Axial flux motor with improved rotor cooling

Abstract

Axial flux motor (1) comprising a housing (5) with at least one disk-shaped stator (2) arranged in the housing (5) and at least one disk-shaped rotor (3) arranged opposite the disk-shaped stator (2) along the axis of rotation (4) of the motor and separated by an air gap, wherein one or more nozzles (6) are arranged in the housing (5), wherein the nozzles (6) are configured to apply a liquid coolant to the rotor surface facing the stator (2), wherein the nozzles (6) are configured to apply the coolant only to the rotor surface areas which are greater than or equal to 0% and less than or equal to 30% away from the axis of rotation (4) with respect to the rotor radius.

Description

[0001] The present invention relates to an axial flux motor. The present invention relates in particular to an axial flux motor with improved rotor cooling.

[0002] Electric motors are increasingly becoming the focus of mobile applications. For use as drives in vehicles, axial flux motors are being used more and more frequently alongside radial flux motors due to their compact design, energy efficiency, and achievable torques. These axial flux motors feature an opposing arrangement of a stator and at least one rotor within a single housing. Effective cooling of the rotors is advantageous for enabling efficient operation of axial flux motors, even at high speeds. Cooling prevents motor overheating, which could lead to demagnetization of the magnets or thermal damage to other motor components.

[0003] However, known rotor cooling systems still have potential for improvement.

[0004] The publication DE 10 2014 213 452 A1 relates to an axial flux machine, with a stator and a disk rotor, wherein an airflow is guided between the disk rotor and the stator.

[0005] The object of the present invention is to overcome at least one disadvantage of the prior art, at least partially. In particular, it is an object of the present invention to provide a solution for effective rotor cooling in axial flux motors, thereby improving the electrical and mechanical efficiency as well as the service life of the motors.

[0006] The present invention is implemented by an axial flux motor having the features of claim 1. Preferred embodiments of the invention are specified in the dependent claims, in the description or the figures, wherein further features described or shown in the dependent claims or in the description or the figures may, individually or in any combination, constitute an object of the invention unless the context clearly indicates otherwise.

[0007] The present invention relates to an axial flux motor comprising a housing with at least one disk-shaped stator arranged in the housing and at least one disk-shaped rotor arranged opposite the disk-shaped stator along the axis of rotation of the motor and separated by an air gap, wherein one or more nozzles are arranged in the housing, wherein the nozzles are configured to apply a liquid coolant to the rotor surface facing the stator.

[0008] Such an axial flux motor offers significant advantages over prior art solutions.

[0009] This text describes an axial flux motor. The basic structure of such an axial flux motor can be of a known design. The motor comprises a coreless, disk-shaped stator and an opposing coreless, disk-shaped actuator, also referred to as the rotor, with the magnetic field driving the rotor running parallel to the axis of rotation of the rotor and stator. The electrical control of the stator sets the rotor in motion, driving, for example, an axle or a wheel. The dimensions and performance data of the axial flux motor can be adapted to the chosen application, such as the type of vehicle or component to be driven by the electric motor.

[0010] The axial flux motor also has a housing. The housing serves to contain various components of the electric motor. To accommodate the stator-actuator assembly, the electric motor housing includes a housing section, which is primarily cylindrical. Ideally, the cylindrical shape of this housing section allows it to be adapted to the external shape of the stator-actuator assembly.

[0011] The axial flux motor described here is further equipped with one or more nozzles arranged in the housing. These nozzles are designed to apply a liquid coolant to the rotor surface facing the stator. The nozzles are therefore part of a cooling system and can deliver a liquid coolant to the rotor surface. The delivery of the liquid coolant can be achieved, for example, by spraying, dripping, or generally by ejecting the coolant through the nozzle. The nozzles can be mounted on or in the housing wall, or on the stator or shaft. It is also possible for both nozzles to be mounted on or near the stator and nozzles on or near the housing wall, provided the coolant is directed towards the rotor surface.Preferably, more than two, more preferably more than four, and even more preferably more than eight nozzles can be used in the motor to cool a rotor. Furthermore, one or more nozzles can also be mounted on the rotor itself, enabling the delivery of coolant to the rotor surface. In principle, any liquid coolant known to those skilled in the art, provided it has a sufficient heat capacity, can be used. A nozzle is understood to be a mostly cylindrical hollow body with an opening that allows a directed flow of liquid to escape. This configuration cools only one surface of the rotor. The surface of the rotor facing away from the stator is not brought into contact with coolant by the nozzle settings. However, the opposite side of the rotor can be cooled independently.

[0012] According to the invention, the specific orientation of one or more nozzles for delivering a liquid coolant onto the rotor surface facing the stator within the housing enables efficient cooling of the rotor at higher speeds and consequently higher temperatures. Reducing the rotor temperature can protect other motor components from overheating and maintain the motor's electrical performance.

[0013] These advantages are achieved in particular by orienting the nozzles towards the rotor surface facing the stator. This type of rotor cooling is significantly more efficient compared to other cooling methods. For example, compared to pure air cooling or air convection cooling, liquid cooling allows for considerably higher energy dissipation from the rotor.

[0014] The aforementioned design therefore enables a particularly advantageous configuration of the rotor cooling system. As described above, significantly higher amounts of energy can be dissipated, thus achieving considerably smoother motor operation even under high loads and high speeds. Overheating under high loads can therefore be prevented very efficiently according to the invention.

[0015] The nozzles are designed to apply the coolant only to those areas of the rotor surface that are greater than or equal to 0% and less than or equal to 30% of the rotor radius away from the axis of rotation. To achieve the most uniform cooling possible across the entire rotor surface, it has proven advantageous to apply the coolant primarily to the areas of the rotor closest to the axis. The resulting centrifugal forces then transport the coolant evenly to the areas of the rotor further away from the axis. This results in uniform cooling of the entire rotor surface. For example, if the radius of a rotor is 10 cm, the coolant will only be applied to those areas of the rotor that are a maximum of 3 cm away from the rotor axis.

[0016] Additionally or alternatively, it can be advantageous for the rotor surface to have recesses designed to direct the coolant from areas near the axis of rotation to areas further away from it. To achieve the most uniform cooling possible across the entire rotor surface, it can be beneficial to incorporate recesses that guide the applied coolant flow in a predetermined direction. These recesses can be, for example, in the form of hemispherical or teardrop-shaped channels, whose specific shape and depth allow for a greater or lesser degree of deflection of the coolant flow onto specific surface areas of the rotor.The recesses on the rotor surface can, for example, have a depth greater than or equal to 0.5 millimeters, more preferably greater than or equal to 0.75 millimeters, and more preferably greater than or equal to one millimeter.

[0017] It may be further preferred that the rotor surface has recesses with different orientations, wherein at least one recess is concentric to the axis of rotation and another recess is not concentric to the axis of rotation. For efficient distribution of the coolant applied to the rotor surface, it can be advantageous to have at least two different types of recesses. These different types of recesses can be distinguished, in particular, by their symmetry with respect to the rotor axis. One or more recesses can be concentric around the rotor's axis of rotation. It is particularly preferred that this type of recess be located closer to the rotor's axis of rotation. In this case, another recess can be oriented non-concentrically with respect to the rotor's axis of rotation.For example, these non-concentric recesses can extend radially towards the circumference of the rotor. These recesses can also be curved rather than straight. It is also possible that the different recesses each have a different profile. This latter feature can direct the coolant more precisely onto the rotor surface.

[0018] It can also be advantageous to apply the coolant to the rotor surface with an angle of elevation of less than or equal to ±89° relative to the rotor's surface normal. The term "less than or equal to" refers to the absolute value of the angle. To ensure the most uniform wetting of the entire rotor surface, it has proven beneficial to apply the coolant not directly, but at a certain angle. This can particularly help to reduce the proportion of coolant that is deflected from the rotor surface directly back towards the stator gap. The surface film of coolant is kept close to the rotor surface, thus preventing the formation of a continuous liquid film extending across the entire gap between the rotor and stator.The specified angular range refers to the vertical angle Gamma relative to the surface normal of the rotor surface. An angular deviation of 89° relative to the normal results in the coolant being applied almost parallel to the rotor surface. The signs indicate whether the coolant is applied with or against the direction of rotation. A lower limit for the angular deviation can preferably be, for example, ±0.5°, at which point the coolant is applied almost perpendicularly to the surface. As a function of the operating point, i.e., as a function of the rotor temperature and / or rotational speed, it can also be advantageous to apply the coolant to the surface with varying lateral angles Theta, for example, in the form of 0° ≤ Theta ≤ 359°.However, it is also possible that, as a function of the operating point, the direction of application of the coolant is varied by an adjustable nozzle direction.

[0019] It may be further preferred that the nozzles are configured to apply a liquid coolant through the rotor onto the rotor surface facing the stator. In this configuration, the coolant is applied through the rotor onto the rotor surface opposite the stator. In this case, the nozzles are attached to the rotor itself or located inside the rotor. This configuration enables particularly precise application of the coolant to the rotor surface, and overall, the rotor can be cooled efficiently with a lower coolant flow rate.

[0020] It can also be advantageous to have at least one coolant outlet on the housing wall. Having at least one coolant outlet on the housing wall has proven beneficial for removing coolant that has been applied and has now warmed up. The outlet can be designed as a valve that allows accumulated coolant to pass out of the housing as a function of the applied pressure or, for example, the temperature.

[0021] It is also preferably possible that the valve is configured to discharge the coolant from the housing as a function of pressure and / or temperature. In particular, the pressure as a control variable for switching the outlet valve can be suitable for removing excess coolant from the housing. Preferably, a pressure range can be specified for controlling the valve, within which the pressure inside the housing is to be maintained. This pressure range prevents both excessively high and excessively low coolant levels in the housing.

[0022] In a preferred embodiment, the coolant can be applied to the rotor surface at a velocity of 0.25 L / min or greater than or equal to 5 L / min. To ensure a directed coolant flow across the surface, it has proven advantageous to apply the coolant within the velocity range specified above. Higher velocities can cause the coolant to be unintentionally drawn back from the rotor surface into the gap between the rotor and stator. Lower velocities can result in the initial direction of the coolant flow across the surface being maintained for an insufficient duration. The specified range is suitable insofar as it provides a sufficient and defined coolant flow for a wide range of rotor speeds.Preferably, the coolant can be applied to the rotor surface at a rate greater than or equal to 0.5 L / min and less than or equal to 2.5 L / min, and more preferably at a rate greater than or equal to 0.75 L / min and less than or equal to 1.5 L / min.

[0023] In an advantageous embodiment, the nozzle or nozzles can be configured to control the amount of liquid coolant supplied over time as a function of the rotor temperature and / or the rotor speed. For demand-based cooling of the rotor surface, it has proven particularly suitable that a constant amount of coolant is not always supplied to the rotor. The amount of coolant delivered per unit of time can be adjusted, in particular, as a function of the rotor temperature or, more generally, as a function of the rotor speed. Both control variables enable demand-based adaptation of the coolant quantity. Preferably, the nozzle or nozzles can be configured to control the amount of liquid coolant supplied over time as a function of both the rotor temperature and the rotor speed.

[0024] The invention is further explained below with reference to the figures, whereby one or more features of the figures, individually or in combination, can constitute a feature of the invention. Furthermore, the figures are to be considered merely exemplary and in no way limiting. Fig. Figure 1 schematically shows a section of a state-of-the-art axial flux motor; Fig. Figure 2 schematically shows a section of an axial flux motor according to the invention; Fig. Figure 3 schematically shows a section of an axial flux motor according to the invention; Fig. Figure 4 shows a rotor surface according to the invention with recesses;

[0025] In the Fig. Figure 1 schematically depicts a section of a prior art axial flux motor 1. The depicted part of the axial flux motor 1 shows a disk-shaped stator 2 and a disk-shaped rotor 3 opposite it, separated by a gap. Rotor 3 and stator 2 share the same axis of rotation 4 and are housed in a casing 5.

[0026] In the Fig. Figure 2 schematically shows a section of an axial flux motor 1 according to the invention. In addition to the features already described in the Fig. In addition to the elements described in Figure 1, this figure further shows that several nozzles 6 are arranged on the housing 5 and on the axis of rotation 4. The axis of rotation 4 can, for example, be in the form of a shaft. The nozzles 6 are each configured to discharge a coolant from the nozzles 6 towards the surface of the rotor 3. In addition to the nozzles 6 shown, further nozzles can be attached to the housing 5 or the stator 2 or to a shaft lying on the axis of rotation 4.

[0027] The Fig. Figure 3 schematically shows a section of an axial flux motor according to the invention. In addition to the possibility of supplying coolant from the direction of the stator 2, coolant can also be supplied through the rotor 3 to the side facing the stator 2. The coolant is fed in through the surface of the rotor 3 facing away from the stator 2 and exits the rotor 3 on the opposite surface. In this way, efficient cooling of the surface of the rotor 3 facing the stator 2 can be achieved.

[0028] The Fig.Figure 4 shows a surface of a rotor 3 according to the invention, with recesses 7 and 8. To selectively drain the coolant from the surface of the rotor 3, recesses 7 and 8 can be provided on the surface of the rotor 3 facing the stator 2. To achieve improved cooling of the entire surface, the recesses 7 and 8 can have different orientations. For example, recesses 8 can be arranged oriented with respect to the axis of rotation. Alternatively, recesses 7 and 8 can be arranged non-concentrically on the surface of the rotor 3. It is also possible for both recesses 7 and 8 to be connected to each other. Furthermore, both recesses can have different profiles. These recesses 7 and 8 ensure uniform and complete wetting of the surface of the rotor 3 with coolant. Reference symbol list 1 Axial flux motor 2 Stator 3 Rotor 4 Rotation axis 5 cases 6 nozzles 7 non-concentric recesses 8 concentric recesses

Claims

[1] Axial flux motor (1) comprising a housing (5) with at least one disk-shaped stator (2) arranged in the housing (5) and at least one disk-shaped rotor (3) arranged opposite the disk-shaped stator (2) along the axis of rotation (4) of the motor and separated by an air gap, wherein one or more nozzles (6) are arranged in the housing (5), wherein the nozzles (6) are configured to apply a liquid coolant to the rotor surface facing the stator (2), wherein the nozzles (6) are configured to apply the coolant only to the rotor surface areas which are greater than or equal to 0% and less than or equal to 30% away from the axis of rotation (4) with respect to the rotor radius. [2] Axial flux motor according to claim 1, characterized by, that the rotor surface has recesses (7, 8) wherein the recesses (7, 8) are designed to direct the coolant from areas near the axis of rotation to areas far from the axis of rotation on the rotor surface. [3] Axial flux motor according to claim 2, characterized by , that recesses (7, 8) with different orientations of the recesses (7, 8) are present on the rotor surface, wherein at least one recess (8) is concentric to the axis of rotation and another recess (7) is not concentric to the axis of rotation (4). [4] Axial flux motor according to one of the preceding claims, characterized by , that the coolant is applied to the rotor surface with a height angle deviation of less than or equal to ± 89° relative to the surface normal of the rotor (3). [5] Axial flux motor according to one of the preceding claims, characterized by, that the nozzles (6) are designed to deliver a liquid coolant through the rotor (3) onto the rotor surface facing the stator (2). [6] Axial flux motor according to one of the preceding claims, characterized by that at least one coolant outlet is arranged on the housing wall. [7] Axial flux motor according to claim 6, characterized by , that the nozzle (6) is designed to regulate the amount of liquid coolant supplied over time as a function of the rotor temperature and / or the rotor speed. [8] Axial flux motor according to one of the preceding claims, characterized by that the coolant is applied to the rotor surface at a rate greater than or equal to 0.25 L / min and less than or equal to 5 L / min. [9] Axial flux motor according to any one of the preceding claims, characterized by, that the nozzle (6) is designed to regulate the amount of liquid coolant supplied over time as a function of the rotor temperature and the rotor speed.

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