Optimized electric machine for driving a rail vehicle
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-31
- Publication Date
- 2026-03-11
Smart Images
Figure EP2024065077_06032025_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] Optimized electric machine for driving a rail vehicle
[0003] The invention relates to an electrical machine for driving a rail vehicle according to the preamble of patent claim 1.
[0004] Electric machines for driving vehicles must meet a wide range of requirements. The optimal design of such a machine for its specific operational application represents a challenging task, particularly since the multitude of different requirements is made more difficult by the fact that these requirements influence one another. Multi-criteria optimization methods are known for solving this optimization task. In these methods, the influence of each variable parameter on the requirements to be met is determined through a large number of simulated design variants for a machine in order to derive the optimal parameter set for an electric machine designed for the operating behavior.
[0005] An optimized electric machine for driving a hybrid vehicle, such as a passenger car, truck, or bus, is known from patent specification EP 3 542 445 B1. The synchronous machine integrated into the internal combustion engine uses a rotor with two pole magnets per pole arranged in a V-shape. The stator has axially running stator slots that run evenly around an axis of the electric machine, and through which a stator winding runs. The rotor comprises axially running poles and is mounted within the stator so that it can rotate about the axis of the electric machine. The pole magnets have a rectangular cross-section and are each arranged in axially running pole openings. The electric machine has a number of holes greater than or equal to 1, where the number of holes is understood to be the number of stator slots divided by the number of phases and divided by the number of poles of the rotor.Using multi-objective optimization, the maximum torque, maximum power, short-circuit current, noise level, tonality, cycle efficiency, material costs, losses, and torque ripple of the machine are optimized. Together with an outer and an inner pole cover and a specific offset angle of the pole magnets, there are two optimized parameter sets for the stator: the ratios of tooth height to yoke thickness, the ratio of tooth width to slot width at the tooth root and at the tooth tip, and the ratio of the slot width at the tooth root to the slot width at the tooth tip.
[0006] Electric machines of the type mentioned above, which are used as traction or drive motors in rail vehicles, must have a high power-to-weight ratio and, at the same time, efficient and cost-effective cooling. Furthermore, manufacturing costs, overall weight and noise emissions must be kept low. Added to this is the very limited installation space in the area of the bogie of a rail vehicle, which is why the machines have to be as compact as possible. Due to the specified driving cycle, i.e. the movement or driving sequence with regard to starting, driving, braking and stopping of the rail vehicle, the operation of the electric machine requires a wide speed and load range with high levels of efficiency. Since a large number of transmission solutions can be used in traction drives for rail vehicles, a transmission ratio of the respective transmission must also be taken into account for optimum driving cycle behavior.Multi-objective optimization is particularly challenging for encapsulated machines, as these machine designs, due to their encapsulated active arrangement, place high demands on sufficient cooling and, at the same time, must be efficient and quiet.
[0007] The invention is based on the object of providing an electrical machine of the type mentioned at the outset which, due to its driving behavior, is optimized with regard to energy efficiency, noise emission, manufacturing costs and, above all, cooling behavior.
[0008] The problem is solved by a generic electrical machine with the features specified in the characterizing part of patent claim 1.
[0009] An electrical machine of the type mentioned at the beginning is designed and intended for driving a rail vehicle, for example a metro train. It comprises an active arrangement which is arranged within a housing of the machine and encapsulated from the machine's surroundings and has a stator and a rotor which can rotate about a rotor axis relative to the stator. The encapsulation protects the active arrangement from moisture and dirt from the environment. The machine further comprises an external cooling path for guiding cooling air drawn in from the environment outside the encapsulated active arrangement and an internal cooling path for guiding cooling air inside the encapsulated active arrangement. The rotor has a hollow cylindrical rotor laminated core which is connected in a rotationally fixed manner to a rotor shaft which is rotatably mounted in the housing and can rotate about the rotor axis.The rotor has a number of magnetic poles, each of which is formed by two permanent magnets arranged in a V-shape relative to one another and fitted into the magnetic pockets that axially penetrate the rotor core. Furthermore, the rotor has at least one cooling hole for each magnetic pole that axially penetrates the rotor core and through which the internal cooling path leads. Preferably, two parallel cooling holes are provided for each magnetic pole. These holes can be arranged, for example, next to one another and at the same radial distance from the rotor axis and can have circular or elongated hole cross-sections.
[0010] According to the invention, the ratio of an intermediate angle to a pole angle is in the range from 0.2 to 0.4. The pole angle here refers to an angular range covered by the permanent magnets of a magnetic pole, measured around the rotor axis. The intermediate angle here refers to an angular range extending between the pole angles of adjacent magnetic poles. In addition, according to the invention, the ratio of a hole angle to the pole angle is in the range from 0.925 to 1.075, preferably 1. The hole angle here refers to an angular range covered by the at least one cooling hole, measured around the rotor axis. The hole angle of a magnetic pole is therefore the smallest angular range that covers the one cooling hole or the several cooling holes of a magnetic pole. By selecting these parameters, an electrical machine with a high level of uniformity in temperature distribution is created while optimizing the target properties mentioned at the outset.
[0011] In an advantageous embodiment of the electrical machine according to the invention, the ratio of a magnet area to a rotor area is in the range between 0.05 and 0.25. The magnet area is the sum of the magnet cross-sectional areas of all the permanent magnets in the rotor core. The permanent magnets can have a rectangular magnet cross-section, the areas of which are calculated from the product of the length and width of the magnet cross-section. Since two permanent magnets are used for each magnet pole, the magnet cross-sectional area must be multiplied by twice the number of poles. The rotor area is the surface area of the annular rotor cross-sectional area of the rotor core. It is calculated from the product of the number n and the difference between the squares of the outer rotor radius and the inner rotor radius.
[0012] In a further advantageous embodiment of the electrical machine according to the invention, the ratio of a hole area to the magnet area is in the range from 0.95 to 1.15, preferably approximately 1.05. The hole area refers to the sum of the hole cross-sectional areas of all cooling holes in the rotor core.
[0013] In a further advantageous embodiment of the electrical machine according to the invention, the stator has a hollow cylindrical stator yoke with an outer shell and an inner shell, wherein the external cooling path leads through groove-shaped cooling channels arranged on a cylindrical inner side of the housing, each of which is delimited by a cooling section of the outer shell of the stator yoke. The ratio of the cooling surface to the surface area of the outer shell of the stator yoke is in the range of 0.40 to 0.75. The cooling surface area refers to the sum of the section areas of all cooling sections.
[0014] In a further advantageous embodiment of the electric machine according to the invention, cooling fins extending into the cooling channels are formed on the outer casing of the stator yoke, forming enlarged cooling sections. The ratio of an enlarged cooling surface to the cooling area is in the range of 1.00 to 1.25. The enlarged cooling area refers to the sum of the enlarged section areas of all enlarged cooling sections.
[0015] In a further advantageous embodiment of the electric machine according to the invention, the ratio of a rotor yoke height to a pole height is in the range between 0.35 and 0.65. The rotor yoke height refers to the radial width of the widest circular ring extending around the rotor axis, which lies radially inside the permanent magnets and radially outside the cooling holes. The pole height refers to the radial width of the narrowest circular ring extending around the rotor axis, within which the permanent magnets are located.
[0016] In a further advantageous embodiment of the electrical machine according to the invention, a ratio of a pole area to the rotor area is in the range between 0.35 and 0.65. The pole area refers to the annular area of the narrowest circular ring extending around the rotor axis, within which the permanent magnets are located.
[0017] In a further advantageous embodiment of the electrical machine according to the invention, the stator has stator teeth which project radially inwards from the inner shell of the stator yoke and are each spaced from one another by axially running stator slots for receiving a stator winding. The ratio of a stator yoke area to a stator area is in the range from 0.36 to 0.65. The stator yoke area refers to the annular area of the circular ring extending around the rotor axis, the outer radius of which corresponds to the radius of the outer shell and the inner radius of which corresponds to the radius of the inner shell of the stator yoke. The stator area refers to the annular area of the circular ring extending around the rotor axis, the outer radius of which corresponds to the radius of the outer shell and the inner radius of which corresponds to the radius of the inner shell of the stator yoke reduced by one tooth height of the stator teeth.
[0018] In a further advantageous embodiment of the electrical machine according to the invention, the ratio of a stator tooth area to a stator slot area is in the range from 0.95 to 1.10, preferably approximately 1.05. The stator tooth area denotes the sum of the tooth cross-sectional areas of all stator teeth. The stator slot area denotes the sum of the slot cross-sectional areas of all stator slots.
[0019] In a further advantageous embodiment of the electrical machine according to the invention, the stator winding is led out of stator slots at the front ends of the stator and led into stator slots to form winding overhangs. The ratio of a winding overhang to a stator length is in the range between 0.10 and 0.40. The winding overhang refers to the length of the axial projection of the winding overhangs above a front end of the stator. The stator length refers to the axial distance between the front ends of the stator, with any end plates of a stator laminated core not being counted towards the active stator length.
[0020] In a further advantageous embodiment of the electrical machine according to the invention, a ratio of the stator length to an outer diameter of the stator is at least 0.75.
[0021] In a further advantageous embodiment of the electrical machine according to the invention, the number of poles is between 6 and 12, preferably 8.
[0022] Further features and advantages will become apparent from the following description of an embodiment of the invention with reference to drawings, in which
[0023] FIG 1 shows a circular section of a cross section through an electrical machine according to the invention, belonging to a magnetic pole, and
[0024] FIG 2 is a schematic illustration of a longitudinal section composed of two half sections through an electrical machine according to the invention.
[0025] 1 shows a circular section of a cross section through an eight-pole electrical machine 1 according to the invention, transverse to a rotor axis R which is perpendicular to the plane of the drawing, the circular section being assigned to one of the eight magnetic poles P. FIG. 2 shows a longitudinal section through the machine 1 according to the invention, which is made up of two half sections. Above the rotor axis R, the half section is shown along section line I 1a - I 1a from FIG. 1, while below the rotor axis R, the half section is shown along section line I 1b - I 1b from FIG. 1. According to FIG. 1 and FIG. 2, an electrical machine 1 for driving a rail vehicle, for example a metro train, comprises an active arrangement 3 which is arranged inside a housing 2 of the machine 1 and encapsulated with respect to an environment U of the machine 1 and has a stator 4 and a rotor 5 which can rotate about the rotor axis R relative to the stator 4.The encapsulation protects the active arrangement 3 from moisture and dirt from the environment U. The machine 1 further comprises an external cooling path 6 through which cooling air drawn in from the environment U is guided outside the encapsulated active arrangement 3, and an internal cooling path 7 for guiding cooling air within the encapsulated active arrangement 3 in order to dissipate the heat generated during operation of the machine 1 used as a traction drive.
[0026] The rotor 5 of the electrical machine 1 has a hollow cylindrical rotor laminated core 8 which is connected in a rotationally fixed manner - for example by shrinking - to a rotor shaft 10 which can rotate about the rotor axis R. The rotor shaft 10 is rotatably mounted in the housing 2, for example via roller bearings 9. The rotor 5 has a number of poles N which indicates the number of magnetic poles P. In the illustrated embodiment, the number of poles is N = 8, but depending on the rail vehicle to be driven it can also be N = 12 or N = 10 or N = 6. Each magnetic pole P is formed by two permanent magnets 11 arranged in a V-shape relative to one another. The rotor laminated core 8 is penetrated by axially extending magnetic pockets 12 into which the permanent magnets 11 are fitted. The permanent magnets 11 have, for example, a rectangular cross-section and are not shown in Fig. 2 for the sake of clarity.The gaps in the magnetic pockets 12 remaining after fitting the permanent magnets 11 are filled with a filler material (not shown). Furthermore, the rotor has at least one cooling hole 13 for each magnetic pole P, axially penetrating the rotor core 8, through which the internal cooling path 7 passes.
[0027] The stator 4 of the electrical machine 1 has a hollow cylindrical stator yoke 14 with an outer shell 15 and an inner shell 16, which can also be designed as a laminated core. The external cooling path 6 leads through groove-shaped cooling channels 18 arranged on a cylindrical inner side 17 of the housing 2, which are each delimited by a cooling section 19 of the outer shell surface 15 of the stator yoke 14. Cooling fins 20 projecting into the cooling channels 18 can be formed on the outer shell 15 of the stator yoke 14, which cooling fins form enlarged cooling sections 21 on the stator yoke 14 compared to the cooling sections 19 without cooling fins 20. The stator 4 has stator teeth 22 projecting radially inward from the inner shell 16 of the stator yoke 14, which are each spaced apart from one another by axially extending stator slots 23 for receiving a stator winding 24.According to FIG 2 , the stator winding 24 is led out of stator slots 23 at the front ends 25 of the stator 4 and is led back into other angularly offset stator slots 23 to form winding heads .
[0028] The mode of operation of a permanent magnet synchronous machine 1 constructed in this way is known per se, with the rotor shaft 10 driving a rail wheel or a wheelset of the rail vehicle via a gear unit (not shown) and optionally coupling elements. This generates heat in the active arrangement 3, which must be dissipated by cooling air. The cooling air circulating in the internal cooling path 7 is conveyed by an internal fan 27 driven by the rotor shaft 10. It flows, absorbing heat, past the first winding heads of the stator winding 24, through the cooling holes 13 in the rotor 5 and past the second winding heads of the stator winding 24 opposite the first winding heads. From there, it flows back through axial channels 26 in the housing 2, releasing heat, where the internal cooling circuit is closed.The cooling air flowing through the external cooling path 6 is sucked in from the environment U of the machine 1 through housing openings by an external fan 28, which is also driven by the rotor shaft 10, and is guided through the cooling channels 18 in the housing 2 along the cooling sections 19, in the illustrated embodiment along the cooling sections 21 enlarged by cooling fins 20, and is blown out again into the environment U through other housing openings in order to transport heat from the stator 4, the housing 2 and the internal cooling path 7 to the environment U.
[0029] Using the multi-objective optimization described above, geometric parameters, in particular ratios of areas, angles, or lengths, of the electric machine 1 according to the invention were optimized to optimize its energy efficiency, noise emissions, manufacturing costs, and, above all, its cooling behavior with regard to the driving cycle behavior of the rail vehicle to be driven. This avoids the occurrence of particularly hot spots in the machine 1 and instead achieves the most homogeneous temperature distribution possible with minimal temperature deviations from an average value.
[0030] Optimized thermal behavior is achieved when the ratio of an intermediate angle WZ to a pole angle WP is in the range from 0.2 to 0.4, preferably approximately 0.3. The pole angle WP denotes an angular range covered by the permanent magnets 11 of a magnetic pole P, measured around the rotor axis R. In other words, the pole angle WP is the smallest angular range in which the permanent magnets 11 of a magnetic pole P are located. For a pole number N = 8, the pole angle WP can be between 34° and 35°. The intermediate angle WZ denotes an angular range extending between the pole angles WP of adjacent magnetic poles P. For a pole number N = 8, the intermediate angle WZ can be between 10° and 11°. Additionally, an optimized ratio of a hole angle WL to the pole angle WP is in the range from 0.925 to 1.075, preferably 1.In the illustrated embodiment, the hole angle WL denotes an angular range covered by the two cooling holes 13, measured around the rotor axis R. In other words, the hole angle WL is the smallest angular range in which the cooling holes 13 of a magnetic pole P are located. The hole angle WL can be approximately 35° with a pole number N = 8.
[0031] A further optimization of the thermal behavior is achieved when the ratio of a magnetic area AM to a rotor area AR is in the range between 0.05 and 0.25, preferably between 0.05 and 0.15, or particularly preferably between 0.10 and 0.11. The magnetic area AR denotes the sum of the magnetic cross-sectional areas A1 of all permanent magnets 11 in the rotor core 8, i.e. AM = 2 -N - A11. The rotor area AR denotes the surface area of the annular rotor cross-sectional area of the rotor core 8, which has an outer radius R8A and an inner radius R8I, and is therefore calculated according to AR = n (R8A 2 - R8I 2 ) .
[0032] Further optimization is achieved when the ratio of a hole area AL to the magnet area AM is in the range of 0.95 to 1.15, preferably 1.05. The hole area AL denotes the sum of the hole cross-sectional areas A13 of all cooling holes 13 in the rotor core 8, thus in the illustrated embodiment according to AL = 2 -N - A13.
[0033] Further optimization with regard to heat dissipation is achieved when the ratio of the cooling surface AK to the surface area A15 of the outer shell 15 of the stator yoke 14 is in the range of 0.40 to 0.75, preferably between 0.40 and 0.60, and particularly preferably approximately 0.45. The cooling surface area refers to the sum of the section areas A19 of all cooling sections 19. The cooling surface AK+, enlarged by the formation of cooling fins 20 in the illustrated embodiment, refers to the sum of the enlarged section areas A21 of all enlarged cooling sections 21 of the stator yoke 14. The optimized ratio of the enlarged cooling surface AK+ to the cooling surface AK is in the range of 1.00 to 1.25, preferably between 1.110 and 1.115.
[0034] Optimized thermal behavior of the electrical machine 1 is further achieved when the ratio of a rotor yoke height H to a pole height Hll is in the range between 0.35 and 0.65, preferably between 0.45 and 0.50. The rotor yoke height H denotes the radial ring width of the widest circular ring extending around the rotor axis R, which lies radially inside the permanent magnets 11 and radially outside the cooling holes 13. The pole height Hll denotes the radial ring width of the narrowest circular ring extending around the rotor axis R, within which the permanent magnets 11 are located. The rotor yoke height H can, for example, be between 12 mm and 13 mm, and the pole height Hll between 26 mm and 27 mm.
[0035] A further optimization of the electric machine 1 is shown when the ratio of a pole area AP to the rotor area AR lies in the range between 0.35 and 0.65, preferably between 0.45 and 0.55. The pole area AP denotes the annular area of the narrowest circular ring extending around the rotor axis R, within which the permanent magnets 11 are located. The outer radius of this circular ring can be assumed to be the outer radius R8A of the rotor laminated core 8; the radial ring width of the circular ring corresponds to the pole height H11.
[0036] In addition to the parameters of the rotor 5, the parameters of the stator 4 also offer optimization options with regard to the cooling behavior of the electric machine 1, which were determined by multi-objective optimization. Accordingly, an optimized ratio of a stator yoke area A14 to a stator area A4 lies in the range from 0.35 to 0.65, preferably between 0.40 and 0.50, particularly preferably approximately 0.45. The stator area A14 denotes the annular area of the circular ring extending around the rotor axis R, the outer radius of which corresponds to the radius R15 of the outer shell 15 and the inner radius of which corresponds to the radius R16 of the inner shell 16 of the stator yoke 14. The stator surface A4 designates the annular surface of the circular ring extending around the rotor axis R, the outer radius of which corresponds to the radius R15 of the outer shell 15 and the inner radius of which corresponds to the radius R16 of the inner shell 16 of the stator yoke 14 reduced by one tooth height H22 of the stator teeth 22.
[0037] A further optimization of the electrical machine 1 is achieved when the ratio of a stator tooth area AZ to a stator slot area AN is in the range of 0.95 to 1.10, preferably approximately 1.05. The stator tooth area AZ denotes the sum of the tooth cross-sectional areas A22 of all stator teeth 22 of the stator 4. The stator slot area AN denotes the sum of the slot cross-sectional areas A23 of all stator slots 23 of the stator 4.
[0038] Further optimization with regard to heat dissipation is achieved when the ratio of a winding overhang L24 to a stator length L4 is in the range between 0.10 and 0.40, preferably between 0.20 and 0.30, particularly preferably approximately 0.25. The winding overhang L24 denotes the length of the axial projection of the winding overhangs of the stator winding 24 above a front end 25 of the stator 4. The stator length L4 denotes the axial distance between the opposite front ends 25 of the stator 4. With a stator length L4 of 300 mm, the winding overhang L24 can be approximately 70 mm.
[0039] An optimization of the electrical machine 1 also results when the ratio of the stator length L4 to an outer diameter D4 of the stator 4, i.e., twice the radius R15 of the outer casing 15, is at least 0.75, preferably approximately 0.88. The stator outer diameter D4 can be approximately 340 mm.
Claims
Patent claims 1. Electric machine (1) for driving a rail vehicle, comprising - an active arrangement (3) arranged within a housing (2) of the machine (1) and encapsulated with respect to an environment (U) of the machine (1), comprising a stator (4) and a rotor (5) rotatable about a rotor axis (R) relative to the stator (4), - an external cooling path (6) for guiding cooling air sucked in from the environment (U) outside the encapsulated active arrangement (3), and - an internal cooling path (7) for guiding cooling air within the encapsulated active arrangement (3), - wherein the rotor (5) is a hollow cylindrical rotor core (8) which is rotatably connected to a rotor shaft which is rotatably mounted in the housing (2) and can rotate about the rotor axis (R) (10) is connected, - wherein the rotor (5) has a number (N) of magnetic poles (P), which are each formed by two permanent magnets (11) arranged in a V-shape relative to one another and fitted into the rotor laminated core (8) axially penetrating magnetic pockets (12), and - wherein the rotor (5) has at least one cooling hole (13) axially penetrating the rotor core (8) for each magnetic pole (P), through which the internal cooling path (7) leads, characterized in that - that the ratio of an intermediate angle (WZ) to a polar angle (WP) is in the range of 0.2 to 0.4, - where the pole angle (WP) is one of the permanent magnets (11) of a magnetic pole (P) covered angular range measured around the rotor axis (R), - where the intermediate angle (WZ) denotes an angular range extending between the pole angles (WP) of adjacent magnetic poles (P), and - that the ratio of a hole angle (WL) to the pole angle (WP) is in the range of 0.925 and 1.075, - wherein the hole angle (WL) designates an angular range covered by the at least one cooling hole (13) and measured around the rotor axis (R).
2. Electrical machine (1) according to claim 1, - where the ratio of a magnet area (AM) to a rotor area (AR) is in the range between 0.05 and 0.25, - where the magnetic area (AM) denotes the sum of the magnetic cross-sectional areas (All) of all permanent magnets (11) of the rotor core (8), and - wherein the rotor area (AR) denotes the area of the annular rotor cross-sectional area (A8) of the rotor laminated core (8).
3. Electrical machine (1) according to claim 2, - wherein a ratio of a hole area (AL) to the magnet area (AM) is in the range of 0.95 to 1.15, - where the hole area (AL) is the sum of the hole cross-sectional areas (A13) of all cooling holes (13) of the rotor core (8).
4. Electrical machine (1) according to one of claims 1 to 3, - wherein the stator (4) has a hollow cylindrical stator yoke (14) with an outer shell (15) and an inner shell (16), and - wherein the external cooling path (6) leads through groove-shaped cooling channels (18) arranged on a cylindrical inner side (17) of the housing (2), which are each delimited by a cooling section (19) of the outer casing (15) of the stator yoke (14), - wherein a ratio of a cooling surface (AK) to the surface area (A15) of the outer shell (15) of the stator yoke (14) is in the range from 0.40 to 0.75, - where the cooling area (AK) denotes the sum of the section areas (A19) of all cooling sections (19).
5. Electrical machine (1) according to claim 4, - wherein cooling fins (20) projecting into the cooling channels (18) are formed on the outer casing (15) of the stator yoke (14), which form enlarged cooling sections (21), - wherein a ratio of an enlarged cooling surface (AM+) to the cooling surface (AM) is in the range of 1.00 to 1.25, - wherein the enlarged cooling surface (AM+) denotes the sum of the enlarged section areas (A21) of all enlarged cooling sections (21).
6. Electrical machine (1) according to one of claims 1 to 5, - wherein a ratio of a rotor height (H) to a pole height (Hll) is in the range between 0.35 and 0.65, - wherein the rotor yoke height (H) denotes the radial ring width of the widest circular ring extending around the rotor axis (R), which lies radially inside the permanent magnets (11) and radially outside the cooling holes (13), and - where the pole height (Hll) denotes the radial ring width of the narrowest circular ring extending around the rotor axis (R), within which the permanent magnets (11) are located.
7. Electrical machine (1) according to one of claims 2 to 6, - where the ratio of a pole area (AP) to the rotor area (AR) is in the range between 0.35 and 0.65, - wherein the pole surface (AP) denotes the annular surface of the narrowest circular ring extending around the rotor axis (R), within which the permanent magnets (11) are located.
8. Electrical machine (1) according to one of claims 1 to 7, - wherein the stator (4) is separated from the inner casing (16) of the Stator yoke (14) has radially inwardly projecting stator teeth (22) which are each spaced apart from one another by axially extending stator slots (23) for receiving a stator winding (24), - wherein a ratio of a stator yoke area (A14) to a stator area (A4) is in the range of 0.36 to 0.65, - where the stator yoke surface (A14) denotes the annular surface of the circular ring extending around the rotor axis (R), whose outer radius corresponds to the radius (R15) of the outer shell (15) and whose inner radius corresponds to the radius (R16) of the inner shell (16) of the stator yoke (14), - wherein the stator surface (A4) denotes the annular surface of the circular ring extending around the rotor axis (R), the outer radius of which corresponds to the radius (R15) of the outer shell (15) and the inner radius of which corresponds to the radius (R16) of the inner shell (16) of the stator yoke (14) reduced by one tooth height (H22) of the stator teeth (22).
9. Electrical machine (1) according to claim 8, - wherein a ratio of a stator tooth surface (AZ) to a stator slot surface (AN) is in the range of 0.95 to 1.10, - where the stator tooth surface (AZ) denotes the sum of the tooth cross-sectional areas (A22) of all stator teeth (22), and - where the stator slot area (AN) is the sum of the slot cross-sectional areas (A23) of all stator slots (23).
10. Electrical machine (1) according to claim 8 or 9, - wherein the stator winding (24) is led out of stator slots (23) at the front ends (25) of the stator (4) and is led into stator slots (23) to form winding heads, - wherein a ratio of a winding head projection (L24) to a stator length (L4) is in the range between 0.10 and 0.40, - wherein the winding head projection (L24) denotes the length of the axial projection of the winding heads over a front end (25) of the stator (4), and - wherein the stator length (L4) denotes the axial distance between the front ends (25) of the stator (4).
11. Electrical machine (1) according to one of claims 8 to 10, - wherein a ratio of the stator length (L4) to an outer diameter (D4) of the stator (4) is at least 0.
75.
12. Electrical machine (1) according to one of claims 1 to 11, - the number of poles (N) being between 6 and 12, preferably 8.