fluid (6) flows, wherein the stator (4) has a cooling element (9) coupled to the jacket (8) of the stator (4) which provides a receiving volume (10) for receiving cooling fluid (6), and a two-way valve (11) is arranged in the first cooling circuit (7), wherein the receiving volume (10) of the cooling element (9) is hydraulically connected to the two-way valve (11), and the two-way valve (11) is configured such that in a first switching position (12) it connects the first cooling circuit (7) to the receiving volume (10) of the cooling element (9) and in a second switching position (13) it disconnects the receiving volume (10) of the cooling element (9) from the first cooling circuit (7), characterized by the fact that In the second switching position (13) the receiving volume (10) is connected via the two-way valve (11) to a cooling fluid reservoir (17), into which cooling fluid (6) can flow from the receiving volume (10) by gravity.

Description

[0001] The present invention relates to an electric machine, in particular for a motor vehicle drive train, comprising a stator and a rotor rotatable relative to the stator, wherein the stator and / or rotor are connected to a first cooling circuit through which a cooling fluid flows. The invention further relates to an electric axle drive train.

[0002] Electric motors are increasingly being used for propulsion in motor vehicles to create alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday usability of electric drives and to offer users the familiar driving comfort.

[0003] A detailed description of an electric drive can be found in an article in the journal ATZ, 113th year, 05 / 2011, pages 360-365, by Erik Schneider, Frank Fickl, Bernd Cebulski and Jens Liebold, entitled: Highly Integrated and Flexible Electric Drive Unit for E-Vehicles. Such drive units are also referred to as e-axles or electrically operated drive trains.

[0004] In addition to purely electric powertrains, hybrid powertrains are also known. Such powertrains in hybrid vehicles typically comprise a combination of an internal combustion engine and an electric motor, enabling – for example, in urban areas – purely electric operation while simultaneously providing sufficient range and availability, especially on long-distance journeys. Furthermore, it is possible to use both the internal combustion engine and the electric motor simultaneously in certain operating situations.

[0005] In the development of electric motors intended for e-axles and hybrid modules, there is a continuing need to increase their power densities, making the cooling of these electric motors increasingly important. Due to the required cooling capacity, hydraulic fluids, such as cooling oils, have become the standard in most designs for dissipating heat from the thermally stressed areas of an electric motor.

[0006] For the stators of electric machines, for example, shell cooling and end-winding cooling are known from the prior art for implementing cooling of electric machines using hydraulic fluids. While shell cooling transfers the heat generated at the outer surface of the rotor lamination stack into a cooling circuit, in end-winding cooling the heat transfer occurs directly at the conductors outside the rotor lamination stack in the area of ​​the winding ends into the fluid.

[0007] Besides cooling the stators, it is also generally known to cool the rotors of electric machines. However, an unwanted leak between the rotor laminations can lead to drag torques in the air gap between the rotor and stator and uncontrolled coolant loss, which is generally undesirable.

[0008] In addition to such fluid-cooled rotors with a hollow shaft, air-cooled rotors are also known in the prior art, for example, with a paddle wheel mounted axially on the rotor. A summary of the relevant prior art can be found, for example, in DE 10 2018 220 810 A1.

[0009] It is also known that centrifugal force can be used to guide a coolant through the rotor at rotational speed. For example, US 11,146,133 B2 describes the use of cooling channels with increasing pitch circle diameters, while DE 10 2017 112 348 A1 describes a conically expanding shaft. In these cases, the work required to circulate the coolant is performed by the electric machine itself and not by an external oil pump.

[0010] From DE 10 2022 213 854 A1 an electrical machine according to the preamble of claim 1 is known.

[0011] In such fluid-cooled drive systems, for example, the motor housing or the oil sump housing of an electric machine is designed, taking into account the temperature-dependent volume change of the hydraulic fluid, so that the hydraulic fluid level can be maintained within predefined limits across the entire temperature range. This generally results in an increased installation space requirement for the electric machine. Thus, on the one hand, the hydraulic fluid level is high at high temperatures, which can lead to, for example, hydraulic fluid splashing through gears (increased resistance). On the other hand, the fluid level is low at low temperatures, which can result in unstable hydraulic fluid flow, for example, when driving uphill or downhill.

[0012] Another challenge in the development of electric drive systems for motor vehicles is the fact that there are conflicting requirements for heat dissipation through the motor housing in hot and cold environments. In hot environments, for example, under high load on the electric motor or on hot summer days, it is desirable for the thermal conductivity of the motor housing to be high. In cold environments, for example, in winter or when the electric motor has not yet reached operating temperature, it is desirable for the thermal conductivity of the housing to be as low as possible so that the heat can be used, for example, to heat the high-voltage battery.

[0013] It is therefore an object of the invention to avoid or at least reduce these disadvantages known from the prior art and to provide an electric machine with improved thermal management. It is also an object of the invention to realize an optimized electric axle drive train.

[0014] This problem is solved by an electric machine, in particular for a motor vehicle powertrain, comprising a stator and a rotor rotatable relative to the stator, wherein the stator and / or rotor are connected to a first cooling circuit through which a cooling fluid flows, wherein the stator has a cooling element coupled to the stator shell which provides a receiving volume for receiving cooling fluid, and a two-way valve is arranged in the first cooling circuit, wherein the receiving volume of the cooling element is hydraulically connected to the two-way valve, and the two-way valve is configured such that in a first switching position it connects the first cooling circuit to the receiving volume of the cooling element and in a second switching position it disconnects the receiving volume of the cooling element from the first cooling circuit.In the second switching position, the receiving volume is connected via the two-way valve to a cooling fluid reservoir, into which cooling fluid can flow from the receiving volume by gravity, so that the cooling fluid can be collected and stored in a controlled manner. It is understood that the cooling fluid reservoir is located below the connection of the cooling element in the direction of gravity.

[0015] This achieves the advantage of optimized thermal management, in which a switchable two-way valve is integrated into an existing cooling circuit for cooling the electric machine, and furthermore a cooling element with a receiving volume for the cooling fluid is thermally coupled to the stator and connected to the two-way valve.

[0016] For example, at high temperatures, the cooling fluid, such as a cooling oil, may expand to a larger volume due to thermal expansion, while the electric motor and / or other components, such as a gearbox, have increased heat dissipation requirements. In such an operating situation, the two-way valve can be moved to a first switching position, in which the first cooling circuit is connected to the cooling element's receiving volume. This allows the cooling fluid to flow into the receiving volume of the cooling element via the first cooling circuit. Filling the receiving volume with the cooling fluid increases the thermal conductivity of the cooling element, as cooling fluid has a higher thermal conductivity than air. Furthermore, this operating situation also compensates for the thermal expansion of the cooling fluid.

[0017] At low temperatures, the cooling fluid has a smaller volume, but in such operating conditions, as much heat as possible should be supplied to thermal consumers in the vehicle. In these situations, the two-way valve can be moved to a second switching position, in which the cooling fluid flows out of the cooling element's receiving volume, thereby reducing the thermal conductivity of the cooling element due to the air flowing into the receiving volume. This also compensates for the thermal expansion of the cooling fluid.

[0018] First, the individual elements of the claimed subject matter of the invention are explained in the order of their relevance or their mention in the claim set, and subsequently, particularly preferred embodiments of the subject matter of the invention are described.

[0019] Electrical machines within the meaning of this application serve to convert electrical energy into mechanical energy and / or vice versa, and generally comprise a stationary part referred to as a stator, armature, or rotor, and a part referred to as a rotor or runner, which is movably arranged relative to the stationary part. In connection with this invention, an electrical machine can be designed, in particular, as a rotary machine. A distinction is made between radial flux machines and axial flux machines of such electrical rotary machines. A radial flux machine is characterized in that the magnetic field lines in the air gap formed between the rotor and stator extend in a radial direction, while in the case of an axial flux machine, the magnetic field lines in the air gap formed between the rotor and stator extend in an axial direction.

[0020] In connection with the present invention, an electric machine is provided, in particular, for use within the powertrain of a fully electric motor vehicle. Specifically, the electric machine is dimensioned such that vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and particularly greater than 100 km / h, can be achieved. The electric machine most preferably has a power output greater than 30 kW, more preferably greater than 50 kW, and particularly greater than 70 kW. It is further preferred that the electric machine provides rotational speeds greater than 5,000 rpm, more preferably greater than 10,000 rpm, and most preferably greater than 12,500 rpm.

[0021] The electric machine can have a housing, also known as a motor housing. The motor housing encloses the electric machine. A motor housing can also accommodate the control and power electronics. Furthermore, the motor housing can be part of a cooling system for the electric machine and be designed such that cooling fluid is supplied to the electric machine via the motor housing and / or heat can be dissipated to the outside via the motor housing surfaces. In addition, the motor housing protects the electric machine and any electronics it may contain from external mechanical and / or chemical influences.

[0022] A motor housing can be made of a metallic material. Advantageously, the motor housing can be formed from a metallic casting material, such as die-cast aluminum, die-cast magnesium, gray cast iron, or cast steel. However, the motor housing can also be made entirely or partially from a plastic. Furthermore, the motor housing of the electric machine can be a single piece or comprised of multiple parts.

[0023] Furthermore, it is also possible that the cooling element is formed as a single piece, particularly monolithically, with the motor housing. In other words, the cooling element can also be integrated into the motor housing.

[0024] For the purposes of this application, motor vehicles are defined as land vehicles that are moved by mechanical power and are not bound to railway tracks. A motor vehicle may be selected, for example, from the groups of passenger cars, trucks, mopeds, light vehicles, motorcycles, buses, or tractors.

[0025] The electric machine can further comprise a control unit. A control unit, such as that used in the present invention, serves in particular for the electronic control and / or regulation of one or more technical systems of the electric machine, such as the control / regulation of the coolant pump and / or the energizing of a stator or rotor winding. A control unit can comprise a plurality of control units, which are preferably arranged spatially separated from one another in the motor vehicle. Control units are also referred to as Electronic Control Units (ECUs) or Electronic Control Modules (ECMs) and preferably have electronic microcontrollers for performing calculations and processing data, particularly preferably by means of software. The control units can preferably be networked with one another, so that wired and / or wireless data exchange between control units is possible.In particular, it is also possible to network the control units with each other via bus systems already present in the vehicle, such as CAN bus or LIN bus.

[0026] A rotor is the rotating part of an electric machine. The rotor includes, in particular, a rotor shaft. The rotor shaft can be hollow, which reduces weight and allows lubricant or coolant to be supplied to the rotor body.

[0027] For the purposes of this invention, a rotor body is understood to be the rotor without a rotor shaft. A rotor body can, in particular, be formed from one or more rotor lamination stacks. A rotor lamination stack is understood to be a plurality of laminated individual laminations, usually made of electrical steel, which are stacked and bundled together to form a stack, the so-called rotor lamination stack. The individual laminations can then be held together in the lamination stack by gluing, welding, or bolting. The rotor can be designed as a permanent magnet rotor or a separately excited rotor.

[0028] A stator of an electrical machine according to the invention may preferably have a stator body. The stator body may be formed in one piece or in multiple pieces, in particular segmented. A one-piece stator body is characterized in that the entire stator body is formed in one piece when viewed from the outside. The stator body is generally formed from a plurality of stacked laminated electrical steel sheets, each of which is formed to form a closed ring. A segmented stator body is characterized in that it is constructed from individual stator segment parts. The stator body may be constructed from individual stator teeth or groups of stator teeth, each individual stator tooth or group of stator teeth being formed from a plurality of stacked laminated electrical steel sheets, each of which is designed as a stator segment sheet part.

[0029] The stator body is preferably formed from one or more stator lamination stacks. A stator lamination stack is understood to be a plurality of laminated individual laminations, usually made of electrical steel, stacked and packed on top of each other to form a stack. The individual laminations can then be held together within the lamination stack, for example, by gluing, welding, or bolting.

[0030] The stator teeth are preferably formed within the stator body. Stator teeth are defined as components of the stator body that are formed as circumferentially spaced, tooth-like, radially inwardly directed parts of the stator body, and between their free ends and a rotor body, an air gap is formed for the magnetic field. The air gap is the gap existing between the rotor and the stator. In a radial flux machine, this is essentially an annular gap with a radial width corresponding to the distance between the rotor body and the stator body.

[0031] The stator is specifically intended for use in an electric machine within the drivetrain of a motor vehicle.

[0032] In a preferred embodiment of the invention, the cooling element can also be formed integrally, particularly monolithically, with the stator body. In other words, the cooling element can be integrated into the stator body.

[0033] An electric machine according to the invention can be used, in particular, in an electrically operated axle drive train of a motor vehicle. An electrically operated axle drive train comprises an electric machine and preferably a transmission assembly coupled to the electric machine. The transmission assembly is particularly coupleable to the electric machine, which is designed to generate a drive torque for the motor vehicle. The drive torque is particularly preferably a main drive torque, so that the motor vehicle is driven exclusively by the drive torque. Preferably, the transmission assembly is designed as a planetary gear set.

[0034] The gearbox assembly and the electric machine form a single structural unit. This can, for example, be formed by means of a drivetrain housing in which the gearbox assembly and the electric machine are jointly accommodated.

[0035] Alternatively, it would of course also be possible for the electric motor to have a motor housing and / or the gearbox a gearbox housing, with the structural unit then being achieved by fixing the gearbox to the electric motor. The gearbox housing is a housing for containing a gearbox. Its function is to guide the existing shafts over the bearings and to grant the gears (possibly cam discs) the degrees of freedom they require under all loads, without impeding their rotational and possibly linear motion, as well as to absorb bearing forces and support moments. A gearbox housing can be single- or multi-shell, that is, undivided or split. The housing should, in particular, dampen noise and vibrations and be able to reliably contain lubricant.The gearbox housing is preferably made of a metallic material, in particular preferably of aluminium, grey cast iron or cast steel, especially formed by means of a primary forming process such as casting or die casting.

[0036] Advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims can be combined in a technologically meaningful manner and can define further embodiments of the invention. Furthermore, the features specified in the claims are specified and explained in more detail in the description, which also presents further preferred embodiments of the invention.

[0037] According to an advantageous embodiment of the invention, it can be provided that the receiving volume of the cooling element surrounds the stator in sections, preferably completely, which has proven to be particularly advantageous with regard to heat dissipation or insulation of the cooling element.

[0038] According to a further preferred development of the invention, it can also be provided that the receiving volume is shaped like a cylindrical ring, which leads to a particularly uniform heat dissipation and insulation of the cooling element.

[0039] Furthermore, it may be preferred that the cylindrical ring-shaped receiving volume extends essentially over the entire axial extent of the stator, which can also contribute to particularly effective and uniform heat dissipation and insulation.

[0040] Furthermore, according to another advantageous embodiment of the invention, the cooling element may have a connection arranged in the direction of gravity at the lowest point of the receiving volume for coupling with the two-way valve. The advantageous effect of this embodiment is that it allows for a gravity-driven outflow of cooling fluid from the receiving volume, thus eliminating the need for additional externally driven conveying devices.

[0041] According to a further particularly preferred embodiment of the invention, the cooling element may have a vent located at the highest point of the receiving volume in the direction of gravity. This allows for pressure equalization, particularly when the cooling fluid flows out of the receiving volume, which can simplify the flow of the cooling fluid.

[0042] Furthermore, the invention can also be further developed in such a way that the cooling element has a buoyancy valve arranged in the direction of gravity at the highest point of the receiving volume, which closes the vent opening once the receiving volume has been filled with cooling fluid to a predefined level. This prevents cooling fluid from escaping the vent opening, thus increasing the operational reliability of the electric machine.

[0043] It can also be advantageous to further develop the invention by arranging a hydraulic pump in the first cooling circuit, by means of which the cooling fluid can be pumped through the first cooling circuit. A hydraulic pump allows the flow rate of the cooling fluid to be precisely controlled, enabling precise temperature control of the electric machine. Furthermore, the hydraulic pump allows for a more flexible design of the cooling circuit system, since, for example, gravity is no longer necessary for the circulation of the cooling fluid, thus enabling the realization of more complex system geometries.

[0044] According to a further preferred embodiment of the invention, it can be provided that the first cooling circuit runs through the cooling fluid reservoir, which can help to reduce the system complexity by providing a common cooling fluid reservoir for the cooling circuit and the outflow of cooling fluid from the cooling element.

[0045] Finally, the problem of the invention can also be advantageously solved by an electric axle drive train of a motor vehicle comprising an electric machine according to one of claims 1-9.

[0046] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0047] It shows: Fig. 1 an electric machine in a schematic block diagram with a two-way valve in a first switching position, Fig. 2 an electric machine in a schematic block diagram with a two-way valve in a second switching position, Fig. 3 an electric machine with a cooling element in a schematic cross-sectional view in a partially filled and a fully filled state with cooling fluid, Fig. 4 A motor vehicle with an electrically operated axle drive train in a schematic representation.

[0048] The Fig. Figures 1-2 each show an electric machine 1, in particular for a drive train 2 of a motor vehicle 3, as exemplified in the Fig. 4 is outlined. In the illustrated embodiment of the Fig. 4 The electric machine 1, which is explained in more detail below, forms a unit with a gearbox 23, which is also referred to as axle drive train 20.

[0049] The electric machine 1 comprises a stator 4 and a rotor 5 rotatable relative to the stator 4, wherein the stator 4 and / or rotor 5 are connected to a first cooling circuit 7 through which a cooling fluid 6 flows. A two-way valve 11, switchable by the actuator 22, is arranged in the first cooling circuit 7.

[0050] In the first cooling circuit 7, a hydraulic pump 18 is arranged, by means of which the cooling fluid 6 can be pumped through the first cooling circuit 7, the first cooling circuit 7 passing through the cooling fluid reservoir 17. A filter 21 is arranged between the cooling fluid reservoir 17 and the hydraulic pump 18 in the pumping direction. Downstream of the hydraulic pump 18, a cooling fluid path is implemented through the stator 4 and / or the rotor 5 of the electric machine 1, via which cooling of the electric machine 1 is achieved. The two-way valve 11 is arranged downstream of the electric machine 1 in the cooling circuit 7 in the pumping direction of the cooling fluid 6. A heat exchanger 19 is located in the cooling circuit 7 between the two-way valve 11 and the cooling fluid reservoir 17 for dissipating heat from the cooling circuit 7.

[0051] The stator 4 has a cooling element 9 coupled to the jacket 8 of the stator 4, which provides a receiving volume 10 for receiving cooling fluid 6. This receiving volume 10 of the cooling element 9 is hydraulically connected to the two-way valve 11.

[0052] The two-way valve 11 is now configured such that, in a first switching position 12, it connects the first cooling circuit 7 to the receiving volume 10 of the cooling element 9. This operating position is in the Fig. 1 shown.

[0053] In a second switching position 13 of the two-way valve 11, which is located in the Fig. As can be seen in Figure 2, the intake volume 10 of the cooling element 9 is separated from the first cooling circuit 7.

[0054] The two-way valve 11 is controlled by the actuator 22. At low temperatures, the two-way valve 11 is switched to the second switching position 13, as shown in the Fig. Figure 2 shows that the intake volume 10 is thus separated from the cooling circuit 7, and the cooling of the electric machine 1 continues via the cooling circuit 7. In this operating position, the cooling fluid 6 flows back from the intake volume 10 of the cooling element into the cooling fluid reservoir 17 due to gravity. At low temperatures, the intake volume 10 is therefore emptied of the cooling fluid 6 so that the thermal conductivity through the cooling element 9 is as low as possible. This is due to the air acting as thermal insulation in the intake volume 10.

[0055] At high temperature, the two-way valve 11 is moved into its first switching position 12, as shown in the Fig. Figure 1 shows the process. The cooling fluid 6 now also flows into the receiving volume 10 of the cooling element 9 until the receiving volume 10 is completely filled with cooling fluid 6. At high temperatures, the receiving volume 10 is thus filled with cooling fluid 6 to ensure that the thermal conductivity of the cooling element 9 is as high as possible, since the cooling fluid 6 has a better thermal conductivity than air.

[0056] What can also be seen from the figure is that in the second switching position 13 the receiving volume 10 is connected via the two-way valve 11 to a cooling fluid reservoir 17, into which cooling fluid 6 can flow from the receiving volume 10 by gravity.

[0057] As can be seen particularly well from the detailed illustrations in the Fig. As can be seen in section 3, the cylindrical ring-shaped receiving volume 10 of the cooling element 9 completely surrounds the stator 4.

[0058] It can also be seen that the cooling element 9 has a connection 14, arranged in the direction of gravity at the lowest point of the receiving volume 10, for coupling with the two-way valve 11, while the cooling element 9 has a vent opening 15, arranged in the direction of gravity at the highest point of the receiving volume 10. The cooling element 9 also has a buoyancy valve 16, arranged in the direction of gravity at the highest point of the receiving volume 10, which closes the vent opening 15 once the receiving volume 10 has reached a predefined level of coolant 6. The buoyancy valve 16 thus ensures that, on the one hand, the vent opening 15 is closed when the receiving volume 10 is completely filled with coolant 6, and on the other hand, that the vent opening 15 is opened when the coolant 6 is drained from the receiving volume 10, thereby allowing oil return when the two-way valve is in the Fig.The circuit shown in section 1 is located there.

[0059] The invention is not limited to the embodiments illustrated in the figures. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Insofar as the claims and the foregoing description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing any hierarchy. Reference symbol list 1 electric machine 2 Powertrain 3 Motor vehicle 4 Stator 5 Rotor 6 Cooling fluid 7 Cooling circuit 8 coat 9 Cooling element 10 recording volume 11 Two-way valve 12 switching positions 13 Switch position 14 connection 15 vent opening 16 Buoyancy valve 17 Cooling fluid reservoir 18 Hydraulic pump 19 heat exchangers 20 axle drive train 21 filters 22 Actuator 23 gearboxes

Images