Liquid-cooled drive unit

Abstract

The invention relates to a drive device (1) with an electric machine designed as an axial flux machine, which comprises two disk-shaped rotors (2) and a stator (3) arranged between the rotors (2), wherein the two rotors (2) each have a rotor shaft extension (4) by means of which the two rotors (2) are radially connected to each other within the stator (3) in a rotationally fixed manner, and the drive device (1) is liquid-cooled. The invention is characterized in that a distributor sleeve (5) is provided which extends between the two rotors (2) so that a liquid collection chamber (6) with a cylindrical surface of the rotor shaft attachments (4) is formed.

Description

[0001] The invention relates to a liquid-cooled drive device. The drive device can be an electric drive train in which a cooling liquid circuit is provided. This allows rotor cooling to be implemented.

[0002] At low speeds, the heat loss from a drive system can usually be dissipated through the surrounding components and the surrounding air. At higher speeds, the surrounding components, especially the rotor stator, are generally significantly warmer, meaning that heat can no longer be dissipated through these components. Rotor cooling is therefore particularly necessary at high speeds, as significantly increasing speeds can lead to increased iron and magnet losses.

[0003] It is therefore known from the prior art to implement rotor cooling for electrical machines using a control solenoid valve. Furthermore, it is possible to use a fixed throttle element in the hydraulic system to achieve predetermined distribution ratios for a coolant volume flow. Such arrangements are usually mounted on the rear side of the rotor. However, the disadvantage is that the highest room temperature is on the opposite side of the magnet, particularly on the side of the air gap.

[0004] JP 2012-151 930 A discloses a cooling device for cooling an electric motor, which has a cooling channel arranged within a motor shaft. A radial piston pump supplies cooling oil from the cooling channel to a stator of the electric motor, depending on the rotor speed of the electric motor.

[0005] JP 2013-55752 A discloses an electric motor with permanent magnets. The rotor shaft of the electric motor has a central bore through which coolant flows. The central bore is connected via two radially directed connecting bores to a cooling channel extending through the rotor core, with a closing mechanism provided between the connecting bores.

[0006] JP 2013-62 912 A describes a cooling device for an electrical machine, which has a rotor shaft with a plurality of through-holes through which a cooling fluid is discharged to the winding heads of a stator. A check valve is arranged in some of the through-holes.

[0007] JP 2009-118 686 A discloses a cooling device for an electrical machine, which has a cooling circuit with a first cooling channel for cooling permanent magnets and a second cooling channel for cooling winding heads, and in which a switching device is provided for switching the cooling channels depending on a speed and a torque.

[0008] JP 2007-228 669 A discloses a cooling device for an electric motor, which has a cooling channel in the interior of a rotor shaft. A supply channel for supplying cooling oil from the cooling channel to the rotor core is provided, as well as a non-return valve through which the cooling oil flow is discharged in only one direction outside the rotor.

[0009] DE 19 04 176 A discloses a liquid-cooled drive device in which the coolant to be discharged is fed pressurelessly into a collection chamber that is never completely filled with the coolant. A valve is arranged in each connecting channel between the rotor and the collection chamber, which automatically closes when the rotor stops. A disadvantage of this approach is the need for a large number of valves. Furthermore, the chamber is not completely filled with liquid, which can lead to air being sucked in.

[0010] The object of the present invention is to provide a liquid-cooled drive device which overcomes the aforementioned disadvantages.

[0011] According to the invention, this object is achieved by a drive device having the features in claim 1, and here in particular in the characterizing part of claim 1.

[0012] Advantageous embodiments and further developments arise from the dependent claims.

[0013] At the core of the drive device according to the invention, a distributor sleeve is provided, which extends between the two rotors, forming a fluid collection chamber with a lateral surface of the rotor shaft extensions. In other words, the liquid-cooled electric drive device according to the invention solves the technical problem of rotor cooling as a function of the rotational speed using a centrifugal force mechanism. This advantageously ensures a full-surface distribution of the cooling fluid across the entire respective rotor disk.

[0014] The drive device has an electrical machine designed as an axial flux machine, which comprises or is formed from two disc-shaped rotors and a stator arranged between the rotors, wherein the two rotors each have a rotor shaft extension by means of which the two rotors are connected to one another in a rotationally fixed manner radially within the stator, and the drive device is liquid-cooled.

[0015] At low speeds, advantageously, no fluid flow is delivered to the rotating rotors. For example, a design can be implemented by defining a speed range above which the cooling fluid flow to the rotors opens. In other words, this can be implemented by a type of switch that can ensure that a full flow can pass above a certain opening speed.

[0016] The drive device according to the invention, in particular, prevents an uneven distribution of the coolant across the respective rotor surface, which can result from a co-rotating outlet opening and manufacturing tolerances in a distributor geometry. In other words, a hydraulically communicating distribution is proposed, which can ensure an even distribution of the coolant across the respective rotor surface.

[0017] The distributor sleeve can be designed as a sleeve-shaped element which in particular forms a type of partition wall.

[0018] Preferably, the distributor sleeve can be arranged radially outside the rotor shaft extensions and radially inside the stator. This allows a type of partition wall to be formed adjacent to the respective rotor with the magnets and adjacent to the stator, which can delimit a fluid collection chamber.

[0019] According to a very advantageous development of the idea, it can be provided that the fluid collection chamber is connected to a centrifugal valve, so that from a certain speed the fluid collection chamber is filled with fluid from a first fluid reservoir. In a resting state, the centrifugal valve is therefore preferably closed by a preload force, in particular a spring. For example, the centrifugal valve can remain closed up to a certain speed, which corresponds to a percentage of the maximum speed. From a certain speed, in particular due to the centrifugal force, the centrifugal valve can be opened so that fluid can flow through a fluid connection between the fluid collection chamber and a fluid reservoir. As a result, the fluid collection chamber can be filled with fluid, in particular an oil.

[0020] According to an advantageous embodiment, a plurality of bores can be arranged in the distributor sleeve, allowing fluid to flow from the fluid collection chamber to the rotor disks. Due to the centrifugal force, which increases with increasing speed, the fluid is distributed over the entire surface of the distributor sleeve. This allows the fluid to reach the bores through which it can flow to the rotor disks.

[0021] A further advantageous embodiment can provide for the bores to be arranged in an axial region of the rotor edges of the two rotors, each of which is directed axially toward the stator. This can particularly advantageously ensure that a continuous and thin liquid film is formed on the rotor, in particular on the two rotor disks with the magnets. Heat exchange can be optimized when the respective continuous liquid film comes into contact with the hot magnets.

[0022] In one embodiment, the holes can each be arranged in an undercut of the respective rotor disk in the distributor sleeve. The undercut can, for example, be designed as an inclined surface with a rounded transition to the rotor surface. The inclined surface with a rounded edge can optimize the adhesion of the respective liquid film, thus preventing flow separation.

[0023] According to a very advantageous development of the idea, it can be provided that a smallest cross-sectional area of ​​the centrifugal valve is larger than the sum of the cross-sectional areas of the bores. In particular, an even distribution of the coolant along the rotor surface is crucial to avoid hot spots in the magnets where no coolant reaches. Therefore, the bores are preferably dimensioned such that the acting centrifugal force always causes less coolant to flow out than can flow in through the centrifugal valve. In particular, the fluid collection chamber is kept completely filled at all times, especially after an initial, short filling phase. This can particularly advantageously ensure the balance of fluid discharge through all bores along the edge region of the distributor sleeve.

[0024] According to an advantageous embodiment, the bores can be arranged in a circumferential edge region of the distributor sleeve, allowing a uniform outflow of the liquid and the formation of a respective liquid film on the rotors and magnets. In particular, the liquid is also guided to an edge region of the surface. The bores are preferably arranged in two opposite edge regions of the surface and, in particular, are distributed over 360° in the distributor sleeve. Thus, the bores can describe a quasi-circular shape, with the bores preferably being arranged at a distance from one another.

[0025] A further advantageous embodiment can provide for a sealing device on the distributor sleeve, by means of which the distributor sleeve is sealed against the rotors. For example, a sealing ring can be provided as the sealing device, which is held in a receptacle on the distributor sleeve. For this purpose, the distributor sleeve can be L-shaped or U-shaped in the edge region, in particular on a peripheral side. The bores are preferably not located in the region of this receptacle, but rather closer to the center of the distributor sleeve.

[0026] A radial sealing sleeve can also be provided axially between the rotor shaft extensions and in an outer circumferential region of a rotor shaft extension interior, which has at least one radial bore for the representation of the fluid connection.

[0027] Furthermore, in one embodiment of the invention, the distributor sleeve can be held axially centered on both sides via a respective radial fit on the two rotors. This embodiment can advantageously ensure a particularly reliable even distribution of the coolant, as tilting of the distributor sleeve can be prevented.

[0028] In one embodiment of the invention, the distributor sleeve can have exactly two rows of holes, each with a plurality of radial holes, wherein the two rows of holes are each arranged in an axial region of a rotor edge directed axially in the direction of the stator.

[0029] According to a very advantageous development of the idea, it can be provided that the liquid contains a cooling oil.

[0030] According to an advantageous embodiment, it can be provided that the centrifugal valve is designed as a ball check valve.

[0031] The rotor shaft extensions can be connected to one another via axial toothing, wherein the axial toothing can be designed in particular in a sequential manner. Radially within the axial toothing, a radial fluid connection can be provided from a hollow rotor shaft extension interior via gaps in the axial toothing to the fluid collection chamber.

[0032] Further advantageous embodiments of the drive device according to the invention also emerge from the exemplary embodiment which is illustrated in more detail below with reference to the figures.

[0033] Showing: Fig. 1 a possible embodiment of the drive device; Fig. 2 a possible embodiment of the drive device with filled liquid collection chamber; and Fig. 3 a possible embodiment of the drive device with filled liquid collection chamber in cooling mode;

[0034] In the presentation of the Fig. Figure 1 shows a possible embodiment of the drive device 1. The illustration shows the situation in which a first fluid reservoir 8 is filled with fluid 9, and a centrifugal valve 7 is closed. This prevents the fluid 9 from entering a fluid collection chamber 6, which is formed by a distributor sleeve 5 and surfaces of a respective rotor shaft extension 4. The illustration shows an axis of symmetry in the lower area, whereby only one half of the drive device 1 is represented. The drive device 1 has rotors 2 with magnets 12 and a stator 3.

[0035] When the drive device 1 is in operation, a centrifugal force is generated by the rotational movement around the rotation axis, as shown in Fig. 2 is shown by the direction of the arrow. This opens the centrifugal valve 7, allowing fluid 9 to flow from the fluid reservoir 8 into the fluid collection chamber 6. Therefore, during a filling phase, the entire fluid collection chamber 6 is first filled with fluid 9 before the fluid can be discharged toward the rotors 2 via the openings in the bores 10.

[0036] When the liquid 9 finally reaches the rotors 2 with the magnets 12 through the bores 10, a respective liquid film 11 can be formed, which rests on the rotor disks as a thin, closed surface. The respective rotor shaft extension 4 therefore has an inclined surface with a rounded portion, over which the liquid 9 can flow to the surface of the magnets 12 once it has left the bores 10 and flows toward the rotor disks. In other words, the respective liquid film forms along the respective inclined surface and the respective rounded portion on the surface of the respective rotor shaft extension 4 and ultimately on the surface of the magnets 12.

[0037] For example, the centrifugal valve 7 can remain closed from a speed of 0% to X% of the maximum speed by a preload of a spring, whereby no liquid 9, in particular no coolant or cooling oil, can pass through the passage with the centrifugal valve 7. The first coolant reservoir, characterized by the liquid reservoir 8, can be filled with coolant by an external supply of an inner rotor shaft, for example by a pump. From a certain speed X, the centrifugal valve 7 can open due to the centrifugal force that occurs, whereby liquid 9 can pass from the liquid reservoir 8 into the liquid collection chamber 6. The liquid collection chamber 6 is delimited by the distributor sleeve 5, wherein the distributor sleeve 5 in particular is tightly fitted between the two rotor disks. A sealing device 13 can therefore be provided, which is designed, for example, as a sealing ring.Due to high centrifugal forces, which increase with increasing speed, the coolant 9 is distributed over the entire circumference inside the distributor sleeve 5, i.e. over the entire inner surface of the distributor sleeve 5. This ensures that the coolant 9 flows evenly through all of the bores 10, with the bores 10 preferably being distributed 360° around the circumference of the distributor sleeve 5. The coolant can flow out through the bores 10 and hit the rotor disks. This creates a continuous liquid film 11 on the rotors 2, specifically in an air gap with direct contact to the magnets 12 of the rotors 2. This optimizes the heat exchange between the hot magnets 12 and the coolant. Even distribution of the coolant is therefore crucial because it prevents hot spots on the magnets 12.Preferably, the bores 10 in the distributor sleeve 5 are dimensioned such that the centrifugal force causes less coolant to flow out than can flow in through the centrifugal valve 7. This ensures that the fluid collection chamber 6 is completely filled at all times.

[0038] In Fig. 3 shows a situation in which cooling can be ensured despite manufacturing and assembly tolerances. The completely filled liquid collection chamber 6 ensures, in particular, that no air is sucked in. The liquid 9 is therefore present at all bores 10, i.e., at all outlet openings. The only disturbance that can result is an uneven distribution in the alignment of the distributor sleeve 5 due to centrifugal force or a liquid column subjected to centrifugal force, as shown in the Fig.3. However, in this situation, it can also be ensured that a liquid film 11 can be formed on both sides of the rotor. For example, the liquid film 11 on the left in the illustration can contain 55% of the cooling liquid, while the liquid film 11 on the right side of the illustration can contain 45% of the cooling liquid. However, complete coverage can be ensured.

[0039] In an exemplary design, a rotor cooling system can open at 10,000 revolutions per minute. The rotor cooling system should be configured to provide reliable cooling performance at speeds up to 14,000 revolutions per minute. The two rotor disks should receive a coolant flow rate of 1 L / min. Approximately 12 holes per rotor disk, each with a bore diameter of approximately 0.2 mm, can be provided as bores 10. This corresponds to 24 holes for two rotor disks, and the total cross-sectional area corresponds to a bore with a diameter of 1 mm. The centrifugal valve is preferably designed to open at 10,000 revolutions per minute and allow a coolant flow rate of 1 L / min. The diameters of the bores 10 depend in particular on the diameter of the centrifugal valve 7.The diameters of the bores 10 and the diameters of the centrifugal valve depend on the diameter of the distributor sleeve 5 and the inner diameter of the fluid reservoir 8. These values ​​are merely examples and are intended for illustrative purposes. Different values ​​are therefore also possible in any variation.

Claims

[1] Drive device (1) with an electrical machine designed as an axial flux machine, which comprises two disc-shaped rotors (2) and a stator (3) arranged between the rotors (2), wherein the two rotors (2) each have a rotor shaft extension (4) by means of which the two rotors (2) are connected to one another in a rotationally fixed manner radially inside the stator (3), and the drive device (1) is liquid-cooled, wherein a distributor sleeve (5) is provided which extends between the two rotors (2), so that a liquid collecting space (6) is formed with a lateral surface of the rotor shaft extensions (4). [2] Drive device according to claim 1, characterized by that the distributor sleeve (5) is arranged radially outside the rotor shaft extensions (4) and radially inside the stator (3). [3] Drive device (1) according to claim 1 or 2, characterized bythat the liquid collecting chamber (6) is fluidly connected to a centrifugal valve (7). [4] Drive device (1) according to claim 1, 2 or 3, characterized by that a plurality of bores (10) are arranged in the distributor sleeve (5) so that liquid (9) can reach the rotor discs from the liquid collecting space (6). [5] Drive device (1) according to claim 4, characterized by that the bores (10) are each arranged in an axial region of a respective rotor edge directed axially in the direction of the stator (3). [6] Drive device (1) according to claim 3 and one of claims 4 or 5, characterized by that a smallest cross-sectional area of ​​the centrifugal valve (7) is larger than a sum of cross-sectional areas of the bores (10). [7] Drive device (1) according to one of claims 4 to 6, characterized bythat the bores (10) are arranged in respective circumferential edge regions of the distributor sleeve (5). [8] Drive device (1) according to one of claims 1 to 7, characterized by that a sealing device (13) is provided on the distributor sleeve (5), by means of which the distributor sleeve (5) is sealed against the rotors (2). [9] Drive device (1) according to one of claims 1 to 8, characterized by that the distributor sleeve (5) is held axially centered on both sides via a respective radial fit on the two rotors (2). [10] Drive device (1) according to one of claims 1 to 9, characterized by that the centrifugal valve (7) is designed as a ball check valve.

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