Electric machine

Abstract

An electric machine (1), in particular for an electrically operated powertrain (2) of a motor vehicle (3), comprising a currentable stator winding (5) arranged in a stator (4) and a rotor (6) rotatable relative to the stator (4), wherein the stator winding (5) is connected in the region of one of its winding heads (7) to a power electronics (9) of the electric machine (1) via an HV terminal (8), and the electric machine (1) has a cooling system (10) with a cooling fluid (11) flowing through the electric machine (1), wherein this fluid exits the cooling system (10) at at least one end-face outlet opening (12) in an axial direction along a spray path (13), wherein the HV terminal (8) has a fluid guide element (14) that engages in the spray path (13) of the exiting cooling fluid (11) and is configured such thatthat at least part of the cooling fluid (11) is directed after impacting the fluid guide element (14) onto the area of ​​the winding head (7) where the HV terminal (8) is positioned.

Description

The present invention relates to an electric machine, in particular for an electrically operated drive train of a motor vehicle, comprising a current-carrying stator winding arranged in a stator and a rotor rotatable relative to the stator, wherein the stator winding is connected to a power electronics of the electric machine via an HV terminal in the region of one of its winding heads, and the electric machine has a cooling system with a cooling fluid flowing through the electric machine, wherein this fluid exits the cooling system at at least one end face outlet opening in an axial direction along a spray path. In the prior art, the basic principle of an HV terminal (high-voltage terminal) or busbar in an electric machine is used to provide a connection point for the motor's high-voltage supply. These terminals serve as the connection point for the high-voltage cables that supply the necessary current to operate the motor, particularly in industrial or power-intensive applications where high currents and voltages are required. To ensure the proper operation of the motor and to avoid safety risks such as short circuits or overheating due to poor connections, these connections must be safe and reliable. Therefore, the proper design and installation of the HV terminals are crucial for the performance and safety of the electric drive system. Electric machines generate heat during operation due to electrical losses and the current flowing through the windings. When electric current flows through a conductor, heat is generated due to the material's electrical resistance. The higher the current flowing through the busbar, the greater the amount of heat generated. Overheating can significantly impair the motor's performance, as it can lead to problems such as component deformation and reduced efficiency. Overheating is a particularly critical issue with high-voltage terminals, as it can cause material damage and thus reduce the motor's lifespan and performance. To reduce the heat generated by high electrical currents, prior art uses oil that flows through channels and is distributed to specific points to cool the components and lower the temperature. However, this cooling system has several disadvantages. A significant drawback is that the oil cannot fully coat all areas within the motor, resulting in uneven cooling and potential hot spots. These inadequately cooled areas can overheat, leading to a deterioration of material properties and ultimately damage to the electric motor. Furthermore, the materials used in the HV terminals, such as plastic overmolding and copper, are limited by their melting points. Overheating can cause these materials to lose their structural integrity, compromising the reliability and safety of the electrical machine. Electrical machines with a fluidic cooling system are known from publications DE 10 2022 128 479 A1 , DE 21 63 697 A , DE 10 2010 021 435 A1 and US 2021 / 0 067 006 A1. The object of the invention is therefore to provide an electrical machine that avoids or at least reduces the problems known from the prior art. This problem is solved by an electric machine, in particular for an electrically operated powertrain of a motor vehicle, comprising a current-carrying stator winding arranged in a stator and a rotor rotatable relative to the stator, wherein the stator winding is connected to power electronics of the electric machine via an HV terminal in the region of one of its winding heads, and the electric machine has a cooling system with a cooling fluid flowing through the electric machine, wherein this fluid exits the cooling system at at least one end-face outlet opening in an axial direction along a spray path, wherein the HV terminal has a fluid guide element that engages in the spray path of the exiting cooling fluid and is configured such that at least a part of the cooling fluid is directed onto the region of the winding head where the HV terminal is positioned after striking the fluid guide element. This electric motor offers the advantage of directing the cooling fluid precisely to the connection area of ​​the winding head with the high-voltage terminal. This results in efficient cooling of this potential hot-spot region of the stator, where high electrical currents flow and significant heat losses can occur. Targeted cooling of this critical area improves thermal stability, prevents overheating, and extends the service life of the electric motor. A further benefit is the increased power output of the electric motor, achieved through efficient hot-spot cooling. Moreover, this is achieved with minimal design effort, reducing the complexity and manufacturing costs of the electric motor. HV terminal For the purposes of this patent application, an HV terminal is a high-voltage capable connection device used in an electric machine to establish a safe and reliable connection between the stator winding and the external power electronics. The HV terminal comprises busbars and insulating sections to ensure the safe and efficient conduction of electrical current. The busbars are made of highly conductive materials that withstand both high electrical and thermal stresses. These busbars ensure the safe and reliable conduction of the high currents and voltages required for the operation of the electrical machine. Insulating sections are integrated into the HV terminal to prevent short circuits and electrical flashovers. These insulating sections are made of materials with high electrical insulation properties and contribute significantly to the safety and reliability of the HV terminal. The high-voltage terminal can preferably be configured for a three-phase electric machine. In this case, it comprises three separate busbars, each assigned to one of the three phases. Each of these busbars is separated from the others by insulating sections to prevent short circuits and ensure safety. This arrangement enables optimal distribution of electrical power across the three phases of the machine and contributes to the efficient and stable operation of the drive system. Another key function of the HV terminal is the simplified connection and electrical contacting of the individual phases of the stator winding at the winding head. Thanks to the spatially defined arrangement of the corresponding busbars within the HV terminal, they do not need to be mounted individually, thus reducing installation time and simplifying assembly. This advantageous design improves the efficiency and reliability of the electric machine, as it ensures precise and consistent contacting of the stator winding. The HV terminal preferably comprises a first annular section for contacting the winding head and a second annular section for connecting to the external power electronics. The two sections are arranged to ensure optimal electrical connection and mechanical stability. Advantageously, a fluid guide element is integrated between these two sections to provide targeted cooling of the connection area. Cooling system For the purposes of this patent application, a cooling system is a device or arrangement that serves to remove heat from an electrical machine in order to ensure its thermal stability and performance. Such a cooling system preferably comprises a cooling fluid flowing through the electric machine, which dissipates heat from the heat-sensitive components of the machine, in particular from the stator windings and the connection areas such as the connection of the winding head to the HV terminal. The cooling system is advantageously designed to ensure continuous circulation of the cooling fluid. This is achieved by a pump that circulates the cooling fluid through the machine's electrical components and then through a heat exchanger, where the absorbed heat is transferred to the environment or another medium. The cooled fluid is then returned to the machine, creating a closed loop. Preferably, the cooling system has one or more end-face outlet openings through which the cooling fluid exits the cooling system in an axial direction along a defined spray path. A fluid guidance element, which engages in this spray path, directs at least a portion of the exiting cooling fluid specifically to the critical areas of the machine, in particular to the connection area of ​​the winding head with the HV terminal. Additionally, the cooling system can incorporate cooling channels that extend through the stator. These cooling channels allow the cooling fluid to be routed directly through the stator, resulting in uniform and efficient heat dissipation along its entire length. This significantly improves the system's cooling performance, as the heat is dissipated immediately at its source, effectively reducing the temperature of the stator windings and surrounding components. Cooling fluid For the purposes of this patent application, a cooling fluid is a medium that circulates through the cooling system of an electric machine to efficiently dissipate the heat generated during operation and thus prevent overheating. The cooling fluid's function is to absorb the heat generated by the hot spots of the electric machine, particularly the winding heads and the high-voltage terminals, and to carry this heat away from the machine. This ensures a uniform temperature distribution, which increases the thermal stability and performance of the machine. Preferably, the cooling fluid can consist of various liquid or gaseous media that have high thermal conductivity and low viscosity to enable efficient heat transfer and smooth circulation. Liquid cooling fluids include water, water-glycol mixtures, and specialty oils. Water is frequently used as a cooling fluid due to its high specific heat capacity and good availability. To prevent corrosion and deposits, it can be mixed with suitable inhibitors. Water-glycol mixtures can be used to lower the freezing point of the cooling fluid, thus enabling a wider operating range across different ambient temperatures. Glycol content also increases the lubricating properties of the cooling fluid. In specific applications, synthetic or mineral oils can also serve as cooling fluids, particularly when electrical insulation is required. The cooling fluid preferably also contains additives that provide corrosion protection and prevent foaming and bubbling. These additives contribute to the long-term stability and efficiency of the cooling system by increasing the service life of the components and preventing the formation of deposits or contaminants. Gaseous cooling fluids include air, nitrogen, and helium. Air is frequently used as a cooling fluid due to its availability and ease of handling. Nitrogen is preferred when an inert gas environment is required to prevent oxidation. Helium offers very effective cooling due to its excellent thermal conductivity and low density. outlet opening For the purposes of this patent application, an outlet opening is a special opening in the cooling system of the electric machine through which the cooling fluid is selectively discharged to cool specific areas within the machine. The function of the outlet is to allow the cooling fluid to escape in a controlled direction and quantity to ensure the cooling of particularly heat-sensitive components of the electric machine, such as the connection area of ​​the winding head with the HV terminal. This targeted cooling increases thermal stability and improves the machine's performance and service life. The outlet opening can be implemented in various designs. For example, it can be a single opening or a series of openings to optimize cooling performance. Preferably, the outlet opening is designed to be arranged radially outside the rotor. This positioning allows the cooling fluid to be efficiently directed towards the components to be cooled without being obstructed by the rotor. Advantageously, the outlet opening can be configured axially along a spray path, ensuring a uniform distribution of the cooling fluid. The geometry of the outlet opening can be designed in various ways to meet the specific requirements of the electric machine. One possible embodiment is a round or oval opening, which allows for a uniform and concentrated discharge of the cooling fluid. Another possible shape is a slot-shaped outlet opening that extends over a certain length, thereby ensuring a wider distribution of the cooling fluid. This slot-shaped opening can preferably be oriented in a direction that optimally utilizes the spray path to achieve effective cooling. Preferably, the outlet opening can be designed such that it causes the fluid to exit parallel to the axis of rotation. Alternatively, the opening can also be arranged at a specific angle to the axis of rotation, which allows for flexible adjustment of the cooling fluid flow and thus enables the cooling to be adapted to different operating conditions of the electric machine. Furthermore, the outlet opening can be configured to produce a spray pattern with a defined opening angle. Preferably, this opening angle is between 0° and 5°. A narrow opening angle ensures that the cooling fluid is concentrated and directed precisely to the critical areas, thus increasing cooling efficiency and optimizing the performance of the electric machine. Preferably, the outlet opening has a flow cross-section between 0.5 and 4.0 mm², particularly preferably between 0.75 and 3.5 mm². Furthermore, it is preferred that the outlet opening has a circular cross-section with a diameter between 1 and 2 mm. Spray path For the purposes of this patent application, a spray path is the targeted exit path of a cooling fluid extending axially from an outlet opening of the cooling system. The spray path is designed to direct the cooling fluid precisely to specific areas of the electric machine to ensure efficient cooling. The function of the spray path is therefore, in particular, to direct the cooling fluid exiting the cooling system directly to critical components of the electric machine. Preferably, the cooling fluid is directed to the connection area of ​​the winding head with the high-voltage terminal to achieve effective heat dissipation there. The spray path can be designed in various ways to maximize cooling efficiency. Preferably, the cooling fluid is expelled from the outlet at a defined angle and speed to achieve targeted distribution onto the areas to be cooled. Preferably, the cooling fluid has a velocity of 0.5–10 m / s, particularly preferably 1–8 m / s, in the area of ​​the outlet opening. Preferably, a volume flow rate of 0.1–0.5 l / min, particularly preferably between 0.19–0.35 l / min, exits from the outlet opening. Fluid guide element For the purposes of this patent application, a fluid guiding element is a component within the cooling system of an electric machine that serves to selectively direct and control the flow of a cooling fluid. This element is configured to influence the direction and distribution of the exiting cooling fluid after it emerges from an outlet opening, in order to ensure optimal cooling of critical areas, such as the connection area of ​​the winding head with the HV terminal. The fluid guide element thus fulfills the primary function of directing the cooling fluid to the areas requiring intensive cooling, particularly the stator's hot-spot regions. This targeted direction of the cooling fluid improves heat dissipation in these areas, contributing to the thermal stability and performance of the electric machine. Preferably, the fluid guide element is arranged on the plastic overmolding of the HV terminal, which ensures stable and secure positioning. Advantageously, the fluid guide element can be formed integrally with the plastic overmolding of the HV terminal, which increases mechanical stability and reduces manufacturing costs. Alternatively, the fluid guide element can also be designed as a separate component. In this case, it is preferably arranged and attached to the HV terminal to ensure targeted and effective cooling. The fluid guide element can protrude radially inwards from the HV terminal, enabling effective guidance of the cooling fluid into the desired area without unwanted turbulence or losses. It can be shaped as an essentially rectangular fin, ensuring simple and cost-effective manufacturing as well as precise guidance of the cooling fluid. Furthermore, the fluid guide element can be oriented at an adjustable angle to the radial axis of extension or the axis of rotation of the rotor. This design allows for flexible adaptation of the cooling fluid guidance to different operating conditions, thereby achieving optimal cooling and thus improved overall performance and reliability of the electric machine. Advantageous embodiments of the invention According to an advantageous embodiment of the invention, the fluid guide element can be arranged on a plastic overmolding of the HV terminal and / or on an HV connection rail. Arranging the fluid guide element on the plastic overmolding of the HV terminal ensures stable and secure positioning of the fluid guide element. This design enables precise guidance of the cooling fluid without additional holding devices for the fluid guide element. This reduces the complexity and manufacturing costs of the electric machine while simultaneously improving reliability and cooling performance. According to a further preferred embodiment of the invention, the fluid guide element can also be formed integrally, and in particular monolithically, with the plastic overmolding of the HV terminal and / or integrally, and in particular monolithically, with an HV connection rail. This results in increased mechanical stability and reliability of the entire assembly, as there are no weak points or potential points of failure between separate components. Furthermore, this simplifies the manufacturing and assembly process and reduces production costs. Furthermore, according to another advantageous embodiment of the invention, the fluid guide element can protrude radially inwards from the HV terminal, thereby effectively directing the cooling fluid into the desired area of ​​the winding head without causing undesirable turbulence or coolant loss. This results in improved cooling performance and a more uniform temperature distribution within the electric machine. According to a further particularly preferred embodiment of the invention, the fluid guide element can be shaped as a substantially rectangular fin. Designing the fluid guide element as a substantially rectangular fin enables simple and cost-effective manufacturing while simultaneously ensuring effective guidance of the cooling fluid. The shape of the fin ensures that the cooling fluid is directed evenly and precisely onto the areas to be cooled, thus increasing the efficiency of the cooling system. Furthermore, the invention can also be further developed in that the fluid guide element is aligned at an angle α ≥ to the radial axis of extension of the fluid guide element, so that the tangential deflection of the cooling fluid after impacting the fluid guide element is adjustable via the angle α. The alignment of the fluid guide element at an adjustable angle to the radial axis of extension allows for flexible adaptation of the cooling fluid guidance to different operating conditions. In a further preferred embodiment of the invention, the fluid guide element can also be aligned at an angle β ≥ to the rotor's axis of rotation, so that the tangential deflection of the cooling fluid after impacting the fluid guide element is adjustable via the angle β. By aligning the fluid guide element at an adjustable angle to the rotor's axis of rotation, the tangential deflection of the cooling fluid can be finely adjusted. This offers the advantage that the cooling can be specifically directed to particular areas of the winding head, thereby achieving improved heat dissipation and increased operating efficiency. It can also be advantageous to further develop the invention such that the outlet opening is arranged radially outside the rotor. Arranging the outlet opening radially outside the rotor ensures that the cooling fluid is directed onto the winding head with high efficiency and without disruptive influences from rotor operation. This improves cooling performance and reduces the risk of hotspots and thermal stresses within the electric machine. According to a further preferred embodiment of the invention, the stator winding can be configured as a hairpin winding. Configuring the stator winding as a hairpin winding offers the advantage of higher packing density and better heat dissipation compared to conventional winding types. This results in an overall more efficient and powerful electric machine that can also be built more compactly. Finally, the invention can also advantageously be implemented such that the HV terminal has a first annular section for contacting the winding head and a second annular section for connection to power electronics, wherein the fluid guide element is arranged circumferentially between the first section and the second section. The fluid guide element arranged between them ensures targeted cooling of these connection points, which increases the thermal stability and electrical performance of the entire assembly. The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention. It shows: Fig. 1 a wound stator with an HV terminal in a perspective view, Fig. 2 an HV terminal in a perspective detail view, Fig. 3 an HV terminal in a top view, Fig. 4 an HV terminal from an axial view, Fig. 5 an electric machine in a cross-sectional view, Fig. 6 a motor vehicle with an electrically operated drive train in a schematic representation, Fig. 7 a cooling system of an electric machine in a schematic representation. Fig. 1 shows a stator 4 of an electric machine 1, in particular for an electrically operated drive train 2 of a motor vehicle 3, as is also shown by way of example in Fig. 6. As can be seen from the comparison of Fig. 1 with Fig. 5, the electric machine 1 comprises a current-carrying stator winding 5 arranged in a stator 4 and a rotor 6 rotatable relative to the stator 4, wherein the stator winding 5 is connected in the area of ​​one of its winding heads 7 via an HV terminal 8 to a power electronics 9 of the electric machine 1. The electric machine 1 further comprises a cooling system 10 with a cooling fluid 11 flowing through the electric machine 1, the fluid exiting the cooling system 10 at at least one end-face outlet opening 12 in an axial direction along a spray path 13. This is shown in Fig. 7. The outlet opening 12 is arranged radially outside the rotor 6. The HV terminal 8 now has a fluid guide element 14 that engages in the spray path 13 of the discharged cooling fluid 11 and is configured such that at least a portion of the cooling fluid 11, after impacting the fluid guide element 14, is directed onto the area of ​​the winding head 7 where the HV terminal 8 is positioned. The fluid guide element can be seen in Figures 2-4. In the illustrated embodiment, the fluid guide element 14 is formed integrally, and in particular monolithically, with the plastic overmolding 15 of the HV terminal 8 and projects radially inwards from the HV terminal 8. In the illustrated embodiment, the fluid guide element 14 is shaped as a substantially rectangular fin. The HV terminal 8 has a first annular section 18 for contacting the winding head 7 and a second annular section 19 for connection to a power electronics 20, wherein the fluid guiding element 14 is arranged circumferentially between the first section 18 and the second section 19. Figure 3 shows that the fluid guide element 14 is aligned at an angle α ≥ 0 to its radial axis of extension 16, which passes through the rotor axis 17, so that the tangential deflection of the cooling fluid 11 after impacting the fluid guide element 14 is adjustable via the angle α. The radial axis 16 passes through the rotor axis 17. Figure 4 shows that the fluid guide element 14 is aligned at an angle β ≥ 0 to the axis of rotation 17 of the rotor 6, so that the tangential deflection of the cooling fluid 11 after impacting the fluid guide element 14 is adjustable via the angle β. 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 Drive train 3 Motor vehicle 4 Stator 5 Stator winding 6 Rotor 7 Winding heads 8 HV terminal 9 Power electronics 10 Cooling system 11 Cooling fluid 12 Outlet opening 13 Spray path 14 Fluid guide element 15 Plastic overmolding 16 Extension axis 17 Rotation axis 18 Section 19 Section 20 HV connection rail

Claims

An electric machine (1), in particular for an electrically operated powertrain (2) of a motor vehicle (3), comprising a currentable stator winding (5) arranged in a stator (4) and a rotor (6) rotatable relative to the stator (4), wherein the stator winding (5) is connected in the region of one of its winding heads (7) to a power electronics (9) of the electric machine (1) via an HV terminal (8), and the electric machine (1) has a cooling system (10) with a cooling fluid (11) flowing through the electric machine (1), wherein this fluid exits the cooling system (10) at at least one end-face outlet opening (12) in an axial direction along a spray path (13), wherein the HV terminal (8) has a fluid guide element (14) that engages in the spray path (13) of the exiting cooling fluid (11) and is configured such thatthat at least part of the cooling fluid (11) is directed after impacting the fluid guide element (14) onto the area of ​​the winding head (7) where the HV terminal (8) is positioned. Electric machine (1) according to claim 1 , characterized in that the fluid guiding element (14) is arranged on a plastic overmolding (15) of the HV terminal (8) and / or on an HV connection rail (20). Electric machine (1) according to claim 2, characterized in that the fluid guiding element (14) is formed in one piece, in particular also monolithically, with the plastic overmolding (15) of the HV terminal (8) and / or in one piece, in particular also monolithically, with and / or on an HV connection rail (20). Electric machine (1) according to one of the preceding claims, characterized in that the fluid guiding element (14) protrudes radially inwards from the HV terminal (8). Electric machine (1) according to one of the preceding claims, characterized in that the fluid guiding element (14) is shaped as a substantially rectangular fin. Electric machine (1) according to one of the preceding claims, characterized in that the fluid guide element (14) is aligned at an angle α ≥ 0 to the radial extension axis (16) of the fluid guide element (14), so that the tangential deflection of the cooling fluid (11) after impacting the fluid guide element (14) is adjustable via the angle α. Electric machine (1) according to one of the preceding claims, characterized in that the fluid guide element (14) is aligned at an angle β ≥ 0 to the axis of rotation (17) of the rotor (6), so that the tangential deflection of the cooling fluid (11) after impacting the fluid guide element (14) is adjustable via the angle β. Electric machine (1) according to one of the preceding claims, characterized in that the outlet opening (12) is arranged radially outside the rotor (6). Electric machine (1) according to one of the preceding claims, characterized in that the stator winding (5) is designed as a hairpin winding. Electric machine (1) according to one of the preceding claims, characterized in that the HV terminal (8) has a first annular section (18) for contacting the winding head (7) and a second annular section (19) for connection to a power electronics (9), wherein the fluid guiding element (14) is arranged circumferentially between the first section (18) and the second section (19).

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