Axial flux motor with improved rotor cooling

Abstract

The invention relates to an axial flux electric machine (1), comprising a housing (5) and at least one disc-shaped stator (2) arranged in the housing and at least one disc-shaped rotor (3) opposite the disc-shaped stator (2) along a rotational axis (4) of the electric machine and separated from the stator by a gap, one or more nozzles (6) being arranged in the housing (5), the nozzle (6) is designed to supply a liquid coolant onto a rotor surface facing the stator (2).

Description

Technical Field

[0001] The present invention relates to an axial flux electric machine / axial magnetic field electric machine. In particular, the present invention relates to an axial flux electric machine with improved rotor cooling. Background Art

[0002] Electric machines are increasingly becoming a focus in automotive applications. As a drive device in vehicles, in addition to radial flux machines, axial flux machines are increasingly being used due to their compact design, energy efficiency and achievable torque. Axial flux machines have an opposing structure consisting of a stator and at least one rotor inside a housing. In order for axial flux machines to operate efficiently even at high speeds, effective cooling of the rotor is important. Cooling prevents the motor from overheating, which could lead to demagnetization of the magnets or thermal damage to other motor components.

[0003] However, known rotor cooling still has potential for improvement. Summary of the invention

[0004] It is therefore an object of the present invention to at least partially overcome at least one disadvantage of the prior art. In particular, it is an object of the present invention to provide a solution for effective rotor cooling in an axial flux electric machine, by means of which the electrical efficiency, mechanical efficiency and lifetime of the machine are improved.

[0005] The solution of the invention is achieved by an axial flux machine having the features of claim 1. Preferred embodiments of the invention are given in the dependent claims, the description or the drawings, wherein other features described or shown in the dependent claims or the description or the drawings may represent the subject matter of the invention alone or in combination, unless the context clearly indicates a mutually exclusive meaning.

[0006] The subject of the invention is an axial flux electric machine comprising a housing and at least one disk-shaped stator arranged in the housing and at least one disk-shaped rotor, the disk-shaped rotor being opposite the disk-shaped stator along the rotation axis of the electric machine and being separated from the stator by a gap, wherein one or more nozzles are arranged in the housing, wherein the nozzles are designed to supply liquid coolant to the rotor surface facing the stator.

[0007] Such an axial flux machine has significant advantages over prior art solutions.

[0008] An axial flux electric machine is thus described. The basic structure of such an axial flux electric machine can be designed in a manner known per se. The electric machine comprises an ironless, disk-shaped stator and an ironless, disk-shaped actuator, also referred to as a rotor, situated opposite the stator, wherein the magnetic field driving the rotor is parallel to the axis of rotation of the rotor and stator. The rotor is moved by electrical control of the stator and drives, for example, a shaft or a wheel. With regard to dimensions and performance data, the axial flux electric machine can be adapted to the selected field of application, for example the type of vehicle or component to be driven by the electric machine.

[0009] The axial flux motor also has a housing. The housing is used to accommodate various components of the motor. In order to accommodate the stator-actuator arrangement, the housing of the motor comprises a housing part, which is in particular cylindrical. Due to the cylindrical shape, the housing part can be optimally matched to the outer shape of the stator-actuator arrangement.

[0010] For the axial flux motor described here, it is also provided that one or more nozzles are arranged in the housing, wherein the nozzle is designed to supply liquid coolant to the rotor surface facing the stator. Therefore, the nozzle is a corresponding part of the cooling system and can deliver liquid coolant to the rotor surface. The delivery of the liquid coolant can be achieved, for example, by spraying, dripping or conventional spraying of the coolant via the nozzle. To this end, the nozzle can be installed on or in the housing wall, or can also be installed on the stator or shaft. The nozzle can also be installed on or near the stator or on or near the housing wall, as long as the discharge direction of the coolant points to the direction of the rotor surface. Preferably, more than 2 nozzles, preferably more than 4 nozzles and more preferably more than 8 nozzles can be used in the motor to cool the rotor. In addition, one or more nozzles can also be installed on the rotor itself, wherein the coolant can be output to the surface of the rotor through the nozzle. In principle, a coolant with sufficient heat capacity known to those skilled in the art can be used as a liquid coolant. The nozzle is usually a cylindrical hollow body that allows the liquid flow to be discharged through the opening in a directional manner. Only one surface side of the rotor is cooled by this structure. By providing the nozzles, the surface side of the rotor facing away from the stator does not come into contact with the coolant. However, the opposite rotor side can also be cooled separately.

[0011] According to the present invention, the specific orientation of one or more nozzles on the rotor surface facing the stator for outputting liquid coolant into the housing enables the rotor to be effectively cooled at higher rotation speeds and therefore higher temperatures. Reducing the rotor temperature can protect other components of the motor from overheating and maintain the electrical performance of the motor.

[0012] In particular, these advantages are achieved by orienting the nozzles in the direction of the rotor surface facing the stator. This type of rotor cooling is significantly more efficient than other cooling solutions. For example, liquid cooling can achieve significantly higher energy dissipation of the rotor than pure air cooling or air convection cooling of the rotor.

[0013] The above-described design thus enables a particularly advantageous rotor cooling design. As described above, a significantly higher amount of energy can be output, so that a smoother operation of the electric machine can be achieved even at high loads and high speeds. According to the invention, overheating under high loads can thus be prevented in a very effective manner.

[0014] Therefore, it is preferred that the nozzle is arranged to supply the coolant only to the following rotor surface area, that is, the distance of the rotor surface area from the rotation axis is greater than or equal to 0% of the rotor radius and less than or equal to 30% of the rotor radius. In order to obtain the most uniform cooling of the entire rotor surface, it has proven to be advantageous that the coolant is more easily supplied to the rotor surface area close to the axis through the nozzle. Due to the centrifugal force generated, the coolant is then uniformly transported to the rotor area away from the axis. Therefore, the entire rotor surface is uniformly cooled. For example, if the radius of the rotor is 10 cm, the coolant is only applied to the rotor surface area that is at most 3 cm away from the rotor axis.

[0015] Additionally or alternatively, it is advantageous that the rotor surface has a notch / recess, which is designed to guide the coolant from an area on the rotor surface close to the rotation axis to an area away from the rotation axis. In order to obtain as uniform cooling as possible over the entire rotor surface, it is advantageous to provide a notch on the rotor surface, which diverts the applied coolant flow to the rotor surface in a predetermined direction. For example, the notch can be in the form of a hemispherical or teardrop-shaped groove, which, due to the specific shape and depth of the groove, enables the impinging coolant flow to be deflected to a specific surface area of ​​the rotor to varying degrees. The depth of the notch on the rotor surface can, for example, be greater than or equal to 0.5 mm, preferably greater than or equal to 0.75 mm, and more preferably greater than or equal to 1 mm.

[0016] More preferably, there are notches with different orientations on the rotor surface, wherein at least one notch extends concentrically with the axis of rotation, and the other notch does not extend concentrically with the axis of rotation. In order to effectively distribute the coolant applied to the rotor surface at one time, it is advantageous to provide at least two different types of notches on the rotor surface. In particular, different types of notches can be distinguished by their symmetry relative to the rotor axis. One or more notches can extend concentrically around the axis of rotation of the rotor. Particularly preferably, this type of notch can be closer to the axis of rotation of the rotor. Other orientations of the notch may not be concentric with respect to the axis of rotation of the rotor. For example, these non-concentric notches can extend radially toward the periphery of the rotor. Non-concentric notches can be curved, for example, rather than straight. It is also feasible that different notches can also have different profiles, respectively. Non-concentric notches can guide the coolant to the rotor surface more specifically.

[0017] Advantageously, the coolant is supplied to the rotor surface with an elevation deviation of less than or equal to ±89° relative to the surface normal of the rotor. Less than or equal to refers to the absolute value of the angle. In order to wet the entire rotor surface as evenly as possible, it is advantageous that the coolant is not supplied to the rotor surface head-on, but with a certain angle deviation. In particular, this helps to reduce the portion of coolant that is directly deflected back from the rotor surface to the stator gap. The surface film of the coolant remains near the rotor surface, and thus prevents the formation of a continuous liquid film extending over the entire gap between the rotor and the stator. Here, the given angle range involves an elevation angle γ relative to the surface normal of the rotor surface. When the angle deviation relative to the normal is 89°, the coolant is almost discharged parallel to the rotor surface. The symbol indicates whether the liquid is supplied along the direction of rotation or against the direction of rotation. Preferably, the lower limit of the angle deviation can be, for example, ±0.5°, wherein, under this deviation, the coolant is supplied to the surface substantially vertically. Depending on the operating point, i.e., for example, as a function of the rotor temperature and / or the rotational speed, it is advantageous to supply the coolant to the surface at a varying azimuth angle θ, for example in the form of 0°≤θ≤359°. However, it is possible that the supply direction of the coolant can also be varied depending on the operating point by means of an adaptable nozzle direction.

[0018] It is also preferred that the nozzles are arranged to supply the liquid coolant through the rotor onto the rotor surface facing the stator. In this embodiment, the coolant is supplied through the rotor onto the rotor surface opposite the stator. In this case, the nozzles are fastened to the rotor itself or are located inside the rotor. This embodiment enables the coolant to be applied particularly precisely to the rotor surface and overall allows effective cooling of the rotor with less coolant flow.

[0019] Advantageously, at least one coolant outlet is arranged on the housing wall. In order to discharge the once applied and now relatively hot coolant from the housing, it is advantageous if at least one coolant outlet is present on the housing wall. The outlet can be designed in the form of a valve which, depending on the applied pressure or, for example, also on the temperature, enables the accumulated coolant liquid to flow out of the housing.

[0020] Preferably, the valve can also be arranged to discharge coolant from the housing in a pressure- and / or temperature-dependent manner. In particular, the pressure as a control parameter for switching the discharge valve can be suitable for removing coolant no longer required from the housing. Preferably, a pressure range can be given to the control valve, within which the pressure in the housing should be maintained. Within this pressure range, an excess or insufficient amount of coolant in the housing can be avoided.

[0021] In a preferred embodiment, the supply speed of the coolant to the rotor surface is greater than or equal to 0.25L / min and less than or equal to 5L / min. In order to form a coolant flow directed to the surface as much as possible, it is advantageous to supply the coolant within the speed range given above. Higher speeds may cause the coolant to return from the rotor surface to the gap between the rotor and the stator undesirably. Lower speeds may cause the initial direction of the coolant flow on the surface to be unable to maintain a sufficient time. Therefore, the given range is suitable for providing sufficient and limited coolant flow for a wide range of rotation speeds of the rotor. Preferably, the supply speed of the coolant to the rotor surface is greater than or equal to 0.5L / min and less than or equal to 2.5L / min, more preferably, greater than or equal to 0.75L / min and less than or equal to 1.5L / min.

[0022] In an advantageous design, one or more nozzles may be arranged to adjust the amount of liquid coolant supplied over time in relation to the rotor temperature and / or the rotor speed. It is advantageous for the on-demand cooling of the rotor surface that a constant amount of coolant is not always supplied to the rotor. In particular, the amount of coolant supplied per unit time may be adjusted in relation to the rotor temperature or in relation to the rotor speed as a whole. These two adjustment parameters enable on-demand matching of the amount of coolant. Preferably, one or more nozzles may be designed to adjust the amount of liquid coolant supplied over time in relation to the rotor temperature and the rotor speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below with reference to the accompanying drawings, in which single or multiple features may constitute features of the present invention alone or in combination. In addition, the accompanying drawings are only exemplary and do not have any limitation.

[0024] Figure 1 schematically shows a cross section of an axial flux electric machine according to the prior art;

[0025] Figure 2 Schematically shows a cross section of an axial flux machine according to the invention;

[0026] Figure 3 Schematically shows a cross section of an axial flux machine according to the invention;

[0027] Figure 4 A rotor surface with notches according to the invention is shown. DETAILED DESCRIPTION

[0028] Figure 1 The cross section of an axial flux machine 1 according to the prior art is schematically shown. The shown part of the axial flux machine 1 comprises a disc-shaped stator 2 and a disc-shaped rotor 3 opposite thereto and separated by a gap. The rotor 3 and the stator 2 have the same rotating axis 4 and are placed in a housing 5.

[0029] Figure 2 A cross section of an axial flux machine 1 according to the invention is schematically shown. Figure 1 In addition to the elements described in the figure, the figure also shows that a plurality of nozzles 6 are arranged on the housing 5 and the rotating shaft 4. The rotating shaft 4 can be designed in the form of a shaft component, for example. The nozzles 6 are correspondingly arranged so that the coolant can be ejected from the nozzles 6 in the direction of the surface of the rotor 3. In addition to the nozzles 6 shown, other nozzles can also be installed on the housing 5 or the stator 2 or on the shaft component at the rotating shaft 4.

[0030] Figure 3 A cross section of an axial flux machine according to the invention is schematically shown. In addition to being able to supply 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 input through the surface of the rotor 3 facing away from the stator 2 and leaves the rotor 3 on the other surface side. In this way, effective cooling of the surface side of the rotor 3 facing the stator 2 can be achieved.

[0031] Figure 4 The surface of the rotor 3 with notches 7, 8 according to the invention is shown. In order to guide the coolant to the surface of the rotor 3 in a targeted manner, notches 7, 8 are provided on the surface of the rotor 3 facing the stator 2. In order to achieve improved cooling of the entire surface, the notches 7, 8 can have different orientations. Therefore, multiple notches 8 can be arranged with reference to the axis of rotation. However, the notch 7 can also be arranged non-concentrically on the surface of the rotor 3. In addition, two notches 7, 8 can also be connected to each other. The two notches can also have different contours. Through these notches 7, 8, it can be ensured that the surface of the rotor 3 is uniformly and completely wetted by the coolant.

[0032] List of reference numerals:

[0033] 1 Axial flux motor

[0034] 2 Stator

[0035] 3 Rotor

[0036] 4 Rotation axes

[0037] 5 Housing

[0038] 6 Nozzles

[0039] 7 Non-concentrically extending notches

[0040] 8 Concentrically extending gaps

Claims

1. An axial flux motor (1), comprising a housing (5) and at least one disc-shaped stator (2) and at least one disc-shaped rotor (3) arranged in the housing (5), the disc-shaped rotor being opposite to the disc-shaped stator (2) along a rotation axis (4) of the motor and being separated from the stator by a gap, characterized in that: One or more nozzles (6) are arranged in the housing (5), wherein the nozzles (6) are designed to supply liquid coolant to the rotor surface facing the stator (2).

2. The axial flux motor according to claim 1, characterized in that: The nozzles (6) are designed to supply cooling liquid only to the rotor surface area whose distance from the rotation axis (4) is greater than or equal to 0% and less than or equal to 30% of the rotor radius.

3. An axial flux electric machine according to any one of the preceding claims, characterised in that The rotor surface has indentations (7, 8), wherein the indentations (7, 8) are designed to guide the cooling liquid from an area on the rotor surface close to the rotating axis to an area far from the rotating axis.

4. The axial flux motor according to claim 3, characterized in that: On the rotor surface there are recesses (7, 8) with different orientations, wherein at least one recess (8) extends concentrically to the axis of rotation, while the other recess (7) does not extend concentrically to the axis of rotation (4).

5. An axial flux electric machine according to any one of the preceding claims, characterised in that The cooling liquid is supplied to the rotor surface at an elevation angle deviation of less than or equal to ±89° relative to the surface normal of the rotor (3).

6. An axial flux electric machine according to any one of the preceding claims, characterised in that The nozzles (6) are arranged to supply liquid coolant through the rotor (3) onto the rotor surface facing the stator (2).

7. An axial flux electric machine according to any one of the preceding claims, characterised in that At least one coolant outlet is arranged on the housing wall.

8. The axial flux motor according to claim 7, characterized in that: The nozzle (6) is provided to regulate the amount of liquid coolant supplied over time as a function of the rotor temperature and / or the rotor speed.

9. An axial flux electric machine according to any one of the preceding claims, characterised in that The coolant supply rate to the rotor surface is greater than or equal to 0.25 L / min and less than or equal to 5 L / min.

10. An axial flux electric machine according to any one of the preceding claims, characterised in that The nozzle (6) is provided to regulate the amount of liquid coolant supplied over time as a function of the rotor temperature and / or the rotor speed.

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